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A comparison of kinetic models describing the sorption of pollutants has been reviewed. The rate models evaluated include the Elovich equation, the pseudo-® rst order equation and the pseudo-second order equation. Results show that chemisorption processes could be rate limiting in the sorption step. The pseudo-second order equation may be applied for chemisorption processes with a high degree of correlation in several literature cases where a pseudo-® rst order rate mechanism has been arbitrarily assumed.

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SynopsisEquilibrium isotherms have been studied for the adsorption of four dyestuffs, namely, Acid Blue 25, Acid Blue 158, Mordant Yellow 5, and Direct Red 84, onto chitin. Langmuir and Freundlich constants have been determined and the effects of chitin particle size and solution temperature have been investigated. Theoretical isotherms have been compared with experimental data and good agreement was obtained using a composite isotherm of the general form: Ye = XJ(1 +&' em) , where i, j , and m are constants.

The kinetics of sorption of three basic dyes, namely, Chrysoidine (B02), Astrazon Blue (BB3) and Astrazone Blue (BB69) onto sphagnum moss peat have been investigated. The study focuses on the application of three sorption kinetic models for predicting the uptake of basic dyes. The sorption behaviour is found to be second order, based on the assumption of a pseudo-second order mechanism. The rate constant of sorption, the equilibrium capacity and initial sorption rate with the effect of various peat doses and initial dye concentrations have also been predicted.On a etudie les cinetiques de sorption de trois teintures de base, a savoir Chrysoidine (BO,), Astrazon Blue (BB3) et Astrazone Blue (BB69) sur une mousse de sphaigne. L'etude porte sur l'application de trois modeles cinetiques de sorption pour la prediction de la consomation des teintures de base. On a trouve que le comportement de sorption etait du second ordre, en s'appuyant sur I'hypothese d'un mecanisme de pseudo-second ordre. On a egalement predit la constante de vitesse de sorption, la capacite d'equilibre et la vitesse de sorption initiale avec I'effet des diverses doses de tourbe et des concentrations de teintures initiales.Keywords: peat, dye, kinetics and sorption.he removal of dye from textile eMuents is one of the T significant environmental problems. Since water is a valuable material it should not be polluted by the discharge of industrial effluents. Sorption techniques produce high quality treated effluents and sorption processes have been investigated as a method to remove dyes from wastewater. Mckay et al. (1981a,b,c;1982;1985; 1987) have used low cost sorbents such as peat, wood, silica, chitin, Fuller's earth and bagasse pith for the removal of acid and basic dyes from aqueous solutions.In recent years, sorption has been accepted as one of the most appropriate processes, for the purification of water and wastewater. The prediction of batch sorption kinetics is necessary for the design of industrial sorption columns. However, sorption kinetics show a large dependence on the physical and/or chemical characteristics of the sorbent material which also influences the sorption mechanism. Other relevant factors include sorbate-sorbent chemical properties and system conditions. The sorption mechanism has usually been described by the pseudo-first order Lagergren equation (Khare et al., 1987;Namasivayam and Yamuna, 1992; Low et al., 1995; Mittal and Gupta, 1996; Banerjee et al., 1997) and multiple first order kinetics have been also represented in some sorption systems such as proteidsilica (Sarkar and Chattoraj, 1993), mercury(II)/kaolinite (Singh et al., 1996) and persistent/kaolinite ( A m and Sismanoglu, 1996).The sorption of dyes on various sorbents has been reported as pseudo-first order by many authors (Namisivayam et al., 1996; Atun and Sismanaglu, 1996;Lee et al., 1996). There is only limited second order data available for sorption kinetics on peat; pseudo-second order mechanisms (Gosset et al., 1986; Ho et al., 1994) have bee...