Uranium(VI) reduction by iron(II) monosulfide mackinawite

Area of Science:

• Environmental Chemistry
• Geochemistry
• Nuclear Chemistry

Background:

• Uranium contamination in subsurface environments poses significant risks.
• Understanding uranium redox behavior is crucial for remediation strategies.
• Iron sulfide minerals are prevalent in reducing subsurface environments.

Purpose of the Study:

• To investigate the reaction between aqueous uranium(VI) and mackinawite.
• To determine the redox state and mineral phase of removed uranium.
• To assess the stability of the formed uranium phase against oxidation.

Main Methods:

• Batch uptake experiments to quantify uranium removal.
• X-ray absorption spectroscopy (XAS) for speciation analysis.
• Equilibrium modeling (Visual MINTEQ) to predict uranium speciation.

Main Results:

• Mackinawite effectively removed uranium(VI) across a wide pH range (5-11).
• Uranium was reduced to uranium(IV) and formed uraninite, associated with mackinawite.
• The formed uraninite was stable against oxidation by dissolved oxygen.

Conclusions:

• Abiotic reduction of uranium(VI) by mackinawite forms stable uraninite.
• Mackinawite plays a key role in uranium redox cycling and sequestration.
• This process is significant for uranium remediation in contaminated subsurface environments.