冻融-化学淋洗法协同修复重金属Cd和Pb污染黏性土
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摘要
针对质地黏重、低渗透性黏性土的淋洗效率低下,该文提出冻融协同化学淋洗的修复方案,并以某冶炼厂受Cd、Pb污染场地黏性土为研究对象,选用乙二胺四乙酸二钠(ethylene diaminetetraacetic acid disodium salt,EDTA)为淋洗剂,进行了冻融-淋洗土柱的实证试验。结果表明,土体的反复冻融(冻胀-吸水、融沉-排水)破坏土体颗粒原有结构,有助于淋洗液与污染物充分接触,淋洗效果明显,经7次冻融后,Cd、Pb去除率分别达到77.24%、37.78%。采用改进的BCR(European Communities Bureau of Reference)连续提取法分析了土柱中Cd、Pb的赋存特征,经7次冻融后,土壤中弱酸提取态、可还原态、残渣态结合的Cd质量分数较淋洗前分别降低了41.46%、63.02%、26.33%,而土壤中可还原态和残渣态结合的Pb质量分数分别降低了32.32%、67.36%。冻融协同化学淋洗修复技术的淋洗剂用量远小于传统淋洗法,为今后利用寒区冻融交替现象,大规模对季冻区重金属污染土壤的异位修复提供了新的思路。
Contamination of heavy metals in agricultural soil has been a worldwide challenge for the food security and the health. Especially, cadmium and lead contamination in soil is a serious problem in China. Therefore, it is imperative to develop remediation techniques, which are able to removal contaminants in a high efficient and cost effective way. Now, the traditional washing method is used for soil remediation on account of its' high efficiency and simple operation. However, the efficiency of traditional washing method is limited by permeability of soils, so this method can only repair a small range of heavy metal contaminated soil, which cannot be produced on a large scale, and the removal effect of the clay soil is generally poor. In order to solve the problem of low washing efficiency resulted from heavy texture and low permeability in clay soil, a cooperative remediation by freeze-thaw and chemical washing method was proposed. In this paper, taking Cd and Pb contaminated soil in a smelter as the research object, the empirical tests of freeze-thaw and washing(FTW) soil columns were conducted with 0.1 mol/L EDTA(ethylene diaminetetraacetic acid disodium salt). The results show that repeated freezing and thawing(frost heave-water absorption, thaw settlement-drainage) of soil destroys the original cohesive force and soil skeleton structure between the soil particles, so that the soil particles were rearranged, which was contributed to the fully contact with the eluent and contaminants. After the freeze-thaw and soil washing tests, the washing effect was significantly improved. The removal rates of Cd in FTW3(FTW treatment with 3 freeze-thaw cycle; adding EDTA at 1 st and 3 rd cycle), FTW5(FTW treatment with 5 freeze-thaw cycle; adding EDTA at 1 st and 2 nd cycle) and FTW7(FTW treatment with 7 freeze-thaw cycle; adding EDTA at 1 st to 3 rd cycle) groups were 9.05%, 64.90% and 77.24% respectively, and the removal rates of Pb in FTW3, FTW5 and FTW7 groups were 2.06%, 14.42% and 37.78%, respectively. The morphology of heavy metals at different depths in the soil column after washing were analyzed by the three-stage continuous extraction method(BCR method) proposed by the European Community Bureau of Reference. The weak acid extracted Cd increased by 20.76%, the average Cd of reducible state decreased by 41.58%, and the residual Cd increased by 193.45% in FTW3. The weak acid extracted Cd decreased by 0.39%, the average Cd of reducible state decreased by 45.75%, and the residual Cd increased by 43.73% in FTW5. The results showed that the weak acid extracted Cd decreased by 41.46%, the average Cd of the reducible state decreased by 63.02%, and the residual Cd decreased by 26.33% in FTW7. And the average Pb of reducible state increased by 11.23%, the average Pb of oxidizable state decreased by 63.12%, and the residual Pb increased by 53.97% in FTW3. The average Pb of reducible state decreased by 0.12%, the average Pb of oxidizable state decreased by 64.13%, and the residual Pb increased by 30.68% in FTW5. The average Pb of reducible state decreased by 32.32%, the average Pb of oxidizable state decreased by 62.05%, and the residual Pb decreased by 67.36% in FTW7. Moreover, the freeze-thaw and washing method has a lower ratio of liquid to soil, the ratio of liquid to soil were 0.32, 0.47 and 0.62, respectively, so that the amount of eluent was much smaller than that of the traditional washing method. Besides, through this study, it provides a method for the ex-situ remediation of heavy metal-contaminated soil in seasonally frozen areas by using the phenomenon of freeze-thaw alternation in cold regions in the future.
