Understanding the adsorption and desorption processes is essential for predicting the mobility of radionuclides in the environment.  Typically, adsorption/desorption reactions are studied in single mineral systems. Here we investigate desorption of plutonium in bi-mineral experiments in an attempt to move towards understanding radionuclide desorption in complex mineral environments.  Pu(IV) was adsorbed to goethite, quartz or montmorillonite for a period of 21 days. After this adsorption period, an aliquot of the mineral suspension was placed inside 5 mL dialysis bags with a cut-off size of 3.5-5 kD.  The dialysis bags were then placed inside cells containing a 175 mL plutonium-free mineral suspension of montmorillonite outside of the dialysis bag. The desorption of plutonium initially adsorbed to goethite, quartz, or montmorillonite placed inside the dialysis bag was monitored by measuring the bulk suspension of plutonium sorbed onto the montmorillonite suspension outside the dialysis bag.  The plutonium sorbed onto the montmorillonite suspension outside the dialysis bag was less than expected. In addition, parallel experiments using radioactive cesium are underway to optimize the quantification of desorption rates based on this experimental framework. Cesium was chosen because of its expected simpler adsorption/desorption behavior. Ultimately we aim to use our data to improve adsorption/desorption parameters for environmental transport models and evaluate the impact of desorption rates on radionuclide transport.   Prepared by LLNL under Contract DE-AC52-07NA27344.This material is based upon work supported by the U. S. Department of Homeland Security under Grant Award Number, 2012-DN-130-NF0001-02 and the U. S. DOE Office of Biological & Environmental Sciences, Subsurface Biogeochemistry Research Program.

Desorption of radionuclides from minerals: The effect of mineral competition

248th National Meeting (2014)

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