Method for separating and isolating gold from copper in a gold processing system

A method for separating gold from copper in a gold ore processing system. Gold ore containing elemental gold and elemental copper is treated with an aqueous cyanide solution to produce a liquid product containing a gold-cyanide complex and a copper-cyanide complex. The liquid product is then delivered to a nanofiltration membrane which prevents the copper-cyanide complex from passing therethrough while allowing passage of the gold-cyanide complex. Nanofiltration of the liquid product specifically produces (1) a retentate which contains the copper-cyanide complex; and (2) a permeate which contains the gold-cyanide complex. In this manner, the gold-cyanide complex is effectively separated from the copper-cyanide complex. The permeate is then treated (e.g. with activated carbon or elemental zinc) to ultimately obtain elemental gold therefrom. The copper-cyanide complex may either be discarded or treated to recover elemental copper from the complex.

BACKGROUND OF THE INVENTION 
The present invention generally relates to the processing of gold ore, and 
more particularly to a method in which gold ore having copper therein is 
treated to effectively separate gold from copper. As a result, a purified 
elemental gold product can be produced from impure ore materials in a 
highly effective and economical manner which avoids excessive reagent 
(e.g. cyanide) consumption. 
In order to recover elemental gold (Au) from gold-containing ore, 
traditional methods involve treating the ore with one or more aqueous 
(e.g. water-containing) cyanide-containing leaching solutions, with this 
term encompassing a wide variety of different dissolved cyanide compounds 
including sodium cyanide (NaCN), potassium cyanide (KCN), and calcium 
cyanide Ca(CN).sub.2 !. Other cyanide-containing materials (e.g. cyanide 
compounds) which may be used for this purpose include but are not limited 
to gaseous hydrogen cyanide (HCN.sub.(g)), ammonium cyanide (NH.sub.4 CN), 
organic alpha-hydroxy cyanides (e.g. lactonitrile), and/or thiocyanates 
(e.g. NaSCN, KSCN, or Ca(SCN).sub.2.) As a result, a "gold-cyanide 
complex" is produced during contact between the ore and the leaching 
solution with this term being defined to involve a chemical complex 
containing one or more gold ions stoichiometrically combined with at least 
one or more cyanide ions (CN).sup.- !. This complex will typically 
consist of Au(CN).sub.2.sup.-1 (also known as an "aurocyanide ion") which 
is associated with one or more counter-ions including, for example, 
Na.sup.+ when NaCN is employed in the leaching solution, K.sup.+ when KCN 
is used, and Ca.sup.+2 when Ca(CN).sub.2 is involved. The 
Au(CN).sub.2.sup.-1 complex has a high level of stability with a K.sub.f 
of about 2.times.10.sup.38. A typical reaction sequence in which a 
gold-cyanide complex is produced using a selected cyanide ion-containing 
leaching solution is as follows: 
EQU 4Au.sub.(s) +8(CN).sup.-.sub.(aq) +O.sub.2(aq) +2H.sub.2 O.sub.(1) 
.fwdarw.4Au(CN).sub.2.sup.-.sub.(aq) +4OH.sup.-.sub.(aq) ( 1) 
This reaction is further described in Brown, T. L., et al., Chemistry, The 
Central Science, Prentice Hall, New Jersey, 4th ed., p. 815 (1988). It is 
important to emphasize that the foregoing reaction will occur when a wide 
variety of different cyanide-containing leaching solutions are employed, 
with the present invention not being restricted to the use of any 
particular materials for this purpose. In addition, if needed and desired 
as determined by preliminary testing and analysis, the cyanide-containing 
leaching solution is maintained at an alkaline pH (optimum=about 9-11) 
using lime (CaO) to maintain a high rate of gold cyanidation. 
A variety of different physical methods may be employed to place the gold 
ore in contact with the selected cyanide-containing leaching solution. Two 
methods of primary commercial interest involve procedures known as (1) 
"heap leaching"; and (2) "vat leaching". In both of these processes, 
crushed gold ore is combined with the selected cyanide-containing leaching 
solution which is allowed to pass through the ore so that gold 
extraction/complex formation can take place. In heap leaching systems, 
individual rock-like portions of gold-containing ore are initially 
provided, with each portion being about 1-4 inches in diameter. The 
rock-like portions of ore are then placed in a pile which is typically 
positioned on a pad made of rubber or the like. In a representative and 
non-limiting embodiment, each pile is normally about 30-50 ft. tall and 
occupies about 1.times.10.sup.7 to 3.times.10.sup.7 ft.sup.3 of space, 
although these values may be varied as needed in accordance with the size 
and capacity of the processing facility under consideration. The selected 
cyanide-containing leaching solution is then applied to the top of the ore 
pile and allowed to travel (e.g. percolate) downwardly therethrough. 
During this procedure, the leaching solution passes into the interior 
regions of the individual ore portions (rocks) which have a porous 
character. As a result, the liquid materials leaving the ore pile at the 
bottom thereof consist of an aqueous solution containing a gold-cyanide 
complex (described above). Further processing of the gold-cyanide complex 
to obtain elemental gold therefrom will be discussed in substantial detail 
below. 
The foregoing procedure (e.g. placing gold ore in contact with a 
cyanide-containing leaching solution) may likewise be undertaken in a 
large containers or "vats" which are entirely or partially closed. These 
vats are typically constructed from stainless steel or lined carbon steel 
and have a representative capacity of about 400-2500 ft.sup.3 in a 
non-limiting and preferred embodiment. Likewise, instead of using 
"rock"-type portions of ore as discussed above, powdered ore may also be 
treated in a vat or heap system as discussed in U.S. Pat. No. 5,264,192. 
In this embodiment, mined ore in the form of large rocks is crushed using 
conventional mechanical systems (e.g. jaw-crushers, roll-crushers, and/or 
attrition mills which are known in the art and of standard design). As a 
result, a powered ore product is generated which has an average particle 
size of about 200 U.S. standard mesh or less. The powdered ore is 
thereafter treated with a selected cyanide-containing leaching solution as 
previously noted. 
Heap or vat leaching processes which incorporate cyanide extraction 
technology are currently in widespread use throughout the United States 
and in other countries. For example, in 1989, the United States had about 
eighty heap or vat leaching operations, with most of them being located in 
Nevada. Other large leaching operations currently exist in Peru, Ecuador, 
Chile, South Africa, Indonesia, Canada, and elsewhere. 
The present invention as described in considerable detail below shall not 
be restricted to any specific leaching procedures (e.g. heap leaching, vat 
leaching, and the like), any particular cyanide-containing leaching 
solutions, or any physical parameters (e.g. size characteristics) 
associated with the gold ore being treated. The invention is applicable to 
any leaching method which places a cyanide-containing leaching solution in 
direct physical contact with gold ore to yield an aqueous product 
containing a gold-cyanide complex. Further general information regarding 
the gold leaching processes described above and operational parameters 
associated with these procedures (including specific examples) are 
presented in U.S. Pat. No. 5,264,192; Thomas, R. (ed.), E/MJ Operating 
Handbook of Mineral Processing, McGraw-Hill, Inc., pp. 22-23 (1977); 
Clennell, J., The Cyanide Handbook, McGraw-Hill, Inc. pp. 102-132 (1915); 
and Bernard, G. M. "Andacollo Gold Production--Ahead of Schedule and Under 
Budget", Mining Engineering, pp. 42-47 (August 1996) which are all 
incorporated herein by reference. 
Once the desired gold-cyanide complex is generated using the processes 
discussed above, it must thereafter be treated to recover elemental gold 
therefrom. This can be done immediately or after the passage of a 
predetermined amount of time. While a number of different procedures may 
be employed for this purpose, two primary methods exist which are 
currently in widespread use. These methods are known as (1) the 
"Merrill-Crowe Process"; and (2) the "Activated Carbon Process". The 
Merrill-Crowe Process is described in numerous references including 
Arbiter, H., et al., Gold--Advances in Precious Metals Recovery, Gordon 
and Breach Science Publishers, New York, pp. 146-153 (1990); and Van Zyl, 
D. J. A., et al., Introduction to Evaluation, Design and Operation of 
Precious Metal Heap Leaching Projects, Society of Mining Engineers, Inc., 
Littleton, Colo., pp. 126-127 and 149-150 (1988) which are also 
incorporated herein by reference. 
The Merrill-Crowe Process (which was initially developed in approximately 
1897) involves a procedure in which the "pregnant" leaching solution 
(which contains the desired gold-cyanide complex therein) undergoes a 
reaction conventionally known as "zinc cementation/precipitation". 
Specifically, the leaching solution containing the gold-cyanide complex is 
combined with elemental zinc (Zn) in accordance with the following 
reaction: 
EQU 2Au(CN).sub.2.sup.-1.sub.(aq) +Zn.sub.(s) .fwdarw.2Au.sub.(s) 
+Zn(CN).sub.4.sup.-2.sub.(aq) ( 2) 
Various lead salts (e.g. lead acetate and/or lead nitrate) may also be 
added to the foregoing reaction process as needed in accordance with 
preliminary pilot tests in order to increase the reaction kinetics of the 
gold precipitation process. Implementation of this technique generates 
solid elemental gold (Au) which resides within a gold-zinc solid 
sludge-type reaction product. This material is ultimately filtered and 
removed from the residual liquid fraction (which consists primarily of 
free cyanide ions (CN).sup.- } and a dissolved 
Zn(CN).sub.4.sup.-2.sub.(aq) complex.) The zinc-gold solid sludge is 
thereafter processed to isolate and remove elemental gold therefrom. A 
number of different methods may be employed for this purpose. For example, 
after being washed with water to remove residual free cyanide ions and 
Zn(CN).sub.4.sup.-2.sub.(aq) complex, the reaction product may then be 
combined with sulfuric acid (H.sub.2 SO.sub.4) in the presence of air in 
order to dissolve excess (unreacted) elemental zinc and other metals 
including copper and cadmium as discussed in Van Zyl, D. J. A., et al., 
Introduction to Evaluation, Design and Operation of Precious Metal Heap 
Leaching Projects, supra, p. 150. The remaining solid materials are 
thereafter washed with water again and dried. If it is determined by 
preliminary experimental testing that the solid product contains 
substantial quantities of mercury (Hg), then the product may be further 
processed in a conventional mercury retort at 400.degree. C. to release 
residual mercury into a condenser assembly which is optimally positioned 
under water to avoid the release of vaporized mercury into the atmosphere. 
In the alternative, as discussed in Brown, T. L., et al., Chemistry, The 
Central Science, supra, p. 815, the sludge-like reaction product may be 
heated in air to form zinc oxide (ZnO) from residual elemental zinc which 
is thereafter sublimed away. 
The elemental gold-containing solid product which results from the 
procedures listed above may then be smelted in combination with a selected 
flux composition which is designed to oxidize elemental zinc (as well as 
other residual non-gold metals) and thereby assist in the removal of metal 
oxides. Representative flux materials suitable for this purpose include 
but are not limited to "borax" (e.g. Na.sub.4 B.sub.4 O.sub.7.10H.sub.2 O) 
and silica (e.g. SiO.sub.2) in combination. The specific flux materials 
and combinations thereof, as well as the amounts of these materials to be 
used in the smelting process will be determined in accordance with 
preliminary pilot studies on the gold-containing solid product being 
processed. Likewise, specific information on the use of flux materials in 
general is again presented in Van Zyl, D. J. A., et al., Introduction to 
Evaluation, Design and Operation of Precious Metal Heap Leaching Projects, 
supra, p. 150. Addition of the flux materials as discussed above generates 
a borosilicate glass "slag", with this term being defined to involve a 
relatively inert reaction product created when flux materials are combined 
with impurities in a metal refining system. It should also be noted that, 
if needed as determined by preliminary pilot testing, feldspar (which 
comprises a silicate of aluminum and possibly other metals) may be added 
at approximately a 3% by weight level as a viscosity modifier. 
After the steps listed above, smelting of the reaction product is initiated 
which takes place in a conventional furnace (e.g. a gas-fired or 
induction-type furnace system which is known in the art) at a temperature 
of approximately 1150.degree. C. Finally, after removing the residual 
"slag" which gravimetrically separates and collects in the furnace, the 
elemental gold (characterized as "dore") is withdrawn from the furnace, 
thereby completing the production process. Again, this basic refining 
procedure is conventional in nature and discussed in substantial detail in 
the foregoing references including Van Zyl, D. J. A., et al., Introduction 
to Evaluation, Design and Operation of Precious Metal Heap Leaching 
Projects, supra. 
The Activated Carbon Process employs a different approach. Specifically, 
the aqueous leaching product/solution having the gold-cyanide complex 
dissolved therein is placed in contact with activated carbon which is 
typically positioned in large column-like structures. The term "activated 
carbon" as used herein involves carbon materials having an amorphous 
character, a large surface area, and a considerable number of pores or 
"activation sites". Activated carbon which is suitable for use in this 
process may be obtained from the charring of coconut shells or peach pits 
at approximately 700-800.degree. C. and will typically have the following 
optimum parameters: (1) surface area=1050-1150 m.sup.2 /gm; (2) apparent 
density=0.48 g/cc; (3) particle density=0.85 g/cc; (4) voids in densely 
packed column=40%; and (5) representative particle sizes=minus 6-plus 16 
mesh or minus 12-plus 30 mesh. However, the present invention and 
activated carbon adsorption processes in general shall not be restricted 
to these particular parameters which are provided for example purposes 
only. 
Once the aqueous leaching solution containing the gold-cyanide complex 
therein comes in contact with the activated carbon, an adsorption process 
occurs which is not yet entirely understood. Specifically, the 
gold-cyanide complex in solution (which is defined herein to encompass 
aurocyanide ions, namely, Au(CN).sub.2.sup.-1) is adsorbed onto the 
surface of the activated carbon in accordance with a number of theoretical 
mechanisms including the possible presence of multiple "surface oxide 
sites" which enable adsorption to take place. This mechanism, as well as 
additional information regarding the Activated Carbon Process, is 
presented in Arbiter, H., Gold--Advances in Precious Metals Recovery, 
supra, pp. 153-164; and Van Zyl, D. J. A., et al., Introduction to 
Evaluation, Design and Operation of Precious Metal Heap Leaching Projects, 
supra, pp. 128-129; 138-149; and 151 which are again incorporated herein 
by reference. Generally, the activated carbon supplies which are employed 
in this method are operated in a "fluidized bed" mode which may be 
achieved through the use of a liquid flow rate of about 25 gpm/ft.sup.2 of 
cross-sectional area associated with the carbon-containing column (or 
other support structure) when minus 6-plus 16 mesh particles are employed. 
