Uranyl Retention on Quartz—New Experimental Data and Blind Prediction Using an Existing Surface Complexation Model

The adsorption behaviour of uranyl onto seven different samples of quartz was studied in batch experiments. Sea-sand (0.1–0.3 mm), Fil-Pro 12/20 (1–2 mm) and five Min-U-Sil samples with smaller particle sizes (5, 10, 15, 30 and 40 μm) were used. The uptake curves show “pH adsorption edges” in the range of pH 4–5. A good agreement of the new data with literature data was found when plotting surface-normalised distribution coefficients versus pH. Differences in the adsorption behaviour for pre-treated and untreated sea-sand samples were detectable resulting in a shift of the pH edge to higher pH values after treatment. A literature surface complexation model was applied for blind predictions of the experimental results. The simulations described the experimental observations quite well for the Min-U-Sil samples. For the two coarser quartz samples, the calculated over-predictions were explained by the larger-than-expected measured specific surface area and measurable amounts of associated minerals, for Fil-Pro 12/20 and sea-sand, respectively. Dissolution of the samples was studied as a function of pH. After 5 days, the measured Si concentrations were all higher than equilibrium quartz solubilities, but lower than those of amorphous silica. With increasing pH, dissolved silica increased. This strongly suggests that formation of dissolved uranyl–silicato complexes have to be considered based on measured silica concentrations.