An environmentally friendly method for extraction of Cobalt and Molybdenum from spent catalysts using deep eutectic solvents (DESs)

Abstract

Abstract There has been a substantially increasing demand for Energy Critical Elements (ECEs) in recent years as energy-related technology has advanced rapidly. Spent catalysts are known as potential sources of ECCs such as Ni, Co, Mo, W, V, and rare earth elements. This study developed an environmentally friendly process for recovering cobalt and molybdenum from spent hydroprocessing catalysts using deep eutectic solvents (DESs). High metal extraction of 93% and 87% were respectively achieved for cobalt and molybdenum at optimum conditions (100°C, pulp density of 20 g/L, and 48 hours) using p-toluenesulfonic acid based DESs. FT-IR and H-NMR analyses were conducted to determine whether hydrogen bonds form between p-toluenesulfonic acid-based DES components. Leaching kinetic models were also developed for DES systems. It was found that shrinking core models fit well with the experimental results. The kinetic studies proved that the diffusion through the product layer was the leaching controlling step of DES-1 (PEG-400:PTSA) with an activation energy of 22.56, and 29.34 kJ/mol for Co and Mo, respectively. On the other hand, DES-2 (ChCl:PTSA) correlates well with the activation energies of 38.09 (cobalt) and 31.48 kJ/mol (molybdenum), indicating that reaction appears to be limited by the mixed control reaction model. This study provides an effective new approach for planning and running ionometallurgical processes in the recycling sector while paying attention to concerns for sustainable development.