Recovery of platinum from spent reforming catalysts by coupled leaching and solvent extraction using deep eutectic solvents

Platinum recovery from spent reforming catalysts is both an economic imperative and an environmental necessity. In this study, we demonstrate a more sustainable alternative to conventional acid leaching by employing a choline chloride–ethylene glycol deep eutectic solvent (DES) system. Two Fractional Factorial Designs (FFD) were applied to screen and analyze the significant parameters for the leaching and solvent extraction (SX) processes. To identify the most influential parameters, statistical analyses were performed on the obtained results revealing that the choline chloride to ethylene glycol ratio plays a critical role by increasing the availability of chloride species for platinum complexation. Under optimized conditions, 10% w/w solids, a 1:1 choline chloride to ethylene glycol ratio, 25% w/w water, 90 °C, and 10% w/w nitric acid, over 92% platinum dissolution was achieved. To further refine the process, solvent extraction with trioctylamine (TOA) was employed, achieving 99.93% recovery of platinum under optimal conditions (10% v/v TOA in kerosene, a 1:1 M ratio of choline chloride to ethylene glycol, 25 °C, 5 min contact time). A key advantage is the inherent selectivity of the DES leach, which results in a significantly cleaner pregnant leach solution (∼200× less iron, ∼3× less aluminum) compared to conventional HCl leaching. This work establishes a combination of DES-SX as a highly effective method for the recovery and purification of platinum from spent catalysts, offering a scalable pathway toward more sustainable metallurgical practices.