U(VI) sorption on sandstone: Experiments and modeling

The sorption of U(VI) on natural and synthetic sandstone was investigated in batch sorption experiments (air atmosphere, 0.1M NaClO4, pH 3-11, [U(VI)] 10-9-10-4M. The synthetic sandstone was a mixture of quartz with muscovite and hematite. The surface area (N2-BET) of quartz was 0.047 m2/g, of muscovite 0.88 m2/g, of hematite 0.89 m2/g and of natural sandstone (mainly quartz) 0.69 m2/g.
The pH dependence shows a maximal sorption between pH 5.5-7.5. The U(VI) sorption varied between 95% (10-9M) and 7% (10-4) on natural sandstone, and between 80% (10-9M) and 2% (10-4M) on synthetic sandstone. Fig. 1 shows the comparison of sandstone with pure components (at similar conditions) quartz, muscovite, and hematite. More U(VI) was adsorbed on natural and on synthetic sandstone, than on quartz. The higher sorption are caused by the other components muscovite and hematite, and by the higher surface area.
The linear Freundlich sorption isotherms indicate one binding type. Sorption predicted by the Diffuse Double Layer Model (using the code FITEQL) agreed with the experimental sorption values within their uncertainty.