Highly-alkaline nuclear waste solutions have leaked into the vadose zone at the US DOE Hanford site, WA, causing dissolution and secondary mineral precipitation upon contact with subsurface sediments. Significantly enhanced immobilization of radionuclide (such as strontium) due to adsorption and coprecipitation with the neo-formed colloid-sized precipitates (such as nitrate-cancrinite) has been reported. However, the stability of these precipitates in the subsurface under changeable field conditions is not clear. Here we tested the remobilization possibility of the Sr-containing secondary precipitates in the subsurface using saturated column experiments under different geochemical conditions. Our results indicate that the remobilization of the neo-formed precipitates could be possible given a change of background geochemical conditions in the field site. The re-mobility of the precipitates increased with the increase of the leaching solution flow rate and pH, as well as with decreasing solution ionic strength. The increased mobility of Sr containing precipitates with changing of background conditions can be a potential source for additional radionuclide transport in Hanford subsurface environments.

Facilitated contaminant transport by remobilization of Sr containing colloid-sized secondary precipitates in Hanford site subsurface

243rd National Meeting (2012)

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