Abstract: When treating scraps WC-Co hard metal with oxygen or air, cobalt tungstate insoluble in water forms in the oxidation products. Thermodynamic equilibriums of Co-W-H₂O system and Co-W-C-H₂O system were studied respectively obtaining a series of equilibrium diagrams to investigate issues related to hydrometallurgical decomposition of cobalt tungstate. The results show that cobalt tungstate is relatively stable in neutral solution. Cobalt tungstate can be decomposed by acid or alkali under certain conditions. Tungsten and cobalt can be separated at the same time. In addition, the decomposition reaction of cobalt tungstate with carbonate can be accomplished at lower excess coefficient of carbonate due to its strong thermodynamic tendency. Solution PH value has a remarkable effect on the reaction.