Process for Winning Gold from Refractory Ores.
Year: 1899

page_text: Date of Application, 13th Nov., 1899
Complete Specification Left, 12th July, 1900 -Accepted, 25th Aug.,
1900
Process for Winning Gold from Refractory Ores.
We, JOSEF DIкTHER, of 3, Annastrasse, Niederlahnstein, Germany, Engineer,
and MAXIMILIAN MERZ, of 216, Hauptstrasse, Aulendorf, Germany, Mining
Engineer, do hereby declare the nature of this invention to be as follows:-
This invention relates to a process for the treatment of refractory gold ores,
that is, gold ores which cannot be successfully treated by such solvents as
chlorine, potassium cyanide or mercury.
Such ores generally contain large proportions of pyrites and in addition
arsenic, antimony and tellurium. They have hitherto been opened up in the
first place by treatment with alkali sulphide and sulphur, where by sulpho-
salts of arsenic, antimony, tellurium and gold are formed; these are leached
from the unattacked constituents by water. To separate the gold from the
injurious elements arsenic, antimony and tellurium in the solution thus
obtained, various precipitants which have only a partial decomposing effect on
the mixture of sulpho-salts have been used. Thus the gold may be precipitated
by acids or by lime, or, according to the later methods, by sundry other sub-
stances, such as ammonium chloride or alkali permanganate. The two last
named precipitants, however, are excluded in practice by their high price.
Precipitation by means of acids is open to the objection that a portion of
the injurious elements is always thrown down together with the gold, so that
the latter is still contaminated with them. Lime is equally objectionable,
for insoluble compounds of lime with the injurious elements are precipitated
together with the gold. Besides, the added lime considerably increases the
quantity of the matter to be separated in subsequently working up the pre-
cipitate and the amount required appreciably raises the cost of the process.
By the present invention the use of a precipitant for decomposing the sulpho-
salts is avoided by employing the correct proportion of water in leaching the
mass and by a suitably regulated addition of sulphur to the mass or to the
solution of the sulpho-salts; in this manner the gold may be obtained free
from the injurious elements.
The process is as follows:-The ore is mixed with alkali sulphide and sul-
phur, the proportion of these added materials depending on the composition
of the ore, and the mixture is heated with exclusion of air or in a reducing
Hame at a bright red heat. Instead of alkali sulphide and sulphur, sodium
sulphate and carbon may be used, for a mixture of these is known to have the
same effect.
The temperature and duration of the heating must be carefully regulated,
as the formation of a double sulpho-salt of alkali and gold, which occurs at a
very high temperature is to be avoided, since such a salt would subsequently
dissolve together with the arsenic, etc. The temperature must be adjusted so
that the sulpho-gold compound produced
ulphide, but remains in such a form that
he gold is dissolved in the colloidal state.
does not combine with the alkali
when the mass is treated with water
The mass, while still hot, is thrown

page_text: ore.
into cold water, which should be from two to three times the weight of the
A thorough mechanical disintegration ensues and the unattacked portion
of the ore settles while the soluble part of the mass is immediately dissolved.
The solution contains the sulpho-salts of arsenic, antimony and tellurium in a
state of true solution, while the gold and a part of the iron sulphide are dis-
solved in the colloidal state. Another part of the iron sulphide is suspended
in the solution in a finely divided form. It should be remarked that the pre-
sence of iron seems to be necessary for the success of the process in so far as
when precipitated it entangles the gold and facilitates its recovery.
The liquid with the suspended iron sulphide in it may now either be decanted
from the unattacked ore, or be allowed to remain over it.
After long standing the liquid gelatinises, either spontaneously (if a suffi-
ciently large proportion of sulphur was added in the heating process) or after
the addition of from 1 to 2 per cent. of sulphur, whereby the dissolved colloidal
gold together with a part of the dissolved colloidal iron, but free from the in-
jurious elements, is precipitated. Accordingly, for recovering the gold the
solution with its suspended iron sulphide may be left to gelatinise spontaneously
if sufficient sulphur has been added before the heating process, or about one
or two per cent. of sulphur may be added and the solution may be left to
gelatinise, which generally happens very soon.
