Sulfidation Unlocks Dual Reductive Pathways in Uranium Immobilization by Iron Sulfide.

Area of Science:

• Geochemistry
• Environmental Science
• Mineralogy

Background:

• Iron sulfide minerals are key in immobilizing uranium in anoxic environments.
• Understanding electron transfer mechanisms in iron sulfides is crucial for contaminant remediation.

Purpose of the Study:

• To investigate the dual pathways of U(VI) reduction mediated by iron sulfide minerals.
• To elucidate the role of structural transformations and pH on uranium immobilization.

Main Methods:

• Comparative experiments using pristine, oxidized, and sulfur-enriched mackinawite (FeS).
• Analysis of redox-driven structural changes and their impact on electron transfer.
• Assessment of pH-dependent uranium reduction and surface passivation.

Main Results:

• Iron sulfide minerals (FeS) exhibit dual pathways for U(VI) reduction via structural S(-II) oxidation or Fe(II) coreduction.
• Sulfidation-induced structural changes in sulfur-enriched FeS activate Fe(II) as a coreductant.
• Uranium reduction is pH-dependent, with surface passivation observed at higher pH.

Conclusions:

• Stoichiometry and structure of iron sulfides significantly regulate uranium reduction and immobilization.
• These findings are critical for predicting the behavior of redox-sensitive contaminants in subsurface environments.