Insight into filter cake structures using micro tomography: The dewatering equilibrium

Colloid mobilization and transport in response to freeze-thaw cycles: Insights into the heavy metal(loid)s migration at a smelting site

Smelting sites often exhibit significant heavy metal(loid)s (HMs) contamination in the soil and groundwater, which are inevitably subjected to environmental disturbances. However, there is limited information available regarding the migration behaviors of HMs in a disturbed scenario. Thus, this work explored the migration of HMs-bearing colloids in response to freeze-thaw treatments by laboratory simulation and pore-scale study. Ultrafiltration results of soil effluents revealed that 61.5 %, 47.6 %, 68.0 %, and 59.2 % of Zn, Cd, Pb, and As were present in colloidal phase, and co-transported during treatments. Nanoparticle tracking analysis (NTA) further confirmed that freeze-thaw cycles were conducive to the generation of colloidal particles and showed the heteroagglomeration among different particles. Pore-network model (PNM) was used to quantify the soil macropore characteristics (macropore diameter, macropore number, coordination number, and Euler value) after treatments. It is evident that freeze-thaw cycles induced the formation of larger macropores while simultaneously enhancing macropore connectivity, thereby establishing an optimal pathway for colloid migration. These findings underscored the importance of environmental disturbances as a trigger for the release and migration of HMs in the smelting site, offering valuable insights for controlling HMs pollution. ENVIRONMENTAL IMPLICATION: The contaminated site has been subjected to prolonged environmental disturbances, causing the exacerbation of pollutants leaching and frequent occurrences of unstable pollution situations. This work explored the migration of HMs-bearing colloids in response to freeze-thaw treatments by laboratory simulation and pore-scale study. The distinct effects of freeze-thaw treatment on colloidal particle number concentration and macropore characteristics may explain the generation and migration of colloid-associated HMs driven by environmental disturbances. This work revealed the underlying mechanisms driving the redistribution of HMs under freeze-thaw cycles, offering valuable insights for risk assessment of soil and groundwater associated with HMs migration.

Membrane-Fabric Composite Filter Media for Continuous Cake Filtration without Gas Throughput Using Paste Dot Coating with Adhesive

In the field of liquid filtration, the realization of gas throughput-free cake filtration has been investigated for a long time. Cake filtration without gas throughput would lead to energy savings in general and would reduce the mechanically achievable residual moisture in filter cakes in particular. The reason why gas throughput-free filtration could not be realized with fabrics so far is that the achievable pore sizes are not small enough, and that the associated capillary pressure is too low for gas throughput-free filtration. Microporous membranes can prevent gas flow through open pores and cracks in the filter cake at a standard differential pressure for cake filtration of 0.8 bar due to their smaller pore size. Since large-scale implementation with membranes was not yet successful due to their inadequate mechanical strength, this work focuses on the development and testing of a novel composite material. It combines the advantages of gas throughput-free filtration using membranes with the mechanical stability of fabrics. For the production of the composites, a paste dot coating with adhesive, which is a common method in the textile industry, was used. Based on filtration experiments, delamination and tensile tests, as well as µCT analysis, it is shown that this method is suitable for the production of composite filter materials for gas throughput-free cake filtration.

Neighborhood Relationships of Widely Distributed and Irregularly Shaped Particles in Partially Dewatered Filter Cakes

A more thorough understanding of the properties of bulk material structures in solid–liquid separation processes is essential to understand better and optimize industrially established processes, such as cake filtration, whose process outcome is mainly dependent on the properties of the bulk material structure. Here, changes of bulk properties like porosity and permeability can originate from local variations in particle size, especially for non-spherical particles. In this study, we mix self-similar fractions of crushed, irregularly shaped Al2O3 particles (20 to 90 µm and 55 to 300 µm) to bimodal distributions. These mixtures vary in volume fraction of fines (0, 20, 30, 40, 50, 60 and 100 vol.%). The self-similarity of both systems serves the improved parameter correlation in the case of multimodal distributed particle systems. We use nondestructive 3D X-ray microscopy to capture the filter cake microstructure directly after mechanical dewatering, whereby we give particular attention to packing structure and particle–particle relationships (porosity, coordination number, particle size and corresponding hydraulic isolated liquid areas). Our results reveal widely varying distributions of local porosity and particle contact points. An average coordination number (here 5.84 to 6.04) is no longer a sufficient measure to describe the significant bulk porosity variation (in our case, 40 and 49%). Therefore, the explanation of the correlation is provided on a discrete particle level. While individual particles < 90 µm had only two or three contacts, others > 100 µm took up to 25. Due to this higher local coordination number, the liquid load of corresponding particles (liquid volume/particle volume) after mechanical dewatering increases from 0.48 to 1.47.