Study On The Factors Of Reduction Cr(Ⅵ) In Waste Water By Direct Electrichamical Method And The Process Characterization Using ORP Electrode

In this study, the feasibility of reduction hexavalent chromium using direct electrichamical method through constant current and constant potential ways under different original concentrations and pH values was investigated. ORP electrode was used to analysed the effect of Cr(Ⅵ) concentration and pH values in liquid, and ORP was used to analyse the process of electrolysis. A electrochemical reactor was designed and used for practical research in reduction process. Electrode distance, group number, other metal ions was investigatigated for the effect to reduction process.The results show that:1. In acid condition, it was avaible to reduction Cr(Ⅵ) in simulated wast water by constant current treatment way. The results showed that at low concentration Cr(Vl) u. v-absorbency at 350nm accorded with Lambert-Beer Law, and the profile of Cr(Ⅵ) degradation was almost linearity, so a relation between degradation rate and ratio in 60min, rate/ratio efficiency coefficientΓ, deduced from experiment could replace instantaneous current efficiency and average current efficiency for analysis. Cr(Ⅵ)'s reaction control condition could be divided into three intervals. From 0.2 mA/cm~2 to 1.0mA/cm~2 current controlled reaction model ICE=1 andΓwas maximum and constant corresponding. From 1.0mA/cm~2 to 2.0mA/cm~2 ICE<1, the condition changed to convective mass transfer andΓ/i was hyperbola. From 2.0mA/cm~2 to 15.0 mA/cm~2, ICE<1, current produced micro-bubble strengthened convection, synchronouslyΓ/i changed smoothly and had limit value.2. The equations from curves of Cr(Ⅵ) reduction can be rate equations of first order reaction formation approximately in constant potential treatment way. Both constant current and potential treatment way were all that the lower pH was the more reduction rate was gotten. And the hole process was pH indicator consumption. In low Cr(Ⅵ) concentration, degradation rate curves accorded with the first order formation.3. The experiment showed that ORP electrode can be used to characterize Nernst relation between Oxidation and Redox Potential and Cr(Ⅵ) concentration and pH values. It can explain the reason of pH and reduction rate. However, because of hydrogen separated out, ORP dropped value in first 1min can described electrochemical efficiency. And it can provide proper controlling information for saving energy.4. The experiment of reactor showed that for the purpose of the minimum of energy consumption, 0.5cm electrode distance, 3 group numbers, the result was proper. Surrounding effective ions experiment showed that ferric ion and cupric ion can improve electrolysis based on different operation mechanism, and zinc ion effect had no been detected.