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Ind. Eng. Chem. Res. 2006, 45, 7362
CORRESPONDENCE Comment on “Adsorption of Reactive Dyes from a Textile Effluent Using Sawdust as the Adsorbent” B. Stephen Inbaraj* Department of Nutrition and Food Sciences, Fu Jen UniVersity, Taipei 242, Taiwan Sir: Chakraborty et al.1 recently published an article on the adsorption characteristics of reactive dyes by modified sawdust adsorbent (CSD). In the modeling of equilibrium data, the authors have used Freundlich, Langmuir, Redlich-Peterson, and Fritz-Schlunder equations to evaluate the best-fit isotherm model(s). However, the limiting behavior of the exponent (ν e 1) in the Redlich-Peterson model was not taken into consideration while fitting the equilibrium data. Consequently, this has resulted in the ν values being >1 (as reported in Table 5 of their work1) for the reactive dyes/CSD system investigated, which is incorrect. Furthermore, it contradicts the limiting condition of the exponent ν stated under the Redlich-Peterson equation on the Page 4734 of the same article.1 The Redlich-Peterson model2 is a three-parameter equation that incorporates the features of both the Freundlich and Langmuir isotherms and may be used to represent adsorption equilibria over a wide range of concentrations.3 This empirical equation is given by
Ye )
KRCe 1 + KPCeν
(1)
where Ye is the amount of solute adsorbed (in units of mg/g), Ce is the equilibrium solute concentration (in units of mg/L), and KR, KP, and ν are constants that characterize the isotherm. The value of the exponent ν must lie between 0 and 1.2-6 The limiting behavior of the constants can be summarized as follows. When ν ) 1, eq 1 reduces to the Langmuir equation (eq 2):2-6
Ye )
KRCe 1 + KPCe
* E-mail:
[email protected].
(2)
When the constants KR and KP are much greater than unity,5,7 the Redlich-Peterson isotherm approaches that of Freundlich. When ν ) 0, the Henry’s Law equation (eq 3) results:4
Ye )
KRCe 1 + KP
(3)
In accordance with the reported theoretical facts discussed previously, it is suggested that the authors refit the equilibrium data with the Redlich-Peterson equation by subjecting the exponent to a limiting factor of 0 < ν < 1 and report its reevaluated fitted parameters and best-fit model(s). Literature Cited (1) Chakraborty, S.; Basu, J. K.; De, S.; DasGupta, S. Adsorption of Reactive Dyes from a Textile Effluent using Sawdust as the Adsorbent. Ind. Eng. Chem. Res. 2006, 45, 4732-4741. (2) Redlich, O.; Peterson, D. L. A Useful Adsorption Isotherm. J. Phys. Chem. 1959, 63, 1024-1026. (3) Allen, S. J.; McKay, G.; Porter, J. F. Adsorption Isotherm Models for Basic Dye Adsorption by Peat in Single and Binary Component Systems. J. Colloid Interface Sci. 2004, 280, 322-333. (4) Ho, Y.-S.; Ofomaja, A. E. Biosorption Thermodynamics of Cadmium on Coconut Copra Meal as Biosorbent. Biochem. Eng. J. 2006, 30, 117123. (5) Inbaraj, B. S.; Chiu, C. P.; Ho, G. H.; Yang, J.; Chen, B. H. Removal of Cationic Dyes from Aqueous Solution Using an Anionic Poly-γ-glutamic acid-based Adsorbent. J. Hazard. Mater. 2006, in press. (DOI: 10.1016/ j.jhazmat.2006.01.057.) (6) Vasanth Kumar, K.; Sivanesan, S. Isotherm Parameters for Basic Dyes onto Activated Carbon: Comparison of Linear and Non-linear Method. J. Hazard. Mater. 2006, B129, 147-150. (7) Ho, Y. S. Selection of Optimum Sorption Isotherm. Carbon 2004, 42, 2115-2116.
IE060816U
10.1021/ie060816u CCC: $33.50 © 2006 American Chemical Society Published on Web 09/08/2006