The conditions necessary for gelatinisation and consequent precipitation of
the gold, are that an excess of sodium sulphide is used in the heating process,
that the heated mass is leached with as little water as possible and that the
correct proportion of sulphur is added either to the mass to be heated or to the
solution of sulpho-salts.
To separate the gold, which is contained in the gelatinised mass, together
with some iron sulphide. in a finely divided state, from the arsenic antimony,
and tellurium, which remain dissolved as sulpho-salts, it suffices to filter-press
the liquid.
A reason for the remarkable tendency of the solution to gelatinise may be
found in the fact that various colloids are present, the tendency of which to
gelatinise is well known.
To avoid the use of a filter-press, the solution obtained by the leaching pro-
cess and containing the suspended iron sulphide, is mixed with sulphur, pre-
ferably crystallinc, until it is saturated therewith. The gold then separates
The precipitate
either at once or on dilution of the solution with water.
obtained in this manner may be separated by ordinary filtration.
For the sulphur in this process may be substituted hydrogen sulphide or
highly sulphurised alkali or alkaline earth sulphides, so far as these are soluble
and will not increase the bulk of the precipitate. Obviously such variations of
the process as necessitate a considerable quantity of water are applicable where
water is abundant, while gelatinisation and filter-pressing are advantageous
where water is scarce.
The recovery of the gold from the precipitate obtained in this process is
effected by known extraction methods.
10. Ja of November 1800
Process for Winning Gold from Refractory Ores.
We, JOSEF DIETHER, of 3, Annastrasse, Niederlahnstein, Germany, Engineer,
and MAXIMILIAN MERZ, of 216, Hauptstrasse, Aulendorf, Germany, Mining

page_text: Engineer, 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 a process for the treatment of refractory gold ores,
that is, gold ores which cannot be successfully treated by such solvents as
chlorine, potassium cyanide or mercury.
Such ores generally contain large proportions of pyrites and in addition
arsenic, antimony and tellurium. They have hitherto been opened up in the
first place by treatment with alkali sulphide and sulphur, where by sulpho-
salts of arsenic, antimony, tellurium and gold are formed; these are leached
from the unattacked constituents by water. To separate the gold from the
injurious elements arsenic, antimony and tellurium in the solution thus
obtained, various precipitants which have only a partial decomposing effect on
the mixture of sulpho-salts have been used. Thus the gold may be precipitated
by acids or by lime, or, according to the later methods, by sundry other sub-
stances, such as ammonium chloride or alkali permanganate. The two last
named precipitants, however, are excluded in practice by their high price.
Precipitation by means of acids is open to the objection that a portion of
the injurious elements is always thrown down together with the gold, so that
the latter is still contaminated with them. Lime is equally objectionable,
for insoluble compounds of lime with the injurious elements are precipitated
together with the gold. Besides, the added lime considerably increases the
quantity of the matter to be separated in subsequently working up the pre-
cipitate and the amount required appreciably raises the cost of the process..
By the present invention the use of a precipitant for decomposing the sulpho-
salts is avoided by employing the correct proportion of water in leaching the
mass and by a suitably regulated addition of sulphur to the mass or to the
solution of the sulpho-salts; in this manner the gold may be obtained free
from the injurious elements.
The process is as follows:-The ore is mixed with alkali sulphide and sul-
phur, the proportion of these added materials depending on the composition
of the ore, and the mixture is heated with exclusion of air or in a reducing
flame at a bright red heat. Instead of alkali sulphide and sulphur, sodium
sulphate and carbon may be used, for a mixture of these is known to have the
samė effect.
