A5055481908- Radioactive element chemistry and processing
- Paleontology and Stratigraphy of Fossils
- Geochemistry and Elemental Analysis
- Mine drainage and remediation techniques
- Chemical Synthesis and Characterization
- Metal Extraction and Bioleaching
- Extraction and Separation Processes
- Hydrocarbon exploration and reservoir analysis
- Iron oxide chemistry and applications
- Heavy metals in environment
- Analytical chemistry methods development
- Marine and coastal ecosystems
- Catalysis and Hydrodesulfurization Studies
- Mercury impact and mitigation studies
- Phosphorus and nutrient management
Minnesota State University, Mankato
2004-2021
University of Maryland, College Park
2002-2004
Molybdenum preserved in organic-rich shales is a key archive employed studying Earth's past oxygenation and Life's evolution. In these shales, positive correlations between Mo Corg are common have been attributed to scavenging from seawater by organic shuttles. Here, we argue that known ligands too weak or scarce capture more than minor amounts of seawater, especially competition with sulfide. Alternatively, demonstrate Mo-Corg can arise simply microbially mediated oxidation SO42−. This...
Relative to continental crust, sediments underlying sulfidic marine waters are molybdenum-rich, a property preserved in the rock record and useful for characterizing paleoenvironments. The enrichment mechanism is not agreed upon but attributed at least partly deposition of Fe–Mo–S compounds, which as yet uncharacterized. Here, we determine composition stability colloidal precipitates formed mildly basic pH H2S(aq) > 10–5 M. first product consists simply FeMoS4, with Ksp = 10–14.95. Within...
Molybdenum profiles in dated sediment cores provide useful historical information about anoxia anthropogenically impacted natural waters but would be of greater service if Mo fixation mechanisms were better understood. Here, we explore scavenging by precipitated FeS a model system consisting an FeIII-bearing kaolinite (KGa-1B) dispersed NaHS solutions. Test solutions contain 18 microM thiomolybdates (mainly MoOS3(2-)). Optically measuring dissolved polysulfides monitors the rate production...
In aquatic ecosystems, availabilities of Fe, Mo and Cu potentially limit rates critical biological processes, including nitrogen fixation, nitrate assimilation N2O decomposition. During long periods in Earth's history when large parts the ocean were sulfidic, what prevented these elements' quantitative loss from marine habitats as insoluble sulfide phases? They must have been retained by formation soluble complexes. Identities key ligands are poorly known but probably include thioanions....
Molybdenum (Mo) in marine sediments has been used as a paleoproxy to provide evidence for past oceanic euxinic and sulfidic conditions through its association with pyrite. Here, we examine the adsorption of Mo pyrite precursors mackinawite greigite assess robustness this during iron sulfide phase transformations. Tetrathiomolybdate (MoS42–) experiments were done using that had characterized powder X-ray diffraction Raman spectroscopy. Adsorption tetrathiomolybdate primarily mixture was...
Molybdenum (Mo) isotopic signature and concentrations can be a geologic indicator of changes in molecular oxygen Earth's oceans atmosphere. However, natural waters that are weakly to strongly sulfidic, few studies have been able determine the exact mechanisms controlling partitioning speciation related fractionation Mo. To understand contribution each Mo species overall bulk isotope signature, we report method measures both concentration composition Mo-bearing during thiolation using...