Effective sorption of selenite by Fe–Mn binary oxide: influence of preparation method

摘要

In this study, two Fe-Mn binary oxide sorbents with a same Mn:Fe molar ratio of 1:3 were prepared using two methods (coprecipitation and mechanical mixing), and they are denoted as Fe-c-Mn and Fe-m-Mn, respectively. Both Fe-m-Mn and Fe-c-Mn are amorphous and have similar structure with 2-line ferrihydrite. The Fe-c-Mn has a much higher specific surface area than the Fe-m-Mn. Selenite sorption on both Fe-m-Mn and Fe-c-Mn is pH dependent, decreasing with an increase in pH value. The estimated maximal sorption capacity of Se(IV) on the Fe-m-Mn and Fe-c-Mn is 48.6 and 70.5 mg/g at pH 7.0, respectively. In addition, the Fe-Mn binary oxide is able to adsorb selenite in the presence of competing anions and across a wide range of pH values. Among the co-existing anions, phosphate is the greatest competitor for adsorptive sites on the surface of oxide. Selenite may be sorbed onto the surface of the Fe-Mn binary oxide by formation of inner-sphere surface complexes. The high sorption capacity, low cost and environmental friendliness of the Fe-Mn binary oxide make it a potentially attractive sorbent for the removal of Se(IV) from water.