Chemical Leaching of Inactive Gold Mine Tailings as a Secondary Source of Cobalt and Nickel-A Preliminary Case Study

Tailings from inactive gold mines, that are not yet successfully restored (generation of As- and Co-contaminated neutral mine drainage), represent a promising secondary source of strategic metals including Co and Ni. Three different mine tailings (sites A, B and C) from Cobalt Mining Camp were collected and characterized. Preliminary chemical leaching tests were conducted with inorganic acids (HCl, H2SO4 and HNO3) to solubilize Co and Ni at different concentrations (0.01-0.5 N). The influence of the number of the leaching steps on the recovery of Co and Ni was also evaluated. Promising concentrations of Co (0.7%) and Ni (0.3%) were reported in tailings from site A, while lower concentrations were measured in tailings from sites B and C (0.02-0.1%), requiring pre-concentration steps (not tested in this preliminary study) before leaching to reduce operating costs. More than 85% of both Co and Ni were solubilized from tailings from site A after only 30 min using H2SO4 (0.25 N) at room temperature. Lower efficiencies (36-62%) were observed for tailings from sites B and C, which can be partially explained by the higher amounts of acid-consuming minerals present in the gangue. Additional experiments are required to better understand the mechanisms involved in Co and Ni solubilization and to optimize operating conditions in terms of Co and Ni recovery.