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我国受镉(Cd)、砷(As)、汞(Hg)、铜(Cu)、锌(Zn)等重金属污染的耕地约有1000万ha,每年因重金属污染的粮食(如“镉米”、“砷米”等)达1000多万t,造成的直接经济损失200余亿元[1]。吉林省农田土壤重金属污染状况表明,玉米田中Cu、Cd含量超标率分别为1.39%和5.56%,大豆田土壤中重金属Cd含量的超标率为6.67%,而水稻田中各重金属元素含量均高于相同pH条件下的土壤环境标准限制[2]。陈亚华等[3]调查发现南京某地区田地土壤Cd、Pb、Zn和Cu等重金属元素含量比国家《土壤环境质量标准》中二级标准值分别高出58%、12%、18%及56%。杨丽等[4]调查和分析衡阳市珠晖区居民绿地土壤Cd、Pb、Zn和Cu总量及其形态,发现Cu、Cd、Pb的含量是国家土壤环境质量二级标准的1—5倍。可见,土壤受重金属Cd、Pb、Zn和Cu复合污染问题日益凸显,对全球土壤质量、土壤生态和人类健康产生重大影响[5-6]。由于土壤固有基质的复杂性,多种重金属之间、重金属与土壤界面之间存在复杂的相互作用,为污染修复和固化剂选择带来了挑战。如何妥善修复土壤重金属污染,尤其是多种重金属复合污染土壤引起了社会的广泛关注。
生物炭具有多孔、比表面积大且富含多种官能团等特性,已被广泛应用于土壤改良、作物增产、污染物治理、固氮及缓解全球气候变化[7-11]。近年来,国内外学者围绕生物炭材料的特性表征、重金属污染修复效果与吸附固持机制方面进行了大量的研究[12-14]。在土壤中施加生物炭不仅能减少土壤中的N、P等营养元素的流失,提高其利用率,同时能增加土壤持水能力[15-16]。生物炭的疏松多孔结构以及巨大的表面积和阳离子交换量(CEC)可以改善土壤理化性质,提高作物产量,还能吸附土壤中的污染物,降低土壤中砷的生物有效性和迁移转化能力[17-18]。陈再明等[19]通过缺氧裂解制备了水稻秸秆生物炭,发现其对重金属Pb2+的吸附量是原秸秆生物质的5—6倍。许超等[20]在污染土壤中施用生物炭,可降低重金属Zn、Cd、Pb、Cu的有效性和生态风险,提高土壤养分含量起到改良土壤作用。为了提高生物炭的物理化学性质,进而提高其对土壤重金属污染的修复能力,改性生物炭成为目前研究的热点。
锰及其氧化物是土壤的重要组分,主要包括软锰矿、斜方锰矿和水锰矿等。近年来,锰氧化物在污染土壤修复方面发挥了重要作用。锰氧化物特有的表面化学性质,影响着土壤对重金属的吸附(沉淀)作用,主要是通过改善土壤的理化性质(pH、氧化还原电位、含水量、孔隙、黏度等),改变重金属或类金属在土壤中的淋溶、移动性、迁移转化[21]。将锰氧化物作为改性材料应用于复合材料的制备一直是国内外学者研究的热点,如锰氧化物-活性炭复合材料用于固化土壤Pb、Cu污染的研究已取得良好的效果[22]。生物炭经锰氧化物负载后,能够显著增加表面的羟基、羧基和酚羟基等官能团的数量,提高对重金属的吸附能力[23-28]。于志红等[21]制备了玉米秸秆生物炭-锰氧化物复合材料,测试了其对红壤吸附Cu的影响表明,复合材料能增加红壤对Cu的吸附能力,降低Cu的可移动性和生物有效性。MnOx/生物炭复合材料对水体中重金属的吸附效果会明显好于单一生物炭[29-30],然而,将其应用于土壤重金属修复时,MnOx/生物炭固化重金属的效果和机理及是否会带来土壤Mn污染鲜见报道。另外,以往的研究大多处理单一重金属污染土壤[31-32],实际污染土壤中往往是多种重金属共存,因此,MnOx/生物炭复合材料对土壤中多种重金属的固化能力及机制需要进一步研究。
本文采用高锰酸钾溶液改性生物炭,研究不同MnOx负载浓度对MnOx/生物炭复合材料的性能影响;通过批量吸附实验和表征分析,探讨MnOx/生物炭复合材料对土壤重金属Cd、Pb、Zn、Cu的固化效果及其机理,以期为利用MnOx/生物炭复合材料环保功能修复重金属复合污染土壤提供科学依据。
MnOx/生物炭复合材料对土壤重金属的固化效果及其机理研究
Immobilization of heavy metals in contaminated soils using MnOx/biochar composites
