Improvements in the Extraction of Gold and Silver from Ores or Matte.
Year: 1893

page_text: Date of Application, 22nd Nov., 1893
Complete Specification Left, 26th July. 1894-Accepted. 15th Sept., 1894
PROVISIONAL SPECIFICATION.
Improvements in the Extraction of Gold and Silver from Ores
or Matte.
I, Dr. BRUNO MIERISCH, Mining Engineer, of Managua in the Republic of
Nicaragua, Central America, do hereby declare the nature of this invention to be
as follows:-
This process is a modification of the chlorination process, and has for its object,
to render innocuous the remnants of sulphur, arsenic, and low oxides in roasted
ores, by means of hypochlorites and chlorates of alkalis and alkaline earths, the
said ores being mixed with a calculated quantity of sodium hydrate, and calcium
hydrate being added in sufficient quantity to separate in the shape of insoluble
calcium salts the sulphuric and arsenic acid which has been formed, thereby
avoiding the contamination of the sodium chloride (common salt) solution with the
sodium sulphate.
By the subsequent action of chlorine, sodium chloride (or calcium chloride),
as well as hypochlorite and chlorate of soda (or hypochlorite and chlorate of calcium),
is obtained.
The metallic chlorides formed are extracted with concentrated sodium chloride
solution, and as much sodium hydrate is added to the solution of common salt, as
may be necessary to produce an alkaline reaction. By this operation the following
among the more important metals are precipitated; iron, copper in the shape of
hydrated oxides; and there remains in solution; gold, silver, platinum, mercury,
lead, zinc. The precious metals and the lead are precipitated from the alkaline
solution by metallic zinc. Finally the zinc is recovered by electrolysis, also the
chlorine, and sodium hydrate, which substances may then be used for a fresh cycle
of operations.
The receptacles used for carrying out this process are similar to those which
have hitherto been found suitable for the extraction of gold. The chlorine is
obtained by the electrolytic decomposition of a hot concentrated solution of common
salt, which at the same time yields sodium hydrate and hydrogen.
The finely divided ore or slime contained in the lye-casks is mixed with sodium
hydrate and slaked lime. If chlorine is now admitted, it combines first with the
alkalis and alkaline earths to form chlorides and bypochlorites, as well as a small
quantity of chlorates.

page_text: of the sodium or calcium hydrate. The liquor flows off through a lead pipe having
an absolute height of more than 5 metres (corresponding to atmosphere). Con-
sequently, no liquor will pass over to the exhaustor, provided, of course, that the
pipe always terminates under liquid.
To the liquor almost completely relieved of its chlorine, is added caustic soda
liquor derived from the electrolysis of common salt, until the reaction becomes
alkaline. By this operation some of the metals, notably iron and copper, are
separated in the form of hydrated oxides, and any arsenic acid that may be present
is separated in the shape of arsenates of these metals. If the quantity of metallic
oxides should not be sufficient for this purpose, some calcium chloride may be
added, or the adınixture of lime may be previously increased in a corresponding
manner.
As the precipitates may casily carry with them some gold and silver, and render
the filtration difficult owing to their voluminous nature, they are relieved of liquid
as much as possible, by suction, or by a filter press, subsequently dried and slightly
calcined, without taking account of any solution of common salt, which they may
still contain. The dried oxides are then pulverized and again introduced in the
process for extraction with chlorine.
The alkaline solution of common salt contains gold, silver (probably as Ag Cl, as
it separates out in this shape when the solution is being diluted), platinum, mercury,
lead (if it has not remained in the ore as insoluble sulphate of lead, which will
frequently occur), also zinc.
The alkaline solution is now conducted through granulated zinc, thereby causing
gold, silver, platinum, mercury and lead to separate, while zinc enters in solution.
This zinc solution is then directly electrolysed, in order to recover the zinc in a
metallic condition; the continued action of the electric current produces chlorine
and soda solution which are again used in the process, thus completing the cycle of
operations. The hydrogen gas formed at the same time may be used for
illuminating or heating purposes.
