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

The development of an aqueous thermodynamic model for polymerized silica sp ecies is presented, which is valid for high ionic strengths and high dissol ved silica concentration (similar to0.1 m) at low temperature (22-25 degree sC). 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 diss olved silica and basic conditions (pH > 10) required the inclusion of monom eric, dimeric, trimeric (linear, cyclic, and substituted), tetrameric (line ar and cyclic), and hexameric (prismatic) species. The standard state equil ibrium constants for the Formation of these species, as well as the necessa ry Pitzer ion-interaction parameters to describe the ionic strength depende nce of the formation reactions were determined.