Recycling

[1K0409-14-03] Complexation-Distribution Separated Solvent Extraction Process Designed for Efficient Recovery of Inert Platinum Group Metals

○ZHIWEI ZHENG¹, Koichiro Takao¹, Tsuyoshi Arai² (1. Tokyo Institute of Technology University, 2. Shibaura Institute of Technology University)

Chairman:Mitsuaki MATSUOKA (Kansai University)

Keywords:Solvent Extraction, Platinum Group Metals, Thermal-Assisted, Water-Soluble Complexant, Phase Transfer Catalyst

Recovery of platinum group metals (PGMs) from wasted materials like automotive catalysts and electronic devices, so-called urban mining, is highly required because of their preciousness in natural environments and usefulness in our current society. If separation of PGMs from the urban mining is successful, recycling of PGMs will be realized. Although we have previously demonstrated that solvent extraction of inert PGMs like Ru(III) and Rh(III) can be accelerated under thermal treatments, there are still several issues about difficulty of temperature control in actual extraction contactors and safety risks arising from heating organic solvents. To address these concerns, we designed a new solvent extraction protocol consisting of two separated steps: (1) complexation of PGM with a water-soluble complexant in an aqueous phase and (2) distribution equilibrium of the formed complex between aqueous and non-aqueous phases assisted by a phase transfer catalyst (PTC). As a result, the water-soluble M-PDA complexes (M = Ru(III), Rh(III)) were successfully formed in 0.5 M HNO₃(aq) as expected. The complexation reactions of Ru(III) and Rh(III) finished within 2 h and 1.5 h, respectively. In the next distribution step, the extractability of Ru(III) and Rh(III) from 0.5 M HNO₃(aq) to 1-octanol quickly reached up to 72% and 48%, respectively, within 5 min under the presence of bis(trifluoromethylsulfonyl)amide (Tf₂N⁻) in the organic phase. The total extractability of Ru(III) and Rh(III) under multistage extraction reached up to 97% and 92%, respectively, when only the distribution step at room teperature was repeated 4 times after completion of the complxation step first. Consequently, the complexation-distribution separated extraction we proposed here was successfully demonstrated in use of appropriately selected PDA ligands and Tf₂N⁻ as water-soluble complexants and an anionic PTC hydrophobic enough, respectively.