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.

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.

Triboelectric separation as an inexpensive and environmentally friendly technique could contribute to material-specific sorting. However, the application as a widespread method is limited due to the complexity of the process. In particle wall collisions, various parameters like collision energy and angle, work function of the contact partners, humidity, surface roughness, etc. influence the particle charging in a hardly predictable way. This study investigates the possibilities of forced triboelectric particle charging by applying an electrical potential to the metal contact partner (copper/steel pipe). The variations included different pipe lengths (0.5 m–3 m), particle materials, and particle sizes for limestone. A distinction is made between the net charge of the particles and the positive, negative, and neutral mass fractions. The work functions of the investigated materials vary from about 3.2 eV to >8.5 eV for glass, limestone, artificial slag, and lithium aluminate particles. With the applied high-voltage potential, the particle net charge can be shifted linearly. For limestone, it is shown that the neutral fraction is highest at the Point of Zero Net Charge (PZNC). This observation may identify an approach for the material selective separation of one target component from a multi-material mixture.

The deflector wheel classifier is a widely used device for the separation of fine powders in different industrial applications. The primary objective of the separation process is to achieve high-quality separation of fine powders characterized by a narrow particle size distribution and high separation sharpness. Theoretically, the reduction in the cut size is accomplished by decreasing the gas flow rate or increasing the rotational speed of the classifier, which amplifies the centrifugal forces compared to the drag forces exerted on the particles. This behavior is, indeed, observed in many cases, but it cannot be extrapolated arbitrarily. At their performance limit, classifiers may, against expectation, show an increase in cut size and, in addition, a reduction in the sharpness of the separation process. The limitation in the reduction in the cut size and in the improvement in the separation sharpness arises due to an imbalance between the operating rotational speed and flow rate, which results in a non-uniform flow field in the classifier. If the balance conditions are fulfilled, an optimum separation with a high separation sharpness can be achieved. In this work, CFD simulations validated by some experimental results are employed to represent this limitation, which is obtained by varying the operating parameters using different material densities with particles ranging from one to ten microns.

In this study, a two-dimensional separation of microparticles based on their settling velocity and triboelectric charge ability is achieved using an air classifier for size fractionation and simultaneous charging, followed by an electrostatic separator. In the first part, considerations for enhancing particle classification with high sharpness and low-pressure drops are discussed through improvements in blade design investigated with CFD simulations and validated experimentally. Blades with extended lengths towards the center of the classifier prevent the formation of high-velocity vortices, thereby minimizing the back-mixing of particles and enhancing separation sharpness. This approach also reduces pressure drops associated with these flow vortices. In the second part of the study, the modified blades within the classifier are utilized for two-dimensional separation. Powders from two different materials are fed into the classification system, where particles become triboelectrically charged, mainly through collisions with the walls of the classification system components. Coarse particles are rejected at the wheel and exit the classifier, while differently charged fine particles of the two materials are directed into an electrostatic separator for material sorting. An enrichment of approximately 25–35% for both materials has been achieved on the electrodes of the separator.

The increasing use of lithium-containing materials highlights the urgent need for their recycling to preserve resources and protect the environment. Lithium-containing slags, produced during the pyrometallurgical process in lithium-ion battery recycling, represent an essential resource for lithium recovery efforts. While multiple methods for lithium recycling exist, it is crucial to emphasize environmentally sustainable approaches. This study employs dry forced triboelectrification (FTC) to recover valuable components from slag powder, commonly known as engineered artificial minerals (EnAMs). The FTC method is used to change the charge of the target material and achieve a neutral state while other materials remain charged. The downstream electrostatic separator enables the charged particles to be separated from the target material, which in this study is lithium aluminate. The results show that the method is effective, and lithium aluminate can be successfully enriched.