An Ammonia Leaching Process for the Recovery of Value Metals from Nickel and Cobalt Slag

The rapid development of lithium-ion batteries has led to a shortage of cobalt and nickel resources. Recycling of nickel and cobalt slag can promote sustainable development and environmental protection. In this study, a reductive ammonia leaching method is proposed for the recovery of Ni and Co from nickel and cobalt slag (NCS) with high Ni and Co contents. The NCS powder was subjected to leaching reaction in NH₃·H₂O and (NH₄)₂SO₃·H₂O solutions. The thermodynamic feasibility of Co and Ni ammonia leaching was analyzed by E-pH diagrams, and Co and Ni could be leached as complexes [Ni(NH₃)_n]²⁺, [Co(NH₃)_n]²⁺. XPS and XRD were used to explore the physical phases of the materials and the chemical reactions occurring during the leaching process. The results showed that the efficient leaching of Ni and Co was achieved under the optimal experimental conditions, with 90.09% leaching rate of Ni and 89.24% leaching rate of Co. Kinetic analysis showed that the leaching process was controlled by diffusion. The complex leaching is selective and can simplify the purification process. This study can provide ideas for the recycling of nickel and cobalt solid waste resources such as spent batteries and slag.