Adsorption of Eriochrome Black T (EBT) dye using activated carbon prepared from waste rice hulls—Optimization, isotherm and kinetic studies

In this study, the adsorptive removal of Eriochrome Black T (EBT) from aqueous solution using rice hull-based activated carbon was investigated. The effects of initial dye concentration, adsorbent dose and pH on the percent removal of EBT were examined. An increase in adsorbent dose, and decrease in initial dye concentration and pH would cause an increase in the removal of EBT. Using the Box–Behnken design, the optimum conditions were obtained to be the following: 95 ppm initial dye concentration, 2.0 g adsorbent dose and pH of 2. The equilibrium data was evaluated using Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm. The Freundlich model best describes the uptake of EBT dye, which implies that the adsorption of EBT dye onto rice hull activated carbon is heterogeneous. The kinetic data were analyzed using pseudo-first order, pseudo-second order and intraparticle diffusion equation. The pseudo-second order exhibited the best fit for the kinetic studies (R2 = 0.9996), which indicates that adsorption of EBT is limited by chemisorption process. The intraparticle diffusion model exhibited a linear relationship (R2 = 0.9921), which shows that pore diffusion is also a limiting step in the overall adsorption process.

► High adsorbent mass, low pH and initial dye concentration decrease % EBT removal. ► Kinetic data follow the pseudo-second order and intraparticle diffusion equation. ► Equilibirum data follow Freundlich isotherm. ► Optimization using Box–Behnken showed a maximum of 96% EBT removal using RHAC.