Boron recovery from wastewater using a self-powered bipolar membrane electrodialysis system

The usage of boron resources results in the production and discharge of a large amount of boron-containing wastewater in the environment, causing irreversible effects on the human nervous and reproductive systems. In this study, a self-powered zinc-air battery (ZAB) bipolar membrane (BPM) electrodialysis (BMED) (ZABBMED) system was used to recover B(OH)4- in the form of zinc borate from wastewater. The OH- generated by the BPM under an electric field combined with H3BO3 in the wastewater compartment. The resulting B(OH)4migrated to the boron recovery compartment and was finally recovered as zinc borate. The zinc anode and charcoal felt cathode formed a ZAB system, which provided energy (an output power of 23.3 x 10-3 mW and an energy density of 8.60 x 10-3 W/m2) for the hydrolysis of the BPM and the migration of B(OH)4- . Furthermore, Zn2+ produced by the zinc anode migrated from the anode compartment to the boron recovery compartment and combined with B(OH)4- to form zinc borate, achieving closed-loop self-generation of electricity and resource recovery. Experimental results showed that electrolyte concentration, initial boron concentration and the selected anode and cathode materials affected the BPM hydrolysis, recovery ratio of B(OH)4- and output power. Under the conditions of an electrolyte (NaCl) concentration of 3.0 g/L, an initial boron concentration of 100 mg/ L, a zinc plate and charcoal felt as the anode and cathode, respectively, and a flow rate of 10 mL/min, 58.3 % of B (OH)4- was recovered. A higher recovery ratio of B(OH)4- (60.8 %) was obtained when two ZAB-BMEDs were used. The results of X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analyses showed that the obtained products were similar to commercial zinc borate. Thus, the ZAB-BMED system can be considered effective for recovering B(OH)4- in the form of zinc borate.