PROCESSING OF WC–Co WASTE WITH SELECTIVE EXTRACTION OF Co3O4 BY OXIDATIVE FUSION IN NaNO3 MELT

The aim of this study was to develop and experimentally validate a selective method for producing high-purity cobalt oxide from WC–Co hard alloy waste using oxidative fusion in a sodium nitrate (NaNO3) melt, followed by combined aqueous and acidic purification of the solid residue. Cemented carbide scrap and waste containing 6–12 wt.% Co were used as feedstock, without prior grinding. It was found that, during heat treatment in the range of 650–900 °C, tungsten predominantly converts into soluble sodium tungstates, while cobalt concentrates in the solid residue as an oxide phase. Optimal process conditions, such as 850°C and a 10-min hold, were shown to provide the best combination of phase separation and cobalt recovery: the Co content in the solid product was approximately 94.08 wt.%, the W content was reduced to 1.14 wt.%, and the cobalt recovery rate in the target solid product reached ΣCo ≈ 97.3%. X-ray diffraction analysis revealed a predominance of the spinel phase Co3O4 with minor traces of WO3. TEM-EDS results confirmed the oxide nature of the product and indicated a high cobalt content with low levels of residual impurities. However, after washing with water, residual sodium remained in the product, requiring an additional desalination step. The use of a triple hot water rinse at 80 °C with ultrasonication followed by short-term treatment in 0.05 M HNO3 at 70 °C for 5 min ensures the effective removal of sodium-containing compounds: the Na content is reduced from 3.28 to 0.09 wt.%, and the final product contains 98.28 wt.% Co with a residual W content of 0.6 wt.%. The obtained results confirm that the proposed approach is technologically feasible, reagent-efficient, and promising for the processing of WC–Co waste with the return of cobalt as a valuable metallurgical raw material.