Improvements in or relating to the Obtaining of Precious Metals from their Solutions.
Year: 1894

page_text: Date of Application, 21st Sept., 1894
Complete Specification Left, 13th July, 1895-Accepted, 17th Aug., 1895
PROVISIONAL SPECIFICATION.
Improvements in or relating to the Obtaining of Precious Metals
from their Solutions.
I, HENRY LIVINGSTONE SULMAN of 60 Gracechurch Street in the City of
London, Analytical Chemist, do hereby declare the nature of this invention to be
as follows:-
This invention relates to the precipitation of precious metals generally, but
particularly to gold and silver, when these are carried in solution; and the process
may be employed with any aqueous solutions of the ordinary salts such as the
cyanides chlorides bromides iodides hyposulphites etc., as obtained by treatment of
various ores containing precious metals with the various solvents in aqueous
solution.
I find that by the addition to the solution containing gold or silver, of certain
metals or alloys in a state of the finest obtainable division-say in the form of dust
or the finest flour I can obtain the precipitation of approximately the whole of the
precious metal contained in the cyanide or other solution. I find that I obtain
more satisfactory results by condensing the metallic vapours of the metal or alloy-
particularly zinc-than by any other means and I therefore prefer to adopt this
course in preparing this dust or flour.
I am aware that certain metals have before now been used for the purpose of
deposition of precious metal-but when employed, as has hitherto usually been the
case, in a state of comparatively coarse division-as for example when the metal
be used in the form of shavings, filiform fragments, or granules. The amount of
the metal requisite to obtain the desired deposition of gold is enormously greater
than the theoretical requirements and is also actually largely in excess of the
amount which I find it necessary to use when in the dust form above described.
This largely unnecessary consumption of metal in the case of deposition of gold
from cyanide solutions is partly caused by the manner in which the deposition of
the precious metal is effected viz.: by the passing of the solution continuously
through a mass of shavings or granules where at any given moment the liquor is in
contact with a huge and unnecessary proportion of the metal used for deposition.
As a result if zinc be the metal used for deposition and be employed in the
ordinary way that is in the form say of sawdust or of fine shavings or filaments
contained in a series of vessels or boxes through which the gold-bearing cyanide
solution is made to percolate continuously, quite one hundred times the theoretical
amount of metallic zinc is often consumed to effect the complete deposition of the
dissolved gold. This gives rise to other loss; not only is there an undue consump-
tion of zinc involving unnecessary outlay and in addition also to the extensive
plant of deposition boxes which such a method of securing gold deposition demands,
there is loss of cyanide by the injurious effect of the excess of dissolved zinc upon
the cyanide solution. The free potassium cyanide in which (as it is drawn from
the ore) is correspondingly deteriorated by formation of soluble double cyanide of
zinc and potassium. This necessitates the use of an extra quantity of cyanide of
potassium to regenerate the solution for solvent purposes when the latter is again
applied to the gold bearing ore.
In carrying out my invention instead of allowing the cyanide or other solution
containing the dissolved precious metals to traverse or percolate through masses of

