稀土矿区土壤氨氮与重金属复合污染特性的表征与机理解析

As an important strategic resource, rare earth elements have been widely used in many fields of national defense and national economy. Up to now, in situ leaching technology which employed ammonia salt as leaching agent is main mining method for rare earth. However, due to incomplete collection of leaching agent, complex pollution issue originated from ammonia and heavy metals has caused widespread concern in the society. This project orients for the specific environmental conditions of soil at rare earth mine which is complexly polluted by ammonia nitrogen and heavy metal. The aims are to explore the specificities of heavy metal pollution in this environmental conditions, and to analyze the relevant mechanisms. The project intends to adopt chemical extraction method and synchrotron radiation X-ray absorption spectrometry simultaneously to analyze the extraction morphology, molecular structural morphology and quantity distribution characteristics of heavy metals in the soil. Furthermore, soil column dialysis experiments operated under different combined conditions will be carried out to analyze the complex interaction mechanisms on the micro interface of soil among three elements constituted of ammonia nitrogen, organic matter fractions or mineral components, and heavy metals, to acquire the dynamic parameters of the relevant processes, and to clarify the formation and transformation mechanism of heavy metal pollutants. The results of this study have an important guiding role for the accurate analysis of the bioavailability of heavy metal pollutants and polluted environmental remediation.

稀土元素作为一种重要的战略资源，在国防和国民经济的诸多领域被广泛应用。稀土采矿目前主要是采用氨盐原地浸矿技术，由于浸矿剂收集不完全而导致的氨氮和重金属复合污染问题已经引起了社会的广泛关注。本项目针对稀土矿区土壤这种氨氮与重金属污染复合共存的特定环境条件进行研究，旨在探索该种情况下重金属污染所表现出来的特异性，并对其发生机理进行解析。本项目拟采用化学提取法和同步辐射X射线吸收光谱法共同分析重金属在土壤中赋存的提取形态、分子化学形态和数量分布特征，并结合不同控制组合条件的土柱渗析实验，分析土壤微界面上氨氮-有机质组分/矿物组分-重金属的三元复杂交互作用机制，获取相关过程的动力学参数，阐明重金属污染物的生成与迁移转化机理。本项目的研究结果对重金属污染物生物可给性精确分析和污染环境修复具有重要的指导作用。

稀土元素是重要的战略资源，尤其南方离子型稀土中含有重稀土元素，在国民经济和军事工业中具有举足轻重的作用。尽管稀土开采已经发展到第三代原地浸矿工艺，但由于需要采用大量高浓度的硫酸铵溶液作为浸矿剂，这些溶液在使用后会在土壤中有一定的残留，可能造成土壤和地下水污染的潜在风险。本项目首先针对典型南方离子型稀土矿区及周边土壤和地下水中重金属与氮污染的分布进行了调查分析，明确了污染分布的一般特征，尤其关注了氮污染对重金属污染分布的影响，结果表明铵污染在一定程度上降低了土壤pH值及酶活性，铵对重金属迁移表现为协同作用，且其自身纵向迁移能力较强。针对矿区土壤污染物化学形态分析表明，原矿富含多种粘土矿物和稀土氧化物，粘土矿物中稀土元素主要以离子可交换结合态存在。矿区污染土壤静态和动态吸附研究表明，铵盐的存在与重金属阳离子的吸附存在竞争效应，不同种类铵盐和pH值对吸附过程具有一定影响，吸附过程属于非均匀多层吸附，适用Langmuir-Freundlich符合等温吸附模型。污染土壤解吸实验表明，清水淋洗对残留铵盐去除能力有限，不能有效降低氨氮污染风险。此外，本项目研究中还针对新型表面活性浸矿剂皂角苷和矿区微生物种群分布等问题同时开展了部分工作。