# The Use of Rapeseed Husks to Remove Acidic and Basic Dyes from Aquatic Solutions
## 3 Results and Discussion
### Maximum Sorption Capacity of RH  
Experimental data obtained from studies into the maximum sorption capacity were described with popular sorption models: Langmuir 1 isotherm, Langmuir 2 isotherm, and Freundlich isotherm (Table 4, Figure 5). An analysis of the values of \(R^{2}\) determination coefficient shows that the Langmuir models better fitted to the data than the [PERSON]'s model in each experimental series. This suggests that only one molecule of dye could be attached to one RH active site. In addition, the adsorbed dyes formed the so-called monolayer on the sorbent's surface, where the dyes could exchange their sorption centers among each other. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Langmuir 1 Model**} & \multicolumn{4}{c}{**Langmuir 2 Model**} & \multicolumn{4}{c}{**[PERSON] Model**} \\ \cline{2-13}
**Dye** & \(Q_{\rm max}\) & \(K_{e}\) & \(R^{2}\) & \(Q_{\rm max}\) & \(b_{1}\) & \(K_{1}\) & \(b_{2}\) & \(K_{2}\) & \(R^{2}\) & \(k\) & \(n\) & \(R^{2}\) \\  & **[mg/g]** & **[L/mg]** & **-** & **[mg/g]** & **[mg/g]** & **[L/mg]** & **[mg/g]** & **[L/mg]** & **-** & **-** & **-** & **-** \\ \hline AR18 & 49.37 & 0.0271 & 0.9895 & 49.37 & 23.60 & 0.0271 & 25.77 & 0.0271 & 0.9895 & 5.754 & 0.375 & 0.8970 \\ AY23 & 41.52 & 0.0231 & 0.9894 & 41.52 & 20.76 & 0.0231 & 20.76 & 0.0231 & 0.9894 & 4.511 & 0.378 & 0.9054 \\ BR46 & 55.59 & 0.0529 & 0.9986 & 59.07 & 12.22 & 0.0086 & 46.85 & 0.0665 & 0.9993 & 9.209 & 0.337 & 0.9155 \\ BV10 & 19.78 & 0.0209 & 0.9995 & 20.93 & 10.08 & 0.0329 & 10.85 & 0.0106 & 0.9997 & 1.314 & 0.493 & 0.9793 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Constants determined from Langmuir 1, Langmuir 2, and Freundlich models (constants determined based on mean values from three measurements). \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & **Dye** & \multicolumn{4}{c}{**Phase I**} & \multicolumn{4}{c}{**Phase II**} & \multicolumn{4}{c}{**Phase III**} \\ \cline{3-10}
**Dye** & **Conc. ** & \(k_{d1}\)***** [**]** & **Durat. ** & \(R^{2}\) & \(k_{d2}\)***** [**]** & **Durat. ** & \(R^{2}\) & \(k_{d3}\)***** [**]** & **Durat. ** & \(R^{2}\) \\  & **[mg/L]** & **[***]** & **[min]** & **-** & **[*]** & **[min]** & **-** & **[***]** & **[min]** & **-** \\ \hline AR18 & 50 & 1.076 & 30 & 0.9996 & 0.655 & 30 & 0.9975 & 0.161 & 90 & 0.9913 \\  & 100 & 2.122 & 30 & 0.9990 & 0.967 & 30 & 0.9969 & 0.385 & 90 & 0. In the experimental series with AR18 and AY23, the \(K_{1}\), \(K_{2}\) and \(K_{C}\) constants determined from the Langmuir models 1 and 2 as well as the \(Q_{max}\) and \(R^{2}\) reached the same numerical values (Table 4), which suggests that only one type of the sorption center played a major role in the sorption of acidic dyes onto RH. Presumably, this function was played by the protonated hydroxyl functional groups. In the experimental series with BR46 and BV10, the Langmuir 2 model was found to describe experimental data better than the Langmuir 1 model, which suggests at least two different mechanisms of dye sorption onto RH. In the case of BR46, its sorption onto RH probably occurred through hydrogen bonds (between hydrogen and nitrogen atoms and between hydrogen and oxygen) and also through its ionic interaction with the ionized carboxyl groups. In contrast, the binding of BV10 on the tested sorbent, apart from hydrogen interactions, could also proceed via electrostatic interactions between the ionized carboxyl group of the dye and the protonated RH groups. The maximum sorption capacities of RH towards AR18 and AY23 were quite similar and reached 49.37 and 41.52 mg/g, respectively. As mentioned earlier, the similar sorption effectiveness of these dyes may result from their similar particle sizes and the same number of acidic functional groups. Figure 5: Isotherms of sorption of: (**a**) AR18, (**b**) AY23, (**c**) BR46, and (**d**) BV10 on RH (average + range). [PERSON] 1,2, [PERSON] models.