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

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 a novel environmentally friendly process for recovering cobalt and molybdenum from spent hydroprocessing catalysts using deep eutectic solvents (DESs). DESs based on p-toluenesulfonic acid achieved high metal extraction at 100 °C and a pulp density of 20 g/L for 48 h which 93% of cobalt and 87% of molybdenum were dissolved. 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. The experimental results were well-matched with the shrinking core models. The leaching controlling step of DES-1 was determined to be the diffusion through the product layer based on kinetic studies, with an activation energy of 22.56 kJ/mol for Co and 29.34 kJ/mol for Mo in DES-1. Similarly, the mixed control reaction with an activation energy of 38.09 kJ/mol for Co and 31.48 kJ/mol for Mo in DES-2 was found to control the leaching kinetic mechanism of the DES-2 sample.

Keywords: Cobalt; Deep-eutectic solvents; Leaching; Leaching kinetics; Molybdenum; Spent catalyst.