磷酸根对稀土元素-矿物界面作用的制约

Rare earth elements (REE) display fractionation and accumulation characters on the surficial mineral surface, e.g., clay minerals and Fe and Mn (hydr)oxides. Due to the strong complexation between phosphate and REE, phosphate should vary the fractionation-accumulation characters of REE on mineral-water interface. This would not only affect the mobility of REE, but also constraint the application of REE as important geochemistry indicator. In this program, the adsorption characters, atomic coordination environment and desorption kinetics of REE on typical surficial minerals, i.e., kaolinite, ferrihydrite and birnessite will be studied with the presence of phosphate, by batch adsorption experiment, in-situ spectroscopic characterization and first-principles calculation. The effect of physico-chemical conditions of environment, REE chemical properties and mineral types on the adsorption-desorption characters of REE will be analyzed, with emphasis on the structure-activity relationship between the atomic coordination environment of phosphate and REE, and the fractionation-accumulation characters and stability of REE on mineral surface. The obtained results will be helpful for better understanding the constrain mechanism of phosphate on the fractionation characters of REE on the mineral-water interface and further grasp of the surficial geochemistry behavior of REE.

稀土元素在粘土矿物、铁锰（氢）氧化物等表生矿物表面具有分异-富集特征。由于磷酸根与稀土离子具有较强的络合作用，磷酸根将改变稀土元素在矿物-水界面的配分特征，不但影响稀土元素的迁移能力，而且制约其作为重要地球化学指标的应用。本项目拟采用模拟实验、原位谱学表征以及量化计算等研究手段，考察磷酸根存在条件下，稀土元素在典型表生矿物（高岭石、水铁矿和水钠锰矿）表面的吸附特征、微观局域环境以及脱附动力学特征，分析物理化学环境、稀土元素化学性质以及矿物类型对稀土元素吸附-脱附特征的影响，重点探讨磷酸根、稀土元素微观局域环境与稀土元素在矿物表面分异-富集特征、稳定性的构效关系，深刻理解磷酸根对稀土元素在矿物-水界面配分特征的制约机制，进一步掌握稀土元素的表生地球化学行为。

本项目围绕“磷酸根对稀土元素-矿物界面作用的制约”这一科学问题，通过采用模拟实验、原位谱学表征以及量化计算等研究手段，考察磷酸根存在条件下，稀土元素在典型表生矿物（高岭石和针铁矿）表面的吸附特征和微观局域环境，分析水化学环境、稀土元素化学性质以及矿物类型对稀土元素吸附-脱附特征的影响，重点探讨磷酸根、稀土元素微观局域环境与稀土元素在矿物表面富集-分异特征的构效关系。在此基础上，探讨稀土与铁氧化物的相互作用及其对铁氧化物相转化的制约，探究稀土磷酸盐矿物在风化过程中的相转变特征，以及揭示磷壁酸对微生物细胞壁富集稀土元素的影响机制。. 本项目主要取得如下重要发现：（1）稀土离子在黏土矿物表面主要以外层吸附为主，而在铁氧化物表面以内层络合为主；（2）磷酸根与稀土离子在针铁矿表面形成三元络合物，导致针铁矿表面更富集中稀土；（3）共存的稀土离子抑制水铁矿向赤铁矿的转化；（4）随风化程度增加，磷灰石和磷铈铝石风化消失，抗风化能力较强的独居石和磷钇矿逐渐积累，导致风化壳矿物相中重稀土元素出现一定程度的富集；（5）细胞壁上的磷壁酸是造成轻-重稀土在细菌表面发生分异的主要位点。. 上述认识有助于深刻理解磷酸根对稀土元素在矿物-水界面配分特征的制约机制，进一步掌握稀土元素的表生地球化学行为。