Arsenic adsorption onto iron oxide-coated cement (IOCC): Regression analysis of equilibrium data with several isotherm models and their optimization

The present work examines the equilibrium sorption of arsenic (III and V) from aqueous environment onto iron oxide-coated cement (IOCC) at 288, 298 and 308 K, and determines the equilibrium sorption isotherms. The equilibrium for both As(III) and As(V) was achieved in 2 h. The experimental isotherm data were analysed using Langmuir, Freundlich, Dubinin–Radushkevich (D–R), Toth and Temkin isotherm equations. In order to determine the best-fit isotherm for each system, both linear and non-linear regressions were carried out. For this, six error analysis methods were used to evaluate the data: the linear coefficient of determination, the sum of the squares of errors, the sum of absolute errors, the average relative error, the hybrid fractional error function and the Marquardt's percent standard deviation. The error values indicated that the Freundlich isotherm was able to provide the best quality of fit for all the experimental data, over the concentration range studied, for both As(III) and As(V) at 288, 298 and 308 K. The values of the parameter sets of the isotherms also indicated that the adsorption of arsenic onto IOCC is a temperature dependent phenomena with As(III) and As(V) exhibiting exothermic and endothermic nature of adsorption, respectively.