Selective cobalt and nickel separation by bioacid-mediated electrowinning

The increasing demand for cobalt (Co) and nickel (Ni) in energy storage and industrial applications highlights the need for their efficient separation from both primary mining and nonconventional sources. Electrowinning presents a greener alternative to incumbent solvent extraction but is hindered by the similar reduction potentials of divalent Co and Ni ions. We show that cost-effective and recyclable bioacids can modify ion solvation environments to amplify the reduction potential difference between Co and Ni, with tartaric acid achieving the highest selectivity through formation of a unique dinuclear complex. When applied to ternary lithium-ion battery leachates, the process achieves 99.1% Co purity in batch mode and, in a scalable flow system, stepwise recovery of metallic Co (95.1%), Ni (96.5%), and manganese dioxide (~100%) with high yields. Technoeconomic analysis and life-cycle assessment highlight superior economic and environmental benefits, establishing a sustainable, generalized electrochemical platform for selective Ni/Co separation from complex feedstocks.