Dissolution behavior of cobalt from WC–Co hard metal scraps by oxidation and wet milling process

•Efficient Co dissolution from WC–Co hard metal scrap discarded after industrial use•Environmentally less harmful wet milling process for Co recovery in acid solution•Optimization of chemical dissolution conditions and ball-milling process•Dissolution of Co from the mixture of WO3 and CoWO4 in H2O2-containing acid solution

Wet milling was fundamentally investigated as a process for dissolution of Co from WC–Co hard metal scrap in this study. The development of a relatively fast and low acid-concentration recycling method of Co from WC–Co hard metal scrap is significant, considering the rare and uneven deposition of Co worldwide. WC–Co scraps were fully oxidized, resulting in a mixture of WO3 and CoWO4. CoWO4 was readily decomposed to produce soluble CoSO4 and insoluble tungstic acid in sulfuric acid solution of pH 2 or less. Dissolution conditions such as the concentration, temperature, and stirring rate of the solution were varied to determine changes in Co dissolution efficiency with dissolution time. Adding 2 vol.% hydrogen peroxide to the solution augmented the Co dissolution rate considerably. Co dissolution by disruption of the tungstic acid layer via wet milling in 1 M sulfuric acid solution with hydrogen peroxide was four times faster than simple chemical dissolution of Co in 1 M sulfuric acid solution. Wet milling is a time-efficient process to recycle Co from WC–Co scraps which uses a relatively low concentration acid solution.