An Improved Process for the Treatment of Auriferous and Argentiferous Antimony Ores.
Year: 1889

page_text: Date of Application, 10th Sept., 1889-Accepted, 16th Nov., 1889
COMPLETE SPECIFICATION.
An Improved Process for the Treatment of Auriferous and
Argentiferous Antimony Ores.
We, CURT SCHREIBER and HANS. KNUTSEN of Broken Hill in the Colony of New
South Wales, Metallurgical Engineers do hereby declare the nature of our Invention
for "AN IMPROVED PROCESS FOR THE TREATMENT OF AURIFEROUS AND ARGENTIFEROUS
ANTIMONY ORES," and in what manner the same is to be performed, to be par-
ticularly described and ascertained in and by the following statement :-
Our Invention relates to Gold and Silver bearing antimony ores. The treatment of
this class of ores has hitherto been attended with great difficulties. Whilst the
expensive nature of the processes employed has rendered the extraction of the gold
or silver unprofitable. Various methods of treatment have been tried but none have
hitherto given entirely satisfactory results.
The usual method of roasting the ores before amalgamation is very expensive and
permits considerable loss both of gold and antimony. The gold in antimony ore
occurs in a metallic state and generally on the surface of the antimony at the
points of contact with the quartz. The particles of gold become in the roasting
coated with oxide of antimony and as a result are withdrawn from the action of the
mercury in the amalgamating process. In addition to this a portion of the antimony
becomes amalgamated and this causing the mercury to sicken renders it unfit for
further reaction.
The process of roasting with Chloride of Sodium gives no better results. In it
the vapour from the fuel or from the ore itself forms a basic chloride of antimony
which by coating the particles of gold causes a similar difficulty in the amalgamating
process.
Our improved process of treating auriferous and argentiferous antimony ores is
based on the solubility of pure grey antimony ore in different reagents and more
particularly on the discovery that sulphides and oxides of antimony can be easily
leached by stirring them in solutions of sulphides of alkalis or alkaline earths and
preferably in a solution of Sulphide of Sodium.
In order that our invention may be the better understood we will now proceed to
describe the same in detail.
In order to secure greater uniformity of treatment the antimony ore is first classified
by hand picking into three classes, more or less, say No. 1 ore containing more
than 25% of Antimony, No. 2 ore containing 5 to 25% and No. 3 ore containing
less than 5%. The ore is then crushed to a suitable fineness and the whole should
readily pass through a sieve of not less than 900 meshes to the square inch. From
the mill or stampers the ore is taken to the lixiviating pans or agitators. In these
with preferably Sulphide of Sodium as the leaching fluid we use the formula
Sb, S3+3 Na, S = 2 Sb Na, S, or in other words obtain the reaction of an antimony
double salt in solution by the combination of 336 parts Sulphide of Antimony
with 234 parts Sulphide of Sodium. We prefer to have an excess of Sulphide of
Sodium say in the proportion of 12 parts to 17 parts Sulphide of Antimony. And
when employing Sulphide of Baryta or Sulphide of Calcium in solution as a
leaching fluid we take an amount of such salt proportionate to its respective molecular
weight.
In practice we find that one cubic yard of solution or say two hundred (200)
gallons per ton of ore is sufficient but vary the strength according to the percentage
of antimony the latter contains. By thus treating the three classes of ore specified
above we obtain three resulting lyes which being of different concentrations require
to be treated in different ways.
In treating the ore so that we may obtain completely saturated solutions and as

