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For increasingly finer powders, the material-specific separation at high loadings is a challenging task, for instance in recycling processes. Here, a combination of triboelectric charging and electrostatic separation was investigated for powder mixtures of talcum and calcite. The dependencies of the triboelectric charge on the mass loading, the gas velocity, and the mixture ratio were investigated. While higher charge levels were achieved with increasing gas velocity, the mass loading had an opposite effect on the net charge. Although bipolar charge distributions were observed within pure materials and mixtures, electrical neutralization did not occur in the mixtures. Therefore, already in a non-optimized setup, a decent degree of material enrichment (of up to 53 %) was found on the separating electrodes.

Concerning the use of air classifiers with cut sizes in the micron range and lower, it is necessary to disperse the feed material properly in an air flow to avoid agglomerates larger than the desired cut size. Commonly used dispersing devices such as injectors use large amounts of air. To reduce the size and costs of the subsequent air classifiers, two new types of dispersing systems were developed, one design being related to a brush feeder and the other to a pin mill. Both apply mechanical rather than fluid mechanical forces in the dispersion process. The brush disperser achieves the same size distributions as the pin mill disperser with much less machinery. Its properties as a feeding and dispersing system are shown and its ability to disperse particles in the submicron range is confirmed by two independent particle size analysis systems: a new diffraction spectrometer and an impactor.

Deflector wheel classifiers are widespread in industry for the separation of powders into fine and coarse powders. Even though this separation process has been known for quite some time, it is not yet fully understood, and existing models fail to precisely predict the separation characteristics. Due to the high throughput of deflector wheel classifiers, it is greatly beneficial to estimate the separation characteristics before the experiment. Here, the developed model critically examines the usual assumptions, such as ideal airflow, neglection of particle–wall and particle–particle interactions, or spherically-shaped particles. First, the investigation of the air flow using a Particle Image Velocimetry (PIV) system showed significant differences to the assumed ideal flow field, then particle sphericity and its influence on the interaction between the particles and the paddles of the deflector wheel was investigated and compared with particle rebound behavior on a static wall. Surprisingly, comminuted glass behaves similarly to comminuted limestone in multiple aspects and not like glass beads. To determine the number of particle–particle collisions, Discrete Element Method (DEM) simulations were performed. The aforementioned aspects found application in the model and the separation behavior was well-estimated.

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