Kinetic, isotherm and thermodynamic studies of the adsorption

Abstract

Agricultural wastes and plant biomass are alternative low-cost adsorbents because they can be used without or with a minimum  processing. In the present study, batch experiments were carried out to study the adsorption of cresol red (CR) unto mango leaf (ML) and  orange peel (OP). Several parameters that affect adsorption process such as pH, adsorbent dosage, contact time, initial dye  concentration and temperature were investigated. FTIR and SEM were used to determine the functional group responsible for  adsorption. The results revealed that the highest adsorption efficiency was at pH 5 for the two adsorbents. It was also discovered that CR  removal efficiency increased with the increase in contact time and adsorbent dosage while adsorption capacity was higher with increase  in initial dye concentration but removal efficiency was lowered. The kinetics conform with the pseudofirst-order kinetic model for mango  leaf but conform with the pseudo-second-order kinetic for orange mesocarp due to the value of the correlation coefficient (R² ). Based on  the value of correlation coefficient, the experimental results for the removal by mango leaf best fitted the Langmuir isotherm model  with monolayer adsorption capacity of 70.64 mg. g-¹ , while Freundlich isotherm model was best fitted to the experimental results for the  adsorption of CR by Orange peel. The thermodynamic results revealed that the process is spontaneous and endothermic.