Removal of silica and sulphur from wolframite concentrates

Wolframite (FeWO4) concentrates of Rajasthan contain impurities like silica (SiO2) and sulphur in amounts, which are much above the desired specifications. The desilication and desulfurisation of natural wolframite concentrates were investigated by curing with hydrofluoric acid solution at ambient temperature followed by roasting the desilicated concentrates at 650 C in oxygen atmosphere. The silica and sulfur contents were brought down to 0.60% and 0.17% respectively without loss of tungsten. The pure concentrates produced would meet the desired specifications.