Contaminant Desorption during Long-Term Leaching of Hydroxide-Weathered Hanford Sediments

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• 作者：Aaron Thompson ; Carl I. Steefel ; Nicolas Perdrial ; Jon Chorover
• 刊名：Environmental Science & Technology
• 出版年：2010
• 出版时间：March 15, 2010
• 年：2010
• 卷：44
• 期：6
• 页码：1992-1997
• 全文大小：235K
• 年卷期：v.44,no.6(March 15, 2010)
• ISSN：1520-5851

文摘

Mineral sorption/coprecipitation is thought to be a principal sequestration mechanism for radioactive ⁹⁰Sr and ¹³⁷Cs in sediments impacted by hyperalkaline, high-level radioactive waste (HLRW) at the DOE’s Hanford site. However, the long-term persistence of neo-formed, contaminant bearing phases after removal of the HLRW source is unknown. We subjected pristine Hanford sediments to hyperalkaline Na−Al−NO₃−OH solutions containing Sr, Cs, and I at 10⁻⁵, 10⁻⁵, and 10⁻⁷ molal, respectively, for 182 days with either <10 ppmv or 385 ppmv pCO₂. This resulted in the formation of feldspathoid minerals. We leached these weathered sediments with dilute, neutral-pH solutions. After 500 pore volumes (PVs), effluent Sr, Cs, NO₃, Al, Si, and pH reached a steady-state with concentrations elevated above those of feedwater. Reactive transport modeling suggests that even after 500 PV, Cs desorption can be explained by ion exchange reactions, whereas Sr desorption is best described by dissolution of Sr-substituted, neo-formed minerals. While, pCO₂ had no effect on Sr or Cs sorption, sediments weathered at <10 ppmv pCO₂ did desorb more Sr (66% vs 28%) and Cs (13% vs 8%) during leaching than those weathered at 385 ppmv pCO₂. Thus, the dissolution of neo-formed aluminosilicates may represent a long-term, low-level supply of ⁹⁰Sr at the Hanford site.