-
随着我国工业的快速发展,广泛应用于电镀、金属加工、制革、染料、钢铁和化工等行业的铬(Cr)已成为一种主要的工业场地土壤污染物[1-2]。Cr主要是以六价铬Cr(Ⅵ)和三价铬Cr(Ⅲ)两种价态形式存在,而且Cr(Ⅵ)的毒性是Cr(Ⅲ)的500倍[3]。Cr(Ⅵ)活性较高,不易被土壤吸附,容易对环境造成影响。因此,土壤中重金属Cr(Ⅵ)的去除已成为污染土壤修复的一个重要课题[4-6]。
Cr污染场地的治理途径主要有两种:一是将Cr从被污染的土壤及地下水中清除;二是改变Cr在土壤中的赋存形态,将Cr(Ⅵ)还原为Cr(Ⅲ),降低其毒性。但是,第二种修复技术并未将Cr(Ⅵ)从土壤中彻底去除,存在修复后受扰动被再次氧化,释放到环境的风险。同时,常用还原剂(如Na2S2O8等)存在二次污染的风险。土壤电动力学修复技术能有效去除土壤中的Cr(Ⅵ),而且具有二次污染风险小的优点,是目前Cr(Ⅵ)污染土壤修复领域研究的热点。
传统电动修复工艺一般从控制土壤pH[7-9]、增加土壤中污染物的溶解能力[10-12]、电动修复与其他修复技术联用[13-14]、优化电极空间构型[15]、在电极室与土壤室之间添加可渗透性反应墙(PRB)[16-17]等几个方面提高效率。Cr(Ⅵ)常以
${\rm{CrO}}_4^{2 - }$ 、${\rm{C}}{{\rm{r}}_2}{\rm{O}}_7^{2 - }$ 、${\rm{HCrO}}_4^ - $ 等的可溶形态在土壤中迁移、扩散[18]。这些带负电的离子在电动力的驱动下向阳极迁移[19-20]。但是,在实际Cr(Ⅵ)污染场地中,常常同时存在Cl−、${\rm{NO}}_3^ - $ 等负电的离子[21]。这些带负电离子的存在,会增加修复过程中电能的消耗,影响Cr(Ⅵ)的去除效率[22]。目前,多数研究都着重于调整运行参数来提高修复效率。了解土壤中常见的阴离子对Cr(Ⅵ)污染土壤电动修复效率的影响有重要意义,有必要对其进行探究,但由于真实的土壤体系中涉及的干扰离子过多,同时土壤中的还原性物质可能会将Cr (Ⅵ)还原,不便于计算单位能量损耗,因此,本文借鉴国内外学者利用黏土矿物纯体系开展研究[17]的思路,也选择在黏土矿物的纯体系中开展研究。为了明晰这些离子对电动力学修复过程中Cr(Ⅵ)迁移的影响,本研究选用高纯蒙脱石模拟Cr(Ⅵ)污染土壤。这是因为,含水率是影响电动修复效率的重要因素之一[23],相比于高岭土和伊利石,蒙脱石在配置成饱水且适用于电动修复的土壤时,含水率最接近实际污染土壤。参考已有的研究成果[24-27],选择以纯水作为电解液,在电压梯度为2 V·cm−1的条件下,选用石墨电极进行电动修复实验。同时,分别向人工配制的Cr(Ⅵ)污染蒙脱石中添加一定浓度的NaNO3、NaCl、NaOH、Na2SO4、Na2CO3、Na3PO4,探究单一阴离子在电动修复中的行为特征,分析其对Cr(Ⅵ)迁移的影响。
铬污染土壤电动修复过程中典型阴离子的迁移特征
Migration characteristics of typical anions in the process of electrokinetic remediating Cr(Ⅵ)-contaminated soil
-
摘要: 为揭示典型阴离子在电动修复六价铬污染土壤过程中的迁移行为,以人工配置的Cr (Ⅵ)污染蒙脱石模拟供试土壤,蒸馏水作为阴阳极电解液,在电压梯度为2 V·cm−1的条件下进行电动修复实验;并分别对比分析各组实验的电流、pH、电导率、能量损耗参数的变化。结果表明,5种阴离子在土壤电动修复过程中的迁移顺序为:
${{\rm{NO}}_3^ - \gt {\rm{Cr}}\left( {{\text{Ⅵ}}} \right) \approx {\rm{C}}{{\rm{l}}^ - } \gt {\rm{SO}}_4^{2 - } \gg {\rm{PO}}_4^{3-}}$ 。相比于酸性土壤,偏中性的土壤环境更利于Cr(Ⅵ)向阳极的迁移,而酸性土壤会导致电动修复过程能耗的增加,更容易产生聚焦现象。土壤中${{\rm{CO}}_3^{2 - }}$ 、OH−和${{\rm{PO}}_4^{3 - }}$ 的存在,能有效地缓解电动修复过程中产生的聚焦现象,而且能加速土壤中Cr(Ⅵ)的去除;${{\rm{PO}}_4^{3 - }}$ 的存在能将Cr(Ⅵ)的去除率提高到99.9%以上。本研究结果可为电动修复六价铬污染土壤电解液的选择提供参考。Abstract: The electrokinetic remediation technology for contaminated soil is a hot topic in the field of environmental engineering around the world. But the existence of a large amount of free-migrating ions in soil increases its energy consumption and limits its application. In order to disclose the migration behavior of typical anions in the process of electrokinetic remediating Cr(Ⅵ)-contaminated soil, the synthetic Cr(Ⅵ)-contaminated montmorillonite was used to simulate the contaminated soil, and the deionized water was taken as the electrolytes,${\rm{NO}}_3^ - $ , Cl−, OH−,${\rm{SO}}_4^{2 - }$ ,${\rm{CO}}_3^{2 - }$ and${\rm{PO}}_4^{3 - }$ were taken as typical anions, the electrokinetic remediation