Prediction of chemical speciation in stabilized solidified wastes using a general chemical equilibrium model II: Doped waste contaminants in cement porewaters

In the previous paper, SOLTEQ demonstrated its ability to represent chemical speciation in the pure s/s binder systems. The objective of this paper is to provide a method for representing doped waste contaminants in SOLTEQ so that their speciation can be determined. To evaluate this method, model predictions were compared with measured concentrations in the porewaters expressed from cement pastes doped with various metal salts. Among doped metals, only mercury showed concentrations that indicated primary control by precipitation. The other metals, such as Cr(VI), Cd, Pb, and Na, showed behaviors that imply sorption as a major immobilization mechanism. The Langmuir isotherm was found to be well suited to describe the sorption of Na+ ions onto the effective surface of CSH. To support the sorption of metal anions onto presumably negatively charged silica surface in cement porewater, a hypothesis of `super-equivalent adsorption' is proposed.

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