Síntese, caracterização e aplicação de hidróxidos duplos lamelares a partir de resíduos de alumínio

Abstract

One of the most important and strategic industries that produce hazardous waste is aluminum production. Aluminum is the third most abundant element on Earth and the second most used metal after iron. Due to inadequate recycling and reuse of aluminum waste, large amounts of these materials are discarded in landfills, presenting risks to health, ecology and safety due to their toxicity and high flammability. These issues are driving the development of new costeffective and ecologically sound methods of reusing aluminum waste. The production of Lamellar Double Hydroxides (LDH) using aluminum residues can be achieved through the leaching of Al3 + ions, in the form of hydroxide, followed by reaction with the divalent ions. Aluminum ions can be extracted by dissolving the residue in an alkaline or acidic medium. This work had as objective the synthesis and characterization of LDHs obtained from the residues of aluminum frames and to evaluate the applicability of the material in the area of adsorption. The syntheses of LDHs were carried out by the co-treatment and hydrothermal treatment methods, maintaining a 3:1 ratio of Mg/Al. The study of the structural properties of the synthesized HDLs was carried out using energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma atomic emission spectrometry (ICP OES), infrared absorption spectroscopy (FT-IR), X-rays (DRX), thermogravimetry (TGA) and specific surface area (BET). The FT-IR wavelengths referring to the synthesized HDL chemical groups did not diverge, the input being commercial aluminum hydroxide or coming from aluminum frames. The X-ray diffractograms of LDHs with indicated peaks characteristic of materials of the hydrotalcite type, which are more intense diffraction elements for the LDH synthesized from the hydrothermal treatment. From the Scherrer equation, an increase in the crystallite size was observed with the increase in the synthesis temperature. A thermogravimetric analysis proceeds by the loss of water adsorbed between the layers, followed by the dehydroxylation of the coverslips with water release, different values in the loss of mass for the studied synthetic conditions. The LDHs obtained showed type IV and the presence of type H3 hysteresis, which evidences the existence of mesoporous structures. The surface area and pore diameter range from 27.66 m2/g to 96.08 m2/g and 36 Ǻ to 39 Ǻ, respectively. From the results obtained, it is possible to verify that LDH produced from aluminum waste has potential for future applications in the areas of catalysis and adsorption. As for the application in adsorption, the experiments were conducted in a finite bath, where it was possible to initially verify the feasibility of using LDH as an adsorbent and, subsequently, evaluate the effect of dosage, the effect of pH, kinetics and adsorption isotherms and parameters thermodynamics. Adsorption kinetics showed equilibrium time of 90 and 60 min and adsorption capacities of 3.07 and 10.1 mg.g-1 for the drug salicylic acid (SA) and for the dye methyl orange (MA), respectively. The pseudo-second order kinetic model fitted better to the experimental data for both SA and MA. The SA and MA adsorption isotherms showed similar behavior to the Freundlich model, indicating the existence of heterogeneous surfaces and multilayer adsorption. The analysis of thermodynamic parameters showed a decrease in the amount adsorbed with increasing temperature, confirming the exothermic nature from ΔH° < 0. According to the values of ΔG°, it was possible to confirm that the adsorption was not spontaneous for SA and spontaneous for MA. The positive values of ΔS° indicated greater randomness at the solid-solution interface. From the obtained results it is possible to verify that the HDL produced from the aluminum residue has potential in the area of adsorption.