The Influence of Different Drying Methods on the Sorption of Estrone onto Na-montmorillonite

The sorption mechanism and effects of pH of Na-montmorillonite dried by two different methods on estrone (E1) were investigated in this study. Freeze-dried and 110 ℃ oven-dried methods were used as the two different drying methods for Na-montmorillonite, and they were used for subsequent sorption isotherms and kinetic experiments. Results show that specific surface area and pore volume of freeze-dried Na-montmorillonite were higher than those of 110 ℃ oven-dried one. However, no significant variations of surface functional groups presented for the two Na-montmorillonites. According to the kinetic results, the two Na-montmorillonites both had rapid sorption rates, reaching sorption equilibrium in 45 min for freeze-dried one and in 20 min for 110 ℃ oven-dried one. Besides, the proposed first-order kinetics equation for the freeze-dried Na-montmorillonite and the pseudo-second-order rate equation for 110 ℃ oven-dried Na-montmorillonite were described. Moreover, the sorption isotherms indicate that freeze-dried Na-montmorillonite had significantly higher sorption affinity with E1 compared to oven-dried Na-montmorillonite. The effects of pH on the sorption of E1 by the two kinds of Na-montmorillonite were comparable. High or low pH value was not conducive to sorption of E1 by Na-montmorillonite, and the optimal pH value for adsorption is 6.