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印制电路板行业在生产印制电路板(PCB)过程中涉及大量有机溶剂、醚类有机物以及表面活性剂等,产生的废液中包含的有机污染物组成复杂、浓度高、毒性大且难以降解[1-2]。目前,企业针对高浓度难降解PCB有机废液的处理方法主要是Fenton氧化法,但该方法存在有机物降解不彻底、Fenton试剂不能循环利用且处理费用高等问题。因此,急需寻找高效、安全且低成本的处理技术来对该类废液进行治理。
高级氧化工艺(AOP)主要包括Fenton/photo-Fenton[3-4]、湿法氧化[5-6]、光催化氧化[7-8]以及臭氧氧化[9-10]等技术。其中,催化臭氧氧化技术克服了臭氧氧化法中存在的不足,能在常温常压下高效降解大部分有机污染物且无二次污染[11-14],从而备受关注。大部分研究[15-17]表明,催化剂的加入会促进活性自由基的产生。其中,羟基自由基( · OH)是催化臭氧氧化过程的主要活性自由基,对有机物的降解起关键性作用。目前,使用较为广泛的是非均相催化剂,主要包括金属和金属氧化物负载、金属氧化物,活性炭以及其他多孔材料等[18-19]。金属氧化物催化剂(如MnO2[20-21]、MgO[22-24]、ZnO[25-26]、TiO2[27-28]、Al2O3[29-30]和CeO2[31]等)、金属氧化物载体的材料(如Al2O3[32]、TiO2[33]等)、多孔材料载体(如石墨烯[34]、碳纳米管[35]等)都已经用于催化臭氧氧化过程,并且已经被证明具有良好的催化活性。然而,很多催化剂在制备及应用时存在一些缺点,如制备工艺复杂、成本较高、重复利用率低等,这些因素限制了催化臭氧氧化技术在实际高浓度难降解工业废液的应用。在催化臭氧化过程中,氧化钙(CaO)很少用于催化臭氧化过程;但初步实验表明,CaO结合臭氧氧化法,在处理实际工业废液中有机污染物时具有很大的优势,并且CaO具有活性高、成本低、毒性低、pH稳定性好和环境友好的特点,因此,将其应用于催化臭氧氧化过程有良好的发展前景[36]。
本研究探讨了PCB废液降解过程中的催化降解机理以及有机物降解途径,考察了催化剂的循环稳定性并分析催化剂失活的可能原因;通过单纯形优化实验考察了CaO在PCB废液的臭氧氧化过程中的催化性能,包括CaO质量、pH、臭氧浓度、降解时间和废液深度对废液中有机物降解率的影响;最后,将CaO催化臭氧过程应用于实际高浓度难降解废水并探讨其应用潜能,为实际工业废水的处理提供参考。
催化臭氧氧化降解PCB有机废液及其机理
Performance and mechanism of PCB organic effluents degradation by catalytic ozonation
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摘要: 为了高效、快速治理高浓度难降解PCB(printed circuit board)有机废液,研究了氧化钙非均相催化臭氧氧化降解PCB废液的催化机理和催化性能。采用叔丁醇淬灭自由基实验和水杨酸羟基化实验探究催化机理;通过GC/MS研究了PCB废液中有机物可能降解途径;通过单纯形优化法对实验因素进行优化,并通过XRD和BET探究催化剂的循环稳定性。结果表明:氧化钙非均相催化臭氧氧化过程遵循羟基自由基机理;在pH为12.97、CaO质量为1.0 g、废液深度为11 cm、降解时间为150 min、臭氧用量为120 mg·min−1时,COD去除率可达到90.045%;氧化钙经过5次循环后,废液的COD去除率没有显著降低,从92.78%降低至84.04%。CaO应用于催化臭氧氧化过程处理高浓度且难降解的PCB废液,能维持良好的催化性能和循环稳定性,具有良好的应用前景。Abstract: In order to high efficiently and rapidly treat refractory organic effluent generated during manufacturing printed circuit boards (PCB) with high concentration, the performance and mechanism of PCB organic effluents degradation by heterogeneously catalytic ozonation with CaO were studied. The catalytic mechanism was investigated by radical quenching test with tert-butanol and hydroxylation test of salicylic acid. The possible degradation pathway of organic matter was studied by GC/MS. The experimental factors were optimized by simplex optimization method, and the cycle stability of the catalyst was explored by XRD and BET. The results showed that the catalytic ozonation process in the presence of calcium oxide followed hydroxyl radicals mechanism. The COD removal efficiency could reach 90.045% at the pH of 12.97, CaO mass of 1.0 g, the solution height of 11 cm, the degradation time of 150 min, and the ozone dosage of 120 mg·min−1. After five cycles, the COD removal ratio of organic matter decreases insignificantly, which changes from 92.78% to 84.04%. CaO can maintain a good catalytic performance and recycle stability during treating refractory organic industrial wastewater with high concentration, which confirms its good prospect in this field.