The temperature and duration of the heating must be carefully regulated,
as the formation of a double sulpho-salt of alkali and gold, which occurs at a
very high temperature is to be avoided, since such a salt would subsequently
dissolve together with the arsenic, etc. The temperature must be adjusted so
that the sulpho-gold compound produced does not combine with the alkali
sulphide, but remains in such a form that when the mass is treated with water
the gold is dissolved in the colloidal state. The mass, while still hot, is thrown
into cold water, which should be from two to three times the weight of the
A thorough mechanical disintegration ensues and the unattacked portion
of the ore settles while the soluble part of the mass is immediately dissolved.
The solution contains the sulpho-salts of arsenic, antimony and tellurium in a
state of true solution, while the gold and a part of the iron sulphide are dis-
solved in the colloidal state, another part of the iron sulphide is suspended
in the solution in a finely divided form. It should be remarked that the pre-
sence of iron seems to be necessary for the success of the process in so far as
when precipitated it entangles the gold and facilitates its recovery.
ore.
The liquid with the suspended iron sulphide in it may now either be decanted
from the unattacked ore, or be allowed to remain over it.
After long standing the liquid gelatinises, either spontaneously (if a suffi-
ciently large proportion of sulphur was added in the heating process) or after
the addition of from 1 to 2 per cent. of sulphur, whereby the dissolved colloidal
gold together with a part of the dissolved colloidal iron, but free from the in-

page_text: jurious elements, is precipitated. Accordingly, for recovering the gold the
solution with its suspended iron sulphide may be left to gelatinise spontaneously
if sufficient sulphur has been added before the heating process, or about one
or two per cent. of sulphur may be added and the solution may be left to
gelatinise, which generally happens very soon.
The conditions necessary for gelatinisation and consequent precipitation of
the gold, are that an excess of sodium sulphide is used in the heating process,
that the heated mass is leached with as little water as possible and that the
correct proportion of sulphur is added either to the mass to be heated or to the
solution of sulpho-salta.
To separate the gold, which is contained in the gelatinised mass, together
with some iron sulphide. in a finely divided state, from the arsenic, antimony,
and tellurium, which remain dissolved as sulpho-salts, it suffices to filter-press
the liquid.
A reason for the remarkable tendency of the solution to gelatinise may be
found in the fact that various colloids are present, the tendency of which to
gelatinise is well known.
To avoid the use of a filter-press, the solution obtained by the leaching pro-
cess and containing the suspended iron sulphide, is mixed with sulphur, pre-
ferably crystalline, until it is saturated therewith. The gold then separates
The precipitate
either at once or ou dilution of the solution with water.
obtained in this manner may be separated by ordinary filtration.
For the sulphur in this process may be substituted hydrogen sulphide or
highly sulphurised alkali or alkaline earth sulphides, so far as these are soluble
and will not increase the bulk of the precipitate. Obviously such variations of
the process as necessitate a considerable quantity of water are applicable where
water is abundant, while gelatinisation and filter-pressing are advantageous
where water is scarce.
The recovery of the gold from the precipitate obtained in this process is
effected by known extraction methods.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed, we declare that what
we claim is:-
1. A process for winning gold from refractory ores by first mixing the ore
with alkali sulphide and sulphur, or with substances which yield alkali sul-
phide when heated, then healing the mixture for a short time at a red heat,
either with exclusion of air or in a reducing flame, then leaching the mass with
a little water, then allowing the solution thus obtained and mixed, if necessary,
with sulphur to stand until it gelatinises and finally separating the gelatinised
matter, substantially as described.
2. A process for winning gold from refractory ores by first mixing the ore
with alkali sulphide and sulphur, or with substances which yield alkali sul-
phide when heated, then heating the mixture for a short time at a red heat,
either with exclusion of air or in a reducing flame, then leaching the mass with
a little water, then saturating the solution thus obtained with sulphur, and
finally separating from the liquid the matter thus precipitated, or precipitated
after adding water, substantially as described.
1011 JT1 1900