原地浸矿后离子型稀土矿体微结构力学特性弱化机制研究

After the execution of mandatory elimination and prohibition of heap leaching/pond leaching in China, in-situ leaching has become the only high-efficiency green technique for exploitation of ion-absorbed rare earth mines. However, the endurance of long-term erosive damages will lead to continuous changes of micros-morphology, which will induce severe weakening of certain mechanical properties in ion-absorbed rare earth ore bodies. The long-term weakening of mechanical properties is a key internal cause for landslide of rare-earth mines. The mechanisms about the changes of physical and mechanical properties and the changing rules of microstructure in common soils have been extensively studied. However, the weakening mechanism of micromechanics properties of ion-absorbed rare earth ore bodies after in-situ leaching has been rarely reported. In this study, we first investigate the relations of physical, chemical and mechanical changes in ion-absorbed rare earth ore bodies after in-situ leaching. On this basis, qualitative characterization analysis methods of micros-morphology in soil micromechanics were introduced. Then the changes of micros-morphology, chemical properties and physical-mechanical properties were quantitatively compared. After that, information fusion analysis methods was used to build a multi-property relational model for ion-absorbed rare earth ore bodies after in-situ leaching. This model helps to reveals the weakening mechanism of micromechanics properties of ion-absorbed rare earth ore bodies after in-situ leaching. Therefore, this study provides a scientific basis for prevention and control of landslips in ion-absorbed rare earth mines after in-situ leaching.

在我国执行强制淘汰制度，禁止采用堆浸、池浸工艺后，原地浸矿法成为了现有离子型稀土矿山唯一的高效绿色开采技术。离子型稀土矿体由于受到浸矿液的长期侵蚀损伤作用，致使其微结构形态不断发生变化，从而导致某些力学特性严重弱化。这些力学特性的长期弱化成为诱发稀土矿山滑坡的关键性内因。国内外文献资料表明，常见土体微观结构的变化规律及物理力学特性变化机制已有大量研究成果，但有关原地浸矿后离子型稀土矿体物理力学特性改变尤其是微结构力学特性弱化的研究鲜见报道。本项目拟从原地浸矿后离子型稀土矿体物理、化学、力学变化的关联性入手，引入土体微结构力学中微结构形态的量化表征分析手段，通过对微结构形态、化学属性和物理力学性质的变化特征进行比对，采用数据融合分析方法建立原地浸矿后离子型稀土矿体多种性质变化关联性模型，揭示原地浸矿后离子型稀土矿体微结构力学特性的弱化机制，为原地浸矿后稀土矿山滑坡防治提供科学依据。

原地浸矿过程中稀土矿体长期处于浸矿液作用下，其微结构形态将呈现出几何-物理-化学模式下的“三相复合演化”，从而弱化其物理力学性质甚至引发滑坡。本项目分析了离子型稀土矿体在浸矿前后微结构形态、化学属性和物理力学性质层面上各种变化特征的量化信息，建立了离子型稀土矿体的细观散体力学平面本构关系。重点分析了浸矿后离子型稀土颗粒破碎过程中粒径分布的分形行为和干湿循环作用下浸矿后离子型稀土力学特性，补充神经网络和正交分析等手段初步建立了原地浸矿离子型稀土矿体微结构力学强度关联性预测模型，进而揭示原地浸矿前后离子型稀土矿体微结构力学特征弱化机制。结果表明：浸矿后矿体中的主要长石类矿物成分被溶蚀，解理缝扩大，次生孔隙出现，微结构形态发生显著变化。部分大颗粒矿物只剩下残余片状，生成的“针棒状”高岭石吸附在长石矿类物表面。表面带负电荷的高岭石吸引水化离子和水分子形成结合水膜使得颗粒间的距离增大，接触区域减小，从而导致颗粒间容易发生错动，粒间物理力学作用弱化。浸矿加速了矿体中原生矿物的风化，生成的次生矿物具有高度分散性，破坏了原有颗粒结构并使得颗粒间孔隙增大，导致某一条带域颗粒间抵抗滑动的能力减弱，从而造成整体抗剪强度的降低。不同初始分布和颗粒大小的稀土试样颗粒均趋向于自相似性的分形分布，这一过程与颗粒破碎量有关，颗粒破碎增长可通过增大的分形维数来描述。由离子型稀土矿体的细观散体力学平面本构模型可知，孔隙比和配位数对其体积模量与剪切模量都有着重要的影响。在干湿循环条件下，浸矿后稀土试样的剪胀趋势由围压大小和干湿循环次数两个因素决定。其强度随着干湿循环次数的增加而减小，且第一次干湿循环后变化幅度最大。相较于高围压，在低围压下抗剪强度弱化率更大。按离子型稀土矿体主要矿物组分建立的正交试验协同BP神经网络离子型稀土矿体相似材料强度关联性预测模型对强度指标c和φ的最大相对误差分别为4.33%和0.84%。