Adsorption of Inorganic Electrolytes on Activated Carbons from Aqueous Solution

Abstract

Adsorption of several inorganic ions from aqueous solution on commercial and their modified activated carbons has been studied. Adsorption tests of halide ion from 1×10^-3mol/l halide solution and sodium ion from 1×10^-4-2×10^-3mol/l sodium ion solution were carried out at various pHs. Halide ion was adsorbed in acidic region and its uptake increased with the lowering of pH (Figs.2, 5). The adsorption of halide ion was largely affected by the kind of halide ions. The order of halide ion uptake was follow; I^->Br^->Cl^- (Fig. 5). Hydrogen ion was simultaneously adsorbed on activated-carbon with halide ion, and the ratio of the adsorbed hydrogen ion to the adsorbed halide ion, H/X, was approximately 1.0 (Fig. 3). Insoluble ashes in activated carbons exerted no effect on the adsorption of these ions (Fig. 6). The activated carbon made by a steam activation method showed higher adsorption ability for these ions than one made by a zinc chloride activation me thod. Hydrogenation or outgassing of activated carbon at high temperature improved the adsorption ability for these ions. On the other hand, oxidation of activated carbon lowered the adsorption ability for these ions (Figs. 8, 9).
Sodium and hydroxide ions were adsorb ed in alkaline region and their uptakes increased with an increase in pH (Fig.2). The amount of adsorbed hydroxide ion was appreciably larger than that of adsorbed sodium ion (Figs. 2, 4). The influence of activation method and the surface modification of activated carbon on the adsorption of these ions were reversed to that on the adsorption of halogenide and hydrogen ions (Figs. 8, 9). The adsorption of halide and hydrogen ions and the adsorption of sodium and hydroxide ions can be explained by a basic surface oxide mechanism and by an ion-exchange mechanism, respectively.