Recovery of nano-sized cobalt powder from cemented carbide scrap

A process is developed to recover nano-sized cobalt from cemented carbide scrap (WC-Co) by nitric acid leaching and finally obtaining a nano-sized spherical pure cobalt powder by ultrasonic spray pyrolysis (USP). The optimization of the leaching and preparation of cobalt powders by USP are conducted within the framework of an environment-friendly and economical process, enabling reduced waste streams. According to the results obtained, it is possible to dissolve cobalt with high efficiencies (91.5%) via HNO₃ leaching of cemented carbide scrap. The optimum leaching conditions were 90 μm, 25 °C, 2 h, 0.5 M HNO₃, 900 rpm, and 1/10 solid/liquid ratio. The leach residue (WC-TiC) has a BET specific surface area of 1.08 m²/g and finds has a wide range of applications in key technologies, varying from mechanical to chemical industries. After leaching, nano-sized cobalt powder (300-700 nm) can be produced from CO(NO₃)₂ by ultrasonic spray pyrolysis with hydrogen reduction. The nano-sized powders can be used for the production of new nano-structured thermoelectric materials, nanomagnets, nanosensors and nano-structured tungsten carbide-cobalt powders.