The kinetic parameters of both first- and second-order models
together with the R2 values are given in Table 3. At current density
of 2 mA/cm2, the R2 values that correspond to both kinetic models
were found to be far from unity for Cr3+, Ni2+ and Zn2+. Hence, neither
first-order nor second-order kinetic model can describe the
removal rate of these heavy metal ions (Cr3+, Ni2+ and Zn2+). The
copper ions were the only heavy metal ions that their removal rate
can be modeled by first-order kinetics since the corresponding R2
values at all current densities were close to unity