Extraction of fission palladium by Aliquat 336 and electrochemical studies on direct recovery from ionic liquid phase

Abstract

The wide electrochemical window and ion exchange properties of a room-temperature ionic liquid (RTIL) have been exploited for the extraction of palladium from nitric acid medium into ionic liquid phase — followed by direct electrodeposition of the metal from the organic phase. Extraction of palladium by commercial Aliquat 336 ionic liquids, tri- n-octylmethylammonium chloride (TOMAC) and tri- n-octylmethylammonium nitrate (TOMAN), was studied as a function of [HNO 3], [NO 3 −] and [TOMAN]. The distribution ratio ( D Pd(II)) of palladium in TOMAN increased with an increase in the concentration of nitric acid and passed through a maximum at 1.0 M nitric acid. In contrast, the D Pd(II) value of palladium in TOMAC decreased continuously with an increase in the concentration of nitric acid. Substantial amounts of water and nitric acid were also co-extracted into the organic phase with palladium. The redox behavior of a solution of Pd 2+ extracted in 0.1 M TOMAN/CHCl 3 and 0.1 M TOMAC/CHCl 3 at glassy carbon working electrode was studied using cyclic voltammetry. The voltammogram consisted of a single reduction and an oxidation wave indicating that Pd 2+ was reduced to palladium metal by a single-step two-electron transfer at the working electrode. Controlled potential deposition of palladium on platinum electrode gave a black deposit, which was characterized to be metallic palladium. Interference of other fission products during extraction and electrodeposition of palladium is also reported.