6. Extraction of bismuth from an oxidized mining concentrate

In the supergene zone of sulfide deposits, the bismuth mineralization in the mine concentrate consists of oxyacid salts. After dissolution in hydrochloric acid, the attack solution is diluted. BiOCl oxychloride precipitates out during dilution. The hydrolysate is then subjected to a further acid treatment, followed by a further precipitation of oxychloride. Finally, the oxychloride is melted with carbon and lime to give bismuth metal.

When the oxidized concentrate contains sulfides, natural oxidation is completed by oxidizing roasting, to remove sulfur and possibly arsenic. The oxidized products are then reduced by carbo-reduction. The bismuth is then sequestered in a mixed metal mass which is etched with HCl. Controlled neutralization with sodium hydroxide leads to the formation of BiOCl, which is recovered by filtration. Residual acidity is maintained to prevent...