Automotive catalytic converters leaching for solubilizing platinum group metals

Recent advancements in Deep Eutectic Solvents (DESs) have yielded promising outcomes, positioning them as potential agents for efficiently extracting various metals, including platinum group metals (PGMs) and gold, from secondary sources like spent automotive catalytic converters and e-wastes. This suggests imminent large-scale applications. DES presents numerous advantages compared to conventional reagents, showing desirable traits such as biodegradability, recyclability, non-toxicity, and cost-effectiveness, among others.

Current research employs calcium and choline-based DES systems to extract Platinum (Pt), Palladium (Pd), and Rhodium (Rh) from mixed three-way spent automotive catalytic converters. This method eliminates the need for corrosive acidic additives and pre-treatment steps, aiming to enhance economic viability and environmental sustainability. Utilizing established state-of-the-art laboratory-scale setups and experimental approaches ensures precision and reliability in the process. This study builds upon previous investigations conducted by MONOLITHOS Catalysts & Recycling Ltd. The primary objectives of the research study are; (1) to identify the most effective Deep Eutectic Solvent (DES) system to maximize the yield of Platinum (Pt), Palladium (Pd), and Rhodium (Rh) (2) and determine the optimal leaching conditions, including temperature, leaching duration, and solid-liquid ratio, to enhance metal extraction efficiency (3) to study the proton conduction and establish the electrochemical properties of the determined DES systems and (4) to evaluate the recyclability of the DES leaching reagent using UV-Vis spectrophotometer. This research covers various aspects related to solvent selection, process optimization, characterization, and sustainability considerations in the context of metal leaching using DES. These steps sought to establish a sustainable and eco-friendly leaching reagent for the efficient recovery of PGMs (Pt, Pd, and Rh) from secondary raw materials as part of the circular economy strategy while eliminating any highly corrosive acidic component and maintaining a single-step process approach. The preliminary results showed recovery of 81%, 95%, and 79% for Pt, Pd, and Rh respectively by the choline chloride: oxalic acid DES system. This establishes the ability of a benign DES system to solubilize metal oxides including Pt, Pd, and Rh with the potential to be used in several leaching cycles. This is a major contribution to the novel DES study and the circular economy strategy for sustainable metal recovery from waste streams and a general contribution to the United Nations Sustainable Development Goals (SDG12).