An efficient electrodialysis metathesis route to recover concentrated NaOH-NH4Cl products from simulated ammonia and saline wastewater in coal chemical industry

Coal chemical industry typically generated a series of wastewater such as ammonia wastewater and saline wastewater. The inappropriate treatment of these systems not only induced serious water pollution but caused waste of resources. To solve this situation, an efficient electrodialysis metathesis (EDM) route was proposed to transform simulated ammonia wastewater and saline wastewater into concentrated NaOH and NH4Cl products with higher added values. During the EDM processes, the influence of operating voltage, simulated ammonia wastewater circulating flow rate and feeding rate was explored and the optimal condition was determined. Under this condition, the NaOH and NH4Cl products were concentrated to 1.63 mol/L and 1.85 mol/L with purity at 80.71 wt% and 90.40 wt%, respectively. To further reveal the process mechanism, the ions especially OH− migration were systematically analyzed. It was found that the rejection rate of cation exchange membrane (CEM) towards OH−, dissociation of ammonia and intrinsic water migration were the three main factors dominating the concentration and purity of the final products. This work could provide potential directions for both high-value resources recycling and treatment of coal chemical industrial wastewater.