Elucidation of the controlling steps of reactive dyes adsorption on activated carbon

In this work, the rate-limiting steps of reactive dye adsorption onto FS-400 activated carbon were elucidated through the investigation of adsorption kinetics. These studies initially revealed that only 20% of the available adsorption capacity was achieved during the first 6 h of mixing. Kinetic profiles showed that the adsorption process was mainly controlled by external diffusion during the first 30 min of the reaction, after which internal diffusion controlled the process. The interruption test method identified the rate-limiting steps; the results showed that sorption of reactive dyes onto FS-400 was mainly controlled by internal diffusion. Furthermore, the external and internal diffusion coefficients and the desorption rate decreased after the interruption period. The same parameters increased when the solution temperature was raised. The thermodynamic parameters studied showed that the adsorption of reactive dyes onto activated carbon was endothermic and is mainly controlled by internal diffusion with a minor effect of external diffusion.

Adsorption Characteristics of Reactive Dyes in Columns of Activated Carbon

Abstract: Adsorption behaviour of reactive dyes in fixed-bed adsorber was evaluated in this work. The characteristics of mass transfer zone (MTZ), where adsorption in column occurs, were affected by carbon bed depth and influent dye concentration. The working lifetime (t(x)) of MTZ, the height of mass transfer zone (HMTZ), the rate of mass transfer zone (RMTZ), and the column capacity at exhaustion (q(column)) were estimated for the removal of remazol reactive yellow and remazol reactive black by carbon adsorber. The results showed that column capacity calculated at 90% of column exhaustion was lower than carbon capacity obtained from equilibrium studies. This indicated that the capacity of activated carbon was not fully utilized in the fixed-bed adsorber. The bed-depth service time model (BDST) was applied for analysis of reactive yellow adsorption in the column. The adsorption capacity of reactive yellow calculated at 50% breakthrough point (No) was found to be 0.1 kg kg(-1) and this value is equivalent to about 14% of the available carbon capacity. The results of this study indicated the applicability of fixed-bed adsorber for removing remazol reactive yellow from solution. (C) 2008 Elsevier B.V. All rights reserved.

Adsorption of methylene blue onto activated carbon produced from steam activated bituminous coal: A study of equilibrium adsorption isotherm.

Chemical Engineering Journal, 124 (2006) 103.

Effect of solution pH, ionic strength, and temperature on adsorption behavior of reactive dyes on activated carbon

The adsorption behavior of C.I. Reactive Blue 2, C.I. Reactive Red 4, and C.I. Reactive Yellow 2 from aqueous solution onto activated carbon was investigated under various experimental conditions. The adsorption capacity of activated carbon for reactive dyes was found to be relatively high. At pH 7.0 and 298 K, the maximum adsorption capacity for C.I. Reactive Blue 2, C.I. Reactive Yellow 2 and C.I. Reactive Red 4 dyes was found to be 0.27, 0.24, and 0.11 mmol/g, respectively. The shape of the adsorption isotherms indicated an L2-type isotherm according to the Giles and Smith classification. The experimental adsorption data showed good correlation with the Langmuir and Ferundlich isotherm models. Further analysis indicated that the formation of a complete monolayer was not achieved, with the fraction of surface coverage found to be 0.45, 0.42, and 0.22 for C.I. Reactive Blue 2, C.I. Reactive Yellow 2 and C.I. Reactive Red 4 dyes, respectively. Experimental data indicated that the adsorption capacity of activated carbon for the dyes was higher in acidic rather than in basic solutions, and further indicated that the removal of dye increased with increase in the ionic strength of solution, this was attributed to aggregation of reactive dyes in solution. Thermodynamic studies indicated that the adsorption of reactive dyes onto activated carbon was an endothermic process. The adsorption enthalpy (?H) for C.I. Reactive Blue 2 and C.I. Reactive Yellow 2 dyes were calculated at 42.2 and 36.2 kJ/mol, respectively. The negative values of free energy (?G) determined for these systems indicated that adsorption of reactive dyes was spontaneous at the temperatures under investigation (298-328 K). © 2007 Elsevier Ltd. All rights reserved.

Textile wastewater treatment using granular activated carbon adsorption in fixed beds

This work involved the treatment of industrial wastewater from a nylon carpet printing plant which currently receives no treatment and is discharged to sea. As nylon is particularly difficult to dye, acid dyes are required for successful coloration and cause major problems with the plant's effluent disposal in terms of color removal. Granular activated carbon Filtrasorb 400 was used to treat a ternary solution of acid dyes and the process plant effluent containing the dyes in a fixed-bed column system. Experimental data were correlated using the bed depth service time (BDST) model to previously published work by the authors for single dye adsorption. The results were expressed in terms of the BDST adsorption capacity, in milligrams of adsorbate per gram of adsorbent, and indicated that there was a 12-25% decrease iri adsorption capacity in the ternary system compared to the single component system; This reduction has been attributed to competitive adsorption occurring in the ternary component system. Dye adsorption from the process plant effluent showed an approximate 65% decrease in adsorption capacity compared to the ternary solution system. This has been attributed to interference caused by the other colorless textile effluent pollutants found in the process wastewater. A chemical oxygen demand analysis on these components indicated that the dyes accounted for only 14% of the total oxygen demand.