CAREER: Nanoscale Mineral Transformations During Biogeochemical Cycling and the Fate of Trace Elements and Nutrients

Washington University, Saint Louis MO

Investigators

Abstract

The availability and speciation of phosphate and trace elements in sediments, soils, and aquatic systems are strongly affected by biogeochemical cycling involving iron and manganese oxide minerals. These phases are commonly thought to affect the fate of such elements through passive means such as adsorption and coprecipitation. While mineral structural transformations during biogeochemical cycling and their impact on trace element and nutrient fate are well studied for the iron oxides, analogous studies are generally lacking for the Mn system. Similar to iron, environments where active biogeochemical Mn cycling is occurring often contain coexisting aqueous Mn(II) and solid Mn(III/IV) oxides. However, the lamellar structure and complex composition of these manganese minerals and the ability of Mn to undergo complex reactions, suggest that interfacial atom exchange and electron transfer reactions will be more involved for Mn oxides than for Fe oxides and likely lead to bulk structural transformations. Such chemical and structural modification of Mn oxides may have a substantial impact on the fate of trace elements and phosphate in biogeochemical systems. The primary research objective of this proposal is to expand our understanding of how atom exchange and electron transfer reactions drive nanoscale mineral transformations and affect trace element and nutrient fate. The PI?s objectives will be accomplished through a series of systematic studies that combine laboratory-based wet chemistry with advanced chemical and structural characterization of the solid bulk and surface structures and the speciation of associated trace elements and phosphate. The proposed research activities will demonstrate the operation of a new class of mineral transformations and trace element and nutrient reactions during biogeochemical cycling. This work will improve our understanding of how Fe and Mn cycling in sediments, soils, and aquatic systems affect phosphate and micronutrient availability and the fate of contaminants. The proposed research will provide potential societal benefits in the form of identifying new processes affecting contaminant fate and transport, suggesting new remediation approaches, and serving as inspiration for novel synthesis routes for battery materials. More importantly, the research described in this CAREER proposal will be leveraged to enhance a number of educational activities. These activities are organized around a theme of inquiry-based learning at the undergraduate and high school level. The proposed research activities will be actively used as learning activities for both undergraduate and high school students. These research-based educational activities will be improved and optimized in the PI?s research group, department, and for a local program providing research opportunities to high school students through the development and implementation of assessment plans. A new undergraduate course on Geology and Human Health that incorporates inquiry-based learning and inquiry-based learning modules for an aqueous geochemistry course will be developed. Course materials, pedagogical approaches, and research results will be widely disseminated through websites, blogs, and publication in scientific and education journals.