High Adsorption Efficiency of Topkhana Natural Clay for Methylene Blue from Medical Laboratory Wastewater: a Linear and Nonlinear Regression

Local natural clay from Topkhana (Sulaimani district, Kurdistan region of Iraq) was characterized with XRD, XRF, FT-IR, and gas adsorption analyzer. The clay sample was dominated by saponite with minor amounts of chlorite. The clay was examined for its efficiency to adsorb and remove methylene blue (MB) from clinical laboratory wastewater by a batch method. The effects of pH, temperature, clay dosage, and initial MB concentration on the adsorption efficiency were investigated. The equilibrium experimental data were analyzed using Langmuir, Freundlich, Temkin, and Redlich-Peterson (R-P) isotherms. Most of the MB adsorption could be explained by cation exchange. The saponite, therefore, was the most important component in the clay. The rate of the adsorption process was found to follow pseudo-second-order kinetics. The conventional linear least squares method was compared with the more accurate method of non-linear curve fitting for the determination of isotherm and kinetic model parameters. Two error functions (the sum of the squared residuals and the correlation of determination) were used to evaluate the linear and non-linear regression analysis applied to the experimental data. Equilibrium thermodynamic parameters indicated a spontaneous and endothermic adsorption process.