Date of Graduation
Eberly College of Arts and Sciences
Dorothy J Vesper
Selenium (Se) concentrations in natural waters may vary over a 24-hour (diel) period in response to temperature changes. Diel cycles of Se have not been reported in coal mine drainage (CMD) waters, and understanding the mechanisms of Se concentration variations in CMD is important for predicting Se fate and mobility. Iron (Fe) is often associated with CMD, and diel cycles of dissolved Fe species concentrations and/or the formation of Fe oxyhydroxide minerals may impact Se mobility. Experiments were conducted in a laboratory setting between July 2014 and April 2015 to determine if selenite (SeIV) concentration changes could be detected in the same experiments with solid 2-line ferrihydrite (a synthesized Fe oxyhydroxide mineral) and dissolved Fe species concentration changes. Light and temperature controls were used to drive Fe species and SeIV concentration changes. Each experiment differed in solution type (Fe-only, Se-only, or Fe-Se combined), length, temperature, and light conditions. Samples were collected and analyzed for SeIV, total Se, FeII and total Fe. Se IV concentration changes were found to be directly correlated with temperature in both Se-only and Fe-Se solutions. The cycles were more pronounced in the presence of 2-line ferrihydrite. Temperature-dependent sorption of SeIV onto 2-line ferrihydrite was the likely cause of Se IV cycles. SeIV did not cycle with temperature in vessel solutions with pH values greater than 3, indicating that pH is a critical factor in SeIV cycling. The experiments were completed at pH values around 3, underwent significant temperature changes ranging from 2.2°C to 36.5°C, and contained solid Fe oxyhydroxide (2-line ferrihydrite). These conditions are known to exist in some CMD waters, suggesting that Se IV diel cycles may exist in these settings.
Waltemyer, Kendi L., "Variations in selenium concentrations by photochemical and temperature-controlled iron cycles" (2015). Graduate Theses, Dissertations, and Problem Reports. 6893.