Reliable information about the micro-processes during filtration and dewatering of filter cakes allows more accurate statements about process development and design in any industrial application with solid-liquid separation units. Distributed particle properties such as shape, size, and material influence the porous network structure with considerable local fluctuations in vertical and horizontal alignment in the cake forming apparatus. The present work relates to a wide range of particle sizes and particle shapes and presents their effects on integral, but preferably local, structural parameters of cake-forming filtration. Current models for the relationship between particle properties and resulting porous structure remain inaccurate. Therefore, the central question focus on the model-based correlation between the obtained data and characteristic cake and process parameters. In combination with X-ray computed tomography and microscopy (ZEISS Xradia 510), data acquisition on the structural build-up of filter cakes is possible on a small scale (filter area 0.2 cm²) and a conventional laboratory scale (filter area 20 cm², VDI 2762 pressure nutsch). Thereby, the work focuses on structural parameters at the local level before, during, and after cake dewatering, such as porosity, coordination number, three-phase contact angle, characteristics of pores and isolated liquid regions, the liquid load of individual particles, tortuosity, and capillary length, and the corresponding spatial distributions. Seven different particle systems in the range of 20 and 500 µm, suspended in aqueous solutions with additives for contrast enhancement, served as the initial raw materials for the filter cake build-up. Image data processing from 16-bit greyscale images with a resolution of 2 to 4 µm/voxel edge length includes various operations from denoising filters and shape enhancement with two-stage segmentation to identify air, solid particles, and liquid phase, resulting in a machine learning-based automated approach. Subsequent modeling and correlation of measured parameters rely on experimentally verified quantities from mercury porosimetry, laser diffraction, dynamic image analysis, static and dynamic droplet contour analysis, as well as filtration and capillary pressure tests according to VDI guidelines. The tomography measurements provide microscopic information about the porous system, quantified using characteristic key parameters and distribution functions.

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  • X-ray tomography scan of partially dewatered filter cakeOpen Access Icon 

    Löwer, Erik (Technical University Bergakademie Freiberg - Institute of Mechanical Process Engineering and Mineral Processing, 2021)
    X-ray tomography image of a partially dewatered filter cake. The initial slurry contains Al2O3 particles suspended in a potassium iodide-glycerol solution. These were separated by cake-forming filtration followed by ...
  • X-ray tomography scan of partially dewatered filter cakeOpen Access Icon 

    Löwer, Erik (Technical University Bergakademie Freiberg - Institute of Mechanical Process Engineering and Mineral Processing, 2021)
    X-ray tomography image of a partially dewatered filter cake. The initial slurry contains Al2O3 particles suspended in a potassium iodide-glycerol solution, which were separated by cake-forming filtration with subsequent ...
  • High-resolved X-ray tomography scan of dewatered filter cakes and sessile dropletsOpen Access Icon 

    Löwer, Erik (Technical University Bergakademie Freiberg - Institute of Mechanical Process Engineering and Mineral Processing, 2021)
    X-ray tomography image of dewatered filter cakes at irreducible saturation. The initial slurry contains Al2O3 particles suspended in a potassium iodide-glycerol solution. These were separated by cake-forming filtration ...
  • X-ray tomography scans of filter cakes (feed slurry: variation in fraction of fines)Open Access Icon 

    Löwer, Erik (Technical University Bergakademie Freiberg - Institute of Mechanical Process Engineering and Mineral Processing, 2021)
    X-ray tomography scans of partially dewatered filter cakes with variation of fine particles within the feed slurry. The mixture composition varies by addition of fines by 0, 20, 30, 40, 50, 60 and 100 vol.-%. The initial ...
  • fully saturated and dewatered filter cakes at different resolutionsOpen Access Icon 

    Löwer, Erik (Technical University Bergakademie Freiberg - Institute of Mechanical Process Engineering and Mineral Processing, 2021)
    Appendix to Publications A to E with investigations of different particle systems (material, size and shape variation). X-ray tomography image of fully and partially dewatered filter cakes. The initial slurries contains ...
  • X-ray tomography scans of filter cakes (feed slurry: variation in solid volume fraction)Open Access Icon 

    Löwer, Erik (Technical University Bergakademie Freiberg - Institute of Mechanical Process Engineering and Mineral Processing, 2021)
    X-ray tomography measurements (Zeiss X-radia Versa 510) of in-situ and in a VDI pressure nutsch built filter cakes (Al2O3 crushed particles in 25 mmol/l KI brine with 24 m.-% glycerol). The filter cakes are measured ...