Improvements in the Treatment of Zinc-lead-sulphide Ores Carrying Gold or Silver, or Gold and Silver.
Year: 1894

page_text: COMPLETE SPECIFICATION.
Improvements in the Treatment of Zinc-lead-sulphide Ores
Carrying Gold or Silver, or Gold and Silver.
A communication from abroad by THE EмMENS ZINC COMPANY, of 52 and
54, William Street, New York, in the State of New York, United States of
America, Metallurgical Corporation.
1, JOHN CORRY FELL, of the Firm of Fell and Wilding of 1 Queen Victoria
Street in the City of London, Chartered Patent Agent, do hereby declare the
nature of the said invention for "IMPROVEMENTS IN THE TREATMENT OF
ZINC-LEAD-SULPHIDE ORES CARRYING GOLD OR SILVER OR GOLD AND
SILVER," 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 this invention is to enable certain so-called “refractory" ores of
Colorado, New South Wales, and other mining districts, to be reduced in a simple
and profitable manner.
The characteristic feature of these ores is the presence of zinc. This is the
refractory element that renders such ores unfit for smelting by ordinary methods,
and is highly prejudicial to the efficient smelting of other ores if they be mixed
therewith. Hence the successful treatment of the ores in question resolves itself
into the problem of separating the zinc from the lead and gold, lead and silver, or
lead gold and silver, with which it is associated.
The present invention consists in an improved method or process for effecting
such separation, and is carried into effect in the following manner :-
First. The ore is crushed or otherwise comminuted to a suitable degree of fineness,
dependent upon its state of aggregation, and upon the quantity and nature of the
gangue by which it is accompanied; a crushing to 20-mesh size being usually
sufficient.
Secondly. The finely comminuted ore is roasted in an oxidizing atmosphere in any
suitable desulphurizing furnace until the greater portion of the contained sulphur
is oxidized; the heat not being allowed to rise materially above dull redness. The
effect of this roasting is to convert most of the metallic contents of the ore into
sulphates and oxides.
Thirdly. The roasted ore is finely pulverized, and then leached with water
containing a small proportion—about one per cent.-of ferrous sulphate. This
leaching extracts the zinc sulphate present in the ore, and the ferrous sulphate
precipitates any silver that may become dissolved.
Fourthly. The once-leached ore is leached with an aqueous solution of ferric
sulphate containing a little ferrous sulphate, the strength of the solution being
determined by the percentage of zinc remaining in the ore after the previous
leaching. Each pound of zinc requires about two pounds of ferric sulphate for its
removal. The object of this second leaching is to dissolve and remove any zinc
that may be left by the first leaching in the state of oxide or sulphide.
Fifthly. The ore is again leached with water containing about one per cent. of
ferrous sulphate to wash out any liquid remaining from the second leaching, and is
then a finished concentrate containing the whole of the original lead, silver and
gold, and may be either sold, as a concentrate, or reduced to metal, bullion, or
matte, by known means.
Sixthly. The water from the third leaching is employed in the first leaching of
the next quantity of ore.

page_text: Seventhly. The liquids from the first and second leachings are mixed together
and heated in a thin stratum with free access of air, the effect produced being that
any ferrous sulphate remaining is peroxidized; and then, by filtration, concentra-
tion, and cooling, a large portion of the zinc sulphate is recovered in a crystalline
form, almost or altogether free from iron.
Eighthly. The mother liquor and precipitate from the seventh stage are mixed
together, and treated with sulphurous anhydride (SO2) obtained either from the
roasting furnace by known means or from any other convenient source. The effect
of this treatment is to produce a solution of mixed zinc and ferrous sulphates.
Ninthly. This mixed solution is electrolysed by known means, and the zinc
thereby separated, leaving a solution of ferric sulphate. A part of this is employed
in the second leaching of a further quantity of ore, and the remainder is reduced
by means of sulphurous anhydride to ferrous sulphate for addition to the liquids
employed in the three leachings of such further quantity of ore.
Certain practical modifications of the herein-described process will suggest
themselves to persons skilled in the art. For example, in the case of very
refractory ore, or imperfect roasting, one or more additional roastings or leachings
may be resorted to; while in the case of very porous ore the second crushing may
be dispensed with. Also, it will be evident that where the concentrates are
sufficiently rich to admit of the presence of a certain percentage of zinc without
thereby being rendered unsaleable or unfit for smelting, the hereindescribed leaching
operations need not be continued until the whole of the zinc is extracted. Or,
again, the mother liquor from the seventh stage may be evaporated to dryness, and
the zinc sulphate thus obtained may be calcined; the acid fumes evolved being led
into the leaching tanks to assist in the solution of the zinc oxide, and to thus reduce
the amount of ferric sulphate required.
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 process of treating zinc-lead-sulphide ores carrying gold or silver or
gold and silver, which said process consists in, first, finely comminuting the ore,
secondly, roasting the same in an oxidizing atmosphere, thirdly, leaching such
roasted ore with water containing ferrous sulphate, fourthly, leaching such once-
leached ore with an aqueous solution of ferrous and ferric sulphates, fifthly,
leaching such twice-leached ore with water containing ferrous sulphate, and, sixthly,
removing iron from the zinc sulphate solution obtained by the first and second of
the said leachings by mixing such solutions together and heating them, in a thin
stratum with free access of air, substantially as hereinbefore specified.
(2.) In the process of treating zinc-lead-sulphide ores carrying gold or silver or
gold and silver, the extraction of a portion of the zinc contents by subjecting the
said ores in a comminuted and well-oxidized condition to lixiviation with an aqueous
solution of ferric sulphate containing some ferrous sulphate, substantially as
herein before specified.
Dated this 20th day of Inno 1801
FELL & WILDING,
1, Queen Victoria Street, London, E.C., Agents for the Applicant.