Solubility relations for aqueous Si, Al, and Cr(III) species in concentrated electrolyte solutions: Development of accurate aqueous thermodynamic models

Accurate chemical equilibrium data and models are required to understand and predict the complex leaching/dissolution behavior of silica, aluminum, and chromium that are important components of waste tank sludges at Hanford. In this study solubility data were obtained on amorphous silica, gibbsite, and amorphous Cr(OH)3 in concentrated simple electrolyte solutions (NaNO3, NaOH,..). These data are being used both to better understand the solubility relations for these compounds, which could be present in the sludges, and to develop the necessary Pitzer ion-interaction parameters for important aqueous species of these elements, so that the effects of different electrolytes on solubilization of these elements can be ascertained. The thermodynamic model, which is based upon data from simple electrolyte solutions, was in most cases tested using experimental data on solutions more complex than those used for model parameterization