Síntese de carvão ativado a partir do fruto da amendoeira (Terminalia Catappa L.) e aplicação no tratamento avançado de águas

Abstract

The presence of toxic metals in water and industrial liquid effluents, at levels higher than regulated, is a very widespread issue in the literature due to its relevance in the global environmental context. In the present study, biochar (C-BIO) and activated charcoal (CAH3PO4), prepared from the almont fruit Terminalia Catappa L., were used to remove Cr(VI) hexavalent chromium from aqueous solutions with initial concentrations of 50 mg L-1 . The characterization of the adsorbents for the textural parameters and chemical composition were carried out using the techniques of physical adsorption of nitrogen, scanning electron microscopy (SEM), point of zero charge (PCZ), energy dispersive X-ray fluorescence (EDX) and elemental analysis (CHN). Kinetic, thermodynamic and adsorption capacity studies were also performed using adsorption isotherms. The BET surface area of the C-BIO was 114.7 m2 g -1 , of which 63% were classified as mesopores. The CA-H3PO4 reached a BET surface area of 1489.7 m2 g -1 , with 54% classified as mesoporous. The pH at which the charge neutralization occurred between the surface of the adsorbent and the solution was equal to 2.0 for both materials. At this pH value, Cr(VI) removal was greater than 80% for CA-H3PO4 and 26% for C-BIO, in experiments with 100 mL Cr(VI) solution at 50 mg L-1 containing 0.05 g of adsorbent. The adsorption behavior followed the pseudosecond order kinetics, with a rate constant of 0.002 and 0.023 g m-1 min -1 for CA-H3PO4 and C-BIO, respectively. The isotherm model that best fit the experimental data, only for activated carbon, was that of Freundlich. The thermodynamic study showed that the adsorption process was spontaneous and endothermic with negative ΔG (-0.156 and -0.474 kJ mol-1 ) and positive ΔH (13,250 kJ mol-1 ). The desorption study was evaluated only for CA-H3PO4, demonstrating that the adsorbent can be regenerated using 0.5 mol L-1 NaOH, partially maintaining its Cr(VI) adsorption capacity at 83.6 mg g -1 , corresponding to 55% of the initial capacity, after the fourth regeneration cycle. Therefore adsorbents produced with and without chemical activation are promising for the treatment of water contaminated with hexavalent chromium.