高岭石、埃洛石对稀土元素的吸附选择性及其制约因素

The heavy rare earth elements (HREEs)-rich ion-adsorption clay deposits, as known as the typical REE resources of China, are the world’s primary source of HREEs. Light REEs (LREEs) and HREEs are fractionated during the process of deposit formation. The fractionation mechanism, however, remains debatable. This not only affects systematically understanding the metallogenic theory of REE and the exploration of ion-adsorption clay REE deposits, but also seriously restricts the efficient extraction of REEs. Kaolinite and halloysite are the main carrier minerals of REEs in the ion-adsorption clay deposits. Therefore, in this project, their adsorption selectivity toward REEs will be studied by simulation experiment. We will focus on the effects of crystal chemical characteristics of mineral (crystallinity, surface active sites density, etc.) and ambient conditions (pH, coexistence anion, etc.) on the adsorption of REEs on kaolinite and halloysite and the selectivity differences. On this basis, the interaction processes and combinations of mineral surface with REEs will be explored at the nano-scale by using micro-beam micro-area characterization technology. It is aimed to clarify the different enrichment conditions and located structures of LREEs and HREEs, revealing the fractionation mechanism and restrictive effects of LREEs and HREEs, and providing a unique perspective for understanding the formation mechanism of ion-adsorption clay REE deposits.

以富集重稀土为特征的离子吸附型稀土矿床是我国的特色资源，也是世界重稀土产品的主要来源。长期以来，对离子吸附型稀土矿床形成过程中的轻-重稀土分异机制的认识存在较大争议，这不仅影响了对稀土成矿理论的系统认识和离子吸附型稀土资源的勘探实践，还严重制约了稀土资源的高效利用。有鉴于此，本项目拟以离子吸附型稀土矿床中稀土的主要载体矿物（高岭石和埃洛石）为研究对象，采用模拟实验方法研究高岭石和埃洛石对稀土元素的吸附选择性及其影响因素。重点考察矿物晶体化学特征（结晶度、表面位密度等）和介质条件（pH、共存阴离子等）对高岭石和埃洛石吸附稀土元素的影响及其选择性差异；在此基础上，利用原位微区微束表征技术，从纳米尺度探究矿物表面与稀土元素的作用过程与结合方式，以期从微观角度揭示轻、重稀土元素的不同富集条件和局域结构环境，阐明轻-重稀土的分异机制与制约因素，为认识和掌握离子吸附型稀土矿床的形成机制提供独特的视角。

离子吸附型稀土矿床以富集重稀土为特征，是世界重稀土产品的最主要来源，也是我国的特色资源。但对离子吸附型稀土矿床表生成矿过程中的轻-重稀土分异机制的尚不清楚，这不仅影响了对稀土成矿理论的系统认识和离子吸附型稀土资源的勘探实践，还严重制约了稀土资源的高效利用。因此，本项目以离子吸附型稀土矿床中稀土的主要载体矿物（高岭石和埃洛石）为研究对象，采用模拟实验方法研究高岭石和埃洛石对稀土元素的吸附选择性及其影响因素。重点考察矿物晶体化学特征和介质条件对高岭石和埃洛石吸附稀土元素的影响及其选择性差异。研究表明，在地下水离子强度下，高岭石和埃洛石主要通过离子交换吸附稀土离子，吸附过程不产生稀土元素分异；其吸附容量与黏土矿物的阳离子交换容量（CEC）与表面位密度相关，而CEC与表面位密度由黏土矿物的晶体化学结构、结晶度等控制；共存阴离子（如碳酸根和有机配体）使轻稀土更易被黏土矿物吸附，引起轻-重稀土分异，这是由轻、重稀土离子和共存阴离子形成的配合物的稳定常数等热力学性质差异导致，表明共存阴离子是重稀土更易迁移的主要原因，这也与风化壳中上部相对富轻稀土，下部富重稀土相符合。本研究的开展进一步从黏土矿物表-界面反应角度揭示了离子吸附型稀土矿床的形成机制。