Selective extraction of valuable metals from spent EV power batteries using sulfation roasting and two stage leaching process

Abstract

Selective extraction of valuable metals from spent electric vehicles (EVs) power batteries was undertaken by a sulfation roasting-water leaching-acidic leaching process. After sulfation roasting (acid-to-lithium molar ratio (nH2SO4:nLi) = 0.95, 550 °C and 3 h), the roasted products were subject to the 1st stage of water leaching. Under optimum conditions (30 °C, 2 h and liquid-to-solid (L/S) ratio of 4 mL/g), the extraction of Li and Mn reached 90% and 10%, whereas extractions of Co and Ni were negligible. The water leaching residues were then treated by the 2nd stage of acidic leaching (2 mol/L H2SO4 solution with L/S ratio of 5 mL/g at 60 °C for 2 h) which resulted in an additional 98% Ni, 97% Co and 90% Mn being leached from the residue. An investigation of the phase transformation mechanism indicated that the extraction behaviors of valuable metals might be induced by the different reduction pathways of the metals while controlling the roasting conditions. With roasting temperature <550 °C and roasting time <2 h, Li within the crystalline LiCoxNiyMn1-x-yO2 was de-intercalated and transformed to soluble Li2SO4, while Ni, Co and Mn in the LiCoxNiyMn1-x-yO2 decomposed to MnCo2O4 and Ni6MnO8 because of the co-existence of sulfuric acid and carbon reductant from the graphite anode material. When nH2SO4:nLi was higher than 1.2, Li was further converted to Li2Mn2(SO4)3. Under the conditions of roasting temperature > 550 °C and roasting time >2 h, MnCo2O4 and Ni6MnO8 were further reduced into low-valence states CoO and (NiO)0.75(MnO)0.25. These results provide a fundamental basis for the development of an efficient and selective extraction strategy for the recycling of valuable metals from spent EV power batteries.