SeO32−-selective properties of inorganic materials synthesized by the soft chemical process

Three groups of inorganic materials were studied with a view to finding adsorbents selective for selenium from aqueous solution in competitive conditions: (A) divalent-cation-substituted bismutite-type compounds (Bi1−x, Mx)2(O1−x, (OH)x)2CO3·nH2O, (B) hydrotalcites [M2+1−xN3+x(OH)2]+x(CO32−)x/2·nH2O and (C) amorphous titanic acid TiO2·nH2O. The first group of materials was synthesized by hydrolyzing mixed solution of M(NO3)2 and Bi(NO3)3 with Na2CO3 solution at Na2CO3/(M+Bi)=20 on a molar basis at room temperature. Other materials were prepared by the soft chemical process according to our previous reports. These materials were identified using powder X-ray diffraction (XRD), FTIR spectra, and TG/DTA. Amorphous titanic acid and bismutite-type compounds showed excellent selectivity for SeO32−. Divalent oxyanions were exchanged with CO32− in the bismutite-type compounds and hydrotalcites through the ion-exchange mechanism. Selenite-selective properties of these materials found in the present study will be useful for its removal from contaminated aqueous effluents.