An-Najah Staff

The biosorption data of Cd(II), Cr(III), and Cr(VI) by saltbush leaves biomass were fit on the Freundlich and Langmuir adsorption isotherms at 297 K. The Cd(II) and Cr(III) solutions were adjusted to pH 5.0 and the Cr(VI) solution was adjusted to pH 2.0. The correlation coefficient values indicated that the data fit better the Freundlich model. The maximal capacities (KF) were found to be 5.79×¹⁰⁻², 3.25×¹⁰⁻², and1.14×¹⁰⁻² mol/g for Cr(III), Cd(II), and Cr(VI), 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 Cd(II) and Cr(III) indicated that these ions were biosorbed spontaneously. The mean free energy values calculated from the Dubinin–Radushkevick equation (10.78, 9.45, and 9.05 for Cr(III), Cr(VI), and Cd(II), respectively) suggest that the binding of Cd(II), Cr(III), and Cr(VI) by saltbush leaves biomass occurs through an ionic exchange mechanism.

The Freundlich and Langmuir isotherms were used to describe the biosorption of Cu(II), Pb(II), and Zn(II) onto the saltbush leaves biomass at 297 K and pH 5.0. The correlation coefficients (R²) obtained from the Freundlich model were 0.9798, 0.9575, and 0.9963 for Cu, Pb, and Zn, respectively, while for the Langmuir model the R² values for the same metals were 0.0001, 0.1380, and 0.0088, respectively. This suggests that saltbush leaves biomass sorbed the three metals following the Freundlich model (R² > 0.9575). The K_Fvalues obtained from the Freundlich model (175.5 · 10⁻², 10.5 · 10⁻², and 6.32 · 10⁻² mol · g⁻¹ for Pb, Zn, and Cu, respectively), suggest that the metal binding affinity was in the order Pb > Zn > Cu. The experimental values of the maximal adsorption capacities of saltbush leaves biomass were 0.13 · 10⁻², 0.05 · 10⁻², and 0.107 · 10⁻² mol · g⁻¹ for Pb, Zn, and Cu, respectively. The negative ΔG^∘ values for Pb and the positive values for Cu and Zn indicate that the Pb biosorption by saltbush biomass was a spontaneous process.