Activity Removal from Liquid Waste Streams by Seeded Ultrafiltration

Abstract

Modern cross-flow filtration techniques allow the removal of very fine particles of solid material from aqueous streams. When the streams contain radionuclides, some small additional activity removal may be achieved by cross-flow filtration even after the stream has been treated by conventional filtration and ion exchange, and despite the concentration of radionuclides being exceedingly small. Much greater activity removal may be achieved, however, if the stream is dosed with additives which absorb or coprecipitate the radionuclides. This paper describes the development and characteristion of several such seed materials (finely divided inorganic ion exchange materials) and an investigation of factors which influence their effectiveness. Individual seeds are, in general, targetted on specific radionuclides (nickel hexacyanoferrate(II) is specific for caesium for instance) and are unlikely, therefore to offer an across-the-board approach to activity removal. Combinations or cocktails of seeds may, however, allow such an approach and this possibility has also been investigated. It is found that under certain circumstances seeds can interfere with one another and actually give worse results than when used individually. With careful selection of materials and conditions, however, it is possible to achieve substantial reductions in a variety of radionuclides simultaneously.