Adsorption of Methylene Blue (MB) Using Novel Synthesized Phosphogypsum Flotation Tailings-Derived Zeolite (PGTZ): Experimental and Modeling Approaches

A phosphogypsum flotation tailings-derived zeolite (PGTZ) was synthesized from the tailings produced during the reverse flotation of phosphogypsum through alkaline fusion and hydrothermal treatment. The response surface methodology (RSM) utilizing a three-level Box–Behnken design (BBD) was used to assess the adsorption of MB by PGTZ. Polynomial regression models were developed to analyze the effects of process parameters on adsorption capacity (qe). The maximum MB adsorption occurred under the following optimized conditions: PGTZ dosage = 5.31 g·L−1; initial MB concentration = 294.59 mg·L−1; pH = 7.42; and adsorption time = 187.89 min. Additionally, adsorption isotherm and kinetic models were fitted to the experimental data to determine model parameters. The Langmuir isotherm model and pseudo-second-order kinetic model incorporating intraparticle diffusion were able to effectively predict MB adsorption onto PGTZ. Thermodynamic analyses indicated that the adsorption process was spontaneous, with strong chemical interactions between MB and PGTZ.