# Cationic and Anionic Dye Adsorption on a Natural Clayey Composite
## 3 Results and Discussion
### Dye Concentration Effect  
When the initial dye concentration increases from 10 to 60 mg/L, the adsorption capacity rises from 0.7 to 5.2 mg/g and 0.8 to 5.7 mg/g for CNB and ADY dye, respectively (Figure 5). The amount of absorbent remains constant and equal to 0.5 g of RC in 50 mL of solution. Figure 5 shows a linear dependency between the amount of adsorbate adsorbed and the initial dye concentration. From Equation (2), we have \(\partial q_{e}/\partial C_{0}=k(1-\partial C_{e}/\partial C_{0})\) where \(k\equiv V/m_{c}\), and \(\partial C_{e}/\partial C_{0}=(1-m/k)\) where \(m\equiv\partial q_{e}/\partial C_{0}\). Therefore, we have a framework helpful in studying the dye concentration effect (Table 4). Figure 4: (**a**) Effect of pH on Basic Navy Blue 2 RN (CNB) removal. (**b**) Effect of pH on Drimaren Yellow Cl-2R (ADY) removal. Adsorbate concentration 50 mg/g. Adsorbent dose 0.5 g/50 mL. For data in Figure 5, the \(k\) value was equal to 0.100, and the \(m\) value was equal to 0.090 and 0.098 for CNB and ADY, respectively. Hence \(m<k\), the system does not reach the complete adsorption condition (\(m=k\)) (Table 4). The full adsorption condition occurs when all the initial dye amount is completely adsorbed. Assuming that the value \(m=V/m_{c}\) will remain constant, the complete adsorption condition would be reached if the amount of adsorbent is equal to 0.555 g/50 mL and 0.510 g/50 mL for the CNB and ADY, respectively. We recall our hypothesis that CNB is mainly removed by chemisorption on IPs. The ADY is removed mainly by physisorption on the KPs and LPs. [PERSON] et al. (2018), [PERSON] and [PERSON] (2019), and [PERSON] et al. (2019) reported that dye removal should decreases at higher dye concentrations, as the adsorbent's active sites become saturated. [PERSON] and [PERSON] (2019) reported that decreased dye removal could be due to an unchanged adsorption capacity. Nevertheless, the CNB and ADY dye removal increased as the dye concentration increased (Figure 6). From 10 to 60, the removal increases from 77% to 87% and 77% to 95% for CNB and ADY dyes, respectively (Figure 6). The results in Figure 6 are in agreement with the explanation given to the information in Figure 5. In both systems, the experimental amount of absorbent is equal to 0.500 g/50 mL (Figure 6). However, the values of adsorbent for complete adsorption should be 0.550 g/50 mL and 0.510 g/50 mL for the CNB and ADY dye, respectively. Thus, the CNB system was working further from the complete adsorption condition, and dye \begin{table}
\begin{tabular}{c c c c} \hline \hline \(m\) & \(\partial q_{g}\partial C_{0}\) & \(\partial C_{e}\)/\(\partial C_{0}\) & **Comment** \\ \hline \multirow{3}{*}{=0} & =0, An increase in \(Co\) implies that there is no change in the amount of adsorbate adsorbed. & =1, An increase in \(Co\) implies an equal increase in \(Ce\). & Upon saturation \\ \hline \multirow{3}{*}{<k} & \textless{k, A change in \(Co\) implies a proportional and minor change in the amount of adsorbate adsorbed.} & \textgreater{}0, An increase in \(Co\) implies an increase in \(Ce\). & Adsorbing \\ \hline \multirow{3}{*}{=k} & =k, A change in \(Co\) implies a proportional and equal change in the amount of adsorbate adsorbed. & =0, An increase in \(Co\) implies that there is no change in \(Ce\). & Full adsorption \\ \hline \multirow{3}{*}{>k} & \textgreater{k, A change in \(Co\) implies a proportional and higher change in the amount of adsorbate adsorbed.} & \textless{0, An increase in \(Co\) implies a decrease in \(Ce\).} & Unlikely \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Framework for the study of the dye concentration effect on the amount of adsorbate absorbed. Figure 5: (a) Effect of the initial Basic Navy Blue 2 RN (CNB)concentration on adsorption capacity. (b) Effect of the initial Drimaren Yellow Cl-2R (ADY) concentration on adsorption capacity. Adsorbent dose 0.5 g/50 mL. pH (cationic) = 6, pH (anionic) = 2.  
removal was smaller than the ADY that was working closer to the complete adsorption condition.