Department of Civil and Environmental Engineering , Massachusetts Institute of Technology , 77 Massachusetts Avenue , Cambridge , Massachusetts 02142 , United States.
Environ Sci Technol. 2018 Apr 3;52(7):4023-4030. doi: 10.1021/acs.est.7b05443. Epub 2018 Mar 16.
Radium (Ra) is a radioactive element commonly found within soils, sediments, and natural waters. Elevated Ra activities arising through natural and anthropogenic processes pose a threat to groundwater resources and human health, and Ra isotope ratios are used to decipher groundwater movement, estimate submarine discharge flux, and fingerprint contamination associated with hydraulic fracturing operations. Although adsorption to metal (hydr)oxides and certain clay minerals is well established as a dominant mechanism controlling Ra transport and retention, the extent of Ra sorption to other minerals and under variable environmental conditions (e.g., pH and salinity) is limited. Accordingly, we present results of sorption studies and surface complexation modeling (SCM) of Ra to ferrihydrite, goethite, montmorillonite, and pyrite, for a range of pH values and common background cations. Ra sorption to all substrates is observed under geochemical conditions considered, but varies according to mineral, solution pH and specific competing cations. Literature derived SCMs for Ra sorption were fitted to match either sorption impacts due to pH or different background cations, but were not able to predict the impacts of different geochemical conditions. Despite this, the use of SCMs provided a more mechanistic understanding of Ra sorption as compared to commonly used distribution coefficients.
镭（Ra）是一种常见于土壤、沉积物和天然水中的放射性元素。自然和人为过程引起的镭活度升高对地下水资源和人类健康构成了威胁，并且镭同位素比值被用来破译地下水运移、估算海底排放通量以及识别与水力压裂作业相关的污染。尽管吸附到金属（氢）氧化物和某些粘土矿物已被确定为控制镭迁移和保留的主要机制，但镭对其他矿物的吸附程度以及在不同环境条件（例如 pH 值和盐度）下的吸附程度是有限的。因此，我们提供了在一系列 pH 值和常见背景阳离子条件下，对针铁矿、赤铁矿、蒙脱石和黄铁矿进行镭吸附的吸附研究和表面络合模型（SCM）的结果。在考虑的地球化学条件下观察到所有底物对镭的吸附，但根据矿物、溶液 pH 值和特定竞争阳离子而有所不同。针对由于 pH 值或不同背景阳离子引起的吸附影响而拟合的镭吸附文献 SCM 无法预测不同地球化学条件的影响。尽管如此，与常用的分配系数相比，SCM 的使用提供了对镭吸附更具机制性的理解。
