基于液液萃取过程优化的高镁锂比盐湖卤水提锂的研究

Lithium is known as the promoting world process meta，and its compounds are widely used in various industrial fields, and the demand is increasing in recent years. The extraction of lithium from salt lake brine has attracted more and more attention, lithium in salt lake brine reserves. Salt lake brine in China with the characteristics of high Mg/Li ratio, multiple components at low temperature and atmosphere, and the current lack of mature industrial production methods need to be solved. It is proposed that lithium could be recovered with a special solvent extraction method with high efficiency and selectivity. On the basis of the fundamental theory, the main researches including: (1) according to the molecular structure and interact force between the extractant and lithium ion, the optimal solvent components and the extraction mechanism for salt lake brine with high Mg/Li ratio are studied to improve the lithium extraction capacity and its selectivity. (2) on the basis of borate anion buffering performance in the salt lake brine, the synergistic extraction effect for lithium-ion was studied to realize the effective use of the complex anion in brine and its improvement on lithium extraction process. (3) according to the properties of metal organic compounds, the extraction properties at equilibrium are investigated systematically to obtain the structure-activity relationships for the multi-component, high concentrations of electrolyte solution LLE system. The project focus on three aspects researches for recover lithium ion from salt lake brine with high Mg/Li ratio by solvent extraction. They are the properties of unconventional extraction system, the influence of the anion, and thermodynamic properties. And it can provide a theoretical foundation and technical support for industrial application of lithium recovery from salt lake brine.

针对目前锂资源的国家发展重大需求以及高镁锂比盐湖卤水提锂的技术难题，提出采用溶剂萃取法进行高效、高选择性提取锂的技术。青海盐湖卤水体系，组成复杂，并具有低温低压的特点。从分子结构及作用力出发，研究非常规条件下高Mg/Li比盐湖卤水萃取分离锂的规律性能，获得对于锂离子具有高效性、高选择性、高经济性的萃取剂组成；依据盐湖水盐体系中硼酸根离子的酸碱缓冲性能，开展杂阴离子协同萃取锂离子的性能及机理研究，实现卤水中杂阴离子的有效利用及其对锂萃取过程强化的调控。从金属有机化合物基本特性出发，研究高Mg/Li比盐湖卤水高效萃取分离锂的机理及规律，获得多组分、电解质溶液体系液液平衡及构效关系。本项目通过非常规条件、杂阴离子的影响及其平衡规律的热力学规律等三个方面的研究工作，可为实现高镁锂比盐湖卤水提锂工业化应用提供坚实的理论基础及技术保障。

我国锂资源相对匮乏，高水平从盐湖提锂技术是国家重大战略需求。青海盐湖卤水体系组成复杂，具有高Mg/Li比的特性，是国际盐湖提锂技术的难点。本项目针对青海盐湖的组成特点，探索溶剂萃取提锂技术的科学原理，研究高Mg/Li比盐湖卤水萃取分离锂的分离规律，获得对于锂元素具有高选择性的萃取剂组成。项目针对“高镁锂比盐湖卤水提锂体系萃取平衡规律与模型化”和“杂阴离子对Li+的协同萃取效应”两个关键科学问题开展研究工作，研究内容主要涉及：高Mg/Li比盐湖卤水萃取分离锂的性能，杂阴离子协同萃取锂离子的性能及机理，盐湖卤水高效萃取分离锂的平衡规律，以及盐湖老卤萃取提锂的工艺研究。研究工作建立了基于离子交换的萃取机理模型用来描述含有NaFeCl4和HFeCl4的再生有机相与模拟卤水MgCl2 + LiCl的萃取平衡，涉及Li+、Mg2+与有机相中Na+、H+的交换反应。在平衡数据的基础上拟合出了表观反应平衡常数。发现察尔汗盐湖老卤中的硼元素以B(OH)4-的形式存在，B(OH)4-能够中和有机相中的H+从而使更多的Li+和Mg2+以离子交换的形式进入有机相。在离子交换机理和B(OH)4-与H+中和反应的基础上成功预测了真实卤水的萃取平衡性质。针对察尔汗盐湖老卤优化了工艺条件，发现铁锂摩尔比为2时，40% TBP/MIBK（体积分数）具有最佳的萃锂能力。在洗涤段采用NaCl + LiCl替代HCl + LiCl显著降低了LiCl浓度，相比为10，维持有机相中的Li+不损失所需的LiCl浓度小于0.5 mol/L，同时Mg2+的洗脱率高达99%。在反萃段采用NaCl + HCl作为反萃剂，HCl浓度低至1 mol/L时仍能获得较高的Li+反萃率，Li+的反萃率达65.4%。采用十级混合澄清槽进行了从察尔汗盐湖老卤中提取锂离子的工艺试验， Li+的萃取率保持在99%左右，Mg2+的洗脱率基本高于90%，Li+的反萃率接近100%，再生段有机相Fe的损失率小于0.16%。项目执行期间共发表SCI论文2篇，项目培养博士研究生3人，硕士研究生1人。