Raman spectroscopic study of the sulfite-bearing minerals scotlandite, hannebachite and orschallite: implications for the desulfation of soils

The structures of the naturally occurring sulfite-bearing minerals scotlandite, hannebachite and orschallite have been studied by Raman spectroscopy. Raman bands are observed for scotlandite PbSO3 at 935, 880, 622 and 474 cm(-1) and are assigned to the (SO3)(2-) nu(1) (A(1)), nu(3)(E), nu(2)(A(1)) and nu(4)(E) vibrational modes, respectively. For hannebachite (CaSO3)(2)center dot H2O these bands are observed at 1005, 969 and 655 cm(-1) with multiple bands for the nu(4)(E) mode at 444, 492 and 520 cm(-1). The Raman spectrum of hannebachite is very different from that of the compound CaSO3 center dot 2H(2)O. It is proposed, on the basis of Raman spectroscopy, that in the mineral hannebachite, the sulfite anion bonds to Ca through the sulfur atom. The Raman spectrum of the mineral orschallite Ca-3[SO4](SO3)(2)center dot 12H(2)O is complex resulting from the overlap of sulfate and sulfite bands. Raman bands at 1005 cm(-1), 1096 and 1215 cm(-1) are assigned to the (SO4)(2-) nu(1) symmetric and nu(3) asymmetric stretching modes. The two Raman bands at 971 and 984 cm(-1) are attributed to the (SO3)(2-) nu(3)(E) and nu(1)(A(1)) stretching vibrations. The formation of sulfite compounds in nature offers a potential mechanism for the removal of sulfates and sulfites from soils. Copyright (C) 2008 John Wiley & Sons, Ltd.