Cobalt–Nickel Separations Using Supported Liquid Membranes for End-of-Life Lithium-Ion Battery Recycling

Lithium-ion battery recycling will be standard practice in the future as the number of batteries used in electric vehicles and energy storage increase and eventually reach their end of life. Cobalt and nickel are the two economic driving forces for battery recycling. Solvent extraction (SX) further separates cathode materials if desired and supported liquid membranes (SLMs) offer an alternate technique to apply SX. Separate extraction, phase separation and stripping stages and possibly saponification of recycled extractant in SX are replaced by a much simpler one-step approach. In this work, Co2+ was recovered using flat sheet (FS)SLM from a synthetic feed with 10,000 ppmw Co2+ and Ni2+ each, 0.5 M sodium acetate buffer and 20% H2SO4 strip phase. Three Co2+ selective extractant systems (commercial phosphorus-based acids) were evaluated based on Co2+ recovery rate and purity in the strip as a function of pH. The best case scenario yielded a Co2+ purity of 99.5% in the strip phase at a recovery of 80%, with a slight decrease to 99.3% when the recovery reached 90%. At 98% recovery the Co2+ purity decreased to 98%. Co2+ recovery rates decreased during all tests, from 10 to 12 gmol/m2/day to 2 gmol/m2/day. X-ray fluorescence-indicated extractants were depleted in the membrane at the end of tests where 100% recovery was not achieved. The FSSLM tests represent a challenging case; the feed contains ~0.051 moles of Co2+ and the membrane 0.00008 moles of extractant, or a molar extractant:Co2+ ratio of ~1:630. Hollow fibre (HF)SLM will have a more favourable ratio. HFSLM testing is expected to commence this year with 12 m2 HF modules and 100 L of feed.