A N T I M O N Y : ITS HISTORY, CHEMISTRY, MINERALOGY ...

THE METALLURGY OS ANT1MOJNY 1.20
amperes (0*026 to 0*03 ampere per square inch). The necessary
E.M.F. is about 2 volts per bath.
The metal thus obtained is in the pulverulent form or in lustrous
scales, according to the density of the current used.
Koepp's method is to treat antimony sulphide with ferric chloride,
thus :—
6FeCl3 + Sb2S3=6FeCl2+2SbCl3 + S3.
The solution is electrolysed at a temperature of 50° C. between
lead plates. Antimony is deposited upon the cathode and ferric
chloride upon the anode. The current used is 3*7 amperes per
square foot. The use of chlorides as electrolytes precludes the possibility
of the process becoming practical.
Siemens and Halske use as solvent either the sulphides, hydrosulphides,
or polysulphides of the alkalis. When the finely ground
ore is thus lixiviated, a double salt is formed, e.g. with NaHS :—
Sb2S3+6£TaHS=Sb2S3.3Na2S + 3H2S.
The liquor is then led into the cathode division of a bath. The
bath is divided up by diaphragms into series of anodes and cathodes;
the former are made of carbon or platinum, and are closed and made
gas-tight; the latter are made of copper or antimony plates. The
reaction at the cathode end is as follows :—
Sb2S8. SNaaS + 6H = 2Sb + 6KaHS.
In this way, not only is metallic antimony obtained, but also the
NaHS solution is regenerated and used to dissolve more of the sulphide.
Another process by Siemens is to electrolyse a solution of the
double salt formed by treating antimony sulphide with sulph-hydrate
of calcium, barium, strontium, or magnesium. Without the use
of diaphragms, the hydrogen liberated at the cathode end combines
with the sulphur of antimony sulphide, and the antimony is deposited,
while at the same moment the sulph-hydrates of other metals are
formed, to be in turn converted into disulphides by the oxygen
developed in the reaction.
These disulphides are treated with carbon dioxide, obtained by
heating a mixture of the, carbonates and sulphur, the result being
the formation of the carbonates of calcium, barium, strontium,
and magnesium, sulphur and hydrogen sulphide. These, with
the exception of the hydrogen sulphide evolved, are heated in
the absence of air, when carbon dioxide and the caustic alkaline
earths are formed. The carbon dioxide is used to decompose disulphide
solutions, and the basic oxides are treated with the hydrogen
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