钙、氯对磷酸盐稳定污染土壤中铅的促进作用研究

为探讨促进磷酸盐稳定污染土壤中铅的方法,在全铅含量为517 mg·kg-1的铅冶炼污染土壤中加入5 mmol·kg-1磷酸盐,同时加入10mmol·kg-1硝酸钙或5 mmol·kg-1氯化钾,在15%或30%的含水率下培养40 d,之后种植黑麦草.结果表明,与单独施用磷酸盐相比,采用磷酸盐与钙、氯结合或增加培养期间的土壤含水率后,土壤DTPA-Pb含量下降3.92%~26.1%;对于同一添加剂处理,培养期间土壤含水率从15%增加到30%,土壤有效铅(DTPA-Pb)含量下降8.83%~24.4%.增加土壤含水率后,土壤有效磷(Olsen-P)含量均显著升高(p0.05).土壤铅的EXAFS分析表明,与未施用磷酸盐的对照相比,土壤中加入磷酸盐后矿物态铅的比例由57%上升至81%,加施钙、氯或增加土壤含水率后,多数处理矿物态铅的比例有所下降,而有机结合态铅比例上升.与对照相比,污染土壤中施用磷酸盐后,植物产量大幅增加,但施用钙、氯或增加培养期间含水率后,部分处理植物产量有所下降.以上结果表明,在铅冶炼污染土壤中加入磷酸盐时,加入钙、氯或者增加土壤含水率均有利于铅的稳定,但以上措施可能对植物生长产生不利影响.

Enhancement of phosphate immobilization of Pb in contaminated soils with Ca and Cl amendment

A lead (Pb) smelting contaminated soil was amended with phosphate and/or calcium (Ca), chlorine (Cl) at different soil moisture contents to investigate methods of gaining better lead immobilization with phosphate. The soil with total Pb concentration of 517 mg·kg^-1 was amended with 5 mmol·kg^-1 phosphate, and/or spiked with 10 mmol·kg^-1 Ca(NO₃)₂, 5 mmol·kg^-1 KCl, and incubated at 15% or 30% soil moisture contents for 40 d, then ryegrass was planted in the soils. The amendment with Ca or Cl or incubated at 30% soil moisture contents resulted in 3.92%~26.1% decrease of DTPA-Pb concentration than the soil amended with phosphate only and incubated at 15% soil moisture. For soils amended with the same additives, increasing soil moisture contents from 15% to 30% during the incubation resulted in 8.83%~24.4% decrease in DTPA-Pb concentrations. Soil Olsen-P contents were significantly higher in soils incubated at 30% moisture content than 15% soil moisture content (p<0.05). X-ray absorption spectroscopy results of the soils indicated that, phosphate amendment resulted in 81% of mineral-adsorbed Pb against the 57% in the control without phosphate amendment. For most of the soils amended with P, Ca and Cl at 30% soil moisture contents, the percentages of adsorbed Pb in soil Pb speciation decreased than the phosphate-only amendment at 15% soil moisture, while the percentages of organic bound Pb increased. Phosphorus amendment increased ryegrass yield substantially, however, further amendment with Ca or Cl or incubated at higher soil moisture resulted in lower ryegrass yield. The results demonstrate that, phosphate amendment of Pb smelting contaminated soils combined with Ca or Cl spiking or incubated at higher soil moisture content enhances immobilization of Pb, but may hinder the growth of plant growth.