The adsorption of Cr(III) and Cr(VI) on activated carbons in the presence of phenol

Abstract

Activated carbons, as selective ion exchangers, can be used to the removing of heavy metals, e.g., chromium from water. It is possible to adsorb anion Cr(VI) and cation Cr(III) on the surface of activated carbons because there can be present functional groups of acid and of basic character on these carbons. In the work there are shown the results of adsorption chromium (III) and (VI) at two pH values 6 and 9. The pH value of the solution, from which a given ion is adsorbed, has influence on the dissociation of functional groups and on the form in which a given ion occurs. And thus this pH value has influence on adsorption effects. In the case of chromium (VI) adsorption on WG-12 carbon there was obtained a high degree of removing (over 94%). Adsorption effects were similar regardless of pH value from which the process was conducted. There were obtained much lower adsorption effects, during the process of Cr(III) adsorption. The degree of removing from the solution of pH = 6 was 74%; and from the solution of pH = 9 about 60%, respectively. There was also examined the effect of phenol presence on Cr(III) and Cr(VI) adsorption. The first part of the research was conducted from unary solution but with the usage of carbon which had been used earlier to phenol adsorption. There was also investigated chromium adsorption on initial carbon but from the binary solution which contains chromium and phenol simultaneously. The concentrations of phenol, which had been used, were much higher than chromium in connection with the occurrence in waters, of much greater amount of organic compounds than ions of heavy metals. In the case of adsorption with the usage of carbon with adsorbed phenol from the solution of pH = 6, both in the case of chromium (III) and chromium (VI) there were obtained smaller adsorption capacities, however, the differences are not large (only a few percent). Still a bit lower effects of adsorption were observed when the adsorption was conducted from binary solution. Considerable lowering of adsorption effects, in relation to unary solution with the usage of fresh carbon, there were observed when pH of the solution was 9 and adsorption was conducted from binary solution. In this case, the degree of Cr(III) adsorption decreased to 35% and Cr(VI) to 6%, respectively.