Separation properties of high temperature reverse osmosis membranes for silica removal and boric acid recovery

In performed laboratory tests, RO silica rejection percentage was over 97%, and boron passage was about 60-65% (molecular weight cut off of 200 or 250 Da) of the solution which contained silica in the range of 1-90 ppm and boron in the range of 7500-15,000 ppm. The separation factor (SF) between boron and silica related to boron concentration could be expressed as the relation, SF = k[boron]0.7. The separation process could be described by a mass balance model. The modeling calculation fitted the experimental results very well, within the acceptable parameters' errors. It was proposed that the boric acid in a boric acid storage tank (BAST) of one studied pressurized water reactor (PWR) plant could be treated with such tf-PA RO. In the prediction, the silica concentration in it would be removed to about 1 ppm, and that the boron could be reused. The waste amount of boron after such treatment was predicted to be less than 1.5%.