Improvements in Obtaining Gold from Certain of its Ores.
Year: 1898

page_text: Improvements in Obtaining Gold from Certain of its Ores.
I, HENRY LIVINGSTONE SULMAN, of 60, Gracechurch Street, in the County of
London, Analytical Chemist, do hereby declare the nature of this invention to be
as follows;-
:
My improvements relate to a process for obtaining gold from base mineral sul-
phide ores especially those containing iron pyrites, marcasite, mispickel, copper
pyrites, galena, blende, &c., by heating them with a solution of alkaline poly-
sulphide, or the polysulphides of the alkaline earths.
It has been stated that metallic gold is very lowly acted upon in the cold by
solutions of alkaline sulphides and polysulphides, and owing to the extreme slow-
ness of such reactions, they have not been applied commercially.
It is well
known that sulphide of gold is readily dissolved by alkaline sulphides and poly-
sulphides, but as there are no well authenticated instances of the occurrence of
gold as natural sulphide the method has received no application.
Processes dependent upon the actual fusion of gold ores with alkaline poly-
sulphides in a furnace and the lixiviation of the dry furnaced product have been
described; but all such reactions take place in the absence of water, at compara-
tively high temperatures, resulting also in attacking other minerals in the ore,
and have never proved commercially successful.
Many years ago Stahl stated that gold is soluble in hot solutions of alkaline
polysulphide or in alkaline solutions containing an, excess of dissolved sulphur:
but in the absence of definite instructions as to degrees of strength requisite for
such solutions, no practical application of the fact has been made. I have now
determined the degrees of strength whereby solutions of alkaline polysulphides
may, under specific conditions, be practically applied for obtaining gold from its
ores, and especially to the recovery of gold from many ores which have hitherto
been either refractory to known treatments for extraction or have demanded
expensive means of reduction such as smelting. I have found that solutions of
the kind referred to must have a certain strength and have to be raised to a cer-
tain temperature before they become practically useful for gold extraction; if,
for example, they are applied cold or more dilute than say a minimum of from
5 to 10 per cent. of alkaline polysulphide the dissolution is extremely slow and
therefore unpractical. I have also found that may of the base metallic sulphurets
occurring in gold ores are practically not acted upon when heated with strong
alkaline polysulphide; and therefore gold ores of such character are advanta-
geously extracted by means of these solvents. Gold ores, however, which contain
more than moderate quantities of oxidised metallic compounds freely destroy
alkaline sulphide (with formation of sulphurets) and are therefore better adapted'.
to other methods of treatment.
By my process I have in an hour or two effected the extraction of 90 per cent..
of gold from a highly refractory pyritic ore which by other known means would!

page_text: have required far more lengthy and expensive treatment-such as prolonged con-
tact with cyanide solutions, or complete roasting and subsequent chlorination.
I use mono-sulphide of sodium solution varying in strength from 10 to 30%
or more, to which the addition of a certain amount of sulphur is made in order to
produce a sodium polysulphide. The actual proportion of the sulphur may be
from 5% to 150% of the weight of the sodium mono-sulphide present and does
not need precise specification as it has a wide range of solvent power.
The sulphur may be present in quantities sufficient to form sodium di-, tri-,
tetra-, or penta-sulphides, either entirely or in part; but the solution still dis-
solves gold if only a small proportion of the disulphide is present. Broadly
speaking, it is merely necessary to have a working excess of sulphur over that
necessary to form the mono-sulphide of sodium, and, though I prefer to use sul-
phur sufficient to produce the tri-sulphide, I do not confine myself to any definite
amount. Nor do I confine myself to any absolute strength of the polysulphides
solution so prepared, but I find that when it. contains less than 10% sulphide of
sodium reckoned as mono-sulphide, the action on the gold is very slow. I there-
fore prefer to use solutions above this strength and find that a 30% solution at
ordinary atmospheric pressure and at a temperature of 85° to 100° C. works well.
At increased temperatures and pressures (using steam heat and pressure) a smaller
percentage of polysulphide of sodium such as 15% to 20% dissolves gold freely
and may be used instead of the stronger solutions.
The polysulphides of potassium and of calcium, and other alkaline earths, may
also be used, but I prefer to employ the sodium compounds; they may be pre-
pared in several ways-either by the addition of sulphur to solutions of the mono-
sulphides or by boiling or fusing alkaline or alkaline earth-hydrates or alkaline
carbonates with excess of sulphur.
