High-gradient magnetic separation (HGMS) and high-field magnetic separation (HFMS)

Conventional circuits (electromagnets, permanent magnets) nevertheless have major drawbacks (magnetic saturation quickly reached, poor recovery of particles smaller than 25 µm, circuit remanence, risk of clogging, heavy and cumbersome equipment). These techniques enable us to obtain a magnetic field of around 1,600 kA/m in the core itself or on the surface of the poles; however, this field can only be used for magnetic separation if a discontinuity is created in the magnetic yoke to act as a separation gap and ensure that the field lines are closed. This gap results in a reduction in the magnetic field available for sorting, a reduction partly offset by the use of a ferromagnetic matrix. These drawbacks have prompted users and manufacturers to look for new materials and new magnetic field generators.

The current trend is to replace induced magnetic masses with solenoids (copper or superconducting). The advantage of solenoid separators is that separation takes place inside the induction coil itself, where a matrix of iron wool or expanded metal plate is used to retain the fine paramagnetic particles.

The complete study of the subject includes the articles :

• "Magnetic separation: theory and modelling" ;

• "Low and high intensity magnetic separation" ;

• [J3 222] "High gradient magnetic separation (HGMS) and high field" (this article);

• "Magnetic separation: economics and special applications" ;

• "Magnetic separation".