The determination of sulfate and sulfide species in hydrous silicate glasses using Raman spectroscopy

Raman spectroscopy is used to identify the sulfur speciation (sulfur valence state) in “technical” iron-free soda-lime and potassium-silicate glasses and in “natural” glass compositions such as basalt, andesite, and rhyodacite. The presence of sulfate (S6+) is marked in Raman spectra of oxidized synthetic and natural glasses by bands at ~990 and ~1000 cm-1, respectively. The presence of sulfide (S2-) in the reduced technical glasses is marked in Raman spectra by a band at 2574 cm-1 indicating that S2- is present as HS- in these Fe-free glasses. Such a band is absent in the Raman spectra of reduced basaltic, andesitic, and rhyodacitic glasses. However, an additional band at ~400 cm-1 appears in the Raman spectra of the reduced S-bearing “natural” glasses when compared to that of S-free reduced “natural” reference glasses indicating that S2- is most likely complexed with Fe in these glasses. Thus, the dissolution mechanism of S2- appears to be different in Fe-free and Fe-bearing glasses and S2- is dissolved as either HS--species or Fe-S complexes, respectively. The data shown here demonstrate the potential of Raman spectroscopy in identifying the sulfur valence state in silicate glasses. In addition, S2- is dissolved as completely different complexes when comparing “technical” iron-free and “natural” iron-bearing, hydrous silicate glass compositions.