Ding Lingyang, Azimi Gisele
Laboratory for Strategic Materials, Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, ON, M5S 3E5, Canada.
Sci Rep. 2024 Jul 13;14(1):16216. doi: 10.1038/s41598-024-67134-2.
This research delves into the intricate nexus of particle size, mineralogical composition, surface attributes, elemental mapping, and rare earth element (REE) adsorption mechanisms within an ion-adsorption clay sample from South America. The investigation entails the fractionation of the ion-adsorption clay into three size categories: S1 (< 0.25 mm), S2 (0.25-0.5 mm), and S3 (0.5-2 mm). Each fraction undergoes meticulous characterization to unveil its elemental composition, mineralogical composition, surface area, morphological characteristics, elemental mapping, and the mechanisms governing REE incorporation. The results indicate that S1 has 31% physiosorbed, 8% chemisorbed, and 61% mineralized REEs, while S2 has 40% physiosorbed, 5% chemisorbed, and 55% mineralized REEs, and S3 has 24% physiosorbed, 5% chemisorbed, and 71% mineralized REEs. The physisorbed REEs are attributed to the presence of kaolinite, conducive to mostly physisorption. In terms of grain size and REE content/type relationship, the results show that REE content decreases with increasing grain size; however, there is not a clear trend in terms of REE occurrence modes with grain size. Heavy rare earth elements (HREEs) are discernibly favored in adsorption over light rare earth elements (LREEs). This preference is underpinned by the weathering processes that led to the formation of ion-adsorption clay, which facilitated the transport and accumulation of HREEs. Notably, the ion-adsorption clay encompasses a substantial content of mineralized REEs, necessitating more demanding extraction methodologies, such as acid baking followed by water leaching if complete extraction of all REEs is desired. Among the desorbable REEs, physisorption dominates, encompassing over 80% of the total. Chemisorbed REEs exhibit versatility in association with various minerals, encompassing kaolinite, quartz, and goethite. In essence, this study unveils the intricate interplay between particle dimensions, mineralogical constitution, surface attributes, and REE adsorption modes within this ion-adsorption clay sample. The ion-adsorption clay in this study contains a significant portion of mineralized REEs that cannot be extracted using the mild conditions typically employed for the desorption process. Additionally, the REE concentration in this ion-adsorption clay is notably higher than the average found in clay deposits worldwide, reaching levels comparable to those of regolith deposits in China, which are a major global source of REEs. This remarkable concentration of REEs, along with the unique modes of their occurrence in this deposit, presents a significant interest to the scientific community.
本研究深入探究了来自南美洲的离子吸附黏土样品中粒度、矿物成分、表面属性、元素映射以及稀土元素（REE）吸附机制之间的复杂联系。该研究将离子吸附黏土分为三个粒度类别：S1（<0.25毫米）、S2（0.25 - 0.5毫米）和S3（0.5 - 2毫米）。对每个部分进行细致表征，以揭示其元素组成、矿物成分、表面积、形态特征、元素映射以及控制REE掺入的机制。结果表明，S1中物理吸附的REE占31%、化学吸附的占8%、矿化的占61%；S2中物理吸附的REE占40%、化学吸附的占5%、矿化的占55%；S3中物理吸附的REE占24%、化学吸附的占5%、矿化的占71%。物理吸附的REE归因于高岭石的存在，这有利于主要通过物理吸附作用。就粒度与REE含量/类型关系而言，结果表明REE含量随粒度增大而降低；然而，REE赋存模式与粒度之间没有明显趋势。重稀土元素（HREEs）在吸附过程中明显比轻稀土元素（LREEs）更受青睐。这种偏好是由导致离子吸附黏土形成的风化过程所支撑的，该过程促进了HREEs的迁移和积累。值得注意的是，该离子吸附黏土包含大量矿化的REEs，如果想要完全提取所有REEs，则需要更苛刻的提取方法，例如酸焙烧后水浸出。在可解吸的REEs中，物理吸附占主导，占总量的80%以上。化学吸附的REEs与多种矿物结合具有多样性，包括高岭石、石英和针铁矿。本质上，本研究揭示了该离子吸附黏土样品中颗粒尺寸、矿物组成、表面属性和REE吸附模式之间的复杂相互作用。本研究中的离子吸附黏土含有很大一部分矿化的REEs，无法使用通常用于解吸过程的温和条件进行提取。此外，该离子吸附黏土中的REE浓度明显高于全球黏土矿床的平均浓度，达到了与中国风化壳矿床相当的水平，而中国风化壳矿床是全球REE的主要来源。这种显著的REE浓度以及它们在该矿床中独特的赋存模式，引起了科学界的极大兴趣。
