McKay, G., Blair, H.S., Gardner, J.R., The adsorption of dyes in chitin, III. Intraparticle diffusion process, J. Appl.Polym.ScL, 1983,28,1767-1778. 11. Riordan C.
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Table 2, The observed dependence of the rate on the initial concentration indicates that removal of Cu (II) from diluted solutions should be achieved much easily, since sorption relative to the -~-~.---._-~--- ------ .. __~nitlaLGQl]~Eurtrationjs more nwIc:L11l dilute.§Qlutions, I.e. a303 greater fraction298 of the Cu (II 308 313 present will be sorbed (Weber). Intraparticle diffusion can be rate limiting step in many cases of adsorption process for porous solids. The effect of intraparticle diffusion on the biosorption of Cu (II) onto residual brewery yeasts was examined by using the equation 161 proposed by Weber and Morris [13]. The results obtained have been presented in Figure 3. As to be seen a linear relationship at lower Cu (II) concentrations was observed, but increasing of initial Cu (II) concentration resulted into nonlinearity over the entire time range. The values of intrapartile diffusion rate constants are found 0.69; 1.15; 1.99 and 2.51 mg/g.min-Q,s for the examined range of concentrations. The obtained results was in accordance with the results reported by Ho et ai., [S,4] and Krim et al. [8].
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The rate constant k2 of the pseudo-second order model was determined empirically as a function of initial Cu (II) concentration by equation 17/ [10] k2 It was found that k2
=
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= m.c;
with coefficient
17/ of regression
0,947. The obtained
value of n indicates that the kinetic of Cu (II) biosorption onto residual brewery yeasts was described better by the pseudo-second order expression rather than by intraparticle diffusion model and intraparticle diffusion was not rate limiting step. The negative value of n was also found in the case of Pb(lI) biosorption onto peat [3,4], which confirmed our results. Parallel to above described experiments the effect of temperature on the Cu (II) biosorption onto residual brewery yeasts was evaluated. The biosorption studies were carried out at different temperatures at 49.82 mg/L initial Cu (II) concentration. It was found that the equilibrium Cu (II) uptake increased slowly with the increasing of temperature from 298 to 313K. The parameters of the second-order rate constant were calculated and have been presented in Table 2.
282
The rate constant ko was found - 1.52.10-4mglg.min and the activation energy 10.47kJ/mol. The increasing of temperature caused slight increasing of the equilibrium Cu (II) uptake. The biosorption of Cu (II) was reported as endothermic, the adsorption heat was found 3,30ccal/mol in the temperature range 298-S08K. Similar values were reported by Kim et aI., [7) for Pb (II) and Cd (II) biosorption onto brewery yeasts. Conclusions The kinetic of biosorption of Cu (II) onto residual brewery yeasts was fitted to a pseudosecond-order model. Increasing of initial Cu (II) concentrations caused decreasing of the equilibrium rate constant and increasing of the equilibrium Cu (II) uptake. On the basis of the calculated activation energy the process of Cu (II) biosorption was determined as endothermic. References 1. Gavrilesku M., Removal of heavy metals from environment by biosorption, Eng. Life ScL, 2004, 4, 219-232. 2. Goksungur Y., uren 5., Guvenc U., Biosorption of copper by caustic treated waste baker's yeast biomass, Turk. J. BioI., 200S, 27, 23-29. 3. Ho, Y.S., Mc Kay, G., Kinetic models for the sorption of dye from aqueous solutions by wood, Process Saf. Environ. Protect, 1998, 76B, 183-191. 283
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