生物炭负载纳米零价铁对地下水中六价铬的修复效果和影响因素研究

Study on the remediation effect and influencing factors of stabilized biochar supported with nano zero-valent iron on Cr(VI)in groundwater

纳米零价铁(nZVI)存在易团聚、钝化和迁移性差等问题,影响对六价铬[Cr(Ⅵ)]污染地下水的原位修复效果。为了开发一种低成本、绿色的nZVI改性材料,以球磨生物炭(BC)为载体负载nZVI,构建了nZVI@BC反应体系,再利用羧甲基纤维素(CMC)稳定nZVI@BC,合成了一种新型高效、抗钝化纳米级别的修复材料CMC-nZVI@BC。对改性前后的nZVI进行表征分析,探究了材料添加量、Cr(Ⅵ)初始质量浓度、初始pH值、温度及地下水化学组分对CMC-nZVI@BC去除Cr(Ⅵ)的影响,并阐明去除Cr(Ⅵ)的机理。得出如下结论:(1)铁碳质量比为2∶1时的nZVI@BC对Cr(Ⅵ)的去除效果最好,3 h内0.6 g/L CMC-nZVI@BC对50 mg/L Cr(Ⅵ)的去除率达99.9%,表现出较高的去除Cr(Ⅵ)的速率和能力;(2)去除Cr(Ⅵ)的主要机制是通过还原和沉淀反应;(3)在pH值2~10范围内,pH值对去除Cr(Ⅵ)有显著影响,温度影响较小;(4)SO_(2-)_(4)的存在促进了Cr(Ⅵ)的去除,而HCO^(-)_(3)、 NO^(-)_(3)、Ca^(2+)、Mg^(2+)和腐殖酸对Cr(Ⅵ)的去除均有不同程度的抑制作用。这些结果表明,CMC-nZVI@BC可以作为有效去除Cr(Ⅵ)的原位修复药剂,为nZVI在地下水原位修复的应用提供了依据。

Nano zero-valent iron(nZVI)has problems such as agglomeration,passivation and poor transportability,which affect the in situ remediation effect of Cr(VI)contaminated groundwater.To develop a low-cost,green nZVI modified material,a low-cost,green modification for nZVI was developed.The nZVI@BC reaction system was constructed by supporting nZVI with ball-milled biochar(BC)as carrier and then stabilized with carboxymethyl cellulose(CMC).CMC-nZVI@BC was synthesized as a novel high-efficiency,anti-passivation nano-scale remediation material.The nZVI before and after modification was characterized and analyzed,and the effects of CMC-nZVI@BC addition,initial concentration of Cr(VI),pH and temperature and chemical fraction of groundwater on the removal of Cr(VI)by CMC-nZVI@BC were investigated,and the mechanism of Cr(VI)removal by CMC-nZVI@BC was elucidated,and the following conclusions were obtained:(1)The best removal of Cr(VI)by nZVI@BC at the Fe and C mass ratio of 2∶1;the removal rate of 50 mg/L Cr(VI)by 0.6 g/L CMC-nZVI@BC within 3 h reached 99.9%,exhibiting a high removal rate and capacity of Cr(VI).(2)The main mechanism of Cr(VI)removal by CMC-nZVI@BC was reduction and precipitation.(3)In the range of 2 to 10,the pH value had a significant effect on the removal of Cr(VI)by CMC-nZVI@BC,with less effect of SO_(2)-4 HCO-3 NO-3temperature.(4)The presence of promoted Cr(VI)removal,while,,Ca^(2+),Mg2+and humic acid,all had different degrees of inhibition on Cr(VI)removal.These results suggest that CMC-nZVI@BC can be an effective in situ remediation agent for Cr(VI)removal,offering the possibility of applying nZVI for in situ groundwater remediation.