Improvements in and relating to the Extraction of Gold and Silver from their Ores.
Year: 1895

page_text: COMPLETE SPECIFICATION.
Improvements in and relating to the Extraction of Gold and Silver
from their Ores.
I, JOHN JEREMIAH CROOKE, of 40 West 46th Street, New York City, in the
County and State of New York, United States of America, Chemist and
Metallurgist, do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in
and by the following statement:-
The present invention relates to the treatment by chlorination of ores carrying
gold, or gold and silver, and is especially adapted to that class of ores which are
rich in gold although generally associated with a small quantity of silver.
The object of this invention is to make a perfect extraction of the gold and
silver, either with or without having recourse to roasting or calcination, and also to
materially reduce the time and cost of extraction.
The invention consists generally in the processes and apparatus for carrying out
the same, hereinafter more particularly described.
Chlorine has long been recognized as an efficient agent for the extraction of gold
and silver from their ores. It is especially useful in its application to refractory
gold ores, in which the presence of sulphides, arsenides, tellurides, and other
compounds, prevent the precious metals from readily amalgamating with mercury.
The Plattner process, in which the pulverized, roasted and moistened ores are
treated in an agitator with chlorine, generated in a separate vessel and introduced
into the agitator, has been extensively employed. This process, although an
improvement on existing methods, rarely extracts more than from eighty to eighty-
six per cent. of the assay value of the ores in gold, and uone of the silver. I am
also aware that modifications have been made in the Plattner process, 'by which
chlorine has been generated in the body or mass of the ore, by mixing chloride of
lime, or chloride of lime and chloride of sodium, with the ore reduced to a flowing
pulp by the addition of water, and then introducing sulphuric or hydrochloric acid
to generate chlorine, and I am informed that by this modification the percentage of
gold extracted has been increased in some cases to 90 per cent., of the assay value
of the ores, while the silver, as chloride, has remained in the tailings.
It occurred to me that, as the chlorine in the last named process was liberated in
direct contact with the ore, and was thereby available to act in its nascent condition
to convert the gold into a soluble chloride, the results should have shown a more
perfect extraction of the gold, and I concluded there must be some defect in the
process, in that the chlorine was not generated with sufficient force or power, or
that the proper effect of the gas was in some way modified or prevented.
Accordingly, I have made a careful study, supplemented with many experiments
and tests, to discover the proper materials or compounds with which ores carrying
gold and silver could be treated to generate or liberate chlorine freely aud
nstantly in the mass of the ore so that, while in its nascent condition, it would be
n intimate contact with the particles of gold and silver and would act to
mmediately convert them into chlorides.
As a result of my investigations, I have discovered that a solution of nitrate of
copper, preferably of a specific gravity indicating 100 degrees by the ordinary
alinometer, water being zero, or about 25 degrees Baume's hydrometer, can be
uccessfully utilized as an oxiding and chlorine-liberating agent, when mixed with

page_text: the ores and chloride of sodium and the mass treated with a chlorine-liberating
acid. For example, if the mass thus prepared is treated with sulphuric or hydro-
chloric acid, a rapid and instantaneous liberation of nitric peroxide and chlorine
takes place.
Sulphuric acid, when used as above set forth, does not act to liberate chlorine
directly, hydrochloric acid being first formed which is immediately decomposed
with the liberation of chlorine, but inasmuch as the sulphuric acid causes the
reactions by which chlorine is liberated, for the purposes of my invention I will
consider sulphuric acid as well as hydrochloric acid as a chlorine liberating acid.
I have also discovered that if a small per cent. of oxide of manganese, preferably
the binoxide or peroxide, or of manganic iron (which latter is an ore generally
containing a large percentage of binoxide of manganese associated with rock and
is abundant in many gold and silver producing localities) be added to the mass to
he treated the efficiency of the solution for the rapid and exhaustive extraction of
the gold is materially increased especially if the ores are raw or only partially
roasted. I do not, however, consider that the presence of oxide of manganese or
manganic iron as an ingredient of the solution in connection with nitrate of copper
and chloride of sodium is essential, but that it simply supplements the action or
efficiency of the nitrate of copper.
I have further discovered that the use of a hot, aqueous solution of chloride of
sodium, preferably slightly acidulated with hydrochloric acid, as the liquid of the
plasma, is of great advantage, especially in the treatment of ores containing silver
associated with gold.
Based on these discoveries and experiments I have devised, developed and
practised the following method, or process, for chlorinating ores carrying gold, or
gold and silver.