experiments were conducted at voltage gradient of 2 V·cm−1. The changes in current, pH, conductivity, energy consumption of each experimental group were compared and analyzed. The results showed that the migration priority of the anions in the soil was${\rm{NO}}_3^ - \gt {\rm{Cr}}\left( {{\rm{VI}}} \right) \approx {\rm{C}}{{\rm{l}}^ - } \gt {\rm{SO}}_4^{2 - } \gg {\rm{PO}}_4^{3 - }$ . In comparison with acidic soil, neutral soil accelerated the migration of Cr(Ⅵ) to the anode, while acid soil could lead to the increase of energy consumption during electrokinetic remediation process, even easily caused the focusing effect. The existence of${\rm{CO}}_3^{2 - }$ , OH− and${\rm{PO}}_4^{3 - }$ in soil could effectively alleviate the focusing effect, and also accelerate the removal of Cr(Ⅵ). The existence of${\rm{PO}}_4^{3 - }$ could increase the Cr(Ⅵ). removal rate above 99.9%. The result of this research can provide a reference for electrolyte selection in the process of electrokinetic remediating Cr(Ⅵ)-contaminated soil. -
表 1 各实验组每天移除Cr(Ⅵ)的质量
Table 1. Daily removal of Cr(Ⅵ)mass in each group
时间/d Cr/mg CN/mg CS/mg CC/mg CO/mg CCl/mg CP/mg 1 188 274 601 650 586 327 872 2 121 109 142 155 178 90.1 526 3 63.0 111 77.2 142 177 49.3 381 4 34.0 97.8 72.2 134 115 52.4 293 5 23.6 111 44.4 106 120 23.4 155 6 17.7 129 38.9 70.9 60.9 31.1 71.5 7 22.4 52.2 48.0 53.2 62.3 27.7 13.5 表 2 实验后各区域土壤中Cr(Ⅵ)与其他阴离子的去除率
Table 2. Removal rate of Cr(Ⅵ)and other anions in different soil regions after experiment
% 实验组 CN组 CS组 CCl组 CP组 ${\rm{NO}}_3^ - $ Cr(Ⅵ) ${\rm{SO}}_4^{2 - }$ Cr(Ⅵ) Cl− Cr(Ⅵ) ${\rm{PO}}_4^{3 - }$ Cr(Ⅵ) S1 82.1 74.2 70.0 99.6 35.3 38.7 73.0 100.0 S2 −7.6 10.6 −119.0 −31.1 −47.1 −55.4 63.2 100.0 S3 4.4 −21.5 12.8 23.0 23.5 38.1 85.7 99.9 S4 58.7 54.5 52.6 53.3 47.1 44.0 91.6 99.9 S5 84.8 86.4 69.0 85.4 76.5 76.6 92.5 100.0 -
[1] SAMANI M R, BORGHEI S M, OLAD A, et al. Removal of chromium from aqueous solution using polyaniline-poly ethylene glycol composite[J]. Journal of Hazardous Materials, 2010, 184(8): 248-254. [2] TANG L, FANG Y, PANG Y, et al. Synergistic adsorption and reduction of hexavalent chromium using highly uniform polyaniline-magnetic mesoporous silica composite[J]. Chemical Engineering Journal, 2014, 254(6): 302-312. [3] SARIN V, PANT K. Removal of chromium from industrial waste by using eucalyptus bark[J]. Bioresource Technology, 2006, 97(1): 15-20. doi: 10.1016/j.biortech.2005.02.010 [4] ZHOU M, XU J M, ZHU S F, et al. Exchange electrode-electrokinetic remediation of Cr-contaminated soil using solar energy[J]. Separation and Purification Technology, 2018, 190(8): 