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摘要: 为了探究高锰酸钾改性生物炭(MnOx/生物炭)对土壤重金属的固化效果与生物炭的差异,本文采用高锰酸钾溶液改性小麦秸秆生物炭,研究不同MnOx负载浓度、复合材料添加量和固化时间对MnOx/生物炭复合材料固化土壤重金属Cd、Pb、Zn和Cu性能的影响及其机理。结果表明,锰氧化物负载能够显著增加生物炭表面的羟基、羧基和酚羟基等官能团的数量。土壤毒性浸出液(TCLP)中重金属浓度变化表明,当固化剂添加量为1%时,MnOx/生物炭对土壤中Cd、Pb、Zn、Cu固化效果是未改性生物炭的2—4倍;在相同固化时间内,MnOx/生物炭复合材料对重金属固定化效果随着添加量和MnOx负载的浓度升高而增大。MnOx/生物炭复合材料的添加可促进重金属Cd、Pb、Zn和Cu由可交换态(EX)和碳结合态(CB)向更加稳定的锰氧化物结合态(OX)、有机物结合态(OM)和残渣态(RS)转化,从而降低污染土壤重金属的活性态比例。MnOx/生物炭主要通过吸附和氧化的共同作用,实现对土壤中重金属的高效固定。固化处理后土壤TCLP浸出液中Mn浓度均低于1.52 mg·L-1,说明使用复合材料不会造成土壤锰污染。MnOx/生物炭复合材料在修复重金属污染土壤中具有较大的应用潜力。Abstract: In this work, potassium permanganate solution was used to modify wheat straw biochar to explore the difference between manganese-modified biochar (MnOx/biochar) and biochar in the immobilization of soil heavy metals. The effect of different MnOx loading concentration, MnOx/biochar dosage, and reaction time on the heavy metals (Cd, Pb, Zn, and Cu) immobilization ability of MnOx/biochar composites and its mechanism were studied. The results showed that manganese oxide loading could significantly increase the number of functional groups on the surface of biochar. The changes in the concentration of heavy metals in the soil toxicity leachate (TCLP) showed that, the immobilization rate of MnOx/biochar on Cd, Pb, Zn, and Cu in the soil was 2—4 times that of unmodified biochar at a MnOx/biochar dosage of 1%. The immobilization ability of MnOx/biochar composite materials on heavy metals increased with the increase of the MnOx/biochar dosage and the concentration of MnOx loading. The addition of MnOx/biochar composite materials promoted the conversion of more accessible Cd, Pb, Zn and Cu (EX and CB) into the less accessible forms (OX, OM, and RS) to reduce the activeness of Cd, Pb, Zn and Cu. Surface sorption and oxidation were dominant mechanisms for heavy metals immobilization. After solidification, the Mn concentration in the soil TCLP leaching solution was lower than 1.52 mg·L-1, indicating that the application of MnOx/biochar would not cause soil manganese pollution. The MnOx/biochar composite material has great application potential in the remediation of heavy metal contaminated soils.