When minus 12-plus 30 mesh carbon is used, a flow rate of about 15 
gpm/ft.sup.2 is preferred. Both of these parameters will typically result 
in a bed expansion of about 60%. 
Regardless of which mechanism ultimately results in adsorption of the 
gold-cyanide complex (e.g. aurocyanide ions) on the activated carbon, the 
following approach may be used to effectively removes the gold-cyanide 
complex from the aqueous leaching product. After adsorption, the 
gold-containing carbon product is filtered to remove residual "barren" 
liquid, followed by "desorption" or removal of the gold-cyanide complex 
from the "loaded" activated carbon (e.g. the gold-containing carbon 
product.) This is accomplished by using a selected eluant solution which 
is placed in direct physical contact with (e.g. passed through) the 
carbon. A representative eluant solution that is suitable for this purpose 
includes but is not limited to a solution of NaOH--NaCN (e.g. optimally 
about 0.5-1.0% by weight NaOH and about 0.1-0.3% by weight NaCN containing 
approximately 20% ethyl alcohol) as specifically mentioned in Van Zyl, D. 
J. A., et al., Introduction to Evaluation, Design and Operation of 
Precious Metal Heap Leaching Projects, supra, p. 139. This solution is 
likewise heated in a preferred embodiment to a temperature of about 
77-120.degree. C. It is theorized that cyanide ions (CN).sup.- ! in the 
eluant solution effectively replace/exchange the adsorbed aurocyanide ions 
(gold-cyanide complex) which are released into the eluant solution. The 
resulting gold-containing eluant product (which contains the desired gold 
species aurocyanide ions/gold cyanide-complex!) is then further processed 
to recover elemental gold therefrom. At this point, it is important to 
emphasize that the overall gold concentration in the gold-containing 
eluant product is substantially greater than the gold concentration in the 
original leaching solution, thereby demonstrating the effectiveness of 
this procedure in producing a concentrated gold product. For example, as 
noted in Arbiter, H., Gold--Advances in Precious Metals Recovery, supra, 
p. 144, a representative leaching solution (after gold extraction) will 
have an overall gold concentration of about 1-10 ppm while an exemplary 
gold-containing eluant product as discussed above will comprise about 
100-2000 ppm of gold therein. 
At this point, the gold-containing eluant product is treated to recover 
elemental gold therefrom. This may again be accomplished in many ways 
(including zinc precipitation in accordance with the Merrill-Crowe Process 
as outlined above), although conventional electrowinning methods are 
preferred as again discussed in Van Zyl, D. J. A., et al., Introduction to 
Evaluation, Design and Operation of Precious Metal Heap Leaching Projects, 
supra, pp. 143-148 and 151. While electrowinning is a known procedure that 
has been employed in the mining industry for decades, the specific details 
of this process will now be summarized. First, an electrowinning "cell" is 
provided which includes one or more cathodes and anodes therein. Both of 
these elements are in fluid communication with the gold-containing eluant 
solution which is supplied to the cell housing having the cathodes and 
anodes therein. A direct current power supply is then operatively 
connected to the cathodes and anodes in each cell which causes the desired 
metal in the solution (e.g. elemental gold in the gold-containing eluant 
product) to be directly deposited onto the cathodes. This process shall 
not be restricted to any particular materials which may be used in 
connection with the cathodes and anodes, with a wide variety of 
conventional compositions being suitable for this purpose. In a 
representative and non-limiting embodiment, cathodes manufactured from 
steel wool (e.g. positioned in a plastic frame or wrapped around a 
stainless steel spool) and anodes produced from stainless steel, carbon, 
or titanium can be employed. Many different sizes, shapes, and overall 
design configurations may be selected in connection with the 
cathodes/anodes, with the claimed process (and the electrowinning 
procedure in general) not being restricted to any particular structures 
and physical parameters. Likewise, the power required for electrowinning 
will vary in accordance with many factors including the particular type of 
cell(s) under consideration, the gold concentration in the gold-containing 
eluant product, the construction materials associated with the 
cathodes/anodes, and the like. However, a representative system will 
involve the application of approximately 2.5 volts between the cathodes 
and anodes in an exemplary electrowinning cell. 
Once the electrowinning process is completed, the elemental gold-containing 
cathodes are removed from the system and treated to recover elemental gold 
therefrom. The cathodes at this stage may contain up to about 50% or more 
gold thereon (e.g. up to about 100 oz. of elemental gold per lb. of 
cathode if steel wool is involved). To process the cathodes, they may 
initially be placed in contact with sulfuric acid (H.sub.2 SO.sub.4) in an 
optional pretreatment step which is designed to dissolve any residual 
non-gold metals including copper, iron, and the like. The need for a 
sulfuric acid pretreatment stage is typically determined in accordance 
with preliminary pilot studies on the electrowinning products (e.g. 
cathodes) under consideration. Likewise, if the cathodes contain 
substantial amounts of mercury (which will not usually be removed by 
sulfuric acid treatment), they may be subjected to conventional retort 
processes as discussed above. The cathodes are then smelted in combination 
with one or more selected flux compositions which are again designed to 
oxidize residual non-gold metals and thereby assist in the removal of 
metal oxides. Representative flux compounds suitable for this purpose 
include but are not limited to "borax" (e.g. Na.sub.4 B.sub.4 
O.sub.7.10H.sub.2 O) and silica (e.g. SiO.sub.2) in combination. The 
specific flux materials and combinations thereof, as well as the amounts 
of these materials to be used in the smelting process will be determined 
in accordance with preliminary pilot studies on the gold-containing 
cathode materials under consideration. More detailed information on the 
use of flux materials for this purpose is again presented in Van Zyl, D. 
J. A., et al., Introduction to Evaluation, Design and Operation of 
Precious Metal Heap Leaching Projects, supra, pp. 150-151. Addition of the 
flux materials results in the production of a borosilicate glass "slag" 
with this term being defined above. It should also be noted that, if 
needed as determined by preliminary pilot testing, feldspar may be added 
at approximately a 3% by weight level as a viscosity modifier. 
After the steps listed above, smelting of the cathodes is initiated which 
takes place in a conventional furnace (e.g. a gas-fired or induction-type 
furnace system that is known in the art) at a temperature of approximately 
1150.degree. C. Finally, after removing the residual "slag" which 
gravimetrically separates and collects in the furnace, the elemental gold 
(e.g. characterized as "dore") is withdrawn from the furnace, thereby 
completing the production process. Again, this basic refining procedure is 
conventional in character and discussed in the references listed above. 
Both the Merrill-Crowe Process and the Activated Carbon Process involve 
established procedures for collecting and isolating gold-containing 
species (e.g. aurocyanide ions) from cyanide-based leaching solutions so 
that elemental gold can be recovered. Further information regarding these 
procedures will be presented below in the Detailed Description of 
Preferred Embodiments section. It is likewise important to emphasize that 
the present invention shall not be restricted to any particular gold 
collection/isolation techniques. The claimed method is instead 
prospectively applicable to any technique for obtaining an elemental gold 
product from cyanide solutions used in heap leaching processes, vat 
leaching methods, and other cyanide-based extraction systems. For example, 
in addition to the Merrill-Crowe Process and the Activated Carbon Process 
(which are both preferred), other representative methods of a conventional 
nature which may be employed to collect and isolate gold-cyanide complexes 
(e.g. aurocyanide ions), following by additional purification to yield 
elemental gold include (1) solvent extraction procedures which use alkyl 
phosphorus esters, as well as primary, secondary, tertiary, and/or 
quaternary amines (alone or combined with phosphine oxides, sulfones, 
and/or sulfoxides) to extract gold-cyanide complex materials from leach 
solutions; and (2) ion exchange methods and compositions (e.g. resins) in 
which aurocyanide ions are extracted from cyanide-based leaching 
solutions, with representative elution materials suitable for use with 
these compositions including sodium hypochlorite, zinc cyanide, 
thiocyanate, a mixture of thiocyanate/dimethyl formamide ("DMF"), and the 
like. Exemplary ion exchange resins which may be employed for this purpose 
include those sold under the trademark DOWEX and others which are 
commercially available from the Dow Chemical Company of Midland, Mich. 
(USA). Both of these gold isolation methods (combined with conventional 
electrowinning and smelting processes as discussed above) represent 
alternative procedures which may be employed to isolate and collect 
elemental gold from cyanide-containing leaching solutions. These 
alternative techniques are discussed in Arbiter, H., Gold--Advances in 
Precious Metals Recovery, supra, pp. 164-185. In accordance with the 
information provided above, the present invention shall therefore not be 
restricted to any particular methods for isolating elemental gold from 
leaching solutions containing gold-cyanide complexes therein, with the 
versatility of the claimed process becoming readily apparent from the 
specific information provided below in the Detailed Description of 
Preferred Embodiments section. 
Regardless of which methods are ultimately used to obtain elemental gold 
from gold-cyanide complexes, numerous technical and economic problems can 
result in various portions of the leaching system when gold ore is 
processed which contains substantial amounts of elemental copper. 
Copper-containing gold ore is obtainable from many countries throughout 
the world including Australia, Chile, Philippines, Saudi Arabia, Canada, 
Argentina, Indonesia, Peru, and Mexico. Significant problems will result 
when the copper-containing gold ore contains about 0.1-2.0% by weight 
elemental copper or more, although the claimed process shall not be 
limited to the treatment of ore containing any particular copper levels. 
In all cyanide-based leaching processes (including heap leaching and vat 
leaching systems), material costs represent a substantial portion of the 
overall operating expense in the processing of gold ore. These material 
costs are primarily associated with the cyanide-containing leaching 
solution as discussed above. The excessive consumption of cyanide 
materials during ore treatment will substantially reduce the operating 
efficiency of the entire gold production facility. It is therefore a goal 
of all cyanide based leaching operations to minimize the use of cyanide 
compositions (e.g. cyanide salts dissolved in aqueous solutions) and to 
avoid excessive losses of these materials. 
However, when copper is present in the gold ore as indicated above, a 
chemical "side-reaction" occurs which results in excessive consumption and 
losses of the cyanide-containing leaching solution. Undesired and 
excessive consumption of cyanide ions (CN).sup.- ! which takes place when 
elemental copper is present in the gold ore involves the following 
chemical reaction: 
EQU 2Cu.sub.(s) +6(CN).sup.-.sub.(aq) .fwdarw.2Cu(CN).sub.3.sup.-2.sub.(aq)( 3) 
This reaction consumes substantial amounts of free cyanide (CN).sup.- ! in 
order to produce a copper-cyanide complex, thereby increasing the overall 
cyanide requirements in the leaching process. The term "copper-cyanide 
complex" as used herein shall be defined to involve a chemical complex 
containing one or more copper ions stoichiometrically combined with at 
least one or more cyanide ions (CN).sup.- !. This complex will primarily 
consist of Cu(CN).sub.3.sup.-2 (also known as a "cuprocyanide ion") which 
is associated with one or more counter-ions including, for example, 
Na.sup.+ when NaCN is employed in producing the leaching solution, K.sup.+ 
when KCN is used, and Ca.sup.+2 when Ca(CN).sub.2 is involved. Much of the 
copper-cyanide complex (Cu(CN).sub.3.sup.-2) which is generated as a 
result of this reaction passes unaffected through the gold extraction and 
isolation processes outlined above, and ultimately resides in the "barren" 
cyanide-containing solution materials which remain after the gold-cyanide 
complex is removed. This barren solution is normally reused/recycled in 
treating incoming amounts of additional gold ore. However, when the barren 
solution contains the copper-cyanide complex therein, this material 
(Cu(CN).sub.3.sup.-2) decomposes via oxidation or other processes to 
Cu(CN).sub.2.sup.-1 during exposure to air, bacterial action, and/or 
sunlight in storage ponds, on heaps of gold ore, and the like. This 
copper-cyanide compound (Cu(CN).sub.2.sup.-1) represents a considerable 
problem in the recycled barren cyanide solution since Cu(CN).sub.2.sup.-1 
is chemically incapable of extracting gold from gold ore to yield the 
desired gold-cyanide complex and recombines with fresh cyanide ions 
(CN).sup.- ! that are added during the reuse and recycling of the barren 
solution. The Cu(CN).sub.2.sup.-1 is then reconverted back into the 
copper-cyanide complex (Cu(CN).sub.3.sup.-2), thus consuming two moles of 
(CN).sup.-. As more copper leaches into the recirculating leaching 
solution (which occurs during reuse of this material and repeated passage 
thereof through incoming quantities of gold ore), increasingly large 
amounts of cyanide are irreversibly lost to this decomposition/(CN).sup.- 
consumption cycle. The presence of copper in the gold ore being treated 
therefore presents significant problems from a functional and economic 
standpoint. 
In summary, the presence of elemental copper in the gold ore being treated 
ultimately increases cyanide consumption in the system by forming a 
copper-cyanide complex (Cu(CN).sub.3.sup.-2) which can decompose to yield 
Cu(CN).sub.2.sup.-1. The Cu(CN).sub.2.sup.-1 in the recycle stream, when 
"conditioned" by the addition of fresh (CN).sup.- is reconverted to 
Cu(CN).sub.3.sup.-2 resulting in the loss of two moles of (CN).sup.- to 
the inert Cu(CN).sub.3.sup.-2 compound. This loss (which involves 
excessive (CN).sup.- reagent consumption) significantly and adversely 
affects the cost efficiency of the entire gold processing operation. 
In addition to excessive cyanide consumption, copper materials within the 
gold ore will also result in an increasingly impure elemental gold 
product. Additional and more costly refining procedures must therefore be 
employed to solve this problem. Likewise, if the Merrill-Crowe Process is 
used (which involves a combination of elemental zinc with the leaching 
solution containing the gold-cyanide complex), extraneous copper materials 
in the solution will dramatically reduce the precipitation efficiency of 
the system by causing zinc passivation, with the term "passivation" 
involving a process in which the zinc is rendered non-reactive to the 
gold-cyanide complex which prevents the gold precipitation process from 
taking place. Additional zinc will therefore be required which again 
increases overall production costs. Excessive copper contamination of the 
leaching solution will also reduce the operating efficiency of the 
smelting process associated with this embodiment by causing prolonged 
smelting times. In systems which employ the Activated Carbon Process, 
copper materials (e.g. copper-cyanide complexes) will substantially 
inhibit the functional capabilities of the activated carbon, thereby 
"fouling" this material and causing increased carbon requirements. Current 
efficiency and consumption are likewise increased in subsequent 
electrowinning stages if copper materials are not removed from the system. 
