Sustainable and Circular Adsorption of Anionic Dye from Textile Wastewater Using Economical Adsorbent

Abstract

ABSTRACT Dyes are significant contributors to the chemical oxygen demand of the wastewater produced by textile industries. In the current study, naturally occurring, inexpensive, non-hazardous clay was pillared and used to remove Acid Green 25 dye (AG) from aqueous solutions. The pseudo-second-order model provided a better fit to describe the adsorption kinetics data for AG, with a rate constant of 9.82 × 10−3 g/mg min. Langmuir isotherm provided a better fit for describing the adsorption isotherm of the AG dye. Thermodynamic analysis revealed that adsorption was exothermic with an enthalpy change of −48 kJ/mol. The effects of pH, adsorbent dosage, and initial concentration of AG dye on adsorption capacity were analyzed, and an empirical model was developed using the response surface methodology approach. Optimization studies revealed that a maximum adsorption capacity of 105.15 mg/g for the AG dye could be achieved at a pH of 2, an adsorbent dosage of 1.5 g/L and an initial dye concentration at its upper limit of 200 mg/L. The adsorbent could be regenerated and reused up to three adsorption cycles, and the desorbed dye and treated water may be reused in the dyeing process, thereby making the entire operation circular. Circularity reduces the cost of production and makes the process more sustainable. Mechanistic insights revealed that electrostatic interaction was the driving force for the adsorption of AG dye. In this work, it has been demonstrated that after pillaring, clay-based material may be used as an effective adsorbent for treating dye-containing wastewater.