# Sorption of Organic Electrolytes and Surfactants from Natural Waters by Heterogeneous Membranes
## 4 Conclusions  
Investigated are the sorption (exchange capacity, sorption isotherms, moisture content) characteristics of the MA-40 and MK-40 ion-exchange membranes in solutions of simple (NaCl, MgCl\({}_{2}\), Na\({}_{2}\)SO\({}_{4}\)) and organic (sodium benzenesulfonate C\({}_{6}\)H\({}_{5}\)SO\({}_{3}\)Na-NaBS and naphthalene-2 sodium sulfonate C\({}_{10}\)H\({}_{7}\)SO\({}_{3}\)Na-NaNS) electrolytes and in a solution of the surfactant--cetylpyridinium chloride C\({}_{16}\)H\({}_{33}\)NC\({}_{5}\)H\({}_{5}\)Cl \(\cdot\) H\({}_{2}\)O-CPCI.  
It was found that the sorption of organic ions by membranes is mainly of an ion-exchange nature, the specificity of the interaction is manifested in a decrease in the sorption rate with an increase in the size of the hydrophobic part of the organic ion and in a decrease in the moisture content of the membranes.  
The kinetics of sorption and the specificity of the interaction is determined by the size of the nonpolar part of the ions; the time of establishment of sorption equilibrium (T) increases in the series of ions: BS\({}^{-}\) \(<\) NS\({}^{-}\)\(<\) CP\({}^{+}\), for CP\({}^{+}\)-T \(>\) 1 month.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Membrane-Adsorbed Counterion** & **Electrolyte** & **Concentration mmol/L** & \(n_{i}\) \\ \hline MK-40- Na\({}^{+}\) & NaCl & 1 & 1.0 \(\pm\) 0.02 \\ MK-40- Ba\({}^{+2}\) & BaCl\({}_{2}\) & 1 & 0.73 \(\pm\) 0.02 (\(n\)(Na\({}^{+}\))) \\ MK-40- CP\({}^{+}\) & NaCl & 1 & 0.37 \(\pm\) 0.02 (\(n\)(Na\({}^{+}\))) \\ MA-40- Cl\({}^{-}\) & NaCl & 1 & 1.0 \(\pm\) 0.02 \\ MA-40- OH\({}^{-}\) & NaOH & 15 & 0.87 \(\pm\) 0.02 \\ MA-40- NS\({}^{-}\) & NaBS & 0.5 & 0.98 \(\pm\) 0.02 \\ MA-40- NS\({}^{-}\) & NaBS & 2 & 0.97 \(\pm\) 0.02 \\ MA-40- NS\({}^{-}\) & NaBS & 10 & 0.87 \(\pm\) 0.02 \\ MA-40- NS\({}^{-}\) & NaNS & 0.5 & 0.97 \(\pm\) 0.02 \\ MA-40- NS\({}^{-}\) & NaNS & 2 & 0.97 \(\pm\) 0.02 \\ MA-40- NS\({}^{-}\) & NaNS & 10 & 0.81 \(\pm\) 0.02 \\ MA-40- NS\({}^{-}\) & NaNS & 15 & 0.77 \(\pm\) 0.02 \\ \hline \end{tabular}
\end{table}
Table 2: The ion transport numbers in the membranes.  
The moisture content and elasticity of the membranes decrease in solutions of organic electrolytes, especially significantly in a CPCI solution, during the sorption of which the membrane becomes brittle.  
The study of the dependence of transport numbers on concentration showed that in the solutions of NaBS and NaNS, the MA-40 membrane retains high electrochemical activity, while the MK-40 in the CPCI solution completely loses it.  
From the data obtained in the work, it follows that organic BS\({}^{-}\) and NS\({}^{-}\) ions are not dangerous when desalting water by electrodialysis, whereas CP\({}^{+}\) sorption leads to membrane poisoning.  
The data obtained in this work can be used to simulate the processes of electrodialysis with ion-exchange membranes during wastewater treatment from organic substances  
Conceptualization, I.B. and T.K.; methodology, I.B. and T.K.; software, I.B.; validation, I.B., T.K., and V.P.; formal analysis, N.D. ([PERSON]) and V.P.; investigation, N.D. ([PERSON]), N.N. and N.D. ([PERSON]); resources, I.B.; data curation, I.B., and N.D. ([PERSON]); writing--original draft preparation, I.B. and T.K.; writing--review and editing, I.B., T.K., A.P. and O.P.; visualization, N.D. ([PERSON]) and A.P.; supervision, V.P.; project administration, O.P. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflict of interest.