Improvement of electrochemical water softening treatment using activated carbon plates in high hardness and low alkalinity water: Enhancing the electrochemical treatment effect while reducing the corrosiveness of the water

The electrochemical water softening technique has the advantages of environmental friendliness, energy saving, and no secondary pollution. However, the easy scaling on the cathode surface affects its hardness removal efficiency, especially for slag-flushing water with high hardness and low alkalinity. In addition, the impact of electrochemically softened water on metal corrosion behavior is unclear and poses potential safety hazards. In this study, a novel electrochemical water softening reactor with a barrier layer structure was designed. By increasing the pH value of the water solution in the cathode region, the precipitation reaction was transferred from the cathode surface to the solution and barrier layer surfaces. The strong oxidizing substances generated by the anodic reaction were adsorbed through the barrier layer, thereby inhibiting their corrosive effect on carbon steel. Compared with the common electrochemical water softening reactor, the improved reactor has increased the pH in the cathode region from 8.58 to 12, increased the hardness removal efficiency from 5.8 % to 53.6 %, and reduced the corrosion rate of carbon steel from 0.396 mm/a to 0.254 mm/a. The significant increase in pH accelerated the rate of precipitation reactions in solution, increased the particle size of the precipitate, and caused rapid settling of the precipitate particles. The average settling rate of precipitated particles was 0.331 mg/s, much higher than the 0.017 mg/s before the improvement. Meanwhile, the strong oxidizing ions of ClO - were effectively adsorbed by the activated carbon plate, which in turn slowed down the corrosion of carbon steel by electrochemical water softening.