Graduate Student Seminars

Posted on 2019-03-12 in Events
Mar 15, 2019

Please join us for the Graduate Student seminars this Friday March 15 at 3:30 pm in rm 155 Geology:

3:30 pm

Colton Vessey

Vanadate attenuation by iron(II)-bearing phases

Vanadium (V) is an environmental contaminant with several anthropogenic sources including mining and mineral processing, and petroleum and coal production. Despite a recent increase in V geochemistry studies, substantial knowledge gaps remain. In particular, very few studies have examined V geochemistry in anoxic environments. We conducted laboratory batch experiments to study aqueous V(V) attenuation rates and mechanisms by Fe(II)-bearing phases–magnetite [Fe3O4], siderite [FeCO3], pyrite [FeS2], and mackinawite [FeS]–commonly found in anoxic soils, sediments, and aquifers.

Synthetic Fe(II)-bearing phases were suspended in a 0.05 M NaCl solution within an anoxic chamber. The suspensions (2 g L−1) were spiked with 100 µM (5 mg L−1) V(V) and continuously stirred for 3 or 48 hours. Suspension samples were collected over time to quantify removal kinetics. Inductively coupled plasma–mass spectrometry (ICP–MS) was used for V quantification and high performance liquid chromatography (HPLC-ICP-MS) was used to quantify aqueous V(V), V(IV), and V(III) concentrations. Solids were flash-frozen, free-dried, and analyzed by transmission electron microscopy - energy dispersive X-ray spectroscopy (TEM-EDX) and X-ray absorption spectroscopy (XAS).

Our results demonstrate V(V) attenuation occurs rapidly with magnetite, siderite, and mackinawite. Limited V(V) attenuation was observed with pyrite. XAS data indicates that sorption and reduction reactions contributed to V(V) attenuation by siderite and mackinawite, whereas magnetite promoted only sorption over the experimental duration. Additionally, HPLC-ICP-MS and XAS results suggest V(V) reduction occurred via surface-mediated electron transfer from Fe(II) or S(−II) atoms rather than dissolved Fe(II). Our new findings indicate that V(V) mobility would be limited by interactions with surfaces of Fe(II)-bearing phases in anoxic environments.

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4:00 pm

Osama El Badri

Measurement of attenuation in seismic sections by using waveform synthetics

Measurement of attenuation effects on seismic waveforms is a critical part of analyzing and correcting seismic records for attenuation effects. However, in such analysis, the true physical properties causing seismic attenuation are not always clearly differentiated from “apparent”, or measured quantities. The usually-measured Q and the associated cumulative attenuation t* are such apparent quantities. These quantities can be frequency-dependent and different for different attenuation mechanisms, such as viscoelastic, pore-fluid flows, solid viscosity, or wave-front focusing. Q and t* also vary for propagating P and S waves, reflections, effects of thin layering, multiples, or surface waves.

The resulting of the cumulative attenuation can be utilized in two ways. First, they can be compared to the attenuation models used for forward modeling (viscoelastic Q in the present examples). Second, accurate attenuation-compensation of the synthetic and real data can be carried out by using the resulting attenuation sections.