Improved Means applicable for use in the Treatment of Ores .or Compounds containing Gold or Silver, and in Means applicable for use in the Treatment of such Materials with the aid of Solvents.
Year: 1897

page_text: PROVISIONAL SPECIFICATION.
Improved Means applicable for use in the Treatment of Ores .or
Compounds containing Gold or Silver, and in Means applicable for
use in the Treatment of such Materials with the aid of Solvents.
"
We, JOHN CUNINGHAME MONTGOMERIE, of Dalmore, Stair, in the County of Ayr,
Scotland, Justice of the Peace, and HENRY PARKES, of 237, Friern Road, Dulwich,
in the County of Surrey, England, Chemist, do hereby declare the nature of this
invention to be as follows:-
This invention relates to the treatment of auriferous and argentiferous ores or
compounds for the purpose of separating and collecting the gold and silver contained
therein; one modification thereof being specially adapted for use with ores or
tailings of a refractory character; the objects of the invention being to secure
expedition, a high percentage of extraction, and economy in the cost of working.
In applying our invention to the treatment of ores containing gold or silver or
gold and silver, we crush the ore sufficiently fine to admit of its passing through a
sieve of from 40 to 60 meshes to the lineal inch. Generally, the finer the ore is
pulverised, the higher the rate of extraction. The pulverised ore is subsequently
treated in a barrel or vessel along with water in sufficient quantity to render the
mixture of the consistency of thin mud. The water is put into the barrel or other
vessel employed and the following substances are added thereto :-(1) Cyanide of
potassium or of sodium or other cyanide or mixtures of cyanides, such as potassium
cyanide with sodium cyanide. (2) Ammonia or sodium oxide or their hydrates or
other alkaline oxide or a hydrate of an alkaline oxide or of an alkaline earth.
(3) Sodium dioxide, or sodium or potassium or other alkaline or earthy nitro-
prusside, bromide or fluoride. Or, barium dioxide or peroxide of lead may be
employed in conjunction with ammonium sulphate or other reagent operating to
liberate oxygen therefrom. Amongst these may be mentioned the alkaline salts of
bromine, fluorine, phosphorus, carbon and sulphur. In some instances, ammonium
sulphate may also with advantage he employed in conjunction with the bromide or
fluoride. Bromine or fluorine water may, if preferred, be substituted for a
bromide or fluoride. The barrel is then revolved for a short time in order to
thoroughly mix its contents; and, the ore having been added, the barrel is then
charged with air under a pressure of from, 50 to 100 lbs. per square inch, and is
maintained in rotation until the precious metals are so far as is practicable dis-
solved the time occupied with average ores being from 4 to 6 hours. The barrel
is thereupon emptied, the contents filtered and washed and the solution treated in
any known manner for the separation of the precious metals. We prefer however
to filter and to proceed as regards the re-use of the liquor in the manner set forth,
in the Specification to Letters Patent granted to me, the said John Cuninghame
Montgomerie, No. 12,641 of 1892, and as regards the recovery of the precious metals
from the solution in the manner described in the Specification to Letters l'atent,
No. 20,343 of 1893.
The treatment above referred to may also be carried out in tanks without air-

page_text: pressure or agitation. Under such circumstances, it is preferable to allow the
solvent liquid to percolate through the mass of ore repeatedly; the liquid, as it
passes away, being fed back to the surface of the ore until the precious metals are
sufficiently dissolved.
By way of example, a freemilling or ordinary refractory ore containing 40 ozs.
6 dwts. 1 grs. of gold and 1 ozs. 6 dwts. 3 grs. of silver per ton may be treated with
14 lbs. of cyanide of potassium, 10 lbs. of caustic soda, 5 lbs. of red lead, and 4 lbs.
of bromide or of sulphate of ammonia. These proportions will be subject to con-
siderable variation with different descriptions of ore, and according to the particular
chemical agents selected; the most suitable proportions being however readily
determinable by experiment. Inasmuch as a very small proportion of the chemicals,
such as the cyanide and caustic soda, is consumed during the treatment of the first
quantity of ore, the requisite quantity of chemicals necessary for the further
strengthening of the solution on re-use in order to bring it up to its original
strength, can only be determined on testing the liquid subsequently. to the treat-
ment of a second quantity of ore. In any case, the chemical agents mentioned'
under the 3rd head must be added to each charge of ore as their chemical action
becomes exhausted with each charge of ore. With ores or tailings operated on by
the tank method of treatment, weak solutions of cyanide and caustic alkali are
generally used, and the time allowed to complete the dissolution of the preciou
metals extended considerably, the rate of extraction being much slower. When
an insoluble salt is used in tank treatment without agitation, it may be mixed
with the ore, or spread upon the top of it, or arranged in layers throughout the ore.
