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Data Sheet 1_Mineral-dependent and calcium-inhibited adsorption of radium-226 onto quartz and kaolinite in a natural sand substrate.docx C. L. Proulx (24988249) C. Cadieux (24988252) D. R. Knaack (14331996) D. Fortin (24771811) R. R. Goulet (24988255) Environmental Chemistry clay minerals competitive adsorption first order kinetic ion exchange radionuclide radium-226 speciation surface complexation <p>Radium-226 (226Ra) is mobilized following the disturbance of ore bodies containing uranium-238. The availability of radium-226 to aquatic organisms is governed by its aqueous speciation and sorption to mineral substrates. This study evaluated the influence of mineral phases, calcium (Ca) concentration, and organic matter content on the partitioning of ²²⁶Ra over 48 h. Tests were conducted across three nominal ²²⁶Ra activity concentrations (1, 5, and 50 Bq L^-1) and four Ca levels (0.9, 7, 35, and 70 mg L^-1) representative of freshwater systems both affected and unaffected by metal-mining effluent. Under solution-only conditions, dissolved ²²⁶Ra remained stable, indicating that Ca concentration alone did not influence ²²⁶Ra solubility. The addition of natural sand resulted in rapid removal of dissolved ²²⁶Ra from solution, reaching up to 86% after 48 h depending on ²²⁶Ra and Ca concentrations. Overall, removal decreased significantly with increasing Ca concentration, suggesting that Ca²⁺ reduced ²²⁶Ra²⁺ adsorption, consistent with competition between ²²⁶Ra²⁺ and Ca²⁺ for sorption sites. The presence of organic matter in the form of algal cells produced a small but consistent additional removal of ²²⁶Ra (∼6%), indicating that interactions between ²²⁶Ra and organic matter were limited relative to mineral processes. Mineral-specific experiments demonstrated that ²²⁶Ra sorption was strongly mineral-dependent, with extensive sorption onto kaolinite (96% ± 2% within 6h; K_d = 49–62 L kg^-1) and minimal sorption onto quartz (10% ± 9% at 48h, K_d = 0–0.55 L kg^-1). These findings demonstrate that ²²⁶Ra partitioning in sandy aquatic environments is governed primarily by the presence of reactive clay minerals rather than quartz or organic matter, and by aqueous Ca concentration. Under the controlled laboratory conditions of this study, these findings provide insight into the factors governing ²²⁶Ra mobility and bioavailability in sandy sediments where clay content and water chemistry strongly influence the fate of ²²⁶Ra.</p> 2026-09-16T14:15:33Z Dataset Dataset 10.3389/fenvc.2026.1912040.s001 https://figshare.com/articles/dataset/Data_Sheet_1_Mineral-dependent_and_calcium-inhibited_adsorption_of_radium-226_onto_quartz_and_kaolinite_in_a_natural_sand_substrate_docx/33854530 CC BY 4.0