Removal of Ash: Potential Use of Electrodialysis

Within an electrodialysis unit, the solutions are separated by alternately arranged anion exchange membranes (permeable only for anions) and cation exchange membranes (permeable only for cations). The membranes are arranged parallel to one another to form an electrodialysis stack. When a potential is applied across the selectively permeable membrane stack, anions selectively move through the anion exchange membrane and cations selectively move through the cation exchange membrane. The transport of ions across the membranes results in ion depletion in some cells (de-ionized, diluent or desalinated stream), and ion concentration (salt concentrate) in alternate cells. Further transport of the ions to the next cell is stopped by the next membrane (Figure 1). The electrodialysis process thus allows for the effective removal or concentration of ions (salts).