Earth Science Frontiers ›› 2022, Vol. 29 ›› Issue (1): 42-53.DOI: 10.13745/j.esf.sf.2021.8.2

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Extraction, characterization and occurrence state of REE-bearing nanoparticles from granite-derived regolith

YI Zebang1(), FU Wei1,*(), ZHAO Qin1, XU Cheng1, LU Jipu2   

  1. 1. Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, Guilin University of Technology, Guilin 541004, China
    2. Guangxi Bureau of Geology & Mineral Prospecting & Exploitation, Nanning 530023, China
  • Received:2021-04-21 Revised:2021-07-02 Online:2022-01-25 Published:2022-02-22
  • Contact: FU Wei

Abstract:

Characterization of REE in nanoparticles extracted from regolith is important for revealing the genesis of regolith-hosted REE deposits in South China. In this study, we used both physical (MilliQ water, MQW) and chemical (Na4P2O7, TSPP) techniques to extract nanoparticles (1-100 nm) from the profile of REE-enriched granite-derived regolith in Pingnan, Guangxi. Hollow fiber flow field-flow fractionation and inductively coupled plasma mass spectrometer (HF5-ICP-MS) were used to separate and characterize the nanoparticles continuously from regolith and simultaneously obtain the particle size distribution. We show that the chemical dispersant can efficiently break up large-size nanoparticle aggregates and achieve much higher (102-103 times) extraction efficiency compared to the physical extraction method, with ~80.5% REE extracted from regolith. The particle size mostly ranged between 2-5 nm and 10-30 nm, and some between 30-80 nm. In 2-5 nm nanoparticles, the REE peak position was closely related to organic matter macromolecules, indicating the association of the two, via ionic interactions; whereas in 10-30 nm nanoparticles, the REE peak position was almost identical to Al element, indicating REE association with clay minerals, via adsorption or ion exchange. Furthermore, the size distributions of light (LREE) and heavy (HREE) REEs in nanoparticles differed. LREEs, represented by La, Ce, Pr and Nd, were mostly in 2-5 nm and 10-30 nm nanoparticles; whereas HREEs, represented by Tb and Lu, were also in 30-80 nm particles, indicating there are other HREE source besides clay mineral and organic matter from regolith. The findings of this study provide new insights into the occurrence states as well as enrichment/differentiation process of REEs in regolith-hosted REE deposits.

Key words: granite weathering regolith, REE, nanoparticle, hollow fiber flow field-flow fractionation coupled with inductively coupled plasma mass spectrometer (HF5-ICP-MS)

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