CAREER: Role of Mn(III) in Limiting Oxidative Transformation of As(III) by Mn(III/IV) Oxides

点击翻译按钮获取中文摘要

Arsenic in water occurs both naturally and as a result of human actions and arsenic is found in drinking water supplies throughout the world. The overall goal of this project is to understand how environmental factors control the form of arsenic that is present, and whether it is dissolved in water or attached to solids like soil. When arsenic is dissolved in water it is more likely to move and impact human health. This work is important because more than 150 million people worldwide are exposed to unsafe amounts of arsenic in drinking water. Minerals with the element manganese are found in many natural sediments and they are powerful chemical reactants. This project will determine how, and how fast, manganese minerals react with arsenic to change its form and therefore how mobile it is. This project also will look at how the very common element iron changes how manganese minerals react with arsenic. Outreach will be conducted to educate people about how minerals affect water quality and there will be work to engage K-12 and undergraduate college students in the field of environmental geochemistry will be. This project will work to increase the number of students from diverse backgrounds who take classes and do research in environmental science.Arsenic (As) is a naturally occurring and anthropogenic contaminant present in drinking water supplies around the world. The environmental mobility of arsenic in natural systems as well as the efficacy and efficiency of removal systems are strongly influenced by its oxidation state. AsV readily sorbs to many mineral components of soil and sediments or to filter bed media and/or coagulant flocs in oxic systems, while AsIII generally forms less stable bonds with these materials. In subsurface environments, oxidation of AsIII is largely driven by interaction with MnIII/IV oxides. Despite their role in controlling the geochemical speciation of As, in addition to other redox-active contaminants, the results of numerous studies to determine oxidation rates and mechanisms are often inconsistent. In particular, the role of solid associated MnIII in limiting contaminant transformation rates and extents is at best, poorly understood. This project will systematically investigate the oxidation of AsIII by various MnIV oxide minerals, with an emphasis on quantifying the effect of solid-phase MnIII and FeIII on AsIII oxidation rate, extent, and the formation of As surface complexes. This proposal aims to combine traditional lab-based measurements with in situ, quick scanning X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy (XPS) to determine the role of MnIII in limiting AsIII oxidation. The research will (1) examine the effect of MnIII content on the kinetics of AsIII oxidation during early time periods (e.g., 1 min), (2) seek to systematically define effects of FeIII substitution in MnIII/IV oxides on AsIII oxidation and sorption, and (3) quantify the fundamental relationship between oxidation kinetics, mechanism, and changes in the MnIII/IV oxide surface.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.