2:00 PM - 2:15 PM
[HCG25-14] Behavior of co-precipitated Se (IV) during the transformation of Fe-oxides at alkaline conditions
Keywords:Selenium behavior, iron oxide transformation, nuclear waste disposal
Se (IV) was co-precipitated with ferrihydrite by adding base to a solution containing both Fe and Se to raise the pH to 10. The resulting slurries were then aged at 80°C for 4 days to induce transformation. Solids and liquids were then separated by centrifugation and filtration. Solution samples were analyzed for Se concentrations while solids were characterized using x-ray diffraction (XRD), infrared (IR) spectroscopy and x-ray absorption spectroscopy (XAS). Results of solution analyses show that co-precipitation sequesters approximately 90% of Se from the solution. Transformation of the ferrihydrite to crystalline hematite and goethite phases at alkaline conditions results in the release of a fraction of the initially sequestered Se, such that only approximately 50% of the original Se is retained by the solids. Spectroscopic studies of the solids suggest that Se is sequestered from solution by sorption on ferrihydrite and not by the formation of an independent Fe-Se phase. During ferrihydrite transformation to crystalline hematite and goethite, Se is similarly retained by sorption on the crystalline phases. The release of Se during transformation may thus be attributed to the lower sorption capacity of crystalline Fe-oxides for Se. The results of this study thus show that post-uptake behavior of hazardous elements must be considered during long-term assessments of high-level waste repository conditions.