磁流体萃取剂的制备及其固定床模式富集低浓度稀土的应用基础研究

The effluent of low-concentration rare earth (RE) discharged from mines and separation industries causes serious waste. Therefore, these valuable resources must be recovered and reused in order to meet increasingly price growth of RE. However, there are some disadvantages for separating and purifying low-concentration RE by conventional methods included solvent extraction and fixed-bed adsorption. The focus of this project is a novel, simple and rapid model of extraction process. The original so-called "magnetic-fluids fixed bed" (MFFB), which bridges solvent extraction and fixed-bed adsorption by the theory of the high gradient magnetic separation, has been explained. The MFFB integrates the advantages of the two above mentioned classical extraction methods and overcomes their drawbacks. In the high gradient magnetic separator filled with ferromagnetic steel wires, the magnetic fluid extractant are immobilized well-distributed as stationary phase in form of liquid-droplet on the surface of wires under non-homogeneous magnetic field. The low-concentration RE ions solved in aqueous solution, as mobile phase, flow through controlled-porosity high gradient magnetic separator and are extracted by magnetic extractant. This method is similar to fixed-bed adsorption in form, but its extraction mechanism is solvent extraction because RE ions are extracted by liquid magnetic fluid extractant. On the basis of previous works, the RE ions are selected as object in our research. The plans of this project are to establish the theoretical model of extraction process, and investigate the effects of various factors on the extraction efficiency of magnetic fluid extractant in detail. The purpose of this project is to verify the feasibility of this method by the experiments and explore a new separation process to be suitable for extraction of low concentration RE ions from aqueous solution.

稀土矿山和稀土分离厂家排放的大量低浓度稀土废水，不仅浪费了宝贵的资源，而且污染环境，急需回收和治理。 针对液-液溶剂萃取、固-液固定床吸附技术在回收低浓度稀土离子废液过程中存在的问题，本项目将溶剂萃取和固定床两种分离模式的优点集于一体，首先制备了一种含四氧化三铁的磁流体萃取剂，并结合高梯度磁分离理论提出了一种全新的集成创新分离模式--磁流体固定床萃取分离。该方法将磁流体萃取剂以液滴的形式固定在分离柱内的金属丝表面，构建了一个磁流体萃取剂液滴在分离柱内均匀分布、且具有一定孔隙率的磁性流体固定床。该方法在分离形式上类似于固定床，但其"吸附剂"是被高梯度磁场控制的磁性流体萃取剂液滴，而非固体颗粒，其分离机理与液-液萃取类似。 本申请人将博士期间研究内容与目前工作领域相结合，以低浓度稀土离子溶液为研究对象，拟系统开展磁流体萃取剂制备和应用的基础研究，为工业化应用解决关键性的科学问题。

针对液-液溶剂萃取、固-液固定床吸附分离技术在回收处理稀土离子废液过程中存在的问题，本课题将溶剂萃取和固定床两种分离模式的优点集成于一体，同时克服了两者各自的缺点，制备了一种磁性流体萃取剂并提出了一个全新的集成创新分离模式——磁性流体固定床萃取分离方法。.首先制备了含萃取剂的煤油基磁性流体，并对其进行了表征和性能分析，比饱和磁化强度达12.85 emu/g，具有超顺磁性，物化性能稳定；设计与构建了用于连续萃取分离低浓度稀土离子的磁性流体固定床的实验装置，针对其特点推导出了磁性流体萃取剂在高梯度磁性分离器中分布状态的数学模型，得出了磁性流体萃取剂在金属丝两侧的聚集半径、轮廓面积和分离器中孔隙率的计算公式，模拟出了磁性流体萃取剂在分离器内部的空间分布状态，以及由其决定的孔隙空间分布状态。结果显示：聚集半径rBa与磁性颗粒磁化系数χp、背景磁场强度H0正相关，而与填充材料丝半径a反相关，可以通过改变这些参数来调整最佳聚积半径和分离器中孔隙率的大小，在固定床内磁流体萃取剂的填充率为28%，固定床内部孔隙率为66 %。.研究了磁性流体固定床萃取分离低浓度稀土离子溶液的工艺流程，分别考查了填充材料的类型和排列方式、萃取剂含量、pH值、温度、起始溶液浓度、流动相流速等因素对萃取单一La(III)离子和含稀土的复杂离子模拟体系的影响，得出了实验最佳条件。在实验温度为20 oC时，萃取La(III)离子的在pH=1、P204浓度为40%时萃取效果较为理想，流动相流速越低、被萃溶液浓度浓度越高萃取效果越好，磁流体萃取剂对稀土的平均萃取率为96 %。通过反萃对比实验，0.25 mol/L的盐酸溶液是负载La(III) 的磁流体萃取剂理想的反萃溶液，反萃率为99 %，总收率大于95 %。.该方法不但实现了溶剂萃取的连续进行，而且萃取持久性很好，对于贵（重）金属资源节约利用和环境污染治理具有重要的科学意义和应用价值。