Multi-component partitioning model to predict leaching from solidified oily wastes
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abstract
Solidification/Stabilization (S/S) is an established remediation process in hazardous waste management. Recently the process has been applied to hazardous organic wastes with mixed results. These results have prompted further studies to examine the effectiveness of this process in containing organic contaminants. The primary goal of S/S is to contain the contaminants in a solidified form, removing them from the environment. This is accomplished by decreasing the contaminant surface area and chemically converting the waste by reducing the contaminant solubility. The most common S/S processes utilize the chemical reactions achieved in cement-based and pozzolanic mixes. The effectiveness of this process is determined by the degree to which contaminants will leach from the waste end-product. Leach models, therefore, are an effective way to predict the leaching of contaminants and to describe the immobilization and binding mechanisms that take place. The multi-component nature of oily wastes requires that a multi-component approach be taken to describe the partitioning between the aqueous and non-aqueous phases. The heterogeneous nature of these wastes precludes analysis of partitioning of all chemical species. A pseudo-component model has been developed that describes the partitioning of TOC as caused by the partitioning of a small number of pseudo-components. A pseudo-component is used to represent a group of chemical species that has similar tendencies to partition between the aqueous and non-aqueous phases. A linear partitioning relationship is used to develop the partitioning model, with the values of the partitioning coefficients chosen to represent strongly sorbed, moderately sorbed, and weakly sorbed components. The partitioning characteristics of the waste were determined in a series of sequential extractions in which different amounts of water were added. After each addition, the system was allowed to equilibrate, the added water was removed by centrifugation, and its TOC was measured. The model predicts that the measured concentrations of TOC are due to the sum of all pseudo-components in the aqueous or mobile phase.
