Kinetics and Thermodynamics of β -Carotene Adsorption onto Acid-Activated Clays Modified by Zero Valent Iron

The adsorption of β-carotene from crude palm oil onto acid-activated clay and clay modified by zero valent iron (ZVI) was investigated in this work. Spectroscopic studies including FTIR, XRD, and SEM were used for its characterization. The adsorption characteristics such as kinetics, mechanism, isotherms, and thermodynamics of β-carotene were studied. The kinetic data were analyzed using the pseudo-first-order kinetic equation, pseudo-second-order kinetic equation, and intraparticle diffusion model. The pseudo-second-order kinetic model is the only one that describes the experimental data well (R2 ≥ 0.969). The chemical analysis of bulk clay showed that the predominant oxides are Al2O3 (57.91 wt%), Fe2O3 (32.54 wt%), SiO2 (3.09 wt%), K2O (2.37 wt%), and CaO2 (1.73 wt%). The adsorption capacity increases with an increase in temperature. The equilibrium data were described better by the Freundlich model for all clays. To determine the best fit kinetic model for each system, three error analysis methods, namely, chi-square (χ2), residual mean squared error (RMSE), and mean percent error (%APE) were used to evaluate the data. A thermodynamic study demonstrated that β-carotene adsorption is spontaneous, endothermic, and an entropy driven process for both forms of clay.