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近年来,随着有色金属的开采与冶炼活动,矿区及其周围土壤出现重度的类金属砷 (As) 、锑 (Sb) 复合污染,大多数的Sb污染来源于熔炼,且经常和As污染同时发生[1–3],As、Sb污染土壤对人类健康和生态风险构成重大威胁,因此有必要针对As、Sb复合污染土壤进行修复治理。目前,固化/稳定化[4–5]、土壤淋洗[6]、电动修复[7]和植物修复[8]被普遍研究应用于修复类金属污染土壤,在这些修复技术中,土壤淋洗是修复As、Sb污染土壤的一种有效方法,因为该技术可以通过淋洗剂提取从土壤中永久去除目标金属[9]。在土壤淋洗技术中,关键在于选用一种高效、绿色的淋洗剂。目前,无机酸和盐 (HCl,H3PO4及其盐类) [6,10]、螯合剂如EDTA[11]以及强碱如NaOH[12],是常应用于修复类金属污染土壤的淋洗剂。然而,EDTA对于修复As、Sb等以氧阴离子形式存在于土壤中的金属并不是非常有效[13];采用常规的强酸、强碱作为土壤淋洗剂会严重破坏土壤结构[9];有研究表明,一些化学淋洗剂会造成土壤养分流失[14]。相较于化学试剂,微生物制剂由于其成本低且无二次污染更具应用前景[15]。微生物的某些代谢物,如有机酸和表面活性物质,可以有效去除重金属[16-17],因此可以考虑应用于土壤修复。黑曲霉(Aspergillus niger)由于其在生长代谢中可以产生大量的低分子有机酸,被应用于重金属污染土壤的淋洗修复[18],然而,单一的生物制剂应用于土壤修复中效率较低,如何提高生物制剂的修复效率已是当今研究的热点之一。
纳米零价铁 (nano zero-valent iron,nZVI) 由于具有比表面积大,强还原性和高反应活性等特点被广泛运用于环境污染的治理,利用nZVI增强淋洗剂的修复效率可能是一种有前景的方法。WANG等[19]发现nZVI能够增强低分子有机酸去除污染土壤中的Pb。CAO等[20]利用nZVI增强有机酸去除污染土壤中的重金属,结果表明,与单一有机酸相比,矿山土壤Cd、Pb和Zn的去除率分别提高了12.8%、24.9%和11.6%,农田土壤Cd、Pb和Zn的去除率分别提高了19.2%、18.1%和8.93%。目前,关于nZVI用于修复As、Sb污染土壤的研究较少,且鲜有研究nZVI联用微生物发酵液淋洗修复类金属污染土壤。
本研究以As、Sb复合污染土壤为对象,探究nZVI对黑曲霉发酵液的增强淋洗,并探究nZVI质量浓度、pH和淋洗时间对土壤中As、Sb去除效果的影响;最后,考察淋洗前后土壤中As、Sb赋存形态的变化情况。
纳米零价铁与黑曲霉发酵液联用对砷锑污染土壤的淋洗修复
Washing remediation of arsenic and antimony contaminated soil by the combination of nano-zero-valent iron and Aspergillus niger fermentation broth
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摘要: 土壤砷 (As) 、锑 (Sb) 污染对生态环境和人体健康有着潜在的风险,采用黑曲霉发酵液 (FB) 与纳米零价铁 (nZVI) 联用淋洗修复As、Sb污染土壤。通过振荡淋洗实验,探究nZVI强化FB淋洗去除As、Sb的效果及不同条件下对As、Sb淋洗效率的影响。结果表明,制备的FB对污染土壤中As和Sb有着较好的去除效果,去除率可达84.1%和71.8%;nZVI对FB去除As、Sb有强化作用,在nZVI质量浓度为0.1 g·L−1、pH为1和淋洗时间为60 min的条件下,其淋洗效果最佳,对As、Sb淋洗效率可达96.6%和95.6%,修复后的土壤达到《土壤环境质量 建设用地土壤污染风险管控标准 (试行) 》 (GB 36600-2018) 二类用地标准。nZVI-FB对土壤中As、Sb的解吸动力学符合拟二级动力学方程。nZVI-FB能够有效的提取土壤中As、Sb的铁铝氧化物结合态。本研究结果可为As、Sb复合污染土壤的淋洗修复提供参考。Abstract: Arsenic (As) and antimony (Sb) contamination in soils pose potential risks to the ecological environment and human health. Remediation of As and Sb contaminated soil by washing with the combination of Aspergillus niger fermentation broth (FB) and nano zero-valent iron (nZVI). The enhancement effect of nZVI combined with the broth in the soil washing process was studied, and