Quantifying uranium complexation by groundwater dissolved organic carbon using asymmetrical flow field-flow...

Area of Science:

• Environmental Science
• Geochemistry
• Analytical Chemistry

Background:

• Actinide mobility in groundwater is critical for nuclear waste disposal and uranium mine management.
• Dissolved organic carbon (DOC) potentially influences uranium transport, but field data are scarce.
• Limited techniques exist for isolating DOC and quantifying complexed metals.

Purpose of the Study:

• To investigate uranium partitioning to DOC in a clay-rich aquitard.
• To determine U-organic matter association constants using field samples.
• To assess the role of DOC in uranium mobility in groundwater.

Main Methods:

• Analysis of 10 groundwater samples from varying depths (2-30 m).
• On-line coupling of Asymmetrical Flow Field-Flow Fractionation (AsFlFFF) with UV absorbance (UVA) and ICP-MS detectors.
• Determination of DOC and uranium concentrations and U-DOC complexation.

Main Results:

• A positive correlation was found between DOC and uranium concentrations.
• AsFlFFF-UVA recovered 47-98% of DOC, with a weight-average molecular weight of 900-1400 Da for the main peak.
• AsFlFFF-ICP-MS indicated that less than or equal to 2% of uranium was complexed with DOC, consistent with speciation modeling.

Conclusions:

• The AsFlFFF-ICP-MS method is effective for analyzing U-organic matter association in small sample volumes.
• Facilitated transport of uranium by DOC appears limited in typical groundwater conditions.
• Findings are crucial for accurate uranium transport calculations and nuclear waste management strategies.