Extraction of rhodium chlorocomplexes and acid through a supported liquid membrane of Kelex 100

The supported liquid membrane (SLM) technique was employed to effect the separation of Rh chlorocomplexes from hydrochloric acid solutions. The liquid membrane consisted of an alkylated 8-hydroxyquinoline extractant (Kelex 100), tridecanol, and kerosene. The nonaquated Rh complexes were transported through the membrane upon ion-pair formation with protonated Kelex 100 molecules. The ion-pair was then dissociated at the strip side of the membrane, releasing the Rh values. The main driving force for this transport process was the acid activity gradient across the membrane. The permeation of acid and water, which were cotransported with the Rh complexes, was partially prevented upon addition of NaCl to the strip phase. However, the accumulation of Cl- ions in the strip phase, in turn, slowed down the extraction of Rh. Optimum Rh extraction performance was obtained when a feed of 2.5 M HCl and a strip solution of pH 1 were used. Under these conditions the membrane was found to be very stable for at least a period of 72 hours (maximum period tested) while the rate of extraction was found to be 2.8 x 10(-6) mol . s(-1). m(-2).