page_text: metallic filaments shreds or granules, I collect the whole of the liquor with which
I wish to deal in one or more suitably sized tanks and proceed to add thereto a
definite small and sufficient quantity of my finely powdered or floured metal in such
a way as to effect the direct precipitation of the dissolved gold. By proceeding in
this way the metal I use is never in excess with regard to any part of the mass of
liquor and moreover I find that not only is the precipitation of the precious metal
complete and rapid, but that the quantity of precipitating metal or "precipitaut"
required to effect this separation of gold is very much less than in the ordinary
method above described. As a consequence the destruction or deterioration of
cyanide in such liquors is far smaller by my process and the total consumption of
cyanide in the treatment of gold bearing ores is very greatly reduced: this alone
is a very important saving. Besides this I require no extensive "zinc-box" plant,
and the gold precipitated being in the shape of dense and flocculent precipitate is
easily removed after deposition from the bottom of the precipitating tank-(which
if desired may be fitted with a bottom of inverted cone shape) or may be collected
by rapid filtration of the liquors through cloth or other suitable medium. This
again avoids the present troublesome operations of separating the gold deposits
from the zinc filaments and the precipitated gold obtained by my process is far
purer than and is easier to refine than that produced by the ordinary method above
described.
I may employ various kinds of finely divided metals such as copper lead or zinc;
or an alloy such as brass- or magnesium-zinc lead-zinc etc.; or a mixture of such
powdered metals or powdered alloys; and I may employ whichever of these I may
elect to use or a mixture of one or more of these in any convenient manner-such
as by dusting or sieving a definite quantity of the powdered precipitant-propor-
tioned to the actual quantity of gold present in the solution operated upon-or by
running the precipitant in as a "suspension" in some of the liquor, or in water.
Moderate agitation I prefer to employ, and this may be provided for in any
desirable manner; where for example the powdered metal is applied by a stream
of water or solution this stream may be employed for the purposes of agitation.
In considering the question of agitation it is important to note that excessive
agitation must be avoided; that is if it would tend to promote aeration or oxidation
of the liquor since the presence of oxygen would tend to dissolve the zinc or other
metallic powder employed in the excess of cyanide without necessarily effecting the
precipitation of the gold. The agitation may be effected by mechanical stirrers or
by suitable circulation say by means of a pump or like appliance capable of
circulating the liquor without aeration; and if necessary the tank or vessel in
which the operation takes place may be entirely closed in and the solution
protected from the air by the application or introduction of an inert gas over the
surface of the liquor.
I find that the advantageous results of this invention increase almost in propor-
tion to the fineness of the powdered metal or alloy introduced and in a secondary
degree to the absence of air in the operation. Operating in the presence of air
with the finest obtainable metallic powder or dust I am able to reduce the amount
of metal required to, for example if zine be employed, from once to three times the
weight of the actual gold present in solution. The powdered metals may
conveniently be of such fineness as is obtainable, by passage through a sieve of
40,000 meshes to the square inch. I do not limit myself to this particular size but
mention it as giving in the case of zinc a product with which I have secured
excellent results. With such a precipitant applied as a suspension in water,
4 dwts. of gold in a ton of liquor can be precipitated completely with from 8 to
12 dwts. of precipitant-and even less. The gold precipitate readily agglomerates
and falls in dark pulverulent blocks and in a short time the precipitation is
complete and the precipitated gold may be readily collected by deposition or
filtration or in any suitable manner. It is of a considerable degree of purity and
may le fused under ordinary fusion mixtures to an ingot.
My process therefore is not a "deposition process "where the gold is deposited

page_text: upon bright and extended metal surfaces from which it has afterwards to be
removed but is practically one of direct precipitation most of the metallic dust
going into solution whilst the gold is thrown down to the bottom of the vessel
containing the solution; and the gold precipitate contains far less of the
precipitating medium than does the product obtained from the zinc boxes in the
ordinary way.
Dated this 21st day of Sentember 1804
W. P. THOMPSON & BOULT,
Agents for the Applicant.
Improvements in or relating to the Obtaining of Precious Metals
from their Solutions.
1, HENRY LIVINGSTONE SULMAN of 60 Gracechurch Street in the City of
London, Analytical Chemist, 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 precipitation of precious metals generally, but
particularly to gold and silver, when these are carried, dissolved in aqueous
solutions of the cyanides.
I find that by the addition to the solution containing gold or silver, of certain
metals or alloys in a state of the finest obtainable division--say in the form of dust
or the finest flour, I can obtain the precipitation of approximately all the precious
metal contained in the cyanide solution. I find that I obtain more satisfactory
results by employing as precipitants the condensed metallic vapours of the metal or
alloy-particularly zinc-than by any other means and I therefore prefer to adopt
this course in preparing this dust or flour. In the case of zinc this product is
technically known as "zine dust" or "zinc fume."
I am aware that certain metals have before now been used for the purpose of
deposition of precious metal-but when employed, as has hitherto usually been the
case, in a state of comparatively coarse division-as for example when the metal be
used in the form of shavings, filiform fragments, or granules. The amount of the
metal requisite to obtain the desired deposition of gold is far greater than the
theoretical requirements and is also actually largely in excess of the amount which
I find it necessary to use when in the dust form above described. This large
consumption of metal in the case of deposition of gold from cyanide solutions is
partly caused by the manner in which the deposition of the precious metal is
effected viz.: by the passing of the solution continuously through a mass of shavings
or granules where at any given moment the liquor is in contact with a great
chemical excess of the metal used for deposition. As a result if zinc be the metal
used for deposition and be employed in the ordinary way that is in the form say of
sawdust or of fine shavings or filaments contained in a series of vessels or boxes
through which the gold-bearing cyanide solution is made to percolate continuously,
one hundred times the theoretical amount of metallic zinc is often consumed to
effect the complete deposition of the dissolved gold. This gives rise to other loss;
not only is there an undue consumption of zinc involving considerable outlay and in
addition also to the extensive plant of deposition boxes which such a method of
securing gold deposition demands, there is loss of cyanide by the injurious effect of
the excess of dissolved zinc upon the cyanide solution, the free potassium cyanide
or other suitable cyanide in which (as it is drawn from the ore) is correspondingly
deteriorated by formation of soluble double cyanide of zinc and potassium. This

