Graduate Students Seminar

Please join us for two graduate student seminars this Friday March 13 starting at 3:30 pm in rm 155 Geology:

3:30 pm

Kamil Chadirji-Martinez

Thorium-Bearing Industrial Wastes and their use for Generation IV Nuclear Reactor Fuel

Interest in experimental liquid fluoride thorium reactors (LFTR) is growing, as a result of superior safety features compared to conventional pressurized water reactors. Moreover, waste from the thorium fuel cycle is much less radioactive than that from the uranium fuel cycle; and LFTRs are highly sustainable due to the high abundance of thorium in the earth’s crust as well as the fact that it can be readily sourced from industrial waste. The world’s largest rare earth element (REE) mine, Bayan Obo in inner Mongolia, China, dissolves bastnaesite/monazite REE ore using the sulfuric acid roast-water leach process (SARWL). In 2008 alone, Bayan Obo produced 92,000 t of REE residue, primarily anhydrite (CaSO4), containing 0.25-0.36 wt.% ThO2 from the SARWL process. The objective of this research project is to synthesize anhydrite and gypsum (CaSO4·2H2O) in thorium-doped sulfuric acid and aqueous solutions under various conditions to understand how thorium may be associating with anhydrite and gypsum in the Bayan Obo REE solid residue. Thorium concentration in hydrothermally grown anhydrite increased with pH and temperature from 2310 ppm to 8880 ppm. The same trend between pH and thorium concentration was also observed in gel-grown gypsum from 62 ppm to 1110 ppm.

In addition, a laboratory-scale SARWL Process was performed on monazite REE ore from Alces Lake, Saskatchewan. The purpose of this was to see if REE solid residue formed from Alces Lake monazite concentrate, similar to anhydrite formation after fluorite (CaF2) impurities in Bayan Obo bastnaesite/monazite concentrate dissolve in sulfuric acid. Powdered X-ray diffraction analysis has shown quartz and zirconium hydrogen phosphate monohydrate are the dominant phases in the REE residue produced from Alces Lake monazite concentrate. Synchrotron X-ray absorption spectroscopy, X-ray fluorescence mapping, laue X-ray diffraction, and electron paramagnetic resonance are being used to study the distribution and local structural environments of thorium in sulfate-rich wastes. The significance of this research is in gaining a fundamental understanding of thorium within the REE solid residue and to aid efforts to develop reclamation processes to remove thorium from the solid residue.

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4:00 pm

Mery Mendoza Rodriguez

Selenium – the most enigmatic of the elements of life

Of the 118 known chemical elements only 28 are needed by living organisms; these are called the elements of life. Of these, selenium is perhaps the most enigmatic. Selenium has the lowest crustal abundance of the elements of life but is a required element for organisms in all six kingdoms of life. Living organisms have incredibly complex and intricate mechanisms for incorporating selenium into biological molecules, and the energetic cost of this incorporation is enormous compared to all other elements. Selenium plays essential roles in human health, but it is also toxic, and the difference between a dose sufficient for health and a toxic dose is smaller than for any other element. The average human body contains only around 14 mg of selenium, mainly involved in redox homeostasis through selenoenzymes such as the glutathione peroxidases and the thioredoxin reductases. Selenium has been implicated in protecting humans from cancer, but the same doses of selenium dramatically increase the risks of developing type 2 diabetes. Selenium has a complex relationship with toxic elements such as arsenic and mercury, in some cases protecting against the toxic effects but in other cases dramatically magnifying the toxicity. This presentation will discuss some of what is known of selenium’s various roles, and discuss how X-ray absorption spectroscopy is shedding light on this most enigmatic of the elements of life.