page_text: more
a consequence tailings entirely free from antimony we employ a process of circulation
of the leaching solution. In this way the ore is treated with three or
solutions i.e. fresh ore is first leached with solution used twice previously then with
solution used once and finally with fresh solution.
The saturated solutions of antimony double salt thus obtained are then removed
for recovery of the antimony in metallic form. For this purpose we make use of
electrolysis.
The precipitation of Antimony by electricity being one of the methods of
estimating it quantitatively we expect to obtain an equal success by applying it on a
large scale. Care must however be taken to regulate the strength of the currents
according to the concentration of the lyes. The reaction in the baths are on the
Kathode on the following formula - Sb₂ S3 + 3 Na 2 S + 6 H
2 Sb6 Na HS.
and on the Anode 6 Na HS + 30 = 3 H, O+ 3 Na₂ S2.
=
During the process we add from time to time to the solutions in the baths a quantity
of hydroxide of Sodium the effect of which is to change the Bi-sulphide of Sodium
into Sulphide of Sodium on the formula Na, S2 + 2 H Na O +2 H =2 Na, S+2 H, O.
In order to increase the conductivity of the solutions we add to the electric baths a
small quantity of common salt and then allow the lyes to circulate continuously from
cell to cell until the whole or nearly the whole of the antimony is precipitated. We
have then in the baths a resultant solution of Sulphide of Sodium which is
returned to the lixiviating pans for further treatment of fresh quantities of ore.
In practice we consider that all solutions which contain a certain quantity of the
double salt of antimony will repay treatment by electrolysis. For this purpose we
mix strong solution with the weaker ones and increase the strength of the weakest
solutions by dissolving in them the sulphide of antimony which results from another
part of the process.
Whilst preferably making use of Sulphide of Sodium in the leaching solution,
Sulphide of Baryta may also be employed and in the case of Sulphate of Baryta
(heavy Spar) being cheaply obtainable it can be employed with great advantage instead
of Sulphide of Sodium. We are also of opinion that Sulphide of Calcium will answer
the same purpose.
The third class solution obtained by leaching 5% or low grade ore we propose
to precipitate by acids. For this purpose we find sulphurous and carbonic acid most
advantageous. We obtain the sulphurous acid by roasting pyrites in calciners and
allow the antimony solution to drip continuously from a precipitating tower about
20 feet high so as to come in contact with the acid gases as they enter from the
bottom. For sulphurous acid the reaction is 4 Sb Na, S + 12 SO2 + 3 H2O = 2 Sb₂
S+ 3 Na₂ S, O + 6 Na HSO, + 6 S and for Carbonic Acid the reaction is
2 Sb Na, S + 3 CO₂ + 3 H₂O = Sh₂ S3 + 3 Na₂ CO3 + 3 H₂ S.
We find in practice that the sulphurous acid process is the better, and more
especially when sulphide of Baryta or Lime is employed in the lixiviating process and
their precipitates are in consequence obtained in combination with the Sulphide of
Antimony. In such case the carbonic acid forms insoluble precipitates of the
respective carbonates. These carbonates are so difficult of treatment by the electrical
process that when they are present it is necessary to reduce the whole precipitate in
muffles or in a reverberatory furnace and smelt it for antimony. With sulphurous
acid however we obtain soluble Alkaline salts and a pure precipitate of sulphide of
antimony. The solution containing sulphide of antimony in suspension as it flows
from the precipitate towers is pumped into filtering vats and the filtrate of hypo-
sulphite and bi-sulphide of Sodium afterwards evaporated by natural or artificial heat
to crystallisation. The salts then obtained can be readily transformed into sulphide of
Sodium by reducing them with powdered charcoal or coke. In this way the whole
of the sulphide of sodium used in the process is recovered. The tri-sulphide of
Antimony obtained from the filters is added to the contents of the electric cells
either for strengthening the weak solution or for replacing the dissociated tri-sulphide.
In order that the tri-sulphide of antimony may not be mixed with the already
precipitated antimony we make use of canvas bags for placing it in the baths
The

page_text: metallic antimony precipitated by the electrolysis we collect as often as necessary
and after washing with hot water press it into cakes which are afterwards simelted in
crucibles for commercial purposes. The antimony obtained by our process being
chemically pure we expect that it will obtain the highest market price.
The ore under treatment being now quite free from antimony can be easily
amalgamated for the recovery of the gold or silver which it may contain. For this
purpose we employ any known method of amalgamation but in practice prefer
Molloy's electric pans which are especially suitable for catching finely divided and
float gold.
We wish it to be distinctly understood that we do not confine ourselves to the
exact formulæ given herein or to the exact proportions of the various Alkalis or
Alkaline earths used in the process but,
•
our said Inven-
Having now fully described and ascertained the nature of
tion and in what manner the same is to be performed, we declare that what we
claim is :-
First. The extraction of Sulphide of Antimony or Oxide of Antimony from their
ores by subjecting them to the action of Sulphide of Sodium or sulphides of other
alkalis or alkaline earths.
Second. In the extraction of sulphide of antimony or oxide of antimony from their
ores by subjecting the latter to the action of an alkaline sulphide the precipitation
of the antimony from saturated solutions by electrolysis in the manner substantially
as herein described.
Third. In the extraction of sulphide of antimony or oxide of antimony from low
grade ores where the lyes from the leaching process with an alkaline sulphide are
obtained of a weak concentration the precipitation of the sulphide of antimony by
means of acids and preferably by sulphurous or carbonic acid vapour substantially as
herein described.
Fourth. In the extraction of sulphide of antimony or oxide of antimony from their
ores by subjecting the latter to the action of an alkaline sulphide the regeneration
or recovery for further use of such alkaline sulphides by the addition of their
respective hydroxides in the manner substantially as herein described.
ALB
Dated us to day
10
CURT SCHREIBER.
HANS KNUTSEN.
W. P. Thompson & Boult,
Agents for the Applicants.