Anodic Dissolution of Tungsten from Super Hard Alloys in Molten Sodium Hydroxide

Anodic dissolution of tungsten in a molten sodium hydroxide bath was investigated at 723K in order to simplify tungsten recycling process from secondary resources like used super hard alloy tools. Cyclic voltammograms suggested that tungsten is easily oxidized and dissolves into the melt. Cobalt, which is used as binder metal, was also oxidized and formed passive film having certain solubility in the melt. When water vapor was introduced into the system, the obtained cyclic voltammograms changed with the partial pressure of water vapor. Based on the above mentioned results, anodic dissolution was carried out at constant cell voltage using throw-away tips as an actual super hard alloy tool. When water vapor was introduced into the system, the cell voltage and duration required to dissolve whole the tips were reduced.