稀土废料中有价元素火法-湿法联合回收过程的基础研究

Wasted new rare earth materials are important secondary resources of rare earth and other valuable metal elements extracting. The generally adopted method of hydrometallurgy has achieved an efficient recovery. However, it needs a large quantity of acid and alkali and has a long circuit as well as a low added value product. While, the method of pyrometallurgy has a short process and a relatively high added value product, but it cannot achieve the cooperate recover of valuable elements. Therefore, a new combined recycling method of hydrometallurgy and pyrometallurgy is proposed by the applicant. In this method, the high purity alloy and REO-SiO2-Al2O3 slag can be obtained by selective oxidation and melting separation, then rare earth oxides can be extracted through the decomposition-leaching-precipitation method. The basic research on rare earth metallurgy by new method will be carried out. By researching on the physical chemistry properties of the slag, the basic properties of the slag will be determined including melting temperature, viscosity, density and surface tension, and the composition of the slag system that produces good results of melting separation and obtains high rare earth oxide will be defined. Also the phase characteristics and the evolution law of the slag will be ascertained. By researching on the process of rare earth extract through slag- hydrometallurgy method, the basic chemical reaction of the decomposition process will be determined and the factors that influence the reaction will be clarified as well as its influence laws. Besides, its metallurgy principle will be revealed. The research of the project will provide theoretical support and scientific basis for the efficient and comprehensive recover of the valuable elements in rare earth waste.

稀土新材料废料是稀土及其它有价金属元素提取的二次资源，普遍采用的湿法回收方法回收率高，但酸碱使用量大、流程冗长、产品附加值低；火法回收方法产品附加值较高、流程短，但未实现有价元素的协同回收。项目申请人提出了火法－湿法联合回收的新方法：采用气体选择性氧化还原－渣金熔分法得到高纯合金和REO-SiO2-Al2O3熔渣，采用分解－浸出－沉淀方法从熔渣中提取稀土。项目拟开展新方法中稀土冶金的基础研究，通过熔渣物理化学性质研究，弄清熔渣的基础性质（熔化温度、粘度、表面张力、密度），确定渣金熔分效果优良且稀土氧化物含量高的渣系组成范围，探明熔渣的物相特征及其演变规律；通过熔渣湿法提取稀土过程的研究，确定分解过程的基本化学反应，弄清反应影响因素及其影响规律，揭示其冶金原理。本项目的研究将为稀土废料中有价元素高效综合回收提供理论支持和科学依据。

以La2O3-SiO2-Al2O3作为基础渣系，采用半球法研究了熔渣的熔化温度，采用旋转柱体法研究了熔渣的黏度。结果表明：3 种La2O3 含量(45%，50%，55%)下，SiO2/Al2O3 质量比约为2 时渣样的熔化温度与黏度最低；少量FeO、B2O3 和MnO 均可降低渣系的熔化温度与黏度，B2O3 的效果尤为显著，同时添加少量FeO 和B2O3 对降低渣系熔化温度与黏度有叠加效应。进一步研究优化的熔渣组成为：对于钕铁硼废料，60%REO-19.30%SiO2-9.70%Al2O3-7%FeO-4%B2O3；对于镍氢电池电极废料，55%REO-25.30%SiO2-12.70Al2O3-7%MnO。 .针对La2O3-SiO2-Al2O3-FeO-B2O3和La2O3-SiO2-Al2O3-MnO渣系，通过快速淬火实验并结合X射线衍射分析（XRD）、扫描电镜（SEM），研究了熔渣的物相特征及其演变规律研究。对于两类熔渣，凝固的熔渣后由稀土结晶相和玻璃体组成；冷却过程中析出的稀土相为六方晶系的铈磷灰石，La2Si2O7和La9.31(Si1.04O4)6O2，RE3+阳离子与SiO43-四面体形成链状结构；稀土析出相化学组成简单，Al、Fe、B、Mn等阳离子未进入结晶相；随着结晶温度降低，析出相不断长大，最后转变为粗壮的条状结晶。 .对于稀土废料直接还原—渣金熔分得到的REO-SiO2-Al2O3-FeO-B2O3和REO-SiO2-Al2O3-MnO两类熔渣，均可采用盐酸浸出法回收稀土。盐酸浸出过程中各组分完全分解，除SiO2分解为H2SiO3外，其它组分以离子形态进入水溶液；控制浸出液的PH值（3～4）可以沉降分离Fe(OH)3和H2SiO3，净化浸出液；可采用盐酸低温常压和高温高压两种浸出方法，两种浸出方法的动力学控速环节不同，高温高压浸出不但能够降低盐酸用量，还可以大大缩短浸出时间。典型熔渣57.58%REO-16.10%SiO2-8.00%Al2O3-6.04%FeO-4.20%B2O3的盐酸浸出结果：低温常压浸出过程，较佳条件为盐酸理论用量1.45倍、温度85℃、时间60min，稀土的浸出率为96.0%；高温高压浸出过程，较佳条件为盐酸理论用量1.05倍、温度110～120℃、时间30min，稀土的浸出率为98%。