SORPTION KINETICS AND INTRAPARTICULATE DIFFUSIVITIES OF METHYLENE BLUE DYE ON WATER HYACINTH SHOOT

The kinetic behaviour of methylene blue dye towards water hyacinth shoot adsorbent was studied with three rate models: pseudofirst-order, pseudosecond- order and Elovich equation. Intraparticle diffusion models such as fractional attainment to equilibrium (FATE), McKay and Poots, Weber and Morris were also used to investigate the predominant sorption mechanism. The rate constants (g/mg min) for the pseudofirst-order model were determined to be 1.3 x 10-3, 1.4 x 10-3, 9.0 x 10-4 and 1.0 x 10-3 for 100 mg/L, 200 mg/L, 300 mg/L and 400 mg/L respectively of adsorbate concentration. Sorption capacities based on the pseudofirst- order model were found to be 13.58 mg/g, 30.20 mg/g, 38.46 mg/g and 49.35 mg/g for adsorbate concentrations of 100 mg/L, 200 mg/L, 300 mg/L and 400 mg/L respectively. The pseudosecond- order model rate constants were 5.78 x 10-2 , 2.27 x 10-2, 2.76 x 10-2 and 1.84 x 10-2 g/mg min for 100 mg/L, 200 mg/L, 300 mg/L and 400 mg/L respectively. Sorption capacities based on the pseudosecond- order model were 13.25, 24.21, 27.77 and 30.96 mg/g for adsorbate concentrations of, 100 mg/L, 200 mg/L, 300 mg/L and 400mg/L respectively. R2 values of kinetic models used showed that pseudosecond- order was the most highly correlated (at R2=1.000) for all concentrations of adsorbate used. Percent removal efficiency increased with respect to time for all concentrations considered and decreased with increase in concentration for all times considered. Sorption diffusion models applied showed that the intraparticle diffusion (percent adsorbed) was the most correlated (at R2 = 0.9624) which indicated that the dominant mechanism was penetrant or pore diffusion. The mass transfer coefficient D, also increased with increase in the concentration of the sorbate.