Contamination of heavy metals in agricultural soil has been a worldwide challenge for the food security and the health. Especially, cadmium and lead contamination in soil is a serious problem in China. Therefore, it is imperative to develop remediation techniques, which are able to removal contaminants in a high efficient and cost effective way. Now, the traditional washing method is used for soil remediation on account of its' high efficiency and simple operation. However, the efficiency of traditional washing method is limited by permeability of soils, so this method can only repair a small range of heavy metal contaminated soil, which cannot be produced on a large scale, and the removal effect of the clay soil is generally poor. In order to solve the problem of low washing efficiency resulted from heavy texture and low permeability in clay soil, a cooperative remediation by freeze-thaw and chemical washing method was proposed. In this paper, taking Cd and Pb contaminated soil in a smelter as the research object, the empirical tests of freeze-thaw and washing(FTW) soil columns were conducted with 0.1 mol/L EDTA(ethylene diaminetetraacetic acid disodium salt). The results show that repeated freezing and thawing(frost heave-water absorption, thaw settlement-drainage) of soil destroys the original cohesive force and soil skeleton structure between the soil particles, so that the soil particles were rearranged, which was contributed to the fully contact with the eluent and contaminants. After the freeze-thaw and soil washing tests, the washing effect was significantly improved. The removal rates of Cd in FTW3(FTW treatment with 3 freeze-thaw cycle; adding EDTA at 1 st and 3 rd cycle), FTW5(FTW treatment with 5 freeze-thaw cycle; adding EDTA at 1 st and 2 nd cycle) and FTW7(FTW treatment with 7 freeze-thaw cycle; adding EDTA at 1 st to 3 rd cycle) groups were 9.05%, 64.90% and 77.24% respectively, and the removal rates of Pb in FTW3, FTW5 and FTW7 groups were 2.06%, 14.42% and 37.78%, respectively. The morphology of heavy metals at different depths in the soil column after washing were analyzed by the three-stage continuous extraction method(BCR method) proposed by the European Community Bureau of Reference. The weak acid extracted Cd increased by 20.76%, the average Cd of reducible state decreased by 41.58%, and the residual Cd increased by 193.45% in FTW3. The weak acid extracted Cd decreased by 0.39%, the average Cd of reducible state decreased by 45.75%, and the residual Cd increased by 43.73% in FTW5. The results showed that the weak acid extracted Cd decreased by 41.46%, the average Cd of the reducible state decreased by 63.02%, and the residual Cd decreased by 26.33% in FTW7. And the average Pb of reducible state increased by 11.23%, the average Pb of oxidizable state decreased by 63.12%, and the residual Pb increased by 53.97% in FTW3. The average Pb of reducible state decreased by 0.12%, the average Pb of oxidizable state decreased by 64.13%, and the residual Pb increased by 30.68% in FTW5. The average Pb of reducible state decreased by 32.32%, the average Pb of oxidizable state decreased by 62.05%, and the residual Pb decreased by 67.36% in FTW7. Moreover, the freeze-thaw and washing method has a lower ratio of liquid to soil, the ratio of liquid to soil were 0.32, 0.47 and 0.62, respectively, so that the amount of eluent was much smaller than that of the traditional washing method. Besides, through this study, it provides a method for the ex-situ remediation of heavy metal-contaminated soil in seasonally frozen areas by using the phenomenon of freeze-thaw alternation in cold regions in the future.
引文
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[2]王金霞,李谢玲,何清明,等.三峡库区典型农业区土壤重金属污染特征及风险评价[J].农业工程学报,2018,34(8):227-234.Wang Jinxia,Li Xieling,He Qingming,et al.Characterization and risk assessment of heavy metal pollution in agricultural soils in Three Gorge Reservoir Area[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2018,34(8):227-234.(in Chinese with English abstract)
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[15]Semer R,Reddy K R.Evaluation of soil washing process to remove mixed contaminants from a sandy loam[J].Journal of Hazardous Materials,1996,45(1):45-57.
