Abstract
The biosorption equilibrium isotherms of copper ions from wastewater onto date stones (DS) and palm-trees Waste (PTW) in
aqueous solution over a range of temperatures between 25 and 70°C were studied and modelled. To predict the biosorption
isotherms and to determine the characteristic parameters for process design, five models frequently used in the literature -
Langmuir, Freundlich, Temkin, Sips and Redlich-Peterson were applied to experimental data.
The Langmuir’s model gives the most accurate fit with high R2 (0.99) for all the tested temperatures. The maximal biosorption
capacity, qm, increases with temperature from 3.07 mg/g at 25°C to 4.36 mg/g at 70°C for DS and decreases with temperature
from 1.53 mg/g at 25°C to 1.27 mg/g at 70°C for PTW. In addition, the affinity of date stones and palm-trees waste for copper,
represented by parameter KL in Langmuir’s model varies from 0.055 to 0.097 L/mg for DS and from 0.19 to 0.08 L/mg for PTW
when the temperature raises from 25 to 70°C. Equilibrium data are well fitted by the Langmuir, Sips and Redlich–Peterson
models as the sum of squared deviations (s2) has a small value (<0.32). Finally, the shape of Langmuir’s model, represented by
the dimensionless parameter RL, shows that copper biosorption on DS and PTW is favourable for all the tested temperatures and
initial copper concentrations. The biosorption isotherm models fitted the experimental data in the order: Langmuir (twoparameter),
Sips and Redlich–Peterson (three-parameter) > Temkin (two-parameter) > Freundlich (two-parameter) for DS, and in
the order: Langmuir ˃ Sips ˃ Redlich–Peterson ˃ Temkin ˃ Freundlich for PTW.