【作者】 王良士；

【导师】 黄小卫；

【作者基本信息】 北京有色金属研究总院 ， 有色金属冶金， 2014， 博士

【摘要】 氟碳铈矿是世界上储量最大的稀土矿物,也是目前开采量最大的稀土矿产资源,全球约70%的稀土产自氟碳铈矿。氟碳铈精矿中含有8-10wt%氟以及0.2-0.3wt%的放射性元素钍,针对目前氟碳铈矿冶炼分离过程存在伴生资源钍、氟浪费与环境污染问题,本文开展了复杂硫酸稀土体系中HEH(EHP)(P507)萃取分离铈、钍、氟新技术应用基础研究。探明了酸性磷类萃取剂HEH(EHP)对钍(Ⅳ)和氟(Ⅰ)元素的萃取机理及平衡规律；配位洗氟过程中氟(Ⅰ)、铈(Ⅳ)和钍(Ⅳ)的分布规律,以及H2O2-HCl还原反萃铈(Ⅳ)与H2SO4反萃钍(Ⅳ)过程；指导完善了氟碳铈矿处理过程中综合回收钍、氟的绿色冶炼分离工艺,并进行了工程化试验研究。以氟碳铈矿氧化焙烧-硫酸浸出得到的含氟、钍、铈硫酸稀土溶液为原料,采用HEH(EHP)萃取分离回收铈、氟和钍。萃取过程中F(Ⅰ)分别与Ce(IV)、Th(IV)形成[CeFx]4-x、[ThFx]4-x配合物,更易于被HEH(EHP)萃取进入有机相中,从而实现与RE(Ⅲ)的分离；负载有机相中的F(Ⅰ)采用Al(Ⅲ)配位洗涤使其进入水相,并以冰晶石产品形式回收；负载有机相再采用H2O2-HCl还原反萃回收Ce(Ⅳ),最后采用硫酸反萃回收Th(Ⅳ),获得纯度为99.95%的CeO2产品以及纯度为99.5%的ThO2产品,避免了危废物氟、钍排放造成的环境污染问题,实现了伴生资源的综合利用。氟碳铈矿氧化焙烧-硫酸浸取液经HEH(EHP)萃取分离回收铈、氟和钍后,萃余液三价稀土硫酸溶液经转型为氯化稀土后进行分离提纯。由于稀土离子价态相同以及相近的离子半径,其化学性质相近,不同稀土离子间分离系数极小,导致稀土元素间分离难度极大,是目前最难分离元素之一,仅次于同位素间的分离。目前稀土分离提纯主要采用酸性萃取剂进行萃取分离,而传统工艺均须采用氨水或碳酸氢铵等无机碱对萃取剂进行皂化处理,以提高有机相中稀土负载量,该过程成本高、污染重。针对课题组提出的非皂化萃取分离稀土新技术,本文开展了非皂化萃取分离稀土元素过程研究,探明了HEH(EHP)、Cyanex272及其混合萃取剂在盐酸介质中对三价稀土元素的萃取机理及协同效应,确定协萃配合物的组成与结构；揭示了稀土浓度梯度控制以及碳酸稀土、钙镁碱性化合物等调节萃取水相平衡酸度的非皂化萃取分离过程,掌握了不同非皂化萃取分离体系萃取稀土离子的行为规律；指导并完善了HEH(EHP)-HCl体系稀土浓度梯度控制技术、萃取过程水相平衡酸度调控技术,为稀土非皂化萃取分离提纯工艺提供理论依据与技术指导。并在江苏国盛稀土公司利用稀土浓度梯度及平衡酸度调控技术,进行了盐酸体系中采用不皂化的HEH(EHP)进行了Gd/Tb分离的工程化试验研究,替代了传统的氨皂化萃取分离工艺,从源头消除氨氮废水污染,并大幅度降低了生产成本,实现了稀土绿色分离提纯。更多还原

【Abstract】 Bastnaesite is the main type of rare earth mining in the world. Output from bastnaesite typically contains0.2-0.3wt%thorium and8-10wt%fluorine in addition to the rare earth. During the common process of bastnasite treatment, however, some environmental issues still remains. One is the discharge of fluorine and radioactive thorium via waste liquid or waste solid. The loss of fluorine from the bastnaesite damages the economy of the process and, more seriously, the environment. Hence, discovering a method to efficiently recover cerium, thorium, and fluorine from bastnaesite is a critical issue in rare earths metallurgy. A new eco-friendly process for the separation and the recovery of thorium and fluorine from bastnaesite treatment was developed and put into industrial application. Solvent extraction of Ce(IV), Th(IV) and F(I) using HEH(EHP)(P507) from a sulfuric acid medium is studied by investigating extraction dependence, with the extraction mechanism determined using slope analysis. The elements distribution were studied during the coordination scrubbing of F(I), the reductively stripping of Ce(IV) and Th(IV) stripping. The new, clean process consists of oxidation roasting, leaching with sulfuric acid, and then recovering the rare earths, fluorine, and thorium using HEH(EHP), and prevents pollution caused by the dumping of thorium and fluorine as hazardous industrial wastes. After oxidation, virtually all RE(III), Ce(IV), Th(IV), and F(I) can be leached out with sulfuric acid. The F(I) coordinates with Ce(IV) and Th(IV) to form [CeFx]4-x and [ThFx]4-x complexes respectively, which can be easily extracted into an organic phase with HEH(EHP) and separated from RE(III) for the negligible extraction of RE(III). The F(I) loaded into the organic phase was scrubbed using Al(III) as the coordination reagent, and recovered as cryolite. After the coordination scrubbing of F(I), the Ce(IV) was reductively stripped using H2O2and HCl while the Th(IV) remained in the organic phase, then recovered as CeO2with a purity of99.95%. In the final step, the Th(IV) was stripped with H2SO4and recovered as ThO2with a purity of99.5%.Normally, the separation factors for different rare earth ions show minimal differences owing to their similar valence and ionic radii. However, this similarity in chemical properties generally makes it difficult to separate and purify individual metals from lanthanides, and the separation of rare earths is perhaps the most difficult task in analytical chemistry. Solvent extraction processes have been well established and have been widely used in industry, and in these processes organophosphorus acids are commonly used as the extractants. The extraction mechanism of rare earths by the organophosphorus acids can be expressed as ions exchange process with hydrogen ion. Thus, conventional acidic extractants, such as HEH(EHP) used widely in rare earth hydrometallurgy, always need to be saponified by NH3H2O, NaOH, or Ca(OH)2to facilitate the cation exchange of rare earths. However, this method undoubtedly results in waste water containing NH4+, Ca2+and Na+, which causes discharge of ammonium nitrogen pollutants and increasing salt concentration. A cleaner extraction process is always more desirable to reduce environmental pollution generated by industry, and for rare earth production it is necessary to look for an appropriate non-saponification separation method to replace the existing system. A new environmentally friendly process for rare earth separation was developed and put into industrial application. A novel ideal for rare earth extraction and separation in hydrochloric acid medium with the mixture of HEH(EHP) and Cyanex272which does not need to be saponified with ammonium was put forward. Extraction mechanism and the behavior of RE(Ⅲ) in the systems were studied. A technique for controlling equilibrium acidity, RE concentration gradient and synergistic extraction achieves ammonia-free emissions during rare earth separation while obtaining an organic phase with high rare earth loading. A pilot test separating Gd and Tb in a HEH(EHP)-HCl system is conducted using the proposed equilibrium acidity control technology, and without saponification, to verify the process and show that the method obtains ammonia-free emissions using an industrial separation process.更多还原