铀矿区放射性核素的污染问题是目前环境领域需要迫切解决的问题之一。铀是铀矿区环境中的典型污染物之一，也是铀矿区环境修复过程中需要重点治理的放射性核素。土壤是铀矿区污染物迁移转化的主要介质之一，腐殖酸胶体是土壤和地下水中的常见组分，会直接影响甚至改变核素在介质中的吸附和迁移行为。因此，在铀矿区核素污染控制及治理技术研究中，研究腐殖酸胶体作用下土壤对核素铀的吸附行为具有较强的应用价值。本研究依托于国家重点研发计划“铀矿区放射性核素污染控制及治理技术”，探究铀矿区土壤放射性核素污染形成机制，以铀矿区土壤为吸附介质，采用静态吸附实验方法，结合吸附动力学模型和热力学模型及多种微观表征技术，探究有无腐殖酸胶体作用下土壤对铀的吸附机理，为控制治理放射性核素污染提供理论依据。

（1）通过静态吸附批实验方法探究了无胶体、20 mg/L腐殖酸胶体和40 mg/L腐殖酸胶体三种体系下，胶体浓度、反应时间、pH、温度和碳酸根离子加入量对土壤吸附U能力的影响。结果表明：腐殖酸胶体对土壤吸附铀具有明显的促进效果，随腐殖酸浓度的增加，土壤对铀的吸附百分比和单位吸附量增大；土壤对铀的吸附可分为快速吸附（0-6 h）和缓慢吸附至平衡（6-168 h）两个阶段，均于168 h达到吸附平衡，吸附百分比分别为34.00%、42.33%和49.33%；随pH值升高，土壤吸附铀的能力呈现出先增大后减少的趋势，中性条件下土壤对铀的吸附能力最强，吸附百分比为73.29%；土壤对铀的吸附为吸附反应，温度增加，吸附能力增强；碳酸根离子会降低土壤的吸附能力，随着碳酸根离子加入量的增加，土壤对铀的吸附能力均降低。

（2）通过吸附动力学模型和等温吸附模型拟合分析实验数据，根据特征参数揭示腐殖酸胶体作用下U-土壤之间的吸附反应模式和吸附类型：无胶体作用下土壤对铀的吸附过程以化学吸附为主导，发生离子交换、络合反应等一系列化学吸附作用，其吸附行为符合准二级动力学模型、耶洛维奇动力学模型和颗粒内扩散模型；腐殖酸胶体作用下，化学吸附仍在吸附作用中占据主导地位，但因溶液中的铀酰会与胶体形成聚合物，扩散机制作用减弱，土壤对铀的吸附可被准二级动力学和耶洛维奇模型更好的描述，但颗粒内扩散模型较差；25℃时，无胶体作用下土壤对铀的吸附主要为多分子层吸附和专性吸附，吸附平衡特征更符合Freundlich等温吸附模型和Henry等温吸附模型；腐殖酸胶体的存在未明显改变土壤对铀的吸附平衡特征，25℃条件下，腐殖酸胶体作用下土壤对铀的吸附仍以多分子层不均匀吸附为主，吸附行为更符合Freundlich等温吸附模型。

（3）借助扫描电子显微镜（SEM）、X射线衍射（XRD）、傅里叶红外光谱（FTIR）和X射线光电子能谱（XPS）等多种光谱表征技术分析吸附反应前后土壤在微观结构、矿物组成、官能团含量及电子价态等方面的变化，明晰土壤吸附铀的反应机理和腐殖酸的影响机制。无胶体作用下，扩散作用、离子交换作用和络合反应是土壤吸附铀的主要机制。在快速吸附阶段，以物理吸附作用为主，体系中的UO₂²⁺因范德华力被吸附到土壤颗粒表面，形成多个吸附层，此过程的特点为吸附速度快而不具有选择性，土壤颗粒的结构和性质不会发生改变，属于可逆反应；在缓慢吸附至平衡阶段，以化学吸附为主，土壤矿物成分中的Ca²⁺、Mg²⁺和Fe³⁺离子可与UO₂²⁺发生离子交换反应，从而使得铀酰离子被吸附到土壤表面；此外，土壤中Si-O、Al-O、Al-OH等官能团可与UO₂²⁺发生络合反应从而将铀吸附到土壤表面。腐殖酸与铀结合成“假胶体”吸附到土壤表面是腐殖酸促进土壤吸附铀的主要影响机制。腐殖酸胶体因富含-OH、-C-O-C等官能团且表面呈现为电负性，可与溶液中的UO₂²⁺形成络合物，进而通过扩散作用被吸附到土壤表面，而后携带核素铀的“假胶体”通过络合反应被吸附到土壤表面，这一过程为不可逆反应。

