Prediction of chemical speciation in stabilized solidified wastes using a general chemical equilibrium model Part I. Chemical representation of cementitious binders

Chemical equilibrium models are useful to evaluate stabilized/solidified wa ste. A general equilibrium model, SOLTEQ, a modified version of MINTEQA2 fo r S/S, was applied to predict the chemical speciations in the stabilized/so lidified waste form. A method was developed to prepare SOLTEQ input data th at can chemically represent various stabilized/solidified binders. Taylor's empirical model was used to describe partitioning of alkali ions. As a res ult, SOLTEQ could represent chemical speciation in pure binder systems such as ordinary Portland cement and ordinary Portland cement + fly ash. Moreov er, SOLTEQ could reasonably describe the effects on the chemical speciation due to variations in water-to-cement, fly ash contents, and hydration time s of various binder systems. However, this application of SOLTEQ was not ac curate in predicting concentrations of Ca, Si, and SO, ions, due to uncerta inties in the CSH solubility model and K-sp values of cement hydrates at hi gh pH values. (C) 1999 Elsevier Science Ltd. All rights reserved.