Síntese conjunta de zeólita A-hidróxidos duplos lamelares a partir de rejeitos da indústria mineral como adsorverdor de corantes

Abstract

For the synthesis of the zeolite A-LDH were used as starting materials, two waste mineral industry: A copper concentrate from the production from the Sossego Carajas region, Southeast Para State; the other one of the kaolin processing from the Rio Capim region, northeast of the State of Pará. The wastes were first activated by acid leaching and calcination. The synthesis consists of in two stages: first the synthesis of LDH by coprecipitation and hydrothermal bath, with the addition of metaculim for the synthesis of zeolite A. The parameters evaluated were: Mg/Fe molar ratio, Zeolite A-LDH mass ratio and reaction time, divided into three experiments. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy coupled to X-ray energy dispersion spectroscopy (SEM/EDS), thermal analysis (TGA), infrared absorption spectroscopy (IR), particle size distribution, N2 physisorption and point zero charge (PZC). After characterization, the mixture was applied in the adsorption of crystal violet (CV) and methylene blue (MB) dyes. The best synthesis condition occurred with theoretical Mg/Fe molar ratio of 3, mass ratio of 7: 1 zeolite A-LDH and reaction time of 6 hours. X-ray diffraction detected high-order structural phases that were quantified by the Rietveld method in: 90,57 zeolite A, 9,21 pyroaurite and 0.22 anatase (% mass). Adsorption tests were performed using several dyes and Zeolite A-LDH presented higher efficiency in the removal of CV and MB dyes when compared to a commercial zeolite used for this purpose, which occurred in multilayers. The adsorption kinetics of the MB obtained a better correlation with the pseudose-order model. The thermodynamic study showed that at 25 °C the adsorption process was favorable and spontaneous. The enthalpy indicates an exothermic reaction, with release of energy and classified as physisorption. The desorption of the dyes showed that the best proportion of the solvents is 50% H2O: 50% Ethanol, desorbing 100% of the dye. The thermal regeneration of ZA-LDH proved to be efficient, allowing its reuse after thermal treatment.