Applications of soil and cement chemistry to stabilization/solidification
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abstract
The main objective of waste stabilization/solidification (S/S) is to add binders to reduce the mobility of toxic contaminants. Immobilization can occur by either physical or chemical means. Physical immobilization occurs when the contaminant is encapsulated in a solid matrix. Chemical immobilization occurs when the contaminant is converted by chemical reaction to a less mobile form. Precipitation and adsorption are examples of chemical processes that can lead to immobilization. Physical processes in soil treatment have received the greatest attention with more data being collected on physical properties of the treated materials. The chemical processes associated with S/S have received less attention, particularly those processes that affect contaminants. Discussed in this paper are applications of cement and soil chemistry to S/S technology. The relative importance of kinetics and equilibrium of chemical immobilization in S/S are also examined. Equilibrium chemistry is presented as a practical method for describing how reactions between binders and soil produce the chemical environment that determines whether contaminants will exist in mobile or immobile forms. The use of chemical equilibrium models and programs such as SOLTEQ are discussed. SOLTEQ, a modification of an EPA-supported program (MINTEQ), can calculate concentrations of contaminants in both mobile and immobile phases and provides mechanisms to integrate chemical information from a variety of systems, including cementitious-pozzolanic systems such as soils or wastes by S/S. The importance of pozzolanic reactions to developing the chemical environment in wastes and soils treated by S/S is also discussed.
