Efficient recovery of strategic materials from spent lithium-ion batteries: Optimization using an experimental design methodology

Abstract

The recovery of critical materials such as cobalt, nickel, lithium, manganese and even graphite from spent lithium-ion batteries of different applications and compositions, was studied. The black mass samples were characterized by X-ray diffractometry, revealing mixed lithium oxide phases, and metal content was determined by acid digestion. Inorganic acids showed high efficiencies in leaching metals from the black mass for their full dissociation and greater emission of protons into the medium, while organic acids were a more biodegradable and environmentally friendly alternative to treat these batteries with a less toxic and aggressive treatment and good results. Oxalic acid rose as an interesting option for selective lithium recovery (around 80 % of lithium purity). The leach residue was characterized by XRD, identified as graphite with high purity and graphitization degrees up to 96 %. High recovery efficiency of graphite was achieved. A 33 factorial experimental design was created to evaluate the statistical significance of various variables in metal leaching. Time and temperature emerged as the most significant factors, their increase enhanced leaching efficiency, while pulp density showed higher leaching efficiency at intermediate values. Final optimization of acid concentration and H2O2 dosing led to recoveries of 93 % of Co, 98 % of Li, 86 % of Ni and 97 % of Mn, at S/L = 10 g/L, T = 75 °C, t = 24 h, H2O2 = 0.5 g/g, and using 1 N gluconic acid as lixiviant, from a black mass with high cobalt content. The present methodology stands out for its applicability to black mass samples of batteries of different origins (computer, electric vehicle, cordless tool…), a simple and effective approach, easily applicable to existing processes at industrial level. It favors the selection of the best lixiviants for each case while considering environmental, economic and engineering criteria.