## 2 Grinding and Classification Circuit  
### Electromagnetic Mill  
Electromagnetic mill [8] puts grinding media into motion by electromagnetic field influence. Grinding media are the ferromagnetic particles in the form of small cylinders (about 10 mm of length and 1 mm of diameter). Six electromagnets (Figure 1a) surround a tube (Figure 1b) and create a working chamber where grinding media move chaotically (Figure 1c), due to impacts in rotating electromagnetic field. It can be seen in Figure 1b, that the unit can be set at an angle that allows for load flowing down. Adjustment of the angle is the simplest way to control grinding material flow [9]. Electromagnetic mill is a novel construction and it is applied in laboratories for research rather than in an industry. Potential advantages of the mill are huge if the circuit is properly constructed and parameterized with respect to material transport, product classification, and recycled. Such a system has been developed [10], intensively examined [11; 12; 13; 14; 15; 16; 17], and finally patented [18] by the consortium of Polish universities and companies: Silesian University of Technology, Gliwice (leader), AGH University of Science and Technology, Krakow (technology of milling), ELTRAF Company, Lubliniec (electromagnetic mill producer), and AMEplus Company, Gliwice (automation equipment). Appendix A gathers more details about the previous works in relation to the manuscript. Figure 2a presents electromagnetic milling system with working chamber 100 mm of diameter that is installed in Silesian University of Technology (Laboratory of Institute of Automatic Control). Other installation was scaled up to 200 mm of the working chamber diameter (Figure 2b) and assembled in ELTRAF Company, where the system with 320 mm of the working chamber was developed as well (yoke of the electromagnets is presented in Figure 2c). It can be seen in Figure 2a,b that the yokes of electromagnets are positioned horizontally, which means that the grinded material is transported vertically. Figure 3 presents the general scheme of the system. The counter-flow pneumatic transport of the processed material is applied. The blower generates under-pressure in the installation and causes air stream flow from the intake up to the outlet. Air flaps adjust respective streams. The feed is loaded from the top by the screw feeder, trough so called preliminary classifier, while the transporting air stream is supplied from the bottom of the working chamber (main air stream). After being grinded, the grains are swept up to the preliminary classifier where the larger ones are taken back down into the working chamber. In this way inner recycle is formed. Lighter grains are swept up to the main classifier. Figure 1: Electromagnetic mill, ELTRAF. Electromagnets (**a**); The mill with the cover and working tube (**b**); and, Working chamber with the grinding media during operation (**c**). After fine classification provided by the main classifier, oversized grains go back to the working chamber (green dashed line in Figure 3), which forms an external recycle. The main classifier is additionally fed by the air stream (additional air stream) to adjust the separation process. Due to under-pressure in the entire circuit, a rotary valve is used in the recycle path to separate different pressures. The recycle stream is directed to the electromagnetic mill from the bottom side using third air stream (recycle air), which is adjusted by a separate flap. Figure 3: General scheme of the milling system with electromagnetic mill. Figure 2: Examples of electromagnetic milling system: (**a**) diameter of the working chamber 100 mm; (**b**) 200 mm; and, (**c**) 320 mm (only the electromagnets yoke). Grains of desired size are transported from the main classifier into the cyclone that separates the material (final product stream) from the transporting air. Again, the rotary valve needs to be applied before the product is collected. The presented grinding system is equipped with subsystems, which enhances its performance.