For effecting the extraction of gold I mix the gold-bearing ore with the alka-
line polysulphide in such proportions that, on the mixture being heated, a fairly
uniform mixture or magma of finely crushed ore and sulphide solution is
obtained. I keep the mass at a temperature of 85° or 90° C. or above this until
the extraction of the gold is commercially complete. The proportion of hot poly-
sulphide solution to ore may be from 40% to 7% or more of the weight of the
ore. The solution, after a few hours, contains all the gold originally present in
the ore dissolved as the double sulphide of gold and alkali metal, and is removed
by drainage assisted by steam pressure if necessary; and the exhausted ore is
washed clean from adherent sulphide solution by water wet or saturated steam
or steam and water spray. As it is desirable to keep the solution at its normal
working strength as far as possible and to avoid the evaporation of liquors in
contact with air in bringing them again up to working strength the latter
methods are preferable.
The gold dissolved in the alkaline sulphide may be recovered by any convenient
means known to chemists but I prefer to electrolyse the hot sulphide solution
causing the gold to be thrown down in the metallic state upon a suitable cathode,
the sulphur being liberated at the anode. By keeping the solution hot, the sul-
phur liberated at the anode is immediately re-dissolved forming polysulphide,
thus the solution is constantly regenerated. The sodium hydrate liberated at the
cathode also aids in the re-solution of the sulphur.
I may use open or closed tanks, which may be of cast iron, so arranged that
the ore and sulphide liquor contents can be heated together either at ordinary
atmospheric or at increased pressures.
Thus the tanks may be steam jacketted and steam may be passed through the
contents.
Apparatus of the following kind may be advantageously employed in carrying
out my process. It consists of steam jacketted vertical cylindrical tanks each
provided with a steam tight cover, a false filter bottom of perforated iron and a
lower removable steam tight bottom. The parts of the tanks below the filter are
connected by a pipe provided with a stop cock or shut-off valve.

page_text: There are suitable connections for admitting steamr to each tank below and
above the ore charge (which may be from 1 to 5 tons or even more) resting upon
the false bottom.
Ore is fitted into the first tank and heated by means of the steam jacket and by
blowing steam through the charge. When the ore is thus heated to the required
teniperature, the sulphide solution (which has been prepared in the second tank)
is forced by steam pressure into the first through the connecting pipe and up
through the false bottom into the charge. The stopcock or valve in the connect-
ing pipe is then closed, and the extraction of the gold by the sulphide solution is
allowed to go on for an hour or so. In the mean time, a fresh ore charge may
be introduced into the second tank and heated. When the extraction of the ore
in the first tank is considered to be complete the stopcock or valve is opened and
the sulphide solution (now containing the gold from the first ore charge) is forced
by steam pressure, applied to the first tank, up through the false bottom into the
charge of the second tank together with the drainings from the first charge
yielded by a wash of wet steam or water spray.
When the sulphide is completely transferred together with the washings to the
second ore charge in the second tank and the stopcock or valve is again closed,
the exhausted contents of the first tank are disharged and a fresh charge is intro-
duced and heated by steam, ready for extraction by the same sulphide liquor now
engaged in extracting the charge in the second tank and so on.
The same liquor charge is thus capable of being used many times over to ex-
tract from successive ore charges without the necessity of precipitating the gold
contents after each extraction, this only taking place when the liquors are
sufficiently rich in gold to make a more thorough washing of the exhausted charge
advisable in order to prevent loss of dissolved gold by the adherence of portions
of rich gold solution to the heated ore.
The liquors are therefore kept from undue contact with air and thus the forma-
tion of hyposulphites is avoided by conducting the solution operations in a closed
circuit..
Finally, the small quantities of washings added are prevented from rendering
the solution increasingly dilute by blowing a little superheated steam through
the fresh ore and liquor charge before finally closing down the upper steam tight
cover for the extraction operation under pressure.
Dated thin 12th day of May 1900
ABEL & IMRAY,
Agents for the Applicant.
COMPLETE
SPECIFICATION.
Improvements in Obtaining Gold from certain of its Ores.
I, HENRY LIVINGSTONE SULMAN, Analytical Chemist, of 60, Gracechurch Street;
in the County of London, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement:-
My improvements relate to a process for obtaining gold from base mineral sul-
phide ores especially those containing iron pyrites, marcasite, inispickel, copper
pyrites, galena blende, &c., by heating them with a solution of alkaline poly-
sulphide or the polysulphides of the alkaline earths."
