Fe(3+) coordinated to amino-functionalized MCM-41: an adsorbent for the toxic oxyanions with high capacity, resistibility to inhibiting anions, and reusability after a simple treatment.

Fe(3+) coordinated to amino ligands fixed on MCM-41 mesoporous silica works as a strong adsorbent for toxic oxyanions. The maximum adsorption amounts were 1.56, 0.99, 0.81, and 1.29 mmol g(-1) for arsenate, chromate, selenate, and molybdate, respectively. When the initial concentrations of oxyanions were less than 1 mmol l(-1), they were removed completely by adsorption and the distribution coefficients K(d) were found to be more than 200000. Inhibition of oxyanion adsorption by abundant competing anions found in nature, NO(3)(-), SO(4)(-), PO(4)(3)(-) and Cl(-), was evaluated at adsorption saturation. Among these anions, the adsorption of the oxyanions was inhibited most in the presence of PO(4)(3)(-) , with which the selectivities for the target oxyanions were still more than 80%. The other coexisting anions, NO(3)(-), SO(4)(-), PO(4)(3)(-) and Cl(-), had little influence on adsorption of the oxyanions except in the case of selenate removal from sulfate solution. The high ability and selectivity to the target oxyanions are attributed to specific interactions between Fe(3+) and the oxyanions. The acid treatment and re-coordination of Fe(3+) lead to a reactivation of the used adsorbent, in which 87-90% of the original adsorption capacity was obtained and the oxyanion/Fe stoichiometries were not changed.