pH effect on the separation of uranium fluoride effluents by the reverse osmosis process

Ammonium fluoride solutions and uranium fluoride effluents (UFE) with solute concentrations from 0.101 to 7.920 kg/m 3, at pH 2.80 to 9.60, have been treated with a continuous feedback reverse osmosis (RO) process. The solute rejections of NH 4+, F”, and U6+ depend heavily on the feed pH value. For ammonium fluoride solutions, the rejection ratio of NH4+ decreases sharply from ca. 90 to 44.2% with the feed pH increased from 3.30 to 9.60, while that of F~ increases abruptly from 44.8 to 99.9% at the same pH change. For UFE solutions, the rejection ratio of U6+ remains greater than 90%.at pH 2.80-7.13, while that of F” decreases steadily from 96.4 to 18.8% with decreasing feed pH. Accordingly, the fluoride ions can be separated from UFE solutions under acidic conditions. The changes of solute rejection with feed pH can be explained by the different solubilities of the solutes in the membrane at different pH values. The UFE solutions with a and β activities at 20.4-53.7 and 8.99-21.3 (x 105 Baq/m3) can be reduced to a level lower than 2.41 and 3.37 (x 105 Baq/m3), respectively, by the current RO process.