A thermodynamic adsorption/entrapment model for selenium(IV) coprecipitation with calcite

Quantum Chemical Investigation of the Selenite Incorporation into the Calcite (101̅4) Surface

“…The determination of the structure of SeO into calcite compared to the gas phase values, because here the oxygen ions are charged less negative compared to the gas phase. This is quite close to the result (168 pm) of Heberling et al 18 The optimization was completely straight forward using the hexagonal unit cell, but we ran into some problems using the monoclinic unit cell. For the monoclinic unit cell we proceeded in two steps.…”

“…(2) and (3) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 the previously proposed entrapment mechanism. 18 Especially the interpretation in terms of entrapment energy, previously used to estimate the supersaturation level, necessary to drive entrapment, gains relevance now as it is demonstrated that the free energy related to a certain surface composition rises abruptly when this surface is buried under an additional layer of calcite.…”

“…(10) to (16) in Heberling et al 18 ) for different cases of substitution we look at the reactions We determined the corresponding reaction energies…”

“…[42][43][44] There are numerous experimental studies investigating various aspects of the calcite(1014)/water interface as well. 18,[45][46][47][48][49][50][51][52][53] In our work we aimed for an improved theoretical understanding of the incorporation mechanism of selenium into calcite surface layers similar as carried out in an earlier experimental work by Heberling et al 18 Hence we studied the incorporation of selenium into bulk calcite, similarly as had been done by Aurelio et al 21 But we extended this study by investigation how selenium is incorporated into the surface and subsurface layers of the calcite (1014) surface. For this we used different models for the dry and hydrated calcite surface allowing an additional view on the influence of surface water.…”

“…We put an emphasis on the structural changes of pure calcite from the dry surface to the hydrated surface induced by the presence of water as well as the arrangement of the water layers adjacent to the surface. In the second part we studied the structural changes upon incorporation of selenite into the bulk phase and the dry and hydrated For this work we compared our results with the already available theoretical and experimental data of Aurelio et al, 21 Lardge et al, [29][30][31] Cheng et al, 45 Geissbühler et al, 47 Heberling et al 18,49 and Fenter et al 50,51 These studies have a similar focus as ours and provide a broad range of theoretical and experimental data to assess the accuracy of our results. This is important to ensure the accuracy of our results in every step of this work.…”