In applying our invention to ores or tailings of a refractory character or to ores
in which the precious metals are combined with copper, zinc, lead, or other base
metals, the ore or other material having been crushed sufficiently fine to admit of
its passing through a sieve of from 30 to 60 meshes to the lineal inch, is calcined
or roasted in a reverberatory or other suitable calcining furnace or apparatus at a
low red heat, till the sulphides are decomposed and the metals converted, so far as
.possible, into sulphates and oxides, care being taken not to drive off the sulphur in
the form of an oxide as is usually done. When treating the "Broken Hill" sul-
phide silver ores or ores of a similar nature, the calcination is carried to a point at
which the ore ceases to gain weight. The calcined ore is then mixed with the
following chemical compound, the quantity necessary being determined by experi-
ment; but for ordinary ores, (including the Broken Hill" silver sulphide ores)
about five per cent. of the weight of the ore before calcination, will be sufficient:
namely: (1) 56 lbs. common salt; (2) 36 lbs. protosulphate of iron; (3) 20 lbs.
nitrate of soda. Instead of protosulphate of iron, mentioned as the second con-
stituent of the chemical compound, the following alternatives may be used, viz. :—
persulphate of iron, solidified sulphuric acid, bisulphate of soda, or of potash,
sulphate of soda, or other suitable sulphate. For the nitrate of soda, mentioned
as the third constituent of the chemical compound, any of the following may be
substituted, viz.:-nitrate of potash, manganate or permanganate of potash or of
soda, nitrate of baryta, pernitrate of iron, nitrate or oxide of lead, red lead (minium)
or peroxide of lead, plumbate of sodium or of potassium, peroxide of manganese,
or other suitable nitrate, oxide, peroxide, or plumbate. If perchloride of iron be
used as the second constituent, the third may be omitted.
66
The mixture is then allowed to remain in the calcining furnace for an hour to an
hour and a half, a dull red or red heat being maintained and the slightest admission
of air guarded against. (As a matter of economy in working, it is advantageous
to run several furnace charges into a special furnace, and then to damp it down;
the heat generated in bulk being sufficient if the compound be mixed with the red
hot calcined ore before it is taken from the furnace). When the mixture of calcined
ore and compound has been retorted for the requisite time, it is turned out, cooled,
ground, and placed in a large suction or gravity filter, and all soluble salts are
washed out with water. If the ore be of a free filtering nature, the filter may be
filled with water and the ore emptied in direct from the furnace after being broken

page_text: ap without being cooled or ground. The soluble salts having been washed out, a
ten per cent. (by volume) solution of sulphuric acid (sp. gr. 1'84) is run on and is
caused to percolate slowly through the mixture for about two hours; the solution
after passing through, being returned to the top of the filter. About 22 cwt: of
solution per ton of ore would be sufficient. It is now drawn off and another ten per
cent. solution of about the same quantity run on and allowed to percolate repeatedly
through it for about 18 hours; it is then drawn off and the ore washed free of acid.
The first acid solution drawn off is passed through another charge of ore in order
to exhaust the acid before the extraction of the metals from the solution.
This
charge of ore is then treated with the acid solutions as before mentioned.
The foregoing operations having extracted the soluble copper and zinc, a strong
solution of hyposulphite of soda (to which a small quantity of dioxide or peroxide of
soda or other suitable oxygen yielding substance may, if desired, be added) is now
run on the ore to extract the silver. The solution is allowed to percolate repeatedly
till the chloride of silver is dissolved; it is then drawn off, and the ore thoroughly
washed free from hyposulphite.
The copper is recovered from the solutions by passing them through a filter of
scrap iron; and the zinc by precipitation with carbonate of soda free
from hydrate, or by bicarbonate of soda, or a mixture of these, or
by electrolysis. The zinc precipitate will contain iron and other impurities
The
be separated from the zinc by distillation.
separated from the hypesulphite solutions in the usual way, as, for example, by
means of sodium sulphide or by electrolysis.
which
may
silver is
The foregoing treatment is suitable for the "Broken Hill" silver sulphide ores
or ores of a similar nature. In treating these ores, care must be taken to use a
sufficient quantity of acid solution in the first instance and of a strength sufficient to
prevent the solution becoming gelatinous. If too much acid be used, the solution
will turn into a jelly, and the charge be rendered unworkable. Ores which contain
arsenic and antimony are calcined at the beginning at a slightly higher temperature
in order to volatilize these metals, the addition of a little charcoal or carbonaceous
matter facilitating the liberation of the metals which may subsequently be
recovered by condensation. When the ore is tolerably free from them, the heat is
reduced to a low red heat, as before specified, and the calcination is continued. In
ores which do not gain weight in calcination, the calcination is carried to a point
which converts the sulphide into sulphates with as little loss in weight of ore as
possible. If too great a heat be used, the sulphates become decomposed and
volatilization of the precious metals takes place.
