Síntese e caracterização da piroaurita a partir de resíduo de mina de cobre e sua aplicação na adsorção do corante vermelho do Congo

Abstract

In this study, the copper flotation tailings extracted from the Sequeirinho pit of the Sossego mine, Carajás region, Southeast of the State of Pará (Brazil), has been used as raw material for the synthesis of Pyroaurite, a potential absorbent of organic dyes. Initially, tailings characterization was performed through X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) techniques. Next, a sample of this characterized material was leached (HCl 1:1 H2O), the obtained solution was filtered and used in the procedures of Pyroaurite synthesis. This solution was kept in the coprecipitation method at constant pH (14) with Mg/Fe molar ratio equal to 6:1, a dripping time of 4 hours, hydrothermal bath of 24 hours at high agitation rate. After, the synthesized Pyroaurite was submitted to characterization by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), Specific Surface Area (ASE) and total pore volume (Wo) techniques. Then, the synthesized Pyroaurite was evaluated for the adsorption process of Congo Red (CR) dye, where 0.025 mg of Pyroaurite were added to 10 mL of CR samples at concentrations of 5, 10, 20, 30, 40, 50 and 80 mg·L-1, respectively. The adsorption results fitted to the Langmuir model (R2 = 0.9614), while the kinetics suggested the pseudo-second order model (R2 = 0.9977). In addition, the temperature of 40ºC showed to be the most pleasant for the adsorption of the CR dye. Finally, the thermodynamic parameters of entropy (ΔSº= 0.0886 kJ·mol-1·K-1) and enthalpy (ΔHº= 8.2999 kJ·mol-1) show that the adsorption process was found to be naturally spontaneous and endothermic.