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作为重要的化工原材料,三氯乙烯(trichloroethylene)应用于金属脱脂、干洗、化工产品原料以及药品生产加工等过程[1]。尽管企业严格控制TCE的使用和处置,但仍存在由于使用管理和废物排放不当或容器泄露等事件引起土壤和地下水的污染。TCE具有粘度低、水溶性差和密度大等特性[2],能够轻易地穿透土壤并迁移至地下水中,在土壤和地下水中长期赋存,进而对环境和人类健康造成持续危害[3]。
近年来,表面活性剂增溶-化学氧化联合修复技术被广泛应用于受有机物污染的地下水治理中,其原理主要是将表面活性剂注入污染区域,通过表面活性剂的增溶作用,使有机污染物溶解到水相中,之后在原位或抽出至地面上通过化学氧化去除污染物[4]。当表面活性剂在水溶液中的浓度大于其临界胶束浓度(critical micellar concentration)时,表面活性剂会形成胶束包裹污染物,发挥其增溶作用[5]。表面活性剂主要分为阴离子、阳离子和非离子型[6],在实际应用中,非离子表面活性剂吐温-80(Tween-80)使用频率较高,因此,本研究选择TW-80作为表面活性剂的代表。目前在污染地下水化学氧化修复技术中常用的氧化剂主要有过一硫酸盐(peroxymonosulfate)、过二硫酸盐(persulfate)和过氧化氢(hydrogen peroxide)等。其中,PMS凭借其不对称结构和高于PDS和H2O2过氧化物键能而展现出更强的氧化能力[7]。在热、紫外、过渡金属或碱等活化方式下,PMS能够生成硫酸根自由基(SO4–·)、羟基自由基(HO·)和超氧自由基(O2–·),进而氧化降解氯代烃和多环芳烃等有机污染物[8]。铁作为廉价的过渡金属常被用作活化剂[9],其中Fe(Ⅱ)能快速活化PMS,产生大量的自由基。但随着反应的进行,Fe(Ⅱ)不断被消耗并转化为Fe(Ⅲ),且以氢氧化物的形式沉淀析出[10],导致反应体系催化性能下降。为了进一步提高体系氧化效率,需要将Fe(Ⅲ)及时还原为Fe(Ⅱ),促进反应过程中Fe(Ⅱ)/Fe(Ⅲ)循环。因此,本研究使用硫化亚铁(ferrous sulfide)作为催化PMS的手段,其中FeS不仅能够提供Fe(Ⅱ),而且可以将反应中生成的Fe(Ⅲ)还原为Fe(Ⅱ),反应过程如式(1)~(4)所示[11]。
目前为止,关于FeS活化PMS降解含表面活性剂水溶液中TCE的研究尚鲜有报道。本研究选择PMS作为氧化剂、FeS作为活化剂、TCE作为污染物、TW-80作为表面活性剂,研究了PMS/FeS体系对含有TW-80水溶液中TCE的降解效果,考察了PMS和FeS投加量、溶液初始pH和无机阴离子对PMS/FeS体系中TCE降解效果的影响,探究了PMS/FeS体系在反应过程中产生的自由基种类以及TCE降解的机制,并在实际地下水中验证PMS/FeS体系对TCE的降解效果,以期为该技术在实际工程中的应用提供参考。
硫化亚铁活化过一硫酸盐降解含表面活性剂水溶液中三氯乙烯的效果与机制
Degradation of trichloroethene in water solution containing surfactant by peroxymonosulfate activated by ferrous sulfide
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摘要: 采用硫化亚铁(FeS)活化过一硫酸盐(PMS)降解含表面活性剂吐温-80(TW-80)水溶液中的三氯乙烯(TCE),考察了PMS和FeS投加量、TW-80浓度、溶液初始pH、无机阴离子(Cl–和HCO3–)对TCE降解的影响,确定了PMS/FeS体系中的主导自由基及TCE降解机理,验证了PMS/FeS体系处理实际地下水中含TW-80的TCE效果。结果表明:增加PMS或FeS投加量有利于TCE的降解,但当其投加剂量分别超过0.8 mmol·L–1和0.6 g·L–1时,TCE降解反而受到抑制,且TCE的降解率随TW-80浓度的增加而下降;PMS/FeS体系对pH有较宽的适用范围,在pH=11时受到抑制,Cl–和HCO3–对TCE降解有抑制作用;通过自由基淬灭实验和电子顺磁共振实验确定了SO4–·、HO·和O2–·是PMS/FeS体系中的主导自由基;相比于其他氯代烃,该体系对四氯乙烯和四氯化碳也有较好的降解效果;实际地下水的处理结果证实PMS/FeS体系在实际应用中具有潜力和优势。Abstract: Ferrous sulfide (FeS) was used to activate peroxymonosulfate (PMS) for trichloroethylene (TCE) degradation in solution containing Tween-80 (TW-80). The effects of PMS and FeS doses, the initial solution pH, inorganic anions (Cl– and HCO3–) on TCE degradation were investigated. The main reactive radicals generated in PMS/FeS system were determined and TCE degradation mechanisms were revealed. The degradation performance of TCE in actual groundwater containing TW-80 was verified by PMS/FeS process. The experimental results showed that the increase of PMS or FeS dosage was favorable to TCE removal, while TCE degradation was inhibited at PMS dose over 0.8 mmol·L–1 or FeS dose over 0.6 g·L–1. In addition, TCE degradation rate decreased with the increase of TW-80 concentration. PMS/FeS system performed well in a wide pH range, but its effect was seriously inhibited at pH = 11. Both Cl– and HCO3– had inhibitive effects on TCE removal. SO4–·, HO· and O2–· were identified as the main reactive radicals in PMS/FeS system by radical scavenging tests and electron paramagnetic resonance detection. Compared with other chlorinated hydrocarbons, PMS/FeS had a better performance on perchloroethylene and carbon tetrachloride degradation. Finally, the test results using actual groundwater demonstrated that PMS/FeS system had a great application potential in actual groundwater remediation.
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Key words:
- trichloroethylene /
- surfactants /
- peroxymonosulfate /
- ferrous sulfide /
- groundwater remediation
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表 1 不同溶液初始pH对TCE降解率的影响
Table 1. Effect of different initial solution pH on TCE degradation
反应前pH 反应后pH TCE降解率/% 3.06 2.69 91.5 5.02 2.76 90.0 7.01 2.86 89.5 9.05 2.88 90.7 11.03 2.93 79.8 表 2 实际地下水试验中反应前后溶液pH变化
Table 2. Change of pH values before and after reactions in actual groundwater tests
PMS(mmol·L−1) FeS(g·L−1) 反应前pH 反应后pH 0.8 0.6 7.49(未调节) 6.45 1.6 1.2 7.48(未调节) 5.97 3.2 2.4 7.49(未调节) 3.22 0.8 0.6 3.04(调节后) 2.82 1.6 1.2 3.05(调节后) 2.73 3.2 2.4 3.02(调节后) 2.54 -
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