Schwertmannite (Fe8O8(OH)6-x(SO4)x·nH2O) plays a major geochemical role in acidic iron- and sulfate-rich environment. However, its structure remains debated, partially due to the unknown sulfate coordination environment. In this study, Sulfur K-edge EXAFS and time-based ATR-FTIR spectroscopy were used to determine the sulfate coordination environment in synthetic schwertmannite samples at various pHs and water contents. EXAFS analysis identified a S-Fe interatomic distance of 3.17 ± 0.05 Å for an air-dried schwertmannite sample, suggesting formation of sulfate bidentate-binuclear complexes. In contrast, no second coordination shells were observed for the wet sample, pointing to sulfate outer-sphere complexes. ATR-FTIR spectral fitting shows that the fraction of the sulfate inner-sphere complexes increased from wet to dry at pH &lt; 5, while no significant changes happened at pH &gt; 5. The results have important implications for understanding schwertmannite structure, formation mechanism, and its role in controlling fate and transport of toxic elements in acidic environment.

Sulfate coordination environment in Schwersmannite

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.

Sulfate coordination environment in </b>Schwersmannite