It has been stated that metallic gold is very slowly acted upon in the cold by.
solutions of alkaline sulphides and polysulphides and owing to the extreme slow-

page_text: 'ness of such reactions they have not been applied commercially. It is well
known that sulphide of gold is readily dissolved by alkaline sulphides and poly
sulphides, but as there are no well authenticated instances of the occurrence c
gold as natural sulphide the method has received no application."
Processes dependent upon the actual fusion of gold ores with alkaline poly-
sulphides in a furnace and the lixiviation of the dry furnaced product have been
described but all such reactions take place in the absence of water, at compara-
tively high temperatures, and as they result also in attacking other minerals in
the ore, they have never proved commercially successful.
Many years ago Stahl stated that gold is soluble in hot solutions of alkaline
polysulphide or in alkaline solutions containing an excess of dissolved sulphur;
but in the absence of definite instructions as to degrees of strength requisite for
such solutions, no practical application of the fact has been made. I have now
determined the degrees of strength whereby solutions of alkaline polysulphides
may, under specific conditions be practically applied for obtaining gold from its
ores and especially to the recovery of gold from many ores which have hitherto
been either refractory to known treatments for extraction or have demanded
expensive means of reduction such as smelting. I have found that solutions of
the kind referred to must have a certain strength and have to be raised to a cer-
tain temperature before they become practically useful for gold extraction; if
for, example, they are applied cold or more dilute than, say, a minimum of from
5 to 10 per cent. of alkaline polysulphide the dissolution is extremely slow. and
therefore unpractical. I have also found that many of the base metallic sulpherets
occurring in gold ores are practically not acted upon when heated with strong
alkaline polysulphide; and therefore gold ores of such character are advanta-
geously extracted by means of these solvents. Gold ores, however, which contain
more than moderate quantities of oxidised metallic compounds freely destroy
alkaline sulphide (with formation of sulphurets) and are therefore better adapted
to other methods of treatment.
By my process I have in an hour or two effected the extraction of 90 per cent.
of gold from a highly refractory pyritic ore which by other known means would
have required far more lengthy and expensive treatment such as prolonged con-
tact with cyanide solutions or complete roasting and subsequent chlorination.
I use mono-sulphide of sodium solution varying in strength from 10 to 30%
or more to which the addition of a certain amount of sulphur is made in order to
produce a sodium polysulphide. The actual proportion of the sulphur may be
from 5% to 150% of the weight of the sodium monosulphide present and does
not need precise specification as it has a wide range of solvent power.
The sulphur may be present in quantities sufficient to form sodium di-, tri-,
tetra-, or penta-sulphides, either entirely or in part, but the solution still dis-
solves gold if only a small proportion of the disulphide is present.
speaking, it is merely necessary to have a working excess of sulphur over that
Broadly
necessary to form the mono-sulphide of sodium, and, though I prefer to. use sul-
phur sufficient to produce the tri-sulphide, I do not confine myself to any definite
amount. Nor do I confine myself to any absolute strength of the polysulphide
solution so prepared, but I find that when it contains less than 10%, sulphide of
sodium reckoned as mono-sulphide, the action on the gold is very slow. I there-.
fore prefer to use solutions above this strength and find that a 30% solution at
ordinary atmospheric pressure and at a temperature of 85° to 100° C. works well.
At increased temperatures and pressures (using steam heat and pressure) a smaller
percentage of polysulphide of sodium such as 15% to 20% dissolves gold, freely
and may be used instead of the stronger solutions.
The polysulphides of potassium, and of calcium, and other alkaline earths,.
may also be used, but I prefer to employ the sodium compounds. The alkaline
or alkaline-earth polysulphides may be prepared in several ways, either by the
addition of sulphur to solutions of the mono-sulphides or by boiling or fusing.
alkaline or alkaline earth-hydrates or alkaline carbonates with excess of sulphur.

page_text: For effecting the extraction of gold I mix the gold-bearing ore with the alka-
line polysulphide in such proportions that, on the mixture being heated, a fairly
uniform mixture or magma of finely crushed ore and sulphide solution is
obtained. I keep the mass at a temperature of 85° or 90°, C. or above this until
the extraction of the gold is commercially complete. The proportion of hot poly-
sulphide solution to ore may be from 40% to 70% or more of the weight of the
ore. The solution, after a few hours, contains all the gold originally present in
the ore dissolved as the double sulphide of gold and alkali metal, and is removed
by drainage assisted by steam pressure if necessary, and the exhausted ore is
washed clean from adherent sulphide solution by water, wet or saturated steain
or steam and water spray. As it is desirable to keep the solution at its normal
working strength as far as possible and to avoid the evaporation of liquors in
contact with air in bringing them again up to working strength, the latter
methods are preferable.