[16]温智,盛煜,马巍,等.退化性多年冻土地区公路路基地温和变形规律[J].岩石力学与工程学报,2009,28(7):1477-1483.Wen Zhi,Sheng Yu,Ma Wei,et al.Ground temperature and deformation laws of highway embankments in degenerative permafrost regions[J].Chinese Journal of Rock Mechanics and Engineering,2009,28(7):1477-1483.(in Chinese with English abstract)
[17]王铁行.多年冻土地区路基冻胀变形分析[J].中国公路学报,2005,18(2):1-5.Wang Tiehang.Analysis of frost heave on subgrade in permafrost regions[J].China Journal of Highway and Transport,2005,18(2):1-5.(in Chinese with English abstract)
[18]Eigenbrod K D.Effects of cyclic freezing and thawing on volume changes and permeabilities of soft fine-grained soils[J].Canadian Geotechnical Journal,1996,33(4):529-537.
[19]Qi J,Wei M,Song C.Influence of freeze-thaw on engineering properties of a silty soil[J].Cold Regions Science&Technology,2008,53(3):397-404.
[20]国家质量技术监督局.中华人民共和国国家标准.土工试验方法标准[M].北京:中国计划出版社,1999.
[21]Takashi T,Ohrai T,Yamamoto H.Decrease of frost heave amount by increasing the viscosity of pore water[J].Journal of Geotechnical Engineering,1980,298:77-85.
[22]陈晓婷,王欣,陈新.几种螯合剂对污染土壤的重金属提取效率的研究[J].环境科技,2005,18(2):9-10.Chen Xiaoting,Wang Xin,Chen Xin.Study on the exaction efficiency of heavy metals by chelates[J].Jiangsu Environmental Science and Technology,2005,18(2):9-10.(in Chinese with English abstract)
[23]Andrade M D,Prasher S O,Hendershot W H.Optimizing the molarity of a EDTA washing solution for saturated soil remediation of trace metal contaminated soils[J].Environmental Pollution,2007,147(3):781-790.
[24]Mulligan C N,Yong R N,Gibbs B F.Remediation technologies for metal-contaminated soils and groundwater:An evaluation[J].Engineering Geology,2001,60(1):193-207.
[25]王洋,刘景双,王国平,等.冻融频次与含水量对黑土中镉赋存形态的影响[J].中国环境科学,2007,27(5):693-697.Wang Yang,Liu Jingshuang,Wang Guoping,et al.The influence of freeze-thaw cycles and water content on the form transformations of cadmium in black soils[J].China Environmental Science,2007,27(5):693-697.(in Chinese with English abstract)
[26]党秀丽,张玉龙,虞娜,等.冻融作用对土壤中重金属镉赋存形态的影响[J].土壤通报,2008,39(4):826-830.Dang Xiuli,Zhang Yulong,Yu Na,et al.Effect of freezethawing cycles on the form transformation of cadmium in soil[J].Chinese Journal of Soil Science,2008,39(4):826-830.(in Chinese with English abstract)
[2]王金霞,李谢玲,何清明,等.三峡库区典型农业区土壤重金属污染特征及风险评价[J].农业工程学报,2018,34(8):227-234.Wang Jinxia,Li Xieling,He Qingming,et al.Characterization and risk assessment of heavy metal pollution in agricultural soils in Three Gorge Reservoir Area[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2018,34(8):227-234.(in Chinese with English abstract)
[3]周建军,周桔,冯仁国.我国土壤重金属污染现状及治理战略[J].中国科学院院刊,2014,29(3):315-320.Zhou Jianjun,Zhou Ju,Feng Renguo,et al.Status of China's heavy metal contamination in soil and its remediation strategy[J].Chinese Academy of Sciences,2014,29(3):315-320.(in Chinese with English abstract)
[4]杜延军,金飞,刘松玉,等.重金属工业污染场地固化/稳定处理研究进展[J].岩土力学,2011,32(1):116-124.Du Yanjun,Jin Fei,Liu Songyu,et al.Review of stabilization/solidification technique for remediation of heavy metals contaminated lands[J].Rock and Soil Mechanics,2011,32(1):116-124.(in Chinese with English abstract)
[5]Paria S,Yuet P K.Solidification/stabilization of organic and inorganic contaminates using Portland cement:A literature review[J].Environmental Reviews,2006,14(4):217-255.
[6]Griffiths R A.Soil-washing technology and practice[J].Journal of Hazardous Materials,1995,40(2):175-189.
[7]Reed B E,Carriere P C,Thompson J C,et al.Electronic(EK)remediation of a contaminated soil at several Pb concentrations and applied voltages[J].Journal of Soil Contamination,1996,5(2):95-120.
[8]Chang B V,Chiang B W,Yuan S Y.Biodegradation of nonylphenol in soil[J].Chemosphere,2007,66(10):1857-1862.
