Abstract
The adsorption of hexavalent chromium on Kaolinite and Illite was studied in order to evaluate their potential for the reduction of hexavalent chromium mobility and their possible application for the treatment of polluted sediment. The influence of various parameters affecting the adsorption of hexavalent chromium, such as the pH of aqueous solution, the ionic strength and the initial metal ion concentration were investigated. The optimal pH range corresponding to the hexavalent chromium adsorption maximum on the Kaolinite and Illite is 2 - 4 and 2 - 2.6, respectively. The results showed that hexavalent chromium sorption on Kaolinite and Illite was strongly influenced by the pH, the ionic strength and the initial metal ion concentration. Langmuir and Freundlich adsorption isotherms are employed to understand the nature of adsorption at room temperature. The characteristic parameters for each isotherm have been determined. This showed that the Freundlich isotherm model well described the equilibrium data. The data suggest that the charge of the clay mineral surface is one of the main factors controlling hexavalent chromium desorption at alkaline pHs.
Highlights
Heavy-metal concentrations in aquatic ecosystems, especially chromium, have increased considerably as a result of inputs from human production and consumption activities
The results showed that hexavalent chromium sorption on Kaolinite and Illite was strongly influenced by the pH, the ionic strength and the initial metal ion concentration
The pH and concentration ranges were used in this study meant that bichromate ( HCrO4 ) in an acidic medium and chromate ( CrO24 ) in an neutral and basic medium would be the predominant form of hexavalent chromium which participate in adsorption [8]
Summary
Heavy-metal concentrations in aquatic ecosystems, especially chromium, have increased considerably as a result of inputs from human production and consumption activities. Sediments are the main sink for these elements, but when environmental conditions change (pH, redox potential, etc.), sediments can act as a source of metals. Sediments contaminated with heavy metals have the potential to impart adverse effects to aquatic organisms and contribute to the degradation of ecosystem function. If dredged sediments are contaminated, it is necessary to propose appropriate treatment techniques that satisfy environmental as well as economic criteria. Trivalent [Cr(III)] and hexavalent [Cr(VI)] chromium are of major environmental significance depending on pH and redox conditions [1,2]. As an hexavalent chromium anions are highly mobile in sediment, soil and water environments. Indicative limits for total chromium concentrations in drinking water and reclaimed wastewater for irrigation are 0.05 [4] and 0.1 - 1 mg/L [5], respectively
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