Cinética de adsorção de diclofenaco sódico em carvão ativado granulado

Abstract

This work aimed to analyze the adsorption kinetics of diclofenac sodium (DS) in synthetic aqueous solution by granular activated carbon (GAC). A central composite design with four factors and five levels was performed, namely: contact time (5, 15, 25, 35 e 45 minutes), concentration of GAC (0.20; 1.40; 2.60; 3.80; e 5.00 g.L-1), concentration of DS (50, 150, 250, 350 e 450 mg.L-1) and pH (5, 6, 7, 8 e 9). Batch adsorption tests were performed, with the water used produced by dissolving a stock solution of the drug. The DS concentrations after the assay were measured by UV spectrophotometry at a wavelength of 274 nm. To obtain the mathematical relationships between the experimentally obtained adsorption capacities and the independent factors, the data were fitted to a second-order polynomial equation and the significance of this model was assessed by an analysis of variance (ANOVA). With the results obtained by the model, curves of adsorption capacity versus contact time were generated. Were also performed fits to the non-linearized kinetic models of pseudo-first-order (PFO), pseudo-second-order (PSO), and intraparticle diffusion (IPD). The maximum adsorption capacity was 74.12 mg.g-1 under an adsorbent concentration of 0.20 g.L-1, initial adsorbate concentration of 450 mg.L-1, pH 9, and contact time of 25 minutes. The PFO model showed the highest correlation (R² = 0.9981). The IPD model indicated that the limiting step for the maximum adsorption capacity condition was diffusion in the film. It was concluded that the adsorption process analyzed was of the physical type, characterized by relatively weak interactions attributed to Van der Waals forces, this process being nonspecific, fast, and reversible, whose driving force is the concentration difference between the solid and liquid phase.