Combined remediation of As(Ⅲ)-contaminated soils by pre-oxidation, stabilization and solidification
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摘要: 固化/稳定化是重金属污染土治理的最常用方法，但因为As(Ⅲ)的迁移性强，固化处理As(Ⅲ)污染土的效果欠佳。提出了As(Ⅲ)污染土的预氧化—稳定化—固化联合修复方法，首先利用Fenton试剂将土中As(Ⅲ)氧化为迁移性弱的As(Ⅴ)，再用FeCl3稳定As(Ⅴ)，最后通过水泥固化进一步固定As(Ⅴ)。通过无侧限抗压强度试验、毒性浸出试验（TCLP）、合成沉降浸出试验（SPLP）、pH测试、连续萃取试验和光谱分析研究了联合修复的效果和机理。结果表明，Fenton预氧化能够有效提高修复效率，当Fe与As的摩尔比为1︰1、添加10%水泥时，TCLP和SPLP得到As的浸出毒性分别低至2.51，1.33 mg/L，修复效率分别高达97.46%，98.53%；FeCl3能促进水泥的水化并改善固化体的孔隙结构，提高固化体的强度；修复方法可将As转化为更稳定的形态，有效降低As的潜在环境风险；大多数As可以与铁的水合氧化物结合而被固定，但随着水泥用量增加pH增加，Fe-As的结合减弱，导致部分As释放；光谱分析结果表明，联合修复可以将土中92.5%的As(Ⅲ)转化为As(Ⅴ)，并通过水化硅酸钙的固封和钙矾石的离子交换将As固定。该研究为As(Ⅲ)污染土的高效修复提供了新的视角。Abstract: The solidification/stabilization (S/S) is the most popular method for treatment of heavy metal-contaminated soils, however, the S/S treatment of As(Ⅲ)-contaminated soils is not effective due to the high mobility of As(Ⅲ). A combined remediation technique is proposed, in which As(Ⅲ) is first oxidized to As(Ⅴ) by the Fenton reagent, then stabilized by FeCl3 and finally stabilized by cement. The unconfined compressive strength tests, toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP), pH measurements, sequential extraction procedure and spectroscopic investigations are carried out to investigate the effects and mechanism of the proposed technique. The results show that the Fenton pre-oxidation process significantly improves the remediation efficiency. Under an Fe-to-As molar ration of 1:1 and a cement dosage of 10%, the leaching toxicity of As in TCLP and SPLP is as low as 2.51 and 1.33 mg/L, and the immobilization efficiency reaches 97.46% and 98.53%, respectively. The hydration degree of the cement and the pore structure of the curing body are improved by FeCl3 and therefore the strength increases. The combined remediation can transform As to more stable phases and effectively reduce the potential environmental risk. The majority of As is bound to hydrous oxides of Fe, but an increase in pH due to the increasing cement dosage will affect the Fe-As binding and cause potential release of As. The spectroscopic investigations show that the proposed remediation can transform 92.5% of As(Ⅲ)to As(Ⅴ) and immobilize As by the encapsulation of calcium silicate hydrate and the ion exchange of ettringite. This study provides a new insight into the effective remediation of As(Ⅲ)-contaminated soils.
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Keywords:
- As(Ⅲ)-contaminated soil /
- pre-oxidation /
- stabilization /
- solidification /
- leaching toxicity
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表 1 试验用土的金属含量
Table 1 Metal contents in test soil
(单位：mg/kg) 金属元素 As Mn Al Fe Ca Mg 含量 8.9 679 67700 13100 9650 2470 
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表 2 连续萃取试验步骤
Table 2 Sequential extraction procedure
形态 萃取剂 萃取条件 固液比 洗涤步骤 F1 (NH4)2SO4 (0.05 mol/L) 震荡4 h，20 ℃ 1︰25 F2 (NH4)H2PO4 (0.05 mol/L) 震荡16 h，20 ℃ 1︰25 F3 草酸铵缓冲液（0.2 mol/L）；pH 3.25 暗处震荡4 h，20 ℃ 1︰25 草酸铵溶液(0.2 mol/L)；pH 3.25；固液比1︰12.5；暗处震荡10 min F4 草酸铵缓冲液(0.2 mol/L)；+抗坏血酸(0.1 mol/L) pH 3.25 开盖和非避光条件下，96 ℃水浴处理30 min 1︰25 草酸铵溶液(0.2 mol/L)；pH 3.25；固液比1︰12.5；暗处震荡10 min F5 HNO3/H2O2 微波消解 1︰50
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