Recovery of boric acid from the simulated radioactive wastewater by vacuum membrane distillation crystallization

Highlights: •VMDC was used for wastewater treatment and boric acid recovery. •Effect of boric acid concentration on VMDC performance was examined. •Effect of operational parameters on permeate flux was studied. -- Abstract: Recovery of boric acid from the simulated radioactive wastewater was investigated by using vacuum membrane distillation crystallization (VMDC). Effect of initial boric acid concentration (0.5 to 100 g/L) and feed solution concentration factor (5 to 200) on nuclides and boric acid rejection ratio was studied. It was found that boric acid could improve nuclides rejection ratio of the membrane by affecting electrical property of the membrane surface. Concentation factor of 200 for the water sample was successfully achieved by VMDC. Nuclides and boric acid rejection ratio at CF 200 was about 96.0% and 99.5% respectively. About 50% boric acid was recovered from the feed solution by single stage of VMDC at 70 °C. Effecs of operation factors including feed concentration (salinity from about 0.55 g/L to 110 g/L), feed temperature (20 °C to 70 °C), permeate side vacuum degree (0.40 to 0.97 atm) and feed velocity (Reynolds Number from 100 to 400) on MD permeate flux were investigated. It was found that the feed temperature had the most significant influence on the permeate flux while the feed concentration had the least. Dusty gas model could estimate the VMDC permeate flux precisely with average relative error of 4.32%. VMDC was an effective method to recover boric acid from radioactive wastewater.