School of Water Resources and Environmental Engineering, East China University of Technology, Nanchang 330013, China.
State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China.
Int J Environ Res Public Health. 2019 Jun 26;16(13):2263. doi: 10.3390/ijerph16132263.
Rare earth elements (REE) are known to be emerging contaminants in hydrosphere, but roles of hydrous manganese oxyhydroxides (HMO) in REE transport in groundwater remains unknown. In this study, groundwater was sampled along a flow path in the North China Plain to determine the behavior of REE surface complexation to HMO by a modeling and field study approach. Results show that the proportion of neodymium (Nd) complexed by HMO ranges from 0.2% to 95.8%, and from 0.3% to 99.6% in shallow groundwater and deep groundwater, respectively. The amount of complexed REE increases along the flow path. REE bound to HMO exhibit decreasing trends with increasing atomic number. The process was determined to be independent of pH, HMO content, and metal loading. This finding further demonstrates HMO-REE complexation plays a key role in transport of REE in groundwater through preferential scavenging of light REE (LREE) over heavy REE (HREE). Nevertheless, carbonate ligands appear to be robust competitors in reducing the amount of REE sorbed to HMO when solution pH rises above 8.0. Assuming that 50% of Mn concentration occurs as HMO, the amount of complexed REE was predicted to show a more marked decrease in LREE compared to that of HREE.
稀土元素（REE）是水圈中已知的新兴污染物，但水合锰氢氧化物（HMO）在地下水REE 迁移中的作用尚不清楚。在这项研究中，我们沿着华北平原的一条水流路径采集地下水，通过模型和现场研究方法来确定 REE 与 HMO 表面络合的行为。结果表明，HMO 络合的钕（Nd）比例在浅层地下水中为 0.2%至 95.8%，在深层地下水中为 0.3%至 99.6%。结合 REE 的数量沿水流路径增加。与 HMO 结合的 REE 随着原子序数的增加呈下降趋势。该过程与 pH 值、HMO 含量和金属负载无关。这一发现进一步表明，HMO-REE 络合通过优先捕获轻REE（LREE）而不是重REE（HREE），在地下水REE 的迁移中起着关键作用。然而，当溶液 pH 值升高到 8.0 以上时，碳酸盐配体似乎会成为减少与 HMO 结合的 REE 数量的强有力竞争者。假设 50%的 Mn 浓度以 HMO 的形式存在，与 HREE 相比，与 HMO 络合的 REE 数量预计会有更明显的减少。
