Solvent extraction fractionation of Li-ion battery leachate containing Li, Ni, and Co

In this research, the separation of Li, Ni, and Co by solvent extraction was studied from synthetic Li-ion battery waste leachate. The purpose was to propose a process for producing all the metals with over 99.5% purities, as the purity demands for battery grade metals are high. Emphasis was also placed on obtaining pure Li raffinate in the early stage of the process, as societal interest in Li is growing rapidly. Thus, the purpose was to first extract Co and Ni selectively yielding pure Li raffinate, and consequently separating Co and Ni as pure products in the stripping stage. The equilibrium behavior of the separation system was studied by constructing the pH isotherms as well as loading and stripping isotherms. Bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) and (2-ethylhexyl)phosphonic acid mono-2-ethylhexyl ester (PC-88A) were used as extractants, both as unmodified and modified with 5% v/v TOA or TBP. Based on the equilibrium results, bench-scale continuous counter-current separation experiments were designed and conducted using 1.0 M Cyanex 272 modified with 5% v/v TOA. Co and Ni were loaded in two stages from the sulfate feed solution containing 2.8 g/L of Li, 14.4 g/L of Co, and 0.5 g/L of Ni. In this step, over 99.6% yields for Co and Ni were achieved, giving 99.9% pure Li raffinate. However, 17-26% of Li was co-extracted, but efficient scrubbing with NiSO4 was designed with equilibrium experiments and demonstrated in continuous operation. In the stripping step, 99.5% pure aqueous Ni solution and 99.2% pure organic Co solution were obtained using two counter-current stages. Adding one more stage increased the Ni and Co purities to 99.7 and 99.6%, respectively. In addition to the high purities of the metals, the suggested process has fewer process steps compared to previously suggested flowsheets for similar fractionation.