Magnetic separation
Our research interest is in fluid dynamics, with a particular emphasis on the effects of electric and magnetic fields in multiphase systems, especially at and around interfaces across various scales. Currently, we are developing separation techniques for rare-earth ions using magnetic fields and innovative experimental tools to analyze the complex transport processes involved. We also start to work with innovative aeration systems towards on-demand O2 supply in microbial process stage. Additionally, we embrace the chance to incorporate machine learning empowered approaches for active flow control and image recognition/ segregation.
Motivation
The rare-earth (RE) elements constitute critical raw materials that play a critical role in the world's ambitious energy and climate goals. Their current annual production is 350,000 ton and is foreseen to boost. However, the REs separation relies on their marginal chemical affinity to specific ligand and their beneficiation generates significant environmental footprint. Boosting current attention are coming about trying to identify innovative methods to address the challenging task for rare-earth separation. Our group is expertised on fluid dynamics prospective of rare-earth separation research. Working together with f-element chemists, we aim to push forward the frontier of rare-earth separation technique and secure a scalable separation method of practical use. This attempt facilitates regions like EU with no regional primary resource production to supplement secondary resources, from their end-of-life product, to the supply chain. This market is gigantic (2021 worth of 236 Million US dollar), unexplored (< 1% recycling rate at present) and expands rapidly (300% increase predicted for 2030).
- Rare-earth magnetic separation & magnetic assisted solvent extraction
- Interferometric measurement and correlation of chemical reaction kinetics law
- On-demand aeration O2 and their input in microbial process stage
- Emulsion system, specifically on dispersion and demulsification solution
In-house developed techniques:
- versatile Mach-Zehnder interferometers
- thermal management system for non-/ isothermal system visualization
- FVM/ FEM hybrid numerical approach for multi-scale and multi-physical transport processes and pattern formation
- Numerical and Experimental iteration coupling high automation degree
- AI/ Model based Data minining
Commericially supplied techniques:
- stero-uPIV
- Shimadzu-2700 UV-Vis Spectrometer
- FT-IR
- ICP-MS Nexion 1100
- CHI 660E electrochemical workstation
- Long-distance microscope
Results
Despite the relevance of the Kelvin force in many physical and electrochemical systems involving magnetic species, the underlying convective flows are scarcely understood. For that purpose, we simulate a simplified rare-earth system in the presence of competing Kelvin and gravity forces. The results are experimentally validated using interferometry and microscopic particle image velocimetry. Based on the excellent agreement of numerical and experimental results, the underlying mechanism of ions magnetic separation can be explained with solutomagnetic convective mechanism. This work paves the way for a prospective application in rare-earth beneficiation contributing to CeRI2.
A novel protocol is developed to enhance and resolve the magnetic term of the Kelvin force. For that purpose, an assembly of partition magnets is created where the individual magnets function in the first quadrant of their magnetic hysteresis loop. The mutual reinforcement is quantified in a particle magnetic levitation system. Modeling the energy density field makes it possible to quantify the equilibrium position of the particle cloud at rest, which is attained via magnetophoresis of the particles regardless of their initial position. This enables the magnetic trapping and manipulation of particles with small hydrodynamic diameters. Optically tracking the transient magnetophoresis enables a high-fidelity, sub-mm resolution of magnetic pressure graident which is further used to quantify the magnetic susceptibility of Ho(III), Tb(III), Er(III), and Gd(III).
A novel approach for obtaining the forward rate law of a rare earth (RE) solvent extraction system is reported in this work. An immiscible water-oil system with a Dy(III) laden aqueous- and a PC88A laden organic- phase with volume ratio 1:1 is studied with total volume of about 0.68 mL. The two phases are poured into a Hele-Shaw cell with a gap width of 1 mm. Hence, a stratified interface formed at the gravitational-perpendicular plane. The Dy(III) concentration boundary layer, as a result of cation exchange, is monitored real time in the aqueous phase by means of a monochromatic laser-based Mach-Zehnder interferometer. With direct access to the mass concentration at the interface, after spatial integration, an interface mass flux at the initial time is quantitatively resolved for varying Dy(III) and PC88A concentration. The system is found to be quasi-first order for Dy(III) and quasi-second order for dimeric PC88A. The method is genuinely applicable to a broad spectrum of reaction kinetics systems which are transparent or translucent with a minimum sample size, 2-3 orders less volume, required compared with conventional method using stirred cells, e.g. Lewis or Akufve apparatus.
On the nanoscale, iron oxides can be used for multiple applications ranging from medical treatment to biotechnology. We aimed to utilize the specific properties of these nanoparticles for new process concepts in flotation. The nanomaterial was used for model experiments on magnetic carrier flotation of microplastic particles, based on magnetically induced heteroagglomeration. We were able to demonstrate the magnetically induced aggregation of the nanoparticles which allows for new flotation strategies. Since the nanomaterial has zero remanent magnetization, the agglomeration is reversible which facilitates the process
Selected publications:
[1] Sun, F., Ortmann, K., Eckert, K., & Lei, Z. (2024). Interferometric Measurement of Forward Reaction Rate Order and Rate Constant of a Dy (III)-PC88A-HCl Solvent Extraction System. In Magnetic Microhydrodynamics: An Emerging Research Field (pp. 131-140). Cham: Springer International Publishing.
[2] Schwaminger, S. P., Schwarzenberger, K., Gatzemeier, J., Lei, Z., & Eckert, K. (2021). Magnetically induced aggregation of iron oxide nanoparticles for carrier flotation strategies. ACS Applied Materials & Interfaces, 13(17), 20830-20844.
[3] Lei, Z., Fritzsche, B., Salikhov, R., Schwarzenberger, K., Hellwig, O., & Eckert, K. (2022). Magnetic separation of rare-earth ions: property database and kelvin force distribution. The Journal of Physical Chemistry C, 126(4), 2226-2233.
[4] Lei, Z., Fritzsche, B., & Eckert, K. (2021). Magnetic separation of rare-earth ions: Transport processes and pattern formation. Physical Review Fluids, 6(2), L021901.
Patent portfolio:
[1] Messanordnungen und Verfahren zum Bestimmen einer magnetischen Gradientenkraft und deren Verteilung, DEUTSCHE Patent DE 10 2021 129 034.1 (2021) PCT/EP2022/080804 als europäische Patentanmeldung (EP) und in den USA (US).
[2] DEUTSCHE Patentanmeldung „Verfahren zur verbesserten, magnetisch unterstützten Abtrennung von Seltenen-Erden" DE 10 2023 122 650.9
[3] DEUTSCHE Patentanmeldung „Messanordnungen und Verfahren zum Bestimmen einer Grenzflächenspannung" DE 10 2024 110 779.0