The Study for Sorption of Trace Arsenite on Clay Minerals

The main objectives of studies were to investigate the characteristics of thermodynamics and kinetics of trace arsenite(≤200 μg·L-1)adsorbed on two typical clay minerals(kaolinite and montmorillonite)respectively in a condition of 20 ℃ and pH=7, modeling anaerobic environment of groundwater with nitrogen-filled continually to avoid oxidation of trivalence arsenic. The adsorbed arsenite analysis was conducted using atomic fluorescence spectrometry(AFS). The results of experiment showed adsorption capacities of kaolinite toward arsenite were higher than montmorillonite, which suggested the exposed hydroxyl groups at particle edges of both clay minerals have a major role in the adsorption of arsenic, the sorption equilibrium reached after reacting 24 hours and Freundlich kinetics equations had a better simulation (R20.98)than Elovich kinetics equation that indicated the reactions were typical nonlinear surface adsorption with limited adsorption sites. The isothermal experiment showed both Langmuir and Freundlich isothermal equations can describe the thermodynamic behaviors of adsorption very well(R20.99), which indicated adsorption of arsenite on clay minerals is mainly chemical specialized adsorption in single molecule layer as complexation reactions of arsenite combined withAlOH bands of clay minerals, provided with slow adsorption rate and invariable adsorbability independent of cover degree, and all of the rate, energy, capacities of adsorption and adsorbability of arsenite on kaolinite were greater than that on montmorillonite.