Equilibrium and kinetic studies for adsorption of iron from aqueous solution by synthetic Na-A zeolites: Statistical modeling and optimization

Abstract

In this study, two different methods were used in the synthesis of Na-A zeolites from kaolinite collected from Aswan area, Egypt: (I) kaolinite was fused with sodium hydroxide prior to hydrothermal treatment to prepare Na-A zeolite (ZAF) and (II) kaolinite was subjected to calcination followed by reaction with alkaline solution to synthesize Na-A zeolite (ZAC). The synthetic Na-A zeolites were characterized by XRD and SEM; surface area was measured using N2 adsorption and the BET equation. The behavior of each synthetic zeolite for iron uptake was evaluated by studying the influence of different experimental parameters such as contact time, initial iron concentration and zeolite mass. Optimization of iron uptake by the synthetic Na-A zeolites was performed using a central composite rotatable design (CCRD) under response surface methodology (RSM). The results showed that the maximum removed amounts of iron by ZAF (5.62 mg/g) was obtained after 5 min of contact time while the highest amount of iron by ZAC (4.3 mg/g) was given after 8 h. By increasing the adsorbent mass from 0.4 g to 0.6 g, the removal efficiency of iron onto the synthetic zeolites increased from 45% to 87.6% for ZAF and from 35% to 86.7% for ZAC. The adsorption process fitted the Langmuir model and the adsorption kinetics correlated very well with the pseudo-second-order equation. Based on the predicted optimized solutions for iron adsorption, the removal efficiency of iron could be enhanced in both of ZAF and ZAC.