Accordingly, the presence of copper-containing species in the leaching 
solution after the treatment of gold ore will cause a number of 
significant problems unless the copper is effectively removed. 
The present invention involves a unique and specialized procedure for 
removing undesired copper (e.g. copper-cyanide complexes) from gold 
extraction systems when copper-containing gold ore is being processed. As 
a result, production costs are greatly reduced which contributes to a 
substantial increase in overall operating efficiency. The claimed process 
is readily applicable to a wide variety of cyanide-based treatment methods 
ranging from heap leaching to vat leaching. It may also be used with many 
different methods for isolating elemental gold from gold-cyanide complexes 
including the Merrill-Crowe Process, the Activated Carbon Process, and 
others. The claimed method is highly versatile, satisfies a long-felt need 
in the gold processing industry, and provides the following important 
benefits: (1) the ability to process impure, copper-containing gold ore in 
an economical manner without the excessive consumption of cyanide 
compositions (e.g. free cyanide (CN).sup.- !); (2) an improvement in the 
operating efficiency of the entire gold processing system by reducing 
cyanide reagent costs; (3) the decreased consumption of other reagents in 
the system including activated carbon and zinc (depending on the 
particular recovery system under consideration); (4) a reduction in 
electricity consumption (if electrowinning is part of the overall 
processing system); (5) improved conservation of resources and reduced 
waste generation which collectively provide important environmental 
benefits; (6) a reduction in the amount of smelting time that is needed to 
yield an elemental gold product; (7) the ability to retain, purify, and 
collect elemental copper from the gold ore which can be sold at 
considerable economic benefit; (8) a high level of versatility and 
applicability to a wide variety of different cyanide-based processing 
methods; (9) improved gold purity levels in connection with the gold 
product "dore"; and (10) a general improvement in the simplicity, 
effectiveness, and efficiency of the gold production system. For these 
reasons and the other factors outlined below, the present invention and 
its various embodiments represent a significant advance in the art of gold 
refining. 
Summary of the Invention 
It is an object of the present invention to provide a method for separating 
gold from copper in a gold processing system which enables the removal of 
copper from the system in a rapid and efficient manner. 
It is another object of the invention to provide a method for separating 
gold from copper in a gold processing system which is readily applicable 
to a wide variety of cyanide-based ore treatment systems and methods for 
converting gold-cyanide complexes into elemental gold. 
It is another object of the invention to provide a method for separating 
gold from copper in a gold processing system which enables the purity 
levels of elemental gold to be substantially improved. 
It is a further object of the invention to provide a method for separating 
gold from copper in a gold processing system wherein the removal of copper 
is accomplished in a manner which enables the reduced consumption of 
cyanide materials so that the overall efficiency of the system is 
improved. 
It is a further object of the invention to provide a method for separating 
gold from copper in a gold processing system which is accomplished in situ 
(e.g. "on-line") without any substantial interruptions in system operation 
and without significant modifications to the system. 
It is a still further object of the invention to provide a method for 
separating gold from copper in a gold processing system which not only 
facilitates the removal of copper so that the foregoing benefits can be 
achieved, but likewise enables the removed copper species to be treated so 
that elemental copper can be recovered therefrom. 
It is an even further object of the invention to provide a method for 
separating gold from copper in a gold processing system in which the 
benefits described above are accomplished through the use of 
nanofiltration membrane technology which represents a new and unique 
method for separating metals in gold recovery systems. 
The present invention involves a highly effective method for treating gold 
ore which also contains elemental copper therein as an impurity. The 
claimed process enables copper materials leached from the ore to be 
removed from the treatment system (e.g. separated from the gold-containing 
species). As a result, a number of problems are avoided which typically 
result when copper remains in the system. These problems are described 
above and range from the production of elemental gold having reduced 
purity levels to the excessive consumption of cyanide caused by the 
formation of Cu(CN).sub.2.sup.-1 in the system which is ultimately 
converted into Cu(CN).sub.3.sup.-2. This process "ties up" "free" cyanide 
(CN).sup.- ! which provides many economic disadvantages. Excessive 
cyanide consumption substantially reduces the overall operating 
effectiveness of the entire production system. Likewise, the presence of 
undesired copper in the system can interfere with the conversion of 
gold-cyanide complexes produced during the cyanide leaching process into 
elemental gold when conventional production methods are employed (e.g. the 
zinc-based Merrill-Crowe Process or the Activated Carbon Process as 
previously discussed.) The presence of copper materials (e.g. 
copper-cyanide complexes) in the system can also interfere with the 
efficiency of smelting and/or electrowinning procedures which are 
ultimately used to recover elemental gold from the gold-cyanide complexes. 
It is therefore desirable from both a technical and practical standpoint 
to remove copper from the processing system for all of the reasons given 
above. 
The claimed process overcomes the problems outlined above in a very 
effective manner which will become readily apparent from the detailed 
information presented below. While specific processing systems and gold 
recovery technologies will be discussed in connection with the claimed 
procedure, the present invention shall not be limited to any particular 
cyanide-based gold extraction methods. Instead, the invention is 
prospectively applicable to any production system which places gold ore in 
physical contact with solutions containing free cyanide ions (CN).sup.- ! 
therein so that a gold-cyanide complex as defined above is generated. 
Accordingly, the claimed process shall not be restricted to any specific 
gold processing operations provided that, in some manner, cyanide 
solutions are used to chemically extract gold from mined ore so that a 
gold-cyanide complex is created. 
A brief overview of the present invention and its main features will now be 
provided. More specific details regarding the invention including specific 
reagents, operational parameters, processing sequences, and equipment will 
be presented below in the Detailed Description of Preferred Embodiments 
section. It should also be noted that, unless otherwise indicated herein, 
the claimed invention shall not be limited to any particular numerical 
parameters, reagent quantities, and other values which may be determined 
in accordance with preliminary pilot studies on the gold ore being 
treated. 
The present invention basically involves a gold separation and recovery 
process which uses a cyanide-containing leaching solution to extract gold 
from gold ore. The ore being processed in the present case likewise 
contains elemental copper therein (along with elemental gold) which must 
be removed to achieve the benefits listed above. As previously indicated, 
unless the copper materials leached from the ore are removed during 
subsequent processing, the presence of copper in the system will cause 
numerous problems ranging from the production of elemental gold having 
reduced purity levels to the excessive consumption of cyanide caused by 
the formation of Cu(CN).sub.2.sup.-1 in the system which is ultimately 
converted into Cu(CN).sub.3.sup.-2. The claimed method effectively removes 
undesired copper materials (e.g. copper-cyanide complexes) at the early 
stages of production in a rapid and efficient manner. 
In accordance with the invention, a supply of gold ore which comprises both 
elemental gold and elemental copper therein is initially provided (either 
in small rock-like portions or in powder form). The gold ore is thereafter 
placed in direct physical contact with a leaching solution comprising 
cyanide therein. As discussed in considerable detail below, this 
particular stage may be accomplished using either conventional 
heap-leaching or vat-leaching techniques. Likewise, the cyanide-containing 
leaching solution shall be defined to encompass an aqueous solution 
comprising cyanide ions (CN).sup.- ! therein in combination with a 
selected counter-ion (e.g. Na.sup.+, K.sup.+, Ca.sup.+2, and the like). 
Representative leaching solutions suitable for this purpose will contain a 
dissolved cyanide compound (salt) therein, with representative examples of 
this material including but not limited to sodium cyanide (NaCN), 
potassium cyanide (KCN), calcium cyanide (Ca(CN).sub.2), gaseous hydrogen 
cyanide (HCN.sub.(g)), ammonium cyanide (NH.sub.4 CN), organic 
alpha-hydroxy cyanides (e.g. lactonitrile), thiocyanates (e.g. NaSCN, 
KSCN, or Ca(SCN).sub.2) and mixtures thereof. When the cyanide-containing 
leaching solution comes in physical contact with the gold ore, it extracts 
both gold and copper from the ore in order to generate a liquid product 
containing a gold-cyanide complex (Au(CN).sub.2.sup.-1) and a 
copper-cyanide complex (Cu(CN).sub.3.sup.-2) as outlined in specific 
detail below. The liquid product will typically include about 
1.times.10.sup.-3 -1.times.10.sup.-4 % by weight gold-cyanide complex and 
about 0.05-1.0% by weight copper-cyanide complex although these values are 
subject to change in accordance with the particular type, grade, and 
character of gold ore being processed. 
In a preferred embodiment of the invention, a unique processing and 
separatory stage is provided which is designed to separate the 
gold-cyanide complex from the copper-cyanide complex so that both of these 
materials can be isolated from each other. Specifically, at least one 
separatory structure known as a "nanofiltration membrane" is provided for 
this purpose. It has been discovered in accordance with the claimed 
invention that a nanofiltration membrane is capable of preventing the 
copper-cyanide complex from passing through the membrane while allowing 
the gold-cyanide complex to pass. In this manner, one or more 
nanofiltration membranes may be employed to effectively separate the 
gold-cyanide complex in the liquid product from the copper-cyanide complex 
in a highly effective and rapid manner at minimal cost. This 
membrane-based system which is used to remove copper-containing species in 
a gold processing operation represents a considerable advance in the art 
of gold production. Likewise, further information will be provided below 
regarding the special characteristics of nanofiltration membranes which 
enable the gold-copper separation process to be achieved. It will become 
readily apparent from the discussion of nanofiltration technology 
presented in the Detailed Description of Preferred Embodiments that 
nanofiltration membranes are considerably different in structure, 
function, and capability from other membrane types including reverse 
osmosis and ultrafiltration membranes. 
Next, the liquid product which contains both the gold-cyanide complex and 
copper-cyanide complex is delivered to the selected nanofiltration 
membrane so that the liquid product flows onto the nanofiltration membrane 
in order to produce a retentate and a permeate. In a representative and 
preferred embodiment, the liquid product is delivered to the 
nanofiltration membrane at a preferred and optimum flow rate of about 
100-10,000 GPM (gallons per minute), although this value may be varied as 
needed in accordance with preliminary pilot studies involving the 
particular system under consideration and its overall capacity. The 
retentate does not pass through the nanofiltration membrane while the 
permeate passes through the membrane. The retentate specifically contains 
the copper-cyanide complex therein while the permeate includes the 
gold-cyanide complex. In this manner (and in accordance with the unique 
character of the present invention) the gold-cyanide complex is 
effectively separated from the copper-cyanide complex. 
As previously noted, the nanofiltration membrane allows the permeate (e.g. 
the gold-cyanide complex) to pass therethrough. Passage of the permeate 
through the nanofiltration membrane typically occurs at an optimum and 
non-limiting membrane flux rate of about 2-20 GFD gallons per ft.sup.2 
per day!), although this parameter may be suitably varied as needed in 
accordance with routine preliminary testing. Finally, the permeate is 
collected and retained (or further processed if desired), followed by the 
treatment thereof to ultimately obtain elemental gold from the 
gold-cyanide complex in the permeate. The terms "treatment" and "treating" 
as applied to the permeate in connection with the recovery of elemental 
gold therefrom may comprise a number of conventional procedures and shall 
not be restricted to any particular gold isolation techniques. For 
example, one treatment method of interest involves a procedure known as 
the Merrill-Crowe Process which is extensively discussed above. In 
accordance with this method (which basically constitutes a 
"substitution"-type zinc cementation reaction), the permeate (which 
contains the gold-cyanide complex) is combined with a supply of elemental 
zinc to produce a reaction product which comprises precipitated elemental 
gold therein along with a liquid fraction containing (1) water; (2) free 
cyanide ions (CN).sup.- !; and (3) small amounts of a zinc-cyanide 
complex Zn(CN).sub.4.sup.-2 !. Thereafter, the elemental gold is removed 
from the reaction product by conventional means as discussed above 
including the controlled smelting of the reaction product. Likewise, the 
liquid fraction can be removed from the reaction product (e.g. by 
conventional filtration or decantation methods) and thereafter re-used in 
treating incoming amounts of gold ore which contain both elemental gold 
and copper therein. Additional information concerning the Merrill-Crowe 
Process is discussed above and will be further addressed in the Detailed 
Description of Preferred Embodiments section. Likewise, a description of 
this process is provided in numerous references including Arbiter, H., 
Gold--Advances in Precious Metals Recovery, Gordon and Breach, supra, pp. 
146-153; and Van Zyl, D. J. A., et al., Introduction to Evaluation, Design 
and Operation of Precious Metal Heap Leaching Projects, supra, pp. 126-127 
and 149-150 which are again incorporated herein by reference. 
Another treatment method of interest involves a procedure conventionally 
known as the Activated Carbon Process which is likewise described in 
considerable detail above. This technique basically involves placing the 
permeate containing the gold-cyanide complex in contact with a supply of 
activated carbon. The activated carbon then extracts the gold-cyanide 
complex (e.g. aurocyanide ions, namely, Au(CN).sub.2.sup.-1) from the 
permeate, with these ions being adsorbed on the activated carbon to yield 
a gold-containing carbon product. The resulting liquid fraction which 
remains after extraction of the gold-cyanide complex (e.g. after passage 
of the permeate through the activated carbon) contains free cyanide 
(CN).sup.- ! therein. If desired, this material can be collected and 
removed from the gold-containing carbon product (e.g. by conventional 
filtration, decantation, or gravimetric methods) and thereafter re-used in 
treating incoming amounts of gold ore which contain both elemental gold 
and copper therein. Next, the gold-cyanide complex is removed from the 
gold-containing carbon product and further processed in a conventional 
manner to yield elemental gold. As specifically outlined below, a 
representative and preferred processing method for accomplishing this goal 
involves applying at least one eluant (stripping) solution to the 
gold-containing carbon product in order to strip the gold-cyanide complex 
from the gold-containing carbon product. This step specifically yields a 
gold-containing eluant product in liquid form which contains the 
gold-cyanide complex dissolved therein. The gold-containing eluant product 
is thereafter treated to recover elemental gold therefrom, preferably by 
subjecting the gold-containing eluant product to electrical current in a 
conventional electrowinning apparatus so that elemental gold is plated 
onto one or more cathodes in the apparatus. The gold-containing cathodes 
are then smelted as previously discussed to obtain a final elemental gold 
product. Further information regarding the Activated Carbon Process will 
be outlined in the Detailed Description of Preferred Embodiments section. 
