Deciphering Ni isotope fractionation at Fe-oxides surfaces

We will study the interactions of Ni ions with iron oxides goethite and maghemite-magnetite solid solutions (Fe3-dO4) in aqueous solution, as well as the impact of natural organic matter on these interactions. We make the hypothesis that adsorption of Ni2+ on different Fe-oxides (or its adsorption on specific crystal faces of a given mineral) will lead to surface complexes with different structures. Because isotope fractionation is sensitive to the local chemical environment and bond distances in the formed complexes, this may affect the fractionation of Ni isotopes, which could be used as a tracer in environmental studies. Here, we propose a Ni K-edge HERFD-XAS on FAME-UHD to determine the local environment of Ni at Fe-oxide surfaces, which is otherwise very challenging to perform on lower resolution beamlines because of the close energies of Ni and Fe K-edges

本研究将探究镍离子与水溶液中的针铁矿（goethite）及磁赤铁矿-磁铁矿固溶体（Fe3-dO4）之间的相互作用，同时考察天然有机质对该过程的影响。我们提出如下假说：二价镍离子（Ni2+）在不同铁氧化物表面的吸附，或是在特定矿物的特定晶面上的吸附，均会形成结构各异的表面络合物。由于同位素分馏对所形成络合物的局部化学环境与键长具有高度敏感性，该过程可能会改变镍同位素的分馏行为，而这一分馏特征可作为环境研究中的示踪剂。鉴于镍与铁K边的能量极为接近，在低分辨率光束线上开展此类实验极具挑战性，因此本研究拟在FAME-UHD光束线上开展镍K边高能量分辨荧光检测X射线吸收谱（Ni K-edge HERFD-XAS）实验，以表征铁氧化物表面镍离子的局部化学环境。