Sorption of Sn(IV) onto pure clay minerals and Boom Clay

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126Sn is a long-lived fission product and it is important to assess Sn sorption onto Boom Clay (BC), which is under investigation in Belgium as a potential host rock for deep geological nuclear waste repository. To better understand Sn(IV) sorption onto the clay minerals constituting BC, sorption of Sn(IV) was here investigated on Illite du Puy (IdP) and montmorillonite STx-1b in various conditions representative of potential repository conditions in BC: NaClO4 0.017 M in presence or absence of isolated BC dissolved organic matter (DOM), NaHCO3 0.015 M and Synthetic Seawater (SSW). Sorption edges were acquired from pH 3 to 12 and isotherms were acquired at pH ~8.4 at different Sn(IV) concentrations. Sn(IV) strongly sorbed on IdP and STx-1b over the full range of the pHs and concentrations investigated (log Rd ranging between 4.2 and 5.6 at pH ~8.4). The data obtained on STx-1b suffered from the influence of the used experimental solid/liquid ratio which complicated their interpretation. In the presence of carbonates, Sn(IV) sorption on IdP was slightly decreased (≤ 0.3 log units), highlighting the Sn(IV)–carbonate complexation. The effect of carbonate on Sn(IV) sorption on STx-1b was less clear. The presence of DOM reduced the Sn(IV) sorption on both clays (~0.5 log units on IdP for 4.5 mgC/L), confirming the strong complexation of Sn(IV) with DOM. The increase of salinity seemed to slightly decrease the Sn(IV) sorption on IdP (0.2 log units), but this result was not confirmed on STx-1b. The results obtained on IdP were modelled with the 2-site protolysis non-electrostatic surface complexation model. The surface complexation constants and aqueous complexation constants with carbonate and DOM were optimized to describe the experimental data. The applicability of the component additivity approach (CAA) was also tested to describe the experimental Sn(IV) sorption isotherm acquired on BC in BC pore water. The CAA provided a rough estimation of Sn(IV) sorption onto BC, but did not allow an accurate prediction highlighting the high sensitivity of the model to the Sn(IV)-DOM complexation.
Original languageEnglish
PublisherSCK CEN
Number of pages48
StatePublished - 27 Jan 2023

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NameSCK CEN Reports
PublisherSCK CEN

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