不同钝化剂对重金属复合污染土壤的修复效应研究

Remediation of Multiple Heavy Metal Polluted Soil Using Different Immobilizing Agents

通过向重金属复合污染土壤分别施加5%和20%(钝化剂与土壤质量比)磷矿粉、木炭、坡缕石、钢渣4种钝化剂,测定了土壤p H值、重金属(Pb、Cd、Cu、Zn、As)生物有效态(单级提取)和各赋存形态(分级提取)的变化,评价了钝化剂对土壤重金属的钝化效果,采用X射线衍射法(XRD)和比表面-孔径分布仪测定了钝化剂的物相组成、比表面积和孔径特征,并探讨了钝化剂的修复机制。土壤重金属生物有效态单级提取结果表明,在20%处理下,坡缕石、钢渣、磷矿粉能显著降低土壤中5种重金属生物有效态含量,其中坡缕石降低Pb、Cd、Cu、As的最高比例可分别达54.3%、48.8%、50.0%、35.0%,钢渣降低Zn则高达43.7%。土壤重金属各赋存形态的分级提取结果表明,20%坡缕石能使植物易吸收的土壤可交换态Pb显著减少,而使难吸收的残渣态Pb显著增加;20%坡缕石、钢渣或磷矿粉能显著降低土壤中可交换态Cd含量;20%钢渣或20%磷矿粉处理后可交换态和碳酸盐结合态Zn含量明显减少,坡缕石处理使残渣态Zn显著增加;钢渣或20%磷矿粉能显著增加残渣态Cu含量;添加20%磷矿粉后生物难吸收的钙型砷含量显著增加。4种钝化剂对重金属的钝化机制各有不同,木炭和坡缕石具有较大的比表面积和孔容,对重金属的钝化以吸附和表面络合为主;钢渣和磷矿粉具有较高的p H值,其对重金属的修复机制以化学沉淀为主。

Four immobilizing agents, namely phosphate rock, charcoal, palygorskite and steel slag, were separately added to a soil polluted combinedly by five heavy metals to evaluate their effectiveness of immobilizing heavy metals. Soil p H and bioavailable fraction(single extraction) and chemical fractionations(sequential extraction) of heavy metals were measured. The phase composition, specific surface area and pore characteristics of four immobilizing agents were also analyzed by X-ray diffraction(XRD) and specific surface area-pore size distribution analyzer. Results showed that bioavailable fraction of five metals decreased significantly after additions of palygorskite, steel slag or phosphate rock at a ratio of 20%. The treatment with palygorskite resulted in the greatest reduction of bioavailable Pb, Cd, Cu and As, which was 54.3%, 48.8%, 50.0% and 35.0%, respectively. Applying steel slag also decreased bioavailable Zn by 43.7%. Exchangeable Pb decreased, while residual Pb increased significantly by addition of 20% palygorskite. Exchangeable Cd was decreased by applying 20% palygorskite, steel slag or phosphate rock. Exchangeable Zn was also decreased by additions of 20% steel slag or 20% phosphate rock. Carbon-ate-bound Zn(a fraction easily taken up by plants) was decreased by 20% phosphate rock or 20% steel slag additions. Residual Zn significantly increased by application of palygorskite. Similar result was also observed in residual Cu when steel slag(5% and 20%) or 20%phosphate rock were added. The Ca-As fractions, an inert fraction for plant uptake, increased significantly with applying 20% phosphate rock. The main immobilizing mechanism of charcoal and palygorskite was adsorption and surface complexation due to their large specific surface areas and pore volumes, while chemical precipitation was dominant immobilizing mechanism for steel slag and phosphate rock because of their high pH values.