Removal of Brilliant Blue FCF from Aqueous Solutions Using an Unmodified and Iron-Modified Bentonite and the Thermodynamic Parameters of the Process

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The sorption behaviors of brilliant blue FCF dye by natural clay and modified with iron chloride were determined. The materials were characterized by X-ray diffraction and scanning electron microscopy, and the zero point charges were also determined. The effects of pH, contact time, dye concentration, and temperature were considered. The results showed that clay does not suffer any important change in its structure after the chemical treatments. The pH influences the sorption of the dye in the unmodified clay, but this effect was not observed in the iron-modified clay. The equilibrium time and the sorption capacity for the unmodified clay were 48 h and 6.16 mg/g, while for the iron-modified clay, 24 h and 14.22 mg/g, respectively. The sorption kinetics results were best adjusted to the pseudo-first-order and pseudo-second-order models. Sorption isotherms were best adjusted to the Langmuir model, indicating that both clays have a homogeneous surface. Thermodynamic parameters (E, ΔS, ΔG and ΔH) were calculated for the natural clay from the data of the sorption kinetics at temperatures between 20 and 50 °C, indicating that the sorption process is exothermic. For the case of the iron-modified clay, it was not possible to calculate these thermodynamic parameters because the sorption capacities were similar in the temperature range selected.