The gold dissolved in the alkaline sulphide may be recovered by any conve
nient means known to chemists but I prefer to electrolyse the hot sulphide solu-
tion causing the gold to be thrown down in the metallic state upon a suitable
cathode, the sulphur being liberated at the anode. I find lead foil is practically
unattacked by the strong alkaline sulphide solutions employed and can be very
advantageously used for anode and cathode. By keeping the solution hot, the
sulphur liberated at the anode is immediately re-dissolved forming polysulphide,
thus the solution is constantly regenerated. The sodium liberated at the cathode
hydrates and aids in the re-solution of the sulphur.
I may use open or closed tanks which may be of cast iron so arranged that the
ore and sulphide liquor contents can be heated together either at ordinary atmó-
spheric or at increased pressures.
Thus the tanks may be steam jacketted and steam may be passed through the
contents. Apparatus such as 'is shewn diagrammatically in vertical section on
the accompanying drawing may be advantageously employed in carrying out my
process. It consists of steam-jacketted vertical cylindrical tanks A A¹ each pro-
vided with a steam tight cover B a false filter bottom C of perforated iron and a
lower removable steam tight bottom D. These bottoms below the filters are
connected by a separable pipe E provided with a three way cock e by which liquid
can be run from either tank to the other or run off from either.
There are suitable connections F for admitting steam to the top of each tank
and there may also be connections for admitting steam below the ore charge
which may be from 1 to 5 tons or even more, resting upon the false bottom C.
This apparatus is worked as follows:-
Ore is filled into the first tank A and heated by the steam jacket and it may
be also by blowing steam through the charge. When the ore is thus heated to
the required temperature, the sulphide solution which is contained in the second
tank A is forced by steam pressure into the first tank A through the connecting
pipe E and up through the false bottom Cinto the charge. The stopcock or
valve e in the connecting pipe is then closed and the extraction of the gold by
the sulphide solution is allowed to go on for an hour or so in the tank A. In the
meantime a fresh ore charge may be introduced into the second tank A' and
heated.
When the extraction of the ore in the first tank A is considered to be com.
plete, the stop cock or valve e is opened and the sulphide solution (now contain-
ing the gold from the first ore charge) is forced by steam pressure, applied to
the first tank A up through the false bottom into the charge of the second
tank A together with the drainings from the first charge yielded by a wash of
wet steam or water spray. When the sulphide solution is completely transferred
together with the washings to the second ore charge in the second tank and the
stop cock or valve e is again closed, part of the pipe E is separated from the cock
or valve e, the bottom of A is opened and the exhausted contents of A are dis-
charged and a fresh charge is introduced and heated by steam, ready for extrac-

page_text: tion by the same sulphide liquor now engaged in extracting the charge in the
second tank and so on.
The same liquor charge is thus capable of being used many times over to
extract gold from successive ore charges without the necessity of precipitating
the gold contents after each extraction. This only takes place when the liquors
are sufficiently rich in gold to make a more thorough washing of the exhausted
charge advisable in order to prevent loss of dissolved gold by the adherence of
portions of rich gold solution to the treated ore.
The liquors are also kept by these means from undue contact with air and the
formation of hyposulphites is avoided by conducting the solution operations in
a closed circuit.
Finally, the small quantities of washings added are prevented from rendering
the solution increasingly dilute by blowing a little superheated steam through
the fresh ore and liquor charge before finally closing down the upper steamtight
cover for the extraction operation under pressure.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed I declare that what I claim
is:-
1. The herein described process for extracting gold from certain ores by treat-
ing them with solutions of polysulphides of metals having as their oxides alkalies
and alkaline earths, thus producing solutions of double sulphides of gold and the
said metals.
2. The herein described process for separating the gold as metallic deposit and
simultaneously recovering the polysulphide solution by electrolysing the hot
solution of double sulphide referred to in the preceding claim.
3. For effecting the process set forth in Claim 1 apparatus arranged and opera-
ting substantially as described with reference to the accompanying drawing.
Dated this 13th day of February 1899.
ABEL & IMRAY,
Agents for the Applicant.