Improvements in the Manufacture of Gold Solvents.
Year: 1895

page_text: PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Gold Solvents.
1, JOHN JAMES HOOD, of 1 Fenchurch Avenue, in the City of London,
Chemist, do hereby declare the nature of this invention to be as follows:-
These improvements relate to the manufacture and preparation in a form
suitable for transport, of certain classes of complex chemical compounds, which
have the property, under particular conditions, of dissolving metallic gold. They
may consequently be employed when dissolved in a suitable medium for extracting
the precious metal from its ores. These compounds may be termed double salts,
and they consist of two bases, and two or it may be only one acid radicle. Of the
two bases one may be an alkaline metal, potassium, or sodium, and the other a
heavy metal like mercury or lead. Of the two acid radicles, one or both may be
cyanogen (CN). To prepare these salts, for example one containing mercury, I
take a crude solution of alkaline cyanide such as that of potassium or sodium
cyanide or mixtures of these from which 1 eliminate the sulphides by any of the
well known processes such as agitation with white lead or litharge and to this
solution I add a quantity of a mercury compound such as the chloride, varying the
amount according to the salt desired, and boil down the mixture to dryness. Or I
concentrate until crystallization begins and then allow the solution to stand till the
process of crystallization of the double salt is complete, subsequently draining and
drying the crystals so obtained. According to the amount of mercury salt
employed relative to the alkaline cyanide, double salts of varying composition are
obtained. For example, by employing two parts by weight of mercury chloride
to one of potassium cyanide, a different compound is obtained to that formed by
using equal weights of the two bodies. Or I may employ less by weight of the
mercury chloride or other equivalent compound of mercury than of the alkaline
cyanide to which I may also add varying quantities of caustic potash or soda, and
evaporate the mixture to dryness for transport, without separating any particular
crystalline double salt from such mixture. To prepare a lead compound, I first
form a soluble compound of lead and caustic alkali, such for instance as may be
prepared by boiling litharge with caustic soda. To this solution I add varying
quantities of potassium or sodie cyanide, or mixtures of these and evaporate the
whole to dryness.
The above described gold solvents are intended to replace potassium cyanide and
sodium cyanide which heretofore have been largely used in the separation of gold
from " tailings" or crushed ore from which the greater part of the gold has been
previously separated.
In the
Not only are these gold solvents more efficient in their action than are the
alkaline cyanides but they are more easily prepared in the solid state.
evaporation of potassium cyanide and sodium cyanide it is difficult to avoid large
loss by decomposition, whereas when the alkaline cyanide has been converted by
the addition of the mercury or other compound as above stated all liability to
decomposition during evaporation is removed.
Dated this 12th dow of January 1895

page_text: improvements in the Manufacture of Gold Solvents.
J, JOHN JAMES HOOD, of 1 Fenchurch Avenue, in the City of London,
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:-
These improvements relate to the manufacture and preparation in a form
suitable for transport, of certain classes of complex chemical compounds, which
have the property, under particular conditions, of dissolving metallic gold. They
may consequently be employed when dissolved in a suitable medium for extracting
the precious metal from its ores. These compounds may be termed double salts,
and they consist of two bases, and two or it may be only one acid radicle. Of
the two bases one may be an alkaline metal, potassium, or sodium, and the other a
heavy metal like mercury or lead. Of the two acid radicles, one or both may be
cyanogen (CN). To prepare these salts, for example one containing mercury, I
take a crude solution of alkaline cyanide such as that of potassium or sodium
cyanide or mixtures of these from which I eliminate the sulphides by any of the
well known processes such as agitation with white lead or litharge and to this
solution I add a quantity of a mercury compound such as the chloride, varying
the amount according to the salt desired, and boil down the mixture to dryness.
Or I concentrate until crystallization begins and then allow the solution to stand
till the process of crystallization of the double salt is complete, subsequently
draining and drying the crystals so obtained. According to the amount of mercury
salt employed relative to the alkaline cyanide, double salts of varying composition
are obtained. For example, by employing two parts by weight of mercury chloride
to one of potassium cyanide, a different compound is obtained to that formed by
using equal weights of the two bodies. Or I may employ less by weight of the
mercury chloride or other equivalent compound of mercury than of the alkaline
cyanide to which I may also add varying quantities of caustic potash or soda,
and evaporate the mixture to dryness for transport, without separating any
particular crystalline double salt from such mixture. Suitable proportions are:-
Mercury chloride
Alkaline cyanide
Caustic alkali
5 parts.
-
10
"
-
1
"
To prepare a lead compound, I first form a soluble compound of lead and caustic
alkali, such for instance as a plumbate of soda which may be prepared by boiling
litharge with caustic soda. To this solution 1 add varying quantities of potassium
or sodic cyanide, or mixtures of these and evaporate the whole to dryness. The
addition of one part of lead in solution to two parts of alkaline cyanide will be
found suitable.
The above described gold solvents are intended to replace potassium cyanide
and sodium cyanide which heretofore have been largely used in the separation of
gold from "tailings" or crushed ore from which the greater part of the gold has
been previously separated.
Not only are these gold solvents more efficient in their action than are the
alkaline cyanides but they are more easily prepared in the solid state. In the
evaporation of potassium cyanide and sodium cyanide it is difficult to avoid large
loss by decomposition, whereas when the alkaline cyanide has been converted by
the addition of the mercury or other compound as above stated all liability to
decomposition during evaporation is removed.
The above-mentioned solvents act upon the ores by substitution that is to say

page_text: they deposit the mercury or the lead which they contain in equivalent proportion
to the gold which they dissolve.
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 means substantially as described whereby in the manufacture of cyanide
solvents of gold I avoid the loss heretofore incurred in the evaporation of a
crude alkaline cyanide solution, such means consisting in adding a mercury or a
lead compound to the solution prior to the evaporation thereof.
2. The manufacture of gold solvents by eliminating sulphides from a crude
solution of alkaline cyanide, then adding chloride of mercury to the solution and
boiling down to dryness or concentrating and crystallising the product.
3. The manufacture of gold solvents as stated in the preceding claim but with
the substitution of a plumbate of soda for chloride of mercury.
4. The manufacture of gold solvents substantially as described by adding to a
solution of an alkaline cyanide, a mercury or a lead compound and caustic alkali
and evaporating the mixture.
Dated this 14th day of October 1895.
CARPMAEL & Co.,
Agents for the Applicant.