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Key words:
- biochar /
- manganese oxide /
- soil /
- heavy metals
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表 1 生物炭及MnOx/生物炭的理化性质
Table 1. Physiochemical properties of biochar and MnOx/ biochars
生物炭
BiocharBET比表面积/(m2 ·g−1)
BET surface areaBJH孔容积/(cm3 ·g−1)
BJH pore volumeBJH孔径/nm
BJH pore size生物炭 7.26 0.011 6.11 1.38%MnOx/生物炭 11.2 0.015 5.41 2.76%MnOx/生物炭 26.5 0.032 4.83 5.52%MnOx/生物炭 11.8 0.025 8.66 -
[1] 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, 350, 272. ZHOU J J, ZHOU J, FENG R G. Status of China's heavy metal contamination in soil and its remediation strategy [J]. Bulletin of Chinese Academy of Sciences, 2014, 29(3): 315-320, 350, 272(in Chinese).
[2] 梁烜赫, 曹铁华, 张磊, 等. 吉林省农田重金属含量及其在作物中的累积 [J]. 吉林农业科学, 2011, 36(6): 59-62. doi: 10.3969/j.issn.1003-8701.2011.06.018 LIANG X H, CAO T H, ZHANG L, et al. Content of heavy metals in farmland soil and accumulation in crops in Jilin province [J]. Journal of Northeast Agricultural Sciences, 2011, 36(6): 59-62(in Chinese). doi: 10.3969/j.issn.1003-8701.2011.06.018
[3] 陈亚华, 黄少华, 刘胜环, 等. 南京地区农田土壤和蔬菜重金属污染状况研究 [J]. 长江流域资源与环境, 2006, 15(3): 356-360. doi: 10.3969/j.issn.1004-8227.2006.03.017 CHEN Y H, HUANG S H, LIU S H, et al. Study of the heavy metal contamination in soils and vegetables in Nanjing area [J]. Resources and Environment in the Yangtze Basin, 2006, 15(3): 356-360(in Chinese). doi: 10.3969/j.issn.1004-8227.2006.03.017
[4] 杨丽, 毛祖莉. 衡阳市绿地Cu、Zn、Cd、Pb形态分布及健康风险评价 [J]. 环境科学与技术, 2019, 42(S1): 227-231. YANG L, MAO Z L. Study on the Speciation of Cu and Zn and Risk Assessment in Urban Green Space in Hengyang City [J]. Environmental Science & Technology, 2019, 42(S1): 227-231(in Chinese).
[5] 宋志政, 周润声. 我国重金属污染土壤的治理与修复研究进展 [J]. 化工设计通讯, 2020, 46(2): 216-217. doi: 10.3969/j.issn.1003-6490.2020.02.144 SONG Z Z, ZHOU R S. Research progress in remediation and remediation of heavy metal contaminated soil in China [J]. Chemical Engineering Design Communications, 2020, 46(2): 216-217(in Chinese). doi: 10.3969/j.issn.1003-6490.2020.02.144
[6] 王丽娟. 土壤重金属污染的危害及修复 [J]. 现代农业, 2017(1): 73-75. doi: 10.3969/j.issn.1008-0708.2017.01.061 WANG L J. Harm and remediation of heavy metal pollution in soil [J]. Modern Agriculture, 2017(1): 73-75(in Chinese). doi: 10.3969/j.issn.1008-0708.2017.01.061
[7] 吕宏虹, 宫艳艳, 唐景春, 等. 生物炭及其复合材料的制备与应用研究进展 [J]. 农业环境科学学报, 2015, 34(8): 1429-1440. doi: 10.11654/jaes.2015.08.001 LV H H, GONG Y Y, TANG J C, et al. Advances in preparation and applications of biochar and its composites [J]. Journal of Agro-Environment Science, 2015, 34(8): 1429-1440(in Chinese). doi: 10.11654/jaes.2015.08.001
[8] 朱灵峰, 何怡雪, 张昊, 等. 锰改性玉米秸秆生物炭吸附去除1, 4-苯醌 [J]. 江苏农业学报, 2016, 32(3): 570-574. doi: 10.3969/j.issn.1000-4440.2016.03.013 ZHU L F, HE Y X, ZHANG H, et al. Adsorptive removal of 1, 4-benzoquinone by Mn-modified cornstalk biochar [J]. Jiangsu Journal of Agricultural Sciences, 2016, 32(3): 570-574(in Chinese). doi: 10.3969/j.issn.1000-4440.2016.03.013