297-306. [5] BANKS M K, SCHWAB A P, HENDERSON C. Leaching and reduction of chromium in soil as affected by soil organic content and plants[J]. Chemosphere, 2006, 62(7): 255-264. [6] LIAO Y P, MIN X B, YANG Z H, et al. Physicochemical and biological quality of soil in hexavalent chromium-contaminated soils as affected by chemical and microbial remediation[J]. Environmental Science and Pollution Research, 2014, 21(6): 379-388. [7] KIM D, JEON C, BAEK K, et al. Electrokinetic remediation of fluorine-contaminated soil: Conditioning of anolyte[J]. Journal of Hazardous Materials, 2009, 161(3): 565-569. [8] LÓPEZ VIZCAÍNO R, YUSTRES A, ASENSIO L, et al. Enhanced electrokinetic remediation of polluted soils by anolyte pH conditioning[J]. Chemosphere, 2018, 199(2): 477-485. [9] CANG L, FAN G P, ZHOU D M, et al. Enhanced-electrokinetic remediation of copper-pyrene co-contaminated soil with different oxidants and pH control[J]. Chemosphere, 2013, 90(11): 2326-2331. [10] GIANNIS A, GIDARAKOS E, SKOUTA A. Application of sodium dodecyl sulfate and humic acid as surfactants on electrokinetic remediation of cadmium-contaminated soil[J]. Desalination, 2007, 211(2): 249-260. [11] ZHOU D M, CANG L, ALSHAWABKEH A N, et al. Pilot-scale electrokinetic treatment of a Cu contaminated red soil[J]. Chemosphere, 2006, 63(6): 964-971. doi: 10.1016/j.chemosphere.2005.08.059 [12] MATURI K, REDDY K R. Simultaneous removal of organic compounds and heavy metals from soils by electrokinetic remediation with a modified cyclodextrin[J]. Chemosphere, 2006, 63(6): 1022-1031. doi: 10.1016/j.chemosphere.2005.08.037 [13] SAWADA A, MORI K, TANAKA S, et al. Removal of Cr(VI) from contaminated soil by electrokinetic remediation[J]. Waste Management, 2004, 24(5): 483-490. doi: 10.1016/S0956-053X(03)00133-8 [14] MA J W, WANG F Y, HUANG Z H, et al. Simultaneous removal of 2, 4-dichlorophenol and Cd from soils by electrokinetic remediation combined with activated bamboo charcoal[J]. Journal of Hazardous Materials, 2010, 176(3): 715-720. [15] 刘芳, 付融冰, 徐珍. 土壤电动修复的电极空间构型优化研究[J]. 环境科学, 2015, 36(2): 678-685. [16] CHUNG H I, LEE M. A new method for remedial treatment of contaminated clayey soils by electrokinetics coupled with permeable reactive barriers[J]. Electrochimica Acta, 2007, 52(10): 3427-3431. doi: 10.1016/j.electacta.2006.08.074 [17] SUZUKI T, KAWAI K, MORIBE M, et al. Recovery of Cr as Cr(III) from Cr(VI)-contaminated kaolinite clay by electrokinetics coupled with a permeable reactive barrier[J]. Journal of Hazardous Materials, 2014, 278(6): 297-303. [18] DHAL B, THATOI H N, DAS N N, et al. Chemical and