光照对无机阴/阳离子在暴露特定晶面赤铁矿上共吸附机制的影响

Nowadays, the geochemical cycle of iron oxides and its ecological environmental effects have drawn great concerns in the fields of geoscience science. Hematite is one of the most thermodynamically stable iron oxides, which is ubiquitous, environmentally friendly and shows high surface reactivity. In view of the fact that inorganic pollutants, such as heavy metal ions, rare earth ions and oxygen-containing anions, are often exposed to illumination in the exploitation, smelting and processing area of metal minerals resources, the project firstly make the controllable synthesis of hematite with the specific facets exposed. Then, we will focus on the effect of illumination on the co-adsorption mechanism of heavy metal (or rare earth) cations and oxyanions on hematite with the specific facets exposed through combining batch adsorption experiments, instrumental characterization (e.g., ATR-FTIR, XPS) with density functional theory ( DFT) calculations. Based on the obtained results, we intend to establish the "structure-effect" relationship between differences of the structure and reactivity of different facets of hematite and the co-adsorption of inorganic anions and cations, and try to understand how the migration of photo-generated electron (or hole) from hematite with the specific facets exposed under illumination can affect the surface reactivity of hematite as well as the redox reaction and co-adsorption process of inorganic anions and cations on hematite. The expected outcomes of this project may provide valuable information for clarifying the mineral characteristics, geochemical behavior and environmental functionality of hematite at earth’s near-surface as well as the scientific basis for the environmental pollution control and ecological remediation in the mining areas of metal mineral resources.

当前，铁氧化物的地球化学循环及其环境效应已成为地球科学领域的研究热点。赤铁矿是一种稳定性最高的铁氧化物，具有分布广泛、环境友好和表面活性高等特征。项目针对金属矿产资源开采、冶炼和加工区无机污染物常常暴露于光照的状况，从可控合成暴露特定晶面赤铁矿出发，将宏观批吸附实验与微观表征手段（ATR-FTIR和XPS）、密度泛函理论（DFT）计算相结合，重点考察光照对重金属（或稀土）离子与含氧酸根阴离子在暴露特定晶面赤铁矿上共吸附机制的影响。在此基础上，建立赤铁矿不同晶面的结构、反应性差异与无机阴/阳离子共吸附之间的“构-效”关系，揭示光照条件下暴露特定晶面赤铁矿如何通过光生电子（或空穴）转移改变其自身表面反应性进而影响无机阴/阳离子的氧化还原和共吸附过程。项目的预期结果可为系统阐明赤铁矿的矿物特征、地球化学行为和环境功能属性提供重要信息，并为金属矿产资源开采区的环境污染治理与生态修复提供科学依据。

本项目围绕“光照对无机阴/阳离子在暴露特定晶面赤铁矿上共吸附机制的影响”为这一科学问题，采用水热法合成了主暴露面为{001}晶面的赤铁矿纳米片和{012}晶面的赤铁矿纳米立方体，分别考察了无光和光照条件下无机阴/阳离子（含氧酸根离子、重金属离子等）在赤铁矿不同晶面上的吸附特征与差异，通过波谱分析等表征手段以及量化计算等研究手段，揭示了赤铁矿晶面反应性与磷酸根、铬酸根等含氧酸根吸附之间的构-效关系。在此基础上，阐明光照对赤铁矿晶面吸附变价金属离子的制约机制。. 项目主要取得如下重要认识：（1）赤铁矿{001}和{012}晶面之间的反应差异性在于二者的表面官能团（羟基类型和Fe3+离子密度等）不同；（2）无光条件下，赤铁矿{012}晶面对Cr(VI)的吸附优于{001}晶面，且分别符合Freundlich和Langmuir等温吸附模型，但均遵循准二级动力学模型，且在热力学上属于放热反应，二者对Cr的吸附以表面络合与静电吸附共同主导，{001}晶面的吸附构型为单齿单核，{012}晶面的吸附构型为双齿双核；（3）无光条件下，赤铁矿{012}晶面对P的吸附优于{001}晶面，均符合Freundlich等温吸附模型和准一级动力学模型，但在热力学上属于吸热反应，二者对P的吸附以表面络合与静电吸附共同主导，{001}晶面的吸附构型为单齿单核，{012}晶面的吸附构型为双齿双核；（4）无光条件下，赤铁矿{012}晶面对W(VI)的吸附优于{001}晶面，均符合Langmuir和Freundlich等温吸附模型和准二级动力学模型，红外图谱表明其形成了Fe-O-W键。（5）在单一Cr和Cr/Cd共存体系中，光照均促进赤铁矿晶面吸附Cr(VI)，且对{001}晶面吸附Cr的提升优于{012}晶面，小分子有机酸可有利于光照促进赤铁矿晶面对Cr的吸附。. 上述研究结果，为理解和掌握赤铁矿的地球化学行为及其环境功能属性提供有价值的新信息，并为金属矿产资源开采区的环境污染治理与生态修复提供科学依据。