Oxidative Dissolution of Tungsten Metal in Na₂CO₃ under Ar–O₂–CO₂ Atmosphere

A novel process for the recycling of tungsten from hard tool scraps using carbonate molten salts is proposed. As a fundamental study, the oxidative dissolution of tungsten metal into molten Na₂CO₃ under Ar–O₂ and Ar–O₂–CO₂ atmospheres was investigated at 1173 K. The results of the oxidative dissolution experiments and the detection of CO gas evolution by infrared spectroscopy revealed the existence of multiple oxidation mechanisms by peroxide/superoxide ions and carbonate ions. The feasibility of each oxidant was discussed by calculating potential–Pco₂ diagrams

Oxidative Dissolution of Cemented Tungsten Carbides in Molten Sodium Carbonate by Addition of Copper(I) Oxide as Oxidizing Agent for Tungsten Recycling

Due to the monopolized supply of tungsten resource, it is important to efficiently recycle tungsten scrap for use as a secondary resource. The recycling of tungsten from cemented carbide tools by the molten carbonate method was investigated using simulated hard and soft scrap (carbide tool tips and WC powder, respectively). The oxidative dissolution of tungsten was examined in molten Na₂CO₃ under Ar–O₂–CO₂ atmospheres at 1173 K. Based on the immersion potentials of Cu, W, Co, C, and WC–Co, Cu₂O was suggested to work as an oxidizing agent for tungsten dissolution. The oxidative dissolution rate for carbide tool tips with 12.8 mol% Cu₂O addition reached 57 mg h⁻¹ for the reaction time of 2.5 h, equivalent to 0.32 mm h⁻¹. The decrease in the dissolution rate after 2.5 h was attributed to the decrease in the Cu(I) ion concentration in the melt and the inhibition of ion diffusion by the deposited metallic Cu. No violent reaction leading to explosion was observed, even for the oxidative dissolution of fine WC powder with a large surface area. Thus, this method provides significant safety improvements compared to the molten nitrate method