Aqueous Solubility Studies of Muscovite: Apparent Nonstoichiometric Solute Activities at Equilibrium

Abstract

AbstractSolubility studies were conducted on three different muscovites. The experiments were designed to conform with a number of well‐established criteria for studying the equilibrium solubility of sparingly soluble compounds. The compositions of the aqueous phase in contact with mixtures of muscovite and a synthetic gibbsite of known solubility, were monitored for over a period of 2 years. At the start of the experiments, the solid phases were characterized by various techniques such as chemical analysis, optical microscopy, X‐ray diffraction, infrared spectroscopy, and electron microscopy. The solids present at the end of the experiments were also examined. Free ion activities and activity ratios were computed from the measured total concentrations of various solutes. The attainment of equilibrium between the solid phases and the solution phase were established by rigorous chemical criteria. Analysis of the equilibrium solubility data indicated that the observed solute activity ratios were incompatible with the dissolution reaction based on the original chemical composition of muscovite. The stoichiometry of the muscovite phase was derived from solution equilibria and the standard free energy of formation of this phase was calculated to be −5501.1 kJ/mol.