Kinetic and equilibrium studies: Adsorption of food dyes Acid Yellow 6, Acid Yellow 23, and Acid Red 18 on activated carbon from flamboyant pods

The adsorption of food dyes, Acid Yellow 6 (AY-6), Acid Yellow 23 (AY-23), and Acid Red 18 (AR-18) onto activated carbon obtained from flamboyant pods (Delonix regia) under optimized conditions (AC(op)) was performed in this work. According to the pH study, the three dyes best adsorbed in acidic solutions (pH = 2). Ten isotherm models, four kinetic models, and the intraparticle diffusion model were applied to fit the experimental data. The Vieth-Sladek isotherm explained the adsorption of the three dyes very well, and the maximum adsorption amounts (Q(m)) found for AY-6, AY-23, and AR-18 were 673.687, 643.041, and 551.799 mg g(-1), respectively. The pseudo-second order model gave the best experimental data fit, although its k(2) parameter indicated that other mechanisms were involved in the adsorption of AY-6 and AY-23. Similarly, the intraparticle diffusion model indicated that adsorption was governed by several mechanisms. AC(op) was shown to be a fast and effective adsorbent for the removal of AY-6, AY-23, and AR-18 from aqueous solutions. (C) 2011 Elsevier B.V. All rights reserved.