Aluminum hydrolysis constants to 250°C from boehmite solubility measurements

Abstract Boehmite solubilities were measured at 150, 200, and 250°C at pH values from 1 to 10 at 100 bars total pressure and used to determine the stability constants for the mononuclear aluminum hydroxide complexes (Al(OH)2+, Al(OH)2+, Al(OH)30, Al(OH)4−),and the solubility product of boehmite. Buffer solutions of HCl-KCl, acetic acid-sodium acetate, sodium bicarbonate-carbonic acid, and boric acid-potassium hydroxide were used to control pH. Our solubility data are in good agreement with boehmite solubility measurements in perchloric acid and sodium hydroxide solutions reported by Kuyunko et al. (1983). The stability constants for the aluminum hydroxide species were determined from the solubility data using a Ridge regression technique. The results indicate that aluminum ion hydrolysis becomes stronger at higher temperatures, and the stability field of the neutral complex Al(OH)30 becomes larger. The results are used to provide a set of equilibrium constants for aluminum hydroxide complex formation and boehmite hydrolysis from 0–300°C.