One of the most important issues for the 21st century will be the challenge of sustainable development of Earth’s resources as the population approaches 9 billion people. It is very exciting to realize that micro-scale processes such as photosynthesis or mineral dissolution are often responsible for macroscopic effects of critical importance to life processes. Dissolution of silicate minerals is linked to buffering of acid rain and sequestration of carbon dioxide. The molecular scale mechanisms of reactivity at the mineral/water interface can have a profound impact on the environment and ecosystem health.  Mineral surface reactions affect the mobility and speciation of metals and organic pollutants, the fertility of soils, the formation of ore deposits and the reactivity of mine tailings. I am interested in understanding these mechanisms in order to predict and mediate past and future environmental degradation particularly in the case of sulfide and actinide minerals.

My research integrates the tools of physics, chemistry and materials science with the questions of geochemical importance. I have focused on the influence of As, Co, and Ni impurities on the abiotic oxidation of pyrite in order to better predict acid mine drainage and the release of toxic metals and metalloids into the environment. This involved growing synthetic pyrite crystals in evacuated quartz tubes at high temperature, characterizing the bulk and surface electronic structure with techniques of semiconductor physics and electrochemistry, and conducting batch and flow through oxidation rate studies. When As, Ni and Co are present in pyrite the oxidation rate increased. I put forth the hypothesis that the mechanism of increased oxidation from impurities is through the introduction of additional defect states occupied by electrons at the mineral-water interface which is now being tested with more advanced electrochemical tecniques.

This work inspires another area of interest: the investigation of photoactive semiconducting pyrite as a possible site for the emergence of primitive life. In the Archean, Earth is thought to have had a carbon dioxide-rich atmosphere and there is evidence for abundant pyrite. Energy from the formation of pyrite by the reaction of FeS and hydrogen sulfide may have contributed to the formation of primitive organic molecules that could have been precursors to the evolution of life. The resulting pyrite may have provided a suitable substrate with iron-sulfur clusters for the onset of primitive metabolism. The photo-activity of pyrite has been shown to allow sunlight to be transformed into an electron flux on naturally occurring pyrite surfaces, a mechanism that is currently under development for solar cells. It is possible that this energy flux could have played a role in prebiotic evolution. Building on my dissertation work characterizing the bulk and surface electronic structure of pyrite with photo-electrochemistry, I aspire to conduct research projects investigating conditions that might have plausibly existed in the Archean, under which photo-active pyrite could have contributed to organic evolution.

Related to the reactivity of minerals containing toxic metals and metalloids is the speciation of the reaction products and associated trace elements in the environment. Laboratory and field based studies are needed to determine the manner in which they can be transported and sorbed onto soil and sediments, and what governs their transformation into more toxic and bioavailable forms. For example, elemental mercury is being distributed atmospherically to pristine lakes in the far North where it is transformed into the more toxic bio-accumulating monomethyl mercury. Sulfate reducing bacteria have been shown to accomplish this transformation in warmer climates but little is known about the process in these Northern lakes. I propose field studies to document the microbial communities present and to characterize the geochemical conditions in these lakes. Then laboratory studies could be carried out approximating those conditions in an effort to uncover the mechanism of Hg methylation.

The possibilities for research are nearly endless but my overall goal is to further understanding of geochemical processes in order to foster long term sustainability of modern civilization. This involves an appreciation of the interconnection between the environment on the macroscopic scale and reactions occurring at the molecular level between minerals and water. Opportunities for students are both laboratory and field based and can encompass undergraduate to PhD level work.

Previous research describes synthesis and characterization of pyrite doped with As, Co, and Ni.

 link to previous research.pdf