China University of Science and Technology proposed a new unit operation of "ion rectification" to achieve the direct extraction of lithium from salt lake brine with high magnesium lithium ratio

Source: HKUST News Network


Recently, Professor Xu Tongwen's team from the University of Science and Technology of China has made important progress in the field of lithium extraction from high-magnesium lithium ratio salt lake brine. Inspired by the traditional multistage plate rectification mechanism and chromatography separation mechanism, in view of the separation problem of complex materials in the field of chemical special separation, the team creatively proposed a concept of "ion rectification", and was first applied to the extraction of lithium from high magnesium lithium ratio salt lake. The ion rectification technology greatly improves the separation efficiency of special materials, and makes lithium products with ultra-battery purity in one step from salt lake brine, which solves the technical problem of extracting lithium from high magnesium lithium compared with salt lake brine. At the same time, the technology also has wide applicability to salt lake brines with different solute systems, and is expected to achieve the fine screening of valuable substances in brine, seawater, minerals, such as potassium, rubidium, cesium, magnesium, boron, etc., to promote the high-value utilization of target materials. The research results are titled Ion- "distillation" for isolating lithium from lake brine, Published as a Letter in the Journal AIChE Journal (2022, e17710. DOI: 10.1002/ AI.17710), this column covers prospective and potentially significant work in the chemical industry.

Lithium is an important raw material for chemical energy storage lithium batteries, and lithium is an important means to solve the traditional energy crisis and promote the solution of the "double carbon" problem. China's salt lake brine has the characteristics of high magnesia-lithium ratio, and lithium magnesium efficiency separation is still a prominent problem in the process of lithium extraction from high magnesia-lithium ratio salt lake, which also directly leads to China's battery grade lithium products are still dependent on imports, and lithium extraction from salt lake has gradually become an important issue to ensure the safety of lithium resources in China.

In view of the separation of lithium and magnesium from salt lake brine with high magnesium to lithium ratio, the team based on the previous work accumulation, focused on the application frontier of chemical special separation, developed a new path, inspired the traditional plate rectification and chromatographic separation technology, and originally proposed the "ion rectification" lithium extraction technology from salt lake. The traditional electrodialysis system uses the negative/cationic selective membrane spacer arrangement, the two ion membranes form a membrane unit, the ion screening performance is limited by a single ion selective membrane. "Ion rectification" breaks the traditional arrangement of functional membranes inside the electrodialysis unit, and based on the principle of "same type and same side", multiple membranes of the same type are arranged in parallel and integrated in the electrodialysis unit. The design concept is shown in Figure 1. The quasi-separation of lithium ions from salt lake brines with high magnesia-lithium ratio is realized by using the multistage screening mechanism of special ions in stacked ion membranes and the amplification effect of ion selectivity. The function of each ion membrane in the ion rectification chamber can be regarded as the tray in the rectification tower. Lithium and magnesium ions migrate between the stacked ion selective membranes. Due to the difference in migration rate between lithium and magnesium ions in the ion membrane phase, the electric blowing separation of lithium and magnesium ions is realized under the drive of electric field force based on the chromatographic separation and chromatography mechanism.

FIG. 1 Design concept of ion rectification technology

The first to fourth stage ion rectification system was constructed, and the salt lake brines with high MG-lithium ratio (MG-lithium ratio > 35) in Dongtai, Qinghai were studied. The results show that the selectivity of lithium magnesium is increased step by step from 30 (primary) to 1104 (secondary), 3297 (tertiary) and 26177 (quaternary). The purity of lithium obtained by secondary and quaternary ion distillation is 99.69% and 99.98%, which exceeds the industrial grade and battery grade standards respectively. The final lithium carbonate and lithium phosphate products obtained from the brine of Jinel Salt Lake in Dongtai, Qinghai Province are shown in Figure 2. As a new chemical unit operation, the separation effect of ion distillation is significantly better than that of various advanced functional membrane materials and membrane separation processes reported in the current literature (as shown in Figure 3).

FIG. 2 Samples of lithium carbonate and lithium phosphate obtained by ion rectification

FIG. 3 Comparison between ion rectification technology and traditional membrane separation technology and advanced functional membrane materials

Ion rectification technology is helpful to solve the problems existing in the traditional membrane separation technology in the lithium extraction industry in the salt lake, and ensure the safety of lithium resources in China. At the same time, as a platform technology, ion distillation integrates the characteristic advantages of balanced separation (high selectivity) and rate separation process (low operating cost), which will provide effective solutions for special separation scenarios such as lithium isotope separation, rare earth separation, seawater purification, fine chemical separation, and biopharmaceutical, and help related process industry technology upgrading. Especially chemical special separation technology innovation. Related technologies have applied for invention patents (CN202110868560.9; CN202110868710.6; CN202110868737.5; CN202111026979.6; CN202110980248.9; CN202110980229.6;)

Associate Researcher Jiang Chenxiao and Postdoctoral researcher Chen Binglun from the University of Science and Technology of China are the co-first authors of the work, and Professor Xu Tongwen is the corresponding author. This work has been supported by the National key research and development Program of the Ministry of Science and Technology "Alkaline ion exchange membrane Preparation Technology and Application" project, the National Natural Science Foundation Youth Project, and the Anhui Province science and Technology major special project.

Full text links: https://aiche.onlinelibrary.wiley.com/doi/10.1002/aic.17710



(School of Chemistry and Materials Science, Department of Scientific Research)