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adsorptive removal of cobalt from aqueous solution by activated carbons

Abstract

Adsorption of Co(II) ions from aqueous solutions using two samples of activated carbon fibers and two samples of granulated activated carbons has been studied. The adsorption isotherms obey Freundlich isotherm equation. The linear Freundlich adsorption isotherms have been used to calculate Xm and n. The adsorption does not depend on the surface area but is strongly influenced by the presence of carbon-oxygen groups on the carbon surface. The amounts of these surface groups was enhanced by oxidation of the carbons with nitric acid and oxygen gas and decreased by degassing of the oxidized samples at 400, 650 and 9500C. The adsorption of Co(II) ions increased on oxidation and decreased on degassing. The increase in adsorption was much larger when the oxidation was carried out with nitric acid. This treatment incidentally results in a larger increase in the amounts of the oxygen surface groups compared to oxidation with oxygen gas. The decrease in adsorption on degassing depends on the temperature of degassing, being larger on degassing at 6500C than on degassing at 4000C. The increase in adsorption on oxidation and the decrease in adsorption on degassing have been attributed to an increase in the concentration of acidic groups on the carbon surface on oxidation and thier decrease on degassing. The presence of acidic carbon-oxygen groups on the carbon surface and their ionization in aqueous solution also changes the pH of the carbon suspension. The effect of solution pH onadsoprtion has also been studies and suitable mechanisms involved in the adsorption of Co(II) ions on activated carbons from solutions have been discussed.

diksha aggarwal and meenakshi goyal

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