外源硅对土壤铬(III)形态转化及生物有效性影响的化学机制

Silicon has the effect for reducing the bioavailability of heavy metals in soil. The mechanism of action is mostly reported in biological mechanisms, but there are few studies on how Si affects the speciation transformation of heavy metals in the aspects of soil chemistry. In view of the previous research, there is a deficiency in changing the pH of the soil system and introduce coexisting ions with Si application. Based on the elimination of the Si source alkalinity and accompanying ions, the soil-rice as a whole is adopted. Research is carried out in a combination of laboratory analysis, model prediction and bioassay experiments. In situ determination of free chromium concentration in soil by field-DMT cell, quantitative analysis of the effect of exogenous silicon on chromium speciation in soil solution. The non-equilibrium distribution and speciation distribution characteristics of exogenous Si on chromium in soil liquid phase and solid phase were predicted by Multi-Surface Model and the applicability of this model was verified under anaerobic conditions. X-ray diffraction (XRD) and Raman spectroscopy (Raman) were used. Infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) techniques were used to characterize the formation of water-soluble silicon-chromium complexes in soil solutions, and the formation of iron oxide-silicon-chromium complexes in the soil solid phase. Finally, the soil chemical mechanism of exogenous silicon affecting chromium speciation transformation in soil liquid and solid phase and its bioavailability is clarified.

施硅具有降低土壤重金属生物有效性的作用，其作用机制多集中报道于生物学机制方面，而有关硅如何影响重金属在土壤中形态转化的土壤化学机制研究尚少。针对以往研究存在因施硅改变土壤pH并引入共存离子的不足，本研究拟在消除硅源碱性和伴随离子差异的基础上，将土壤-水稻作为一个整体，采用室内分析、模型预测与生物验证试验相结合的方式开展研究。利用原位道南膜装置（Field-DMT cell）原位测定土壤中自由态铬浓度，以定量角度分析外源硅对土壤溶液中铬形态的影响，并结合多表面模型（Multi-Surface Model）预测外源硅对土壤液相及固相中铬的非平衡分配及形态分布特征并验证厌氧条件下多表面模型的适用性；综合运用XRD、Raman、FT-IR和XPS光谱技术表征硅与铬在土壤溶液中形成水溶性硅-铬复合物，在土壤固相中形成铁氧化物-硅-铬复合物。最终阐明外源硅对土壤铬形态转化及其生物有效性影响的化学机制。

硅作为环境友好型改良剂具有降低土壤重金属生物有效性的作用，但有关硅如何影响重金属在土壤中形态转化的土壤化学机制研究尚少。本项目针对以往研究存在因施硅改变土壤pH并引入共存离子的不足，在消除硅源碱性和伴随离子差异的基础上，将土壤-水稻作为一个整体，采用室内分析、模型预测与生物验证试验相结合的方式开展了研究。研究发现：外源硅抑制了铬对水稻幼苗的毒害作用并降低了其对水稻的生物有效性；外源硅降低了土壤液相自由态铬浓度并促进土壤固相铬向无效态转化；光谱技术表征阐明了硅与铬在土壤固相形成了铁氧化物-硅-铬复合物以降低其生物有效性。上述研究结果阐明了外源硅对土壤铬形态转化及其生物有效性影响的化学机制，研究结果有助于为重金属土壤污染修复与利用提供理论依据。