The gold and silver precipitated by the zinc are further treated by any of the
known methods.
Dated this 22nd day of November 1893.
FAIRFAX & WETTER,
Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in the Extraction of Gold and Silver from Ores
or Matte.
I, Dr. BRUNO MIERISCH, Mining Engineer, of Managua, in the Republic of
Nicaragua, Central America, 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 process is a modification of the chlorination process, and has for its object,
to render innocuous the remnants of sulphur, arsenic, and low oxides in roasted ores,
by means of hypochlorites and chlorates of alkalis and alkaline earths, the said ores
being mixed with a calculated quantity of sodium hydrate, and calcium hydrate
being added in sufficient quantity to separate in the shape of insoluble calcium salts
the sulphuric and arsenic acid which has been formed, thereby avoiding the
contamination of the sodium chloride (common salt) solution with the sodium
sulphate.
By the subsequent action of chlorine, sodium chloride (or calcium chloride), as
well as hypochlorite and chlorate of soda (or hypochlorite and chlorate of calcium)
is obtained.

page_text: The metallic chlorides formed are extracted with concentrated sodium chloride
solution, and as much sodium hydrate is added to the solution of common salt, as
may be necessary to produce an alkaline reaction. By this operation the following
among the more important metals are precipitated; iron, copper, in the shape of
hydrated oxides; and there remains in solution; gold, silver, platinum, mercury,
lead, zinc. The precious metals and the lead are precipitated from the alkaline
solution by metallic zinc. Finally the zinc is recovered by electrolysis, also the
chlorine and sodium hydrate, which substances may then be used for a fresh cycle
of operations.
The receptacles used for carrying out this process are similar to those which have
hitherto been found suitable for the extraction of gold. The chlorine is obtained
by the electrolytic decomposition of a hot concentrated solution of common salt,
which at the same time yields sodium hydrate and hydrogen.
The finely divided ore or slime contained in the liquor casks is mixed with sodium
hydrate and slaked lime. If chlorine is now admitted, it combines first with the
alkalies and alkaline earths to form chlorides and hypochlorites, as well as a small
quantity of chlorates.
4 NaOH + 4 Cl = 2 Na Cl + 2 CI O Na + 2 H, O,
The reaction of the oxychlorides on the oxydisable bodies is indicated by 1
owing equations, the reaction of the pure chlorine being, for the sake
parison, always placed first.
2 S12 Cl + 8 H₂O = 2 H, SO₁ + 12 H CI,
2 S + 2 CIO, O Na + 2 H, O = Na, SO + H₂SO, + 2 H C1,
2 S6 CIO Na + 2 H, O = 2 Na, SO, + 2 Na Cl + 4 H Cl,
3 As, O, +12 Cl + 6 H, O = 3 As, O. + 12 H Cl,
3 As, O, + 2 CIO, O Na = 3 As, O, + Na Cl,
3 As, O, + 6 CI O Na = 3 As, O, + 6 Na Cl,
4 Fe + 12 Cl 4 Fe Cl₂,
=
4 Fe +2 CIO, O Na = 2 Fe, 0, + 2 Na Cl,
4 Fe +6 C1 O Na =
2 Fe, O, 6 Na Cl,
3
3 Cu, O+ 6 Cl = 3 Cu Cl, + 3 Cu O,
3 Cu, O + Cl, O, O Na
3 Cu, O + 3 CIO Na
=
1
6 CuO + Na Cl,
6 CuO+ 3 Na Cl,
12 Fe S108 Cl + 48 H,O = 4 Fe, SO, + 4 Fe Cl, + 96 H Cl,
12 Fe S18 CIO, O Na :
12 Fe S+54 CI O Na =
-
9 Na, SO, + Fе, S₁ O₁₂ + 6 Fе Cl, + 2 Fes
12 Na, SO₁ + 8 Fe Cl, + 2 Fe, 0, + 30 Na Cl,
4 Fe S2 + 60 Cl + 82 H, O= 2 Fe, S, O₁₂ + 2 H, SO, + 60 H Cl,
3 19
4 Fe S, +10 CIO, O Na + 2 H2O = 5 Na, SO, + Fe, S, O₁, + 2 Fe Cl
4 H Cl,
4 Fe S2 + 30 CI O Na + 2 H2O = 8 Na, SO, +4 Fe Cl, + 4 H Cl + 14 Na

page_text: According to the above equations, the consumption of chlorine is neither smaller
nor larger, than what it has been hitherto.
