双极膜电渗析应用于高盐废水再生酸碱的影响因素

Influencing factors of bipolar membrane electrodialysis applied to regeneration of acid and base from high-salt wastewater

高盐废水的处理是煤化工废水零排放的关键环节.双极膜电渗析(BMED)可将盐转化为相应的酸和碱,并回用于酸碱调整等内部工艺过程,对煤化工高盐废水的资源化利用有重要意义.针对“预处理-纳滤分盐-反渗透浓缩-二次预处理-电渗析提浓-BMED再生酸碱”的煤化工废水集成处理工艺,以配制的NaCl溶液模拟纳滤产水作为BMED的原水,探讨其制备NaOH和HCl过程中的关键影响因素.采用三隔室构型BMED装置,以碱浓度、反应速率、电流效率及能耗等作为主要评价指标,考察盐室初始/残液浓度、电流密度、膜堆循环流量和电极液浓度及类型等对BMED运行性能的影响.结果表明,在盐室初始NaCl质量分数15%,盐室NaCl残液质量分数5%,电流密度500 A/m^(2),膜堆各室循环流量90 L/h,电极液3%NaOH的优化运行条件下,NaOH浓度可达1.50 mol/L,电流效率60%,能耗2079 kWh/t-NaOH.研究结果可为推进BMED在煤化工高盐废水资源化处理中的应用提供参考.

The treatment of high-salt wastewater is the key process for zero-discharge of coal chemical wastewater. Bipolar membrane electrodialysis device(BMED) can convert salts into corresponding acids and bases, and reuse them in internal processes such as acid-base adjustment, which is of great significance for the resource utilization of coal chemical high-salt wastewater. In this paper, the process of “pretreatment-nanofiltration separation-reverse osmosis-secondary pretreatment-electrodialysis-BMED” was explored. NaCl solution was used to simulate nanofiltration production water as the raw water of BMED, and key factors in the preparation of NaOH and HCl from BMED was studied. The BMED with three-compartment configuration was used, and the main evaluation indexes such as base concentration, reaction rate, current efficiency and energy consumption were used to investigate the influencing factors such as the initial/residual salt concentration, current density, stack circulation flow, and the concentration and type of the electrode solution. The results show that in the NaCl initial mass fraction of 15%, residual mass fraction of 5%, current density of 500 A/m^(2), stack circulation flow of 90 L/h, and electrode solution of 3% NaOH, the NaOH concentration can reach 1.50 mol/L, the current efficiency is 60%, and the energy consumption is 2079 kWh/t-NaOH. The results can serve as a basis for promoting the industrial application of BMED to recycling high-salt wastewater from coal chemical industry.