Polarity reversal electrochemical process for water softening

Abstract

• Polarity reversal has been tested for scale detachment in the electrochemical water softening process. • Effective scale detachment was achieved. • High softening efficiency and low energy consumption could be obtained stably. • The DSA used could keep active steadily in polarity reversal condition. Electrochemical precipitation has attracted widespread attention in the treatment of recirculating cooling water in recent years. In order to guarantee continuous water softening efficiency, periodic scale detachment of cathode is indispensable. Nevertheless, periodic mechanical scrapping, prevalent scale detachment technique currently, increases the interelectrode gap, resulting in the decline of water softening efficiency and the rise of energy consumption. In this paper, polarity reversal was applied in the electrochemical precipitation process for removing scale deposits. The results showed that scale deposits were removed effectively and high water softening efficiency were accomplished steadily. The precipitation rate obtained was 53.9–73.4 g/h/m 2 . The reactor still could remove hardness ions efficiently after the scale detachment by polarity reversal. The energy consumption maintained in the range of 17.3–23.6 kWh/kg CaCO 3 . The total hardness removal efficiency was 16.4–21.4%. Repeated experimental results demonstrated that the electrochemical precipitation process adopting polarity reversal for scale detachment could operate steadily without any performance degradation detected. Cyclic voltammetric investigation showed good electrochemical stability of dimensionally stable anode (DSA) used. Accelerated life test indicated that it could keep active steadily in polarity reversal condition.