In oxidizing by means of chlorates and hypochlorites, the formation of free acid
is completely avoided, provided that the ore does not contain free sulphur, either
as such, or in the shape of undecomposed pyrites. This is rarely the case, if the
crushed ores have been roasted with ordinary care. But even with the presence of
free sulphur, the quantity of acids being formed is far less than when pure chlorine
is used for oxidation. My new process thus avoids a great evil of the chlorination
processes hitherto used, namely the serious contamination of the liquor by the
formation of large quantities of worthless chlorides, and the solution of otherwise
insoluble bodies, such as gypsum, silicic acid, arsenates etc.
If the ore only contains metallic oxides capable of higher oxidation, the oxida-
tion by means of chlorates is not attended with the solution of any chlorides, but
the metals remain in an insoluble form in the ore, as shown by the example given
above for the oxidation of Cu, O. Only the precious metals, which always occur
in a metallic shape, or (as is the case with silver) in the shape of sulphates, enter
into solution during the further action of chlorine. The liquors are therefore very
pure.
The lixiviation takes place by means of concentrated solution of common salt,
the solution being sucked off at about half the atmospheric pressure, which may be
effected by setting the extraction casks into communication with a receptacle in
which the air has only one half the pressure of the atmosphere. A tank containing
a solution of (caustic) soda or of slaked lime is inserted between the two, in order to
absorb the chlorine, which at half the atmospheric pressure will escape from the
liquor almost completely. In the tank a mixture of chloride and hypochlorites will
be formed, which are again used in the process by adding them to the ore instead
of the sodium or calcium hydrate. The liquor flows off through a lead pipe having
an absolute height of more than 5 metres (corresponding to atmosphere). Conse-
quently, no liquor will pass over to the exhaustor, provided, of course, that the pipe
always terminates under liquid.
To the liquor almost completely relieved of its chlorine, is added caustic soda
liquor derived from the electrolysis of the common salt, until the reaction becomes
alkaline. By this operation some of the metals, notably iron and copper, are
separated in the form of hydrated oxides, and any arsenic acid that may be present
is separated in the shape of arsenates of these metals. If the quantity of metallic
oxides should not be sufficient for this purpose, some calcium chloride may be
added, or the admixture of lime may be previously increased in a corresponding
manner.
As the precipitates may easily carry with them some gold and silver, and render
the filtration difficult owing to their voluminous nature, they are relieved of liquid
as much as possible, by suction, or by a filter press, subsequently dried and
slightly calcined, without taking account of any solution of common salt, which
they may still contain. The dried oxides are then pulverised and again introduced
in the process for extraction with chlorine.
The alkaline solution of common salt contains gold, silver, (probably as Ag CL
as it separates out in this shape when the solution is being diluted), platinum,
mercury, lead (if it has not remained in the ore as insoluble sulphate of lead,
which will frequently occur), also zinc.
The alkaline solution is now conducted through granulated zinc, thereby
causing gold, silver, platinum, mercury and lead to separate, while zinc enters in
solution.
This zinc solution is then directly electrolysed, in order to recover the zinc in
a metallic condition; the continued action of the electric current produces chlorine
and soda solution which are again used in the process, thus completing the cycle
of operations. The hydrogen gas formed at the same time may be used for
illuminating or heating purposes.

page_text: The gold and silver precipitated by the zinc are further treated by any of the
known methods.
