高盐环境下Cr(VI)/亚硫酸盐体系氧化降解效能研究

鉴于亚硫酸盐处理含Cr(VI)废水时会产生氧化性极强的硫酸根自由基和羟基自由基，使得亚硫酸盐的消耗量增加，为提高亚硫酸盐的利用率并将产生的活性自由基加以利用，选取了常见的偶氮染料酸性橙7(AO7)作为目标有机污染物用以捕获产生的活性自由基，以达到含Cr(VI)废水和有机污染废水协同处理的目的。通过紫外可见吸收光谱法和显色法测定AO7、Cr(VI)和亚硫酸盐等各反应物的浓度变化，采用自由基捕获方法鉴定反应中的活性氧化物种。结果表明，Cr(VI)/亚硫酸盐体系能够在降解AO7的同时，将Cr(VI)转化为Cr(III), S(IV)氧化为硫酸根离子。在Na2SO3]0=0.5 mM、Cr6+]0=0.1 mM、pH=3.0条件下，Cr(VI)/亚硫酸盐体系对AO7的降解效果最好，反应60 min后，AO7降解率和Cr(VI)的还原率分别为86.1%和82.0%，且氯离子的加入几乎无影响。在反应体系中加入0.1 mM乙醇或叔丁醇后，AO7的降解受到不同程度影响，在Cl?= 0/300 mM条件下，AO7的降解率分别变为56.6%/71.7%和80.7%/81.5%，证明该体系中的主要氧化物为SO4?? 和?OH，且起主要作用的是SO4??。AO7降解实验、可吸附卤代物(AOX)和气相色谱-质谱联用(GC-MS)结果表明，Cr(VI)/亚硫酸盐体系在高盐环境下能保持较高的降解效率，且不会增加氯代二次产物的生成，这种新型的氧化降解体系有望在高盐工业废水处理中得到应用。

Potential of Chromium(VI)/Sulfite for Treating Highly Saline Wastewater

When wastewater containing Cr(VI) is treated with sulfite, the sulfate and hydroxyl radicals are generated, increasing sulfite consumption. In this study, a common azo dye acid, Orange 7 (AO7), was selected as a representative organic pollutant. The research objective was to improve the utilization of sulfite and increase free radical effectiveness. The factors affecting the degradation efficiency of AO7 in the Cr(VI)/sulfite system were investigated and a detailed mechanism for simultaneous degradation of Cr(VI) and organics was proposed. Changes in the concentrations of AO7, Cr(VI) and sulfite were quantified by UV-Vis spectroscopy. The reactive oxygen species (ROS) were identified with radical scavenging experiments. Results show that the Cr(VI)/sulfite system effectively degraded AO7 in aqueous solution and simultaneously converted hexavalent chromium Cr(VI) to trivalent chromium Cr(III) and sulfite, S(IV), to sulfate, S(VI). The degradation efficiency of AO7 was optimal at Na2SO3]0=0.5 mM, Cr6+]0=0.1 mM and pH=3.0; after 1 hr, 86.1% of the AO7 had been degraded and 82.9% of the Cr(VI) had been reduced. Further, chloride had little effect on the conversion rates of AO7, S(IV) or Cr(VI). The addition of ethanol and t-butanol had different effects on the Cr(VI)/sulfite system. In the absence of Cl?, the degradation extent of AO7 was 56.6% with ethanol and 80.7% with t-butanol and, at Cl? = 300 mM, the AO7 respective degradation rates were 71.7% and 81.5%. This indicates that SO4?- and ?OH, together with other unidentified oxidants, are responsible for degrading AO7. The absorbed organic halogen (AOX) content did not significantly increase in the presence of chloride. No secondary chlorinated byproducts in the Cr(VI)/sulfite/Cl- system were detected by gas chromatography-mass spectrometry (GC-MS) after 60 min. This system displays good degradation efficiency, is unaffected by high concentrations of chloride and does not lead to the formation of chlorinated by-products. Further, the simultaneous conversion of Cr(VI), sulfite and organics is highly desirable. These characteristics indicate that the Cr(VI)/sulfite system has excellent potential for treating saline industrial wastewater.