淹水对土壤重金属浸出行为的影响及机制

Effect and mechanism of water inundation on the leaching behavior of heavy metals in contaminated soils

为了明确淹水对土壤重金属浸出行为的影响及其作用机制,以实际场地重金属污染土壤为研究对象,开展了淹水实验。对淹水过程中土壤重金属的浸出浓度、氧化还原电位、pH、铁氧化物浓度及重金属形态等相关指标进行测定了分析。结果表明,淹水后,重金属浸出浓度随淹水时间呈现先增长后降低趋势。淹水初期(30 d),Cu、Zn、Cd和Pb浸出浓度分别增加了6.71%、4.03%、3.56%和4.55%。pH降低、有机质降解和铁氧化物还原溶解是导致重金属浸出浓度升高的主要原因。随淹水时间的持续增加,重金属浸出浓度逐渐降低并于90 d时趋于稳定。淹水结束时(180 d),Cu、Zn、Cd和Pb浸出浓度分别降低了23.78%、16.78%、15.48%和15.45%。重金属形态分析表明,淹水促使重金属赋存形态由酸可提取态转化为可还原态和可氧化态,降低了重金属活性;矿物成份分析证实了金属硫化铜物相的生成。新形成的无定形氧化铁对重金属的吸附作用和硫化物与重金属的化学沉淀作用是重金属浸出浓度降低的主要机制。该研究为淹水条件下重金属污染土壤风险控制提供了依据。

A highly smelter-contaminated and aged soil was used to study the leaching behavior of typical heavy metals induced by water inundation in batch experiments.The leaching concentration of heavy metals,Eh,pH,content of iron oxides and heavy metal speciation during the experiment were studied.The results showed that the leachate concentrations of heavy metals increased first and then decreased with the incubation time.At the first 30 days of flooding treatment,the leachate concentrations of heavy metals:Cu,Zn,Cd and Pb increased by 6.71%,4.03%,3.56%and 4.55%,respectively,which was mainly due to pH decreasing,organic matter degradation and iron oxides reduction and dissolution induced by water inundation.However,leachate levels of heavy metals decreased drastically between 30 and 90 days,and remained relatively constant thereafter.At the end of flooding treatment(180 d),the leaching contents of Cu,Zn,Cd and Pb decreased by 23.78%,16.78%,15.48%and 15.45%,respectively.Speciation analysis revealed that forms of occurrence of soil heavy metals changed from an acid extractable one to a reducible or oxidizable one,which decreased the activity of heavy metals.Meanwhile,increase of peak intensity for copper sulfide was observed via X-ray diffraction analysis.The decreased leachate contents of heavy metals were attributed to the adsorption of newly formed amorphous iron oxides and the chemical precipitation of sulfides and heavy metals.This study has implication for the formulation of risk control for heavy metals in contaminated soils under water inundation condition.