Use of Aluminosilicate Residue from Insulators of High Voltage Transformers for the Adsorption of Basic Dyes

In this study, an aluminosilicate residue from insulators of high voltage transformers was used for the adsorption of basic dyes. The absorbent was characterized by X-ray fluorescence analysis, X-ray diffraction analysis, scanning electron microscopy, multimolecular adsorption theory (Branauer-Emmet-Teller (BET)) and determination of the point of zero charge (pHPZC). The effect of solution pH and adsorbent mass, the kinetic and thermodynamic behavior at different temperatures and the application of non-linear isotherm models of Langmuir, Freundlich, Temkin and Dubinin-Radushevich were investigated. The pHPZC value for the aluminosilicate was 3.7. The best conditions for adsorption of methylene blue and crystal violet dyes were pH 8.0 and adsorbent mass of 1100 mg in 25 mL. The best fit for the experimental data was obtained applying the pseudo-second-order kinetic model, with an equilibrium time of 480 to 720 min, and the activation energy suggests a physical adsorption mechanism. Isothermal parameters suggest a heterogeneous, favorable and predominantly physical surface adsorption. The thermodynamic studies indicated that the adsorption process is not spontaneous and is exothermic and the Gibbs energy values (∆Gº) suggest physisorption.