Kinetics of hexavalent chromium adsorption on granular activated carbon [articol]

Abstract

The kinetics of Cr(VI) adsorption on granular activated carbon (GAC) Nobrac CG 700 was investigated in batch system, over the pH range of 1.10 – 4.05, at 24o C. The effect of pH was observed and experimental data has been interpreted in terms of zero-order, first-order, second-order, pseudo first-order and pseudo second-order integrated kinetic models. It was noticed that Cr(VI) adsorption rates decreased significantly with increasing pH. Moreover, at pH = 4.05 and higher, the adsorption process was found to be negligibly slow; therefore, all further kinetic interpretations were performed only for the pH range of 1.10 – 3.06. The adsorption process proceeds in two stages: high adsorption rates were observed within the first time interval, whereas a strong decrease in the Cr(VI) adsorption occurs in the second one. The results obtained indicate pseudo second-order kinetics for the first time interval, and zero-order kinetics for the second time interval. The rate coefficients were determined for both stages of the adsorption process.