Evaluation of an unsymmetrical dialkylphosphinic acid INET 3 2020 Minerals

Cobalt and nickel are important strategic resources. Solvent extraction is an efficient way to separate and recover cobalt and nickel from spent batteries like ternary LIBs, NiMH, and Ni-Cd batteries. In this paper, we introduce an unsymmetrical dialkylphosphinic acid INET-3 – which possesses excellent extraction and separation performance for heavy REEs – to cobalt/nickel separation for the first time. We investigated its extractabilities for cobalt and nickel and did some comparisons with those of MEXTRAL507P and Cyanex272. We studied the effects of several parameters on cobalt/nickel separation including saponification ratio, Ni/Co ratio, temperature, and anions (SO4 2− and Cl−). We also evaluated its extraction capacity for cobalt via two methods: one is contacting the organic phase continuously with fresh working solutions, and the other is increasing phase ratio A/O. Besides, we explored its selectivity for impurities including copper, zinc, manganese, calcium, and magnesium, and studied the stripping behaviors of cobalt and nickel coordinated with INET-3. The results show INET-3 has stronger extractability for cobalt and nickel than Cyanex 272, while weaker extractability than MEXTRAL 507P. High saponification ratio and temperature favor cobalt/nickel separation, while SO4 2− and Cl− are the contrary. For systems with Ni/Co ratio ≤81:1, the Co/Ni separation factors all exceeded 130. The selectivity of INET-3 was in the order Zn2+ > Cu2+ > Mn2+ > Co2+ > Mg2+ ≈ Ni2+ > Ca2+. Its extraction capacity for cobalt was less than that of Cyanex 272 at the same initial conditions. The loaded cobalt can be easily stripped by diluted sulfuric acid.