Characterization of complex mineral assemblages: Implications for contaminant transport and environmental remediation

Surface reactive phases of soils and aquifers, comprised of phyllosilicate and metal oxohydroxide minerals along with humic substances, play a critica l role in the regulation of contaminant fate and transport. Much of our kno wledge concerning contaminant-mineral interactions at the molecular level, however, is derived from extensive experimentation on model mineral systems . Although these investigations have provided a foundation for understandin g reactive surface functional groups on individual mineral phases, the info rmation cannot be readily extrapolated to complex mineral assemblages in na tural systems. Recent studies have elucidated the role of less abundant min eral and organic substrates as important surface chemical modifiers and hav e demonstrated complex coupling of reactivity between permanent-charge phyl losilicates and variable-charge Fe-oxohydroxide phases. Surface chemical mo difiers were observed to control colloid generation and transport processes in surface and subsurface environments as well as the transport of solutes and ionic tracers. The surface charging mechanisms operative in the comple x mineral assemblages cannot be predicted based on bulk mineralogy or by co nsidering surface reactivity of less abundant mineral phases based on resul ts from model systems. The fragile nature of mineral assemblages isolated f rom natural systems requires novel techniques and experimental approaches f or investigating their surface chemistry and reactivity free of artifacts. A complete understanding of the surface chemistry of complex mineral assemb lages is prerequisite to accurately assessing environmental and human healt h risks of contaminants or in designing environmentally sound, cost-effecti ve chemical and biological remediation strategies.