This research study was aimed at recovering palladium from used aqua regia by means of a hollow fiber thoroughly supported with liquid membrane. The liquid membrane, consisting of two extractants--thioridazine·HCl and oleic acid-solubilized in chloroform--was used to coat the microporous hollow fiber throughout. Sodium nitrite, a stripping agent, which was fed through the shell side, flowed counter-currently with the feed solution fed via the tube side. The following factors were investigated: the concentrations of the two extractants and of sodium nitrite, the pH of used aqua regia, the flow rates of both the feed and stripping solution, and the number of runs in the hollow fiber module. It was found that after a 30-minute operation, 29.10% of palladium ion was optimally recovered at 0.0005- M thioridazine and 0.05-M oleic acid. With reference to the precious metals recovered, the following order was recorded: Pd(II) > Pt(IV) > Cu(II) > Au(III). It was observed that synergistic extraction could be gained at the concentration level of the extractants, regulated in the experiment. The liquid membrane system had long-term stability and even after the third run, it could still recover palladium up to 65%.
Farbu L, Alstad J, Auguston JH, 1974. cited in G. Duyckaerts and J.F. Desreux, 1977, "Recent Development and New Combinations of Extractants in Synergistic Processes," Proceedings of International Solvent Extraction Conference, 1977
Mathur JN, Sol. Extraction Ion Exchange, 1(2), 349, 1983
Myers D, "Liquid Crystals, Vesicles and Liquid Membranes," Surfactants Science and Technology, Weinheim: VCH Publishers, New York, 1988
Patthaveekongka W, "Influence of Acetic Acid-sodium Acetate Solution Concentration on Extraction of Zinc Ions via a Hollow Fiber Supported Liquid Membrane," Master's thesis, Dept. of Chem. Eng., Chulalongkorn University, 1999
Rosen MJ, "Physiocochemical Properties of Surfactants & Polymers Containing Oxyethylene Groups and Intermolecular Interactions," Surfactants and Interfacial Pehnomena, John Wiley, New York, 1988