In Situ Reduction and Immobilization of Radionuclides and Metals Using Hydrogen Gas as a Reductant

Preethi Talla, Amor Mondal, David Ramirez, and Lee W. Clapp
Environmental Engineering, Texas A&M University - Kingsville, Kingsville, TX

Due to increased in situ recovery (ISR) uranium mining activity in recent years, interest in improved post-mining groundwater restoration technologies has increased significantly. This study evaluated the feasibility of using membrane-delivered hydrogen to achieve in situ reduction and immobilization of U(VI) in groundwater, using Cr(VI) as a chemical analog. Three parallel lab-scale column reactors were packed with aquifer sediments from the Oak Ridge National Laboratory's Field Research Center and continuously fed groundwater spiked with 1 mg/L of Cr(VI). Each column was equipped with two membrane modules in series, each containing two gas-permeable hollow-fiber silicone membranes to provide bubbleless gas transfer. Hydrogen gas was supplied to the membrane modules in the first two columns, and nitrogen gas was supplied and in the third column as a negative control. Aqueous samples were routinely collected from ports along the length of each column and analyzed for dissolved hydrogen, Cr(VI), and pH. The results demonstrated that, while Cr(VI) removal in the nitrogen-supplied control column was negligible, over 90% Cr(VI) removal was achieved in the hydrogen-supplied soil columns. On-going studies are currently being conducted to measure concentrations of precipitated reduced Cr(III) present in the soil columns using microwave digestion and inductively coupled plasma mass spectrometry (ICP-MS).

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas