PhreeqC modeling of Friedel's salt equilibria at 23±1 °C

A series of slurries containing Friedel's salt (3CaO.Al2O3.CaCl2.10H(2)O) in equilibrium with other solids that include Al(OH)(3), Ca(OH)(2), and 3CaO-Al2O3-6H(2)O were produced at room temperature (23 +/- 1 degreesC). The liquid phases were analyzed for calcium, aluminum, and chlorine, and the speciation program PhreeqC was used to model the equilibria that were established between the solid and liquid phases. By matching closely, the experimentally determined solution parameters with those calculated using PhreeqC, important information concerning equilibria in the CaO-Al2O3-CaCl2-H2O system was obtained. For example, it was shown that the stable phase pair, Friedel's salt/ 3CaO-Al2O3-6H(2)O, acts to buffer against rising chloride concentrations by acting as a chloride sink. PhreeqC calculations have estimated the solubility product of Friedel's salt to fall within the range - 28.8 < log K-sp < - 27.6. (C) 2004 Elsevier Ltd. All rights reserved.