离子型稀土矿区土壤中氮化物迁移规律及转化机理研究

Ionic type rare-earth are mined out using the method of ion- adsorption type rare-earth ore insitu leaching mining which need lots of electrolyte solution such as ammonium sulfate to be used in mining process.Thus a lot of nitrogen compounds enter into soil and accumulate in the soil with time, which contaminate the soil and affect ecological environment of mining area seriously. Taking typical southern ionic type rare-earth mine as the research object as while as through ionic type rare-earth ore field sampling and analysis of soil, the aim ofthis study is to elucidate the the migration and transformation mechanism of nitrogen compounds in southern soil including ionic type rare-earth.The research contents are as follows: rare earth compounds in the distribution of mine soil and its form; nitrogen compounds migration and transformation; the effects of rare earth element types and content to nitrogen compounds interaction between migration and transformation; the effects of nitrogen compounds pollution to environmental ptotection. The rearch is to establish a theory on nitrogen compounds migration and transformation in southern soil including ionic type rare-earth based on survey and test analysis of nitrogen compounds pollution in rare earth mine soil.The results will form relatively complete theory about nitrogen compounds migration and transformationn in rare earth mine soil, which lay the theoretical and technological foundation for mine soil nitrogen pollution prevention, ionic type rare-earth ore reasonable mining and ecological protection.

离子型稀土浸矿开采过程中，因大量使用硫酸铵作浸矿剂，造成土壤中氮化物累积，引发矿区土壤及水体氮化物严重污染，危害了矿区土壤及水体生态安全与环境可持续发展。课题以赣南稀土矿区土壤为研究对象，采取科学划定稀土矿区、土壤甄别与采样与分析、实验室土壤柱模拟试验等相结合的研究方法，对其土壤中氮化物迁移与转化机理进行系统研究。研究内容包括稀土矿区土壤中稀土元素种类、含量及分布；氮化物的形态、含量与分布；氮化物的迁移规律及转化；稀土元素对氮化物分布、迁移与转化的影响因素及交互作用；氮化物污染对稀土矿区环境影响效应等。项目研究旨在研究土壤中稀土元素与氮化物的相互影响与交互作业，揭示氮化物在特殊土壤中的迁移规律及转化机理，形成较完整的离子型稀土矿区土壤中氮化物迁移规律与转化机理理论，对离子型稀土高效合理均衡开采、稀土矿区土壤生态保护与可持续发展、土壤氮化物污染防治与土壤复垦以及研究无氨技术开采稀土意义深远。

因大量使用硫酸铵开采离子型稀土，造成土壤中氮化物污染，威胁了矿区生态环境和生态文明。以南方离子型稀土-龙南足洞矿土壤为研究对象，科学选定区域、采样和测试分析数据，掌握了氮化物污染现状，绘制了氮化物污染现状图。.通过研制土壤柱模拟试验，取得较好研究成果。研究内容为土壤中氮化物形态及分布特征；土壤对铵态氮吸附特性；铵态氮赋存形态及迁移机理；氮化物迁移转化规律及运移机制；稀土对氮化物交互作用机理；氮化物污染环境效应等。主要成果：.⑴土壤氮化物主要由总氮、铵态氮、硝态氮等指标体现，总氮含量最高可达650mg/kg，氮化物污染主要以铵态氮为主。尾矿总氮含量远高于原矿和附近农田土壤，原矿和尾矿土壤中氮化物含量随取样深度增加而降低，铵态氮、总氮含量的垂直分布特征基本一致。土壤有机质缺乏，显弱酸性（pH=6.2～6.8）。⑵植被种植条件下，在试验后期（59d），表层土壤中铵态氮含量仍有45mg/kg，表明植物根系具有固氮作用，降低了铵态氮的迁移能力。植被能促使表层土壤中铵态氮在一定程度上向硝态氮转化。不同深度土壤中总氮含量与降雨量、淋溶时间之间的相关性可用4种方程拟合，土壤中氮化物的运移主要受到对流-机械弥散作用的影响。⑶稀土元素增强了原矿土壤的固氮能力，具有“低促高抑”的特点，对硝态氮的累积具有抑制效果，稀土元素与氮化物的交互作用机理主要为交换解吸作用。⑷原矿土壤对铵态氮的吸附热力学符合Langmiur模型，吸附动力学符合准二级动力学模型；土壤中铵态氮含量随深度变化的最优拟合方程均为三次函数，R2均大于0.9。⑸土壤中铵态氮的赋存形态分为水溶态、交换态以及固定态，交换态比例最高，铵态氮迁移依次为完全浸出带、有效浸出带、高峰浓度带、二次吸附带以及未浸出带。⑹水体氮化物距稀土开采点越近，污染越严重；不同植物叶片中MDA、NR、POD含量受土壤氮化物污染程度影响。.研究成果揭示了稀土矿区土壤中氮化物迁移规律与转化机理，对矿区土壤氮化物防治、复垦和生态保护具有重要科学意义。