Project Details
Projekt
Formation of critical compounds in recycling slags - a study of the melt chemistry with MD simulations and of the solidified compounds in a micro preparation approach
Subject Area
Mechanical Process Engineering
Chemical and Thermal Process Engineering
Chemical and Thermal Process Engineering
Term
since 2021
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 470367641
The recovery of Li from slags emanating from the pyrometallurgical recycling of Li-ion batteries is an essential step toward a truly circular economy. The semi-crystalline slag consists mainly of the oxides of Ca, Si, Li as well as Mn, Al and Mg. Without Mn, Li can be directed into a major LiAlO2 phase by adding aluminium to the pyrometallurgical melt. LiAlO2 is easily recoverable in the downstream processes and can be regarded as an engineered artificial mineral (EnAM). However, if novel Mn-bearing cathode materials are introduced to the recycling, the formation of LiAlO2 is suppressed, and Li is dispersed over several other compounds. In the first part of the project, very promising alternatives to the lithium aluminate i.e. lithium manganates like Li2Mn(IV)O3, were identified. Depending on the Mn oxidation state and in the absence of Al, these can incorporate all the lithium in a single phase. Manganese is also incorporated into silicates, however in a different oxidation state. By studying quasi-amorphous slags, we found evidence for melt liquid-liquid separation and the separated phases having significantly different viscosities. The phase with the lower viscosity exhibited the higher Mn oxidation state. Our hypothesis derived from these observations is, that the manganese oxidation state is significantly governed by phase separation and viscosity. Both have a decisive influence on the permeability of oxygen and other redox active gases (e.g., CO). The local composition is also governed by phase separation, solid-liquid resulting in gradual concentration change in the melt and liquid-liquid in a sharp concentration difference. The concentration gradients can be treated as incremental volumes of homogeneous composition. Hence, in this project our objective is to understand the solidification processes including Mn valence manifestation from oxidic melts of the elements Li, Si, Ca as well as Mn, Al and Mg by describing molecular structure and viscosities considering sharp and continuous concentration gradients. We will synthesize slag analogues with different Mn oxidation states and predict viscosities using MD simulations. We will subject the slag melts to different temperature gradients and oxygen partial pressures and observe the influence on phase separation and Mn oxidation state. Viscosity, individual ion diffusivity and network breaking will be determined by MD simulations. Slag analogues and pure compounds will be prepared in small batches and with micro-synthesis from picoliter printing of incremental composition. Using material characterization, the predictions obtained from the MD simulations and the used parameters will be evaluated.
DFG Programme
Priority Programmes
