三价铁促进生物氧化锰稳定土壤砷的效果和机制

Promoting effect and mechanism of Fe(Ⅲ) on the stabilization of arsenic by biogenic Mn oxides in contaminated soil

通过室内模拟实验,研究了三价铁对生物氧化锰(BMO)稳定化砷污染土壤的促进效果与作用机制.实验结果表明:三价铁的添加提高了BMO对土壤中砷的稳定化效率,当三价铁以质量分数百分比(以Fe计)为0.5%、1%、2%和4%添加时,砷的稳定化效率由单独BMO处理的63.02%增加至86.04%、93.86%、96.56%和97.98%;由连续提取实验结果可知,添加三价铁能够促进土壤中砷的结合形态由可交换态、专属吸附态向无定型铁锰结合态和结晶型铁锰结合态转变,增强土壤中砷的稳定化作用;风险分析进一步表明添加三价铁后砷的环境风险由中风险转变为低风险;矿物晶体结构分析表明,添加三价铁后土壤中出现水铁矿、纤铁矿等次生铁氧化物,这些铁氧化物对土壤中砷有良好的吸附固定能力.总体而言,三价铁的存在能够提高BMO对砷污染土壤的稳定化效率,但三价铁的添加量不宜过高,否则会引起土壤酸化问题.

The promoting effect and mechanism of Fe(Ⅲ) ions on the stabilization efficiency of arsenic(As) using biogenic manganese oxides(BMO) in contaminated soil were investigated by laboratory culture experiments. The results indicated that the addition of Fe(Ⅲ) ions(Fe, wt) improved the stabilization efficiency of As by BMO, and the stabilization efficiencies of As were enhanced from 63.02% in only BMO treatment to 86.04%, 93.86%, 96.56% and 97.98% in the presence of 0.5%, 1%, 2% and 4% Fe(Ⅲ), respectively. The sequential extraction tests indicated that the exchangeable and specifically-adsorbed As were transformed to amorphous and crystalline hydrous oxides of Fe/Mn bond As after addition of Fe(Ⅲ), which increased the chemical stabilization of As. According to the results of risk analysis, the potential risk of As in contaminated soil changed from medium risk to low risk after the addition of Fe(Ⅲ). Moreover, the analysis of mineral crystal structure indicated that the secondary iron oxides including ferrihydrite and akaganeite were generated after addition of Fe(Ⅲ) ions, which have strong abilities to adsorb and immobilize As in soils. Overall, the addition of Fe(Ⅲ) can improve the stabilization efficiency of As in contaminated soils, but the dosage of Fe(Ⅲ) should not be too high, otherwise it will cause soil acidification.