the impacts of different conditions (such as pH, time, etc.) on the As and Sb washing efficiency were also investigated. The results showed that Aspergillus niger fermentation broth demonstrated good washing efficiencies on As and Sb in the contaminated soil, reaching 84.1% and 71.8%, respectively. The best elution effect was achieved at the nZVI addition of 0.1 g·L−1, pH 1 and 60 min of washing time, with the removal efficiency of 96.6% and 95.6% for As and Sb, and the As and Sb concentrations that remained in soil were lower than the standard value in Soil Environmental Quality, Risk Control Standard for Soil Contamination of Development Land in China. The kinetics of desorption of As and Sb from soil by nZVI-FB is consistent with the proposed secondary kinetic equation. The mixed washing agent can effectively extract the Fe/Al oxide bound state of As and Sb from the soil. The results of this study can provide a reference for the remediation of leaching of As and Sb contaminated soil.
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表 1 供试土壤的基本理化性质
Table 1. Basic physicochemical properties of the test soil
土壤质地 粒径分布/% pH 有机质
/ (g·kg−1)As
/ (mg·kg−1)Sb
/ (mg·kg−1)Fe/% Al/% 砂粒
(>20 um)粉粒
(2~20 um)黏粒
(<2 um)砂质壤土 54.83 39.62 5.57 4.42 7.68 970.10 525.16 4.20 2.51 表 2 黑曲霉发酵液的性质
Table 2. Properties of Aspergillus niger fermentation broth
pH 草酸/ (g·L−1) 葡萄糖酸/ (g·L−1) 柠檬酸/ (g·L−1) 苹果酸/ (g·L−1) 1.39 8.44 1.15 0.43 1.05 表 3 Wenzel连续形态提取法
Table 3. Wenzel sequential extraction procedures
次序 形态 提取剂 提取步骤 1 非专性吸附态(F1) 25 mL 0.05 mol·L−1 (NH4)2SO4 室温振荡4 h,离心10 min,取上清液过滤 2 专性吸附态(F2) 25 mL 0.05 mol·L−1 NH4H2PO4 常温振荡16 h,离心10 min,取上清液过滤 3 无定型铁铝氧化物结合态(F3) 25 mL 0.2 mol·L−1草酸铵溶液 (pH=3.25) 黑暗中常温振荡4 h,离心10 min,取上清液过滤 4 晶质铁铝氧化物结合态(F4) 25 mL 0.2 mol·L−1草酸铵+0.1 mol·L−1
抗坏血酸溶液光环境下以96±3 ℃振荡30 min,离心10 min,
取上清液过滤5 残渣态(F5) 2 mL HCl+6 mL HNO3+2 mL HF 消解后测定 表 4 nZVI-FB对土壤中As、Sb的解吸动力学参数
Table 4. Desorption kinetic parameters of As and Sb in soil in the washing of the nZVI-FB
类金属 拟一级动力学方程 拟二级动力学方程 Elovich方程 R2 RMSE R2 RMSE R2 RMSE As 0.9923 22.28 0.9965 15.08 0.9885 27.16 Sb 0.9790 20.28 0.9948 10.17 0.9921 12.46 -
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