Περίληψη:
The Cr(VI) uptake from aqueous solutions by polyhexamethylene-guanidine-modified natural zeolitic materials from Metaxades, Greece (PHMG-MTX) and Tedzami, Georgia (PHMG-TZ) was investigated using batch techniques. Spectrophotometry using 1,5-diphenylcarbazide for colour development was used for Cr determination. The Cr(VI)-solution concentration varied between 5 and 50 mg/L and the initial pH was adjusted to 3.0, 4.0 and 5.0. Additional experiments were conducted in the presence of competing anions (background electrolyte I = 0.1 M established by 0.1 M NaNO3 and 0.033 M Na2SO4) on solutions with unadjusted pH. For comparison, the Cr(VI) adsorption by Tedzami tuffs modified by octadecylpolyhexamethylene-guanidine-chloride (ODPHMG-TZ) was also investigated. All investigated materials adsorbed considerable amounts of Cr(VI)-oxyanions. It was shown that the Cr(VI)-uptake strongly depended on pH and the presence of competing anions. The Cr(VI)-oxyanion uptake by PHMG-TZ was slightly higher than that observed for ODPHMG-TZ, whereas the sorption capacity of PHMG-MTX was of the same order of magnitude as Metaxades tuffs modified by hexadecyl-trimethylammonium-bromide. The experimental data obtained for pHinit = 3.0 were selected for modeling the adsorption behavior of the materials using six isotherm equations (Freundlich (F), Langmuir (L), Langmuir-Freundlich (L-F), Dubinin-Radushkevich (D-R), Redlich-Peterson (R-P), Toth (T)). The obtained modeling results indicated that, although the three-parameter models, taking into account the surface heterogeneity, provided the closest approach to the measurement data, the parameters estimates could be highly biased. On the other hand, the two-parameter Langmuir isotherm was sufficient to describe the process equilibrium in terms of smallest number of adjustable parameters and approximation of the sorption capacity. © 2007 Elsevier Inc. All rights reserved.
Συγγραφείς:
Misaelides, P.
Zamboulis, D.
Sarridis, Pr.
Warchoł, J.
Godelitsas, A.
Λέξεις-κλειδιά:
Adsorption; Chromates; Concentration (process); pH effects, Clinoptilolite; Polyhexamethylene-guanidine, Zeolites, Adsorption; Chromates; Concentration (process); pH effects; Zeolites
