Department of Soil, Water and Environmental Science, University of Arizona, Tucson, Arizona 85721, USA.
Environ Sci Technol. 2010 Mar 15;44(6):1992-7. doi: 10.1021/es902043e.
Mineral sorption/coprecipitation is thought to be a principal sequestration mechanism for radioactive (90)Sr and (137)Cs 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-AI-NO(3)-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 pCO(2). 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, NO(3), 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, pCO(2) had no effect on Sr or Cs sorption, sediments weathered at <10 ppmv pCO(2) did desorb more Sr (66% vs 28%) and Cs (13% vs 8%) during leaching than those weathered at 385 ppmv pCO(2). Thus, the dissolution of neo-formed aluminosilicates may represent a long-term, low-level supply of (90)Sr at the Hanford site.
矿物吸附/共沉淀被认为是放射性（90）Sr 和（137）Cs 在受美国能源部汉福德场地高碱性、高放废物（HLRW）影响的沉积物中的主要隔离机制。然而，在去除 HLRW 源后，新形成的、含有污染物的相的长期持久性尚不清楚。我们将原始汉福德沉积物置于含有 Sr、Cs 和 I 的高碱性 Na-AI-NO(3)-OH 溶液中，浓度分别为 10(-5)、10(-5)和 10(-7)摩尔，CO2 分压分别为<10 ppmv 或 385 ppmv，反应 182 天。这导致了类沸石矿物的形成。我们用稀的、中性 pH 的溶液对这些风化的沉积物进行淋洗。经过 500 个孔隙体积（PV）后，流出物中的 Sr、Cs、NO(3)、Al、Si 和 pH 值达到稳定状态，浓度高于进水的浓度。反应传输模拟表明，即使经过 500 PV，Cs 的解吸可以用离子交换反应来解释，而 Sr 的解吸则最好用 Sr 取代的新形成的矿物的溶解来描述。虽然 CO2 分压对 Sr 或 Cs 的吸附没有影响，但在 CO2 分压<10 ppmv 下风化的沉积物在淋洗过程中比在 CO2 分压 385 ppmv 下风化的沉积物释放更多的 Sr（66%比 28%）和 Cs（13%比 8%）。因此，新形成的铝硅酸盐的溶解可能代表汉福德场地长期的、低水平的（90）Sr 供应。
