Comparative Study of the Sorption Capacity and Contact Time of Congo Red Removal in a Binary and Singular System

The objective of the present paper is to remove Congo red (CR) from wastewater onto Barbary fig skin (BFS) using binary sorption system (\(\hbox {CR}/\hbox {Zn}^{++}\)) at ambient temperature and study the variance of contact time and sorption capacity to that of the singular system. The SEM images, the iodine value (436 mg/g) and the specific surface area (\(368.49\,\hbox {m}^{2}/\hbox {g}\)) show that the used sorbent has a high surface area. The characterization of the surface sorbent by \(^{13}\hbox {CNMR}\), energy-dispersive X-ray, FTIR spectroscopy and Boehm titration test shows the availability of carbonyl, carboxyl, ester and hydroxyl functional groups on this surface as. The Boehm titration test indicates the presence of these functions with almost equivalent amounts (acid groups \(=\) 047 meq \(\hbox {g}^{-1}\), basic groups \(=\) 0.52 meq \(\hbox {g}^{-1}\)). The study of the sorption kinetics indicates a gain of 45 min of contact time in the binary system. The sorption isotherms are very well described by the Langmuir model. According to the Langmuir model, the maximum sorption capacity for CR in binary system (\(Q_{\max } = 161.21 \, \hbox {mg}/\hbox {g}\)) is higher than in singular system (\(Q_{\max } = 151.51 \, \hbox {mg}/\hbox {g}\)). These results show that the sorption of CR onto BFS presents a synergistic phenomenon, not competitive sorption in an aqueous solution which already contains \(\hbox {Zn}^{++}\) (multi-solute system \(\hbox {CR}/\hbox {Zn}^{++}\)).