Study of Isothermal Parameters for Adsorptive Uptake of Orange G Dye: An Overview of Non-linear Approach and Error Analysis

In this research, effort to convert waste to wealth was explicated in the usage of agro waste materials of regenerative resource, almond endocarp (Terminalia catappa) and tamarind seeds (Dialium guineense), as precursors for activated carbon production through thermal and chemical activation. The equilibrium adsorptive uptake of Orange G dye (OG) on almond endocarp salt activated (AESA) and tamarind seeds salt activated (TSSA) adsorbents was described using two-parameter (Langmuir and Freundlich) and three-parameter (Redlich-Peterson (R-P), Toth and Khan) isotherms employing the non-linear regression method. The best fit model in optimum isotherm prediction was investigated using four different error functions namely: root mean square error (RMSE), chi square (χ2), mean absolute error (MAE) and coefficient of determination (R2). Evaluation of the error estimation methods at 323K and 313K solution temperatures revealed that Khan and Toth; and Toth and Freundlich isotherms best described the experimental equilibrium data for AESA and TSSA sorption processes respectively. Examination of Langmuir’s separation factor and Freundlich’s surface heterogeneity factor suggest that the sorption process is favourable. Analysis of the calculated ANOVA F-values and probability values show that all the error functions under investigation were adequate in approximating the experimental data. The Coefficient of non-determination (K2) values were useful in identifying the best error function in selecting the best isotherm. For the two-parameter isotherm at 323K solution temperature, RMSE function best minimized the error distribution between the experimental equilibrium data and theoretical isotherms while RMSE and R2 functions were found to be the best for three-parameter isotherms studied.