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

Abstract

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 lm) 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 seasand, 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.

A conceptual model to predict uranium removal from aqueous solutions in water–rock systems associated with low- and intermediate-level radioactive waste disposal

“…The adsorption of U to quartz and silica gel is well studied in the pH range between 3 and 9, with the result that the majority of adsorption occurs at neutral pH with the specic adsorption edges/envelopes changing with surface area, U concentration, and ionic strength. [6][7][8][9] As a specic example having similar experimental conditions as our study, Huber and Lützenkirchen 9 equilibrated U solutions with 10-30 ppb U(VI) with seven different quartz samples and found that nearly all U(VI) was adsorbed at pH above 5 via surface silanol groups. Other geomaterials have been studied for their potential to immobilize soluble U(VI), such as granite, iron oxides, clays, aquifer sediments, and volcanic rock.…”

“…Deprotonated silanol groups readily adsorb metal cations and positively charged U species would be adsorbed. These results have been echoed by studies looking at U sorption to silica gels and quartz, 6,8,9 where U sorption increased with increasing pH from no adsorption at pH 2 to nearly 100% adsorption by pH 7.…”

Influence of eolian deposition and rainfall amounts on the U-isotopic composition of soil water and soil minerals

“…Similar formulations have been used to interpret the U isotopic composition of pore waters from deep (ca. 40 m) unsaturated zones, marine sediments and aquifers (Tricca et al, 2001;Reynolds et al, 2003;Maher et al, 2004Maher et al, , 2006Bourdon et al, 2009;Huber and Lü tzenkirchen, 2009). Variations in the pore fluid compositions of soils, and in particular semi-arid soils, have not to our knowledge been considered within this framework, although isotopic variations within the soil zone are useful for interpreting the U isotopic composition of groundwaters, rivers and secondary soil precipitates such as clays, Fe-oxides, opal and carbonate.…”

U(VI) removal kinetics in presence of synthetic magnetite nanoparticles

“…Various processes occurring in the subsurface environment (adsorption onto minerals (see e.g. (Waite et al, 1994;Duff and Amrhein, 1996;Barnett et al, 2000;Davis et al, 2004;Huber and Lü tzenkirchen, 2009)) or abiotical and microbial induced redox processes causing precipitation of sparingly soluble U phases under anoxic conditions (see e.g. (Lovley et al, 1991;Liger et al, 1999;Wall and Krumholz, 2006)) influence the migration of U leading to retardation/retention.…”