Discipline: Chemistry and Chemical Sciences
Subcategory: Chemistry (not Biochemistry)
Nhat Nguyen - New Mexico State University
Problem Statement and Objective: Clean potable water is scarce on the Navajo Nation forcing people to consume uranium-contaminated water with levels greater than 30 ppb. The result is an epidemic known as ‘Navajo neuropathy’ along with other serious health related problems. Natural clays have proven to be a great sorbent with excellent ability to sorb heavy metals, especially uranium, via their unique cation exchange capabilities. This is a cost effective means to clean water resources using clays that can be easily obtained locally. Although effective, clays themselves are difficult to physically manage. Thus, clay pellets are being fabricated.
Methodology: For this study, three well-known, well-studied reference clays and two regional clays are being utilized. Arizona, Texas, and Wyoming represent reference clays while Gallup and Berino (New Mexico) are used for regional clays. With their own unique chemical and physical characteristics, each clay needs to be analyzed individually and precisely. Gallup clay is analyzed in order to set up initial protocols for later analysis of other clays. A variety of tests and experiments will be performed to ensure robustness and integrity for safe and effective sorption, transport and disposal. Firstly, all clays will go through the same purification process including drying, grinding and sieving. Next, because water is a key component, pellet fabrication is initiated by testing different clay to water ratios. Subsequently, the TGA/DSC instrument is used to monitor how different clays behave at different temperatures over time. Afterwards, the clays are molded and fritted into pellet form at high temperatures using a furnace. Then compression tests are carried out both before and after pellet sorption. Last but not least, many alternative disposal options for used-pellets are also being considered. And as previously mentioned, each clay will need to be studied and tested individually due to its unique characteristics.
Expected Results and Significances: After being processed, all clays are standardized to approximately the same size, consistency, and homogeneity prior to pellet fabrication. Water plays a significant role when forming clay pellets. Thus, precise clay to water ratios are essential for pellet fabrication. The three best clay to water ratios for pellet fabrication would be determined and used for pellet fabrication and future testing. Subsequently, the TGA/DSC data can be interpreted for ideal ranges of temperature and time to optimize the pellet-fritting process with minimal energy consumption. If the clays were fritted under insufficient temperature and time condition, the pellets would not be robust enough. On the other hand, if they were fritted at a too high temperature or for too long, they would turn into glass thus also resulting in substantially decrease of heavy metals abatement rates. Furthermore, compression test results aid in determining the most robust pellet. Robust pellets are essential to optimize safety and ease of physical management and transportation. The most important aspect of this study unarguably is uranium abatement, which will be shown via sorption tests. All of these analytical tests above are to find the optimal clay to water ratio, temperature and time to fabricate the most robust pellet with highest uranium sorbing capacity. Finally, an effective disposal method is needed to ensure human and environmental safety under the EPA standards.
Funder Acknowledgement(s): FY 17 NM WRRI Student Grant; USDA I-Discover
Faculty Advisor: Antonio Lara, firstname.lastname@example.org
Role: Temperatures play a significant role when forming clay pellets. Precise dehydroxylation temperatures are essential for pellet robustness. If the clays were fritted under insufficient temperature and time condition, the pellets would not be robust enough. On the other hand, if they were fritted at a too high temperature or for too long, they would turn into glass thus also resulting in substantially decrease of heavy metals abatement rates. The TGA-DSC instrument is used to monitor how different clays behave at different temperatures over time. For Gallup, the dehydroxylation temperature range is between between 672.4°C and 715.2°C with the optimal temperature at 699.3°C resulting in a 1.67% overall mass loss.