The
The ores to be treated are pulverized, preferably to about 40 to 50 mesh, and
are preferably roasted or partially roasted. If they contain about $150 gold value
per ton, they are intimately mixed with about 6 per cent. of chloride of sodium, an i
the mass is then charged into a digester of any suitable shape and construction
which contains a hot solution composed mainly of water, to which is added as the
essential active ingredient about 3 per cent. of solution of nitrate of copper of
100 degrees gravity, and preferably about 2 per cent. of chloride of sodium, the
solution being preferably slightly acidulated with hydrochloride acid.
preparation of ores and solution should be so related that, when intimately mingled,
they will form a plasma of about the consistency of thin paste. The digester is
provided with means for closing it substantially gas tight, and for introducing
charges of acid from time to time, preferably at or near its bottom, and with means
for thoroughly agitating its contents, as hereinafter more fully described.
A chlorine-liberating acid, preferably sulphuric acid, is then introduced into the
plasma in small charges at frequent intervals of time.
The quantity of chlorine-liberating acid required is generally from three to
six per cent. of the weight of the ore under treatment, depending, however, upon
the richness of the ore, and consequently the quantity of chlorine required to
convert the gold and silver to chlorides. The plasma should be kept under
constant agitation during the introduction of the acid in order to evenly distribute
the chlorine through the plasma. As chlorine is about twice as heavy as air, its
production can be readily controlled by the amount of acid introduced from time
to time, so that in a properly constructed digester but little free gas will rise
beyond the top of the plasma during the conversion of the gold and silver into
chlorides.
As the violent reaction brought about by the acid causes an increase of
temperature throughout the mass, its introduction should be sufficiently slow to
prevent a rise of temperature above 180 degrees Fahrenheit. When charges of
six tons are treated about one hour is consumed in the acid stage, charges of from
15 to 20 lbs. of acid being introduced at intervals of from half to one minute.
After the acid has been thoroughly mixed by agitation with the plasma the charge

page_text: should not be noved, but allowed to remain at rest for about six hours, at a
temperature of about 100 degrees Fahrenheit, which is maintained by injecting
dry steam into the digester from time to time.
As before stated, the operation above described will generally be more efficient
to convert the gold into a chloride and facilitate its rapid and exhaustive extraction,
if a small per rent. of oxide of manganese is present in the mass during the chlori-
nating operation. The presence of this compound in the solution appears to
increase the efficiency of the nitrate of copper and is attended with a more rapid
release of oxygen and perhaps in greater quantity, which not only combines with
the sulphur arsenic and other refractory constituents of the ores to leave the gold
and silver in condition to be converted into chlorides, but also combines with the
sodium of the chloride to release the necessary chlorine.
When manganic iron containing about 50 per cent. of binoxide of manganese is
used, it is preferred, in order to uniformly distribute the chloride of sodium and
manganic iron throughout the ore to be treated, to first make an intimate mixture
of about 6 per cent. of chloride of sodium as heretofore stated with about 3 per cent.
of manganic iron to each ton of ore, by grinding or otherwise intimately associating
The mass
them together, and then thoroughly mixing this mass with the ores.
thus formed, composed of ores, chloride of sodium and manganic iron, is then
charged into the digester containing a hot aqueous solution of the kind heretofore
described, whose principal active ingredient is nitrate of copper, and is then treated
by agitation and the introduction of repeated charges of acid, all as hereinbefore
set forth.
I have found that the nitrate of copper becomes more effective as an active
re-agent when a small per cent. of oxide of mangauese or manganic iron is present
in the solution, especially when the ores are of a very refractory character and are
in a raw or unroasted condition.
After the mass has been treated in the digester as heretofore described till the
conversion is complete, the plasma is forced preferably by steam pressure from the
digester into lixiviation tanks, through suitable openings. This filtrate is delivered
directly into a precipitating tank in which the gold, copper, and silver are
precipitated in a metallic condition by contact of the metallic bearing filtrates to
surfaces of sheets of soft iron immersed in the precipitating tank. When the precipi-
tation is complete, and by this method it will be exhaustive, the solution deprived
of all its valuable constituents is syphoned from the precipitate. The metallic
residuum or precipitate is placed upon a large table filter and washed. It is then
conveyed to a suitable vessel and treated with nitric acid. This treatment will
dissolve the silver and copper, and leave the gold absolutely pure. The solution
of copper and silver is then separated from the gold by filtration, and thus gives a
solution of nitrate of copper and silver which may be used in the treatment of
other charges of ores for the production of chlorine and peroxide of nitrogen as
above described.
