Equilibrium sorptionof methylene blue on clinoptilolite
Abstract
To expand the scope of aluminosilicates, in particular, clinoptilolite, as carriers and sorbents, various ways of their modification are used. The effect of acid activation on the structural characteristics of aluminosilicate can be determined by experimental data of the study of the equilibrium of sorption of methylene blue (MG). Sorption fixation of MG allows to get an idea about the surface of clinoptilolite formed by pores more
than 1.5 nm. The object of the analysis was selected organic dye - methylene blue, sorbent - clinoptilolite frame aluminosilicate (deposits of the Subpolar Ural of Ugra) in the native and activated with hydrochloric acid state. The equilibrium of MG sorption on acid-activated clinoptilolite was studied at a temperature of 295±2K under static conditions by the method of variable concentrations. The interval of used MG concentrations
was 0.150-4.0 mmol/dm3.
An S-shaped type of isotherms was revealed, which suggests a change in the mechanism of sorption fixation of MG with an increase in its concentration in the external solution. In the region of low concentrations of the dye solution, the formation of a monolayer of sorbate is observed. For a quantitative description of the sorption equilibrium in the concentration range corresponding to the formation of a monolayer, the Langmuir equation was used. The presentation of the experimental data of the equation in a linear form made it possible to determine the limiting capacity of the monolayer, the specific surface area and the coefficient of sorption equilibrium. Monolayer fixation of MG in the form of cation on the native sample of clinoptilolite is possible as a result of an equivalent exchange with non-carcass cations due to electrostatic interaction with available negatively charged centers of the sorbent matrix. After completion of the formation of the monolayer, sorption acquires a polymolecular character, which is manifested on the isotherm in a sharp increase in the sorption capacity due to the presence in the solution of dye associates formed as a result of Van der Waals interactions and hydrogen bonds.
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References
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