耕作土壤中磷肥钒释放特征及其迁移转化机理研究

Vanadium is widely existed in fertilizer products, and it has higher contamination in phosphate. Vanadium and such toxic elements have released into cultivated soils through long-term application of phosphate, which directly threatens human health and ecological safety. However, the release process of phosphate is very complex, and now it is difficult to predict the long-term stability and potential environmental risks of heavy metals such as vanadium. Therefore, it is very urgent to study the impact of phosphate on vanadium migration and transformation in agricultural soils, which can provide theoretical and technical support for vanadium pollution control..Based on the evaluation of typical grain production areas of China (Wuchang, Cangzhou and Shangrao district), the mineral and chemical composition of phosphate, the geochemical behavior of vanadium released from reaction process of phosphate and water, and the effects of phosphate application to surface soil will be studied. Chemical extraction methods will be used in chemical speciation analysis, including single-extraction procedures and BCR sequential extraction procedure. Detailed structure and cation distribution of vanadium in soil particles will be studied by x-ray absorption fine structure (XAFS) under on-reaction conditions, including x-ray absorption near-edge structure (XANES), extended x-ray absorption fine structure (EXAFS) and synchrotron radiation x-ray fluorescence (SRXRF). And geochemical model will be used to simulate vanadium transformation in water-soil system. .The main goal of this project is to explore the geochemical mechanism of vanadium released from phosphate, the migration and transformation of vanadium incultivated soils and its main influence factors, and the environmental risk of vanadium released to farmland. These results will greatly enrich geochemistry basic theory of vanadium, and provide a useful help for pollution controlling and making its environmental quality standards of China.

钒广泛存在于化肥产品，尤其在磷肥中含量更高。磷肥的长期不当施用，会促使钒等有毒有害污染物的释放，是农田土壤污染的重要来源。但是磷肥-水-土作用过程十分复杂，目前难以预测钒等重金属元素在耕作土壤中的长期稳定性及潜在环境风险。基于此，本申请项目在我国典型粮食产区土壤环境调查的基础上，利用化学提取法、同步辐射技术和地球化学模型，通过对磷肥矿物组成、化学组成、磷肥-水作用过程中钒释放的地球化学行为、磷肥施用对耕作土壤的影响等内容进行系统研究，致力于揭示磷肥钒释放的地球化学特征及其在耕作土壤中的迁移转化机理，深入探索影响其迁移转化的主要因素，进而评价磷肥钒释放对农田的潜在环境风险。该项研究的开展不仅可以极大地丰富钒的环境地球化学的基础理论，还可以为我国钒的环境质量标准的制定及钒污染防治提供科学依据，具有重要的理论意义和应用价值。

化肥在农业活动中发挥着重要的作用。但是，化肥中除含有丰富的营养元素外，受生产工艺和原材料制约，还不可避免的含有大量重金属元素。近年来化肥的不合理施用，不仅导致了土壤酸化及营养元素失调，也使重金属等有毒有害污染物直接释放到土壤中。钒在化肥尤其是磷肥中广泛存在，长期不合理施肥将有可能导致农田土壤钒污染，对人体健康和生态系统构成威胁。.为探究磷肥中钒的释放特征及施肥土壤中钒的迁移转化规律，采用了化肥水解试验以及室内土柱淋溶实验，测定了化肥中V在不同pH水溶液中溶解性，并对土壤的基本理化性质及不同粒径土壤中V含量和不同形态V含量等进行了测定。主要研究结果如下：.（1）供试化肥中V含量基本都低于土壤中V的限量标准，但可溶态V含量较高，易于释放，具有潜在的环境风险。因此要避免过度施肥造成的V在土壤中的累积。.（2）供试红壤、褐土和黑钙土中V(Ⅴ)和有效态V含量较低，因此土壤中V的环境危害较小，但仍具有一定的潜在风险。土壤粒径越细，V含量越高，且土壤中V含量与Fe含量具有显著的正相关关系。.（3）土壤对一定pH范围内的降雨有一定的缓冲作用，但当淋溶液pH较低时，且淋溶达到一定体积之后，土壤对其缓冲能力降低。磷肥的添加对渗滤液中pH、EC值、胶体浓度以及V浓度均有影响，并影响了土壤对酸雨的缓冲能力，且与施肥量和磷肥种类有关。淋溶液pH为2.0时，V的释放量低于pH为4.5和7.0时的淋溶条件，但当淋溶体积达到3000-4000ml时，V的释放量随着渗滤液pH的降低有所增加。.（4）长期酸雨的淋溶会导致土壤的酸化，尤其是对上层土壤。降雨促进了土壤中V的迁移转化，增强了V的生物有效性，且V在土壤下层发生了累积，磷肥的添加对其影响较小。通过相关性分析发现，影响土壤中V迁移转化的主要因素是土壤pH；土壤中V(Ⅴ)含量与有效态V含量相关性达到0.948，因此土壤中V(Ⅴ)的含量也可作为土壤中V潜在危害的评价指标。