Selective extraction of palladium(II) from hydrochloric acid solutions with phosphonium extractants

► Quaternary phosphonium salts as selective extractants of Pd(II) over other metals. ► Extractionof Pd(II) from acidic media is fast, efficient and selective. ► Recovery and separation of metals were investigated in extraction-stripping system. ► Separation of Pd(II) from all other metals in the examined process looks promising. The selectivity of palladium(II) extraction over nickel(II), copper(II), lead(II), iron(III), rhodium(III), ruthenium(III) and platinum(IV) with quaternary phosphonium salts: trihexyl(tetradecyl)phosphonium chloride (Cyphos®IL 101) and trihexyl-(tetradecyl)phosphonium bis-2,4,4-trimethylpentylphosphinate (Cyphos®IL 104), in the presence of toluene, has been investigated. Over 99% of palladium(II) can be effectively extracted with Cyphos®IL 101 and Cyphos®IL 104 from 0.1 M HCl in the presence of nickel(II), copper(II), lead(II), iron(III), rhodium(III) and ruthenium(III), while less than 10% of the other metals is transported to the organic phase. Separation of palladium(II) from platinum(IV) is not so effective; about 70–75% palladium(II) and 60–68% platinum(IV) is extracted. The selectivity of palladium(II) extraction over lead(II), iron(III) and platinum(IV) depends upon the acidity of aqueous solution and with increasing HCl concentration, the selectivity decreases. Palladium(II) can be separated from platinum(IV) successfully through stripping of palladium(II) from the loaded organic phase with 0.5 M ammonia solution.