Investigation of adsorption properties of fly ash based geopolymers in removal of colorants

Today, rapidly increasing environmental pollution is a great concern. In recent years many studies have focused on economical and environmentally friendly adsorbents for the removal of dyestuffs from wastewater. In this study, geopolymer was used as an adsorbent for the removal of methyl violet and malachite green from aqueous solutions. The effects of initial concentration, temperature, amount of adsorbent, pH, contact time and reusability parameters on adsorption capacity and removal efficiency were investigated. The highest adsorption capacity and the adsorption efficiency of the methyl violet at an initial concentration of 50 mg/L, at 240 minutes contact time and 0.2 g adsorbent were found as 11.7 mg/g and 99.85%, respectively. The highest adsorption capacity for malachite green was obtained as 11.627 mg/g at an initial concentration of 50 mg/L, at 120 minutes and at 0.2 g adsorbent and the adsorption efficiency was found as 99.47% under the same conditions. When the adsorption isotherms were examined, it was seen that the Freundlich isotherm model was compatible with the process for both colorants. While the adsorption studies of methyl violet on the geopolymer represent a pseudo-second-order kinetic model, it was observed that the result for malachite green colorant was found to be in agreement with the pseudo-first-order kinetic model. The results revealed that fly ash based geopolymer is a very promising material that can be used as an adsorbent for the removal of methyl violet and malachite green