Direct and Selective Electrodeposition of Palladium from Betainium Bis(trifluoromethanesulfonyl)imide Ionic Liquid Phase after Solvent Extraction together with Other Platinum Group Metals

Abstract

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］ ［ Tf 2 N］ ) in this process, we investigated the electrochemical behavior of Ru (III) , Rh (III) , and Pd (II) actually extracted from HNO 3(aq) to the ［Hbet］ ［ Tf 2 N］ phase. Through the potentiostatic electrolysis of Pd (II) in ［Hbet］ ［Tf 2 N］ , 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］ ［ Tf 2 N］ solutions was observed. We also examined the potentiostatic electrolysis of a mixture of Pd (II) , Ru (III) , and Rh (III) in ［Hbet］ ［ Tf 2 N］ 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.