【作者】 胡少平；

【导师】 陈英旭；

【作者基本信息】 浙江大学 ， 环境工程， 2009， 博士

【摘要】 重金属是农业土壤环境和农产品中的重要污染物,重金属在土壤矿物、生物等界面的迁移和形态转化决定其在土壤圈中的归趋和生态效应。近年来,随着环境分子科学的发展和研究方法的突破,从分子水平深入认识重金属污染物在环境介质中的反应机制成为环境科学新的研究热点。本论文在传统分析方法的基础上,通过引入同步辐射X射线吸收光谱技术(SRXAS),对重金属在粘土矿物、土壤颗粒和植物根-土界面的分子形态进行了一些探讨,主要研究结论如下:明确了Cu在蒙脱石和赤铁矿表面结合的分子形态。在蒙脱石和赤铁矿表面,Cu原子赤道平面上的四个水分子被O原子取代,形成Cu-O配位。在蒙脱石表面,Cu除了与片层边缘O原子配位吸附外,还形成多核沉淀;在赤铁矿表面,Cu除与O原子结合外,还存在两种可能的结合形态,分别是形成内层配位和表面沉淀。通过草酸、Cu耐性植物海州香薷(Elsholtzia splendens)根分泌物、Cu耐性微生物(Pseudomonas putida CZ1)对矿物表面Cu结合分子形态影响研究表明,草酸和海州香薷根分泌物将赤铁矿和蒙脱石表面的Cu沉淀转化为有机酸结合态,在矿物表面表现出活化作用;Cu的耐性微生物CZ1促进了Cu在赤铁矿和蒙脱石中的吸附,且形成稳定性更好的Cu沉淀物,在矿物表面表现出固定作用,在CZ1作用下,赤铁矿和蒙脱石表面吸附的部分Cu转化为草酸酸和氨基酸络合态。突破了传统的土壤重金属形态分析方法,对Cu在污染土壤中结合的分子形态及其转化过程进行量化。以矿区污染土壤为材料,以硫化物结合态、矿物吸附态、腐殖质结合态的Cu为参比,通过不同分子形态Cu的同步辐射X射线吸收光谱特征分析,证明土壤中Cu含量大小依次为腐殖质结合态、赤铁矿结合态、水铁矿结合态、硅酸盐矿物结合态和硫化物结合态;在根分泌物影响下,土壤溶液中以草酸和根分泌物类似络合态Cu为主,土壤中水合离子态Cu显著下降,表明海州香薷根分泌物对土壤溶液中的Cu具有络合稳定作用;硫处理显著促进了土壤的酸化,硫处理后土壤中水溶态Cu含量显著上升,土壤溶液中85.5%的Cu以有机酸类似络合态存在。揭示了土壤中的Cu、Pb、As以胶体颗粒态迁移的规律,并对土壤可移动胶体颗粒中Cu的分子形态进行了探讨。以诸暨矿区和上虞矿区污染土壤中的Cu、Pb、As为研究对象,通过土柱模拟淋溶实验,发现土壤重金属在迁移过程中,逐渐向胶体颗粒富集,并随之迁移,证明土壤中重金属迁移的主要形态是胶体吸附态,而不是水溶态。通过SEM和TEM-EDX分析,发现土壤中可移动颗粒主要由硅酸盐矿物和有机质及铁铝氧化物胶结物组成,在胶体颗粒表面,存在一些含Fe氧化物和重金属硫化物的纳米颗粒;通过同步辐射X射线吸收光谱分析,证实可移动胶体颗粒中有机质、Fe氧化物是重金属的主要运移载体,并对不同分子形态的Cu含量进行了定量。揭示了在海州香薷根-土界面Cu的分子形态转化规律。通过同步辐射X射线吸收光谱技术分析,海州香薷根系活动对Cu的分子形态产生了较大的影响,在海州香薷根际区域,根分泌物促进了赤铁矿吸附态Cu的溶解,Cu主要与根分泌物中的羧基基团结合;阐明了硫处理对海州香薷根-土界面Cu分子形态的影响机制,发现硫处理首先促进了土壤中硅酸盐矿物和无定形氧化铁矿物中Cu的溶解,继而转化为与根分泌物络合,并且硫处理促进了海州香薷根表Fe氧化物的溶解和根系对Fe、Cu的吸收,根系吸收的Cu主要累积在根细胞壁中。更多还原

