Investigations On Electro-oxidation Preparation Of Chlorine Dioxide Solution

Chlorine dioxide is a strong oxidant, which is also internationally recognized asthe new generation of green disinfectant, due to advantages of high efficiency,broad-spectrum, safe and non-toxicity for all the microorganisms, including bacteria,viruses, fungi, etc. It has been used widely in disinfection of industrial wastewater anddrinking water, air sterilization, food preservation, pulp bleaching, oil blocking andother fields. Chlorine dioxide has been listed as grade A1, safe and efficientdisinfectant by World Health Organization （WHO） and Food and AgricultureOrganization （FAO）.Several chemical methods are normally involved in the generation of chlorinedioxide by reducing acid solutions of chlorate with a reducing agent, such as,methanol, hydrogen peroxide, sulfur dioxide, etc. However, chemical preparationprocesses have the drawbacks of low purity of chlorine dioxide, high cost forstabilizing the product and difficulty in control the formation reaction, etc. So theapplication is limited. Electrochemical methods for chlorine dioxide generation havebeen considered more suitable, because the electrochemical processes do not need theuse of any chemical activators, and do not generate any unique impurities orby-products, since “electron”, a clean reagent, is used to achieve oxidation andreduction. In this paper, we used the Pb₂/Ti electrode as the working electrode,homebred anion exchange membrane as a diaphragm, and soluble salt as supportingelectrolyte to electrolyze the sodium chlorite. The saturated solution of sodiumchlorite was employed as purification agent, and ultra-pure water solution was used toabsorb chlorine dioxide for obtaining high purity chlorine dioxide solution. The electrolytic method in this study is rarely reported. The specific contents are asfollows:In the first part, a method for the spectrophotometric determination of chlorinedioxide was developed based on the oxidation of Rhodamine B by chlorine dioxide.In NH₃–NH₄Cl buffer solution （pH=10）, effects of the dosage of rhodamine B andbuffer solution, reaction time, order of adding reagents and other factors on thedetermination of chlorine dioxide were investigated in detail. The optimal conditionsfor measurement were selected. The linear concentration range of chlorine dioxide is0.0⁴.0mg/L. The method exhibited a wide linear range, high sensitivity andselectivity in determination of chlorine dioxide, which can be used for quantitativedetection of chlorine dioxide.In the second part, effects of the concentration of sodium chlorite and sulfatesupporting electrolyte, as well as the electrode materials on preparation of chlorinedioxide via electro-oxidation method were studied by cyclic voltammetry. Preliminaryidentification of factors, such as anodic potential, electrolytic quantity and electrolytictemperature that influenced electro-oxidation of chlorine dioxide, were carried out bypotentiostatic experiment.In the third part, four factors and three levels orthogonal experiment wasdesigned by using the Pb₂/Ti as the working electrode. The influences of sodiumchlorite concentration, soluble salt concentration, anodic potential and electrolyticquantity on the current efficiency for electro-oxidation preparation of chlorine dioxidewere investigated. The optimal electrolytic parameters were determined. Under theoptimum reaction conditions, the current efficiency of preparation of chlorine dioxidefrom sodium chlorite by constant potential electrolysis was up to90.56%. Theelectro-oxidation experiment at constant concentration of reactants was also studied atmeantime. The current efficiency was basically maintained at about80%when theelectrolytic quantity reached40%.In the fourth part, the bactericidal efficacy of chlorine dioxide on sulfatereducing bacteria was studied. The minimal concentration of chlorine dioxide forsterilization of sulfate reducing bacteria was determination. The experimental results showed that the sterilization rate reached100%when0.98mg/L of chlorine dioxidewas used to sterilize sulfate reducing bacteria. Therefore, chlorine dioxide has strongkilling ability on sulfate reducing bacteria.