04/03/2013
Analyzing the Complexity of Interactions with Mineral Surfaces
Summary
Minerals have a profound effect on the fate and transport of contaminants in subsurface environments. Surface complexation modeling (SCM) enables predictions of adsorption over a broader range of conditions than can be accommodated by adsorption isotherm equations or ion exchange models. A newly published review article discusses the current status of SCM and its applications to a range of systems. The main focus is on multidentate surface complexes, formed when an ion or molecule in solution binds to two or more adjacent active sites on the surface. Spectroscopic measurements often provide evidence for the presence of multidentate surface complexes, but there has been ambiguity and confusion in the literature regarding the best ways to incorporate such complexes into SCM. The article describes and evaluates several approaches to modeling these interactions and discusses examples of model applications, as well as the need for improvements in textbooks, computer programs, and the clarity of future publications to bridge the gap between theory and practice in SCM. This section is illustrated by a modeling discussion of surface complexation of uranium (VI) on the mineral goethite, a system that is a research focus of the Department of Energy’s Office of Biological and Environmental Research (BER). Many of the experimental results referenced in this review were obtained in BER research projects. The article concludes with advice for SCM users.
References
Wang, Z., and D. E. Giammar. 2013. “Mass Action Expressions for Bidentate Adsorption in Surface Complexation Modeling: Theory and Practice,” Environmental Science and Technology 47(9), 3982–96. DOI: 10.1021/es305180e.