Determination of the conditions for the modification of AN-31 and ARA-8p anion exchangers by immobilization of 5-(4-carboxyphenyl-azo)-rodanine

Abstract

        The paper is devoted to the determination of optimal conditions for the modification of the ARA-8P and AN-31 anion exchangers with an analytical organic reagent - 5-(4-carboxyphenyl-azo)-rodanine in order to obtain new chelating sorbents.
         Studies were conducted in a static mode at different pH values, time and concentrations of the reagent. Quantitative changes in the “water phase - anion exchanger” system were estimated by the optical densities of aqueous solutions, which were measured by spectrophotometric analysis (at 420 nm) on a LEKI SS 1207 spectrophotometer.
       The optimal conditions for the sorption of 5-(4-carboxyphenyl-azo)-rodanine on the highly basic anion exchanger APA-8P and the weakly basic anion exchanger AN-31 have been established. The sorption of the modifier by anion exchangers in the pH range from 1.0 to 12.0 was investigated. It is determined that the optimal sorption of the reagent is observed at pH 5.0-9.0. Given that the solubility of the reagent is higher
in an alkaline medium, subsequent experiments were carried out at pH 9.0. The dependence of the modifier sorption on the phase contact time was studied. The maximum degree of sorption of - 5-(4-carboxyphenylazo)- rodanine on ARA-8P is observed after 10 minutes of contact of the sorbent with the sorbate, and on AN-31 - after 30 minutes. The sorption capacities of AN-31 and ARA-8P were determined by reagent, which
were 0.5 mmol/g and 1.18 mmol/g, respectively. The shape of the initial sections of the sorption isotherm is related to class H, indicating extremely strong adsorption at very low concentrations and the formation of chemical bonds. This fact also indicates that the interaction between the adsorbed structural particles is negligible and the activation energy does not depend on the degree of surface filling. The stability of modified
sorbents in solutions of HCl, NaCl, NaOH of various concentrations was investigated. From the data obtained, it can be concluded that the sorbent obtained on the basis of ARA-8P anion-exchanger is more stable.
         These results can be used for extracting organic reagent from aqueous solutions, and the resulting polymer sorbents for the extraction of toxic metal ions from natural and waste waters.