If an ore contain a large quantity of silver and a small quantity of gold, it is
expedient, after calcining the ore and treating it with the chemical compound
herein before described and washing out the soluble salts, first to treat it with a
hy posulphite solution, with a view to the extraction of the silver, and then to subject
the ore to a cyanide or chlorination process, for the purpose of extracting the gold.
If the ore be a gold one with little silver, not sufficient to repay the extra cost of
extraction by hyposulphite, it should be treated by the cyanide process, preferably
that covered by the hereinbefore recited Letters Patent, No. 12,641 of 1892, or by
the cyanide process hereinbefore described, or by a chlorination or bromination
process.
Ores which contain little or no copper and zinc may, after calcination, be washed
to remove the soluble salts and be then treated by the herein before mentioned
cyanide processes without the intervention of the compound treatment; but should
the cyanide fail to extract a satisfactory percentage of the gold and silver, or should
the consumption of the cyanide be too high for profitable working, then the ore
must undergo treatment by the chemical compound. The gold and silver are
recovered from the cyanide, chloride or bromide solutions by the charcoal process,
the subject of Letters Patent, No. 20,343 of 1893.
After washing out the soluble salts, the wash water usually contains gold, copper,
and zinc, when these metals are present in the ore treated. The acid solutions also
contain these metals. In order to separate the copper and zinc, or copper or zinc,

page_text: from the gold, we pass these solutions through a charcoal filter or series of filters
constructed in every respect like those used for a cyanide solution as hereinafter
described. The gold is retained in the charcoal, and the copper and zinc pass
through with the liquid. Should silver be present, it will also be extracted with
the gold. The copper and zinc are then extracted from the solutions in the manner
before described. For cyanide solutions of the precious metals containing copper
or zinc or both combined, we have found the same process applicable for the
separation of the gold and silver; the filtration being conducted in a similar way
to that described for the cyanide solutions hereinafter described. All solutions
containing copper and zinc passed through a charcoal filter for the extraction of the
precious metals should be washed out with water. The charcoal is then regener-
aied for reuse, in the manner hereinafter described. We have found that by merely
drying the charcoal (preferably in the sun) its precipitating qualities are restored.
For the extraction of the gold or silver or gold and silver at one operation, the
following process may be adopted; the same being also applicable in the extrac-
tion of gold, silver and cyanide from cyanide solutions of the precious metals.
Assuming the ground ore to have been treated with a solution of potassium
cyanide and filtered for the purpose of separating the solid from the liquid portion
of the charge, the effluent, containing the unused chemicals and the precious metals
in solution, is passed through a wood charcoal filter (preferably made from hard-
wood) or a series of such filters, the construction of which is hereinafter more
particularly described. The precise action of the charcoal on such a solution is
somewhat doubtful, but the chemical reactions appear to be as follow:-The
precious metals are liberated from the double cyanide of gold (or silver) and
potassium, and precipitated in a metallic state upon the charcoal; whilst the
cyanogen is absorbed by the charcoal. A portion of the free cyanide of potassium
is decomposed; the potassium, forming with the water a hydrate, passing through
the charcoal, whilst the cyanogen liberated is converted into hydrocyanic acid and
is absorbed therein. The following equations represent the probable reactions:-
Au CN.KCN+xC=(Au+xC+CN)+KCN; KCN+xC+H,=KHO+(xC+HCN).
The result of this action is that the charcoal in a short time ceases to effect the
separation and precipitation of the precious metals. This stage having been
reached, the charcoal is, according to the present practice, burnt for the purpose of
recovering the precious metals, the cyanogen present being dissipated by the heat
and lost.
Instead of burning the charcoal as above described, we retort it or pass super-
heated steam or hot air, or a combination thereof, through the same, for the purpose
of decomposing the cyanogen; its nitrogen uniting with the hydrogen of the steam
when used, and of the steam generated from the water of saturation contained in
the charcoal, and forming ammonia. By a secondary reaction, the ammonia is
converted into ammonium cyanide and ammonium bicarbonate by the action of the
carbonic oxide and carbonic acid. The following equations represent the probable
reactions:
(CN),+3 H,O=2NH,+CO+CO,. 3NH,+CO+CO,=NH_CN+NH_HCO,.
The hydrocyanic acid evolved in the decomposition of the cyanide of potassium
in the former equation is converted into ammonium cyanide and ammonium bi-
carbonate by the action of the heat and steam upon the charcoal and hydrocyanic.
The following equation represents the probable reactions:-
acid.
10 HCN+3CO,+14 H,O = 2 NH,CN+5NH,HCO,+5 CO+CH,+N+H.
The gases and vapour yielded pass off and are condensed, yielding ammonium
cyanide and ammonium bicarbonate in solution.
