Improvements in the Treatment of Ores containing Precious Metal, for the Recovery of the Precious Metal therefrom.
Year: 1898

page_text: Date of Application, 26th Mar., 1898-Accepted, 18th Feb., 1899
Improvements in the Treatment of Ores containing Precious Metal,
for the Recovery of the Precious Metal therefrom.
I, HENRY WETHERED, of Ferncliffe, Tyndall's Park, Clifton, Bristol, Gentleman,
do hereby declare the nature of this invention (which has been communicated to me
from abroad by James Anderson Gilmour, Mines Manager, and Henry Stow Young,
Analytical Chemist, both of Santa Francesca Mines, Leon, Nicaragua, Central
America) and in what manner the same is to be performed to be particularly de-
scribed and ascertained in and by the following statement:-
This invention has principally for its object to economically treat ores especially
slimy ore, or slimes, containing gold, or silver, or both (which I will hereinafter
refer to as the precious metal), for the recovery of the precious metal therefrom.
With ores which are not slimy and where a solution process is used, the precious
metal has been dissolved by a solvent, and the solution has been separated from
the magma, and the precious metal has been recovered from the solution by pre-
cipitation, or electrolysis; but in the case of slimy ore, or slimes, as the solution
is not readily separable from such slimy ore, or slimes, either the precious metal
is lost, or the costly and inconvenient preliminary operation of roasting the ores
has been resorted to, or the slimes have been separated from the ore and treated
by an expensive plant for settling and decanting.
According to this invention the ground ore especially slimy ore, or slimes, after
having been subjected to the action of a cyanide solvent such as cyanide of
potassium, cyanide of sodium, cyanide of calcium, or other cyanide compound, or
after having been subjected to the joint action of mercury and cyanide of potassium,
or other cyanide solvent as aforesaid hereinafter called "the solvent," is or are
treated with an amalgam, or mixture of amalgams, so as to precipitate from the
magma the precious metal in solution without first separating the solution from
the magma. The precious metal (both that dissolved by the solvent and that
directly amalgamated by the mercury), is thus obtained in combination with mer-
cury from which the said precious metal can be recovered in the usual way.
Suitable amalgams for precipitation are zinc amalgam, copper amalgam, tin
amalgam, lead amalgam, and aluminium amalgam, or mixtures of two, or more,
of them.
The process according to this invention may be carried out as follows:-
The operations may be divided into three stages, or steps, viz. :—-
1. Amalgamation and dissolving, or dissolving alone.
2. Precipitation.
3. Separation of mercury containing precious metal from the magma.
The first and second stages may be conducted in the same vessel provided with
agitators, or stirrers, or in separate vessels provided with agitators or stirrers.
The third stage may be effected in a settler provided with slow agitators, or
stirrers, or by means of concentration tables.
A charge of ground ore, in quantity according to the vessel employed for agitating
or stirring, along with a sufficient amount of water, is gradually charged into the

page_text: vessel while the stirrer, or agitator, is in motion. A quantity of mercury is then
added sufficient for ordinary pan amalgamation, and then there is added
immediately, or after an interval of time, a quantity of the solvent in solid form or
in solution according to the particular ore under treatment, and the agitation, or
stirring, is continued for a further period of time. Or the solvent may be added
alone without any mercury, or both the solvent and the mercury may be added
at the same time according to the ore under treatment.
After the dissolving of the precious metal is effected the charge is subjected to
the action of one, or more, of the aforesaid amalgams, and the agitation, or stirring,
is continued for a sufficient time to allow the precious metal to be precipitated and
amalgamated with the mercury. If desired heat may be applied, for example, by
blowing through steam. This operation may be conducted in the same vessel as
that in which the first stage is conducted, or the charge may be run from that vessel
into another vessel provided with agitators, or stirrers.
In treating ores for the recovery of gold a mixture of zinc and copper amalgams
is very efficacious, whilst for the recovery of silver a mixture of lead and tin
amalgams is suitable.
The charge after being subjected to the said second stage of the treatment is run
into the settler provided with a syphon cup and straining bag and the amalgam
of precious metal allowed to settle and pass into the syphon cup, and from thence
into the strainer the precious metal being obtained therefrom by retorting, and
refining, as usual, the tailings being run off to deposit, or to waste.
Instead of a settler, concentration tables may be used in the ordinary manner.
In the process I have described, the difficulties hitherto experienced as aforesaid
in treating slimy ores, or slimes, are overcome, the metals being all brought into
combination with the mercury by solution and precipitation and amalgamation of
the precipitated metals or partly by direct amalgamation.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, I declare that what I claim is:-
1. In the treatment of ores containing precious metal (gold, or silver, or both)
for the obtainment of the precious metal therefrom, treating a charge of ore,
especially slimy ore, or slimes, which has, or have been subjected to the action of
a cyanide solvent, or of mercury and a cyanide solvent, with an amalgam of a
metal (or mixtures of amalgams) so as to cause the precipitation and amalgamation
of the precipitated precious metal without separation of the solution from the
charge; substantially as described.
2. In the treatment of ores containing precious metals (gold, or silver, or both)
for the obtainment of the precious metal therefrom first treating the charge with
cyanide of potassium, cyanide of sodium, cyanide of calcium or other cyanide
compound, or with mercury and cyanide of potassium, cyanide of sodium, cyanide
of calcium, or other cyanide compound and then with an amalgam of zinc, copper,
tin, lead, or aluminium (or two, or more of them); substantially as hereinbefore
described.
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.