Biosorption of Azure Dye with Sunflower Seed Hull: Estimation of Equilibrium, Thermodynamic and Kinetic Parameters

-Biosorption potential of sunflower seed hull to remove reactive textile dye contaminated solutions was the purpose of this investigation. Azure A chloride dye was chosen as a model for this investigation. Pretreatment, initial pH, biomass dosage, contact time, initial dye concentration and temperature were evaluated in batch mode studies. Preliminary results indicate that acid and base pretreatment affected the dye biosorption properties of the milled hull. Particles retained on the ASTM sieves 250 μm and 425 μm had the highest biosorption capacity. The optimum pH for azure dye biosorption was 6.0, and the values of percent dye biosorbed and biosorption capacity increased with contact time and dosage of dried sunflower seed hull (DSSH). Batch equilibrium data obtained at different temperatures (22.5, 25, 30, 35, 35, 40 and 45 o C) were modeled by Freundlich, Langmuir and Dubinin–Radushkevich (D–R) isotherms. Langmuir and Freudlich isotherms model fitted the equilibrium data, at all studied temperatures. The highest monolayer biosorption capacity was found to be 22.27mg g -1 dry biomass at 40 o C. The changes in Gibbs free energy (ΔG * ), enthalpy (ΔH * ) and entropy (ΔS * ) of biosorption were also evaluated for the biosorption of Azure dye onto DSSH. The results indicate that the biosorption was spontaneous and exothermic. The kinetic properties were studied; the data fitted the first and pseudo second order model at room temperature (22.5 o C). The pseudo-second-order kinetic model was observed to provide the best correlation of the experimental data among the kinetic models studied. The biosorbent–dye interaction mechanisms were investigated using Fourier transform infrared spectroscopy.