Chemical pumping of rhodium by a supported liquid membrane containing Aliquat 336 as carrier

The mass transfer of Rh(III) from aqueous feed chloride solutions containing SCN through a solid-supported liquid membrane (SSLM) consisting of Aliquat 336 dissolved in dodecane has been studied. The influence of hydrodynamic conditions as well as the chemical composition of the system on the permeation rate was investigated. Among the reagents tested as carriers, quaternary amines have been shown to be the most effective for the metal transport. Aliphatic organic diluents were chosen to avoid the degradation of the polymeric support, and 1-dodecanol was used as a modifier to increase the solubility of the extractant. The presence of thiocyanate in the feed solution was essential for the extraction of Rh(III). Furthermore, previous heating of the feed solution was necessary in order to form the extractable complex Rh(SCN)6/3-. Different reducing compounds were tested as stripping agents, and 1.0 M NaHSO3 solution was found to be the most effective to strip Rh(III) from the organic phase. Under these conditions, transport of Rh(III) through the membrane against its concentration gradient was achieved. The transport behavior of palladium and platinum in the proposed liquid membrane system was also studied. The obtained results reveal the possibility of exploiting the kinetic differences in the chemistry of the platinum group metals in the design of a process for the separation of these three metals.