江西721铀矿区土壤-地表水-水稻中铀的迁移富集规律研究

It is a very common sight that uranium tailings are stacked in the open air. So, this phenomenon has led to uranium migration into the surface water. Uranium transprotation mechanism from uranium tailings into the surface water and the effects on nearby rice crops haven't been studied. The Jiangxi No. 721 Uranium Mine is the largest volcano-type uranium deposit in China. Under the support of the GIS Fractal Geostatistics Method and Vector machine, this project measures uranium from uranium tailings, uranium surface water, nearby soil and nearby rice fields as the research object. The project will describe four things:① uranium content and its spatial distribution characteristics in soil, surface water and rice of different areas in the No. 721 Uranium Mine; ② find the spatial coupling relation and establish connection number model about the uranium content in soil, in surface water and in rice(focus on grain); ③ describe the uranium migration mechanism from the uranium tailings to surface water to nearby soil and to nearby rice patties; and ④ describe uranium contamination of rice and the possible influencing factors (e.g., pH, stagnant water versus flowing water). This study can reveal the uranium migration, the transformation and the enrichment mechanism in the No. 721 Uranium Mine tailings and understand the influence of factors like pH and water speed on the mechanism of uranium contamination on rice. The report will provide a scientific basis for the No. 721 Uranium Mine tailings planning, governance and its surrounding environment safety evaluation.

我国铀矿尾矿渣的露天堆放极为普遍，导致铀易随地表水迁移。江西721铀矿是目前最大的火山岩型铀矿，其露天矿渣中铀在地表水中的迁移规律及其对矿区主产作物如水稻的相互作用未见研究。本项目以'铀矿尾矿渣→地表水→土壤→水稻'体系为研究对象，运用GIS支持下的分形地统计学方法和支持向量机，研究：①铀矿区不同类型区域内土壤、地表水和稻谷中铀的含量及空间分布特征；②水稻（以稻谷为重点）与土壤、地表水中铀含量的空间藕合关系，建立稻谷与土壤、地表水中铀含量之间的关联数量模型；③'铀矿尾矿渣→地表水→土壤→水稻'体系中核素铀的迁移规律；④探索矿区水稻对铀的富集机制及可能的影响因素。本项研究能够揭示我国大量存在的露天铀矿渣中铀的迁移、转化和富集规律，了解铀对水稻等作物的影响机制，为铀矿渣的治理及其周边环境的安全评价提供科学依据。

相山铀矿已有50余年的开采历史，铀矿开采过程中产生的大量尾矿和含矿废水没有得到有效处置，对矿区环境造成了较为严重的放射性铀污染。本项目系统研究了铀矿区水稻土-地表水-水稻体系中铀含量和空间分布，展开铀污染评价，探究了水稻土-地表水中铀含量的空间耦合关系，对稻米中铀元素开展健康风险评价，构建了水冶厂区稻米中铀含量预测模型，深入分析了水稻土、稻米中铀含量分布成因。. 研究结果表明相山铀矿区水稻土、地表水和稻米中铀含量明显高于对照区和江西省背景值，矿区水稻土中铀含量平均值分别是对照区平均值和江西省背景值、国家背景值的11.18倍、6.07倍和8.82倍，地表水中铀含量平均值分别是对照区平均值和江西省背景值的64.34倍、199.45倍，稻米中铀含量平均值分别是对照区平均值和江西省背景值的2.43倍和2.18倍；正在采矿区水稻土、地表水和稻米中铀含量明显高于含矿未采区，其铀含量平均值分别是含矿未采区铀含量平均值的5.20倍、38.40倍和1.55倍。矿井及水冶厂产生的含铀废水、露天堆放的尾矿是影响矿区水稻土中铀含量的最主要因素。尾矿堆中的铀元素受天然降水的淋溶作用活化进入溪流，然后通过灌溉在水稻土中富集，水稻土与地表水中铀含量空间分布具有高度耦合性。同时，多个土壤剖面不同深度土层铀含量均呈现从表层到底层递减的规律，也证实了表层水稻土中铀元素的富集主要是受铀矿采冶等人为因素影响，而非受基岩本底值的影响。铀矿区儿童直接饮食稻米具有一定的致癌风险；开采矿井区和水冶厂区的成人直接饮食稻米存在一定致癌风险，首次提出了江西省大米铀元素致癌风险斜率系数为0.00104 (d•kg)/mg。. 研究表明土壤-地表水-水稻体系中铀元素迁移途径为：铀尾矿渣→地表水→水稻土→稻米，查明了铀污染源，为矿区铀污染防治及居民健康提供了数据支撑。此外，本项目在完成研究计划内容的基础上，对相山铀矿区土壤-地表水体系中铅、镉等重金属的含量、空间耦合性等方面也进行了研究，取得了较好的研究成果。