The linear plots of Langmuir and Freundlich equations
representing Cu(II) adsorption by the chicken eggshells are
illustrated in Figs. 3 and 4. The adsorption constants of
Langmuir and Freundlich equations and their correlation
coefficients (R2) are presented in Table I. The value of R2 is a
measure of the goodness-of-fit of experimental data on the
isotherm models [2]. Results showed that the adsorption
process by chicken eggshells was better repres ented by the
Freundlich equation compared to the Langmuir isotherm, where
the R2 values were found to be 0.9818 and 0.7360, respectively.
This indicated that the uptake of copper on chicken eggshells
was happened through heterogeneous adsorption.