Separation of Pt(IV), Pd(II), Rh(III) and Ir(IV) from concentrated hydrochloric acid solutions by solvent extraction

Abstract

A new process for complete separation of Pd(II), Pt(IV), Ir(IV) and Rh(III) from concentrated hydrochloric acid solutions was proposed by employing solvent extraction. In the HCl concentration range from 1 to 6 M, only Pd(II) was extracted by LIX 63 and the Pd(II) in the loaded LIX 63 was stripped by thiourea. Extraction of the Pd(II) free raffinate with TBP at 6 M HCl solution led to selective extraction of Pt(IV) over iridium and Rh(III) and stripping of the loaded TBP with dilute HCl solution resulted in pure Pt(IV) solution. The extraction of iridium by TBP and Aliquat 336 indicated the possibility of Ir(IV)’s reduction to Ir(III) during the extraction with LIX 63. After adding NaClO₃ as an oxidizing agent to the Pd(II) and Pt(IV) free raffinate, extraction of the resulting solution with Aliquat 336 led to selective extraction of Ir(IV) over Rh(III). Use of HClO₄ solution could strip the Ir(IV) from the loaded Aliquat 336. This process can be utilized for the recovery of the four PGMs with high purity from diverse resources.