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 2 WO 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 2 W 12 O 42 ·4H 2 O) with low levels of impurities.