纳米零价铁物相转变对砷污染土壤稳定化效果和潜在毒性的影响

为探究纳米零价铁团聚作用和氧化反应等物相转变对土壤中砷的稳定化效果和潜在毒性影响机制,选择纳米零价铁以及其可能的物相转变产物,包括微米零价铁、纳米级Fe₂O₃、微米级Fe₂O₃、纳米级Fe₃O₄等,通过室内模拟实验,研究纳米零价铁物相转变对砷污染土壤稳定化效果和潜在毒性的影响。结果表明:1)相比而言,纳米Fe0对土壤中砷的稳定化效率最优,当其添加量为5%时,水溶性砷含量由稳定化处理前的2.20 mg/kg降至0.11 mg/kg,稳定化效率为94.90%,同时,砷的环境风险由处理前的中等风险降至无风险;2)由浸出实验结果可知,团聚作用引起纳米零价铁向微米零价铁转变时,其对砷稳定化效率的影响并不显著(P>0.05);3)由植物毒性实验可知,纳米零价铁的团聚和氧化作用产物均会抑制油菜籽根系生长,影响种子相对根长,而对种子发芽率和种子发芽率指数无抑制作用;4)基于形态分析、植物毒性和风险分析可知,微米级Fe₂O₃和纳米级Fe₃O₄对土壤中砷的稳定化效率较低,稳定化处理后仍有一定环境风险。因此,在实际修复过程中,纳米零价铁物相转变引起土壤中砷的环境风险变化值得关注。

EFFECT OF PHASE TRANSFORMATION OF NANO-ZERO-VALENT IRON ON STABILIZATION AND POTENTIAL TOXICITY OF ARSENIC IN CONTAMINATED SOIL

In order to explore the effect of nano-zero-valent iron agglomeration and oxidation reaction on the stabilization effect and potential toxicity of arsenic (As) in soil, nano-zero-valent iron and its possible phase-transition products, including micro-zero-valent iron, nano-Fe₂O₃, micro-Fe₂O₃ and nano-Fe₃O₄ were selected, and the effect of phase transition of nano-zero-valent iron on the stabilization effect and potential toxicity of As-contaminated soils were studied. The results showed that:1) in comparison, nano-zero-valent iron had the best efficiency for As stabilization in the soil, and the water-soluble As content decreased from 2.20 mg/kg to 0.11 mg/kg, the stabilization efficiency was 94.90% when its addition amount was 5%. At the same time, the environmental analysis of As decreased from the medium risk to no risk level; 2) based on results of leaching experiments, it was found that the agglomeration of nano-zero valent iron to micro-zero-valent iron had no significant on the stabilization efficiency of As (P>0.05); 3) the phytotoxicity experiments indicated that the aggregation and oxidation products of nano-zero-valent iron could inhibit the growth of roots and affect the relative root length of rapeseed seeds, however, it had no inhibitory effect on relative seed germination rate and seed germination index; 4) according to morphological analysis, phytotoxicity and environmental risk analysis, we found that micro-Fe₂O₃ and nano-Fe₃O₄ had low efficiency for As stabilization in soils, certain environmental risks remained after stabilization treatment. Therefore, in the actual remediation process, the environmental risk of As induced by the phase transition of nano-zero-valent iron needs attention.