Likewise a description of this process is provided in numerous references 
including Arbiter, H., Gold--Advances in Precious Metals Recovery, supra, 
pp. 153-163; and Van Zyl, D. J. A., et al., Introduction to Evaluation, 
Design and Operation of Precious Metal Heap Leaching Projects, supra, pp. 
128-12; 138-149; and 151 which are again incorporated herein by reference. 
The claimed process which involves the use of nanofiltration technology to 
separate gold materials from copper compositions shall not be restricted 
to any particular method for collecting and isolating gold-containing 
species (e.g. aurocyanide ions) from the liquid product (the "leachate") 
to ultimately produce elemental gold. Other representative methods 
suitable for this purpose include (1) solvent extraction procedures which 
use alkyl phosphorus esters, as well as primary, secondary, tertiary, 
and/or quaternary amines (alone or combined with phosphine oxides, 
sulfones, and/or sulfoxides) to extract gold-cyanide complex materials 
from leach solutions; and (2) ion exchange methods and compositions (e.g. 
resins) in which aurocyanide ions are extracted from cyanide-based 
leaching solutions, with representative elution materials suitable for use 
with these compositions including sodium hypochlorite, zinc cyanide, 
thiocyanate, a mixture of thiocyanate/dimethyl formamide ("DMF"), and the 
like. Accordingly, the present invention is prospectively applicable to a 
number of alternative methods and procedures for ultimately isolating, 
refining, and collecting elemental gold as a final product. 
Finally, an additional optional step in the claimed process involves 
treating the copper-cyanide complex in the membrane retentate to recover 
elemental copper therefrom. Specific methods for accomplishing this goal 
will be outlined below in the Detailed Description of Preferred 
Embodiments section. However, a basic and conventional method for doing so 
involves the addition of a selected acid (e.g. sulfuric acid H.sub.2 
SO.sub.4 !) to the retentate. As a result, a precipitation reaction occurs 
in which the copper-cyanide complex is precipitated as solid CuCN, with 
free cyanide ions (CN).sup.- ! being converted to HCN.sub.(aq). This 
basic procedure is discussed in U.S. Pat. No. 996,179 which is 
incorporated herein by reference. The solid CuCN may thereafter be 
processed in accordance with a number of conventional methods to obtain 
elemental copper, with the claimed invention not being restricted to any 
particular recovery techniques. For example, representative procedures for 
achieving this goal include reduction roasting with H.sub.2 gas to yield a 
"copper sand" that is subsequently smelted. 
Alternatively, a procedure may be employed in which the copper-cyanide 
complex in the membrane retentate is acidified as noted above along with 
the addition of sodium sulfide (Na.sub.2 S) to yield a Cu.sub.2 S 
precipitate. This material may then be smelted to obtain a final elemental 
copper product. Further detailed information concerning this particular 
process will be discussed below and is outlined in U.S. Pat. No. 778,348 
which is also incorporated herein by reference. It is again important to 
emphasize that this portion of the claimed process (e.g. treatment of the 
copper-cyanide complex to recover elemental copper therefrom) is optional 
and may involve many known copper recovery techniques for this purpose, 
with the present invention not being restricted to any particular copper 
recovery methods or the recovery of copper in general. Alternatively, 
instead of processing the copper-cyanide complex as outlined above, this 
material (e.g. the retentate) may be discarded in a suitable manner. 
The claimed gold-copper separation method provides excellent results and 
enables a highly purified elemental gold product to be obtained from 
impure, copper-containing gold ore using a minimal amount of equipment, 
reagents, and labor. It likewise allows effective conservation of 
cyanide-containing species (e.g. free cyanide ions (CN).sup.- !) by 
effectively removing the copper-cyanide complex from the system. Removal 
of the copper-cyanide complex in this manner avoids the formation of 
Cu(CN).sub.2.sup.-1 in the system which is ultimately converted into 
Cu(CN).sub.3.sup.-2. This undesired side-reaction (which is prevented by 
the present invention) consumes large amounts of "free" cyanide 
(CN).sup.- ! and is therefore undesirable. The elimination of 
copper-containing species (e.g. the copper-cyanide complex) from the 
system also prevents the interference of this material with subsequent 
processing steps including electrowinning and smelting stages. As a 
result, "impure" gold ore (which was previously considered economically 
undesirable from a treatment standpoint) can be processed in a 
cost-effective manner. Finally, it is important to emphasize that the 
present invention does not simply involve a membrane separation method for 
metal ions per se. It is instead directed to the use of a very specific 
membrane system (e.g. one or more nanofiltration membranes) in a 
particular application. This application involves the differential 
separation of gold from copper in a gold ore processing system wherein 
gold is allowed to pass through the membrane system while copper is 
blocked. For this reason and the other factors outlined below, the claimed 
invention represents an important development in the art of gold ore 
treatment. 
These and other objects, features, and advantages of the invention shall be 
discussed further below in the following Brief Description of the Drawings 
and Detailed Description of Preferred Embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
In accordance with the present invention, a unique and highly efficient 
method is disclosed for removing copper-containing materials (e.g. 
copper-cyanide complexes) from a cyanide-based gold-processing system. The 
claimed method is particularly designed for use in connection with gold 
ore which includes both elemental gold and elemental copper therein. 
Following the initial cyanide leaching stage as discussed below, the 
invention uses a unique membrane-based approach to remove copper-cyanide 
complexes from the system while allowing gold-cyanide complexes to remain 
therein for subsequent processing. Removal of the copper-cyanide complexes 
from the processing system provides many benefits including the more 
efficient production of a highly purified elemental gold product and the 
conservation of materials within the system. Regarding the last item, 
unless copper-containing species (copper-cyanide complexes) are removed, 
they can form cyanide compounds (e.g. Cu(CN).sub.2.sup.-1) which 
chemically consume cyanide ions (CN).sup.- ! to form Cu(CN).sub.3.sup.-2 
in the system. This situation (which involves a continuous consumption of 
cyanide ions by inert copper-containing complexes) increases the overall 
operating cost of the gold refining facility under consideration. The 
presence of copper-cyanide materials can also cause a reduction in 
operational efficiency at many other stages of the system including 
electrowinning and smelting steps (if employed). Finally, in the absence 
of effective treatment and recovery methods involving copper-cyanide 
complexes, a substantial amount of valuable copper is wasted. The claimed 
process enables the copper-cyanide complexes of concern to be isolated in 
a sufficiently complete manner to allow the further treatment of these 
materials so that elemental copper can be recovered therefrom. 
To facilitate a complete overview of the invention and its various 
embodiments, the following discussion will be divided into sections, with 
the first section describing the basic gold-leaching process. 
A. The Initial Gold Leaching Process 
As stated above, the present invention involves a unique, economical, and 
highly effective method for producing a purified gold product from raw ore 
which not only contains elemental gold therein, but likewise includes 
elemental copper. Prior to development of the claimed invention, the 
processing of copper-containing gold ore presented numerous economic 
problems including the production of reduced-purity gold, increased 
reagent consumption, and interference with many operational procedures in 
the processing system. The present invention solves these problems and 
enables the rapid and economically-viable treatment of copper-containing 
gold ore. The initial cyanide-based leaching stage of the treatment 
process will be substantially the same in all embodiments of the 
invention. However, to provide a thorough and complete understanding of 
the claimed system from start to finish, the initial leaching stage will 
now be described. 
With reference to the gold ore processing system 10 schematically 
illustrated in FIG. 1, a supply of gold ore 12 is initially provided. The 
present invention shall not be limited to any particular parameters, 
materials, components, ore grades, and equipment used in connection with 
the leaching process and system 10. Any cyanide-based leaching procedure 
can be used provided that an aqueous liquid product is obtained from the 
ore 12 which contains a gold-cyanide complex therein. However, this 
invention is primarily directed to the use of gold ore 12 which not only 
contains elemental gold (Au) therein but likewise includes substantial 
amounts of elemental copper (Cu). Gold ore 12 of this type originates in 
many geographic locations including but not limited to Australia, Chile, 
Philippines, Saudi Arabia, Canada, Argentina, Indonesia, Peru, and Mexico. 
In a representative and non-limiting embodiment, most gold ore 12 of 
concern in the claimed invention will contain about 0.0001-0.0005% by 
weight elemental gold and about 0.1-2% by weight elemental copper therein. 
However, it is important to note that the invention shall not be 
restricted to the treatment of gold ore 12 having any particular copper 
content. 
As shown in the embodiment of FIG. 1, the gold ore 12 is provided in the 
form of rock materials 14 which are configured in a heap or pile 16. The 
term "rock materials" as used herein may involve discrete portions or 
"chunks" of rock having an average diameter of about 1-4 inches, 
crushed/powered rock (e.g. with an average non-limiting! particle size of 
about 200 U.S. standard mesh or less), or large sections/deposits of ore, 
all of which are normally treated at a mine site. This invention and the 
cyanide treatment processes of concern shall not be restricted to any 
particular physical characteristics in connection with the gold ore 12, 
with the discussion of rock materials 14 (and the dimensional parameters 
listed above) being provided for example purposes. Size reduction of the 
ore 12 to a desired level (e.g. to create the rock materials 14 having the 
desired size characteristics as previously described) may be undertaken in 
a conventional manner using standard equipment including jaw crusher 
units, attrition mills, and/or roll crusher systems which are known in the 
art for this purpose. The pile 16 of gold ore 12 is normally of 
significant size. For example, representative ore piles 16 may typically 
be about 30-50 ft. tall and will occupy about 1.times.10.sup.7 
-3.times.10.sup.7 ft.sup.3 of space, although these values can be varied 
as needed in accordance with the mine site/processing facility under 
consideration. In a preferred embodiment, each pile 16 of ore 12 (e.g. 
rock materials 14) is placed on a pad 20 manufactured of rubber or other 
composition which is substantially inert relative to the cyanide salts 
and/or hydrocyanic acid (HCN) materials that are normally encountered in 
the leaching process. 
Thereafter, a leaching solution containing cyanide therein (e.g. a 
"cyanide-containing leaching solution" 22) which is initially retained 
within a containment vessel 24 made of stainless steel or other inert 
material is applied to the pile 16 of ore 12 via tubular conduit 26. The 
tubular conduit 26 is operatively connected to a spraying assembly 30. The 
spraying assembly 30 may be of any conventional design which optimally has 
multiple nozzles 32 associated therewith (FIG. 1). The term 
"cyanide-containing leaching solution" shall not be restricted to any 
particular composition provided that it is water-based (e.g. aqueous) and 
contains "free" (e.g. dissolved) cyanide ions (CN).sup.- ! therein. Many 
different materials may be used for this purpose including but not limited 
to aqueous solutions having the following cyanide salts/compositions 
dissolved therein: sodium cyanide (NaCN), potassium cyanide (KCN), calcium 
cyanide (Ca(CN).sub.2), gaseous hydrogen cyanide (HCN.sub.(g)), ammonium 
cyanide (NH.sub.4 CN), organic alpha-hydroxy cyanides (e.g. lactonitrile), 
thiocyanates (e.g. NaSCN, KSCN, or Ca(SCN).sub.2), and/or mixtures 
thereof. While the cyanide concentration of the leaching solution 22 may 
be varied in accordance with a wide variety of parameters including the 
type and character of the gold ore 12 being treated, a representative and 
preferred leaching solution 22 will contain about 0.1-2% by weight 
dissolved cyanide-containing compound (e.g. KCN, NaCN, Ca(CN).sub.2, etc.) 
therein. It should also be noted that the conduit 26 (as well as any of 
the other conduits in the system 10 as outlined below) may include one or 
more in-line pumps therein (not shown) if needed in accordance with 
preliminary pilot studies on the specific processing system under 
consideration. The particular pump which may be employed for this purpose 
can be of any conventional type suitable for transporting the materials 
under consideration including but not limited to centrifugal, 
positive-displacement, and/or other pumps known in the art. 
In most cases, it is desirable and important from a safety and efficiency 
standpoint to ensure that the pH of the leaching solution 22 be maintained 
at a level of about 9-11. At pH levels below 9, noxious gases are 
generated which endanger personnel. At pH levels above 11, recovery of the 
desired gold-cyanide complex (discussed below) can be hindered. To 
accomplish this goal as determined by preliminary and routine pilot 
studies, it may be necessary to periodically test and adjust the pH of the 
leaching solution 22 prior to and/or during use by adding a selected 
alkali composition to the solution 22. Preferred compounds suitable for 
this purpose include calcium oxide (which is also known as "lime" or CaO), 
as well as NaCO.sub.3 and/or NaOH. The alkali composition is schematically 
shown in FIG. 1 at reference number 34, and is introduced into the system 
10 via tubular conduit 36. The amount of alkali material to be used (if 
necessary) will vary depending on the relative pH of the leaching solution 
22, the chemical content of the ore 12 being processed, and other 
parameters including the specific type of processing system under 
consideration. The quantity of alkali material (and the general need for 
such an additive) may therefore be determined in accordance with routine 
testing procedures involving standard pH analyzing equipment which will 
provide a continuous monitoring of the leaching solution 22 before and 
during use thereof. In a representative and non-limiting embodiment, about 
0.1-1 g of calcium oxide (CaO) will typically be used per liter of the 
leaching solution 22 which is formulated as discussed above. Nonetheless, 
it is important to emphasize that the use of alkali materials (as well as 
any other additives) in the leaching solution 22 is optional, with the 
need for such materials again being determined in accordance with 
preliminary studies on the gold ore 12 being treated and other factors. 
The same situation exists in connection with the overall amount of 
leaching solution 22 to be employed in connection with the heap or pile 16 
of ore 12. However, in a representative and non-limiting embodiment (which 
is subject to variation if necessary as determined by preliminary 
analysis), about 200-500 gallons of the leaching solution 22 having the 
characteristics listed above will typically be used per ton of ore 12 (in 
rock or powder form). 
