Adsorption of malachite green and methyl orange onto waste tyre activated carbon using batch and fixed-bed techniques: isotherm and kinetics modeling

The adsorption of malachite green (MG) and methyl orange (MO) from aqueous solution by waste tyre-derived activated carbon (WTAC) using in batch and fixed-bed column methods was studied. Freundlich model with high correlation coefficient (0.99) described the adsorption data more suitably than other models, indicating multi-layer adsorption of dyes onto heterogeneous WTAC surface. The maximum Langmuir monolayer adsorption capacity was 29.23 g/kg for MG and 13.56 g/kg for MO. The adsorption obeyed pseudo-second order model, following both film-diffusion as well as intra-particle diffusion mechanisms. The thermodynamic parameters indicated spontaneous and endothermic adsorption. Fixed-bed column studies at varying flow rates between 3-5 mL/min for MG and 2-3 mL/ min for MO, initial dye concentration (40-50 mg/L), and bed heights (1-2 cm) indicated that breakthrough time and exhaustion time increased with decreasing flow rate, increasing bed height and decreasing initial dyes concentration. The experimental data fitted well with Thomas and Adams-Bohart models with maximum Thomas model adsorption capacity of 71.71 g/kg for MG and 6.86 g/kg for MO. Thus, WTAC proved a promising adsorbent for the removal of MG and MO from aqueous solution.