These products may be decomposed by heat, the ammonia yielded being conveyed
into water, and recovered therefrom in the usual way, and converted into sulphate
of ammonia, or used in the manufacture of a cyanide. We prefer, however, to use

page_text: the solution, the result of the aforesaid process of condensation, in the extraction
of the precious metals. Should it be found deficient in cyanogen, it must be
fortified to the original strength.
The charcoal is now free from the cyanogen or its compounds, which rendered it
inert, and is fit for further use in the extraction of the precious metals from cyanide
solutions containing the same.
By frequent regeneration of the charcoal in the manner above described we
have been enabled to deposit at the rate of 2,000 ozs. of the precious metals in a ton
of charcoal before resorting to the burning of the charcoal.
Before reusing the charcoal we cool it down to the temperature of the atmosphere
by passing cold air therethrough. In passing hot air or steam through the charcoal,
care must be taken not to apply them at such a temperature as to cause combustion,
of the charcoal.
A charcoal filter adapted for use in our improved process, comprises an enamelled
iron or other suitable vessel containing wood charcoal, in a powdered or granulated
state, capable of passing a to inch mesh sieve about 2 feet thick and lightly
rammed. The vessel is provided with a false bottom covered with asbestos or
other non-combustible fabric or material. A sheet of asbestos cloth or a piece of
perforated iron, stoneware or tile, is also placed upon the top of the charcoal tq
prevent it floating and to protect it against disturbance. The filter is closed with
a removeable top, and is furnished with pipe connections for the liquid and air and
for the resultant gases flowing to the condenser respectively. Beneath the false
bottom is a chamber for the reception of the filtered liquid, cocks being provided
for draining the chamber.
Another mode of charging the filter is to grind the charcoal to a powder, mix it
with a little water to form a paste, and then press it evenly into the filter; suction
being at the same time applied below. In this case, a thickness of six inches will
suffice; but in working, suction must be applied to draw the liquid through the
comparatively dense mass of filtering material.
By the foregoing method, the whole of the precious metals may be extracted from
the solution, as shown by fire assay, the consumption of charcoal largely
economised, and a large portion of the cyanide recovered in the form of ammonium.
evanide and ammonium bicarbonate, or sulphate of ammonia if desired.
Cyanide solutions which have been employed in the extraction of the precious
metals and which, in addition to such metals, contain caustic alkali, dioxides,
nitrates, nitrites, sulphates, carbonates, or bicarbonates, bromine, chlorine, or their
compounds, may be treated in a similar manner for the recovery of the precious
metals and of the cyanogen and its compounds.
Doted this 21st day of April 1897
Improved Means applicable for use in the Treatment of Ores or
Compounds containing Gold or Silver, and in Means applicable for
use in the Treatment of such Materials with the aid of Solvents.
We, JOHN CUNINGHAME MONTGOMERIE, of Dalmore, Stair, in the County of Ayr,
Scotland, Justice of the Peace, and HENRY PARKES, of 237, Friern Road, Dulwich,
in the County of Surrey, England, Chemist, do hereby declare the nature of this

page_text: °
invention and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement:―
This invention relates to the treatment of auriferous and argentiferous ores or
compounds for the purpose of separating and collecting the gold and silver contained
therein; one modification thereof being specially adapted for use with ores or tail-
ings of a refractory character; the objects of the invention being to secure expedi-
tion, a high percentage of extraction, and economy in the cost of working.
or
In applying our invention to the treatment of ores containing gold or silver or
gold and silver, we crush the ore sufficiently fine to admit of its passing through a
sieve of from 40 to 60 meshes to the lineal inch. Generally, the finer the ore is
pulverised, the higher the rate of extraction. The pulverised ore is subsequently
treated in a barrel or vessel along with water in sufficient quantity to render the
mixture of the consistency of thin mud. The water is put into the barrel or other
vessel employed and the following substances are added thereto :-(1) Cyanide of
potassium or of sodium or other cyanide or mixtures of cyanides, such as potassium
cyanide with sodium cyanide. (2) Sodium oxide or its hydrate (caustic soda)
other alkaline oxide or a hydrate of an alkaline oxide or of an alkaline earth.
(3) Sodium dioxide, or sodium or potassium or other alkaline or earthy nitro-
prusside, bromide or fluoride. Or, barium dioxide or peroxide of lead or other
suitable oxygen-yielding substance may be employed in conjunction with
ammonium sulphate or other reagent operating to liberate oxygen therefrom.
(Amongst these may be mentioned the alkaline salts of bromine, fluorine, phos-
phorus, carbon and sulphur). In some instances ammonium sulphate may also
with advantage be employed in conjunction with the bromide or fluoride. Bromine
or fluorine water may, if preferred, be substituted for a bromide or fluoride.