The silver contained in this copper solution, when sufficiently enriched by
repeated applications to charges of ores in the chlorinating process, can be recovered
by any of the well known methods.
As my invention relates particularly to the operations directly connected with
the chlorinating steps of the process hereinbefore set forth, I will describe a form
and general construction of digester and lixiviating tank which I prefer to use, and
which are illustrated in the accompanying drawing, the several parts being shown
in section.
In the drawing, A. represents the digester, which in practice I make of a
capacity for treating about five or six tons of material. It is preferably circular
in cross-section and in the form of a truncated cone, and, for the capacity above
referred to, should be about six feet in diameter at its bottom and four feet at its
top, and about seven feet high. It is provided with an agitator which consists of
a perforated dasher B fixed to its shaft C, which works in bearings in the cross-
piece D and passes through cover E, the latter being preferably made in two parts

page_text: each hinged to projections F on the cross-piece. Packing rings or gaskets G, H,
of rubber or other suitable material, form tight joints between the cover and the rim
of the digester. A ring I is clamped tight down upon the cover E by means of the
clamping buttons J, which turn upon the screws which secure them to the cover.
A flexible cone-shaped hook K is secured at its lower edge to the under side of the
ring and serves to seal this joint while its upper edge is tightly secured to the
shaft C, there being sufficient slack in the material of the hood to permit an
upward throw of the shaft of about four feet without straining the hood. This
hood can be made of strong canvas soaked in paraffin to make it gas tight. The
agitator may be caused to reciprocate by any desired mechanism, as by a wheel L,
and connecting crank rod M, pivotally secured to the top of the shaft; N is a fixed
steadying guide through which the shaft passes. The digester is further provided
with a channel O extending through the cover E and downwardly through the
side wall and communicating with the interior near the bottom of the digester, and
is preferably about 2 inches in diameter, through which acid and steam can be
admitted. P is a channel communicating with the air, through which any excess
of gas can escape and be removed by an attached hose or other means.
digester is also preferably provided with large discharge pipes Q and means for
opening and tightly closing the same, as a valve R operated by a hand screw S.
The interior walls of the digester as well as the dasher and shaft of the agitator
are preferably made of wood and may be soaked or painted with paraffine or other
gas and acid proof substance. The digester is provided with steam pipes a
entering its bottom and the desired agitation of the plasma may be effected by the
introduction of a jet or jets of steam. Both the dasher B and jets of steam may
be employed for this purpose or either one alone. Steam for aiding the rapid
discharge of the contents of the digester may be admitted through the orifice P
and hot water to wash out the interior may be admitted through the same or any
other convenient channel.
The
TT are lixiviating tanks located directly beneath the discharge pipes Q of the
digester to receive its contents, and are provided with filters U of any efficient
construction; the capacity of each tank should be at least equal to that of the
digester. V is an exit by which the filtrate can be delivered directly into a
precipitating tank not shown, W is a sluice way for removing the tailings, which
are washed out by water introduced into the tanks under required pressure. I
prefer to make these tanks large at their bottom as compared with their top
portions in order to give a large filter surface and to make them, as well as the
digester, gas, steam and air tight in order to utilize the pressure of steam or
compressed air to force the rich solutions rapidly from the sands and clays with
which they are associated, and for this purpose they are provided with one or more
pipes near their tops. They are also provided with a manhole Y to obtain access
to their interior and through which water can be introduced.
In the working of my process for extracting gold and silver from its ores I use
the digester and tanks above described in the following manuer :
About four hundred gallons of the hot aqueous solutions heretofore described
containing about 3 per cent. of the solution of nitrate of copper, is drawn from a
stock tank into the digester.
The mass to be treated, containing the pulverized ores, chloride of sodium, and
oxide of manganese and manganic iron if used, mixed in the proportions
substantially as set forth, is fed by power conveyors, or otherwise, into the digester
through the opened cover E until about six tons have been entered.