[9]李玉双,胡晓钧,孙铁珩,等.污染土壤淋洗修复技术研究进展[J].生态学杂志,2011,30(3):596-602.Li Yushuang,Hu Xiaojun,Sun Tieheng,et al.Soil washing/flushing of contaminated soil:A review[J].Chinese Journal of Ecology,2011,30(3):596-602.(in Chinese with English abstract)
[10]李光德,张中文,敬佩,等.茶皂素对潮土重金属污染的淋洗修复作用[J].农业工程学报,2009,25(10):231-235.Li Guangde,Zhang Zhongwen,Jing Pei,et al.Leaching remediation of heavy metal contaminated fluvio-aquatic soil with tea-saponin[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2009,25(10):231-235.(in Chinese with English abstract)
[11]Papassiopi N,Tambouris S,Kontopoulos A.Removal of heavy metals from calcareous contaminated soils by EDTAleaching[J].Water Air&Soil Pollution,1999,109(1/2/3/4):1-15.
[12]Sun B,Zhao F J,Lombi E.Leaching of heavy metals from contaminated soils using EDTA[J].Environmental Pollution,2001,113(2):111-120.
[13]Mulligan C N,Yong R N,Gibbs B F.Surfactant enhanced remediation of contaminated soil:A review[J].Engineering Geology,2001,60(1):371-380.
[14]Kuhlman M I,Greenfield T M.Simplified soil washing processes for a variety of soils[J].Journal of Hazardous Materials,1999,66(1/2):31-45.
[15]Semer R,Reddy K R.Evaluation of soil washing process to remove mixed contaminants from a sandy loam[J].Journal of Hazardous Materials,1996,45(1):45-57.
[16]温智,盛煜,马巍,等.退化性多年冻土地区公路路基地温和变形规律[J].岩石力学与工程学报,2009,28(7):1477-1483.Wen Zhi,Sheng Yu,Ma Wei,et al.Ground temperature and deformation laws of highway embankments in degenerative permafrost regions[J].Chinese Journal of Rock Mechanics and Engineering,2009,28(7):1477-1483.(in Chinese with English abstract)
[17]王铁行.多年冻土地区路基冻胀变形分析[J].中国公路学报,2005,18(2):1-5.Wang Tiehang.Analysis of frost heave on subgrade in permafrost regions[J].China Journal of Highway and Transport,2005,18(2):1-5.(in Chinese with English abstract)
[18]Eigenbrod K D.Effects of cyclic freezing and thawing on volume changes and permeabilities of soft fine-grained soils[J].Canadian Geotechnical Journal,1996,33(4):529-537.
[19]Qi J,Wei M,Song C.Influence of freeze-thaw on engineering properties of a silty soil[J].Cold Regions Science&Technology,2008,53(3):397-404.
[20]国家质量技术监督局.中华人民共和国国家标准.土工试验方法标准[M].北京:中国计划出版社,1999.
[21]Takashi T,Ohrai T,Yamamoto H.Decrease of frost heave amount by increasing the viscosity of pore water[J].Journal of Geotechnical Engineering,1980,298:77-85.
[22]陈晓婷,王欣,陈新.几种螯合剂对污染土壤的重金属提取效率的研究[J].环境科技,2005,18(2):9-10.Chen Xiaoting,Wang Xin,Chen Xin.Study on the exaction efficiency of heavy metals by chelates[J].Jiangsu Environmental Science and Technology,2005,18(2):9-10.(in Chinese with English abstract)
[23]Andrade M D,Prasher S O,Hendershot W H.Optimizing the molarity of a EDTA washing solution for saturated soil remediation of trace metal contaminated soils[J].Environmental Pollution,2007,147(3):781-790.
[24]Mulligan C N,Yong R N,Gibbs B F.Remediation technologies for metal-contaminated soils and groundwater:An evaluation[J].Engineering Geology,2001,60(1):193-207.
[25]王洋,刘景双,王国平,等.冻融频次与含水量对黑土中镉赋存形态的影响[J].中国环境科学,2007,27(5):693-697.Wang Yang,Liu Jingshuang,Wang Guoping,et al.The influence of freeze-thaw cycles and water content on the form transformations of cadmium in black soils[J].China Environmental Science,2007,27(5):693-697.(in Chinese with English abstract)
[26]党秀丽,张玉龙,虞娜,等.冻融作用对土壤中重金属镉赋存形态的影响[J].土壤通报,2008,39(4):826-830.Dang Xiuli,Zhang Yulong,Yu Na,et al.Effect of freezethawing cycles on the form transformation of cadmium in soil[J].Chinese Journal of Soil Science,2008,39(4):826-830.(in Chinese with English abstract)