Chromium (VI) Ion Adsorption onto Maleic Acid Red Onion Skin Extract Resin (MRER) in Aqueous Solution

Feasibility studies on the thermodynamics of Cr (VI) ions adsorption in aqueous medium by maleic acid red onion skin extract resin (MRER) was undertaken. The acetone extract of red onion skin was used in the synthesis of MRER. The regression analysis of the models at different temperatures and concentrations was found to closely fit the experimental data in the order: Freundlich > Langmuir > Temkin. Investigation of the thermodynamics of adsorption reaction revealed values for the change in enthalpy   (- 34.05414 kJ/mol), Gibbs free energy (-18.001, -17.362, -17.860, -15.809 and -16.154 kJ/mol) and entropy (-52.7839 J/K/mol), which reflected the process spontaneity, exothermic nature and feasible affinity of the interacting metal ions at the adsorption sites. Dubinin-Radushkevich (DR) isotherm was applied in studying the sorption pathway, and it was observed that physisorption is the dominant pathway. Kinetic study showed that pseudo-second order best describe the experimental data with respect to its highest correlation coefficient (R2) values.