Closed-loop process for selective leaching and recovery of palladium from spent auto-exhaust catalysts using iodotrihalide ionic liquids.

The recovery of palladium from spent auto-exhaust catalysts (SAE-catalysts) is of great significance for resource sustainability. Herein, we proposed an efficient closed-loop leaching and recovery method for palladium from SAE-catalysts using iodotrihalide ionic liquids (ILs). Recovery design was explored aimed at green leaching and process simplification. Iodotrihalide ILs exhibited exceptional performance in terms of leaching efficiency (99.1%), selectivity (selectivity > 6.8 ×10) and reusability (over 6 cycles). The mechanism study revealed that excellent leaching performance was attributed to the redox and complexation. Additionally, the chemical reaction-controlled model was best suited to describe the leaching process. Notably, under the optimal conditions determined by the response surface methodology, a high-purity Pd(II) solution (purity > 99.8%) was obtained. More significantly, it was ideal for practical applications due to the low-viscosity (36.0 cP), mild (55 °C) and one-step leaching and recovery. In conclusion, this work provides an eco-friendly method for recovering palladium from SAE-catalysts with its non-high corrosiveness and low environmental impact.