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

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 degrees 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.

Automated summary

In recent years, there has been an increasing demand for energy critical elements (ECEs) due to the rapid advancement of energy-related technology. Spent catalysts have the potential to be a valuable source of ECEs such as Ni, Co, Mo, W, V, and rare earth elements. This study developed an environmentally friendly process using deep eutectic solvents (DESs) to recover cobalt and molybdenum from spent hydroprocessing catalysts. The experimental results showed high metal extraction, with 93% of cobalt and 87% of molybdenum being dissolved at 100 degrees C and a pulp density of 20 g/L for 48 hours. FT-IR and H-NMR analyses were conducted to investigate the formation of hydrogen bonds in the DESs.