海泡石和磷酸盐对镉铅污染稻田土壤的钝化修复效应与机理研究

摘要

采用盆栽实验,研究了海泡石、酸改性海泡石以及二者与磷酸盐联合使用对镉铅复合污染稻田土壤的钝化修复效果,并通过培养实验和重金属形态分析探讨了不同钝化剂处理的作用机理.结果表明:添加海泡石可以显著提高污染土壤pH值,而磷酸盐和改性海泡石则对土壤pH值无显著影响.钝化处理能显著降低土壤TCLP提取态Cd、Pb的质量分数,最大降低率分别可达23.3％和47.2％,钝化剂复配处理对土壤TCLP提取态重金属的抑制效果优于单一处理.施用海泡石和磷酸盐,通过提高土壤pH值、物理化学吸附以及生成矿物沉淀等作用,可以促进污染土壤中的Cd、Pb由活性高的交换态向活性低的残渣态转化,从而显著降低Cd、Pb的生物有效性和迁移能力.添加钝化剂可以显著提高水稻各部位的产量,稻谷和稻草的最大增产率分别为34.3％和26.6％；钝化剂复配处理对水稻的增产作用明显优于单一处理.施用钝化剂可以显著降低水稻各部位的Cd、Pb质量分数,最大可使精米的Cd、Pb质量分数分别降低35.8％和40.9％,钝化剂复配处理对水稻吸收Cd、Pb的抑制作用明显优于单一处理,海泡石和磷酸盐复配处理中精米的Cd、Pb质量分数符合国家食品卫生标准要求.综合分析不同钝化处理的增产作用、降低作物Cd、Pb吸收以及土壤Cd、Pb可迁移性的作用可知,海泡石与磷酸盐复配处理对稻田土壤Cd、Pb复合污染的钝化修复效果最佳.%The effect of sepiolite, acid-modified sepiolite and their compound treatments with phosphate on immobilization of cadmium and lead in contaminated paddy soil was investigated using a pot-culture experiment, and the immobilization mechanism of these amendments was clarified through incubation experiment and analysis of heavy metal fractions. The sepiolite treatments could markedly increase pH values of soils, while the treatments with phosphate and acid-modified sepiolite could not significantly affect pH values. The immobilization treatments could significantly reduce concentrations of toxicity characteristic leaching procedure (TCLP) extractable Cd and Pb, with maximal reductions of 23.3% and 47.2%, respectively. The compound immobilization treatments appeared more efficient than the single treatments in reducing TCLP extractable Cd and Pb. Through increasing soil pH values, physicochemical adsorption, and the formation of mineral precipitation, sepiolite and phosphate could promote transformation of exchangeable Cd and Pb into residual fraction, resulting in significant reduction of heavy metals bioavailability and mobility. Addition of these amendments markedly increased biomass of rice plant parts, with maximal increase of 34.3% in grain and 26.6% in straw, respectively. The compound immobilization treatments appeared more effective than the single treatments in increasing biomass of rice. The immobilization treatments markedly decreased Cd and Pb concentrations in rice plant parts, with maximal reduction of 35.8% and 40.9% in polished rice, respectively, and the compound immobilization treatments appeared more effective than the single treatments in reducing Cd and Pb uptake of rice. The Cd and Pb concentrations in polished rice under the combined treatment of sepiolite and phosphate were lower than the maximum levels permitted by Chinese standard for cadmium and lead in foods (GB 15201-94, GB 14935-94). In summary, the combined treatment of sepiolite and phosphate was the most effective treatment for immobilization of Cd and Pb in contaminated paddy soil.