Tokunaga Tetsu K, Wan Jiamin, Pena Jasquelin, Sutton Stephen R, Newville Matthew
Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Environ Sci Technol. 2004 Jun 1;38(11):3056-62. doi: 10.1021/es035289+.
Uranium contamination of soils and sediments often originates from acidic or alkaline waste sources, with diffusion being a major transport mechanism. Measurements of U(VI) diffusion from initially pH 2 and pH 11 solutions into a slightly alkaline Altamont soil and a neutral Oak Ridge soil were obtained through monitoring uptake from boundary reservoirs and from U concentration profiles within soil columns. The soils provided pH buffering, resulting in diffusion at nearly constant pH. Micro X-ray absorption near edge structure spectra confirmed that U remained in U(VI) forms in all soils. Time trends of U(VI) depletion from reservoirs and U(VI) concentration profiles within soil columns yielded Kdvalues consistent with those determined in batch tests at similar concentrations (approximately 1 mM) and much lower than values for sorption at much lower concentrations (nM to microM). These results show that U(VI) transport at high concentrations can be relatively fast at non-neutral pH, with negligible surface diffusion, because of weak sorption.
土壤和沉积物中的铀污染通常源于酸性或碱性废物源，扩散是主要的迁移机制。通过监测边界储层的吸收情况以及土壤柱内的铀浓度分布，获得了从初始pH值为2和pH值为11的溶液向微碱性的阿尔塔蒙特土壤和中性的橡树岭土壤中U(VI)扩散的测量结果。土壤提供了pH缓冲作用，导致在几乎恒定的pH值下发生扩散。微X射线吸收近边结构光谱证实，在所有土壤中铀均以U(VI)形式存在。储层中U(VI)的消耗时间趋势以及土壤柱内U(VI)浓度分布得出的分配系数值与在类似浓度（约1 mM）下的批量试验中确定的值一致，且远低于在低得多的浓度（纳摩尔至微摩尔）下的吸附值。这些结果表明，由于吸附较弱，在非中性pH值下高浓度的U(VI)迁移可能相对较快，且表面扩散可忽略不计。
