Electrochemical removal of calcium and magnesium ions from aqueous solutions

The present study shows upon, electrochemical removal of Ca2+ and Mg2+ ions from aqueous solutions. Calcite and brucite precipitation occurs through a chemical process following the electrochemical generation of OH− ions in the vicinity of the electrode surface. The kinetics of the electrochemical calcite and brucite precipitation were examined by measuring the electric conductivity as a function of time using different voltages and concentrations. The electric current density initially augments the electrochemical precipitation of calcite, but at a sufficiently higher current density the precipitation rate tends to an asymptotic limit. Furthermore, the precipitation rate of calcite is limited by diffusion kinetics of HCO3− ions and does not vary with the Ca2+ concentration. In contrast, the electrochemical precipitation of brucite correlates with current density, as there are no limitations in diffusion kinetics. With increasing Mg2+ concentration the rate constant of brucite decreases as small Mg2+ concentrations or high pH values promote the generation of MgOH+(aq.) species in the reaction zone, which are responsible for an enhanced precipitation rate. In addition the specific energy consumption required for 1 mmol/L Ca2+ removal strongly increases with the applied voltage, whereas the energy consumption required for 1 mmol/L Mg2+ removal is nearly independent of the applied voltage.