Continuous separation of cobalt from sulphate solutions using saponified D2EHPA and Cyanex 272 in a Taylor-Couette Disc Contactor

The urgent need to reduce the amount of spent lithium-ion battery (LIB) waste, combined with a tremendous supply risk of valuable metals, such as cobalt, render the development of an efficient recycling process for lithium-ion batteries a high-priority task. The aim of this study is to develop a selective, easily scalable, and continuously operated recycling process for cobalt in an agitated extraction column, a Taylor-Couette Disc Contactor (TCDC). A two-step solvent extraction process from sulfate solutions was investigated. In the first step, manganese, copper, and iron were extracted using D2EHPA. Cobalt was separated from nickel in the second step using Cyanex® 272. The concentration as well as the saponification of the extraction agents at varying degrees, times, and temperatures were investigated in batch mode. Afterwards, the two-step solvent extraction process was implemented in the TCDC, optimizing the organic to aqueous phase ratio (O:A-ratio) and residence time. An extraction efficiency of cobalt of 73.77%, a separation factor for cobalt over nickel of 111.17, and a selectivity of 77.32% were achieved in the second extraction step. This work proves the concept of a continuously operated recycling route in which cobalt can be recovered with a high degree of purity in the TCDC.