Selective Selenate Adsorption on Cationated Amino-Functionalized MCM-41

A large distribution coefficient and large sorption capacity were observed during selenate adsorption by cation (Fe^3+, Cu^2+, and H^+)-anchored diamino-functionalized MCM-41. Moreover, these synthetic adsorption media showed excellent selectivity for selenate sorption in the presence of other anions. In a pure potassium selenate solution, the distribution coefficients, Kd, exceeded 200000 when [selenate] < 25 mg in 1 g of these adsorbents (i.e., when the coverage of selenate < 0.4). The adsorption capacities of these three adsorption media were 117, 83.0, and 123 mg (g-adsorbent)^-1, respectively, with the Fe and Cu centers having the capacity to bind 1.5 and 1.1 selenate anions on average. Tests on mono- (N-), di- (NN-), and triamino- (NNN-) functionalized MCM-41 showed that the diaminofunctionalized varieties exhibited the largest value for Kd when cationated by Fe3+ and Cu^2+. In the case of Fe/NN-MCM-41, diamino-functionalized MCM-41 cationated by Fe^3+, the degree of inhibition caused by coexisting SO4^2- was much lower than the value reported for aluminum oxide. Cu/NN-MCM-41 showed the largest resistance to inhibition by Cl^-. For the adsorbents that we tested, the effects of coexisting nitrate were smallest for these three anions. The local structure of the adsorption center in Fe/NN-MCM-41 was analyzed by EXAFS spectroscopy.