Produção de CaAl/HDL a partir de resíduo calcinado de concha de Mytella falcata para remoção dos corantes azul de metileno e alaranjado de metila

Abstract

The residues produced by malacoculture activities generate great impact and high costs for treatment and adequate disposal, constituting one of the great environmental problems in the world. Faced with this problem, the feasibility of using malacoculture waste to produce Double lamellar hydroxides (HDLs) was studied. Residues of Mytella falcata (RMF) were used to produce calcium oxide, which was later used as a reagent for the synthesis of HDLs by the coprecipitation method. The thermal behavior of the materials was mapped up to 900 °C through the determination of TG/DTG curves, while the textural and surface characteristics were studied by zero-load pH (pHPCZ), Scanning Electron Microscopy (SEM) and by adsorption/ desorption of N2 (BET, BJH), the composition was determined by Energy Dispersive X-ray Spectroscopy (EDS), the chemical groups by Fourier Transform Infrared (FTIR) and the crystallinity along with other structural properties were determined by X-Ray Diffraction (XRD). The characterizations allowed us to identify the composition of the Mytella falcata residue, consisting mainly of calcium carbonate with aragonite and calcite polymorphs, with low surface area, irregular and rough morphology composed of conglomerate of overlapping plates. Calcium oxide was obtained from the calcination of shells at temperatures above 800 °C, showed morphology, granulometric distribution, decomposition intervals, crystallinity and other characteristics similar to commercial material, indicating that it is a possible substitute in the synthesis of HDLs. The CaAl/HDL – RE material was produced with calcium oxide from Mytella falcata residue with high crystallinity, surface area 65.62% greater than the CaAl/HDL – PA material, produced with a commercial reagent, classified as mesoporous, formed by plates in the form of hexagonal sheets arranged in an overlapping manner, with a potential of zero charge equal to 12.25. With removal efficiency of 97.29% of methyl orange (AL) and 93.64% of methylene blue (AM) in aqueous solution, without temperature and pH adjustments. The adsorption kinetics and equilibrium adsorption isotherm fitted well to the pseudo-second order kinetic model and to the Freundlich isotherm model. According to the calculated thermodynamic parameters, ΔG°, ΔH° and ΔS°, the adsorption of AL and AM by HDL/CaAl – RE was spontaneous, exothermic and chemical. Thus, these results corroborate the use of RMF for the production of CaO – RE, synthesis of CaAl/HDL – RE and the use of the produced HDL as an adsorbent for efficient removal of organic and inorganic pollutants in aqueous solution.