Bipolar membrane electrodialysis for mixed salt water treatment: determination of optimum conditions by topsis-based taguchi method

The distillation waste (DW) is the biggest handicap of soda ash production with the Solvay process. The DW mainly consists of CaCl2 and NaCl, and especially the recent studies clearly show the damage it causes to the environment. With the aim to develop an alternative to the distillation unit in Solvay process, an experimental work was performed to investigate the effect of the working parameters on the different performance criteria for the production of NaOH+NH3.H2O mixture and HCI from simulated salt mixture of NaCI and NH4CI by bipolar membrane electrodialysis, and on the determination of the optimum working conditions. The performance criteria were taken as the acid and base concentrations, product-based salt conversion, product-based flux, energy consumption in the electrodialysis cell, desalination, and impurities in the products. The working parameters were chosen as the initial salt concentration, initial acid and base concentrations, initial acid and base volumes, current density, amount of impurity in product, and anolyte and catholyte concentrations. The experimental design and the search for the optimum working conditions for the performance criteria were performed by the Taguchi-based-multi-criteria decision-making method. Under optimum conditions, the products of 4.04 M HCl with 93.5% purity and 3.66 M NaOH + NH3.H2O with 98.7% purity (on dry basis), and 99.8% desalination were obtained.