The cover E is then closed and the hook K secured at its edge, and with the
exception of a valvular opening through the top of the tank (to permit the
regulation of pressure) the whole apparatus is virtually gas tight. The mass is
now agitated by the movement of the dasher B or jets of steam entered through
the lower part of the tank near the bottom, or both, and will, by this treatment, be
quickly converted into a homogeneous pulp or plasma. The acid is then introduced
at short intervals in charges of from ten to twenty pounds through the channel O,

page_text: or any other suitable opening in the gas-tight cover of the tank, but preferably so
that it will be delivered near the bottom of the digester. Chlorine and nitric
peroxide are immediately generated or liberated with great freedom and volume,
and are quickly and evenly distributed through the plasma by the operation of the
steam jets, or any other proper stirring contrivance.
The minute volumes of gases being liberated in a nascent condition immediately
combine with the metals and change them eventually to chlorides.
After the several charges of acid have been thoroughly incorporated with the
plasma, the steam jets are closed and the contents of the digester is preferably
allowed to remain at rest for about six hours. It is then removed from the
digester into the lixiviation tank through a suitable orifice in the bottom of the
digester. This is rapidly accomplished by steam pressure and warm water entered
on the top of the charge. The digester is now ready for recharging, and the above
described operation can be repeated.
The plasma, after being passed into the lixiviation tank, will have a temperature
of about 120 degrees Fahrenheit, and is preferably allowed to stand an hour.
Hot two per cent. chloride sodium solution, preferably slightly acidulated with
hydrochloric acid, to the amount of about four hundred gallons is then entered
upon the leaching charge. The exit of the lixiviation tank is then opened and the
gold and silver solution, after passing the tank filter, is directly received into a
precipitating tank. When most of the solution has passed the filter the charge
remaining in the lixiviating tank should be thoroughly washed with hot water until
the filtrate gives no reaction for gold or silver.
The gold will be in a state of chloride, the silver as double chloride of silver
and sodium, both soluble in the menstruum, the copper as a soluble hydrated cupric
chloride.
The gold, silver and copper are precipitated from the solution together by
exposure to surfaces of soft iron plates, and separated as hereinbefore described.
I have found that by the use of the process and apparatus above described I can
extract over 99 per cent. of the assay value of the gold and silver contained in
refractory ores.
I ascribe the efficiency of the process largely to the introduction of the nitrate
of copper as a powerful oxidizing element, which in my judgment operates with the
other elements to cause instantaneous reactions, by which chlorine and peroxide of
nitrogen are generated or liberated with great power in a nascent condition, and are
brought into direct contact with the metals, to effect the conversion of the gold
and silver into chlorides even in the presence of sulphur, arsenic and tellurium
compounds.
The presence of chloride of sodium in the solution for forming the plasma,
causes the chloride of silver to be dissolved as rapidly as formed, and consequently
prevents it from forming a coating upon the particles of gold which would
otherwise be the case and would greatly retard the dissolving action and ultimately
prevent an exhaustive extraction of either gold or silver. If the solution is
slightly acidulated with hydrochloric acid its efficiency for the above purposes is
increased.
As before stated, I prefer to use sulphuric acid as the active agent for liberating
chlorine in the plasına, inasmuch as this acid, when in contact with the elements
introduced in the ore, forms nitrohydrochloric acid, nitric peroxide, and liberates
chlorine, all efficient agents for freeing the particles of gold and silver from foreign
elements, as well as to cause their immediate dissolution.
It has been heretofore stated that the plasma should be subjected to agitation in
the digester during the time the chlorine-liberating acid is acting to produce
chlorine. This is important to facilitate the operation and to produce the best
results. I do not, however, consider it indispensable, inasmuch as if the plasma
remained at rest, the acid would gradually be distributed throughout the mass
and operate to generate the chlorine, but the operation would be very much
prolonged.

page_text: Where proportions or percentages of the various elements or compounds have
been herein referred to, it should be understood that these are to be by weight an
not by volume, unless otherwise stated.
I do not desire to limit my invention to the use of any specific form of
construction of apparatus for carrying it into effect, or, to any special means or
devices for agitating the plasma during any part of the stage of the chlorination,
as it is evident that many forms of apparatus, means and devices may be employed
for these purposes. Neither do I desire to limit my invention to any specific
proportions of chloride of sodium or other chloride of alkaline metals, or of oxide
of manganese or manganic iron, or of nitrate of copper or chlorine-liberating acid,
to be employed in treating a given quantity of ores, as the quantity of these
several ingredients or agents which should be used to produce the best results will
depend largely upon the character of the ores, their richness in gold and silver,
and a variety of other conditions, with which metallurgists are more or less
familiar.
I will further state that I consider that the use of nitrate of copper constitutes
an important and efficient element in carrying out my invention so as to produce
the best results.
