Competitive adsorption of dye metanil yellow and RB15 in acid solutions on chemically cross-linked chitosan beads

One kind of adsorbent with a high adsorption capacity for anionic dyes was prepared using ionically and chemically cross-linked chitosan beads. A batch system was applied to study the adsorption behavior of one acid dye (MY, metanil yellow) and one reactive dye (RB15, reactive blue 15) in aqueous solutions by the cross-linked chitosan beads. The adsorption capacities was 3.56 mmol g−1 (1334 mg g−1) for dye MY and 0.56 mmol g−1 (722 mg g−1) for dye RB15 at pH 4, 30 °C. The Langmuir model agreed very well with the experimental data (R2 > 0.996). The kinetics of adsorption for a single dye and the kinetics of removal of ADMI color value in mixture solutions at different initial dye concentrations were evaluated by the nonlinear first-order and second-order models. The first-order kinetic model fits well with the dynamical adsorption behavior of a single dye for lower initial dye concentrations, while the second-order kinetic model fits well for higher initial dye concentrations. The competitive adsorption favored the dye RB15 in the mixture solution (initial conc. (mM): MY = 1.34; RB15 = 1.36); while it favored the dye MY in the mixture solution (initial conc. (mM): MY = 3.00; RB15 = 1.34) and the adsorption kinetics for dye RB15 has the tendency to shift to a slower first order model.