Ceramic nanofiltration and membrane distillation hybrid membrane processes for the purification and recycling of boric acid from simulative radioactive waste water

To reduce the emission of radioactive waste water and reuse high-value B-rich nuclear-grade boric acid from a nuclear power plant, a two-step membrane process was proposed based on the combination of two types of ceramic membranes. First, a ceramic nanofiltration membrane was used to purify the boric acid by removing the nuclide. Then, the purified boric acid solution was concentrated by a vacuum membrane distillation process based on a hydrophobic ceramic membrane. The operating parameters of both membrane processes were systematically discussed and optimized. In the nanofiltration process, the retention rates of Co and Ag ions were approximately 99.2% and 75.8%, respectively, and the permeation flux was stable at approximately 178 L m h. When a two-stage NF process was implemented, the removal of Co ions was higher than 99.9%, and the removal of Ag ions was greater than 95%. In the membrane distillation process, the boric acid was concentrated from 1 to 107 g L. Meanwhile, the permeation flux was maintained above 20 L m h, and the retention rate of boric acid was maintained at a high level (>99.9%) throughout the entire enrichment process. The hybrid membrane processes are suitable candidates for the purification and recycling of boric acid from radioactive waste water.