【Abstract】 Heavy metals show significant influence on quality and safety of soil environment or agricultural products.At the mineral and biological interface,the characters of transportation behavior and speciation play an important role on heavy metal eco-toxicity and their end-result in pedosphere.With the developing of molecular environmental theory and the evolution of new technologies in recent years, a late hotspot in the environmental science is that how to understanding the reaction mechanisms of heavy metals in environment medium at molecular scale.Based on the traditional analysis methods,the synchrotron radiation X-ray absorption spectroscopy (SRXAS) were used in present study.The aim of our study was to clarify the changes of heavy metals molecular speciation and their transportation mechanism at the surface of clay minerals,soil particles and root-soil interface.The main results were as follows:The results showed that at the surface of montmorillonite and hematite,the first shell of Cu was bonded to four equatorial O atoms.At the surface of montmorillonite, Cu is adsorbed by edge-sharing O atoms in mineral slice,or adsorbs as binuclear complexes.At the surface of hematite,Cu is adsorbed by O atoms and forms as inner-sphere complexes or binuclear complexes at the mineral surface.The influence of oxalate,root exudates from Elsholtzia splendens and bacteria(Pseudomonas putida CZ1) on molecular speciation of Cu at the surface of minerals were studied.Results showed that at the montmorillonite and hematite surface,the Cu molecular speciation was changed by oxalate and Elsholtzia splendens root exudates,the binuclear complexes were dissolved and complex with organic acid.Studies clarified that oxalate and Elsholtzia splendens root exudates can activate metals on mineral surface. Our studies showed that Pseudomonas putida CZ1 promotes Cu adsorption at the montmorillonite and hematite surface,and more stable deposits were formed at the mineral surface.Studies clarified that Pseudomonas putida CZ1 can stabilize metals on mineral surface by organic acid and amino acid.Using Cu sulfide,mineral adsorbed Cu and humus adsorbed Cu as model references,the character of Cu XAFS showed that Cu were mainly bonded by humus, hematite,ferrihydrite,silicate minerals and sulfide in sampling soil collected from Zhuji mine site.In soil solution,Cu is mainly complex with oxalate and root exudates under the influence of Elsholtzia splendens root exudates.The hydrate Cu concentration significantly decreased in soil solution after Elsholtzia splendens root exudates were added into soil,this revealed that the Elsholtzia splendens root exudates can stabilize Cu in soil solution.The soil pH was significantly decreased and dissolved Cu increased after sulfur treatment.In soil solution,85.5%Cu were complex with organic acid.Column experiments studies showed that particle-facilitated transport of heavy metals is likely to represent the dominant transport pathway in soil influenced by acid rain.Silicate minerals could be a carrier of heavy metals to facilitate transport in soil, Fe oxide could partially dissolve to increase heavy metals release in soil at more acid pH,or could act as a vector of heavy metals transport in soil.Results from SEM-EDX analysis demonstrated that some nano-particles such as sulfide or Fe oxide are absorbed onto mobile soil particles.We quantitatively analyzed the heavy metal absorbance in mobile soil particles and results from SRXAS analysis demonstrated that the dominant heavy metal vectors are mainly composed with organic matters and Fe oxides.Results from SRXAS analysis showed that a competitive absorption occurred between the Elsholtzia splendens root exudates and soil particles,the hematite adsorbed Cu were dissolved by root exudates and complex with carboxyl.The present studies clarified the mechanisms that how sulfur influence the Cu molecular speciation at root-soil interface.Results showed that sulfur promotes the desorption of Cu from silicate and ferrihydrite,the released Cu were re-adsorbed by Elsholtzia splendens root exudates.It was illustrated that sulfur can promote the uptake of Cu and Fe in Elsholtzia splendens,and Cu is mainly precipitated on cell walls in Elsholtzia splendens root.更多还原