PNNL

Abstract

The Hanford site is currently one of the largest and most expensive cleanup sites for hazardous, radioactive waste. Over 20% of the waste found at the Hanford site is in the form of an insoluble sludge designated as high-level waste (HLW). The insoluble solids in the sludge will need to be concentrated before vitrification processing can begin. One proposed option for concentrating the insoluble solids is gravity settling in the storage tanks. Metal oxide compounds containing aluminum and iron make up the majority of the insoluble solids in the HLW, therefore understanding the behavior of these compounds in various tank waste matrices can facilitate sludge pretreatment options. A study of non-radioactive slurry solutions containing Al(OH)3 (Gibbsite), AlO(OH) (Boehmite), and Fe2O3 (Iron (III) Oxide) was conducted to determine the time dependent interface behavior and settling rates of these compounds. Variations in solids loading and sodium concentration were evaluated to represent HLW processing conditions and the results of these settling studies were compared with prior tank waste settling tests. Information gathered from these studies can be used to inform future decisions on HLW treatment processes of insoluble solids processed at the Hanford site.