Recovery of strategic metals (cobalt, nickel) from lithium-ion batteries through adsorption and desorption: Insights in desorption mechanisms and ultrasound enhancement

Abstract

The purification of wastewater and the recovery of strategic metals from spent batteries, such as Co2+ and Ni2+ were carried out using a sorption–desorption process with a chemically activated mesoporous carbon. The mesoporous carbon was chemically activated in mild conditions with NaClO2 and H2O2, and its textural and chemical properties were characterized using FTIR, BET, TGA and BET techniques. The activated carbon exhibited a SBET of 400 m2/g, with oxygenated functional groups such as carboxylic acids and lactones that were developed on the surface. The activation increased the concentration of acidic groups from 0.36 to 1.06 meq/g, as determined by conductometric titration. High cobalt sorption capacities were observed, exceeding 20 mg/g (an 11-fold increase), with rapid kinetics (under 20 min) and sorption equilibrium data fitted to the Sips isotherm model, and a maximum sorption capacity of 21.5 mg/g. In the desorption experiments, eluents such as acid, alkaline, and salt solutions were tested, with H2SO4 and CaCl2 exhibiting high desorption efficiencies (over 80 %) due to the pH shift effect and ionic exchange mechanisms. A significant improvement was achieved by using an ultrasonic-assisted desorption process, which allowed for almost complete cobalt recovery (99 %) with a 98 % reduction in desorption time, attributed to the synergistic effect of the acidic pH shift and the ultrasonic irradiation on chemical bond breaking and metal detachment from surface. Significant sorption selectivity towards divalent cations (Co2+/Ni2+) was attained in a multi-metallic solution (qCo/qLi and qNi/qLi around 60), while lithium remained in the solution (2 % removal). The ultrasound-assisted desorption process enabled Co and Ni concentrations to reach up to 500 mg/L, 2.4 times the initial concentration.