A Method for the Extraction of Gold.
Year: 1894

page_text: Date of Application, 31st Oct., 1894—Accepted, 1st Dec., 1894
A Method for the Extraction of Gold.
1, PROSPER DE WILDE, residing at No. 339 Avenue Louise, Brussels, Belgium,
Professor of Chemistry, 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 :-
The object of my invention is a method for the extraction of gold, and the
manner in which it is carried out is particularly described in all its details in the
following description :-
:-
First operation. Dissolving the gold. Instead of dissolving the gold existing
in the ores or tailings" as it is made at the Transvaal in a weak solution containing
only cyanide of potassium or of sodium (KCy or NaCy) I employ, in the
preparation of this solution, ordinary water which has been in contact by stirring
for some minutes with minium (Ph³04) or with protoxide of lead (PbO) preferably
of the variety known under the name of massicot.
The cyanide of potassium or of sodium may be first dissolved in the water,
and the solution thus obtained put into contact with the minium or the protoxide
of lead.
Care should be taken to stir frequently and the solution employed is decanted
after the precipitation of the oxide of lead.
In a solution thus obtained the gold contained in the ores or the "tailings" is
dissolved very rapidly, and large economies in the employment of cyanide may be
effected.
Second operation.-Utilisation and recovery of the alkali cyanide in excess.―
Only a very small portion of the alkali cyanide used for dissolving the gold is
really utilised, and the major part is lost in the solutions which are emptied away
as residues notwithstanding the fact that they contain a terrible poison.
In my method the cyanide in excess is recovered and utilised in the following
manner :-
The solution resulting from the first operation which contains the dissolved gold
in the form of double cyanide of gold and potassium (or of sodium) (AuKCy
or AuNaCy2) is carefully added to, whilst stirring, by a solution of about
ten per cent. of ferrous chloride (FeCl2) or ferrous sulphate (FeSO* green
vitriol).
A yellow orange precipitate is first obtained which soon becomes green and
flocculent. A small quantity of the liquid is filtered from time to time and a few
drops of the filtrate are treated with a weak solution of cyanide of potassium, or a
weak solution of red prussiate of potassium.
When with the first reagent, a yellowish tint, or a blueish tint with the second
reagent is produced the precipitation may be considered finished.
The green precipitate formed of a combination of alkali cyanide and ferrous
cyanide is rapidly deposited. This precipitate is separated from the liquid by
means of a filter press or a vacuum filter. It is afterwards diluted in ordinary
water acidulated by sulphuric acid. It is thus instantly transformed into Prussian
blue. This latter is washed in water, separated by the filter press, and drained in
the well known manner.
The green precipitate diluted in water may also be treated by a solution of
caustic potash, or of caustic soda. A precipitate of hydroxide of iron is obtained
solution of yellow prussiate of potassium or of sodium (Cy*FeK*
and
a
or CFN₂4)

page_text: After separation of the hydroxide of iron by the well known means the yellow
prussiate may be crystallised by evaporation and cooling in the known manner.
The yellow prussiate may, by well known means, be transformed into cyanide of
potassium or of sodium to again serve for the extraction of gold.
Third operation.-Precipitation of the gold.-The solution from the filter press
or from the vacuum filter in the second operation contains all the dissolved gold in
the form of double cyanide of gold and of potassium (or of sodium) (AuKCy³).
Instead of precipitating the gold by means of zinc shavings, I acidulate the
solution by dioxide of sulphur (SO) or by a solution of sulphurous acid (SO³H³)
or by kalium or natrium metasulphite (S2O'K2 or S2O'Na²) or by any acid
sulphite. After which I add a solution of cupric salt like cupric sulphate or blue
vitriol (CuSO) until I obtain on a portion of filtered liquid the characteristic
brown reaction by means of yellow prussiate of potassium.
A solution of cuprous chloride (Cu²C12) in weak muriatic acid may also be
employed even without the intervention of sulphurous acid or its acid salts. In
either case I obtain by stirring a white caseous precipitate formed of a mixture
of aurous cyanide (AuCy) and cuprous cyanide (CuCy) containing all the gold
which was dissolved in the first operation.
After a washing and desiccation the precipitate may be calcined in a reverberatory
furnace. It is transformed into a mixture of gold and cupric oxide (Au + CuO).
Or it may be calcined in a closed crucible and a mixture or an alloy of gold and
copper is obtained. In both cases the calcined product treated with hot sulphuric
acid or diluted nitric acid will leave the gold as a residue and the copper or its
oxide will be dissolved.
The precipitate of aurous and cuprous cyanides may also be attacked in its hot
condition by sulphuric acid at 60° Baumé; the two cyanides become decomposed
and pure gold remains as a residue.
By another plan, the precipitate may be treated by diluted muriatic acid or
nitric acid which only dissolves the cuprous cyanide. The aurous cyanide after
washing and draining yields pure gold by calcination.
None of the above treatments or operations cause any notable loss of gold.
Advantages of my method.
a. All the gold is obtained in a pure state.
b. The expenses are less than with existing methods.
c. A very large part of the alkali cyanide which hitherto has been lost is
recovered in the form of Prussian blue or yellow prussiate.
d. The waste solutions contain no venomous ingredients.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed I do not desire to encroach
on the rights secured by other Patents but I declare that what I claim as my
invention is :-
1. The employment of water which has been in contact with minium or of
protoxide of lead for the preparation of solutions of cyanide of potassium or of
sodium employed for the extraction of gold contained in mineral ores or in
"tailings," as herein before set forth.
2. Placing the above solutions of cyanide of potassium or of sodium into
contact with minium or with protoxide of lead before serving for the extraction of
gold, as described.
3. The recovery and utilization of the alkali cyanide in excess by means of a
ferrous salt as above described and obtaining a green precipitate which may be
transformed into Prussian blue or into yellow prussiate, as above described.
4. The precipitation of the gold in the form of a mixture of aurous cyanide
(AuCy) and cuprous cyanide (CuCy) by acidulating, as above described, the
solution with dioxide of sulphur or sulphurous acid or the alkaline metasulphites
or the acid sulphites generally, and afterwards adding a solution of a cupric

page_text: salt (CuSO), or a solution of a cuprous chloride (Cu'Cl³) in muriatic acid;
without, in the latter case, the intervention of dioxide of sulphur, sulphurous acid,
or acid sulphites, as explained.
Dhin 214 daw of Ontahau 1901
H. GARDNER,
Patent Agent, 166, Fleet Street, London,
Agent for the said Prosper De Wilde.
H. GARDNER,
Patent Agent, 166, Fleet Street, London,
Agent for the said Prosper De Wilde.