Analysis of a hydrometallurgical route to recover base metals from spent rechargeable batteries by liquid–liquid extraction with Cyanex 272

A hydrometallurgical route is proposed to recover zinc and manganese from spent alkaline batteries in order to separate base metals such as nickel, copper, aluminium, cadmium, lithium and cobalt which constitute the main metallic species of spent NiCd, NiMH and Li-ion rechargeable batteries. The route comprises the following main steps: (1) sorting batteries by type, (2) battery dismantling to separate the spent battery dust from plastic, iron scrap and paper, (3) leaching of the dust with sulphuric acid and (4) metal separation by a liquid–liquid extraction using Cyanex 272 (bis-2,4,4-trimethylpentyl phosphinic acid) as extractant. The metal content of NiCd, NiMH and Li-ion batteries from three distinct manufacturers has been evaluated. A factorial design of experiments was used to investigate the leaching step using operational variables such as temperature, H2SO4 concentration, S/L ratio and H2O2 concentration. Analysis of metal separation by the liquid–liquid extraction with Cyanex 272 identified a pH1/2 2.5–3.0 for zinc and aluminium, pH1/2 4.0–4.5 for manganese, cadmium, copper and cobalt, pH1/2 6.5 for nickel and pH1/2 8.0 for lithium. These results indicate that batteries must be previously sorted by type and treated separately. In addition, data fitting to an equilibrium model proposed for the reactive test system by the European Federation of Chemical Engineering (EFChE) have indicated that MR2(RH)2 and MR2 complexes (where M = Zn, Mn, Co, Cd and Cu) co-exist in the organic phase with Cyanex 272 depending on the loading conditions. The route has been found technically viable to separate the main metallic species of all batteries considered in this study.