Improvements in or relating to the Extraction of Precious Metals from their Ores.
Year: 1894

page_text: Date of Application, 1st Oct., 1894
Complete Specification Left, 20th July, 1895-Accepted, 24th Aug., 1895
PROVISIONAL SPECIFICATION.
Improvements in or relating to the Extraction of Precious Metals
from their Ores.
'
We, HENRY LIVINGSTONE SULMAN, and FRANK LITHERLAND TEED, D.Sc.,
Analytical Chemists, of 60, Gracechurch Street in the County of London, and
15 Victorin Street, Westminster, in the County of Middlesex, respectively, do
hereby declare the nature of this invention to be as follows:-
This invention relates to the solution of precious metals generally but particularly
to that of gold and silver from their ores.
By present known methods or processes where cyanide of potassium is used the
time required for perfect extraction by solution is lengthy and such processes can
only be successfully applied in particular cases, such for example as the following;—
The gold must be in a state of very fine division amongst the other compounds or
substances present in the ore, and the substances in the ore (other than precious
metals or their compounds) must not be capable of rapidly destroying or
deteriorating the solution of cyanide used; further the precious metal contents
of the ore must not be relatively great; thus, ores containing "coarse gold" or
a high value of gold per tou whether coarse or fine, copper compounds and
certain other metalliferous substances cannot be successfully treated by
cyanide, and pyritic ores give rise to many difficulties and cyanide losses.
Even under the most favourable conditions a great loss of cyanide occurs owing
among other causes to the action of the carbonic acid in the air, residual
alkali in the prepared ore, the formation of Prussian blue and other compound
cyanides, etc. etc. These losses are caused or accentuated by the fact that
potassinin cyanide alone is incapable of dissolving gold and requires oxidation,
atmospheric or otherwise, to effect the production of the soluble double cyanide
of potassium and gold, and that even with the aid of air the solvent power of
cyanide on gold is comparatively feeble and requires a lengthened period to effect
complete solution.
Now we have found that halogen compounds of cyanogen to wit the chlorides
bromides or iodides of cyanogen, when added in certain proportions to cyanide of
potassium in water, form a series of solvents for precious metals, particularly gold,
of great power and efficiency. The solution of the precious metal in such solvents
is rapid and complete and whilst the solution is kept alkaline the secondary
reactions of the solvent on the other compounds of the ore such as copper or iron
pyrites are very limited' in extent, the shortness of the time required to dissolve
the gold out of the ore reducing them to a minimum.
The solvent reaction which occurs may be represented by the following chemical
equation -
Cy Br+3 KCƑ + Aug
= 2 KAuCy+ KBr.
It is to be noticed here that nó oxygen nor oxygenation process is required but

page_text: baloid element, but the whole reaction is complete as between the chemicals
employed and the gold, i.e. without the further intervention of any extraneous
agent.
We may proceed in carrying out our invention in any of the following ways
1. We may form separately a chloride bromide or iodide of cyanogen by any
known and suitable method and add a requisite proportion of any one or a
mixture of such products to the requisite proportion of cyanide of potassium in
water this solution suitably diluted is then applied to the crushed ore or
ore-products which may be contained in any suitable tank or vessel, open or
closed, constructed of any suitable material such as wood. The solution of the
gold or precious metal is effected in a very short time (in the case of some of our
experiments an hour has been sufficient to extract the gold from a copper and
iron pyrites and quartz matrix) and the gold bearing solution is then drawn
off and the precious metal recovered therefrom by addition of any suitable
precipitating or depositing agent such as zinc. The cyanogen baloid may if
desired be applied after the cyanide of potassium has been mixed with the ore.
2. We may proceed also by acting upon the solution of potassium cyanide or
the solution of any suitable cyanide of the alkalies or alkaline earths by chlorine,
bromine or iodine in quantity sufficient to produce the requisite amount of the desired
cyanogen haloid according to the chemical equation "Cl, + Key = KCl + Cycl
and keeping undecomposed a sufficient excess of cyanide of potassium for the
required combined solvent action, on the precious metal. The solution thus
prepared is then applied in the same manner as specified in the preceding
paragraph.
3. A further alternative is to act by the addition of the haloid elements, or of
mixtures capable of yielding the same, to compounds containing or yielding
cyanogen (other than the cyanides before specified) such as the double cyanides,
sulphocyanides, &c. which shall -thus by their mutual interaction Field products
which contain the desired corresponding haloid cyanogen compound.
A further application of our invention relates to the treatment of the waste
liquors which are obtained from the process of the extraction of the gold or
precious metals from tho solvent solution by the action of zinc on these latter.
The addition of a halogen element or of mixtures capable of yielding the same,
decomposes the double cyanide of. zinc and potassium which is found therein with
the formation of insoluble cyanide of zinc (which may be separated from the
liquors by filtration or other means) and effects the regeneration of the haloid
cyanogen compound, which can thus be used again for fresh solvent purposes when
mixed with a suitable proportion of potassium cyanide. This may be represented
by the following chemical equation
K,ZnCy, +2 Cl, = 2 KCl + ZnCy, + 2 CyCl.
{
Although we have herein indicated certain proportions in which the haloid
cyanogen compound may be added to the potassium cyanide or other suitable
cyanide we do not bind ourselves to these proportions and may use any inixture
of the above substances or compounds in any state of dilution in water, and may
act with such solvents upon ore in any convenient manner-either at the ordinary
or at increased or reduced temperatures aud' pressures and upou greater or less
proportions of ore or precious metal containing compound.

