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Study on cathode scaling and descaling methods

Views:5     Author:Site Editor     Publish Time: 2021-09-03      Origin:Site

A key problem in the practical application of electrolytic active chlorine sterilization is cathode fouling. 

During the electrolysis process, the PH of the cathode area increases, resulting in the formation of CaCO3 (Equation 6) and Mg(OH)2 (Equation 7) on the cathode surface.

(6) Ca2++HCO3+OH→ CaCO3+H2

(7) Mg2++2OH → Mg(OH)2 

Even if a thin layer of scale is formed on the cathode surface, the yield of active chlorine will be reduced. 

Household acid disinfection machine price - qinhuangwaterCathode fouling can be removed by continuous rotating brushes or rotating blades, pickling, pulse current, ultrasound, reverse poles and other methods. Rotating brushes or rotating blades are usually used for continuous descaling on the surface of a circular cathode. On-line descaling is timely, but the long-term energy efficiency is low. Pickling usually uses low-concentration hydrochloric acid to regularly clean the cathode surface scale. 

The method is simple but there is a problem of post-treatment of the hydrochloric acid waste liquid, and the pulse current usually produces a large number of bubbles. Reverse is currently the best automated in-situ descaling method. During the inversion process, the previously fouled cathode serves as the anode to continue electrolysis, the pH value of the nearby area decreases, and the cathode fouling layer is dissolved (Equations 8 and 9), and finally the cathode descaling is achieved.

(8) CaCO3+2H+ → Ca2++CO2+H2

(9) Mg(OH)2+2H+ → Mg2++2H2

Inverted poles will significantly affect the catalytic activity of the electrode. 

A.Kraft et al. studied the influence of the inversion on the activity of Ti/IrO2 and Pt/Ti electrodes, and found that: after the Pt/Ti electrode was inverted, the yield of active chlorine generated by electrolysis increased instantaneously, and then dropped rapidly and stabilized. 

After the Ti/IrO2 electrode was reversed, the initial yield of active chlorine produced by electrolysis was very low, and then slowly increased and stabilized, but it was lower than the yield before the reversed electrode. The Pt/Ti electrode has good redox reversibility and is reproducible during the reversed pole process, and the catalytic activity is less affected by the reversed pole. The oxidation-reduction reversibility of the Ti/IrO2 electrode is relatively poor, and it is impossible to completely oxidize and regenerate when the electrode is reversed, and its catalytic activity is relatively greatly affected by the reverse electrode.

When selecting electrode materials, in addition to considering electrode activity, it is also necessary to consider electrode life. Inverted poles will shorten the electrode life, especially for Ti/IrO2, Ti/RuO2, Ti/IrO2-RuO2 electrodes with poor redox reversibility. The rapid rise of the cell voltage indicates that the active film on the surface of the electrode material is completely peeled off, that is, the electrode fails. 

A. Kraft et al.’s research results show that Ti/RuO2 electrodes have the shortest lifespan, followed by Ti/IrO2 electrodes (3 months), and Ti/IrO2-RuO2 electrodes have a longer life, about 1 year; Pt/Ti electrodes It has the longest lifespan. It has been running stably for 8 years under the same operating conditions without obvious attenuation. This is mainly because the redox reversibility of metal Pt is better.

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