## 3 Results and Discussion
### Langmuir Isotherm and Maximum Removal Capacity  
The performance of an adsorbent can be studied by adsorption isotherm data. Modeling the adsorption isotherm data is an essential way for predicting and comparing the adsorption performance, which is critical for optimization of the adsorption mechanism pathways, expression of the adsorbents capacities, effective design, and applicable practice of the adsorption systems [72]. The Langmuir isotherm model was used to evaluate the maximum removal capacity of the different materials such as waste bricks [33], organoclays [58], and zeolite materials [73]. The linear equation of the Langmuir model is presented in the following Equation (1) [74]:  
\[\frac{C_{e}}{q_{e}}=\frac{1}{q_{\text{max}}.K_{L}}+\frac{C_{e}}{q_{\text{max}}}. \tag{1}\]  
A straight line with a slope of \(1/q_{\text{m}}\) and an intercept of \(1/q_{\text{m}}K_{\text{L}}\) is obtained when \(C_{e}/q_{\text{e}}\) is plotted against \(C_{e}\). Table 4 summarizes the values of these parameters. The regression coefficients are in order of 0.994 to 0.997, indicating the feasibility of the model to determine the maximum removal capacities of different materials, and confirming the monolayer coverage of dye onto WB particles.  
The Med-WB exhibited higher removal capacities at different conditions compared to the Jed-WB. By increasing the removal temperatures, the efficiency of the waste bricks was further improved and a maximum of 120 mg/g was achieved for the Med WB, at 60 \({}^{\circ}\)C. However, the Jed WB material exhibited a removal of 42 mg/g even at 60 \({}^{\circ}\)C. The treatment of the waste brick by NaOH also modified the removal properties and an increase of 35% to 50% was achieved.  
The Langmuir constant (\(K_{\text{L}}\)) indicates the extent of the interaction between the adsorbate and the surface. If the value of \(K_{\text{L}}\) is relatively larger it indicates that there is a strong interaction between adsorbate and adsorbent, while a smaller value implies a weak interaction. In our case, the values were quite low and reflected the weak affinity of the BB-41 dye to the surface of the WB materials (Table 4).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Samples** & **q\({}_{\text{m}}\) (mg\(\cdot\)g\({}^{-1}\))** & \(K_{\text{L}}\) (L-g\({}^{-1}\))** & \(\mathbf{R}^{2}\) \\ \hline Med-WB & 29.01 & 0.096 & 0.9932 \\ Jed-WB & 16.81 & 0.007 & 0.9861 \\ Med-WB-30 \({}^{\circ}\)C & 32.15 & 0.234 & 0.9885 \\ Jed-WB-30 \({}^{\circ}\)C & 20.83 & 0.004 & 0.9787 \\ Med-WB-50 \({}^{\circ}\)C & 34.89 & 0.256 & 0.9861 \\ Jed-WB-50 \({}^{\circ}\)C & 30.03 & 0.060 & 0.9932 \\ Med-WB-60 \({}^{\circ}\)C & 58.47 & 0.439 & 0.9975 \\ Jed-WB-60 \({}^{\circ}\)C & 36.40 & 0.053 & 0.9767 \\ B-Med-WB & 43.50 & 0.210 & 0.9962 \\ B-Jed-WB & 34.36 & 0.029 & 0.9654 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Langmuir parameters of the BB-41 removal by different brick wastes and at different conditions.  
The investigated waste bricks materials have a good efficiency for this dye, compared to other silicate materials (Table 5). The local clays exhibited the highest removal amount because they were not calcined at high temperatures and were used as received.