It will be observed that, though I do not limit my invention to the use of the
special apparatus herein described and shown in the drawing, yet such form of
apparatus has advantages, especially in the converging side-walls which approach
each other from the bottom towards the top of the digester. This convergence
acts to somewhat retard the ascent of the chlorine liberated at or near the bottom
of the digester aud to bring it into a smaller compass as it rises through the plasma
so that, if the acid is introduced in proper charges and at proper intervals, the
chlorine will have combined with the gold and silver before it reaches the top of
the digester and there will be little or no excess to be conducted through the exit P
and consequently the chlorine can be fully utilized.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what
1 claim is
1. The hereinbefore described process of chlorinating gold producing ores, which
consists in forming a plasma containing pulverized ores, an alkaline chlorine and
nitrate of copper, and subjecting the plasma to the action of a chlorine-liberating
acid, for the purpose set forth.
2. The hereinbefore described process of chlorinating gold producing ores, which
consists in forming a plasma containing pulverized ores, an alkaline chloride and
nitrate of copper, and subjecting the plasma while the same is under agitation to
the action of a chlorine-liberating acid, for the purpose set forth.
3. The hereinbefore described process of chlorinating gold producing ores, which
consists in forming a plasma containing pulverized ores, an alkaline chloride, oxide
of manganese and nitrate of copper, and subjecting the same, while under agitation,
to the action of a chlorine-liberating acid, for the purpose set forth.
4. The herein described process of chlorinating gold and silver producing ores,
which consists in mixing the pulverized ores with an alkaline chloride and oxide of
manganese and then introducing the mass into a hot acidulated solution of nitrate
of copper and chloride of sodium, subjecting the plasma so formed to agitation, and
introducing the chlorine-liberating acid, for the purpose set forth.
5. The hereinbefore described process of chlorinating gold and silver producing
ores, which consists in forming a plasma containing the pulverized ores, an alkaline
chloride and nitrate of copper, and then subjecting the plasma to the action of
small charges of a chlorine-liberating acid introduced at frequent intervals, for the
purpose set forth.
6. The herein before described process of extracting gold from its ores, which
consists in forming a plasma containing pulverized ores, an alkaline chloride and
nitrate of copper, subjecting the plasma to the action of a chlorine-liberating acid,

page_text: filtering the plasma, precipitating the gold from the filtrate and recovering the
nitrate of copper for reuse in other charges of plasma, substantially as and for the
purpose set forth.
7. The hereinbefore described process of extracting gold and silver from their
ores, which consists in forming a plasma containing the pulverized ores, an alkaline
chloride and nitrate of copper, subjecting the plasma to the action of chlorine-
liberating acid, filtering the plasma, precipitating the gold, silver and copper from
the filtrate and recovering the nitrate of copper and silver in solution for reuse in
other charges of plasma, and finally separating the silver from the copper solution
when sufficiently enriched therewith, for the purpose set forth.
8. In the process of converting gold and silver contained in ores into chlorides,.
the introduction of small charges of chlorine-liberating acid at frequent intervals at
or near the bottom of a digester or vessel containing a pulp or plasma of ores and
alkaline chlorides, whereby chlorine is liberated at intervals and in such volume
that as it rises through the plasma it will unite with the metals and thereby
unnecessary waste of chlorine by escape from the vessel is prevented.
9. The herein described process of chlorinating gold and silver ores, which
consists in treating a pulp or plasma containing pulverized ores,
alkaline chlorides
and a hot aqueous acidulated solution of chloride of sodium, in a suitable vessel
under agitation, with a chlorine-liberating acid, whereby chlorine is liberated in the
pulp and acts in its nascent condition to convert the gold and silver into chlorides.
10. A digester for treating ores by chlorination, consisting of an upright vessel
provided with side walls converging from the bottom upward for the purpose of
concentrating the ascending volume of chlorine, a vertically reciprocating agitator,
a channel for introducing acid at the bottom of the digester, a sluice door or exit
way and a channel near the top of the digester for carrying off any excess of
chlorine, substantially as set forth.
11. In a digester for treating ores by chlorination, the combination, substantially
as described and shown, with an agitator consisting of a dasher attached to a shaft
constructed and arranged to reciprocate vertically in the digester and passing
through the top thereof, of a flexible hood whose lower or outer edge is secured to.
the top of the digester and its central portion is secured gas tight to the shaft.
Dated this 25th day of June 1895.
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicant.