Previously, the authors demonstrated  that the redistribution of acid and basic sites on the modified with tungsten sulfide surface changes the degree of dye (Congo red) sorption (Re) from solutions with various concentrations (1000, 800, 600, 400, 75 mg/L).
Fig. 1 − The dependence of the dye (Congo red) degree sorption (Re) on the concentration: from left to right (Saponite); (Saponite+WS2); (MCC); (MCC+WS2).
The significant improvement of dye sorption for sorbents contained tungsten sulfide is presented in Fig. 1. It should be noted that the activity of the Saponite + WS2 sample is commensurate with the activity of the MCC + WS2 sample for all values of the dye concentration. The modification of cheap native Saponite by tungsten sulfide makes this process profitable. This fact is the rational argument in favour of solving applied problems of water treatment from pollutants. The use of a magnetically modified sorbent (MCC; MCC + WS2) significantly improves the process of separating the precipitate for low concentrations of the dye, but it is more expensive. It would be logical to use a two-stage scheme of water purification from dyes. In the first stage of removing the dye from a solution with a concentration of from 1000 to 400 mg/L, Saponite + WS2 can be applied. In the second stage of purification and separation, MCC + WS2 can be used.
Thus, the study of modified sorbents based on Saponite clay demonstrated the change in the acid-base characteristics of the surface and sorption activity to the anionic dye (Congo red). The increase of the degree of dye sorption correlates well with the increase of the number of Bronsted acid sites on the surface of the sorbents. These centers can be active sorption sites for anionic pollutants from solutions. From the presented data, it can be concluded that results of research have discovered broad perspective to use the process of modified native clays, e.g. Saponite with magnetite and tungsten sulfide, for further use of modified sorbents in technologies of water purification.