Electrolytic extraction of pure bismuth from an industrial residue from the treatment of an auriferous mineral

Abstract

A direct electrolytic extraction procedure for very pure bismuth (99.991 %) from bismuthiferous dusts recovered following the industrial treatment of a gold-bearing mineral has been developed. An attack by nitric acid on these dusts leaves an insoluble residue containing the major part of the lead, antimony and silver. An hydrolysis of the solution in the presence of chloride ions precipitates an oxychloride of bismuth freed from iron and copper. A redissolution of the oxychloride of bismuth in chloride media followed by the boiling of the solution in the presence of a reducing agent eliminates arsenic.

As the electrochemical study had shown that traces of antimony still present in the electrolyte can deposit at the same time as the bismuth, they are complexed by an addition of tartaric acid (4 g.1⁻¹).The conditions of electrolysis (C_Bi ³+:30 g.1⁻¹,pH=0.7,i=3A.dm⁻²,t=70°C) are chosen in order to obtain, with maximum yield (95%), an adherent and well-crystalline deposit of bismuth.

The analysis of the metal produced by this procedure shows that the titre obtained is very superior to that of an industrial metal produced by a pyrometallurgical process (99∶99.6%).