Abstract
Deep eutectic solvents (DESs) are becoming a popular area of research as lower-volatility, possibly more sustainable, alternatives to traditional leaching media to recover desired metals in spent lithium-ion battery (LIB) black mass. In this work, choline chloride (ChCl) was initially produced by extraction of the starting feedstock using aqueous solution, then gravity filtration, extended low-temperature evaporation and ultimate dehydration/solidification at 105 o C to form solid ChCl. Three DESs containing ChCl as a hydrogen bond acceptor and urea, ethylene glycol or citric acid as hydrogen bond donors (reline 1:2, ethaline 1:2, and ChCl:citric acid 1:1) were subsequently prepared. These systems demonstrated exhibited different physical characteristics of low-viscosity homogeneity (ethaline) and high viscosity containing visible inclusions (citric acid DES). Experiments on leaching were carried out by putting LIB black mass in touch with each DES at a ratio of black mass: DES mass ratio 1:25 under stirring at a temperature of 80 C. The color of all mixtures became dark within the period of approximately 2 h, in which there was progressive dissolution, and total visual dissolution occurred after 6 h and addition of water was needed to counter the rise in viscosity and partial solidification in the ethylene glycol and citric acid systems. Overall, the results demonstrate the practical feasibility of ChCl-based DESs for low-temperature black mass dissolution, while highlighting solvent-dependent handling challenges that should be considered in downstream separation and metal recovery workflows.