风化壳中稀土元素三维空间分布及注入液体流动方向的基础研究

Weathered crust elution rare earth deposits (WCE-RED, or called as ion adsorption type rare earth deposits) are the most important type of rare earth (RE) resources in China, particularly for heavy RE elements and yttrium. This type of WCE-RED contains exchangeable RE elements and yttrium which were formed by the mineralization in weathering crusts of parent rocks ranging in composition from granite to acidic volcanic rocks and lamprophyre. The study of the geochemical fractionation of REs in weathering crusts is important not only from the theoretical and pedogenetic viewpoints but also because of its applied value in industrial production of REs. However, the obtained fractionation of REs in weathering crusts was only for variation in vertical direction, and is lack in information for the distribution of RE in three-dimensional (3D) space, and therefore has not been well used in the study on extracting RE from WCERED. To increase the recover percentage of extrating RE from WCERED by an in-situ leaching process, it is necessary to determine the distribution of RE in 3D space of WCERED and the flow direction of liquid injected in for leaching RE. In the present study, we select two typical WCEREDs as objects for the study on geochemical fractionation of REEs by determining their distribution in 3D space of WCERED and on the surface of minerals with different particle sizes as well as the existing states of REs in deposits using ICP-MS technology. At the same time, the adsorption characterization of different REs on weathering minerals with different particle sizes will be carried out for determining the thermodynamic and kinetic parameters of adsorption, evaluting the existing states and the migration ragularity of RE ions on the surface of mineral particles in weathering crust, and establishing mathematical models for RE migration in different directions of WCERED. With these data and computer technology, we can discuss the spatial and temporal significance of REs fractionation, draw the distribution of REs in 3D space of WCERED and the flow directions of electrolyte solution in leaching process of REs. Furthermore, a simple and valuable method will be established to get stereograms including the distribution of REs in 3D space of WCERED and the possible flow directions of liquid injected in for leaching REs. Therefore, the results of this study have potential for understanding the geochemical fractionation of REs in weathering crusts, calculating the resource amount of REs in a deposit, selecting the best leaching model for a particular deposit, proposing a technique for extracting ion adsorption type of REs adsorped by strong adsorbents, planning the detail technical solutions for the in-situ leaching of REs with high efficieny and low cost. It is of significance for the efficient green extraction of REs from WCERED.

风化壳淋积型稀土矿是我国拥有的一类独特资源。但其开采回收率低，因为缺乏风化壳中稀土含量分布及液流方向信息。本研究选择2个代表性矿山，采集不同空间位置的矿物样品，按粒子大小分级，用化学方法区分浸取不同状态的稀土，采用ICP-MS测定样品中的稀土含量和配分，系统研究稀土元素在三维空间和不同矿物之间的分异特点和规律；研究不同粒级矿物粒子对各种稀土离子的吸附特征，确定其热力学和动力学参数，评估离子态稀土的存在形式及其在矿物表面的迁移规律，建立稀土在矿中迁移的数学模型。结合计算机技术，研究测定和绘制稀土元素在风化壳三维空间的分布图以及浸取稀土过程中的溶液流向图的方法原理及所需要的基本测试数据，并用于风化壳中稀土元素地球化学研究、稀土储量计算、浸矿方式选择等等；提出酸性盐可交换离子态稀土的浸取方法和工艺流程、优化离子型稀土高效低成本原地浸取技术，为离子型稀土的高效绿色提取奠定科学基础。

稀土在风化壳中三维空间的分布和分异特征是离子吸附型稀土矿床历经几百万年风化迁移的结果，也是体现矿床内资源分布和液流方向并可用于稀土高效绿色提取的重要信息。本研究对8个代表性原矿和3个尾矿的30多个采样井内不同深度的近200个矿样进行了筛分和区分浸取，测定了16个稀土元素和10余种杂质离子的含量,与采样位置和粒级相关联，研究了稀土在三维空间的分布以及在垂直和水平方向及粗细颗粒之间的分异规律；证明轻重稀土比值在垂直方向的分异并非都是随深度增加重稀土含量增加，而是与稀土总量分布一样呈峰值变化，只是其峰值要相对滞后1-3米距离，且规律性更好。稀土分异方向与风化壳类型相关，在原积型和坡积型风化壳中，重稀土的分异方向相反。稀土分异也并不总是显示为钆断效应，其分界元素可在钐铕钆铽镝之间移动；据此，确定了基于稀土含量和分异特征来计算资源量和确定风化壳中水流方向的生产勘探方法，并用于指导离子吸附型稀土原地浸出技术规范的制定，获国家稀土标准委员会优秀奖；研究了原地浸出稀土尾矿中残留稀土和氨氮的分布特征，并用于风化壳矿层结构和水流方向的判定。提出了进一步提高原地浸出效率的方法，工业生产证明稀土收率提高了近20%；研究了稀土在不同粒级粘土矿物上的吸附特征及其迁移能力，证明了稀土从粗颗粒向细颗粒的迁移现象；测定了吸附和解吸过程的热力学和动力学参数，确定了各种电解质溶液浸取稀土后粘土矿物的zeta电位与浸取率之间的相关性。结合矿物粒子在浸取后水浸洗过程的zeta电位变化和阴阳离子行为，用双电层模型和水化理论全面解释了不同电解质对稀土浸出能力的次序，提出了新的浸取机理，讨论了不同电解质浸矿对环境的影响。利用粗细颗粒黏土矿物和胶体粒子对稀土的吸附差异，提出了分别用粗细颗粒黏土来回收稀土和提高难浸稀土提取效率的多套工艺方法，并在矿山得到应用。研究结果对于离子吸附型稀土的高效绿色开采具有非常重要的意义。出版专著1部，申请发明专利10项，发表论文3篇。