Processing of sodium sulphate solutions using the EED method: from a batch toward a continuous process

In a batch electro-electrodialysis (EED), sodium sulphate solution with an initial concentration of 80.90 g/dm³ was converted to obtain solutions of sodium hydroxide (13.96%) and sulphuric acid (10.15%) and a dialysate (3.23 g/dm³ of sulphate ions). Changes in the EED process′ performance (temperature, cell voltage, concentrations, energy consumption) with an increasing conversion degree of salt are presented. Based on the presented results of the batch experiment, conditions necessary to run the process continuously are discussed. A single pass method is inapplicable due to excessive heating of the electro-electrodialyser. A cascade method enables interstage cooling of the solutions, providing temperatures suitable for ion-exchange membranes to work. Increasing the number of stages in the cascade reduces both the number of electro-electrodialysers and specific electric energy consumption, providing the same production capacity. However, this increases the investment cost.