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.