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Abstract Static granular packings play a central role in numerous industrial applications and natural settings. In these situations, fluid or fine particle flow through a bed of static particles is heavily influenced by the narrowest passage connecting the pores of the packing, commonly referred to as pore throats, or constrictions. Existing studies predominantly assume monodisperse rigid particles, but this is an oversimplification of the problem. In this work, we illustrate the connection between pore throat size, polydispersity, and particle deformation in a packed bed of spherical particles. Simple analytical expressions are provided to link these properties of the packing, followed by examples from Discrete Element Method (DEM) simulations of fine particle percolation demonstrating the impact of polydispersity and particle deformation. Our intent is to emphasize the substantial impact of polydispersity and particle deformation on constriction size, underscoring the importance of accounting for these effects in particle transport in granular packings. 

Abstract Membranes facilitate scalable and continuous lithium concentration from hypersaline salt lakes and battery leachates. Conventional nanofiltration (NF) membranes, however, exhibit poor monovalent selectivity in high‐salinity environments due to weakened exclusion mechanisms. This study examines polyamide NF membranes coated with polyelectrolytes enriched with ammonium groups to maintain high monovalent cation selectivity in hypersaline conditions. Over 8000 ion rejection measurements are recorded using salt lake brines and battery leachates. The experiments exemplify the coated membrane's ability to reduce magnesium concentrations to 0.14% from salt lakes and elevate lithium purity to 98% from battery leachates, in a single filtration stage. The membrane's selectivity is retained after 12 weeks in acidic conditions. Molecular dynamics analyses reveal that the ammonium groups create an electrostatic barrier at low pH, selectively hindering multivalent cation transport. This is corroborated by the Coulombic attraction between cations and carboxylate groups, along with a repulsive barrier from ammonium groups. Despite a 14.7% increase in specific energy, a two‐stage NF system using the coated membranes for lithium recovery significantly reduces permeate magnesium composition to 0.031% from Chilean salt lake brines. For NMC leachates, the coated membranes achieve permeate lithium purity exceeding 99.5%, yielding enhanced permeate quality with minor increases in energy demands. 

Abstract In dense flowing bidisperse particle mixtures varying in size or density alone, smaller particles sink (percolation‐driven) and lighter particles rise (buoyancy‐driven). But when particle species differ from each other in both size and density, percolation and buoyancy can either enhance (large/light and small/heavy) or oppose (large/heavy and small/light) each other. In the latter case, a local equilibrium can exist in which the two mechanisms balance and particles remain mixed: this allows the design of minimally segregating mixtures by specifying particle size ratio, density ratio, and mixture concentration. Using DEM simulations, we show that mixtures specified by the design methodology remain relatively well‐mixed in heap and tumbler flows. Furthermore, minimally segregating mixtures prepared in a fully segregated state in a tumbler mix over time and eventually reach a nearly uniform concentration. Tumbler experiments with large steel and small glass particles validate the DEM simulations and the potential for designing minimally segregating mixtures.