Recovery of cobalt from pyritic tailings

Cobalt is utilised particularly in various high-tech products such as jet engines, super alloys and rechargeable batteries. In view of its relatively high economic importance and supply risk, European Union (EU) has listed cobalt as one of the "critical raw materials." In this regard, recovery of cobalt from secondary resources has become increasingly important. In this study, recovery of cobalt from pyritic tailings produced from a flotation plant was considered. In leaching tests, extraction of cobalt was investigated by using different lixiviant systems (H2SO4-H2O2, HCl-H2O2, HNO3, H2SO4-NaNO3). Acidic peroxide leaching tests yielded low cobalt extractions (≤%22.1 Co). In nitric acid leaching tests, effects of acid concentration, temperature and ultra-fine grinding on Co extraction were studied. Increasing temperature and acid concentration was found to improve the leaching of Co. Ultra-fine grinding enhanced leaching kinetics. Complete Co extraction was achieved in nitric acid leaching under suitable conditions (2 M HNO3-HNO3). High correlation (r=0.995) between the dissolution of Co and Fe is consistent with the presence of Co in the pyrite lattice as an isomorphic substitute. In H2SO4-NaNO3 leaching tests, after evaluation of various parameters in preliminary tests, effects of concentration of nitrate, ultra-fine grinding and temperature on Co extraction was examined in detail using experimental design techniques. The most influential parameters were determined to be in the decreasing order of temperature and concentration of nitrate. The effect of ultra-fine grinding was statistically insignificant in the range tested. In H2SO4-NaNO3 leaching 100% Co extraction was also obtained under suitable conditions. These findings demonstrate that, high oxidising conditions/reagents (i.e. HNO3/NaNO3) is required to achieve high cobalt extractions from pyritic tailings.