microbial remediation of hexavalent chromium from contaminated soil and mining/metallurgical solid waste: A review[J]. Journal of Hazardous Materials, 2013, 251(1): 272-291. [19] WANG Y X, HUANG L H, WANG Z X, et al. Application of Polypyrrole flexible electrode for electrokinetic remediation of Cr(VI)-contaminated soil in a main-auxiliary electrode system[J]. Chemical Engineering Journal, 2019, 373(5): 131-139. [20] 杜玮, 张光生, 邹华, 等. 铬-菲复合污染土壤的电动修复效果[J]. 环境科学研究, 2016, 29(8): 1163-1169. [21] ZHU F, LI L W, REN W T, et al. Effect of pH, temperature, humic acid and coexisting anions on reduction of Cr(Ⅵ) in the soil leachate by nZVI/Ni bimetal material[J]. Environmental Pollution, 2017, 227(5): 444-450. [22] YUAN L Z, XU X J, LI H Y, et al. The influence of macroelements on energy consumption during periodic power electrokinetic remediation of heavy metals contaminated black soil[J]. Electrochimica Acta, 2017, 235(3): 604-612. [23] SHIN S, PARK S, BAEK K. Soil moisture could enhance electrokinetic remediation of arsenic-contaminated soil[J]. Environmental Science and Pollution Research, 2017, 24(10): 9820-9825. doi: 10.1007/s11356-017-8720-3 [24] YUAN L Z, XU X J, LI H Y, et al. Development of novel assisting agents for the electrokinetic remediation of heavy metal-contaminated kaolin[J]. Electrochimica Acta, 2016, 218(9): 140-148. [25] FU R B, WEN D D, XIA X Q, et al. Electrokinetic remediation of chromium (Cr)-contaminated soil with citric acid (CA) and polyaspartic acid (PASP) as electrolytes[J]. Chemical Engineering Journal, 2017, 316(1): 601-608. [26] LIU L W, LI W, SONG W P, et al. Remediation techniques for heavy metal-contaminated soils: Principles and applicability[J]. Science of the Total Environment, 2018, 633(3): 206-219. [27] 薛浩, 孟凡生, 王业耀, 等. 酸化-电动强化修复铬渣场地污染土壤[J]. 环境科学研究, 2015, 28(8): 1317-1323. [28] GUEMIZA K, COUDERT L, METAHNI S, et al. Treatment technologies used for the removal of As, Cr, Cu, PCP and/or PCDD/F from contaminated soil: A review[J]. Journal of Hazardous Materials, 2017, 333(3): 194-214. [29] ZHANG K L, CHEN L, LI Y F, et al. Interactive effects of soil pH and substrate quality on microbial utilization[J]. European Journal of Soil Biology, 2020, 96(1): 31-41. [30] 马兵兵, 姜滢, 罗燕, 等. 超声提取-离子色谱法测定土壤中10种水溶性阴离子[J]. 土壤, 2019, 51(6): 1253-1256. [31] 张雪梅, 汪徐春, 许晨晨, 等. 土壤中有效磷快速测定方法的研究[J]. 安徽科技学院学报, 2015, 29(5): 50-54. doi: 10.3969/j.issn.1673-8772.2015.05.010 [32] 唐静, 闫海涛, 王鑫光. 离子色谱法测定土壤中氯离子、硫酸根离子、硝酸根离子[J]. 化学分析计量, 2017, 26(3): 57-60. doi: 10.3969/j.issn.1008-6145.2017.03.013 [33] 郭军玲, 金辉, 王永亮, 等. 含碳物料对晋北苏打盐化土理化性质的影响[J]. 