Adsorption Capacity, Isotherm, Kinetics, and Thermodynamics Examinations on the Removal of a Textile Azo Dye by Local Natural Adsorbent

Abstract

The discharge of industrial wastewater containing toxic dyes has significantly increased, posing risks to human health and aquatic ecosystems. The growing demand for dyes in the textile industry has driven research into effective and economical removal methods. Adsorption is widely preferred due to its low cost, non-toxic by-products, and eco-friendly nature. This study investigates the removal of Reactive-Blue-160 textile azo dye using a local natural clay mineral. The effects of contact time, pH, adsorbent dosage, and temperature on adsorption are examined, along with adsorbent characterization. Optimal conditions (pH 5.70, adsorbent dosage 2.0 g L⁻¹, contact time 60 min, and dye concentration 150 mg L⁻¹) achieve 93.05% removal. Characterization reveals a heterogeneous clay surface dominated by smectite and chlorite. The adsorption data are evaluated using isotherm and kinetic models, with Freundlich and pseudo-second-order providing the best fit. Thermodynamic analysis indicates spontaneous and endothermic adsorption, with a negative Gibbs free energy and a positive enthalpy change of 15.71 kJ mol⁻¹, confirming physical adsorption. These findings highlight the potential of natural clay minerals for dye removal, offering a sustainable solution for industrial wastewater treatment.