![]() ![]() At 45 ☌, NaNO 2 and NaNO 3-containing systems exhibited Al enhc values of 2.70 and 1.88, respectively, indicating significant enhancement. Specific anion effects were expressed as an enhancement factor (Al enhc) conveying the excess of dissolved aluminum. Measured dissolved aluminum concentrations were compared with those predicted by an α-Al(OH) 3 solubility model derived for simple Al(OH) 4 –/OH – systems. Rapid equilibration was enabled by use of a highly pure and crystalline synthetic nano-gibbsite of well-defined particle size and shape. In the study reported herein, we systematically examined the influence of more » key anions, nitrite (NO 2 –) and nitrate (NO 3 –), as sodium salts on the solubility of α-Al(OH) 3 in NaOH solutions taking care to establish equilibrium from both under- and oversaturation. The solubility of gibbsite (α-Al(OH) 3) is often not well predicted because other ions affect the activity of hydroxide (OH –) and aluminate (Al(OH) 4 –) anions. Department of Energy legacy sites, such as the Hanford Site, Washington State. Aluminum hydroxide solid phase solubility in concentrated sodium hydroxide (NaOH) solutions is one such case, with major implications for ore refining, as well as processing of radioactive waste stored at U.S. « lessĭespite widespread industrial importance, predicting metal solubilities in highly concentrated, multicomponent aqueous solutions is difficult due to poorly understood ion–ion and ion–solvent interactions. The results of these investigations are summarized in this report. Finally, an experimental program is outlined to aid prediction of the outcomes of DFLAW staged feed dilution with respect to significant variables that influence gibbsite dissolution and precipitation. The dependence of aluminum concentration on hydroxide concentration in analyses of actual tank waste solutions also was surveyed for tanks that have a long-term static inventory and tanks suspected of containing or known to contain substantial gibbsite solid phase in their sludge solids. Experience from the aluminum industry, particularly the Bayer process, also was surveyed to gain insight into the precipitation and dissolution of gibbsite in sodium hydroxide solutions. As a first step to help inform this more » investigation, a survey was conducted of Hanford waste-related tests documenting the processing of tank waste materials (solutions, salt cakes, sludges) or their simulants for instances of gibbsite dissolution and precipitation. The operational and mission impacts of using other dilution fluids such as inhibited water, demineralized water, or a 2 M sodium hydroxide solution also must be assessed. ![]() The technical bases to support the One System River Protection Project Integrated Flowsheet assumption for diluting staged Direct Feed Low-Activity Waste (DFLAW) from the Hanford waste tanks with raw river water must be assessed in light of the risk of aluminum hydroxide (gibbsite) precipitation prior to the subsequent transfer of tank contents into the Low-Activity Waste Pretreatment System (LAWPS) from days to months after dilution. The results of these more » investigations are summarized in this report. An experimental program to aid in the prediction of gibbsite solubility in NaOH solutions containing a range of sodium nitrate and sodium nitrite concentrations up to the solubility limit at a range of temperatures has been conducted. Based on a review of waste solubility data and the impact of dilution on solution stabilities with specific focus on aluminum hydroxide, data gaps associated with the impact of these variables on the prediction of gibbsite solubility with temperature were identified. ![]() These variables include (i) other solution components that meaningfully affect the activity coefficient of either hydroxide or the aluminate ion, particularly nitrate and nitrite and (ii) temperature. Aluminum solubility must be predicted as a function of the significant variables that influence gibbsite dissolution and precipitation. The technical basis to support the One System River Protection Project Integrated Flowsheet assumption for diluting staged direct feed low-activity waste (DFLAW) from the Hanford waste tanks with raw river water must be assessed in light of the risk of aluminum hydroxide (gibbsite) precipitation prior to the subsequent transfer of tank contents into the low-activity waste pretreatment system (LAWPS) and/or the Tank Side Cesium Removal (TSCR) system from days to months after dilution. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |