Separation of cobalt, lithium and nickel from the “black mass” of waste Li-ion batteries by ionic liquids, DESs and organophosphorous-based acids extraction

Abstract

New methods of metal extraction from the “black mass” (BM) from spent lithium-ion batteries have been presented with ionic liquids (ILs), Deep Eutectic Solvents (DESs) and organophosphorous-based acids. The low-temperature method of extraction of cobalt, nickel, lithium and other metals without pre-leaching of BM with acids have been proposed in comparison with many methods already described in the literature. Extraction has been studied in detail with ILs: methyltrioctylammonium chloride ([N8,8,8,1][Cl], Aliquat 336), trihexyltetradecylphosphonium chloride ([P6,6,6,14][Cl], Cyphos IL 101), trihexyltetradecylphosphonium thiocyanate ([P6,6,6,14][SCN]), benzethonium tricyanomethanide ([Benzet][TCM]), as well as with DESs mixtures and well known organophosphorous-based acids: bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) and di-(2-ethylhexyl) phosphoric acid (D2EHPA). It was shown that fast and efficient extraction, with 90–100 wt% recovery of Co(II), may be obtained using DESs. Well known for the extraction of metal ions from the aqueous phase ILs, binary mixtures of ILs (synergistic effect) and Aqueous Biphasic System (ABS) method with NaCl, {[P4,4,4,14][Cl] + NaCl + Co(II)} have shown very low efficiency in the recovery of metals from BM. The extraction of cobalt (30–58 wt%) and the high extraction efficiency of lithium (41–92 wt%) and nickel (37–52 wt%) was obtained using Cyanex 272 in a mixture with diethyl phosphite. Process factors such as solvent content, extraction additivities, stripping and precipitation methods, temperature, holding time, pH and liquid/solid as well as organic/water ratios were studied. For all extractions, the selectivity and distribution ratios were described. A schematic flow chart for the selective recovery of cobalt(II), lithium(I) and nickel(II) from BM has been proposed. The presented extraction processes can compete with the costly hydrometallurgical methods for recovering metals from secondary waste.