A two-step electrochemical method for separating Mg(OH) 2 and CaCO 3 : Application to RO reject and polluted groundwater

The process of removing Ca and Mg ions typically results in the co-precipitation of Ca and Mg along with other salt waste. To improve water treatment efficiency towards a zero-waste goal, it is crucial to separate Ca and Mg and recover them in their purified form. This study proposes a two-step electrochemical approach that separately recovers Ca as CaCO and Mg as Mg(OH) . The first step uses an undivided cell with 3D electrodes and controlled flow directions to selectively precipitate CaCO on the electrode, keeping the cell removal efficiency. The second step employs a two-compartment cell with a cationic exchange membrane to recover Mg(OH) . This approach was evaluated on RO reject water with high Ca to Mg ratio and industrial effluent-polluted groundwater with a low ratio. Treatment of domestic RO reject water using undivided cell specifically recovered 64% of CaCO , although the low conductivity of the RO reject water limited further Mg recovery. Conversely, treating industrial effluent-polluted groundwater with this two-step process successfully recovered 80% of CaCO and 94% of Mg(OH) . SEM, EDAX, and XRD analysis confirmed the quality of the recovered products.