Mass transfer and related phenomena for Cr(VI) adsorption from aqueous solutions onto Mangifera indica sawdust

Present study was undertaken to evaluate the efficacy of Mangifera indica sawdust for the removal of Cr(VI) from aqueous solutions. Batch experiments were performed to evaluate the influence of various operating conditions viz., pH, contact time, initial concentration, adsorbent dose, etc. on Cr(VI) removal efficiency. Characterization of the adsorbent showed that OH, CO and NO groups might be responsible for Cr(VI) adsorption. Adsorption was found to be exothermic with first-order rate kinetics which followed both Langmuir and Freundlich isotherms. Thermodynamic parameters like standard free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) were obtained as −1.0045 kJ mol−1, −24.8 kJ mol−1 and −0.0798 kJ mol−1 K−1 respectively at 298 K. The electrostatic attraction and film diffusion were found most favorable for Cr(VI) adsorption augmentation.

• Mangifera indica sawdust as an efficient adsorbent for removal of Cr(VI) from aqueous solutions.
• The Langmuir and Freundlich model well described the adsorption equilibrium.
• Adsorption kinetics followed the pseudo-first-order kinetic model.
• Both boundary layer and intraparticle diffusion are found to affect the adsorption.