Gibbsite Solubility Measurements in NaOH + NaNO3 Solutions at 60 °C, and a Thermodynamic Model for Interactions of Aluminate Ion (Al(OH)4–) with Nitrate

Abstract

The interactions of aluminate ion (Al(OH)₄⁻) with nitrate are important to numerous fields including nuclear waste management, and extraction of aluminum from bauxite ores. In the field of nuclear waste management, aluminum (Al) is a prevalent component in tank waste sludge phase at various sites, and accounts for high percentages of the total inventory of tank waste sludge. Three predominant Al-bearing solid phases are sodium aluminate [NaAl(OH)₄], gibbsite [α-Al(OH)₃], and boehmite. Nitrate and nitrite have high concentrations in the supernatant liquids. Therefore, the knowledge of the interactions of aluminum with nitrate and nitrite is important to the realization of a scientifically sound and effective pretreatment approach for tank waste sludge. To gain a deeper knowledge of such interactions, we are conducting systematic experiments coupled with the thermodynamic modeling. In this work, we report our solubility measurements at 60 °C. Based on our experimental data, we develop a thermodynamic model to describe the interactions of aluminate ion with nitrate. Then, the thermodynamic model is tested against the experimental data of gibbsite in mixtures of NaOH and NaNO₃ from the literature. Those literature data are not utilized in the model development. The tests show that the values predicted by the model are in good agreement with the experimental data that are independent from the model development.