Anionic dye removal from aqueous solutions using modified zeolite: Adsorption kinetics and isotherm studies

The natural zeolite was modified with hexamethylenediamine (HMDA) and used as adsorbent to remove anionic dyes, namely Reactive Red 239 (RR-239) and Reactive Blue 250 (RB-250). And, the adsorption equilibrium and kinetic studies of anionic dyes were carried out. In presented work, the origin of the zeolite (Heulandite) used was in Turkey. The adsorption of reactive dyes on modified zeolite (HMDA-Z) was investigated by batch adsorption experiments. The effects of pH, temperature, sorbent dosage and the initial dyes concentrations were investigated. While the increase in temperature resulted in a higher RB-250 loading per unit weight of the modified zeolite, adsorption capacity of modified zeolite did not constitute a noticeable change for RR-239. As an additional factor effecting the removal of reactive dyes, the effects of competitive ions such as nitrate, sulfate and chloride were investigated. The adsorption results indicate that the natural zeolite had a limited adsorption capacity for reactive dyes but is substantially improved upon modifying its surfaces with HMDA. The isotherm data of both investigated dyes were analyzed by the Langmuir, Freundlich, and Redlich–Peterson isotherm model according to temperature. The most appropriate model for the equilibrium process of both dyes was the Freundlich model. The kinetic studies indicated that the adsorption of reactive dyes followed the pseudo-second-order kinetic. Thermodynamic calculations showed that the adsorption of both investigated dyes was a spontaneous and endothermic process for RB-250 and an exothermic process for RR-239.