The quantity of caustic soda solution which should be added as described above,
is ascertained in the following manner :-
1 gramme of the ore is treated with bromine or cblorine at a high temperature,
until the absorption ceases; after lixiviation and filtration, the filtrate is heated,
until the smell of chlorine or of bromine ceases. The filtrate is divided into two
parts, and the quantity of chlorine determined in one part by means of silver
nitrat while the contents of sulphuric acid in the other part are determined by
means of barium chloride. For every atom of chlorine, one molecule of caustic
soda is then used. In the same manner the quantity of lime to be added is
calculated from the quantity of sulphuric acid contained in the filtrate. For
instance, for every 1000 kilos. of ore which absorbs 6-522 per cent. of chlorine,
(that is for 5-22 kilos.) 5.98 kilos. of Na OH would have to be added.
If for instance, 2 per cent. of sulphuric acid have been found by analysis, the
quantity of Ca (O H), to be added for 1000 kilos. of ore is 18.5 kilos. If
the ore contains sulphates soluble in water, these must also be taken into account,
so that for instance in the case of an ore containing 0.55 per cent. of Fe S and
3 per cent. of SO, in the shape of soluble salts, 24-75 kilos. of Na OH and
32-375 kilos. of Ca (O H), are to be used for 1000 kilos.
The consumption of sodium chloride is theoretically nil, but in practice slight
losses are inevitable. The consumption of fuel may be reduced to the quantity
necessary for heating to 100° C. the liquor flowing into the electrolysing apparatus.
Lime or calcium chloride is only used in the case of ores rich in sulphur or arsenic.
The consumption of hydrochloric acid depends on the method of precipitating the
heavy metals by means of common salt solution containing soda. One litre of
this solution contains about 85-5 grammes of Na O H. For neutralising this,
about 78 grammes of H Cl are required. One kilogramme of crude hydro-
chloric acid, however, contains about 350 grammes of H Cl. Consequently, an
excess of at least 4-5 litres of soda liquor per 100 kilos. would increase the
consumption of hydrochloric acid by 1 kilo. for every 1000 kilos.
As the neutralisation of the solutions can be ascertained very easily, the con-
sumption of hydrochloric acid will be limited to a few hundred grammes per
1000 kilos. The loss of zinc is theoretically nil, but in practice, slight losses are
unavoidable.
The process described above enables the metallurgist to recover the precious
metals by the chlorination process in a very complete manner and with the
following advantages:
1. Great simplicity of operation.
2. The possibility of dispensing with chemicals except hydrated lime in the case
of pyritous or arsenious ores. Only the mechanical waste of common salt is to
be replaced, for actual chemical losses of chlorine or sodium hydrate are not con-
ceivable, inasmuch as the consumption of chlorine is always attended with the
formation of an equivalent quantity of caustic soda, however large the consumption
of chlorine may be; the decomposed sodium chloride is always fully regenerated.
If the ores contain some zinc sulphide, it is not even necessary, to replace the
mechanical waste of zinc.
3. The possibility of using for the reactions a force (the electric current) which
may be easily transmitted from a considerable distance, and consequently the
possibility of utilizing a distant water power.
4. Avoidance of very tedious roasting (for oxidation); as the chlorine only
serves as an intermediary, the real agent being the electric current, a residue of
sulphur does not imply a loss of chlorine, but a loss of electric energy, which is
cheaper than the equivalent quantity of chlorine, which in the ordinary chlorination
process is obtained by the action of hydrochloric acid on manganic oxide and
would represent a direct loss.

page_text: Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is ;-
1. The process for the extraction of gold and silver from roasted pyritous and
arsenious ores, which consists in causing hypochlorites and chlorates to act in a
nascent state by mixing the ore with sodium hydrate and then treating the
mixture with chlorine, the admixture of sodium sulphate to the concentrated salt
solution serving for lixiviation being prevented, if necessary, by replacing a portion
of the sodium hydrate with a corresponding quantity of calcium hydrate,
substantially as described.
2. The separation of the precious metals, lead and zinc from the iron and copper
in the solution obtained as specified above, by super-saturating the brine with
sodium hydrate, substantially as described.
Dated this 4th day of T.1 1004
FAIRFAX & WETTER,
433, Strand, London, Agents.