镁盐体系稀土浸出液Mg/Ca联合－分步沉淀过程调控机理研究

At present, there have a serious ammonia-nitrogen problem in the rare earth leaching and enriching process of the ion-adsorption type rare earth ore. In the project, the rare leaching liquor obtained with magnesium compound leaching agent was used as research object, and the "Mg/Ca united-step precipitation" enrichment thoughts without ammonia was innovatively proposed. the researches on the dissolution behavior of calcium sulfate in the MgSO4-CaSO4-RE2(SO4)3-H2O complex system, the regulation mechanism of rare earth hydrate crystal form and the control of sulfate introduction process for the rare earth hydrate were all systematic developed, in order to solve the key problems in the Mg/Ca united-step precipitation process, namely the crystal form control of rare earth precipitation in the Mg-Ca-RE system and the purity control of rare earth concentrate. Finally, the theoretical basis for the "Mg/Ca united-step precipitation" technique of the rare earth leaching liquor in magnesium salt system was preliminary established. Meanwhile, the study in this project could cooperate with the works on non-ammonia leaching process during the doctor period, and realize the green leaching and enriching process of ion-adsorption type rare earth ore.

目前，离子吸附型稀土矿中稀土的浸取、富集过程存在较严重的氨氮问题。本项目以镁盐复合浸取剂浸取离子吸附型稀土矿获得的稀土浸出液为研究对象，提出“Mg/Ca联合－分步沉淀”无氨富集新思路。通过系统的开展MgSO4-CaSO4-RE2(SO4)3-H2O复杂体系中硫酸钙溶解行为研究、氢氧化稀土晶型调控机制研究和氢氧化稀土中硫酸根引入过程控制研究，重点解决Mg/Ca联合－分步沉淀过程中Mg-Ca-RE沉淀体系稀土沉淀晶型调控及离子型稀土精矿纯度控制的关键问题，初步建立镁盐体系稀土浸出液“Mg/Ca联合－分步沉淀”技术的理论基础。同时与申请人博士期间的无氨浸取过程研究相配合衔接，最终实现离子吸附型稀土矿的无氨绿色提取富集。

针对离子吸附型稀土矿浸取、富集过程中存在的氨氮问题，申请人在延续博士期间关于镁盐无氨浸取的基础上，提出了镁盐浸取-钙镁碱性化合物联合分步沉淀富集技术，可实现钙镁的有效循环，最终解决离子吸附型稀土矿浸取、富集全过程的氨氮问题。然而，在钙镁碱性化合物沉淀稀土浸出液的过程中存在沉淀产物过滤性能差、硫酸根含量高的问题，为此，本项目首先绘制了MgSO4-CaSO4-RE2(SO4)3-H2O等复杂体系下硫酸钙溶解度相图，并通过钙镁碱性化合物沉淀实验研究，明确了精矿中CaO和SO3含量与硫酸钙溶解行为无直接关系，确定了镁盐体系稀土浸出液氧化钙单独沉淀工艺。然后通过沉淀产物的沉淀结晶过程的研究，明晰了不同沉淀条件下沉淀产物成核和生长的规律，从而确定了提高沉淀产物沉降性能的操作窗口。最终，通过热力学计算和实验验证，揭示了沉淀产物中硫酸根引入机理，确定了氧化钙沉淀过程控制条件，开发了助剂搅洗除硫和配位沉淀除硫的工艺。此外还对助剂的加入对浸取过程中的影响进行了研究，发现了离子相配位强化浸取和胶态相还原浸取的事实，进而开发了离子吸附型稀土矿高效浸取的技术。本项目的研究解决了沉淀产物晶型调控及稀土精矿纯度控制的问题，并通过技术集成提出了两个离子吸附型稀土矿绿色高效提取新工艺，为离子吸附型稀土矿中稀土高效绿色提取提供理论依据和技术支持。