STABILITY OF FLAT SHEET SUPPORTED LIQUID MEMBRANES IN THE TRANSPORT OF RADIONUCLIDES FROM REPROCESSING CONCENTRATE SOLUTIONS

The stability of a flat sheet supported liquid membrane (FSSLM) has been studied by using various kinds of diluents. The influence of several properties of the diluents on the stability of the SLM as well as on water transport have been analyzed. The high interfacial tensions and low water solubilities were the principal characteristics of the membrane solvents, together with their surface tension being lower than the critical surface tension of the support, which permits a long SLM lifetime. Under our own working conditions (osmotic pressure gradient across the membrane and the use of a solid support) a membrane lifetime of over 200 hr was attained by using membrane solvents with a water solubility lower than 12 g-l(-1) and, simultaneously, a drop point of the SLM higher than 1.1 bar. These conditions could be obtained with isotridecanol or with aromatic diluents having aliphatic groups of six or more carbon atoms (like hexylbenzene) with a long chain alcohol as a phase modifier. Isotridecanol was found to be the best phase modifier (the most stable on an SLM). Measurements of water transport across the SLMs showed different stabilities for SLMs with 1-decanol, 4-nonylphenol or isotridecanol as phase modifiers, for which the SLM has a lifetime longer than 200 hr.