posted on 2022-12-23, 15:03authored byJulia Neumann, Jessica Lessing, Sang Soo Lee, Joanne E. Stubbs, Peter J. Eng, Maximilian Demnitz, Paul Fenter, Moritz Schmidt
Interactions of heavy metals with charged mineral surfaces
control
their mobility in the environment. Here, we investigate the adsorption
of Y(III) onto the orthoclase (001) basal plane, the former as a representative
of rare earth elements and an analogue of trivalent actinides and
the latter as a representative of naturally abundant K-feldspar minerals.
We apply in situ high-resolution X-ray reflectivity to determine the
sorption capacity and molecular distribution of adsorbed Y species
as a function of the Y3+ concentration, [Y3+], at pH 7 and 5. With [Y3+] ≥ 1 mM at pH 7, we
observe an inner-sphere (IS) sorption complex at a distance of ∼1.5
Å from the surface and an outer-sphere (OS) complex at 3–4
Å. Based on the adsorption height of the IS complex, a bidentate,
binuclear binding mode, in which Y3+ binds to two terminal
oxygens, is proposed. In contrast, mostly OS sorption is observed
at pH 5. The observed maximum Y coverage is ∼1.3 Y3+/AUC (AUC: area of the unit cell = 111.4 Å2) for all the investigated
pH values and Y concentrations, which is in the expected range based
on the estimated surface charge of orthoclase (001).