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A Correlation between the Kinetic and Thermodynamic Adsorption Characteristics of an Optical Brightener on a Pulp Surface

“…The present investigation also shows that the pre-exponential factor A decreases as the value of α increases (Veleva et al 2001) (Figure 1), i.e. ln A = ln A 0 -aα (9) This suggests that the decrease in rate results from the decrease in the pre-exponential factor which, in turn, is connected with the increase in steric hindrance and the exhaustion of active adsorption centres on the pulp surface.…”

“…The present investigation was undertaken on the basis of kinetic and thermodynamic studies of the process which have shown that the pulp surface exhibits inhomogeneous entropy (Veleva et al 2001;Radeva et al 2006Radeva et al , 2008a. As has been pointed out above, the kinetic inhomogeneity coefficient, a [equation (6)], is independent of the initial concentration and the temperature, which in turn implies that it only characterizes the entropy inhomogeneity of the surface [equation (1)] (Veleva et al 2001;Radeva et al 2006). When entropy factors determine the surface inhomogeneity, equation (7) provides the kinetic equation which describes the investigated chemisorption process.…”

“…Equation (7) is valid in those cases when the rate of adsorption decreases because of depletion of the active centres on the pulp surface and because of steric hindrance in access to such centres caused by the pulp matrix (Radeva et al 2006). This equation has been employed for calculating the values of the quantities a, ν 0 and ν for the two brighteners Leucophor AP and Tinopal UP (Veleva et al 2001).…”

“…Our previous investigations have shown that the surface of a pulp is uniformly inhomogeneous with ensembles containing identical numbers of active centres but with different degrees of adsorptivity (Veleva et al 2001;Radeva et al 2006). According to the model of a uniformly inhomogeneous surface, the active centres on the surface of the adsorbent are linearly distributed in terms of their adsorption enthalpies and entropies.…”

“…where m is a coefficient which characterizes the interval of entropy inhomogeneity on the uniformly inhomogeneous pulp surface (Radeva et al 2006(Radeva et al , 2008a. The adsorption kinetics of optical brighteners onto a pulp surface have been studied by the application of an exponential kinetic equation valid for adsorption processes taking place on uniformly inhomogeneous surfaces (Veleva et al 2001;Radeva et al 2006). This is generally written as:…”