Adsorption of hexavalent and trivalent chromium to a clayey silt soil : batch kinetic and equilibrium studies Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9593tx495

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  • Chromium, an element of widespread use, is toxic in some forms. Improper disposal of waste chromium products has resulted in contamination of many sites throughout the United States, including the United Chrome Products Superfund site in Corvallis, Oregon. A better understanding of chromium chemistry is needed to facilitate the remediation of these contaminated sites. The purpose of this study was to investigate the characteristics of adsorption of hexavalent and trivalent chromium (Cr(VI) and Cr(III), respectively) to a clayey silt soil similar to that found at the United Chrome Products site. The effects of pH on adsorption rates and magnitudes, and the effectiveness of selected extractant solutions in removing adsorbed chromium from soil, were evaluated. Simple mathematical models were used to describe adsorption kinetics and equilibrium, and the chemical nature of the adsorption reactions were postulated. Cr(VI) adsorption magnitudes and rates increased as pH decreased. Neither distilled water or groundwater were effective extractants of adsorbed Cr(VI); an 0.02 molar orthophosphate solution was a moderately successfull extractant. Cr(VI) adsorption kinetics were diphasic in nature, and could be described with an irreversible two-site adsorption reaction model. Cr(VI) uptake by the soil was thought to be adsorbed to metallic oxide surfaces rather than reduced to insoluble Cr(III). Trivalent chromium (Cr(III)) was most effectively adsorbed between pH values of four and five. At lower pH values, Cr(III) adsorption magnitudes decreased proportionally with hydrogen ion concentration; at higher pH values, the decrease in Cr(III) adsorption was probably due to complexation with soluble and colloidal organic matter released from the soil. EDTA was only moderately effective in extracting adsorbed Cr(III) from soil.
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