The leaching solution 22 is introduced into the pile 16 of rock materials 
14 (e.g. gold ore 12) at the top 40 thereof so that the leaching solution 
22 is placed in direct physical contact with the ore 12. Thereafter, the 
leaching solution 22 is allowed to pass downwardly (e.g. percolate) 
through the pile 16, extracting gold from the rock materials 14 (ore 12) 
as it passes over and through the ore 12. This process is facilitated by 
the fairly porous nature of the rock materials 14/ore 12 as discussed 
above. The resulting liquid product (shown in FIG. 1 at reference number 
42) is collected as it exits the pile 16 at the bottom 44 thereof. 
At this point, the liquid product 42 will contain unreacted cyanide 
materials therein (e.g. cyanide ions (CN).sup.- !), along with (1) a 
gold-cyanide complex; and (2) a copper-cyanide complex. The term 
"gold-cyanide complex" shall be defined to encompass a chemical complex 
containing one or more gold ions therein stoichiometrically combined with 
one or more cyanide ions (CN).sup.- !. This complex will typically 
consist of Au(CN).sub.2.sup.-1 (also known as an "aurocyanide ion") which 
is associated with one or more counter-ions including, for example, 
Na.sup.+ when NaCN is employed in producing the leaching solution 22, 
K.sup.+ when KCN is used, and Ca.sup.+2 when Ca(CN).sub.2 is involved. The 
Au(CN).sub.2.sup.-1 complex has a high level of stability with a K.sub.f 
of about 2.times.10.sup.38. A typical reaction sequence in which a 
gold-cyanide complex of the type described above is produced using a 
selected cyanide-containing leaching solution 22 is as follows: 
EQU 4Au.sub.(s) +8(CN).sup.-.sub.(aq) +O.sub.2(aq) +2H.sub.2 O.sub.(1) 
.fwdarw.4Au(CN).sub.2.sup.-.sub.(aq) +4OH.sup.-.sub.(aq) (4) 
This reaction is further described in Brown, T. L., et al., Chemistry, The 
Central Science, supra, p. 815. It is again important to emphasize that 
the reaction listed above will occur in connection with a wide variety of 
different cyanide-containing leaching solutions, with the present 
invention not being restricted to the use of any particular materials for 
this purpose. As discussed in considerable detail below, the gold-cyanide 
complex which results from the leaching process shown in FIG. 1 is 
subsequently treated to recover elemental gold therefrom. 
However, a discussion of the copper-cyanide complex is also warranted at 
this point. Regardless of which methods are used to obtain elemental gold 
from the gold-cyanide complex in the liquid product 42, a number of 
technical and economic problems can result in the cyanide leaching system 
10 when gold ore 12 is processed which contains substantial amounts of 
elemental copper therein. In all cyanide-based leaching processes of the 
type illustrated in FIG. 1, the costs associated with the initial 
cyanide-containing leaching solution 22 represent a substantial portion of 
the overall operating expense incurred in the processing of gold ore 12. 
The excessive consumption of cyanide materials will cause a considerable 
reduction in the operating efficiency of the entire processing system 10. 
It is therefore a goal of all cyanide-based gold leaching operations to 
minimize the use of cyanide compositions and avoid excessive losses of 
this material. However, when copper is present in the gold ore 12 as 
outlined above, a chemical "side-reaction" occurs which results in the 
excessive consumption of cyanide ions (CN).sup.- ! from the leaching 
solution 22. This side-reaction makes fewer cyanide materials available 
for the leaching of gold. Undesired and excessive cyanide ion consumption 
which occurs in the system 10 when elemental copper is present in the gold 
ore 12 takes place in accordance with the following chemical reaction: 
EQU 2Cu.sub.(s) +6(CN).sup.-.sub.(aq) .fwdarw.2Cu(CN).sub.3.sup.-2.sub.(aq)(5) 
This reaction consumes substantial amounts of free cyanide (CN).sup.- ! in 
order to produce a copper-cyanide complex, thereby increasing the overall 
cyanide requirements in the leaching process. The term "copper-cyanide 
complex" as used herein shall be defined to involve a chemical complex 
containing one or more copper ions stoichiometrically combined with one or 
more cyanide ions (CN).sup.- !. This complex will typically consist of 
Cu(CN).sub.3.sup.-2 (also known as a "cuprocyanide ion") which is 
associated with one or more counter-ions including, for example, Na.sup.+ 
when NaCN is employed in producing the leaching solution 22, K.sup.+ when 
KCN is used, and Ca.sup.+2 when Ca(CN).sub.2 is involved. Much of the 
copper-cyanide complex (Cu(CN).sub.3.sup.-2) which is generated as a 
result of this reaction passes unaffected through the gold extraction and 
isolation processes outlined above, and ultimately resides in the "barren" 
cyanide-containing solution materials which remain after the gold-cyanide 
complex is removed. This barren solution is normally reused/recycled in 
treating incoming amounts of additional gold ore 12. However, when the 
barren solution contains the copper-cyanide complex therein, this material 
(Cu(CN).sub.3.sup.-2) decomposes via oxidation or other processes to 
Cu(CN).sub.2.sup.-1 during exposure to air, bacterial action, and/or 
sunlight in storage ponds, on heaps 16 of gold ore 12, and the like. This 
copper-cyanide compound (Cu(CN).sub.2.sup.-1) represents a considerable 
problem in the recycled barren cyanide solution since Cu(CN).sub.2.sup.-1 
is chemically incapable of extracting gold from gold ore 12 to yield the 
desired gold-cyanide complex and instead recombines with fresh cyanide 
ions (CN).sup.- ! that are added during the reuse and recycling of the 
barren solution. As a result, the Cu(CN).sub.2.sup.-1 is then reconverted 
back into the copper cyanide complex described above 
(Cu(CN).sub.3.sup.-2), thus consuming two moles of (CN).sup.-. As more 
copper leaches into the recirculating leaching solution 22 (which occurs 
during reuse of this material and repeated passage thereof through 
incoming quantities of gold ore 12), increasingly large amounts of cyanide 
are irreversibly lost to this decomposition/cyanide consumption cycle. The 
presence of copper in the gold ore 12 being treated therefore presents 
significant problems from a functional and economic standpoint. 
In summary, the presence of elemental copper in the gold ore 12 being 
treated ultimately increases cyanide consumption in the system 10 by 
forming a copper-cyanide complex (Cu(CN).sub.3.sup.-2) which can decompose 
to yield Cu(CN).sub.2.sup.-1. The Cu(CN).sub.2.sup.-1 in the recycle 
stream, when "conditioned" by the addition of fresh (CN).sup.- is 
reconverted to Cu(CN).sub.3.sup.-2 resulting in the loss of two moles of 
(CN).sup.- when the Cu(CN).sub.3.sup.2 compound is reformed. This loss 
(which involves excessive (CN).sup.- reagent consumption) significantly 
and adversely affects the cost efficiency of the entire gold processing 
operation. 
In addition to excessive cyanide consumption, copper materials within the 
gold ore 12 will also result in the production of an impure elemental gold 
product. Additional and more costly refining procedures must therefore be 
used to solve this problem. Likewise, if the Merrill-Crowe Process is 
employed (which involves a combination of elemental zinc with the leaching 
solution 22 containing the gold-cyanide complex therein), extraneous 
copper-containing materials (e.g. Cu(CN).sub.3.sup.-2) in the solution 22 
will dramatically reduce the precipitation efficiency of the Merrill-Crowe 
system by causing zinc passivation, with this term being defined above. 
Additional zinc will therefore be required which again increases overall 
production costs. Excessive copper contamination in the liquid product 42 
will also reduce the operating efficiency of the smelting process 
associated with this embodiment by causing prolonged smelting times. 
In systems which employ the Activated Carbon Process, copper materials 
(e.g. copper-cyanide complexes) can substantially inhibit the functional 
capabilities of the activated carbon, thereby "fouling" this material and 
causing increased carbon requirements. Current efficiency and consumption 
are likewise increased in subsequent electrowinning stages when copper 
materials are not removed from the system 10. Accordingly, the presence of 
copper-containing species in the liquid product 42 can cause a number of 
serious problems unless the copper is effectively removed. Regarding the 
amount of copper-cyanide complex (Cu(CN).sub.3.sup.-2) in the liquid 
product 42 at this point, it will typically contain about 
1.times.10.sup.31 3 -1.times.10.sup.-4 % by weight gold-cyanide complex 
and about 0.05-1.0% by weight copper-cyanide complex, although the claimed 
process shall not be restricted to a liquid product 42 having these 
parameters which will vary in accordance with the type of gold ore 12 
being processed and other extrinsic factors. 
The liquid product 42 may thereafter pass via tubular conduit 46 into an 
optional solids filter 50 which is used to remove extraneous particulate 
matter (e.g. residual ore materials or "gangue") from the liquid product 
42. In a preferred embodiment, the solids filter 50 will consist of a 
backwashable sand bed filter known in the art or other conventional system 
of comparable design. Solid materials trapped by the solids filter 50 
(schematically designated at reference number 52 in FIG. 1) are ultimately 
routed out of the filter 50 and system 10 for disposal through tubular 
conduit 54. The use of a solids filter 50 for this purpose is again 
optional as determined by preliminary pilot studies on the particular 
liquid product 42 under consideration and its overall solids content. 
After passage of the liquid product 42 through the solids filter 50 (if 
used), the liquid product 42 is ready for further processing in accordance 
with the unique method of the present invention. However, it is again 
important to emphasize that all embodiments of the claimed process shall 
not be restricted to any particular type of initial leaching process, with 
any procedure being suitable for use herein provided that some type of 
dissolved cyanide-containing solution is placed in physical contact with 
the gold ore under consideration. In addition to the "heap leaching" 
procedure outlined above and illustrated in FIG. 1, the invention is 
likewise applicable to a procedure known as "vat leaching" Vat leaching 
basically involves a technique in which the gold ore 12 is placed in large 
containers or "vats" which are entirely or partially closed (not shown). 
These vats are discussed in detail above. The gold ore 12 (in the form of 
rock materials 14 or powder) is then placed in direct physical contact 
with the leaching solution 22 inside the vat(s). All of the other 
information provided above regarding heap leaching (including the chemical 
content of the cyanide-containing leaching solution 22) is equally 
applicable to vat leaching techniques. Heap or vat leaching facilities are 
currently in widespread use throughout the United States and in other 
countries. For example, in 1989, the United States had about eighty heap 
leach or vat leach operations, with most of them being located in Nevada. 
Other large leaching operations are currently taking place in Peru, 
Ecuador, Chile, South Africa, Indonesia, Canada, and elsewhere. Further 
general information regarding the leaching process of FIG. 1 (and 
cyanide-based gold leaching in general), as well as various parameters 
associated with these procedures are presented in U.S. Pat. No. 5,264,192; 
Thomas, R. (ed.), E/MJ Operating Handbook of Mineral Processing, 
McGraw-Hill, Inc., pp. 22-23 (1977); Clennell, J., The Cyanide Handbook, 
McGraw-Hill, Inc., pp. 102-132 (1915); and Bernard, G. M. "Andacollo Gold 
Production--Ahead of Schedule and under Budget", Mining Engineering, pp. 
42-47 (August 1996) which are all incorporated herein by reference. 
The completed liquid product 42 containing (1) the gold-cyanide complex; 
and (2) the copper-cyanide complex is now ready for further processing in 
accordance with the embodiment of FIG. 1 so that both of these 
compositions can be separated from each other. It should also be noted at 
this point that the liquid product 42 may likewise contain other materials 
therein (e.g. dissolved metal containing-species derived from a number of 
different metals including silver (Ag), lead (Pb), and the like). The type 
and amount of these additional materials in the liquid product 42 will 
depend on the particular ore 12 being treated, although such materials are 
typically present in very small quantities which shall be considered 
negligible and of minimal consequence for the purposes of this invention. 
The liquid product 42 may either be temporarily stored in one or more 
large outdoor pond-type structures (not shown) or immediately subjected to 
further processing, depending on the overall capacity of the system 10 as 
determined by preliminary testing. The unique separation process 
associated with the gold-cyanide complex and the copper-cyanide complex in 
the liquid product 42 will now be outlined in detail. 
B. The Gold-Copper Separation Process 
With continued reference to FIG. 1, the liquid product 42 is routed 
directly from the pile 16, the solids filter 50 (if used), or a temporary 
holding pond (if employed) into the separatory system 56 of the present 
invention via tubular conduits 60, 62. The separatory system 56 generally 
consists of at least one and preferably multiple nanofiltration membrane 
units. A single, representative nanofiltration membrane unit 64 is 
illustrated in schematic format in FIG. 1. However, it should be noted at 
this point that the present invention shall not be restricted to any 
specific arrangement or number of nanofiltration membrane units. If 
multiple membrane units are employed, they may be configured in series, in 
parallel, or in a combination of both as discussed in greater detail below 
(along with specific examples). The ultimate arrangement of nanofiltration 
membrane units in the separatory system 56 will depend on a variety of 
factors including the chemical character and content of the liquid product 
42, the overall size/capacity of the system 10, the incoming flow rate of 
the liquid product 42, the size of the nanofiltration membrane units under 
consideration, and other factors as determined by preliminary testing. For 
example, in applications involving a liquid product 42 having a relatively 
high incoming flow rate (e.g. exceeding about 1000 GPM or more), the 
liquid product 42 is preferably divided into a plurality of portions which 
are passed through a series of nanofiltration membrane units operated in 
parallel, followed by passage of the liquid product 42 through a series of 
nanofiltration membrane units operated in series. This technique enables 
relatively large initial feed streams to be handled and treated in a more 
rapid and efficient manner without overloading the system 10. In addition, 
the ultimate number of nanofiltration membrane units in the separatory 
system 56 will likewise vary (ranging from one to multiple units), again 
depending on the amount of liquid product 42 to be treated, the 
concentration of the copper-cyanide complex and gold-cyanide complex in 
the liquid product 42, the initial flow rate, and other factors. As 
previously noted, specific examples of multiple nanofiltration membrane 
systems which are suitable for use herein will be provided below. 
The claimed invention shall likewise not be limited to any incoming flow 
rate in connection with the liquid product 42 as it enters the separatory 
system 56. Regardless of whether a single or multiple nanofiltration unit 
system is employed, it is preferred that the liquid product 42 be 
delivered to the selected separatory system 56 (e.g. nanofiltration 
membrane unit(s)) at a representative, non-limiting flow rate of about 
100-10,000 GPM (gallons per minute), with this parameter being varied as 
needed in accordance with routine preliminary testing procedures. 
However, prior to filtration of the liquid product 42 using the 
nanofiltration membrane separatory system 56 as discussed in substantial 
detail below, another important factor merits further consideration. 
