Date of Award

4-2013

Degree Name

Master of Science

Department

Geosciences

First Advisor

Dr. Carla Koretsky

Second Advisor

Dr. Duane Hampton

Third Advisor

Dr. R.V. Krishnamurthy

Access Setting

Masters Thesis-Open Access

Abstract

Hexavalent chromium is a very common contaminant most often associated with industrial processes, it is quite mobile in the subsurface and a better understanding of its mobility and interactions with soil constituents will help ongoing remediation efforts.

Hydrous manganese oxides (HMO) are a very common soil constituent and thus would be likely to interact with Cr(VI) in contaminated shallow subsurface environments. The goal of this study is to develop a working model that can improve predictions of Cr(VI) mobility in natural systems. A diffuse double layer surface complexation model (DLM) was developed by deriving reaction stoichiometries and stability constants for formation of Cr(VI) surface complexes on HMO. These reaction stoichiometries and their respective stability constants were derived based on a DLM already developed by Tonkin et al. (2004) to describe the surface charging behavior of HMO.

To derive the Cr adsorption reaction stoichiometries and their respective stability constants, adsorption edge experiments were conducted under varying pH (~3-10) and ionic strength (0.001 to 0.1 M NaNO3) under 0% pCO2 conditions on synthetic hydrous manganese oxide. These adsorption edge data were used to constrain the Cr surface reactions in the absence of carbonate using the optimization program FITEQL. To account for carbonate interactions in natural systems, reaction stoichiometries and stability constants for competing carbonate surface complexes were derived using experimental data collected under varying pH and ionic strength at 5% pCO2. The DLM was tested against experimental data collected at atmospheric and 2.5% pCO2 under a wide range of pH and ionic strength conditions.

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