Role of Manganese Oxyhydroxides in the Transport of Rare Earth Elements Along a Groundwater Flow Path

Haiyan Liu (1) , Huaming Guo (1) , Olivier Pourret (2, 3) , Yi Chen (4) , Rongxiao Yuan

1 China University of Geosciences [Beijing]
2 UniLaSalle
3 AGHYLE - Agro-écologie, Hydrogéochimie, Milieux et Ressources
4 USTB - University of Science and Technology Beijing [Beijing]

Rare earth elements (REE) are known to be emerging contaminants in hydrosphere, but 13 roles of hydrous manganese oxyhydroxides (HMO) in REE transport in groundwater remains 14 unknown. In this study, groundwater was sampled along a flow path in the North China Plain to 15 determine the behavior of REE surface complexation to HMO by a modeling and field study 16 approach. Results show that the proportion of neodymium (Nd) complexed by HMO ranges from 17 0.2% to 95.8%, and from 0.3% to 99.6% in shallow groundwater and deep groundwater, 18 respectively. The amount of complexed REE increases along the flow path. REE bound to HMO 19 exhibit decreasing trends with increasing atomic number. The process was determined to be 20 independent of pH, HMO content, and metal loading. This finding further demonstrates HMO-21 REE complexation plays a key role in transport of REE in groundwater through preferential 22 scavenging of Light REE (LREE) over Heavy REE (HREE). Nevertheless, carbonate ligands appear 23 to be robust competitors in reducing the amount of REE sorbed to HMO when solution pH rises 24 above 8.0. Assuming that 50% of Mn concentration occurs as HMO, the amount of complexed REE 25 was predicted to show a more marked decrease in LREE compared to that of HREE. 26

Mots clés: Lanthanides; Critical zone; China; Aquifer; Cerium anomaly; Modeling; Sorption

Domaines: Géochimie

Haiyan Liu, Huaming Guo, Olivier Pourret, Yi Chen, Rongxiao Yuan. Role of Manganese Oxyhydroxides in the Transport of Rare Earth Elements Along a Groundwater Flow Path. International Journal of Environmental Research and Public Health, 2019, 16 (13), pp.2263. ⟨10.3390/ijerph16132263⟩. ⟨hal-02265968⟩