You are here:
EFFECT OF BACTERIAL SULFATE REDUCTION ON IRON-CORROSION SCALES
Citation:
Lytle*, D A., T L. Gerke, AND J. B. Maynard. EFFECT OF BACTERIAL SULFATE REDUCTION ON IRON-CORROSION SCALES. M. Lacey (ed.), JOURNAL OF AMERICAN WATER WORKS ASSOCIATION. American Water Works Association, Denver, CO, 97(10):109-120, (2005).
Description:
Iron-sulfur geochemistry is important in many natural and engineered environments including drinking water systems. In the anaerobic environment beneath scales of corroding iron drinking water distribution system pipes, sulfate reducing bacteria (SRB) produce sulfide from naturally-occurring sulfate in the bulk water. This sulfide subsequently can affect iron geochemistry of the scale and the protective qualities of the scale. The effect of bacterial sulfate reduction on the nature of iron corrosion scales collected from a surface water and a ground water drinking water distribution system, each with similar aqueous sulfate concentrations, about 100 mg/L was studied. Reduced sulfur proved to be a significant component of all iron scales studied, reaching up to 22% (wt. %) in the scale from the groundwater system and 2% in the surface water system. X-ray diffraction revealed the presence of elemental sulfur (S0) and FeS2 (marcasite). Sulfur extractions showed major S0 and FeS2 in all scales, but only minor amounts of FeS and SO42-. Sulfur isotope measurements showed δ34S in the scales to be 20 to 40 permil (parts per thousand) lighter than in the source SO42-, confirming the important role of SRBs in forming the reduced sulfur. Other important iron minerals found were goethite (α-FeOOH) and lepidocrocite (γ-FeOOH). Magnetite (Fe3O4), which is believed to be an important mineral in protecting iron pipes from extensive corrosion and iron release, was present in iron scales collected from the surface water system but not in those from the groundwater system.