Removal of methylene blue by mango seed kernel powder

Batch experiments were carried out for the sorption of methylene blue onto mango seed kernel particles. The operating variables studied were initial solution pH, temperature, adsorbent mass, initial dye concentration and contact time. Equilibrium data were fitted to Freundlich and Langmuir isotherm equation and the equilibrium data were found to well represented by Langmuir isotherm equation. The monolayer sorption capacity of mango seed kernel for methylene blue sorption was found to be 142.857 mg/g at 303 K. The sorption kinetics was found to follow pseudo first order kinetic model. The methylene blue uptake process was found to be controlled by both surface and pore diffusion with surface diffusion at the earlier stages followed by pore diffusion at later stages. The average effective diffusion coefficient was calculated and found to be 5.66 × 10−4 cm2/s. Analysis of sorption data using Boyd plot confirms that the external mass transfer as the rate limiting step in the sorption process. Various thermodynamic parameters such as enthalpy of sorption ΔH, free energy change ΔG and entropy ΔS were estimated. The positive value of ΔH and negative values of ΔG shows the sorption process is exothermic and spontaneous. The positive value of entropy ΔS shows the increased randomness at the solid-liquid interface during the sorption of dye ions onto mango seed kernel particles.