【作者】 于永海；

【导师】 王栋；

【作者基本信息】 大连理工大学 ， 环境工程， 2008， 硕士

【摘要】 用直接电解法还原模拟含铬废水,选择恒电流法,恒电位法分别对还原Cr(Ⅵ)时的初始浓度,初始pH值等影响因素进行考察,并利用ORP电极对Cr(Ⅵ)浓度,pH值影响进行分析,再利用ORP电极对电解过程进行表征分析,在此基础上设计并利用反应器考察极间距,极板组数和其他金属离子影响,得到如下结果。1.酸性条件下,利用恒电流直接还原模拟废水中的Cr(Ⅵ)。发现,Cr(Ⅵ)还原降解曲线均呈较强线性关系,由此建立模型得到反应速率与60min时的还原降解率的对应关系,并使用模型导出的速率/电流效率系数Γ代替瞬时电流效率和平均电流效率进行分析。认为,Cr(Ⅵ)反应控制条件分为三个区间,从0.2mA/cm~2到1.0mA/cm~2控制条件为电流因素,模型ICE=I,Γ相对最大且较为恒定。1.0mA/cm~2到2.0mA/cm~2,JCE＜1,控制条件转为体相对流传质,Γ/i呈双曲线形。2.0mA/cm~2到15.0mA/cm~2,ICE＜1,控制条件为电解产生气泡间接加强对流传质,Γ/i变化平稳且存在极限。2.恒电位条件下,Cr(Ⅵ)还原降解曲线可以拟合成一级动力学过程。在恒电流和恒电位条件下,pH值越低,相同条件降解率越大,且还原过程为耗酸过程。Cr(Ⅵ)低浓度范围内,还原曲线符合所得到的拟合方程。3.实验发现,ORP电极可用来描述人工配制溶液中ORP值与Cr(Ⅵ)浓度、pH值间的能斯特关系,并跟踪了pH值越低降解率越大的现象和过程。对于电解过程中电极析氢引起的1min内ORP下降值,本研究认为可以表征电解过程电能效率,从而1minORP下降值出发,给出适当调节方案,可以达到节能目的。4.反应器实验考察中,从单位能耗最小的指标考察,得到了极间距0.5cm,电极组数为3组时综合处理效果较好的结果。另外,环境影响离子的实验表明,铁离子和铜离子对电解还原过程有促进作用,但是作用机理可能不同,锌离子对电解还原过程的影响未发现明显效果。更多还原

【Abstract】 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.更多还原