page_text: COMPLETE SPECIFICATION.
..
12 3
Improvements in or relating to the Extraction of Precious Metals.
from their Ores..
I.
3
We, HENRY LIVINGSTONE SULMAN of 60 Gracechurch Street, City of London,.
and FRANK LITHERLAND TEED, D.Sc., of 15 Victoria Street, Westminster, in
the County of Middlesex, Analytical Chemists, 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 :-
This invention relates to the solution of precious metals generally but particularly
to that of gold and silver froin their ores.
By present known methods or processes where cyanide of potassium is used the
time required for perfect extraction by solution is lengthy and such processes can
only be successfully applied in particular cases, such for example as the following:
The gold must be in a state of very fine division amongst the other compounds or
-substances present in the ore, and the substances in the ore (other than precious
metals or their compounds) must not be capable of rapidly destroying or
deteriorating the solution of cyanide used; further the precious metal contents of
the ore must not be relatively great; thus, ores containing "coarse gold' or a.
high value of gold per ton whether coarse or fine, copper compounds and cortain
other metalliferous substances, cannot be successfully treated by cyanide, and.
pyritic ores give rise to many difficulties and cyanide losses. Even under the inost
favourable conditions a great loss, of cyanide occurs owing among other causes.to.
the action of the carbonic acid in the air, residual alkali in the prepared ore,
the formation of Prussian blue and other compound cyanides, etc., etc. These losses
are caused or accentuated by the fact that potassium cyanide alone is incapable of
dissolving gold and as at present employed requires oxidation, atmospheric or
otherwise, to effect the production of the soluble double cyanide of potassium and
gold, and that even with the aid of air the solvent power of cyanide on gold is.
comparatively feeble, and requires a lengthened period to effect complete solution.
Now we have found that halogen compounds of cyanogen, to wit, chloride-
bromide or iodide of cyanogen, when added in certain proportions to cyanide of
potassium in water, form a series of solvents for precious metals, particularly gold,.
of great power and efficiency. The solution of the precious metal in such alkaline
solvents is rapid and complete and the secondary reactions of the solvent on the
other compounds of the ore such as copper or iron pyrites are very limited in
extent, the shortness of the time required to dissolve the gold of the ore reducing-
them to a minimum.
The solvent reaction which occurs may be represented by the following chemical.
equation:-
It is to be noticed here that no oxygen nor oxygenation process is required but.
that it is a chemical reaction independent of the oxygen of the air or of the-
oxygen of the water.
It is also to be noticed' in this connection that these haloid compounds of cyanogen
are of considerable stability and do not act by the liberation of the haloid clement,.
bat the whole reaction is complete as between the chemicals employed and the
gold i.e. without the further intervention of any extraneous agent.
We may proceed in carrying out our invention in any of the following ways.
1. We may form separately chloride bromide or iodide of cyanogen by any-
known and suitable method and add a requisite proportion of any one or a mixture
of such products to the requisite proportion of cyanide of potassium in water;

page_text: this solution suitably diluted is then applied to the crushed ore or ore products
which may be contained in any suitable tank or vessel, open or closed, constructed
of any suitable material such as wood. The solution of the gold or precious metal
is effected in a very short time and the gold bearing solution is then drawn off and
the precious metal recovered therefrom by any known means. The cyanogen
haloid may if desired be applied after the oyanide of potassium has been mixed
with the ore.
"
2. We may proceed also by acting upon the solution of potassium cyanide or
the solution of any suitable cyanide of the alkalis or alkaline earths by chlorine,
bromine or iodine in quantity sufficient to produce the requisite amount of the
desired cyanogen haloid according to the chemical equation Cl, + KCy = KCI +
CyCl and keeping nodecomposed a sufficient excess of cyanide of potassium for
the required combined solvent action on the precious metal. The solution thus
prepared is then applied in the same manner as specified in the preceding
paragraph.
A further application of our invention relates to the treatment of the wasto
liquors which are obtained from the process of the extraction of the gold or
precious metals from the solvent solution by the action of zinc on these latter.
The addition of a halogen element or of mixtures capable of yielding the same,
decomposes the double cyanide of zinc and potassium. which is found therein. with
the formation of insoluble cyanide of zinc (which may be separated from the
liquors by filtration or other means) and effects the regeneration of the haloid
cyanogen compound, which can thus be used again for fresh solvent purposes when
mixed with a suitable proportion of potassium cyanide. This may be represented
by the following chemical equation
K,ZnCy, 2C), = 2 KCl + ZnCy, + 2 CƑCl.
Although we have herein indicated certain proportions in which the haloid
oyanogen compound may be added to the potassium cyanide or other suitable
cyanide we do not bind ourselves to these proportions and may use any mixture of
the above substances or compounds in any state of dilution in water, the essence
of our invention consisting in the employment of the haloid compounds of cyanogen
in combination with free cyanide of potassium or other suitable cyanide of the
alkalis or alkaline earths as a solvent for precious metals from their ores, and we
may act with such solvents upon ore in any convenient manner-either at the
ordinary or at increased or reduced temperatures and pressures and upon greater
or less proportions of ore or precious metal containing compound.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed we declare that what we
claim is ;-
The use of chloride bromide or iodide of cyanogen (whether formed in the
solution or otherwise) in combination with free cyanide of potassium or other
suitable cyanide of the alkalis or alkaline earths as a solvent of precious metals
from their ores.
Dated this 19th day of July 1895.