30-8 Experimental Determination of Gibbsite Dissolution Kinetics in NaOH Solutions: Applications to Hanford Tank Waste Sludge and to Extraction of Aluminium from Gibbsitic Bauxite Ores

Session: Geological and Geochemical Investigations of Critical Minerals in New Mexico and Beyond, and Technological Advances in Extraction of Critical Minerals

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Abstract:

The Hanford waste site contains an estimated 54 million gallons of radioactive waste, with aluminum being a significant component in the sludge phase, approximately 4,140 metric tons.  Among the various aluminum-bearing solid phases, gibbsite (a-Al(OH)₃) is of particular importance.  The tank waste contains high concentrations of NaOH, NaNO₂, and NaNO₃, requiring an understanding of gibbsite dissolution/precipitation kinetics in these solutions in pretreatment of Al-bearing sludge.  In addition, gibbsite is a dominant phase in gibbsitic bauxite ores, and alkaline solutions dominated by NaOH are used for extraction of aluminum.

We have determined the gibbsite dissolution kinetics in mixtures of NaOH + NaNO₂ and NaOH + NaNO₃.  This work reports the results of experiments regarding the dissolution kinetics of gibbsite in the presence of pure NaOH solutions.  The results from this work serve as the baseline for the gibbsite dissolution kinetics in mixtures of NaOH + NaNO₂ and NaOH + NaNO₃, as all of the experiments used the same starting material.  Data from this work in combination with our results in mixtures of NaOH + NaNO₂ and NaOH + NaNO₃ and with the data in NaOH solutions from the literature contributes to development of reactive transport model regarding gibbsite in alkaline solutions dominated with hydroxyl and nitrite ions which is applicable to tank waste pretreatment strategies and extraction of aluminum from gibbsitic bauxite ores.

Sandia National Laboratories is a multi-mission laboratory operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525. This work was supported by the U.S. Department of Energy (DOE) Office of Environmental Management (EM) through the Laboratory Policy Office Hanford Tank Waste R&D Program.

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