环境地球化学国家重点实验室知识库

Ferrihydrite (FHY), a widespread Fe(III) (hydr)oxide, is abundant in earth surface and critical in affecting the environmental behavior of soil elements, such as rare earth elements (henceforth referred to REEs). Under anoxic conditions, the coexisting Fe(II) induces FHY conversion to the minerals with high crystallinity, such as lepidocrocite, goethite, or magnetite, where the phase transformation processes were affected by the coexisting ions. The interactions between REE ions (henceforth referred to Ln(III)) and FHY in the transformation system, however, are still not well understood. We therefore investigated Fe(II)aq-induced FHY transformation affected by four kinds of Ln(III) (Ce3+, Nd3+, Tb3+, and Lu3+). The discernible inhibition was found among the different treatments with different Ln(III), and both the FHY transformation and Fe atom exchange ratios decreased with coexistent Ln(III) that have larger atomic number. In this study, the Fe atom exchange ratios with different coexistent Ln(III) were linearly negatively depended on the molar enthalpy values of Ln(III), which are explained by the molar enthalpy considered to be important in affecting the adsorption behaviors of Ln(III). Furthermore, the adsorption behaviors can affect the incorporation efficiency of the Ln(III), so as to affect the Fe atom exchange and FHY phase transformation. The Ln(III) with larger atomic number can be stabilized more, which results from the effects of incompatible REEs in determining the efficiency of immobilizing Ln(III) in the transformed iron (hydr)oxides. Our research suggested the important role of FHY in the distribution of REEs and the key properties of REEs in affecting their different distribution characteristics in earth surface environments.