The barrel is revolved for a short time in order to thoroughly mix its contents;
and, the ore having been added, the barrel is then charged with air under a pressure
of from 50 to 100 lbs. per square inch, and is maintained in rotation until the..
precious metals are, so far as is practicable, dissolved; the time occupied with
average ores being from 4 to 6 hours. The barrel is thereupon emptied, the
contents filtered and washed and the solution treated in any known manner for the
separation of the precious metals. We prefer however to filter and to proceed as
regards the re-use of the liquor in the manner set forth in the Specification to
Letters Patent granted to me, the said John Cuninghame Montgomerie, No. 12,641
of 1892, and as regards the recovery of the precious metals from the solution in the
manner described in the Specification to Letters Patent, No. 20,343 of 1893.
The treatment above referred to may also be carried out in tanks without air-
pressure or agitation. Under such circumstances, it is preferable to allow the
solvent liquid to percolate through the mass of ore repeatedly; the liquid, as it
passes away, being fed back to the surface of the ore until the precious metals are
sufficiently dissolved.
By way of example, a freemilling or ordinary refractory ore containing 40 ozs.
6 dwts. 1 grs. of gold and 1 ozs. 6 dwts. 3 grs. of silver per ton may be treated with
14 lbs. of cyanide of potassium, 10 lbs. of caustic soda, 5 lbs. of red lead, and 4 lbs.
of bromide or of sulphate of ammonia. These proportions will be subject to con-
siderable variation with different descriptions of ore, and according to the
particular chemical agents selected; the most suitable proportions being however
readily determinable by experiment. Inasmuch as a very small proportion of the
chemicals, such as the cyanide and caustic soda, is consumed during the treatment
of the first quantity of ore, the requisite quantity of chemicals necessary for the
further strengthening of the solution on re-use in order to bring it up to its original
strength, can only be determined on testing the liquid subsequently to the treatment
of a second quantity of ore. In any case, the chemical agents mentioned under the
3rd head must be added to each charge of ore as their chemical action becomes
exhausted with each charge of ore. With ores or tailings operated on by the tank
method of treatment, weak solutions of cyanide and caustic alkali are generally
used, and the time allowed to complete the dissolution of the precious metals

page_text: extended considerably, the rate of extraction being much slower.
When an
insoluble salt is used in tank treatment without agitation, it may be mixed with
the ore, or spread upon the top of it, or arranged in layers throughout the ore.
In applying our invention to ores or tailings of a refractory character or to ores
in which the precious metals are combined with copper, zinc, lead, or other base
metals, the ore or other material having been crushed sufficiently fine to admit of
its passing through a sieve of from 30 to 60 meshes to the lineal inch, is calcined or
roasted in a reverberatory or other suitable calcining furnace or apparatus at a
low red heat, till the sulphides are decomposed and the metals converted, so far as
possible, into sulphates and oxides, care being taken not to drive off the sulphur (in
the form of sulphurous acid gas or any other oxide) as is usually done. When
treating the "Broken Hill" sulphide silver ores or ores of a similar nature, the
calcination is carried to a point at which the ore ceases to gain weight.
The
calcined ore is then mixed with the following chemical compound, the quantity
necessary being determined by experiment; but for ordinary ores (including the
"Broken Hill silver sulphide ores) about five per cent. of the weight of the ore
before calcination, will be sufficient; viz.:-(1) 56 lbs. common salt; (2) 36 lbs.
protosulphate of iron; (3) 20 lbs. nitrate of soda. Instead of protosulphate of iron,
mentioned as the second constituent of the chemical compound, the following
alternatives may be used, viz.:-Persulphate of iron, solidified sulphuric acid,
bisulphate of soda, or of potash, sulphate of soda, or other suitable sulphate. For
the nitrate of soda, mentioned as the third constituent of the chemical compound,.
any of the following may be substituted, viz.:-Nitrate of potash, manganate or
permanganate of potash or of soda, nitrate of baryta, pernitrate of iron, nitrate or
oxide of lead, red lead (minium) or peroxide of lead, plumbate of sodium or of
potassium, peroxide of manganese, or other suitable nitrate, oxide, peroxide, or
plumbate. If perchloride of iron be used as the second constituent, the third may
be omitted.
The constituents of the chemical compound may be varied to some extent to suit
the character of the ore under treatment; such adjustments being readily deter-
minable by experiment.
