Biosorption Of Cu, Zn And Pb By Eichhornia Crassipes: Thermodynamic And Isotherm Studies

The present work mainly concentrates on biosorption studies of Cu, Zn and Pb by Eichhornia crassipes. The biosorption data of Cu, Zn and Pb by Eichhornia crassipes were fit on the Freundlich and Langmuir adsorption isotherms at 297 K. The CU and Zn solutions were adjusted to pH 4.0 and the Pb solution was adjusted to pH 3.0. The correlation coefficient values indicated that the data fit better the Freundlich model. The maximal capacities (KF) were found to be 5.75 * 10-2 , 3.20 * 10-2, and 1.10 × 10-2 mol/g for Cu, Zn and Pb respectively. Similar results were obtained using the
Langmuir and the Dubinin–Radushkevick equations. Thermodynamic parameters calculated from the Khan and Singh equation and from the qe vs.ce plot show that the equilibrium constants for the biosorption of the metals follow the same order of the maximal capacities. The negative Gibbs free energy values obtained for Cu and Zn indicated that these ions were biosorbed spontaneously. The mean free energy values calculated from the
Dubinin–Radushkevick equation (10.75, 9.40, and 9.00) for Zn, Pb and Cu respectively suggest that the binding of Cu, Zn and Pb by Eichhornia crassipes occurs through an ionic exchange mechanism.