THE STABILITY OF ALUMINUM SILICATE COMPLEXES IN ACIDIC SOLUTIONS FROM 25 TO 150-DEGREES-C

摘要

The equilibrium constant of the reaction Al3+ + H4SiO40 (ag) = AlH3SiO42+ + H+ (K-1) has been determined at temperatures from 25 to 150 degrees C from the pH of aqueous solutions containing H4SiO4(aq), HCl, and KCl with and without added AlCl3. Log K-1 values obtained in this study at 25, 90, and 150 degrees C are -2.38 +/- 0.10, -0.35 +/- 0.20, and 1.07 +/- 0.30, respectively. These values are linearly related to the reciprocal temperature and yield an association enthalpy of 66.6 kJ/mol. The K-1 value derived at 25 degrees C is in close agreement with that determined by Farmer and Lumsdon (1994) and implies that aluminum silicate complexes do not play a significant role in most surficial natural waters. However, thermodynamic calculations indicate that these complexes form in significant amounts in acid (pH <3) hydrothermal solutions where they can affect the solubility of Al/Si-bearing minerals. [References: 53]