Sequential Separation of Pd(II), Pt(IV), and Rh(III) from Synthetic Hydrochloric Acid Leaching Solution of Spent Automotive Catalyst Containing Al(III) and Ce(III) by Chemical Reduction, Precipitation, and Solvent Extraction

The need for platinum group metals (PGMs) is increasing, and thus the recovery of PGMs from secondary resources is important. Spent automotive catalysts contain palladium, platinum, and rhodium together with aluminum and cerium. Separation experiments were done to recover these three PGMs from the leaching solutions containing excess amounts of Al(III) and Ce(III). For this purpose, precipitation, solvent extraction, ion exchange, and chemical reduction experiments were done at room temperature by employing synthetic hydrochloric acid solutions with 3 mol/L HCl. First, complete separation of Pd(II) was possible by solvent extraction with LIX 63 and precipitation with DMG. Moreover, the Pd(II) extracted into LIX 63 was easily stripped by a thiourea solution. Second, a pure Pt(IV) solution was selectively recovered from the raffinate by extraction with TBP followed by thiourea stripping. Conditions for quantitative extraction and stripping of Pd(II) and Pt(IV) were identified. Third, chemical reduction with NaBH4 led to the recovery of pure rhodium metal from the raffinate after separation of Pd(II) and Pt(IV). Although anion exchange resins selectively loaded Rh(III) over Al(III) and Ce(III), elution of Rh(III) from the loaded resins was incomplete. The purities of the recovered solutions of Pd(II) and Pt(IV) by solvent extraction were determined to be higher than 99.9%, whereas the purity of the metallic rhodium was estimated to be higher than 99.9% based on ICP-OES measurements. From the results, a process was proposed to recover Pd(II), Pt(IV), and Rh(III) by solvent extraction and chemical reduction from the synthetic hydrochloric acid leaching solutions of spent automotive catalysts.