page_text: deterioration necessitates the use of an extra quantity of cyanide to regenerate the
solution for solvent purposes when the latter is again applied to the gold-
bearing ore.
In carrying out my invention instead of allowing the cyanide solution containing
the dissolved precious metals to traverse or pere late through masses of metallic
filaments shreds or granules, I collect the whole of the liquor with which I wish to
deal in one or more suitably sized tanks and proceed to add thereto a quantity of
my finely powdered or floured metal prepared in the manner before specified, so as
to effect the direct precipitation of the dissolved gold. By proceeding in this way
I find that not only is the precipitation of the precious metal very rapid, but that
the quantity of precipitating metal or "precipitant" required to effect this
separation of goid is much less than in the ordinary method above described. As
a consequence the destruction or deterioration of cyanide in such liquors is far
smaller by my process and the total consumption of cyanide in the treatment of
gold bearing ores is very greatly reduced: this is a further important saving.
Besides this I require no extensive "zinc-box" plant, and the gold precipitated
being in the shape of a dense and flocculent precipitate is easily removed after
deposition from the bottom of the precipitating tank (which if desired may be fitted
with a bottom of inverted cone shape) or may be collected by rapid filtration of the
liquors through cloth or other suitable medium. This avoids the present trouble-
some operations of separating the gold deposits from the zinc filaments and the
precipitated gold obtained by my process is purer and more easy to refine than that
produced by the ordinary method above described.
"
I may employ various kinds of finely divided vapour-condensed metallic powders
such as lead or zine; or an alloy similarly prepared such as magnesium-zine
lead-zinc etc.; or a mixture of such powdered metals or powdered alloys; and I
may employ whichever of these 1 may elect to use or a mixture of one or more of
these in any convenient manner-such as by dusting or sieving a definite quantity
of the powdered precipitant-proportioned to the actual quantity of gold present
in the solution operated upon-
-or by running the precipitant in as a "suspension
in some of the liquor, or in water. Moderate agitation I prefer to employ, and this
may be provided for in any desirable manner; where for example the powdered
metal is applied by a stream of water or solution this stream may be employed for
the purposes of agitation. In considering the question of agitation it is important
to note that excessive agitation must be avoided that is if it would tend to
promote aeration or oxidation of the liquor since the presence of oxygen would
tend to dissolve the ziuc or other metallic powder employed in the excess of cyanide
without necessarily effecting the precipitation of the gold. The agitation may be
effected by mechanical stirrers or by suitable circulation say by means of a pump
or like appliance capable of circulating the liquor without aeration; and if necessary
the tank or vessel in which the operation takes place may be entirely closed in and
the solution protected from the air by the application or introduction of an inert
gas over the surface of the liquor.
I find that the advantageous results of this invention increase almost in proportion
to the fineness of the powdered metal or alloy introduced and in a secondary degree
to the absence of air in the operation. Operating in the presence of air with the
finest obtainable metallic powder or dust I am able to reduce the amount of metal
required to for example if zinc be employed, from once to three times the weight
of the actual gold present in solution. The powdered metals may conveniently be
of such fineness as is obtainable, by passage through a sieve of 40,000 meshes to
the square inch. I do not limit myself to this particular size but mention it as
giving in the case of zinc fume a product with which I have secured excellent
results. With such a precipitant applied as a suspension in water, 4 dwts. of gold
in a ton of liquor can be precipitated completely with from 8 to 12 dwts. of
precipitant and even less. The gold precipitate readily agglomerates and falls in
flocks and in a short time the precipitation is complete and the precipitated
66
"

page_text: gold may be readily collected by deposition or filtration or in any suitable manner.
It is of a considerable degree of purity and may be fused under ordinary fusion
mixtures to an ingot.
"
My process therefore is not a deposition process as generally understood
where the gold is deposited upon bright and extended metallic surfaces from which
it has afterwards to be removed but practically amounts to one of direct precipi-.
tation most of the metallic dust going into solution whilst the gold is thrown down
to the bottom of the vessel containing the solution; and the gold precipitate
contains far less of the precipitating medium than does the product obtained from
the zinc boxes.
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 I
claim is :-
1. The employment for the precipitation of precious metals from their cyanide
solutions of zinc, or other suitable metal or alloy in the exceedingly fine state of
division set forth with the exclusion of air substantially as herein described.
2. In the precipitation of precious metals from their cyanide solutions the
employment of zinc or other metal or alloy in an extremely fine state of division.
obtained by condensing the vapours of the said metal or alloy.
Noted this 19th dev of Jul 1895
Doted this 19th day of
1895
H. L. SULMAN.
Boult & Wade,
Agents for the Applicant.
H. L. SULMAN.
Boult & Wade,
Agents for the Applicant.