Equilibrium and thermodynamic characteristics of sorption 2-(4'-sulfophenylazo)chromotropic acid by highly basic anion exchanger

Abstract

The article investigates the sorption equilibria azocompound – 2-(4'-sulfophenylazo)chromotropic
acid (SPADNS) between the aqueous phase and of the anion exchange resin - AB-17-8 to obtain the
equilibrium sorption and thermodynamic parameters of the interaction. Studies were performed in static
mode at different pH values, temperatures and concentrations of the initial reactant. Quantitative changes in
the system of «queous phase – anionite» evaluated by absorbance of aqueous solutions, which was measured
spectrophotometrically (at 510 nm) relative to the zero solution. Sorption SPADNS anion exchange resin
from the aqueous solutions in the pH range from 1 to 10 was investigated. We found that the degree of
adsorption of the azocompound is practically independent of the acidity in the test range. The dependence of
the amount of the reagent in phase anion exchanger from its equilibrium concentration at temperatures of 298
K, 308 K, 318 K and 328 K was studied. We constructed the corresponding sorption isotherm. Using the
method of least squares, the relevant experimental data sorption models Langmuir, Freundlich, Temkin and
Dubinin-Radushkevich was checked. Calculated corresponding coefficients of equations models. By
comparing the coefficients of determination (R2) shows that, the Langmuir model most adequately describes
the experimental data. This suggests that, the adsorption of the modifier on selected centers of anion
exchanger to form a monomolecular layer. The capacity of the AB-17-8 according SPADNS increases with
temperature: 0.14, 0.15, 0.32, 0.43 mmol/g at 298 K, 308 K, 318 K and 328 K, respectively. For the resulting
Langmuir coefficients (KL) at respective temperatures were calculated enthalpy change (25.6 kJ/mol),
entropy (156.6 J/mol·K-1) and isobaric-isothermal potential (21.25 kJ/mol at 298 K). Because .H has a
positive value, which indicates the endothermic process taking place, the entropy factor performs as the
driving force of the sorption process The studies of sorption SPADNS by ion exchanger, values of sorption
capacity of AB-17-8 at different temperatures were obtained, Langmuir-type of sorption isotherms was
found, thermodynamic parameters were calculated. It should also be noted, that the AB-17-8 modified
SPADNS is interested as a selective sorbent for extracting heavy metal ions from natural and waste waters.