Specifically, at least one antiscalant composition may optionally be added 
to the liquid product 42 prior to nanofiltration in the separatory system 
56. The use of an antiscalant composition is preferred when the liquid 
product 42 contains substantial amounts of dissolved calcium or other 
sparingly soluble salts therein. For example, the addition of an 
antiscalant composition is desirable when the liquid product 42 contains 
more than about 0.1 g/l of calcium ions therein. Dissolved calcium within 
the liquid product 42 may come from the ore 12 being treated and/or can 
result from the use of "hard" water to initially prepare the aqueous 
leaching solution 22. With reference to FIG. 1, a supply of a selected 
antiscalant composition (discussed further below) is shown at reference 
number 66 which is delivered to the liquid product 42 prior to treatment 
in the nanofiltration membrane separatory system 56 via tubular conduit 
70. 
The addition of at least one antiscalant composition 66 (FIG. 1) will 
prevent the formation of calcium precipitates or other sparingly soluble 
salts (e.g. CaSO.sub.4 and/or CaCO.sub.3) during nanofiltration. Such 
precipitates can clog (e.g. foul) the selected nanofiltration membrane(s) 
in the separatory system 56, thereby reducing the operational efficiency 
of the entire processing system. The amount of antiscalant composition 66 
to be employed will depend on numerous factors, including but not limited 
to the chemical character of the liquid product 42, the pH of the liquid 
product 42, the amount of dissolved calcium within the liquid product 42, 
and other extrinsic factors. In this regard, preliminary pilot tests on 
the liquid product 42 of interest may be used to determine whether 
antiscalant compositions are needed and how much antiscalant compositions 
should be used. However, in a representative and non-limiting embodiment 
involving a situation in which the use of a selected antiscalant 
composition 66 is warranted, about 1.times.10.sup.-2 -1.times.10.sup.-4 
grams of the selected antiscalant composition 66 will typically be used 
per liter of the liquid product 42. Again, this value may be varied as 
needed. It should also be noted that the antiscalant composition 66 may 
simply be added to the liquid product 42 in the foregoing amount as a 
routine practice without conducting preliminary analyses of the calcium 
ion content thereof. 
Numerous materials may be used in connection with the antiscalant 
composition 66, and the present invention shall not be limited to any 
particular antiscalant material. Exemplary compounds suitable for use as 
the antiscalant composition 66 include but are not limited to sodium 
hexametaphosphate and sodium polyacrylate in water (commercially available 
from the American Cyanamid Company of Wayne, N.J. (USA) under the name 
"Cyanamer P-70"). 
With continued reference to FIG. 1, the specialized treatment process 
involving the liquid product 42 will now be discussed. As previously 
indicated, the separatory system 56 uses nanofiltration technology to 
isolate the desired materials in this case. Nanofiltration is a unique 
concept which was first recognized and developed in the late 1980s. While 
most commercially available nanofiltration membranes are proprietary in 
nature, they all have specific characteristics as described in Lein, L., 
"Nanofiltration: Trend of the Future|", Water Conditioning & Purification, 
pp. 24-27 (September 1992). Further information regarding nanofiltration 
is also presented in U.S. Pat. No. 5,476,591 to Green which is 
incorporated herein by reference. Nanofiltration membranes will typically 
prevent the passage therethrough of materials (e.g. ions, particles, and 
the like) which have a size (average diameter) that exceeds about 10-20 
angstroms. In contrast, ultrafiltration membranes will typically prevent 
the passage therethrough of materials having a size (average diameter) 
exceeding about 50-200 angstroms. Of even greater importance in this case 
is the substantial difference in filtration capability between 
nanofiltration membranes and reverse osmosis membranes. Reverse osmosis 
membranes will normally prevent the passage therethrough of compositions 
having a size (average diameter) greater than about 2-5 angstroms. 
There is a significant and substantial difference between nanofiltration 
systems and other membrane technologies including reverse osmosis. 
Regarding separation characteristics, nanofiltration is located between 
reverse osmosis and ultrafiltration, and fills the "gap" that exists 
between these two technologies as outlined in Cheryan, M., et al., 
"Consider Nanofiltration for Membrane Separations", Chemical Engineering 
Progress, pp. 68-74 (March 1994) which is incorporated herein by reference 
and fully explains the substantial differences between nanofiltration and, 
for example, reverse osmosis. The significant dissimilarities in capacity 
and operational ability which exist between nanofiltration membranes and 
reverse osmosis membranes include many items. For example, according to 
the above-listed article, nanofiltration membranes effectively operate at 
lower pressures of about 1.4 MPa/200 psi compared with reverse osmosis 
membranes which normally have operating pressure requirements exceeding 
about 4 MPa. Most commercially available nanofiltration membranes also 
have a very high membrane flux which enables them to operate at relatively 
low fluid pressures (e.g. 75-200 psi). The term "membrane flux" as used 
herein is defined as the flow rate/capacity of materials through the 
selected membrane as a function of the membrane area in, for example, 
gallons per ft.sup.2 per day ("GFD"). There are also differences in the 
types of materials which can pass through these membranes as discussed in 
the foregoing article. 
The use of one or more nanofiltration membranes in the separatory system 56 
of the present invention provides numerous advantages compared with other 
membrane types including reverse osmosis. These advantages again include 
but are not limited to lower required operating pressures, higher flux 
levels, and reduced fouling tendencies. Likewise, it has been discovered 
in accordance with the present invention that nanofiltration membranes are 
particularly well-suited (compared with other membrane types) for 
effectively differentiating between the copper-cyanide complex and the 
gold-cyanide complex in the liquid product 42 generated within the system 
10 so that these materials can be separated from each other. The high 
degree of separation efficiency achieved by nanofiltration membranes 
involving copper and gold-containing species results from the ability of 
these membranes to differentiate between metal ions based on charge, with 
the scientific basis for this ability not being currently understood. For 
this reason, nanofiltration membranes are preferred for use in the 
separatory system 56 of the invention and represent a unique development 
in the art of the gold processing, especially in the treatment of "impure" 
copper-containing gold ore 12. 
A number of different commercially available nanofiltration membrane units 
may be employed in the separatory system 56 (e.g. as the nanofiltration 
membrane unit 64 shown in FIG. 1.) A representative nanofiltration 
membrane cartridge unit suitable for use herein is produced by 
Desalination Systems, Inc. of Escondido, Calif. under the name "Desal-5". 
This membrane unit is typically configured in the form of an elongate 
cartridge which is illustrated schematically in FIG. 2 at reference number 
100. Each cartridge 100 is typically about 40 inches long and preferably 
between about 4-8 inches in diameter. The cartridge 100 includes a housing 
102 having a first end 104 and a second end 106. The first end 104 and the 
second end 106 are both open so that fluids may pass through the housing 
102. In the center of the cartridge 100 is an elongate conduit 110 having 
numerous openings 112 therethrough. Surrounding the conduit 110 are 
multiple, spirally-wound layers 114 of filter membrane material which is 
proprietary in structure and chemical composition. Also associated with 
the layers 114 of filter membrane material are layers 116 of a porous 
spacer material (e.g. a proprietary plastic/polymer mesh) and layers 120 
of a porous membrane backing material (e.g. also manufactured of a 
proprietary porous plastic composition) to which the layers 114 of filter 
membrane material are affixed. In use, the fluid to be treated (e.g. the 
liquid product 42) enters the first end 104 of the cartridge 100 in the 
direction of arrow "X". The selected fluid is not allowed to enter the 
elongate conduit 110 which is designed to receive filtered permeate as 
described below. As a result, the incoming fluid (liquid product 42) 
passes between and through the layers 114 of filter membrane material. A 
retentate is formed between the layers 114 of filter membrane material 
which consists of materials that cannot pass through the layers 114 (e.g. 
the copper-cyanide complex in the liquid product 42 as discussed further 
below). In contrast, liquids and other materials associated therewith 
(e.g. the gold-cyanide complex of the present invention) which actually 
pass through the layers 114 of membrane material, layers 116 of spacer 
material, and layers 120 of backing material are collectively designated 
as the permeate. The permeate ultimately enters the conduit 110 via the 
openings 112 therethrough. It should be noted that the permeate flows 
inwardly toward the conduit 110 in a direction "Y" which is perpendicular 
to the direction of arrow "X". As a result, the permeate is allowed to 
leave the conduit 110 at the second end 106 of the cartridge 100 in the 
direction of arrow "P". The retentate flows along and between the layers 
114 of filter membrane material and ultimately leaves the cartridge 100 at 
the second end 106 thereof in the direction of arrow "R". The flow of 
retentate in this manner (which is conventionally characterized as 
"cross-flow" filtration) is facilitated by continuous fluid pressure 
exerted on the system by incoming fluid materials (e.g. the liquid product 
42). 
As stated above, the cartridge 100 illustrated in FIG. 2 is available from 
Desalination Systems, Inc. of Escondido, Calif. under the name "Desal-5". 
However, other commercially-available nanofiltration systems/cartridge 
units may be used in connection with the present invention including but 
not limited to those produced by Osmonics, Inc. of Minnetonka, Minn. (USA) 
under the product designation "B-type TLC"; Hydranautics, Inc. of 
Oceanside, Calif. (USA) model 4040-TFV-7450!; and Film Tech, Inc. of 
Minneapolis, Minn. (USA) model NF-45!. Accordingly, the claimed invention 
shall not be restricted to any particular type or arrangement of 
nanofiltration units. Furthermore, as previously noted, the number of 
cartridges 100 which function as the nanofiltration membrane unit(s) 64 in 
the separatory system 56 may be selectively varied, depending on the type 
and amount of incoming fluid (e.g. liquid product 42) to be treated. For 
example, if 10,000 gallons of the liquid product 42 having the composition 
values/ranges listed above are to be treated at an incoming flow rate of 
about 100 GPM, optimum results will be achieved if 36 "Desal-5" cartridges 
100 are used in series, with each cartridge 100 being about 40 inches long 
and about 8.0 inches in diameter. Likewise, in cases involving a 
relatively high incoming flow rate (e.g. exceeding about 1000 GFD or 
more), the liquid product 42 is preferably divided into a plurality of 
portions which are passed through a series of nanofiltration membrane 
units operated in parallel, followed by passage of the liquid product 42 
through a series of nanofiltration membrane units operated in series. This 
technique enables relatively large initial feed streams to be handled and 
treated in a more rapid and efficient manner without overloading the 
system 10. While a number of different nanofiltration cartridge unit 
arrangements may be employed for this purpose (with the present invention 
not being restricted to any specific arrangement), a representative system 
would involve first dividing the incoming liquid product 42 into two equal 
fractions. Each fraction would thereafter be treated in a separate 
"branch" or stage of the nanofiltration separatory system 56. In a 
preferred embodiment, each stage would include two cartridges 100 (e.g. of 
the type discussed above including "Desal-5" cartridges) in parallel, 
followed by two cartridges 100 in series. The retentates and permeates 
from both "stages" would then be rejoined at the end of the separatory 
process for further treatment, etc. However, this particular system 
represents a single, non-limiting embodiment with a number of other 
nanofiltration systems having different arrangements of cartridge units 
also being suitable for use herein. 
Having presented a specific discussion of nanofiltration membrane 
technology and its distinctive character relative to other filtration 
membrane types including reverse osmosis membranes and ultrafiltration 
membranes, the unique abilities of nanofiltration technology in connection 
with the claimed process will now be addressed. Specifically, upon 
delivery of the liquid product 42 to the nanofiltration membrane 
separatory system 56 (e.g. the nanofiltration membrane unit 64), a 
retentate 130 is generated which does not pass through the nanofiltration 
membrane(s) associated with the separatory system 56 (membrane unit 64) 
and a permeate 132 is produced which does, in fact, flow through the 
nanofiltration membrane(s) associated with the separatory system 56. In a 
representative and non-limiting embodiment involving the preferred flow 
rates indicated above, the permeate 132 will optimally pass through the 
nanofiltration membrane(s) of the separatory system 56 (e.g. which uses a 
single nanofiltration unit or multiple units) at a representative membrane 
flux rate of about 2-20 GFD. In addition, it is desired that the system 10 
be capable of processing at least about 100-10,000 gallons of the liquid 
product 42 per minute which can be accomplished in accordance with the 
numerical parameters listed herein. 
The retentate 130 comprises the copper-cyanide complex therein as discussed 
above, while the permeate 132 contains the desired gold-cyanide complex, 
with both of these materials being effectively separated from each other 
using the nanofiltration membrane separatory system 56 (e.g. the 
nanofiltration membrane unit 64 shown in FIG. 1.) The retentate 130 is 
specifically routed out of the separatory system 56 via tubular conduit 
134, with the permeate 132 being directed out of the system 56 using 
tubular conduit 135. The retentate 130 may either be discarded, sent to a 
suitable storage facility, or (more preferably) reprocessed as discussed 
in substantial detail below to recover elemental copper therefrom. In this 
regard, the present invention shall not be restricted to any particular 
method, process, or use in connection with the retentate 130. Nonetheless, 
for the reasons discussed above, it is of primary importance that the 
copper-cyanide complex be isolated and removed from the system 10 in this 
embodiment. As a result, an elemental gold product of greater purity can 
be produced since any possible interference with subsequent gold refining 
stages by the copper-cyanide complex is substantially eliminated upon the 
removal of this material from the system 10. Likewise, separation of the 
copper-cyanide complex from the gold-cyanide complex in the liquid product 
42 using the techniques discussed above avoids reintroducing the 
copper-cyanide complex into the system 10 during the subsequent 
recirculation and recycling of cyanide-containing solutions. 
Reintroduction of the copper-cyanide complex into the system 10 can cause 
substantial cyanide losses as outlined in considerable detail above and is 
therefore undesired. 
By using the membrane-based separatory system 56 which involves the 
application of nanofiltration technology in an entirely unique manner 
(e.g. in connection with the processing of "impure" copper-containing gold 
ore 12), the gold-cyanide complex and the copper-cyanide complex can be 
separated from each other in a highly effective manner. In accordance with 
this technique, approximately 80-98% of the copper-cyanide complex can 
ultimately be removed from the liquid product 42 which provides the many 
benefits listed above. Likewise, the use of nanofiltration technology for 
this purpose is equally applicable to a wide variety of different cyanide 
leaching systems and shall not be exclusively restricted to the system 10 
shown in FIG. 1. 
