Extractant impregnation into polymer chain grafted onto porous membrane for high-speed separation of metal ion

The analysis of radionuclides in radioactive wastes is essential to the safe and economical disposal of such wastes. Among radioactive species, actinides such as uranium and plutonium should be purified prior to radiometric measurements. Porous hollow-fiber membranes with a functionalized polymer chain can satisfy the requirements of speed and capacity for the separation of metal ions. In this study, Aliquat 336, tri-n-octylmethylammonium chloride, was impregnated to carboxy pentyl-amino (CPA) and octadecylamino (C18NH) group-containing polymer chains grafted onto a porous hollow-fiber membrane. The electrostatic interaction between the carboxyl moiety of the CPA group and the quarternary ammonium group of Aliquat 336 gave rise to a high-density impregnation of Aliquat 336. The C18NH group reinforced a hydrophobic interaction of the octadecyl part of the C18NH group of the graft chain with the alkyl moiety of Aliquat 336 which leads to stable impregnation of Aliquat 336 to the graft chain in aqueous solution. A mixture of water and ethanol was employed as a solvent for the impregnation of Aliquat 336. A higher water volume fraction induced a higher extension of the graft chain, resulting in an increase in the amount of Aliquat 336 impregnated. The amount of impregnated Aliquat 336 was 1.2 mol per kg of the GMA-grafted porous hollow-fiber membrane, which was 1.7 times higher than that using ethanol as a solvent of Aliquat 336. Palladium chloride (100 mg-Pd/L) dissolved in 1 M hydrochloric acid was forced to permeate through the pores of the Aliquat 336-impregnated membrane. The binding efficiency, defined as the ratio of number of moles of palladium adsorbed to half the number of moles of impregnated Aliquat 336, was found to be 69%. (author)