In situ reductive dissolution to remove Iodine-129 from aquifer sediments.

Area of Science:

• Environmental Remediation
• Geochemistry
• Analytical Chemistry

Background:

• Iodine contamination in Hanford Site sediments is associated with iron oxides.
• Understanding iodine speciation and release mechanisms is crucial for effective remediation.

Purpose of the Study:

• To evaluate sodium dithionite as a remedial agent for iodine removal from Hanford sediments.
• To assess the impact of treatment on iodine extraction efficiency and speciation.

Main Methods:

• Laboratory study using Na-dithionite and K-carbonate buffer on contaminated sediments.
• X-ray fluorescence (XRF) and X-ray absorption near edge structure (XANES) for iodine and iron analysis.
• Groundwater leaching and batch extraction experiments to measure iodine and iron release.

Main Results:

• Sodium dithionite treatment increased iodine mass removal by 2.9x and accelerated release rates.
• Treatment reduced Fe(III)-oxides, facilitating iodine release.
• Elevated iodine concentrations persisted in treated samples over 750 hours, with evidence of iodide precipitation.
• Iodine-129 was removed more readily than iodine-127, suggesting different origins and phases.

Conclusions:

• Sodium dithionite is effective in removing significant iodine mass from Fe-oxide associated iodine in Hanford sediments.
• Long-term leaching behavior and potential precipitation issues necessitate further research for field-scale dithionite application.
• Differential removal of iodine-129 and iodine-127 indicates distinct sources and geochemical behaviors.