Green extraction of pure ferromagnetic nickel from spent hydroprocessing catalysts via deep eutectic solvents

Spent catalysts can be extremely hazardous to the environment and human health if not properly managed. In this study, a novel environmentally friendly flowsheet based on deep eutectic solvents (DESs) was developed to efficiently recover nickel from spent hydroprocessing catalysts. The potential of eight different DES (binary and ternary) to leach Ni from two different spent catalyst hydroprocessing samples was evaluated. The p-toluenesulfonic acid-based DES-1 (PEG-400:PTSA) and DES-8 (ChCl:EG:PTSA) showed high nickel extraction (>90 %). The effect of time, temperature, and solid to liquid ratio on nickel extraction was investigated. Selective nickel extraction was obtained under the pulp density of 20 g/L, a temperature of 100 degrees C, and a leaching time of 48 hrs. The shrinking core models fitted well with the experimental results. The ferromagnetic face-centered cubic (FCC) nickel powder was produced successfully using the cementation method. This study establishes a novel green approach based on DES for recovering nickel from spent catalysts without any roasting or oxidative agent addition.