Direct Electrochemical Preparation of Cobalt, Tungsten, and Tungsten Carbide from Cemented Carbide Scrap
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DUCTION
TUNGSTEN, as well as its alloys, is one of the widely used metal elements because of its excellent physical and chemical properties such as wearability and corrosion resistance. Generally, tungsten is used to produce cemented carbide, which is composed of refractory metal carbides (WC, TiC) and metal binder (Co, Ni, and Mo). The tungsten-cobalt cemented carbide is one of the most common species of hard metal.[1,2] In recent decades, the outputs of cemented carbide and cemented carbide scraps are increasing rapidly with the rapid development of society and industry, whereas the resource reserves of tungsten are declining annually. According to U.S. geological survey, the total reserves of tungsten decreased to 3.3 million tons in 2014.[3] Therefore, a novel method that extracts cobalt and tungsten from cemented carbide scraps must be developed. Various traditional methods, such as chemical methods,[4,5] oxidation–reduction methods,[6–9] electrochemical methods,[10–13] and other methods,[14–17] have been used to extract metallic cobalt and tungsten for many years. Khoshandam obtained the optimal craft parameter of producing metallic cobalt by reducing cobalt
XIANGJUN XIAO and LIWEN MA, Postgraduates, XIAOLI XI and ZUOREN NIE, Professors, and LIWEN ZHANG, Lecturer, are with the College of Material Science and Engineering, Beijing University of Technology, Beijing 100124, China. Contact e-mail: [email protected] Manuscript submitted June 7, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
oxide with methane.[18] Erdogan produced tungsten powder by direct electrochemical reduction of tungsten compounds such as tungsten trioxide (WO3) and calcium tungstate (CaWO4).[19] Singh introduced a method for synthesizing nanocrystalline WC from milled scheelite ore at low temperature.[20] To our knowledge, extraction of element cobalt and tungsten from WC-6Co scrap has not been reported. In this work, we proposed a novel method to prepare cobalt, tungsten, and tungsten carbide from cemented carbide scrap by molten salt electrolysis. Generally, molten salt electrolysis is effective in producing refractory metals. WC-6Co and NaCl–KCl salt were used as a sacrificial anode and electrolyte for the direct electrolytic extraction of metal element from cemented carbides, respectively. In electrolysis, WC-6Co was dissolved as cobalt and tungsten ions, and the ions were discharged on the cathode to deposited cobalt and tungsten. The extra carbon drifted on the melt as an atom, and then the carbon atoms were adsorbed by the cathode reacting with tungsten to produce tungsten carbide. The dissolution potential of cobalt and WC and the total redox reaction were investigated by various electrochemical techniques. The preparation technique and the optimum conditions for the preparation of cobalt, tungsten, and tungsten carbide are also studied.
II.
EXPERIMENT
All experiments were performed in hermetically sealed three-electrode cells under a high-purity argon
atmosphere. Figure 1 shows the schematic of hermetically sealed three-ele
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