Resource utilization of coal chemical waste salt by bipolar membrane electrodialysis with thermal pretreatment

The aim of this study is to explore the feasibility of applying bipolar membrane electrodialysis (BMED) to treat coal chemical waste salt with different pretreatments of organic pollutants. The organic content in the real waste salt reached 0.6 ± 0.1 % with a weight averaged molecular weight of 641 g/mol. Only 26.5 % of the total COD in a 250 g/L waste salt solution could be removed by the coagulation pretreatment, resulting in no apparent improvement in BMED performance. Thermal pretreatment at 850 °C for 180 min completely removed organics from the waste salt, resulting in efficient control of membrane fouling in the BMED. At the current density of 50 mA/cm2 and 250 g/L waste salt solution, the base concentration in the BMED with 850 °C pretreatment of waste salt was higher than that with 550 °C pretreatment and without any pretreatment (58.2 ± 1.0 vs. 56.0 ± 2.4 and 53.6 ± 2.0 g/L) within 180 min, respectively. The average current efficiency based on base productions with 850 °C pretreatment of the waste salt reached 91 ± 5 % in the BMED within 180 min. Our results should be useful for the resource utilization of coal chemical waste salt.