Direct and selective electrodeposition of palladium from betainium bis(trifluoromethanesulfonyl)imide ionic liquid phase after solvent extraction together with other platinum group metals

We propose an extraction-electrodeposition process involving the solvent extraction of platinum group metals (PGMs) to an ionic liquid phase followed by the direct electrodeposition of a selected metal from the ionic liquid phase to separate and recover PGMs efficiently. To examine the compatibility of betainium bis(trifluoromethanesulfonyl)imide ionic liquid ([Hbet][Tf2N]) in this process, we investigated the electrochemical behavior of Ru(III), Rh(III), and Pd(II) actually extracted from HNO3 (aq) to the [Hbet][Tf2N] phase. Through the potentiostatic electrolysis of Pd(II) in [Hbet] [Tf2N], fine particles of Pd metal were deposited over time at applied potentials at -500, -600, and -750 mV vs Fc/Fc+. In contrast, no electrodeposition of Ru(III) and Rh(III) from [Hbet][Tf2N] solutions was observed. We also examined the potentiostatic electrolysis of a mixture of Pd(II), Ru(III), and Rh(III) in [Hbet][Tf2N] at -600 mV vs Fc/Fc+. As a result, Pd(II) was selectively electrodeposited in a nearly quantitative yield( >99%) with high purity( >97%), while little Ru and Rh were included in the deposit.