Doctor of Philosophy (PhD)


Plant, Environmental Management and Soil Sciences

Document Type



Arsenic transport in soils and aquifers is highly dependent on the adsorption-desorption reactions in the solid phase. Results from our kinetic batch experiments indicated that adsorption of arsenate [As(V)] was highly nonlinear and strongly kinetic. Desorption of As(V) were hysteretic in nature and a significant amount of As(V) was irreversibly adsorbed on all soils. Results from column experiments indicated strong As(V) retardation followed by slow release or extensive tailing of the breakthrough curves (BTCs). Sharp decrease in As(V) concentration during flow interruption verified the extensive non-equilibrium condition which was likely due to the dominance of kinetic retention processes. We evaluated several multireaction model (MRM) formulations for its prediction capability of As(V) retention and transport in soils and concluded that nonlinear reversible along with a consecutive or concurrent irreversible reactions were the dominant mechanisms. The use of batch rate coefficients for the predictions of As(V) BTCs underestimated the extent of retention and overestimated the extent of As(V) mobility for all soils. When utilized in an inverse mode, the MRM model provided good predictions of As(V) BTCs. The competition between arsenate and phosphate (P) has the potential of increasing arsenic mobility and bioavailability in soils. Our kinetic batch studies demonstrated that rates and amounts of As(V) adsorption by soils were significantly reduced by increasing P additions. In a separate experiment, the presence of P in soils increased mobility of As(V) in saturated columns. The use of flow interruptions verified the dominance of time-dependent sorption during As(V) and P transport in soils. We further extended the MRM model to simulate retention and transport of multiple solutes in soils. The formulated multicomponent multireaction model was capable of predicting the competition effect of P on As(V) retention and transport given appropriate kinetic coefficients. The mobilization of colloidal particles and its effect on the transport of arsenite [As(III)] was investigated using miscible displacement experiments. Mobilization of colloidal amorphous material and enhanced transport of As(III) was observed when the input solution was replaced with deionized water. Peaks of colloid generation coincided with the peak concentrations of Fe, indicating mobilization of Fe oxides and facilitated transport of As(III).



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Committee Chair

Hussein M Selim