[9] 陈温福, 张伟明, 孟军, 等. 生物炭应用技术研究 [J]. 中国工程科学, 2011, 13(2): 83-89. doi: 10.3969/j.issn.1009-1742.2011.02.015 CHEN W F, ZHANG W M, MENG J, et al. Researches on biochar application technology [J]. Strategic Study of CAE, 2011, 13(2): 83-89(in Chinese). doi: 10.3969/j.issn.1009-1742.2011.02.015
[10] 何振嘉. 生物炭对土壤重金属污染修复研究 [J]. 安徽农业科学, 2019, 47(21): 12-13. doi: 10.3969/j.issn.0517-6611.2019.21.004 HE Z J. Study on biochar’s remediation of heavy metal pollution in soil [J]. Journal of Anhui Agricultural Sciences, 2019, 47(21): 12-13(in Chinese). doi: 10.3969/j.issn.0517-6611.2019.21.004
[11] LV H H, ZHAO H, TANG J C, et al. Immobilization of hexavalent chromium in contaminated soils using biochar supported nanoscale iron sulfide composite [J]. Chemosphere, 2018, 194: 360-369. doi: 10.1016/j.chemosphere.2017.11.182 [12] 吴诗雪, 王欣, 陈灿, 等. 凤眼莲、稻草和污泥制备生物炭的特性表征与环境影响解析 [J]. 环境科学学报, 2015, 35(12): 4021-4032. WU S X, WANG X, CHEN C, et al. Characterization of biochar derived from water hyacinth, rice straw and sewage sludge and their environmental implications [J]. Acta Scientiae Circumstantiae, 2015, 35(12): 4021-4032(in Chinese).
[13] 孟梅, 华玉妹, 朱端卫, 等. 生物炭对重金属污染沉积物的修复效果 [J]. 环境化学, 2015, 35(12): 4021-4032. MENG M, HUA Y M, ZHU D W, et al. Remediation effect of biochar on sediment contaminated by heavy metals [J]. Environmental Chemistry, 2015, 35(12): 4021-4032(in Chinese).
[14] 尹光彩, 陶琳, 宋小旺, 等. 不同原料生物炭的改性及其吸附/钝化Cd(Ⅱ)效果 [J]. 土壤通报, 2020, 51(3): 748-756. YIN G C, TAO L, SONG X W, et al. A review on the modification, Cd(Ⅱ) adsorption/passivation of biochars prepared by different raw materials [J]. Chinese Journal of Soil Science, 2020, 51(3): 748-756(in Chinese).
[15] 吴蔚君, 徐云连, 邢素林, 等. 生物炭对土壤氮磷转化和流失的影响 [J]. 农学学报, 2018, 8(9): 20-26. doi: 10.11923/j.issn.2095-4050.cjas17050013 WU W J, XU Y L, XING X L, et al. Effect of Biochar on soil nitrogen and phosphorus transformation and loss [J]. Journal of Agriculture, 2018, 8(9): 20-26(in Chinese). doi: 10.11923/j.issn.2095-4050.cjas17050013
[16] ZHENG H, WANG Z, DENG X, et al. Impacts of adding biochar on nitrogen retention and bioavailability in agricultural soil [J]. Geoderma, 2013, 206: 32-39. doi: 10.1016/j.geoderma.2013.04.018 [17] 武玉, 徐刚, 吕迎春, 等. 生物炭对土壤理化性质影响的研究进展 [J]. 地球科学进展, 2014, 29(1): 68-79. doi: 10.11867/j.issn.1001-8166.2014.01-0068 WU Y, XU G, LV Y C, ey al. Effects of biochar amendment on soil physical and chemical properties: current status and knowledge gaps [J]. Advances in Earth Science, 2014, 29(1): 68-79(in Chinese). doi: 10.11867/j.issn.1001-8166.2014.01-0068
[18] BEESLEY L, MORENO-JIMENEZ E, GOMEZ-EYLES J L, et al. A review of biochars'potential role in the remediati on, revegetation and restoration of contaminated soils [J]. Environmental Pollution, 2011, 159(12): 3269-3282. doi: 10.1016/j.envpol.2011.07.023 [19] 陈再明, 方远, 徐义亮, 等. 水稻秸秆生物碳对重金属Pb2+的吸附作用及影响因素 [J]. 环境科学学报, 2012, 32(4): 769-776. CHEN Z M, FANG Y, XU Y L, et al. Adsorption of Pb2+ by rice straw derived-biochar and its influential factors [J]. Acta Scientiae Circumstantiae, 2012, 32(4): 769-776(in Chinese).
