Removal of Malachite Green from Aqueous Solution Using Purolite C100 Ion Exchange Resin: Insights into Adsorption Kinetics, Equilibrium, and Thermodynamics through Nonlinear Regression

This study investigates the removal of malachite green (MG) dye from aqueous solutions using the strong acid cation-exchange resin, Purolite C100. Batch adsorption experiments were conducted to evaluate the influence of key operational parameters, including initial pH, resin dosage, initial dye concentration, and temperature. Kinetic analysis revealed that the pseudo-second-order (PSO) model provided an excellent fit to the experimental data (R2 > 0.99), suggesting that the rate-limiting step involves chemisorption-type interactions. Equilibrium data were best described by the Redlich–Peterson isotherm model, indicating a hybrid adsorption mechanism. The Langmuir model also provided a good fit, yielding a high maximum monolayer sorption capacity (qₘ) of 277.80 ± 9.63 mg g–1 at 50°C. Thermodynamic analysis revealed that the process is thermodynamically favorable under standard conditions (∆G° < 0), endothermic (ΔH° = +7.7 ± 0.1 kJ mol–1), and characterized by an increase in system entropy (ΔS° = +84.0 ± 1.1 J mol–1 K–1). Overall, this study confirms that Purolite C100 is a highly efficient and promising material for the sequestration of malachite green from contaminated wastewater.