Application of activated carbon derived from waste Delonix regia seed pods for the adsorption of acid dyes: kinetic and equilibrium studies

A ctivated carbon prepared from Delonix regia (DR) seed pod has been used as adsorbent for the removal of anionic dyes from aqueous solution. Three anionic textile dyes (C.I. Acid Blue 15, C.I. Acid Red 114, C. I. Acid Violet 17) and one dye mixture were used as model compounds. The capacity of DR to adsorb anionic dyes from aqueous dye solution was evaluated at different contact times, dosage, pH, and initial adsorbent concentration. Results show that the highest dye removal (>95%) was obtained at pH 2 for the adsorption of all the selected dyes. Four isotherms (Langmuir, Freundlich, Temkin, and Redlich-Peterson) were used to fit the equilibrium data. The adsorption equilibrium showed that the Langmuir equation represented best fit of the experimental data than others. The adsorption isotherm indicates that the adsorption capacities are 151.51, 113.63, and 129.87 mg dye per gram of DR for AR-114, AV-17, and AB-15 Acid dyes, respectively. In order to investigate the mechanism of adsorption and rate-controlling steps, pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich equations have been used to test the experimental data. The adsorption kinetics was found to follow pseudo-second-order kinetics with correlation coefficients greater than 0.99. It was found that at the higher initial acid dye concentration, intraparticle diffusion is becoming significant rate-controlling step.