Two-stage leaching of manganese and silver from manganese–silver ores by reduction with calcium sulfide and oxidation with copper(II)

Abstract

The development of a hydrometallurgical process to recover manganese and silver from manganese–silver ores is reported. Insoluble manganese(IV) was reduced to soluble manganese(II) in an aqueous medium with calcium sulfide (CaS) as the reductant, and the resultant residue was then leached by a sulfuric acid solution. Thiosulfate (S2O32−) was produced in situ in the reduction stage. The S2O32− by-product was reserved and used as the lixiviant for the subsequent silver leaching step with copper(II) and ammonia additives. The production of S2O32− was 0.168mol/L in the reduction stage and the recovery of manganese reached 98.0% in the acid leaching stage under the optimum conditions. Notably, 57.5% of silver was recovered when only the S2O32−-containing liquor from the reduction stage was used, and 92.0% of silver was recovered when a small amount of supplementary S2O32− was used.