The mixture is then allowed to remain chlorinating in the calcining furnace
without being stirred for an hour to an hour and a half, a dull red or red heat being
maintained and the slightest admission of air guarded against. (As a matter of
economy in working, it is advantageous to run several furnace charges into a
special furnace, and then to damp it down; the heat generated in bulk being
sufficient if the compound be mixed with the red hot calcined ore before it is taken
from the furnace). When the mixture of calcined ore and compound has been
retorted for the requisite time, it is turned out, cooled, ground, and placed in a large
suction or gravity filter, and all soluble salts are washed out with water. If the
ore be of a free filtering nature, the filter may be filled with water and the ore
emptied in direct from the furnace after being broken up without being cooled or
ground. The soluble salts having been washed out, a ten per cent. (by volume)
solution of sulphuric acid (sp. gr. 1'84) is run on and is caused to percolate slowly
through the mixture for about two hours; the solution, after passing through,
being returned to the top of the filter. About 22 cwt. of solution
per ton of ore
would be sufficient. It is now drawn off and another ten per cent. solution of about
the same quantity run on and allowed to percolate repeatedly through it for about
18 hours; it is then drawn off and the ore washed free of acid. The first acid solu-
tion drawn off is passed through another charge of ore in order to exhaust the acid
before the extraction of the metals from the solution. This charge of ore is then
treated with the acid solutions as before mentioned.
The foregoing operations having extracted the soluble copper and zinc, a strong
solution of hyposulphite of soda (to which a small quantity of dioxide or per-
oxide of soda, or other suitable oxygen-yielding substance, may, if desired, be
added) is now run on the ore to extract the silver. The solution is allowed to
percolate repeatedly until the chloride of silver is dissolved; it is then drawn off,
and the ore thoroughly washed free from hyposulphite.

page_text: The copper is recovered from the solutions by passing them through a filter of
scrap iron; and the zinc by precipitation with carbonate of soda free from hydrate,
or by bicarbonate of soda, or a mixture of these, or by electrolysis. The zino
precipitate will contain iron and other impurities which may be separated from
the zinc by distillation. The silver is separated from the hyposulphite solutions in
the usual way, as, for example, by means of sodium sulphide or by electrolysis.
The foregoing treatment is suitable for the "Broken Hill" silver sulphide ores or
ores of a similar nature. In treating these ores, care must be taken to use a
sufficient quantity of acid solution in the first instance and of a strength sufficient
to prevent the solution becoming gelatinous. If too much acid be used, the solu-
tion will turn into a jelly, and the charge be rendered unworkable. Ores which
contain arsenic and antimony are calcined at the beginning at a slightly higher
temperature in order to volatilise these metals, the addition of a little charcoal or
carbonaceous matter facilitating the liberation of the metals which may sub-
sequently be recovered by condensation. When the ore is tolerably free from them,
the heat is reduced to a low red heat, as before specified, and the calcination is
continued. In ores which do not gain weight in calcination, the calcination is
carried to a point which converts the sulphides into sulphates with as little loss in
weight of ore as possible. If too great a heat be used, the sulphates become decom-
posed and volatilisation of the precious metals takes place.
If an ore contain a large quantity of silver and a small quantity of gold, it is
expedient, after calcining the ore and treating it with the chemical compound
herein before described and washing out the soluble salts, first to treat it with a
hyposulphite solution, with a view to the extraction of the silver, and then to
subject the ore to a cyanide or chlorination process, for the purpose of extracting
the gold. If the ore be a gold one with little silver not sufficient to repay the extra
cost of extraction by hyposulphite, it should be treated by the cyanide process,
preferably that covered by the herein before recited Letters Patent, No. 12,641 of
1892, or by the cyanide process herein before described, or by a chlorination or
bromination process.
Ores which contain little or no copper and zinc may, after calcination, be washed
to remove the soluble salts and be then treated by the herein before mentioned
cyanide processes without the intervention of the compound treatment; but should
the cyanide fail to extract a satisfactory percentage of the gold and silver, or should
the consumption of the cyanide be too high for profitable working, then the ore
must undergo treatment by the chemical compound. The gold and silver are
recovered from the cyanide, chloride or bromide solutions by the charcoal process,
the subject of Letters Patent, No. 20,343, of 1893.
After washing out the soluble salts the wash water usually contains gold, copper,
and zinc, when these metals are present in the ore treated. The acid solutions
also contain these metals. In order to separate the copper and zinc, or copper
or zinc, from the gold, we pass these solutions through a charcoal filter or series of
filters constructed in every respect like those used for a cyanide solution as herein-
after described. The gold is retained in the charcoal, and the copper and zinc
pass through with the liquid. Should silver be present, it will also be extracted
with the gold. The copper and zinc are then extracted from the solutions in the
manner before described. For cyanide solutions of the precious metals containing
copper or zinc or both combined, we have found the same process applicable for
the separation of the gold and silver; the filtration being conducted in a similar
way to that described for the cyanide solutions hereinafter described. All
solutions containing copper and zinc passed through a charcoal filter for the extrac-
tion of the precious metals should be washed out with water. The charcoal is then
regenerated for re-use, in the manner hereinafter described. We have found that by
merely drying the charcoal (preferably in the sun) its precipitating qualities are
restored.
