Valorization of desalination brines by electrodialysis with bipolar membranes using nanocomposite anion exchange membranes

Abstract

Electrodialysis with bipolar membranes (EDBM) is a promising technology that simultaneously treats and valorizes desalination brines into acids and bases. An important techno-economic challenge of EDBM in this application is the purity of the products, related to the need for more selective ion exchange membranes with good stability working with acids and bases. This work presents the results of the treatment of model desalination brines by EDBM using nanocomposite anion exchange membranes in order to reduce the sulfate content as the main impurity in the acid stack. These membranes are composed by polyethylene, polypropylene, sulfonated poly (2,6-dimethyl-1,4-phenylene oxide) (sPPO) and different loads of Fe2O3-SO42 − nanoparticles. A reduction of the sulfate content in the acid stack was observed when using nanocomposite membranes. The stability of these membranes was evaluated measuring the Cl−/SO42 − selectivity after 31 h, 62 h and 93 h of operation. FTIR spectra before and after 93 h of operation also confirmed the stability of the membranes. The evolution of the main impurities in the acid and the base stacks versus time when applying different current densities is included and related to current efficiency. An estimation of the proton and hydroxyl ions leakages at the different current densities is also presented.