CIS - Networking doctoral candidates

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In order to advance work on interface-driven problems and support the launch of the Center, the Center of Interface Studies is equipped with three specifically placed networking doctoral students. They will conduct cross-institute research on pressing topics such as the development of resource technologies to reduce Germany's and Europe's dependence on critical raw materials and ensuring the storage of radioactive materials in repositories. The concrete topics are:

• Thin-film interferometry for resource processes
• Interfacial solution for prior-to-equilibrium rare-earth separator with magnetic-assisted solvent extraction
• Stochastic multiscale approaches for surface effects in heterogeneous mineral phases for transport modeling in nuclear waste repository research

Thin-film interferometry for resource processes

Froth flotation is a widely used technology for separating valuable materials and gangue by selectively attaching the particles to air bubbles. A critical aspect of this process is the rupture of liquid films. This process occurs during particle attachment to air bubbles, during bubble coalescence in the flotation apparatus and during film coalescence in the foam phase. Nevertheless, the dynamics of liquid films in particle-containing systems are not sufficiently understood. Thin-film interferometry is a versatile tool for investigating film dynamics.

In this project, on the one hand, the effects of heterogeneous surface properties on the formation of the three-phase contact line when particles adhere to bubbles will be investigated. On the other hand, the stability of liquid films in the presence of hydrophobic particles will be examined. The knowledge gained is used for modeling the flotation process and simulating multiphase flows. In addition, the relationships to film stability are required for efficient performance and control of the flotation process, e.g. for optimal dosing of reagents.

Interfacial solution for prior-to-equilibrium rare-earth separator with magnetic-assisted solvent extraction

Solvent extraction (SX) is a modern process for separating mixtures of trivalent rare earths, RE(III), which has been used since the 1960s. It is based on cation exchange at the interface between the organic and aqueous phases. The conventional SX has a non-ideal separation factor due to the similar chemical equilibrium constants of the different REs.

This project investigates a novel method to achieve a higher separation selectivity of RE(III) by applying a tailored magnetic field during solvent extraction and separating the phases before reaching the thermodynamic equilibrium state. The aim is to selectively enrich valuable and heavy RE(III) with high magnetic susceptibility, e.g. Dy(III), in the presence of light rare earths, Pr(III) and Nd(III), using solutomagnetic convection induced by the Kelvin force. This includes the development, construction and proof of concept in a multiphase interfacial reactor. The topic has direct application with regard to the increasingly important problem of recycling rare earth magnets at the end of life.

Stochastic multiscale approaches for surface effects in heterogeneous mineral phases for transport modeling in nuclear waste repository research

In research on nuclear waste repository, relevant aspects of heterogeneities over several spatial scales, solution equilibria and mineral transformations have so far been insufficiently considered due to a lack of suitable methods. It is also essential in resources deposit research to determine which rocks (including their heterogeneity) have a good retention capacity for critical metal-loaded fluids carrying raw materials. As chemical analogs are often used to model the mobility of radionuclides, the element ensembles that are relevant in both subject areas are similar, e.g. lanthanides (rare earths), barium, nickel and cobalt.

In this project, methods for quantifying the effects of micro-, meso- and macrostructures of the earth and their use in models of the geological barrier, in particular for reactive transport along surfaces, are to be developed. For this purpose, stochastic models of the relevant geological structures will be adapted to data for real structures at repositories at the three scales. These scales address on the one hand the level of pore spaces and pathways in the micrometer range, on the other hand the range of mineral grains down to the millimeter range, and finally the transition to the continuum scale down to the decimeter range, which is still experimentally accessible for validation. For this purpose, methods and models from stochastic geometry, multiple point statistics (MPS) and geostatistics are used for the respective scale. An improved understanding of the processes and principles benefits the assessment of geological barriers of deep geological repositories for radioactive waste or of the metalogenesis of deposits to be explored being relevant both for exploration and mining.