不同钝化剂对外源铅在土壤中的钝化效果及粒径分布的影响

通过室内钝化培养实验比较了羊厩肥、石灰和磷酸盐对土壤外源Pb的钝化效果和钝化修复后Pb的粒径分布特征。结果表明：3种钝化剂均能显著降低土壤中DTPA-Pb的含量，且钝化效果与钝化剂添加量成正比；磷酸盐对外源Pb钝化效果最好，P10处理下土壤中DTPA-Pb的含量降幅达80.53%，羊厩肥钝化效果最差，GM1对DTPA-Pb含量的降幅为6.51%；羊厩肥与磷酸盐将弱酸提取态Pb和可还原态Pb转变为活性更低的可氧化态Pb和残渣态Pb，以降低其活性，石灰将可还原态Pb转化为可氧化态Pb，以降低其活性；3种钝化剂添加均会提升土壤Olsen-P的含量。土壤磷淋溶临界值模型显示，当土壤Olsen-P含量>124.25 mg·kg⁻¹时，会发生磷素淋溶现象；Pb在土壤粗砂粒、细沙粒、粉粒和黏粒中的含量差别很大，但赋存形态无明显差异，钝化剂添加会影响外源Pb在各粒级颗粒中的富集及形态分布。相关性分析结果表明，钝化剂主要通过将细沙粒、粉粒和黏粒中的可还原态Pb转化为粉粒和黏粒中的可氧化态Pb来降低土壤Pb的毒害性。研究结果可为3种钝化剂在Pb污染土壤修复中的高效利用及修复后土壤的潜在生态风险管控提供参考。

Effects of different passivators on the immobilization effect and particle-size distribution of exogenous lead in soil

In order to compare the differences of immobilization effects of goat manure, lime and phosphate, and the characteristic of exogenous Pb distributions in soil particle-size fractions after remediation, exogenous Pb-contaminated soil incubation experiments were conducted. The results showed that three types of amendments could significantly reduce the DTPA-Pb contents in soil, and the immobilization effect was proportional to the dosages of amendments. Among three amendments, phosphate has the best immobilization performance on exogenous Pb, and the contents of DTPA-Pb in P10 treated soil decreased by 80.53%; while the immobilization effect of goat manure was the worst, and the DTPA-Pb contents in GM1 treated soil decreased by 6.51%. Goat manure and phosphate could convert the weak acid extractable fraction and reducible fraction of Pb into the oxidizable and residual fractions so as to reduce the soil available Pb, while lime could convert the reducible fraction into oxidizable fraction. The Olsen-P content of soil increased with the addition of these three amendments. The soil phosphorus leaching critical value model showed that when the Olsen-P contents were over 124.25 mg·kg−1, phosphorus leaching into the groundwater occurred. There was a large difference of Pb contents in coarse sand, fine sand, silt and clay, yet there was no significant difference regarding Pb speciation distribution. The addition of amendments affected the enrichment and speciation distribution of exogenous Pb in each soil particle-size fractions. The correlation analysis showed that toxicity of soil Pb was reduced by amendments mainly through converting the reducible fraction of Pb in the fine sand, the silt and the clay into the oxidizable fraction in the silt and the clay. This work provides theoretical support for the efficient use of three amendments on Pb contaminated soil and the potential ecological risk control afterwards.