It should also be noted that, if desired in accordance with preliminary 
testing procedures, the permeate 132 can optionally be re-filtered (e.g. 
passed through another nanofiltration stage) to further improve the purity 
of the permeate 132. This may be accomplished in the embodiment of FIG. 1 
by rerouting the permeate 132 back into the nanofiltration separatory 
system 56 (e.g. the membrane unit 64) via tubular conduit 136 shown in 
dashed lines in FIG. 1. Alternatively, in situations involving large 
volumes of permeate 132 which are being generated in a high-capacity 
system (e.g. which are characterized by flow rates of about 1000 GPM or 
more), an auxiliary nanofiltration separatory system not shown! separate 
from the main separatory system 56 can be employed for this purpose. In a 
representative and non-limiting embodiment, an exemplary auxiliary system 
would involve passing the permeate 132 through two nanofiltration 
cartridges 100 (e.g. of the type discussed above including "Desal-5" 
cartridges) in parallel, followed by two nanofiltration cartridges 100 in 
series. However, it is again important to emphasize that the use of an 
auxiliary separatory system as outlined above is optional and employed on 
an as-needed basis as determined by many factors including the chemical 
content of the permeate 132 and the overall operating capacity of the 
entire system 10. 
At this stage, isolation and collection of the gold-cyanide complex (which 
resides within the permeate 132) is now completed. The gold-cyanide 
complex can thereafter be treated in any known manner to collect and 
refine elemental gold therefrom, with the claimed invention not being 
restricted to any subsequent gold treatment/isolation methods. However, to 
provide a complete disclosure of the present invention, a number of 
representative gold isolation techniques will now be discussed. 
C. Isolation and Recovery of Elemental Gold From the Membrane Permeate 
A number of different approaches exist which may be used to treat the 
membrane permeate 132 so that elemental gold can be obtained therefrom. 
Representative, non-limiting processes suitable for this purpose will now 
be discussed. The first procedure of interest involves a technique known 
as The Merrill-Crowe Process. The Merrill-Crowe Process (which was 
initially developed in approximately 1897) is also conventionally known as 
"zinc cementation/precipitation". Specifically, the permeate 132 (which 
primarily comprises water in combination with the gold-cyanide complex) is 
combined with elemental zinc (Zn) in accordance with the following 
reaction: 
EQU 2Au(CN).sub.2.sup.-1.sub.(aq) +Zn.sub.(s) .fwdarw.2Au.sub.(s) 
+Zn(CN).sub.4.sup.-2.sub.(aq) (6) 
Various lead salts (e.g. lead acetate and/or lead nitrate) may also be 
added to the reaction process as needed in order to improved the 
efficiency of the zinc cementation process. The amount of elemental zinc 
to be used in this procedure will vary as determined by routine 
preliminary testing in accordance with numerous factors including the 
amount of gold-cyanide complex to be treated. However, it is preferred 
that the quantity of zinc combined with the permeate 132 be carefully 
controlled so that excesses of zinc are avoided (for economic reasons and 
to control the production of large amounts of undesired zinc by-products 
e.g. zinc-cyanide complexes, namely, Zn(CN).sub.4.sup.-2 !.) In a 
representative and non-limiting embodiment, approximately 0.003-0.015 g of 
elemental zinc powder (typically having a particle size of about 40-400 
microns) is used per liter of the permeate 132 which contains the 
gold-cyanide complex therein. Again, this quantity may be varied as needed 
and desired in accordance with preliminary testing. 
With reference to FIG. 1, the Merrill-Crowe Process is schematically 
illustrated. Specifically, a supply of powdered elemental zinc 138 having 
the characteristics listed above is combined with permeate 132 via tubular 
conduits 139, 140. Implementation of this process generates solid 
elemental gold which resides within a gold-zinc solid sludge reaction 
product 142. This material is thereafter routed via tubular conduit 146 
into a refining system 148 (schematically illustrated in FIG. 1) which is 
used to obtain purified elemental gold from the reaction product 142. The 
refining system 148 may involve a number of conventional steps, 
procedures, and materials which will now be discussed. For example, in a 
preferred embodiment of the refining system 148, the reaction product 142 
is filtered in order to remove residual liquid materials therefrom (which 
contain free cyanide ions (e.g. (CN).sup.- !) and very small amounts of 
the zinc-cyanide complex Zn(CN).sub.4.sup.-2 ! discussed above). The 
resulting liquid fraction (designated at reference number 150 in FIG. 1) 
can thereafter be re-used in the system 10 as a source of valuable cyanide 
ions for the treatment of incoming gold ore 12 which contains both 
elemental gold and copper. Because the copper-cyanide complex (which now 
resides in the membrane retentate 130) is not present in the liquid 
fraction 150, free cyanide ions (CN).sup.- ! in the liquid fraction 150 
are not "tied up" and may effectively be reused to treat incoming amounts 
of gold ore 12. Because the permeate 132 actually includes only about 1-5 
ppm of gold therein (which is nonetheless a significant amount in the gold 
mining industry), a correspondingly small quantity of elemental zinc 138 
is employed in this process. As a result, only a minor (e.g. negligible) 
quantity of the above-listed zinc-cyanide complex is produced. In 
accordance with this small amount of zinc-cyanide complex (compared with 
the large quantities of copper-cyanide complex previously in the system 
10), as well as chemical differences between the zinc-cyanide complex and 
the copper-cyanide complex, the liquid fraction 150 containing the 
zinc-cyanide complex can be re-used without the problems caused by the 
copper-cyanide complex. In the embodiment of FIG. 1, the valuable 
cyanide-containing liquid fraction 150 is re-routed back into the initial 
stages of the system 10 to be combined with fresh quantities of the 
cyanide-based leaching solution 22, thereby producing considerable cost 
savings. 
The liquid fraction 150 is separated from the solid portions of the 
reaction product 142 in the refining system 148 using conventional 
mechanical filtration devices known in the art or decantation/settling 
processes, and is thereafter routed out of the separation stages of the 
refining system 148 via tubular conduit 152. The liquid fraction 150 is 
then transferred via tubular conduit 154 back into the initial stages of 
the system 10 (e.g. into the vessel 24 containing the leaching solution 
22.) This important benefit (which enables impure copper-containing gold 
ore 12 to be processed in an economical manner) is directly achieved using 
the unique nanofiltration membrane separatory system 56 and corresponding 
method of the present invention. By removing the copper-cyanide complex 
from the system 10 as outlined above, the resulting "barren" 
cyanide-containing liquid fraction 150 can be reused while avoiding the 
excess consumption of cyanide which occurs when the copper-cyanide complex 
is present. Other benefits achieved by removal of the copper-cyanide 
complex include the production of a final gold product with increased 
purity levels and the avoidance of interfering side-reactions in 
subsequent stages of the refining system 148. 
The "dewatered" reaction product 142 is thereafter treated in the refining 
system 148 to isolate and remove elemental gold therefrom. A number of 
different techniques may again be employed for this purpose within the 
refining system 148 which shall not be restricted to any single method. 
For example, after being washed with water to remove residual free cyanide 
ions and any remaining Zn(CN).sub.4.sup.-2 complex, the reaction product 
142 may be combined with sulfuric acid (H.sub.2 SO.sub.4) in the presence 
of air in the refining system 148 to dissolve excess (unreacted) elemental 
zinc and other metals including copper and cadmium. This step is discussed 
in Van Zyl, D. J. A., et al., Introduction to Evaluation, Design and 
Operation of Precious Metal Heap Leaching Projects, supra, p. 150. The 
remaining solid materials are thereafter washed with water again and 
dried. If it is determined by preliminary experimental analysis that the 
resulting solid product contains substantial quantities of mercury (Hg), 
then the product may be further processed in a conventional mercury retort 
at about 400.degree. C. to release residual mercury into a condenser 
assembly which is optimally positioned under water to avoid the release of 
vaporized mercury into the atmosphere. In the alternative, as discussed in 
Brown, T. L., et al., Chemistry, The Central Science, supra, p. 815, the 
sludge-like reaction product 142 may instead be heated in air to form zinc 
oxide (ZnO) from residual elemental zinc which is thereafter sublimed 
away. 
The elemental gold-containing solid product which results from the 
procedures listed above may then be smelted within the refining system 148 
in combination with a selected flux composition that is designed to 
oxidize any remaining elemental zinc (as well as other residual non-gold 
metals) and thereby assist in the removal of metal oxides. Representative 
flux compounds suitable for this purpose include but are not limited to 
"borax" (e.g. Na.sub.4 B.sub.4 O.sub.7.10H.sub.2 O) and silica (e.g. 
SiO.sub.2) in combination. The specific flux materials, as well as the 
amounts of these compositions to be used in the smelting stage of the 
refining system 148 will be determined in accordance with preliminary 
pilot studies on the gold-containing solid product being processed. 
Likewise, specific information on the use of flux materials in general is 
again presented in Van Zyl, D. J. A., et al., Introduction to Evaluation, 
Design and Operation of Precious Metal Heap Leaching Projects, supra, p. 
150. Addition of the flux materials results in the generation of a 
borosilicate glass "slag" during smelting with this term being defined 
above. It should also be noted that, if needed as determined by 
preliminary pilot testing, feldspar may be added at approximately a 3% by 
weight level as a viscosity modifier. 
Smelting of the reaction product 142 takes place in a conventional furnace 
within the refining system 148 (e.g. a gas-fired or induction-type furnace 
system which is known in the art) at a temperature of approximately 
1150.degree. C. Finally, after removing the residual "slag" which 
gravimetrically separates and collects in the furnace, the elemental gold 
(e.g. characterized as "dore") is extracted from the furnace, thereby 
completing the production process. The elemental gold product is 
schematically designated in FIG. 1 at reference number 156. Again, the 
Merrill-Crowe Process is of conventional design and discussed in the 
foregoing references including Van Zyl, D. J. A., et al., Introduction to 
Evaluation, Design and Operation of Precious Metal Heap Leaching Projects, 
supra, pp. 126-127 and 149-150. It should also be noted that while the 
refining system 148 discussed above basically involves the steps of (1) 
filtration "dewatering"!; and (2) smelting, the system 148 may likewise 
incorporate a number of different steps. The term "refining" as used in 
connection with system 148 shall therefore encompass a variety of 
different processes which may be used to yield the final elemental gold 
product 156. 
Another method of interest in treating the membrane permeate 132 having the 
gold-cyanide complex therein involves a technique known as the Activated 
Carbon Process. The Activated Carbon Process employs a different approach 
compared with the Merrill-Crowe Process, with the Activation Carbon 
Process being schematically illustrated in FIG. 1 within dashed box 170. 
Specifically, the membrane permeate 132 which contains the gold-cyanide 
complex is placed in direct physical contact with a supply of activated 
carbon 172 via tubular conduits 174, 176 (FIG. 1). While not shown in the 
schematic representation of FIG. 1, this step typically occurs in large 
column-like structures. The term "activated carbon" as used herein 
involves particulate carbon materials having an amorphous character with a 
large surface area and a considerable number of pores or "activation 
sites". Activated carbon may be obtained from the charring of coconut 
shells or peach pits at approximately 700-800.degree. C., and will 
typically have the following optimum parameters (1) surface area=1050-1150 
m.sup.2 /gm; (2) apparent density=0.48 g/cc; (3) particle density=0.85 
g/cc; (4) voids in densely packed column=40%; and (5) representative 
particle sizes=minus 6-plus 16 mesh or minus 12-plus 30 mesh. However, the 
claimed invention (and activated carbon adsorption processes in general) 
shall not be restricted to these particular parameters which are provided 
for example purposes only. 
Once the membrane permeate 132 containing the gold-cyanide complex comes in 
contact with the activated carbon 172, an adsorption process occurs which 
is not yet entirely understood. Specifically, the gold-cyanide complex 
(which is defined herein to encompass aurocyanide ions, namely, 
Au(CN).sub.2.sup.-1) is adsorbed onto the surface of the activated carbon 
172 using a number of theoretical mechanisms including the possible 
presence of multiple "surface oxide sites" which enable adsorption to 
occur. This mechanism, as well as other general information regarding the 
Activated Carbon Process, is discussed in Arbiter, H., Gold--Advances in 
Precious Metals Recovery, supra, pp. 153-163 (1990); and Van Zyl, D. J. 
A., et al., Introduction to Evaluation, Design and Operation of Precious 
Metal Heap Leaching Projects, supra, 128-129; 138-149; and 151 which are 
again incorporated herein by reference. Generally, the supply of activated 
carbon 172 which is used in this method is operated in a "fluidized bed" 
mode which may be achieved through the use of a representative flow rate 
of about 25 gpm/ft.sup.2 associated with the carbon-containing column(s) 
when minus 6-plus 16 mesh carbon 172 is employed. When minus 12-plus 30 
mesh carbon 172 is used, a flow rate of about 15 gpm/ft.sup.2 is 
preferred. Both of these parameters will typically result in a bed 
expansion of about 60%. While this embodiment of the claimed invention 
shall not be restricted to any particular amount of activated carbon 172 
(which will be determined in accordance with routine preliminary testing), 
a representative and non-limiting example will involve the use of about 
2.5-10 g of activated carbon 172 (having the physical characteristics 
listed above) per liter of the permeate 132. 
Regardless of which mechanism ultimately results in adsorption of the 
gold-cyanide complex on the activated carbon 172, this approach 
effectively removes the gold-cyanide complex from the permeate 132 and 
generates a gold-containing carbon product 180 schematically illustrated 
in FIG. 1. The gold-containing carbon product 180 consists of the carbon 
172 having the gold-cyanide complex combined therewith. This process also 
results in the generation of a "barren" (e.g. stripped) liquid fraction 
182 which contains substantial amounts of water and free cyanide ions 
(CN).sup.- !, but lacks the copper-cyanide complex and gold-cyanide 
complex therein. This liquid fraction 182 can subsequently be recycled and 
reused to treat incoming amounts of gold ore 12 which provides a 
substantial conservation of resources and considerable economic 
advantages. In the embodiment of FIG. 1, the valuable cyanide-containing 
liquid fraction 182 is initially separated from the gold-containing carbon 
product 180 using conventional mechanical filtration devices or known 
decantation/settling processes. The liquid fraction 182 is then collected 
and transferred away from the remaining "dewatered" gold-containing carbon 
product 180 via tubular conduit 184. The liquid fraction 182 is 
subsequently re-routed back into the initial stages of the system 10 to be 
combined with fresh quantities of the cyanide-based leaching solution 22, 
thereby producing considerable cost savings. As shown in FIG. 1, the 
liquid fraction 182 is routed via tubular conduit 186 back into the 
initial stages of the system 10 (e.g. into the vessel 24 containing the 
fresh leaching solution 22.) This important benefit (which enables impure 
copper-containing gold ore 12 to be processed in an economical manner) is 
directly achieved using the specialized nanofiltration membrane separatory 
system 56 and corresponding method of the present invention as discussed 
above. By removing the copper-cyanide complex from the system 10, the 
resulting "barren" cyanide-containing liquid fraction 182 can be reused 
while avoiding the excess consumption of cyanide which occurs when the 
copper-cyanide complex is present. Other benefits achieved by removing the 
copper-cyanide complex include the production of a final gold product with 
increased purity levels and the avoidance of interfering side-reactions in 
subsequent stages of the refining process. 
