UV/氯降解铜络合物的特性与机理

Performance and mechanism of Cu(Ⅱ)-organic complexes degradation by UV/chlorine advanced oxidation process

本研究选取Cu-EDTA、Cu-NTA、Cu-柠檬酸和Cu-酒石酸4种典型的铜络合物来探讨UV/氯工艺在酸性和中性条件下降解重金属络合污染物的潜力,并以Cu-EDTA为代表物详细考察了[NaClO]0/[Cu]0(物质的量比)、初始溶液pH值和NO3^-、SO4^2-等共存物质对UV/氯破络性能的影响.结果表明,UV/氯对多种铜络合物具有高效的氧化破络能力,可将Cu浓度从初始的19.2 mg·L^-1降至1.0 mg·L^-1以下.在[NaClO]0/[Cu]0为60、初始溶液pH为3.0~5.0的条件下, UV/氯对Cu-EDTA的破络效果较好,Cu和TOC的去除率分别高于95%和70%,但共存的NO3^-、SO4^2-、Ca^2+和NOM对Cu-EDTA的破络有一定抑制作用.自由基捕获实验和竞争动力学研究结果表明,UV/氯通过HO·和Cl·两者的共同作用实现Cu-EDTA破络,在pH=5.0时的贡献分别为60%和40%.产物鉴定结果证明,Cu-EDTA降解为N-C键逐步断裂的脱羧过程,其中,-N-(CH2-COOH)2和-N-CH2-CH2-N-基团上的N-C键断开生成Cu-ED3A和Cu-NTA,分别贡献约80%和20%.UV/氯对实际络合铜废水仍具有良好的处理效果,Cu浓度由初始的20.4 mg·L^-1降至约1.0 mg·L^-1.

The applicability of UV/chlorine advanced oxidation process for the decomplexation of heavy metal complexes was performed using four typical Cu(Ⅱ)-organic complexes including Cu(Ⅱ)-EDTA, Cu(Ⅱ)-NTA, Cu(Ⅱ)-citrate and Cu(Ⅱ)-tartrate under acidic and neutral pH. As well, the effects of the molar ratio of initial NaClO to initial Cu([NaClO]0/[Cu]0), initial solution pH and co-existing matters(e.g., NO-3 and SO■) on the process were systematically investigated using Cu(Ⅱ)-EDTA as a representative compound. The results indicated that those Cu(Ⅱ)-organic complexes can be efficiently destructed by UV/chlorine, with the residual Cu(Ⅱ) below 1.0 mg·L-1 from 19.2 mg·L^-1. Efficient decomplexation of Cu(Ⅱ)-EDTA was achieved by UV/chlorine, with higher than 95% of Cu(Ⅱ) removal and 70% of TOC elimination, at the [NaClO]0/[Cu]0 of 60 and initial solution pH of 3.0~5.0. However, the efficiency was slightly inhibited by the co-existing matters of NO-3, SO■, Ca2+ and NOM. The radical scavenging and competitive kinetics experiments proved that the degradation of Cu(Ⅱ)-EDTA was attributed to the combined oxidation by HO· and Cl·, and their relative contributions at pH 5.0 were about 60% and 40%, respectively. Based on the analysis of degradation products using HPLC, a decarboxylation process through stepwise cleavage of N—C bond was found to be responsible for the degradation of Cu-EDTA, wherein the separate cleavage of N—C bond from —N—(CH2—COOH)2 to form Cu-ED3 A and —N—CH2—CH2—N— to Cu-NTA contributed about 80% and 20% to the overall process. Efficient removal of Cu(Ⅱ) from a realistic electroplating effluent was also achieved using UV/chlorine method, with the residual Cu(Ⅱ) concentration decreasing to 1.0 mg·L^-1 from 20.4 mg·L^-1.