Taguchi L16 orthogonal array optimization for Cd (II) removal using Carpinus betulus tree leaves: Adsorption characterization

Taguchi orthogonal design was used for multivariate optimization of Cd(II) removal by Carpinus betulus tree leaves from an aqueous solution in a batch system. Effective factors on adsorption process, such as temperature, amount of sorbent, initial concentration of Cd(II), pH value, and particle size were considered using an L-16 orthogonal array design. Taguchi analysis is based on choosing the best run by analyzing signal-to-noise ratio (S/N), whose form depends on the experiment objective. Thus, the removal percentage (R%) and capacity uptake (q) of Cd(II) were transformed into an accurate S/N ratio for a high is better response. The best conditions for biosorption of Cd(II) were determined by the Taguchi method and desirability approach as pH = 4.8, sorbent dose of 2 g l(-1), initial Cd(II) concentration of 140 mg l(-1), temperature 25 degrees C, and sorbent size of 0.12-0.17 mm. In addition, metal interactions with sorbent were analysed by FT-IR spectroscopy, SEM, and XRD methods. Potentiometric titration modeling also denotes that the C. betulus tree leaves may be characterized by two kinds of active sites (carboxylic and hydroxyl). A nonlinear regression was applied to fit the experimental data with Langmuir, Freundlich, Dubinin-Radushkevich, and Sips isotherms. As a result, the Sips isotherm showed the best concordance as an equilibrium model. The biosorption process was kinetically fast and followed by a pseudo-second order kinetic model. Thermodynamic investigations showed that the biosorption process was spontaneous and exothermic. (C) 2013 Elsevier Ltd. All rights reserved.