土壤中铅锌的稳定化处理及机制研究

Stabilization Treatment of Pb and Zn in Contaminated Soils and Mechanism Studies

本研究采用磷酸二氢钾、生石灰、氯化钾以一定比例混合,对铅锌矿区污染土壤进行稳定化处理,并通过TCLP和Tessier连续提取法对稳定化效果进行分析和评价.利用X射线衍射仪(XRD)和扫描电子显微镜(SEM)对土壤进行形态和结构研究,分析稳定化机制.结果表明,P/Pb摩尔比在2~4,ω(Ca O)/ω(Soil)投加比在0.1%~0.5%,氯化钾投加量在0.02~0.04 mol时,Pb的稳定效率在80%以上,且Pb、Zn浸出浓度远低于标准限值.土壤中铅、锌的稳定化处理主要是将铅、锌从交换态转化为了残渣态,有效地限制了重金属离子的迁移.XRD和SEM分析表明,稳定化处理后形成的Ca-P-Pb沉淀、磷酸铅盐[PbHPO_4、Pb_3(PO_4)_2]、类磷氯铅矿(Pb-PO_4-Cl/OH)及混合重金属沉淀物(Fe-PO_4-Ca-Pb-Zn-OH)相互交联将重金属离子裹缚起来,形成稳定的结构,使得重金属离子难以浸出.

In the present work,the combined application of potassium dihydrogen phosphate,quick lime and potassium chloride was used to immobilize the Pb and Zn in contaminated soils. The efficiency of the process was evaluated through leaching tests and Tessier sequential extraction procedure. The mechanism of stabilization was analyzed by X-ray diffraction( XRD) and scanning electron microscope( SEM) to reveal the mechanism of stabilization. The results showed that the stabilizing efficiency of Pb contaminated soils was above 80% and the leaching concentrations of Pb,Zn were far below the threshold when the ratio of exogenous P and soil( mol·mol^(-1)) was 2∶ 1-4∶ 1,the dosing ratio of Ca O was 0. 1%-0. 5%( mass fraction) and the dosage of potassium chloride was 0. 02-0. 04 mol. Meanwhile,Pb and Zn in soil were transformed from the exchangeable fraction into residual fraction,which implied that the migration of Pb, Zn in soil could be confined by the stabilization treatment. XRD and SEM analysis revealed that Ca-P-Pb precipitation,lead orthophosphate [Pb HPO_4,Pb_3( PO_4)_2],pyromorphite( Pb-PO_4-Cl / OH) and mixed heavy metal deposits( Fe-PO_4-Ca-Pb-Zn-OH) could be formed after solidification / stabilization in which Pb and Zn could be wrapped up to form a solidified composition and to prevent leaching.