# Removal of Metals and Dyes in Water Using Low-Cost Agro-Industrial Waste Materials
## 3 Results and Discussion
### Adsorption Kinetic and Isotherm  
From Figure 10A and Table 4, it is observed that the experimental equilibrium adsorption data of MB are adjusted by [PERSON]'s model, indicating that the adsorbent surface is heterogeneous with many unequal active sites and different adsorption energies. Regarding Cr (VI) (Figure 10B), it can be said that the process is described by [PERSON]'s isotherm, denoting that at equilibrium, monolayer sorption of the solute occurs at a fixed number of sorption sites homogeneously distributed over the sorbent surface and that these sites also have equal affinity for the adsorbate [51]. Furthermore, it is estimated that the surface effects given by the modification with KOH have positively influenced the affinity between the adsorbate and the adsorbent [52].  
Figure 10: Adsorption isotherms of **(A)** MB and **(B)** Cr (VI) using MWBC.  
Figure 9: Effect of the initial concentration onto Cr (VI) adsorption using MWBC.  
Considering Figure 11A and Table 5, it is evidenced that the MB adsorption kinetic is described by the pseudo-second-order model and [PERSON]. The above indicates that the process is controlled by physisorption, where the adsorption rate of the dye is proportional to the available sites on the adsorbent, and the reaction rate depends on the amount of dye on the adsorbent surface. Furthermore, there is a coexisting chemisorption mechanism, where the adsorption rate of the dye will decrease exponentially as the amount of dye adsorbed increases [53]. On the other hand, Cr (VI) kinetic was adjusted by [PERSON]'s model, indicating that the process occurs by chemisorption involving electrostatic interaction and ionic exchange between the adsorbate and adsorbent [54,55].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Model** & **Parameters** & **MWBC—MB** & **MWBC—Cr (VI)** \\ \hline \multirow{3}{*}{Langmuir} & \(q_{max}^{L}\) & 186,375.375 & 90.723 \\ \cline{2-4}  & \(K_{L}\) & \(7.015\times 10^{-5}\) & \(1.385\times 10^{-2}\) \\ \cline{2-4}  & \(\text{R}^{2}\) & 0.756 & 0.959 \\ \hline \multirow{3}{*}{Freundlich} & \(K_{F}\) & 9.460 & 3.2698 \\ \cline{2-4}  & \(n\) & 0.598 & 1.6562 \\ \cline{2-4}  & \(\text{R}^{2}\) & 0.918 & 0.969 \\ \hline \hline \end{tabular}
\end{table}
Table 4: MB and Cr (VI) adjustment isotherm parameters.  
Figure 11: (**A**) MB and (**B**) Cr (VI) kinetic modeling onto MWBC.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Model** & **Parameter** & **MWBC—MB** & **MWBC—Cr (VI)** \\ \hline \multirow{3}{*}{Pseudo-first order} & \(q_{e}\) & 11.812 & 8.05363 \\ \cline{2-4}  & \(K_{I}\) & 0.424 & 0.07054 \\ \cline{2-4}  & \(\text{R}^{2}\) & 0.926 & 0.49151 \\ \hline \multirow{3}{*}{Pseudo-second order} & \(q_{e}\) & 12.129 & 9.20214 \\ \cline{2-4}  & \(\text{K}_{2}\) & 0.078 & 0.00865 \\ \cline{2-4}  & \(\text{R}^{2}\) & 0.945 & 0.66108 \\ \hline \multirow{3}{*}{Elovich} & \(\alpha\) & \(2.172\times 10^{8}\) & 4.3733 \\ \cline{2-4}  & \(\beta\) & 2.050 & 0.74117 \\ \cline{1-1} \cline{2-4}  & \(\text{R}^{2}\) & 0.967 & 0.87572 \\ \hline \hline \end{tabular}
\end{table}
Table 5: MB and Cr (VI) kinetic adjustment parameters.