华北农学报, 2019, 34(4): 199-207. doi: 10.7668/hbnxb.201751724 [34] PEDERSEN K B, JENSEN P E, OTTOSEN L M, et al. Influence of electrode placement for mobilising and removing metals during electrodialytic remediation of metals from shooting range soil[J]. Chemosphere, 2018, 210(7): 683-691. [35] SHEN Z M, CHEN X J, JIA J P, et al. Comparison of electrokinetic soil remediation methods using one fixed anode and approaching anodes[J]. Environmental Pollution, 2007, 150(2): 193-199. doi: 10.1016/j.envpol.2007.02.004 [36] CHOWDHURY S R, YANFUL E K, PRATT A R. Chemical states in XPS and Raman analysis during removal of Cr(VI) from contaminated water by mixed maghemite-magnetite nanoparticles[J]. Journal of Hazardous Materials, 2012, 236(8): 246-256. [37] RICHARD F C, BOURG A C M. Aqueous geochemistry of chromium: A review[J]. Water Research, 1991, 25(7): 807-816. doi: 10.1016/0043-1354(91)90160-R [38] GUEDES P, LOPES V, COUTO N, et al. Electrokinetic remediation of contaminants of emergent concern in clay soil: Effect of operating parameters[J]. Environmental Pollution, 2019, 253(7): 625-635. [39] LI G, GUO S H, LI S C, et al. Comparison of approaching and fixed anodes for avoiding the ‘focusing’ effect during electrokinetic remediation of chromium-contaminated soil[J]. Chemical Engineering Journal, 2012, 203(7): 231-238. [40] LI D, XIONG Z, NIE Y, et al. Near-anode focusing phenomenon caused by the high anolyte concentration in the electrokinetic remediation of chromium(Ⅵ)-contaminated soil[J]. Journal of Hazardous Materials, 2012, 230(6): 282-291. [41] CAMESELLE C. Enhancement of electro-osmotic flow during the electrokinetic treatment of A contaminated soil[J]. Electrochimica Acta, 2015, 181(2): 31-38. [42] REZAEE M, ASADOLLAHFARDI G, GOMEZ-LAHOZ C, et al. Modeling of electrokinetic remediation of Cd- and Pb-contaminated kaolinite[J]. Journal of Hazardous Materials, 2019, 366(11): 630-635. [43] LI T P, YUAN S H, WAN J Z, et al. Pilot-scale electrokinetic movement of HCB and Zn in real contaminated sediments enhanced with hydroxypropyl-β-cyclodextrin[J]. Chemosphere, 2009, 76(9): 1226-1232. doi: 10.1016/j.chemosphere.2009.05.045 [44] DIMIRKOU A, IOANNOU A, DOULA M. Preparation, characterization and sorption properties for phosphates of hematite, bentonite and bentonite-hematite systems[J]. Advances in Colloid and Interface Science, 2002, 97(1): 37-61. [45] IBRAHIM Y, ABDULKAREM E, NADDEO V, et al. Synthesis of super hydrophilic cellulose-alpha zirconium phosphate ion exchange membrane via surface coating for the removal of heavy metals from wastewater[J]. Science of the Total Environment, 2019, 690(7): 167-180.