For the extraction of the gold or silver or gold and silver at one operation, the
following process may be adopted; the same being also applicable in the extraction
of gold, silver and cyanide from cyanide solutions of the precious metals.

page_text: Assuming the ground ore to have been treated with a solution of potassium
cyanide and filtered for the purpose of separating the solid from the liquid portion
of the charge, the effluent, containing the unused chemicals and the precious metals
in solution, is passed through a wood charcoal filter (preferably made from hard-
wood) or a series of such filters, the construction of which is hereinafter more
particularly described. The precise action of the charcoal on such a solution is
somewhat doubtful, but the chemical reactions appear to be as follows:-The
precious metals are liberated from the double cyanide of gold (or silver) and
potassium, and precipitated in a metallic state upon the charcoal; whilst the
cyanogen is absorbed by the charcoal. A portion of the free cyanide of potassium
is decomposed; the potassium, forming with the water a hydrate, passing through
the charcoal, whilst the cyanogen liberated is converted into hydrocyanic acid
and is absorbed therein. The following equations represent the probable
reactions:-
Au CN. KCN+xC=(Au+xC+CN)+KCN; KCN+xC+H, 0=KHO+(xC+HCN).
The result of this action is that the charcoal in a short time ceases to effect the
separation and precipitation of the precious metals. This stage having been
reached, the charcoal is, according to the present practice, burnt for the purpose of
recovering the precious metals, the cyanogen present being dissipated by the heat
and lost.
Instead of burning the charcoal as above described, we retort it or pass super-
heated steam or hot air, or a combination thereof, through the same, for the purpose
of decomposing the cyanogen; its nitrogen uniting with the hydrogen of the steam
when used, and of the steam generated from the water of saturation contained in
the charcoal, and forming ammonia. By a secondary reaction, the ammonia is
converted into ammonium cyanide and ammonium bicarbonate by the action of the
carbonic oxide and carbonic acid. The following equations represent the probable
reactions:-
(CN),+3 H, 0=2NH,+CO+CO, 3NH,+CO+CO,=NH, CN+NH, HCO,
The hydrocyanic acid evolved in the decomposition of the cyanide of potassium
in the former equation is converted into ammonium cyanide and ammonium bi-
carbonate by the action of the heat and steam upon the charcoal and hydrocyanio
acid. The following equation represents the probable reactions:-
I
10 HƠN +3 CO,+U+ H, 2 NH, ÔN +Ổ NH, HCŪg+a CO+CH,+N+H.
The gases and vapour yielded pass off and are condensed, yielding ammonium.
cyanide and ammonium bicarbonate in solution. These products may be decom-
posed by heat, the ammonia yielded being conveyed into water, and recovered
therefrom in the usual way, and converted into sulphate of ammonia, or used in the
manufacture of a cyanide. We prefer, however, to use the solution, the result of
the aforesaid process of condensation, in the extraction of the precious metals.
Should it be found deficient in cyanogen, it must be fortified to the original
strength.
The charcoal is now free from the cyanogen or its compounds, which rendered it
inert, and is fit for further use in the the extraction of the precious metals from
cyanide solutions containing the same.
By frequent regeneration of the charcoal in the manner above described, wo
have been enabled to deposit at the rate of 2,000 ozs. of the precious metals in a ton
of charcoal before resorting to the burning of the charcoal.
Before re-using the charcoal we cool it down to the temperature of the atmos-
phere by passing cold air therethrough. In passing hot air or steam through the
charcoal, care must be taken not to apply them at such a temperature as to cause
combustion of the charcoal.
A charcoal filter adapted for use in our improved process is represented in the
accompanying drawings, whereof Fig. 1 is a view partly in vertical section and partly

page_text: in elevation and Fig. 2 a plan of the lower portion of the apparatus. It comprises
an enamelled iron or other suitable vessel A containing wood charcoal B, in a
powdered or granulated state, capable of passing a to inch mesh sieve, about
2 feet thick and lightly rammed. The vessel is provided with a false bottom a
covered with asbestos or other non-combustible fabric or material a². A sheet of
asbestos cloth b or a piece of perforated iron, stoneware or tile, is also placed upon
the top of the charcoal B to prevent it floating and to protect it against disturbance.
The filter is closed with a removeable top C, and is furnished with pipe connections c
and c', for the liquid and air and for the resultant gases flowing to the condenser
respectively. D is a chamber beneath the false bottom a for the reception of the
filtered liquid, and d d are cocks for draining the said chamber.
Another mode of charging the filter is to grind the charcoal to a powder, mix it
with a little water to form a paste, and then press it evenly into the filter; suction
being at the same time applied below. In this case, a thickness of six inches will
suffice; but in working, suction must be applied to draw the liquid through the
comparatively dense mass of filtering material.
