Recovery of tungsten and cobalt from cemented tungsten carbide wastes using carbonate roasting and water leaching

Tungsten and cobalt can be recovered from cemented tungsten carbide-Co (WC-Co) scraps using a novel process based on roasting of the scraps with Na2CO3 and water leaching of the calcine containing Na2WO4. The process was evaluated at different conditions testing several parameters, including Na2CO3/WC molar ratio 1:1-2:1, roasting temperature in the range 400-900 degrees C, roasting time at 1-3 h, leaching temperature at ambient - 90 degrees C and leaching time 1-3 h. Thermodynamic modeling of the roasting and leaching stages using HSC and Stabcal software allowed an understanding of the speciation of the products at different conditions. Subsequent experiments to determine an optimized conditions of both roasting and water leaching were conducted aiming to yield recoveries of both W and Co in solution over 95%. Roasting of the scraps with Na2CO3 at 800 degrees C in 3 h using Na2CO3/WC molar ratio of 1:1 will produce a Na2WO4 which can be easily water leached. Over 95% W was recovered after water leaching the calcines at 60 degrees C in 3 h. Over 94% Co was recovered as soluble CoSO4 using 1 M H2SO4 with 1.5 M H2SO3 added as a reductant. The double step of CoCO3 precipitation using 1.5 M Na2CO3 and conversion to Co(OH)(2) using 8 M NaOH allows a high purity product (>99.5% purity) to be produced with most of the major impurities as Cr and Fe remaining in the residual Na2CO3 and NaOH liquors. The levels of these major impurities are 0.05% Cr and 0.3% Fe in the final Co hydroxide product. Implications: This is a new process to treat W-Co wastes and recover W and Co. To the best of our knowledge, no study was done before in this area.