Recycling of WC–Co hardmetal sludge by a new hydrometallurgical route

Abstract

A hydrometallurgical process based on aqua regia treatment of WC–Co hardmetal sludge was developed to simultaneously extract cobalt in solution and forming tungstic acid as residue in a single step. The parameters such as aqua regia concentration, temperature and time of reaction, and pulp density were optimized to process the sludge containing 60.9 wt.% W, 5.99 wt.% Co, 3.38 wt.% Fe and 12.64 wt.% C as the major components. Almost complete leaching of cobalt was achieved with 100 vol.% of aqua regia at 100 °C temperature, 60 min reaction time and 400 g/L pulp density. Complete conversion of tungsten carbide of the sludge to tungstic acid was observed at and below the pulp density of 150 g/L under this condition. The progress of reaction and conversion of tungsten carbide to tunstic acid (H 2WO 4) were investigated by XRD phase identification of the residues under different conditions. The tungstic acid produced from the acid treatment was purified by dissolving tungsten in 11.20 mol/L of ammonia solution at 60 °C while rejecting insoluble metallic impurities as a residue. Tungsten from the ammoniacal solution was recovered by evaporation–crystallization process as high purity (99.97%) ammonium paratunstate (APT, (NH 4) 10·H 2W 12O 42·4H 2O) with low levels of impurities.