Sorption-desorption behavior of strontium-85 onto montmorillonite and silica colloids

Strontium-90 ( 90Sr) is one of the major radioactive contaminants found in DP Canyon at Los Alamos, New Mexico, USA. Radioactive surveys found that 90Sr is present in surface water and shallow alluvial groundwater environments in Los Alamos National laboratory (LANL). Colloids may influence the transport of this radionuclide in surface and groundwater environments in LANL. In this study, the authors investigated the sorption/desorption behavior of radioactive Sr on Ca-montmorillonite and silica colloids, and the effect of ionic strength of water on the sorption of Sr. Laboratory batch sorption experiments were conducted using 85Sr as a surrogate for 90Sr. Groundwater, collected from Well LAUZ-1 at DP Canyon and from Well J-13 at Yucca Mountain, Nevada, and deionized water, were used. The results show that 92–100% of the 85Sr was rapidly adsorbed onto Ca-montmorillonite colloids in all three waters. Adsorption of 85Sr onto silica colloids varied among the three waters. The ionic strength and Ca 2+ concentration in groundwater significantly influence the adsorption of 85Sr onto silica colloids. Desorption of 85Sr from Ca-montmorillonite colloids is slower than from silica colloids. Desorption of 85Sr from silica colloids was faster in LAUZ-1 groundwater than in J-13 groundwater and deionized water. The results suggest that clay and silica colloids may facilitate the transport of Sr along potential flowpaths from DP Canyon to Los Alamos Canyon.