The separation of tritiated water using supported polyphosphazene membranes

Carboxylated poly(diaryloxy)phosphazene was examined as the active constitu ent of the composite membranes to separate tritiated water (HTO) from light water. These membranes were tested with wafer containing 10 800 pCi/l and 3 mu Ci/l of tritiated water, respectively, under cross-flow filtration con ditions. Reductions in the permeate of nearly 30% HTO were observed with th ese tritium concentrations. Low temperature (5 degrees C), low pressure (13 7.9-551.6 kPa), and high pH (near 10 or above) were required to obtain such reductions (rejection). Salt species (Na2SO4, CaCl2 and CaSO4) at various concentrations and pressures, within a 137.9-551.6 kPa range, did not appea r to affect the HTO separation efficiency. Mass balances performed during t hese experiments indicate an unaccounted small amount of tritium (0.5-2.2%) . Sorption experiments with the polyphosphazene suggest that the membrane d oes not operate by an ion exchange mechanism; that is, tritium accumulation within the membrane. (C) 1999 Elsevier Science B.V. All rights reserved.