Síntese de compósito MgAl-HDL/biocarvão de osso bovino para aplicação como agente adsorvente

Abstract

Studies on the use of adsorbents have been increasing, especially when it comes to treatment of effluents. Biochars are referred to as solid fractions from lignocellulosic materials charred by pyrolysis and are being used as adsorbents to support nanometric particles, such as double-lamellar hydroxides (HDLs). HDLs are also called anion clays and consist of stacking mixed hydroxides of di and trivalent cations where hydrated anions occupy the spaces between layers. In this work, composites were synthesized using bovine bone charcoal as support for HDL containing magnesium and aluminum cations, synthesized in different molar proportions of Mg: Al (2:1, 3:1, 4:1), by the method of co-precipitation at increasing pH. The composites were synthesized as well as the pure biochars by EDS, EDX, FTIR, BET, TG, DTG and MEV, confirming the presence of the cations on the surface of the biochar and subsequently used in adsorption tests performed in the finite bath with the purpose of removing methylene blue. In the adsorption studies of methylene blue it was possible to verify that the pH 12 of the aqueous solution of the dye is more favorable to the adsorption process, presenting a removal capacity of more than 95% for all the composites, the kinetic study states that the system equilibrium in the first 20 minutes and the experimental data are best described by the pseudo-second order model, the isotherms are best represented by the Redlich-Peterson model, presenting a maximum adsorption capacity value at 40 °C of 406.47 mg.g-1. For the pollutant studied, the positive values of ΔH° indicate the physical nature of the adsorption, the positive values of ΔS° indicate that there was a change in the structure of the adsorbent and increase of the randomness during the fixing of the dye and the negative values of ΔG° confirm the spontaneity of the process. The biofilm/MgAl 2:1 composite underwent six cycles of regeneration after the adsorption processes, however, after the regeneration process the HDLs presented difficulties to maintain their structure due to the ease in which they are exfoliated, so, after six cycles, observed the composite removal capacity was reduced.