Optimized quantitative analysis of rare earth elements associated with typical secondary minerals in regolith-hosted deposits

IF 3.6 2区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Chemical Geology Pub Date : 2025-06-19 DOI:10.1016/j.chemgeo.2025.122942

Puqiu Wu , Xurui Li , Xiaoliang Liang , Xiaoju Lin , Jianxi Zhu

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Abstract

Regolith-hosted rare earth element (REE) deposits are a major source of REEs, particularly the economically valuable heavy REEs (HREEs). Quantitative analysis of the various REE species is crucial for evaluating both the economic potential and mining efficiency of these deposits. The sequential extraction procedure (SEP) is widely used to quantify the speciation of heavy metals, but its applicability to REE analysis remains largely unexplored. Herein, SEP was optimized to quantify the occurrences of REEs associated with typical secondary minerals, specifically clay minerals and Fe (oxyhydr)oxides. The changes in mineral structure and morphology during extraction were examined using metal leaching experiments, transmission electron microscopy, and Mössbauer spectrum. These extractants demonstrated promising performance: 0.5 mol L⁻¹ (NH₄)₂SO₄ at pH 7 for ion-exchangeable REEs, 0.2 mol L⁻¹ (NH₄)₂C₂O₄ at pH 3 and 50 °C for amorphous Fe (oxyhydr)oxide–associated REEs; and a mixed solution of 0.2 mol L⁻¹ (NH₄)₂C₂O₄ and 0.1 mol L⁻¹ ascorbic acid at 90 °C for crystalline Fe (oxyhydr)oxide–associated REEs. This optimized protocol was successfully applied to separate REE fractions adsorbed on Fe (oxyhydr)oxide–clay mineral composites, the dominant REE carriers in regolith-hosted deposits. The results show that ion-exchangeable REEs, primarily associated with clay minerals such as kaolinite, constitute the main fraction, while Fe (oxyhydr)oxides such as goethite and hematite are preferentially enriched in HREEs. The efficiency and selectivity of the optimized SEP were further evaluated in relation to the chemical properties of extractants, mineral reactivity, and their relevance to geochemical applications.

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风化岩型矿床典型次生矿物稀土元素优化定量分析

风化岩型稀土元素（REE）矿床是稀土的主要来源，特别是具有经济价值的重稀土（hree）。各种稀土元素的定量分析对于评价这些矿床的经济潜力和开采效率至关重要。顺序萃取法（SEP）被广泛用于重金属形态的定量分析，但其在稀土元素分析中的适用性仍未得到充分的探讨。本文对SEP进行了优化，以量化与典型次生矿物（特别是粘土矿物和铁（氧）氧化物）相关的稀土元素的产状。采用金属浸出实验、透射电镜和Mössbauer光谱等方法对浸出过程中矿物结构和形态的变化进行了研究。这些萃取剂表现出良好的性能：0.5 mol L−1 (NH4)2SO4在pH 7下可用于离子交换稀土，0.2 mol L−1 (NH4)2C2O4在pH 3和50 °C下可用于无定形铁（氧）氧化物相关稀土；以及0.2 mol L−1 (NH4)2C2O4和0.1 mol L−1抗坏血酸在90 ℃下的混合溶液，用于结晶铁（氧）氧化物相关稀土。该优化方案成功地应用于分离吸附在铁（氧）氧化物-粘土矿物复合材料上的REE组分，这是风化岩矿床中主要的REE载体。结果表明：稀土元素以离子交换稀土为主，主要与高岭石等粘土矿物伴生，铁（氧）氧化物如针铁矿和赤铁矿优先富集。从萃取剂的化学性质、矿物反应性及其与地球化学应用的相关性等方面进一步评价了优化后的SEP的效率和选择性。

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来源期刊

Chemical Geology 地学-地球化学与地球物理

CiteScore

7.20

自引率

10.30%

发文量

374

审稿时长

3.6 months

期刊介绍： Chemical Geology is an international journal that publishes original research papers on isotopic and elemental geochemistry, geochronology and cosmochemistry. The Journal focuses on chemical processes in igneous, metamorphic, and sedimentary petrology, low- and high-temperature aqueous solutions, biogeochemistry, the environment and cosmochemistry. Papers that are field, experimentally, or computationally based are appropriate if they are of broad international interest. The Journal generally does not publish papers that are primarily of regional or local interest, or which are primarily focused on remediation and applied geochemistry. The Journal also welcomes innovative papers dealing with significant analytical advances that are of wide interest in the community and extend significantly beyond the scope of what would be included in the methods section of a standard research paper.