By the foregoing method, the whole of the precious metals may be extracted from
the solution, as shown by fire assay, the consumption of charcoal largely econo-
mised, and a large portion of the cyanide recovered in the form of ammonium
cyanide and ammonium bicarbonate, or sulphate of ammonia if desired.
Cyanide solutions which have been employed in the extraction of the precious
metals, and which, in addition to such metals, contain caustic alkali, dioxides,
nitrates, nitrites, sulphates, carbonates or bicarbonates, bromine, chlorine or their
compounds, may be treated in a similar manner for the recovery of the precious
metals and of the cyanogen and its compounds.
Having now particularly described and ascertained the nature of our said in-
vention and in what manner the same is to be performed, we claim :-
1. In the extraction of gold and silver from ores or compounds containing the
same by means of cyanide and a caustic alkali, the employment of ammonia or a
salt of ammonia, bromine or a salt of bromine, or fluorine or a salt of fluorine in
conjunction with a dioxide, peroxide, or other suitable oxygen-yielding substance,
substantially as herein described.
2. In the extraction of gold and silver by means of cyanide and caustic alkali,
the employment of an alkaline or earthy dioxide or nitro prusside, or of a peroxide
or other suitable oxygen-yielding substance in conjunction with a reagent operating
to liberate oxygen therefrom, substantially as herein described.
3. In the treatment of ores, particularly those of a refractory character, for the
extraction of the gold and silver contained therein, as also of the copper, zinc, or
other base metals, calcining the ore until the sulphides are converted into sulphates
and oxides, mixing the calcined ore with a chemical compound, consisting of
common salt, protosulphate of iron, and nitrate of soda, substantially in the propor-
tions respectively specified (or composed of their respective alternatives), maintain-
ing the mixture for a certain time at a dull red or red heat, without admission of
air, and, after washing out the soluble salts, treating the ore with solutions of sul-
phuric acid, again washing it, treating it with hyposulphite of soda to extract the
silver, and ultimately extracting the gold by a cyanide or other suitable known
process.
4. In the extraction of gold and silver from cyanide solutions containing the
same, the herein described process consisting in filtering the solution through a
charcoal filter, heating the filtering material on the same becoming surcharged with
cyanogen or its compounds, condensing the resultant gases and obtaining
ammonium cyanide and other ammonium salts in solution, applying the regenerated
charcoal (still containing the precious metals) in the filtration of a further charge
or charges of the solution and ultimately recovering from the charcoal the precious
metals accumulated therein.
5. In the extraction of gold and silver from cyanide solutions with the aid of a

page_text: charcoal filter, or in the separation by the same means of the precious metals from
solutions containing copper and zinc, the herein described method of treating the
filtering material for the regeneration of the charcoal and the recovery of the
cyanogen compounds or of the precious metals; such method consisting in repeat-
edly heating the filtering material as often as it becomes inert, condensing the gases
evolved, recovering the cyanogen compounds from the products of such condensation
and the precious metals from the filtering material.
6. In the treatment of auriferous and argentiferous solutions, which also contain
base metals, the employment of a charcoal filter, substantially as herein described;
the gold and silver being retained in the charcoal, whilst the copper and zinc pass
through the liquid, whence they may be subsequently recovered.
7. The regeneration of a charcoal filter by drying the charcoal preferably in
the sun, and repeatedly doing so on its ceasing to precipitate the precious metals
until it ultimately becomes unfit for use as filtering material.
8. In the treatment of refractory ores containing precious metals, calcining the
ore at a low heat till it ceases to gain weight, then mixing with it a chemical com-
pound containing common salt, protosulphate of iron and nitrate of soda, or their
respective alternatives, and submitting the mixture of ore and compound to heat
without stirring or admission of air.
9. In the treatment of refractory ores containing precious metals, calcining the
ore at a low heat till the sulphides are mostly converted into sulphates, then mixing
with it a chemical compound containing common salt, protosulphate of iron and
nitrate of soda or their respective alternatives, and submitting the mixture of ore
and compound to heat without stirring or admission of air.
10. In the treatment of refractory ores containing precious metals, calcining the
ore at a low heat till the sulphides are mostly converted into sulphates, then mixing
with it a chemical compound containing common salt, protosulphate of iron and.
nitrate of soda or their respective alternatives, submitting the mixture of ore and
compound to heat without stirring or admission of air, then washing out the
soluble salts, and finally treating the ore with hyposulphite of soda to extract the
silver, and then with a cyanide if gold be present.
Dated this 15th day or
1090.
For the Applicants,
G. G. M. HARDINGHAM.
Chartered Patent Agent, 191, Fleet Street, London, E.C.