Concentrating brine from seawater desalination process by nanofiltration-electrodialysis integrated membrane technology

Extraction and concentrating of NaCl from brine were promising technologies to solve the disposition problem of seawater desalination. A novel nanofiltration-electrodialysis (NF-ED) integrated membrane technology was proposed and investigated. The separation of monovalent & bivalent ions and concentrating of solute were realized in NF and ED process, respectively. A kind of NF membrane with high SO42 − rejection and common homogeneous ion exchange membrane were investigated. The results showed that the operating pressure and feeding solution concentration have obvious effect on the water permeate flux and ions rejection ratios. Due to the special properties of NF membrane, almost all of the SO42 − in the brine was rejected. The rejection of Ca2 + and Mg2 + was 40% and 87%. The concentrations of Ca2 + in permeate were 392 mg/L in a brine-recycle experiment, which induce lower scaling potential when used as the raw water of ED. The highest NaCl concentration in the concentrating cell could be as high as 160 g/L and the NaCl recovery was about 70% after 5 h under 15 V, while total concentration of “impure ions” (K+, Ca2 + and Mg2 +) was about 5 g/L. A concept process was also proposed attempting to realize comprehensive utilization of brine.