Next, the "dewatered" gold-containing carbon product 180 is filtered again 
to remove residual liquid materials therefrom, followed by "desorption" or 
removal of the gold-cyanide complex from the carbon product 180. This is 
accomplished by using a selected eluant solution which is placed in direct 
physical contact with the gold-containing carbon product 180. With 
reference to FIG. 1, a supply of eluant solution 190 is combined with 
(e.g. passed through) the gold-containing carbon product 180 via tubular 
conduit 192. A representative eluant solution suitable for this purpose 
includes but is not limited to a solution of NaOH--NaCN (e.g. optimally 
about 0.5-1.0% by weight NaOH and about 0.1-0.3% by weight NaCN containing 
approximately 20% ethyl alcohol) as specifically discussed in Van Zyl, D. 
J. A., et al., Introduction to Evaluation, Design and Operation of 
Precious Metal Heap Leaching Projects, supra, p. 139. This solution is 
likewise heated in a preferred embodiment to a temperature of about 
77-120.degree. C. The claimed invention shall not be restricted to any 
particular amounts of eluant solution 190 which shall be determined in 
accordance with preliminary tests on the gold-containing carbon product 
180 being treated. However, in a representative and non-limiting 
embodiment, approximately 2-4 liters of the eluant solution 190 are 
typically used per kg of the gold-containing carbon product 180 (which 
this amount being subject to adjustment as needed). 
It is theorized that cyanide ions (CN).sup.- ! in the eluant solution 190 
described above effectively replace/exchange the adsorbed aurocyanide ions 
(gold-cyanide complex) which are released into the eluant solution 190. 
The resulting gold-containing eluant product 196 (which is in the form of 
a liquid and comprises the "released" gold cyanide-complex therein) is 
then collected from the "stripped" carbon product 180 via tubular conduit 
200 and further processed to recover elemental gold therefrom. The 
remaining "stripped" carbon product not shown! can be discarded or 
regenerated using conventional methods as discussed in Arbiter, H., 
Gold--Advances in Precious Metals Recovery, supra, pp. 159-160. 
At this point, the gold-containing eluant product 196 is transferred via 
tubular conduit 202 to a refining system 204 which is schematically shown 
in FIG. 1. The refining system 204 (which may involve a number of 
different treatment steps of conventional design) enables the recovery of 
elemental gold from the eluant product 196. Accordingly, this embodiment 
of the invention shall not be restricted to any particular methods, 
techniques, or processing equipment in connection with the refining system 
204. For example, gold isolation, collection, and recovery within the 
refining system 204 may be accomplished using zinc precipitation in 
accordance with the Merrill-Crowe Process as outlined above, although 
conventional electrowinning methods are preferred as part of the refining 
system 204. Electrowinning is discussed in Van Zyl, D. J. A., et al., 
Introduction to Evaluation, Design and Operation of Precious Metal Heap 
Leaching Projects, supra, pp. 143-148 and 151 which is again incorporated 
herein by reference. While electrowinning is a known procedure that has 
been employed in the mining industry for decades, the specific details of 
this process will now be summarized. First, an electrowinning "cell" not 
shown! is provided which includes one or more cathodes and anodes therein. 
Both of these elements are in fluid communication with the gold-containing 
eluant product 196 which is supplied to the cell housing having the 
cathodes and anodes therein. A direct current power supply is then 
operatively connected to the cathodes and anodes in each cell which causes 
the desired metal in solution (e.g. elemental gold in the gold-containing 
eluant product 196) to be directly deposited onto the cathodes. This 
process shall not be restricted to any particular materials used in 
connection with the cathodes and anodes, with a wide variety of 
conventional compositions being suitable for this purpose. In a 
representative and non-limiting embodiment, cathodes manufactured from 
steel wool (e.g. positioned in a plastic frame or wrapped around a 
stainless steel spool) and anodes produced from stainless steel, carbon, 
or titanium can be employed. Many different sizes, shapes, and overall 
design configurations may be selected in connection with the 
cathodes/anodes, with the claimed process (and the electrowinning 
procedure in general) not being restricted to any particular structures 
and physical parameters. While the power required for electrowinning will 
vary in accordance with many factors including the particular type of 
cell(s) involved, the gold concentration in the gold-containing eluant 
product 196, and the construction materials associated with the 
cathodes/anodes, a representative system will involve the application of 
approximately 2.5 volts between the cathodes and anodes in an exemplary 
electrowinning cell. 
Once the electrowinning process is completed, the elemental gold-containing 
cathodes are removed from the system and treated to recover elemental gold 
therefrom. The cathodes at this stage may contain up to about 50% or more 
gold thereon (e.g. up to about 100 oz. of elemental gold per lb. of 
cathode if steel wool is involved). To process the cathodes, they may 
initially be placed in contact with sulfuric acid (H.sub.2 SO.sub.4) in an 
optional pretreatment step which is designed to dissolve residual non-gold 
metals including copper, iron, and the like. The need for a sulfuric acid 
pretreatment stage is typically determined in accordance with preliminary 
pilot studies on the electrowinning products (e.g. cathodes) under 
consideration. If the cathodes contain substantial amounts of mercury 
(which will not usually be removed by sulfuric acid treatment), they may 
be subjected to conventional retort processes as discussed above. The 
cathodes are then smelted in combination with one or more selected flux 
compositions which are again designed to oxidize residual non-gold metals 
and thereby assist in the removal of metal oxides. Representative flux 
materials suitable for this purpose include but are not limited to "borax" 
(e.g. Na.sub.4 B.sub.4 O.sub.7.10H.sub.2 O) and silica (e.g. SiO.sub.2) in 
combination. The specific flux compositions and the amounts of these 
materials to be used in the smelting process will be determined in 
accordance with preliminary pilot studies on the gold-containing cathode 
materials being treated. More detailed information regarding the use of 
flux materials for this purpose is presented in Van Zyl, D. J. A., et al., 
Introduction to Evaluation, Design and Operation of Precious Metal Heap 
Leaching Projects, supra, pp. 150-151. Addition of the flux materials 
during smelting will result in the production of a borosilicate glass 
"slag" with this term being defined above. It should also be noted that, 
if needed as determined by preliminary testing, feldspar may be added at 
approximately a 3% by weight level as a viscosity modifier. 
The refining system 204 further includes a smelting stage in which each 
cathode is smelted in a conventional furnace (e.g. a gas-fired or 
induction-type furnace system that is known in the art) at a temperature 
of approximately 1150.degree. C. After removing the residual "slag" which 
gravimetrically separates and collects in the furnace, the elemental gold 
(e.g. characterized as "dore") is collected from the furnace, thereby 
completing the production process. The completed elemental gold product is 
schematically shown at reference number 206 in FIG. 1. Again, more 
detailed information regarding the Activated Carbon Process is described 
in the references cited above. It should also be noted that, while the 
refining system 204 in the present embodiment involves the steps of (1) 
electrowinning; and (2) smelting, the system 204 may likewise incorporate 
a number of different steps. The term "refining" as used in connection 
with system 204 shall therefore encompass a variety of different processes 
which may be used to yield the final elemental gold product 206. 
Both the Merrill-Crowe Process and the Activated Carbon Process constitute 
established procedures for collecting and recovering gold-containing 
species from cyanide-based leaching solutions (e.g. the membrane permeate 
132). It is likewise important to emphasize that the present invention 
shall not be restricted to any particular gold collection/isolation 
techniques. Instead, the claimed process is prospectively applicable to 
any method for recovering elemental gold from the membrane permeate 132. 
In addition to the Merrill-Crowe Process and the Activated Carbon Process 
(which are both preferred), other representative methods which may be 
employed to collect and isolate gold-cyanide complexes, following by 
additional purification to yield elemental gold include (1) solvent 
extraction procedures which use alkyl phosphorus esters, as well as 
primary, secondary, tertiary, and/or quaternary amines (alone or combined 
with phosphine oxides, sulfones, and/or sulfoxides) to extract 
gold-cyanide complex materials from leaching solutions; and (2) ion 
exchange methods and compositions (e.g. resins) in which aurocyanide ions 
are extracted from leaching solutions, with representative elution 
materials suitable for use with these compositions including sodium 
hypochlorite, zinc cyanide, thiocyanate, a mixture of thiocyanate/dimethyl 
formamide ("DMF"), and the like. Exemplary ion exchange resins which may 
be employed for this purpose include those sold under the trademark DOWEX 
and others which are commercially available from the Dow Chemical Company 
of Midland, Mich. (USA). Both of these gold isolation methods (combined 
with conventional electrowinning and smelting processes) represent 
alternative methods which may be used to isolate and collect elemental 
gold from the membrane permeate 132. These alternative techniques are 
discussed in Arbiter, H., Gold--Advances in Precious Metals Recovery, 
supra, pp. 164-185. 
D. Isolation and Recovery of Elemental Copper From the Membrane Retentate 
Finally, in accordance with the present invention, the membrane retentate 
130 (which contains the copper-cyanide complex) may be handled in two 
different ways. First, it can be disposed of by transfer to a waste dump 
site or other collection facility. Alternatively, it can be processed to 
recover elemental copper therefrom. A number of different methods exist 
for accomplishing this goal, with the claimed invention not being 
restricted to any particular procedure for this purpose. The term 
"treating" as used in connection with this optional stage is therefore 
applicable to a wide variety of refining processes. Specific methods for 
accomplishing this goal include but are not limited to the methods 
discussed below. 
As shown in FIG. 1, if subsequent treatment of the membrane retentate 130 
is desired, it can be routed via tubular conduit 210 into a refining 
system 212 so that a final elemental copper product 214 can be generated. 
The refining system 212 may involve the addition of a selected acid (e.g. 
sulfuric acid H.sub.2 SO.sub.4 !) to the membrane retentate 130 which 
causes a precipitation reaction to occur wherein the copper-cyanide 
complex is precipitated as solid (stable) CuCN, with "free" cyanide ions 
(CN).sup.- ! being converted to HCN.sub.(aq). The basic reaction 
associated with this process is as follows: 
EQU H.sub.2 SO.sub.4(aq) +Cu(CN).sub.3.sup.-2.sub.(aq) 
.fwdarw.SO.sub.4.sup.-2.sub.(aq) +2HCN.sub.(aq) +CuCN.sub.(s)(7) 
This procedure (which involves one example of a process which may be 
employed within the refining system 212) is specifically discussed in U.S. 
Pat. No. 996,170 which is incorporated herein by reference. The solid CuCN 
may thereafter be treated in accordance with a number of conventional 
methods to obtain the final elemental copper product 214. For example, 
representative procedures for achieving this goal include 
reduction-roasting with H.sub.2 gas to yield a "copper sand" that is 
thereafter smelted. 
Alternatively, another procedure which may be employed in connection with 
the refining system 212 involves combining the membrane retentate 130 with 
a selected acid (e.g. sulfuric acid H.sub.2 SO.sub.4 !) and sodium 
sulfide (Na.sub.2 S) to yield a Cu.sub.2 S precipitate in accordance with 
the following reaction: 
EQU Na.sub.2 S.sub.(s) +2H.sub.2 SO.sub.4(aq) +2Cu(CN).sub.3.sup.-2.sub.(aq) 
.fwdarw.2SO.sub.4.sup.-2.sub.(aq) +CU.sub.2 S.sub.(s) +4HCN.sub.(aq) 
+2NaCN.sub.(aq) (8) 
The Cu.sub.2 S precipitate may then be smelted to obtain the final 
elemental copper product 214 (FIG. 1). Further information regarding this 
particular process is outlined in U.S. Pat. No. 778,348 which is also 
incorporated herein by reference. 
In summary, the present invention involves a unique and highly-efficient 
method for separating gold-cyanide complexes from copper-cyanide complexes 
in a gold processing operation. The claimed method is highly versatile and 
provides the following important benefits: (1) the ability to process 
impure, copper-containing gold ore in an economical manner without the 
excessive consumption of cyanide compositions (e.g. free cyanide 
(CN).sup.- !); (2) an improvement in the operating efficiency of the 
entire gold processing system by reducing cyanide reagent costs; (3) the 
decreased consumption of other reagents in the system including activated 
carbon and zinc (depending on the particular recovery system under 
consideration); (4) a reduction in electricity consumption (if 
electrowinning is part of the overall processing system); (5) improved 
conservation of resources and reduced waste generation which collectively 
provide important environmental benefits; (6) a reduction in the amount of 
smelting time that is needed to yield an elemental gold product; (7) the 
ability to retain, purify, and collect elemental copper from the gold ore 
4 which can be sold at considerable economic benefit; (8) a high level of 
versatility and applicability to a wide variety of different cyanide-based 
processing methods; (9) improved gold purity levels in connection with the 
gold product "dore"; and (10) a general improvement in the simplicity, 
effectiveness, and efficiency of the gold production system. For these 
reasons and the other factors outlined below, the present invention and 
its various embodiments represent a significant advance in the art of gold 
production. 
Having herein described preferred embodiments of the invention, it is 
anticipated that suitable modifications can be made thereto by individuals 
skilled in the relevant art which nonetheless remain within the scope of 
the invention. For example, unless otherwise indicated herein, the 
invention shall not be limited to any particular structures, components, 
and hardware in connection with the claimed processes. Likewise, this 
invention shall not be restricted to any specific cyanide based leaching 
procedures or any refining methods involving the isolation of elemental 
gold and/or elemental copper from mined ore. The present invention shall 
therefore only be construed in accordance with the following claims: