A Pitzer model for the Na-Al(OH)4-Cl-OH system and solubility of boehmite (AlOOH) to high ionic strength and to 250 °C

- A Pitzer model for the Na-Cl-OH-Al(OH)4 system to high temperatures is presented.
- The model is of value to many fields.
- It would provide accurate descriptions of aluminum in high ionic strength fluids.
- Solubility of boehmite can be potentially used as a pHm sensor/buffer in experiments.

In this study, a Pitzer model for the Na-Cl-OH-Al(OH)4 system, and solubility of boehmite (AlOOH) to high ionic strengths, and to high temperatures up to 250 °C, has been developed by evaluating equilibrium quotients concerning boehmite in NaCl solutions to 5.0 mol·kg− 1, and boehmite solubility data in NaOH solutions to ~ 13 mol·kg− 1. This model is validated by comparing model-predicted solubilities with solubility data of boehmite in NaOH solutions that are independent from the model development. This model is of value to many fields, including accurate modeling geochemical behavior of aluminum in hydrothermal solutions with high ionic strengths at high temperatures up to 250 °C, extraction of aluminum via the Bayer process from various ores, stability of borosilicate glass, aluminum silicate materials as waste forms for long-lived radio nuclides, and bentonite as engineered barrier, in geological repositories.Based on the model developed in this work, solubility of boehmite can be potentially used as a pHm (hydrogen ion concentration on molal scale) sensor/buffer in hydrothermal experiments under neutral to alkaline conditions in NaCl solutions in the absence of silica. This pHm sensor/buffer would enable experimentalists to conduct hydrothermal experiments in a wide range ionic strength under well-controlled pHm conditions.