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Key words:
- catalytic ozonation /
- calcium oxide /
- PCB effluents /
- hydroxyl radicals
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表 1 2,3-DHBA和2,5-DHBA不同时间的含量
Table 1. Contents of 2,3-DHBA and 2,5-DHBA at different times
降解时间/min 2,3-DHBA浓度/(mg·L−1) 2,5-DHBA浓度/(mg·L−1) 4 0.037 3 0.015 5 8 0.022 1 0.014 4 12 0.020 0 0.013 7 表 2 异丙醇降解30 min和60 min的降解产物
Table 2. Products of IPA at 30 min and 60 min degradation
异丙醇降解30 min质谱结果 异丙醇降解60 min质谱结果 保留时间/min 分子式 相对分子质量 相对峰面积/% 保留时间/min 分子式 相对分子质量 相对峰面积/% 2.385 C2H4O2 60.05 46.014 2.278 C2H4O2 60.05 68.57 2.775 C2H8O2Si 92.169 9.246 2.769 C2H8O2Si 92.169 2 11.175 2.865 C3H6O2 74.08 22.436 3.170 C3H8O2 76.09 20.255 3.257 C3H8O2 76.09 22.304 表 3 乙二醇单丁醚降解30 min和60 min的降解产物
Table 3. Products of EB at 30 min and 60 min degradation
乙二醇丁醚降解30 min质谱结果 乙二醇丁醚降解60 min质谱结果 保留时间/min 分子式 相对分子质量 相对峰面积/% 保留时间/min 分子式 相对分子质量 相对峰面积/% 2.184 C4H10O 74.12 7.624 2.329 C2H4O2 60.05 42.980 2.384 C2H4O2 60.05 19.742 2.793 C2H8O2Si 92.169 7.158 2.831 C2H8O2Si 92.169 2 1.453 2.859 (CH2OH)2 62.068 29.959 2.898 (CH2OH)2 62.068 12.649 3.642 C4H8O2 88.105 3.316 3.660 C4H8O2 88.105 1 2.856 4.692 C6H14O2 118.17 12.300 4.605 C6H14O2 118.17 28.126 4.843 C6H14O2 118.17 4.287 4.680 C6H14O2 118.17 25.537 4.854 C4H6O2 86.09 2.013 表 4 因素的初始值和变化值
Table 4. Initial and change values of factors
初始值与变化值 pH CaO质量/g 废液深度/cm 降解时间/min 臭氧用量/(mg·min−1) 初始值 12.0 0 7 60 80 变化值 0.2 1.0 2 20 20 表 5 初始实验条件
Table 5. Initial experimental conditions
实验序号 pH CaO质量/g 废液深度/cm 降解时间/min 臭氧用量/(mg·min−1) 1 12.2 2.0 11 140 200 2 12.4 4.0 13 80 180 3 12.6 6.0 9 160 160 4 12.8 1.0 13 100 140 5 13.0 3.0 9 180 120 6 13.2 5.0 11 120 100 表 6 单纯形优化结果
Table 6. Result of simplex optimization
实验序号 pH CaO质量/g 废液深度/cm 降解时间/min 臭氧用量/
(mg·min−1)COD去除率/% 标准差 0.7η+0.1/t+0.2/m 1 12.2 2.0 11 140 200 66.31 0.987 6 0.607 1 2 12.4 4.0 13 80 180 66.97 0.120 2 0.552 1 3 12.6 6.0 9 160 160 83.21 0.720 8 0.653 3 4 12.8 1.0 13 100 140 64.26 2.716 2 0.709 7 5 13.0 3.0 9 180 120 83.4 1.419 3 0.683 8 6 13.2 5.0 11 120 100 62.36 1.007 0 0.526 5 7 12.2 1.4 11 144 200 67.97 1.689 9 0.660 3 8 12.7 1.36 9 180 150 87.24 1.225 3 0.791 1 9 13.2 3.38 9 172 100 91.81 1.565 4 0.736 7 10 12.9 1.0 11 150 120 90.04 0.431 3 0.870 3 11 13.2 2.77 9 175 100 86.8 0.671 7 0.714 3 12 13.2 1.0 11 130 120 75.72 2.517 3 0.776 2 13 13.2 2.804 9 180 100 88.51 2.026 4 0.724 2 -
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