生物炭复配磷酸盐对Pb-Cd污染土壤原位钝化修复的研究

Effect of biochar combined with phosphate on in-situ immobilization of Pb and Cd in contaminated soil

采用小区试验方法,选取生物炭、磷酸盐及两者复配材料作为钝化剂原位修复工业遗留场地Pb-Cd污染土壤,通过毒性浸出方法(TCLP)以及欧共体标准物质局(BCR)连续提取法分析钝化修复效果,以期获取最优化的钝化修复方法。结果表明,生物炭、磷酸盐及两者复配材料均能够有效降低土壤Pb、Cd的生物有效性和迁移能力。生物炭能提高土壤pH,使TCLP提取态Pb、Cd分别降低56.26%和83.54%,生物炭能促进重金属沉淀的形成进而提升残渣态Pb、Cd比例;磷酸盐主要通过矿物沉淀作用促使重金属由弱结合态向强结合态方向的转化,使TCLP提取态Pb、Cd分别降低70.66%、89.94%,残渣态Pb、Cd比例显著提升,进而有效降低Pb、Cd的生物有效性和迁移能力。生物炭和磷酸盐复配材料相比单一钝化剂材料未表现出协同作用,但复配材料在保证钝化修复效果的前提下,能补偿酸性磷酸盐造成的土壤酸化,在修复实践中更具应用优势。

Biochar,phosphate and composite material consisting of the above two materials were selected as immobilizing agents for the in-situ remediation of Pb and Cd contaminated soils using plot experiment in a brownfield site.In order to obtain the best immobilization approach,toxicity characteristic leaching procedure(TCLP)and European Community Bureau of Reference(BCR)sequential extraction procedure were employed to investigate the immobilization effectiveness.Compared to the control,all amendments decreased the bioavailability and the mobility of Pb and Cd in the soil.The addition of biochar increased soil pH,and decreased the concentrations of TCLP extractable Pb and Cd by56.26%and83.54%respectively;whereas the residual Pb and Cd were enhanced owning to the precipitation of heavy metals under biochar treatment.Addition of phosphate promoted the transformation of the weakly bound fractions of heavy metals to the strongly bound ones primarily through formation of insoluble minerals.TCLP extractable Pb and Cd under the phosphate treatment were decreased by70.66%and89.94%,while residual fraction contents were increased greatly,resulting in reduction of bioavailability and mobility of Pb and Cd.Composite material showed no synergetic effect on the immobilization comparing to single biochar or phosphate.However,the use of composite material could effectively neutralize the soil acidity caused by the acidic phosphate,which had advantages in soil remediation practice.