An aqueous thermodynamic model for polymerized silica species to high ionic strength

The development of an aqueous thermodynamic model for polymerized silica species is presented, which is valid for high ionic strengths and high dissolved silica concentration (similar to0.1 m) at low temperature (22-25 degreesC). The model is based on the Pitzer equations and has been parameterized from solubility, electromotive force (emf), and nuclear magnetic resonance (NMR) data. The description of the silica speciation reactions at high dissolved silica and basic conditions (pH > 10) required the inclusion of monomeric, dimeric, trimeric (linear, cyclic, and substituted), tetrameric (linear and cyclic), and hexameric (prismatic) species. The standard state equilibrium constants for the Formation of these species, as well as the necessary Pitzer ion-interaction parameters to describe the ionic strength dependence of the formation reactions were determined.