Extraction of cobalt(ii) by methyltrioctylammonium chloride in nickel(ii)-containing chloride solution from spent lithium ion batteries

Spent lithium batteries contain valuable metals such as cobalt, copper, nickel, lithium, etc. After pretreatment and recovery of copper, only cobalt, nickel and lithium were left in the acid solution. Since the chemical properties of cobalt and nickel are similar, separation of cobalt from a solution containing nickel is technically challenging. In this study, Co(ii) was separated from Ni(ii) by chelating Co(ii) with chlorine ions, Co(ii) was then extracted from the aforementioned chelating complexes by methyltrioctylammonium chloride (MTOAC). The effects of concentrations of chlorine ions in the aqueous phase ([Cl-](aq)), MTOAC concentrations in organic phase ([MTOAC](org)), ratios of organic phase to aqueous phase (O/A), and the initial aqueous pH on cobalt separation were studied. The results showed that [Cl-](aq) had a significant impact on cobalt extraction efficiency with cobalt extraction efficiency increasing rapidly with the increase in [Cl-](aq). The effect of initial pH on cobalt extraction efficiency was not significant when it varied from 1 to 6. Under the condition of [Cl-](aq) = 5.5 M, [MTOAC](org) = 1.3 M, O/A = 1.5, and pH = 1.0, cobalt extraction efficiency reached the maximum of 98.23%, and nickel loss rate was only 0.86%. The stripping rate of cobalt from Co(ii)-MTOAC complexes using diluted hydrochloric acid was 99.95%. By XRD and XRF analysis, the recovered cobalt was in the form of cobalt chloride with the purity of cobalt produced reaching 97.7%. The mode of cobalt extraction was verified to be limited by chemical reaction and the kinetic equation for cobalt extraction was determined to be: R-(Co) = 4.7 x 10(-3)[MTOAC]((org))(1.85)[Co]((aq))(1.25).