# Review of Coal-Fired Electrification and Magnetic Separation Desulfurization Technology
## 5 High Gradient Magnetic Separation Technology
### The Development of High Gradient Magnetic Separators  
High gradient magnetic separator is a rapidly developing magnetic separator in recent decades. Since its emergence, scholars at home and abroad have carried out extensive and in-depth research on it. Domestic and foreign scholars first began to study electromagnetic high gradient magnetic separation equipment. In the late 1960s, Professor [PERSON] of the Massachusetts Institute of Technology Magnet Laboratory used the coil cavity as the separation space, which greatly improved the processing capacity of the unit weight magnetic separation device. A stainless steel magnetic conductive material is used in the magnetic polymer, which makes the magnetic field gradient high in the tiny space and makes the weak magnetic fine particles and even the semi-colloidal particles to be effectively removed. The first high gradient magnetic separation equipment was developed by Professor [PERSON] and the patent of high gradient magnetic separation without iron core [48] was put forward, which opened up a new world of high gradient magnetic separation. For better separation of minerals, MIT, Erize [49] and the IRD company in Britain has done a lot of work on HGMS. The Czech Republic formed a VMS type HGMS on the basis of an MRVK type [50]. The new equipment also includes: charged high gradient, vibration-pulsating HGMS, etc., but the representative is the Sala rotation. In 1989, Maanshan Institute of Mines invented DMG electromagnetic pulsation HGMS. In the 1990s, Changsha Institute developed the CRIMM series of HGMS, which successively produced several non-metal removals for kaolin [51]. In 1998, Guangzhou Nonferrous Metal Research Institute made an SLHG wet vertical ring HGMS [52]. In 2004, it developed SSS-II wet double frequency pulse double vertical ring high efficiency HGMS [53]. In order to improve the efficiency of sorting and solve the blockage of media, the Ganzhou Nonferrous Metallurgy Research Institute has developed a new generation of Slon-type HGMS, which has significantly improved the level of high gradient magnetic separation technology [54]; the Slon-type vertical ring pulsating HGMS [55] has been serialized and Slon HGMS represents the highest level at home and abroad. In 2007, the Institute designed and manufactured Slon-1000 dry vibration HGMS [56]. With the development of science and technology, almost all kinds of magnetic separators are developing towards permanent magnetization. Compared with electromagnetic high gradient magnetic separators, permanent magnet high gradient magnetic separators can save a lot of electric energy, simplify the structure of the equipment and reduce the weight of the machine. The earliest permanent magnet high gradient magnetic separator is a wheeled structure consisting of a vertical ring with a magnetic medium and a permanent magnet. The vertical ring is rotated in the magnetic field generated by the permanent magnet for sorting, using an adjustable horizontal magnetic field and gravity to feed the ore. The result is better in hematite separation [57]. After the rare earth permanent magnet came out, Maanshan Mine Research Institute developed the rare earth permanent magnet high gradient magnetic separator with Nd-Fe-B material. The background magnetic induction intensity can reach 0.6 T, and the separation index can reach the level of the similar electromagnetic high gradient magnetic separator [58]. The Bateman Company in America produces a vertical ring type \"iron wheel\" type permanent magnet HGMS, and the magnetic magnetic medium is steel wool or metal mesh, which is used for the recovery of tailings fine iron ore from the iron ore rock selection plant [59]. The Eriez company in America developed a Reium100 permanent magnet HGMS, which is the development of \"iron wheel\" type, field strength is 0.6 T, the magnetic medium is steel plate net, placed vertically, the l2 \(\upmu\)m magnetite is separated from 850 \(\upmu\)m coal particles, and the recovery of magnetic material is 96-99% [60].