SPECTROSCOPY LETTERS, vol.43, no.1, pp.68-78, 2010 (SCI-Expanded)
The adsorption of Cr(VI) from aqueous solutions onto raw and acid-activated claysnamely, Resadiye region clay (R, raw Resadiye region clay; R-H2SO4, acid-activated with H2SO4 Resadiye region clay; R-HCl, acid-activated with HCl Resadiye region clay) and Hancl region clay (H, raw Hancl region clay; H-H2SO4, acid-activated with H2SO4 Hancl region clay; H-HCl, acid-activated with HCl Hancl region clay)was studied in a batch system. For optimization of the Cr(VI) adsorption on raw clays and acid-activated clays, the effect of pH, temperature, initial Cr(VI) concentration, time, and adsorbent dosage were investigated. X-ray diffraction analyses of raw and acid-activated clays were used to determine the effects of acid-activating on the layer structure of the clays. The surface characterizations of clays and modified clays were performed by using FT-IR spectroscopy. The Langmuir and Freundlich adsorption models were employed to describe the equilibrium isotherms, and thus the isotherm constants were determined. The data obtained from our investigations were well described by the Langmuir model. The adsorption capacity of the adsorbents Resadiye and Hancl clays were found to be 0.0269, 0.0144, and 0.0170mmol/g for H, H-HCl, and H-H2SO4 and 0.0356, 0.0276, and 0.0422mmol/g for R, R-HCl, and R-H2SO4, respectively. The results show that the adsorption was strongly dependent on pH of the medium, initial Cr(VI) concentration and temperature. The removal of Cr(VI) reached saturation in about 120min, and the adsorption process of Cr(VI) was observed as exothermic. A maximum removal of 73% was noted at 1.0x10-4M concentration of Cr(VI) in solution for H-HCl. Furthermore the enhancement of removal of Cr(VI) was observed from pH 3 to 4. The results are discussed to highlight the influence of acid activation on Cr(VI) adsorption characteristics of the clays.