Separation of cobalt and tungsten from grinding waste of cemented carbide by a mildly process of chloridizing roasting and water leaching combining

Abstract

Tungsten is primarily used to produce cemented carbide tools, generating substantial amounts of grinding waste of cemented carbide (GWCC) during machining. GWCC mainly comprises tungsten carbide (WC) and cobalt, which have significant economic value and are worth recovering. This work proposes a mildly recovery process involving chloridizing roasting and water leaching, introducing a novel transition and decomposition method for GWCC through chlorination roasting using CaCl₂ as the chlorinating agent. Initially, Co and W in the GWCC are converted into CoCl₂ and CaWO₄, WO₃ via chloridizing roasting. Subsequently, water leaching of the roasting product yields a CoCl₂ solution and tungstate residue. Pure cobalt hydroxide precipitation is then obtained by adjusting the pH of the solution. The thermodynamic equilibrium of the WC–Co–CaCl₂ system was first calculated, demonstrating that W and Co are entirely transformed into CaWO₄ and CoCl₂ above 400 °C with an initial chlorine-to‑cobalt ratio (n_Cl/n_Co ratio) of 2.0. Detailed roasting experiments reveal that the maximum cobalt leaching efficiency was achieved at 600 °C. The n_Cl/n_Co ratio significantly influences the conversion, and insufficient CaCl₂ and low temperature lead to cobalt tungstate and cobalt chloride formation. Optimal roasting conditions were determined to be a temperature of 600 °C, a n_Cl/n_Co ratio of 2.4:1, and a reaction time of 1 h, achieving a cobalt leaching efficiency of 94.32 %. Finally, pure cobalt hydroxide was precipitated, and the separated tungstate residue was a high-quality raw material used for tungsten smelting.