Dresden 2026 – scientific programme

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O: Fachverband Oberflächenphysik

O 36: Focus Session: Mineral-water interfaces II

O 36.6: Talk

Tuesday, March 10, 2026, 12:15–12:30, HSZ/0403

The mechanism of selenite incorporation into the calcite surface revealed by atomic-scale imaging — •Marie Luigs, Ralf Bechstein, and Angelika Kühnle — University of Bielefeld, Bielefeld, Germany

Selenium is an essential trace element for human health. However, the margin between its required and toxic intake is very narrow, making its distribution in soils and waters an important subject of research. Moreover, the interaction between the nuclear waste component 79Se and minerals in the Earth's crust is relevant for the selection of nuclear waste disposal sites. Selenium in the form of selenite can be incorporated into the mineral calcite by substituting for carbonate ions. However, the mechanism of selenite incorporation into calcite remains unknown. Here we demonstrate that selenite incorporation occurs at step edges during calcite crystal growth. Atomic-scale atomic force microscopy (AFM) images of the calcite surface exposed to a selenite-rich calcium carbonate growth solution shows that calcite layers grown in the presence of selenite displayed a significantly higher defect density than layers that were exposed to selenite only after their formation. These observations indicate that significant selenite incorporation into calcite, reflected by an increased defect density, does not occur via ion exchange on terraces but via step edge growth. Our results give further insights into the conditions required for selenite incorporation into calcite and present the first atomic-scale AFM images of a selenite-rich calcite surface.

Keywords: Selenite; Calcite; AFM; Incorporation