Reduction of Se(IV) in boom clay: XAS solid phase speciation

Area of Science:

• Geochemistry
• Environmental Science
• Nuclear Waste Management

Background:

• Selenium's dual role as an essential micronutrient and toxic element.
• Selenium's presence in high-level radioactive waste (HLRW).
• Need for understanding selenium's long-term geochemical fate in disposal sites.

Purpose of the Study:

• Investigate the solid-phase speciation of selenium.
• Determine selenium's behavior in Boom Clay under reducing conditions.
• Inform predictions of HLRW disposal safety.

Main Methods:

• X-ray Absorption Spectroscopy (XAS) based investigation.
• Long-term batch sorption experiments.
• Linear Combination XANES and ITFA-based EXAFS analysis.

Main Results:

• Identified Se0 as the dominant solid-phase speciation of selenium.
• Observed selenium interaction with Boom Clay, a potential HLRW repository.
• Demonstrated the formation of elemental selenium from Se(IV) in reducing clay environments.

Conclusions:

• Elemental selenium (Se0) is the primary form of selenium in Boom Clay.
• This speciation is critical for predicting the long-term behavior of HLRW.
• Provides foundational data for safe geological disposal of radioactive waste.