A new family of anion exchangers: mixed hydroxide carbonates of Bi3+ and divalent metals showing high selectivity for SeO32−

Mixed hydroxide carbonates containing Bi3+ and divalent metals were synthesized by hydrolyzing mixed solutions of M(NO3)2 (M = Mg, Zn) and Bi(NO3)3 with Na2CO3 solution at room temperature. The materials were studied using powder X-ray diffraction (XRD), IR spectra, N2 adsorption/desorption and thermogravimetric and differential thermal analyses (TG/DTA). Simultaneous substitution of a divalent metal ion (Mg2+ or Zn2+) and hydroxyl group for the Bi2O22+ layer in the bismutite structure occurred, forming hydroxide carbonates. Their chemical composition and the lattice parameters were represented by (Bi0.910, Mg0.090)2(O0.910, (OH)0.090)2CO3·0.51H2O with ao = 0.3862(2) nm and co = 1.3673(6) nm, and (Bi0.233, Zn0.767)2(O0.233, (OH)0.767)2CO3·0.38H2O with ao = 0.3864(2) nm and co = 1.3657(9) nm. The BET surface area of the bismutite, 6 m2/g, increased to 35–40 m2/g with the former and to 16–18 m2/g with the latter. Both hydroxide carbonates showed an excellent ion-exchange selectivity for SeO32−. These materials are promising for selective removal of SeO32− ion from selenite-contaminated aqueous effluents.