A step towards a circular economy: Processing waste effluents to acid and alkaline using ion exchange membrane electrodialysis

Abstract

The rising global energy demand has boosted industrial production to new heights, especially in battery production sectors, which relies heavily on raw materials from the metallurgical and mining sectors. These sectors use sulfuric acid and sodium hydroxide in processing, thus generating large quantities of sodium sulfate as waste. This kind of effluent is not exclusive to hydrometal-lurgical or mining industries; precursors for cathode active material (pCAM) manufacturers are also producing it as a by-product, compounding environ-mental concerns if discharged improperly. Similar issues arise in the pulp & paper industry, where the kraft pulping process produces green liquor, con-taining chemicals like sodium carbonate (Na2CO3), sodium sulfide (Na2S), and NaOH. Addressing these effluents through salt valorization technologies (SVT) such as electrodialysis (ED) and bipolar membrane electrodialysis (BPED) is crucial for recycling valuable chemicals and supporting water reuse strategies, aligning with circular economy principles. These processes, however, are not completely novel in the field of industrial effluent treatment but still require further engineering and research to become more sustainable in long-term usage. In this perspective, thesis is focused on studies of ion exchange mem-branes, especially BPED of electrolytes containing sodium, sulfate, and car-bonate ions. To better understand the ionic transport across the ion exchange membrane, a finite element modelling tool is employed to reveal some novel insights at the macro-scale level that are impossible to discover from a large-scale system. This dissertation considers mainly four topics: (i) ion exchange membrane simulations, (ii) the importance of diffusion coefficients and their calculation for strong and weak electrolytes, (iii) streaming potential studies across the membranes and other porous materials, and (iv) finally the BPED technology.