Simulated plume development and decommissioning using the breakthrough curves of five cations
Rinas, Crystal Dawn
The primary objective of this research was to investigate multicomponent transport of five major cations, Ca2+, Mg2+, NH4+, K+ and Na+, in laboratory soil columns. The soil columns were packed with soils from two different sites and were equilibrated with fresh groundwater from each respective site. Experimental data was obtained by flushing a simulated contaminant through the soil columns. The soil columns were then flushed with fresh groundwater to simulate decommissioning activities. The breakthrough data and soil exchange capacities obtained from both tests were used to identify key processes affecting the transport of the geochemical species. During the simulated contaminant flushing stage, NH4+ and K+ replaced Ca2+ and Mg2+ on the soil exchange sites. Breakthrough of NH4+ was attenuated by factors of 3.2 and 6 for Sites 1 and 2 soils, respectively. Breakthrough of K+ was attenuated by factors of 3.2 and 5.4 for Sites 1 and 2 soils, respectively. Generally, ions with higher valency will exchange for those of lower valency, but in this case the majority of the ions (NH4+ and K+) in the solution has a lower valency and will exchange with those of higher valency by mass action. Ca2+ was the first to be replaced, followed by Mg2+ once the ionic strength of the solution increased. The displacement of calcium and magnesium created a concentration pulse of these cations that coincides with the chloride breakthrough curve. Calcium and magnesium concentrations reached up to approximately 275% and 2000%, respectively, higher than the freshwater originally in the column. During the freshwater flushing stage, freshwater infiltrated the soil columns to assess the permanency of contaminant attenuation and to identify the geochemical mechanisms of contaminant release. Concentrations of NH4+ and K+ declined quickly. Ninety-five percent of attenuated NH4+ was released by the soil. Therefore, the attenuation of NH4+ is reversible but this occurs over several pore volumes at concentrations lower than those in the simulated contaminant and therefore would not result in a mass loading to the environment. Cation exchange was identified as the mechanism responsible for the release of the adsorbed ammonium and potassium into the soil pore water.
DegreeMaster of Science (M.Sc.)
DepartmentAgricultural and Bioresource Engineering
ProgramAgricultural and Bioresource Engineering
Copyright DateJune 2011