Application of Nonlinear Regression Analysis for Methyl Violet (MV) Dye Adsorption from Solutions onto Illite Clay

Dyes are toxic chemicals and the main source of color pollution in the textile wastewaters. Therefore, the use of illite clay as an adsorbent to remove methyl violet dye from solutions was investigated in this study. Equilibrium experiments were carried out in batch mode as a function of temperature, ionic strength, and pH. The equilibrium was attained within 24 hours. The capacity of illite clay increased when pH, temperature, and ionic strength were raised. Four adsorption isotherm models, viz, the Langmuir, Freundlich, Khan, and Sips, were used to analyze the equilibrium data. The nonlinear optimization technique was used to fit the data to the isotherm models, and for this purpose five error functions were used. The equilibrium data could be explained by the Sips isotherm model, and among the entire error equations generally the HYBRID error function provided the lowest sum of the normalized error values. Thermodynamic parameters indicated that dye adsorption had endothermic and unspontaneous nature. Also, the positive enthalpy change indicated that dye uptake occurred by physical binding. The maximum dye capacity of illite was found as 159.95 mg g(-1) at 60 degrees C. High dye capacity exposed that illite would be used effectively in cationic dye removal.