[20] 许超, 林晓滨, 吴启堂, 等. 淹水条件下生物炭对污染土壤重金属有效性及养分含量的影响 [J]. 水土保持学报, 2012, 26(6): 194-198. XU C, LIN X B, WU Q T, et al. Impacts of biochar on availability of heavy metals and nutrient content of contaminated soil under waterlogged conditions [J]. Journal of Soil and Water Conservation, 2012, 26(6): 194-198(in Chinese).
[21] 于志红, 谢丽坤, 刘爽, 等. 生物炭-锰氧化物复合材料对红壤吸附铜特性的影响 [J]. 生态环境学报, 2014, 23(5): 897-903. doi: 10.3969/j.issn.1674-5906.2014.05.026 YU Z H, XIE L K, LIU S, et al. Effects of biochar-manganese oxides composite on adsorption characteristics of Cu in red soil [J]. Ecology and Environmental Sciences, 2014, 23(5): 897-903(in Chinese). doi: 10.3969/j.issn.1674-5906.2014.05.026
[22] 杨永军. 生物炭负载铁锰氧化物对铅、铜污染土壤的稳定化研究[D]. 咸阳: 西北农林科技大学, 2018. YANG Y J. Study of modified biochar on the stabilization of heavy metals lead and copper contaminated soil[D]. Xianyang: Northwest A&F University, 2018 (in Chinese).
[23] O′REILLY S E, HOCHELLA JR M F. Lead sorption efficiencies of natural and synthetic Mn and Fe-oxides [J]. Geochim Cosmochim Ac, 2003, 67(23): 4471-4487. doi: 10.1016/S0016-7037(03)00413-7 [24] 于志红, 黄一帆, 廉菲, 等. 生物炭-锰氧化物复合材料吸附砷(Ⅲ)的性能研究 [J]. 农业环境科学学报, 2015, 34(1): 155-161. doi: 10.11654/jaes.2015.01.022 YU Z H, HUANG Y F, LIAN F, et al. Adsorption of arsenic(Ⅲ) on biochar-manganese oxide composites [J]. Journal of Agro-Environment Science, 2015, 34(1): 155-161(in Chinese). doi: 10.11654/jaes.2015.01.022
[25] 樊伟, 卞战强, 田向红, 等. 固载化纳米MnO2对砷的吸附性能研究 [J]. 水处理技术, 2013, 39(1): 60-64. doi: 10.3969/j.issn.1000-3770.2013.01.013 FAN W, BIAN Z Q, TIAN X H, et al. Study on absorption of arsenic by immobilized nano-manganese oxide [J]. Technology of Water Treatment, 2013, 39(1): 60-64(in Chinese). doi: 10.3969/j.issn.1000-3770.2013.01.013
[26] 董爱琴, 谢杰, 刘佳, 等. 土壤重金属钝化材料生物炭的研究进展 [J]. 环境污染与防治, 2017, 39(3): 319-325. DONG A Q, XIE J, LIU J, et al. Advances on heavy metal passivation material of biochar in soils [J]. Environmental Pollution & Control, 2017, 39(3): 319-325(in Chinese).
