Electrochemical behavior of tungsten carbide-cobalt alloy using molten hydroxide as electrolyte under low temperature

Abstract

Tungsten carbide-cobalt alloys (WC–Cos), which are used for cutting tools, are mainly composed of tungsten carbide and cobalt with minor elements including chromium, tantalum, nickel. Recycling WC–Cos requires a large amount of energy and chemicals for leaching tungsten. We previously showed that tungsten in WC–COs can be leached by potentiostatic electrolysis at − 0.7 V in molten sodium hydroxide (NaOH) at 723 K; tungsten constituted 99.7 mass% of the leached component in the molten salt. In this study, we investigated tungsten leaching at a lower temperature by using a eutectic mixture of 51.5 mol% NaOH and 49.5 mol% potassium hydroxide (KOH) as the electrolyte. Tungsten was leached from the alloy at temperatures above 623 K, which was 100 K lower than the previous study. Cobalt dissolved in the molten salt, although it formed a passive layer. Chromium underwent oxidization and dissolved as a hexavalent ion below 623 K. Tantalum dissolved even without electrolysis. Tungsten was leached at 623 K in this system. Highly purifying tungsten could be obtained by dissolving the cooled molten salt in water and bringing it in contact with air to precipitate other metal ions. Therefore, the electrochemical process is expected to be used for separating tungsten from WC–Cos.