The problem of radionuclide pollution in uranium mining area is one of the urgent problems to be solved in the environmental field. U is one of the typical pollutants in the environment of uranium mining area, and it is an element that needs to be focused on in the process of remediation and treatment of uranium mining area. Soil is one of the main media for the migration and transformation of pollutants in uranium mining areas. Humic acid colloid is a common component in soil and groundwater, which directly affects the adsorption and retardation effect of soil on nuclides. Therefore, in the study of nuclide pollution control and treatment technology in uranium mining areas, it is of great application value to study the adsorption behavior of U by humic acid colloid on soil. Based on the national key research and development plan " Control and treatment technology of radionuclide pollution in uranium mining area, " this study focuses on the formation mechanism of radionuclide pollution in soil of uranium mining area. The soil of uranium mining area is used as the adsorption medium. Static adsorption and desorption experiments, combined with kinetic and thermodynamic models and various characterization techniques, were used to explore the adsorption mechanism of under the action of humic acid colloids, and provide theoretical basis for controlling radionuclide pollution.

（1）The effects of colloid concentration, reaction time, pH, temperature and bicarbonate ion addition on the adsorption capacity of U in soil were studied by static adsorption experiments under three systems : without colloid, 20 mg/L humic acid colloid and 40 mg/L humic acid colloid. The results showed that humic acid colloids had a significant promoting effect on uranium adsorption by soil, and the percentage and unit adsorption of uranium by soil increased with the increase of humic acid concentration；The adsorption of uranium by soil can be divided into two stages: rapid adsorption (0-6 h) and slow adsorption to equilibrium (6-168 h), both reaching adsorption equilibrium at 168 h. The percentages of adsorption were 34.00%, 42.33% and 49.33%, respectively；The adsorption capacity of soil for uranium showed a trend of increasing and then decreasing with increasing pH, and the strongest adsorption capacity of soil for uranium under neutral conditions; the adsorption of soil for uranium was an adsorption reaction, and the adsorption capacity of soil for uranium increased with increasing temperature; bicarbonate ions would reduce the adsorption capacity of soil, and the adsorption capacity of soil for uranium decreased with increasing the addition of bicarbonate ions.

（2）Sorption kinetic model and isothermal sorption model fitting and their characteristic parameters analysis were used to reveal the sorption reaction pattern and type of sorption between U-soil under the action of humic acid colloids. The adsorption of uranium by soil without colloid conforms to the pseudo-first-order kinetic model, Elovich kinetic model and the intra-particle diffusion model, indicating that the adsorption process of uranium by soil is dominated by chemical adsorption, and a series of chemical adsorption such as ion exchange and complexation reaction occur. The sorption of uranium by soil under the action of humic acid colloids can be better described by the pseudo-first-order kinetic model and Elovich models, but the intra-particle diffusion model is poor, indicating that chemisorption under the action of humic acid colloids still dominates the sorption, but the role of diffusion mechanism is weakened by the formation of polymers with colloids by uranyl in solution.The adsorption behavior of soil on uranium without colloid at 25°C was more consistent with the Freundlich and Henry models, indicating that the adsorption of uranium by soil was mainly multi-molecular layer adsorption, and specific uranium ion adsorption sites existed on the soil surface; the adsorption behavior of soil on uranium by humic acid colloid at 25°C was more consistent with the Freundlich isothermal adsorption model, indicating that the adsorption of uranium by soil under the action of humic acid colloid was still mainly multi-molecular layer inhomogeneous adsorption, and the presence of humic acid colloid did not significantly change the adsorption equilibrium characteristics of soil on uranium.

（3）Scanning electron microscope (SEM), X-ray Diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) characterization techniques were used to analyze the changes of soil microstructure, element content, crystal structure and functional group types, element valence and electronic structure before and after adsorption reaction, and the adsorption mechanism was speculated. In the absence of colloid, diffusion, ion exchange and complexation are the main mechanisms of uranium adsorption by soil. In the rapid adsorption stage, physical adsorption is the main effect. UO₂²⁺ in the system is adsorbed to the surface of soil particles due to van der Waals force, forming multiple adsorption layers. This process is characterized by fast adsorption speed and no selectivity. The structure and properties of soil particles will not change, which is a reversible reaction. In the slow adsorption to equilibrium stage, chemical adsorption is dominant, and Ca²⁺, Mg²⁺ and Fe³⁺ ions in the soil mineral composition can undergo ion exchange reaction with UO₂²⁺, so that uranyl ions are adsorbed to the soil surface. In addition, Si-O, Al-O, Al-OH and other functions in the soil can react with UO₂²⁺ to adsorb uranium to the soil surface. The combination of humic acid and uranium into 'pseudocolloid 'adsorbed to the soil surface is the main mechanism of humic acid promoting soil adsorption of uranium. Humic acid colloids are rich in functional groups such as-OH, -C-O-C, and the surface is electronegative. It can form a complex with UO₂²⁺ in the solution, which is adsorbed to the soil surface by diffusion, and then the ' pseudocolloid ' carrying uranium is adsorbed to the soil surface by complexation reaction. This process is an irreversible reaction.