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

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 (n _{H 2SO 4} :n _Li) = 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 H ₂SO ₄ 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 LiCo _xNi _yMn _1-x-yO ₂ was de-intercalated and transformed to soluble Li ₂SO ₄, while Ni, Co and Mn in the LiCo _xNi _yMn _1-x-yO ₂ decomposed to MnCo ₂O ₄ and Ni ₆MnO ₈ because of the co-existence of sulfuric acid and carbon reductant from the graphite anode material. When n _{H 2SO 4} :n _Li was higher than 1.2, Li was further converted to Li ₂Mn ₂(SO ₄) ₃. Under the conditions of roasting temperature > 550 °C and roasting time >2 h, MnCo ₂O ₄ and Ni ₆MnO ₈ 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.