An experimental and modeling study of metal and proton binding in heterogeneous systems

The focus of this dissertation is the development of a transport model that will aid in evaluating metal leaching in the subsurface. To develop such a model, the main challenge is to critically examine heterogeneous sorption and develop a modeling framework for a heterogeneous system. To address the broad research objective, the hypothesis of this study is that at fixed ionic strength, electrostatic and sorbent heterogeneity effects may be approximated by empirical power functions of H+ and metal loading, respectively.; To test the research hypothesis, a general composite model called the variable reactive model that describes metal and proton sorption to heterogeneous sorbents has been developed. The model is based on the surface complexation modeling approach, where metal ion binding is conceptualized as occurring at a single binding site with variable reactivity. Following the model development, multidimensional data sets from the literature and laboratory studies involving proton and metal binding to heterogeneous materials in batch and column settings were used to test the validity and robustness of the model. Attempts to have a consistent set of batch and column parameters was not a complete success, but this exercise revealed that a “well-designed” column experiment provides for a very extensive and diverse database of information, which might suffice if the goal is field application.; In final analysis, this research provides a model that can be used to quantify sorption on heterogeneous media in batch and column settings. The model reasonably simulates observed sorption data, is simple to parameterize and use and can be easily incorporated into a general transport modeling framework. The model is limited in that parameter estimates are conditional on ionic strength and may not be thermodynamically consistent, which may limit its predictive capability. Potential model applications include analysis of site remediation alternatives and risk assessment.