The study of the adsorption of contaminants in soils is a very active area of research in the fields of geochemistry and soil physical-chemistry. Some important constituents of soils, like clays, iron oxides, carbonates or sulfate minerals are of particular interest because their capacity to adsorb elements that are potentially risky for the environment, in the form of cations or oxyanions.

Carbonates are present in many near-surface environments. Specifically, calcite is a very abundant mineral and so its fundamental importance in many fields, related to immobilization of both inorganic and organic species. For this reason, ion incorporation in the structure of carbonate minerals is a subject of major concern, as well as the nanoscale mechanisms by which the ions are exchanged or substituted. In this context, co-precipitation is the most important mechanism by which an ion can get trapped into the bulk of a mineral, retarding its transport and subsequent availability to the environment.

In this work we present a systematic study of synthetic calcite samples co-precipitated with As(III), As(V), Se(IV) and Se(VI), to understand the sites and mechanisms of incorporation of their oxyanions. Combining spectroscopic (Neutron and X-ray Diffraction, EXAFS) and modeling (DFT) techniques, we probe the bulk minerals and gain insight into the substitution processes that take. Simulations help us to understand and predict which sites within the structure of the mineral would be more favorable for the substitution to occur.

The precise knowledge of the concentration of substituted As or Se in the bulk of the minerals is very important to predict the fate of these ions upon its release to the environment.

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1. Partial Structure Factors of Molten and Glassy Zinc Chloride
2. Sm³⁺ AND Eu³⁺ in Clay Interlayer: Neutron Diffraction with Isotopic Substitution