(320ap) Adsorption of Chromium(VI) from Water Solutions on Activated Carbon Fiber

The adsorption of Cr(VI) from aqueous solution on an activated carbon fiber (ACF) in the form of felt was studied in this work. The ACF was made-up from polyacrylonitrile. The textural and physicochemical properties of the ACF were determined experimentally by the Nitrogen-BET method and acid-base titration. Its surface area and Point of Zero Charge were 1220 m2/g and 4.3, respectively. The experimental adsorption equilibrium data of Cr(VI) on the ACF were obtained in a batch adsorber and the Langmuir isotherm model better fitted the experimental data. The effect of solution pH and temperature on the adsorption of Cr(VI) on ACF was investigated by varying the pH and temperature. The Cr(VI) adsorption capacity of ACF diminished when the solution pH was increased from 6 to 10 but was reduced slightly decreasing the temperature from 35 to 15°C. The effect of the pH was attributed to the interactions between the surface of the ACF and the Cr(VI) anions present in the water solution. According to the Cr(VI) speciation diagram the predominant species are HCrO₄^- and CrO₄^-2 in the pH range from 6 to 10. Thus, each ion or both ions would be adsorbed on the ACF. The reversibility of the adsorption of Cr(VI) was investigated by first adsorbing Cr(VI) on the ACF and then desorbing the Cr(VI) adsorbed. It was noticed that Cr(VI) did not desorbed at any pH. At pH=6 and T=25°C the Cr(VI) adsorption capacity of ACF was compared to that of a commercial granular activated carbon (GAC) prepared from coconut shell. It was found that adsorption capacity of the GAC was about twice that of the ACF.