Semester

Spring

Date of Graduation

2008

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Lian-Shin Lin.

Abstract

Removal of selenite from aqueous phase using iron-coated granular activated carbons (GAC) was investigated in this study. Five different types of GAC were used for iron coating by oxidizing ferrous chloride with sodium hypochlorite and tested for selenite removal. Nitrogen adsorption-desorption analyses indicated that Brunauer-Emmett-Teller (BET) surface area, pore size, and pore volume deceased with the iron coating. The Darco 12x20 GAC was shown to be the most effective adsorbent among the five tested GACs after iron coating. Among the different concentrations used for iron coating, the Darco 12x20 GAC coated with 0.1 M ferrous chloride achieved the highest selenite removal (97.3%).;High removal efficiency of selenite occurred in a wide range of pH (i.e., 2 to 8), but the efficiency decreased when pH was higher than 8. A range of initial selenium concentrations (0.5, 1 and 2 mg/L) at three temperature (25, 35, 45°C) were used to examine the adsorption behavior of the Fe-GAC. Adsorption kinetics showed that selenite removal efficiency reached more than 90% after 6-hour adsorption for initial selenium concentration of 2 mg/L and equilibrium was obtained after 48 hours. Activation energy was calculated to be 30.42 KJ/mol. A pseudo-second-order kinetic model was found to characterize the adsorption kinetics well for all the initial selenium concentrations and temperatures tested (R2 ≥ 0.9969).;Adsorption isotherms for three different initial selenium concentrations were developed and the data generally fit the Langmuir model well (R 2 ≥ 0.994). The adsorption capacity reached as high as 1.68 mg-Se/g-adsorbent at equilibrium for initial concentration of 2 mg/L at 25°C. The Gibbs free energy was determined to be negative, indicating the spontaneous nature of the adsorption reaction. Oxyanion competitive adsorption showed that sulfate (0.1--5 mM) barely affected selenite adsorption. Other anions (phosphate, silicate and carbonate) impact selenite adsorption to various degrees with phosphate completely excluded selenite adsorption at 5 mM.

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