Pb污染土壤的钝化处理及Pb形态转化研究

将矿粉∶水泥熟料∶硅粉以51∶9∶40的质量比混合配制钝化剂处理人工配置Pb污染土(Pb分别为500、10 000mg/kg),通过对固化体试件力学性能、Pb浸出特性及形态分布的分析,探究土壤钝化剂对Pb的钝化效果与钝化机制。结果表明,两种Pb污染土经钝化处理后,养护28d的固化体试件无侧限抗压强度均能达到2.0 MPa以上,满足填埋的强度需求。其中,低浓度固化体试件养护28d的Pb浸出质量浓度均在0.6mg/L以下,Pb的钝化率高达97%以上。高浓度固化体试件养护28d的Pb浸出质量浓度降至50mg/L以下,Pb的钝化率达87%以上。钝化处理后,土壤中的Pb从不稳定的酸可提取态、可还原态向稳定的可氧化态、残渣态转化,磷化物及氯化物的添加可以增强钝化剂对Pb的钝化效果。钝化剂水化生成钙矾石和水化硅酸钙,并与Pb发生化学吸附及同晶替代反应生成固溶体是Pb钝化的主要机制。

Study on passivation of Pb contaminated soil and transformation of Pb forms

A passivator was prepared by mixing mineral powder,cement clinker and silica powder at a mass ratio of 51∶9∶40 to treat artificially disposed Pb contaminated soil(Pb concentration was 500,10 000 mg/kg,respectively).The passivation effect and passivation mechanism of soil passivator on Pb were explored by analyzing the mechanical properties,leaching characteristics and morphological distribution of solidified specimens.The results showed that the unconfined compressive strength of solidified specimens cured for 28 days could reach more than 2.0 MPa after passivation treatment,which met the strength requirement of landfill.The leaching mass concentration of Pb in low concentration solidified specimens maintained for 28 days was below 0.6 mg/L,and the passivation rate of Pb was over 97%.After 28 days of curing,the leaching mass concentration of Pb in high concentration solidified specimens reduced to 50 mg/L,and the passivation rate of Pb was over 87%.After passivation treatment,Pb in soil transformed from unstable acid extractable state and reducible state to stable oxidizable state and residue state.Addition of phosphide and chloride could enhance passivation effect of passivator on Pb.The main passivation mechanism of Pb was the formation of ettringite and calcium silicate by hydration of passivator,chemical adsorption and isomorphic substitution reaction with Pb to form solid solution.