The effects of secondary mineral precipitates on ⁹⁰Sr mobility at the Hanford Site, USA

The effects of secondary precipitates on ⁹⁰Sr transport at the Hanford Site were investigated using quartz column experiments with simulated caustic tank waste leachates (STWL). Significantly enhanced retardation of Sr transport was observed in the column contacted with STWL due to Sr sorption and co-precipitation with neo-formed nitrate cancrinite. However, the column results also suggest that neo-formed secondary precipitates could behave like native mobile colloids that can enhance Sr transport. Initially immobilized Sr within secondary precipitates could re-mobilize given a change in the pore water background conditions. The mobility of the neo-formed Sr-bearing precipitates increased with increased solution flow rate. In the field, pore water contents and flow rates can be changed by snow-melt (or storm water) events or artificial infiltration. The increased pore water flow rate caused by these events could affect the mobility of ⁹⁰Sr-containing secondary precipitates, which can be a potential source for facilitated Sr transport in Hanford Site subsurface environments. (authors)