[27] SONG Z G, LIAN F, YU Z H, et al. Synthesis and characterization of a novel MnOx-loaded biochar and its adsorption properties for Cu2+ in aqueous solution [J]. Chemical Engineering Journal, 2014, 242: 36-42. doi: 10.1016/j.cej.2013.12.061 [28] LI B, YANG L, WANG C Q, et al. Adsorption of Cd(Ⅱ) from aqueous solutions by rape straw biochar derive d from different modification processes [J]. Chemosphere, 2017, 175: 332-340. doi: 10.1016/j.chemosphere.2017.02.061 [29] 杨兰, 李冰, 王昌全, 等. 改性生物炭材料对稻田原状和外源镉污染土钝化效应 [J]. 环境科学, 2016, 37(9): 3562-3574. YANG L, LI B, WANG C Q, et al. Effect of modified biochars on soil cadmium stabilization in paddy suffered from original or exogenous contamination [J]. Environmental Science, 2016, 37(9): 3562-3574(in Chinese).
[30] 孙彤, 付宇童, 李可, 等. 锰基改性生物炭对弱碱性Cd污染土壤团聚体结构以及Cd含量特征的影响 [J]. 环境科学, 2020, 41(7): 3426-3433. SUN T, FU Y T, LI K, et al. Effect of Mn-modified biochar on the characteristics of aggregate structure and the content of Cd in weakly alkaline Cd-contaminated soil [J]. Environmental Science, 2020, 41(7): 3426-3433(in Chinese).
[31] 蒲生彦, 上官李想, 刘世宾, 等. 生物炭及其复合材料在土壤污染修复中的应用研究进展 [J]. 生态环境学报, 2019, 28(3): 629-635. PU S Y, SHANGGUANG L X, LIU S B, et al. A review of the application of biochar and its composites in soil remediation [J]. Ecology and Environmental Sciences, 2019, 28(3): 629-635(in Chinese).
[32] 于志红. 锰氧化物—生物炭复合材料对砷的生物有效性的影响[D]. 北京: 中国农业科学院, 2015. YU Z H. A Effects of biochar-manganese oxide composites on bio-availability of arsenic[D]. Beijing: Chinese Academy of Agricultural Sciences, 2015 (in Chinese).
[33] TESSIER A, CAMPBELL P G, BISSON M. Sequential extraction procedure for the speciation of particulate trace metals [J]. Analytical Chemistry, 1979, 51: 844-851. doi: 10.1021/ac50043a017 [34] HE R Z, PENG Z Y, LYU H H, et al. Synthesis and characterization of an iron-impregnated biochar for aqueous arsenic removal [J]. Science of the Total Environment, 2018, 612: 1177-1186. doi: 10.1016/j.scitotenv.2017.09.016 [35] FU H, MA S, ZHAO P, et al. Activation of peroxymonosulfate by graphitized hierarchical porous biochar and MnFe2O4 magnetic nanoarchitecture for organic pollutants degradation: Structure dependence and mechanism [J]. Chemical Engineering Journal, 2019, 360: 157-170. doi: 10.1016/j.cej.2018.11.207 [36] 张志军, 胡佳伟, 程萍. 生物炭载铁锰氧化物催化H2O2氧化含油废水 [J]. 水处理技术, 2019, 45(8): 61-66. ZHANG Z J, HU J W, CHENG P. Treatment of oily wastewater by charcoal supported iron-manganese oxides catalytic H2O2 oxidation [J]. Technology of Water Treatment, 2019, 45(8): 61-66(in Chinese).
[37] LIU L, WANG B, YAO X, et al. Highly efficient MnOx/biochar catalysts obtained by air oxidation for low-temperature NH3-SCR of NO [J]. Fuel, 2021, 283: 119336. doi: 10.1016/j.fuel.2020.119336 [38] LYU H, TANG J, HUANG Y, et al. Removal of hexavalent chromium from aqueous solutions by a novel biochar supported nanoscale iron sulfide composite [J]. Chemical Engineering Journal, 2017, 322: 516-524. doi: 10.1016/j.cej.2017.04.058 [39] LYU H H, GONG Y Y, TANG J S. Immobilization of heavy metals in electroplating sludge by biochar and iron sulfide [J]. Environmental Science and Pollution Research, 2016, 23(14): 14472-14488. doi: 10.1007/s11356-016-6621-5