| Magnetic separation as an effective method plays a significant role in treatment of iron ore. The development of iron ore beneficiation technology is based on development of magnetic separation devices and technology. Large-scale and permanent magnetic devices will be the topic of the development of magnetic separation. Since Nd-Fe-B permanent magnetic material came out, permanent magnetic separation devices have developed dramatically. It is practically significant to do some researches on pre-concentration of hematite by permanent high-intensity magnetic separation, permanent high gradient magnetic separation and some corresponding devices, so as to improve the utilization rate of available hematite and reduce the cost of processing.In this paper, for the extremely poor Anshan-type hematite which have not been utilized in China, a dry permanent high-intensity magnetic separator of350mm in diameter and1100mm in length was developed for pre-concentration. It mainly consisted of permanent magnetic roller, star distributor, transporting system by belt, feed hopper, driving electromotor and controlling system. Permanent magnetic roller with a polar distance of40mm, was made from high-performance permanent magnetic material Nd-Fe-B and permeability magnetic material DT5A, and magnetic induction on the surface of the magnetic system can reach771.9kA/m by design of extruded magnet. It can be seen by measuring magnetic field properties of the roller that magnetic induction descended significantly with a distance between0to10mm from the belt and the average magnetic field gradient can reach5.41X104kA/m2and that magnetic induction decreased slowly when the distance was more than15mm and magnetic field gradient was2.39X104kA/m2and magnetic induction was still159.2kA/m when the distance was farther than20mm. Circumferential magnetic field intensity changed uniformly.Slon vertical-ring pulsating high-gradient magnetic separator has made an importat role in the process of effective separation of Anshan-type hematite. There are still some shortcomings such as high energy consumption, complex structure and trouble with maintaining operation. So, in this paper, a permanent high-gradient magnetic separator was developed, consisting of permanent magnetic cylinder, cell body, feed chute, discharging system, rack, arranger and frequency control system of motor speed, with a transmission power of3.0kW. The magnetic system in the permanent magnetic cylinder was closed, made from improved Nd-Fe-B permanent magnetic material N35and covered by magnetic matrices. Three pairs of pole were arranged alternately in the circumferential direction. Auxiliary magnetic pole was adopted between the poles, so as to improve the action deep of magnetic field, with a background magnetic field intensity of596.8kA/m. Regularly arranged stainless steel rods2mm in diameter, were used for magnetic matrices. Magnetic field intensity in the separating area reached more than756.0kA/m. Magnetic induction descended significantly with a distance between0to1Omm from the surface of cylinder and the average magnetic field gradient can reach3.18×105kA/m. Magnetic induction decreased slowly when the distance was more than15mm and magnetic field gradient was1.59×105kA/m2. Magnetic induction was lower than159.2kA/m when it was farther than35mm.Dry permanent high-intensity magnetic pre-concentrator was adopted to pre-concentrate the extremely poor hematite of Anshan-type. Pre-concentration tests were done at different rotating speed for different size fractions-75+50mm,-50+20mm,-20+5mm and-5mm with one roughing and one scavengin. After the pre-concentration, the Fe ore grade was improved by5.3%-6.8%if the original grade was17%-18%, i.e.,the recovery rate is higher than55%and tailing grade around13%with the yield of tailing higher than55%. It can be seen from the chemical phase analysis of tailings of-20+5mm that iron was mainly in hematite and iron bearing silicate minerals. Iron content in hematite was only8.60%, which was much lower than that in raw ore and that in iron silicate was4.44%.Permanent high-gradient magnetic separator was adopted to separate the feed of high-gradient magnetic separation in Qidashan Iron Ore Dressing Branch. And iron concentrate with Fe grade of40.21%at recovery of78.09%and tailings of11.8%were obtained on optimum conditions. After recleaning, iron concentrate with Fe grade of43.49%at recovery of76.86%and tailings of11.66%were obtained. When combined with Slon vertical-ring pulsating high-gradient magnetic separator(background magnetic field of1.0T), iron concentrate with Fe grade of44.57%at recovery of77.34%and tailings of11.35%were obtained after two stages of separation. What is much more important is the load of Slon vertical-ring pulsating high-gradient magnetic separator was decreased by50%, which was beneficial to energy conservation.Mineral particles moved as horizontal projectile motion in the permanent high-intensity magnetic separator for pre-concentration under magnetic force, centrifugal force, gravity and frictional force with the rotating of the magnetic roller. Weekly magnetic and non-magnetic particles were separated under different forces. Take hematite particles of20mm in diameter as an example, in the dry permanent high-intensity magnetic separator for pre-concentration, with a distance between0to10mm from the belt, the average magnetic induction and magnetic field gradient were about318.3kA/m and4.77×104kA/m2respectively, thus specific magnetic force of the particle was24.5N/kg, which was2.45times of its weight, and they can be recovered completely by pre-concentrator. The magnetism of particles is mainly influnced by the characteristics of magnetic field and the centrifugal force is mainly influnced by the speed of magnetic roller. They are the key factor affecting the result of pre-concentration and in addition the material properties, the thickness of feed layer and the mechanical inclusion.Weakly magnetic particles are subjected to magnetism, fluid resistance and gravity in permanent high-gradient magnetic separator (For fine magnetic particles, gravity is negligible). Take hematite particles of0.15mm in diameter as an example, in the text of permanent high-gradient magnetic separator, with background magnetic field596.8kA/m and average field gradient2.39×105kA/m2. Thus specific magnetism of the particle was229N/kg, which was22.9times of its weight, and ratio by the fluid viscous force5.27×104, they can be recovered completely by separator. What affects the selectivity of the high-gradient separator is the match and arrangement of magnetic matrices, carrier properties and pulp flow, dispersion degree of material and mechanical inclusion etc. The key factors affecting the result of separation are ore properties, pulp density, barrel speed as well as the water pressure and operational capacity on condition that the magnetic field of permanent high-gradient separator is constant.The permanent high-intensity magnetic pre-concentration developed in this paper can provide a new device and technology for discarding tailings from weekly magnetic and poor hematite, promoting reserves of resources, extending working life of mines, improving feed grade for grinding, reducing grinding consumption and boosting mineral processing efficiency. A new method of effective utilization of poor hematite can be put forward. Permanent high-gradient magnetic separator developed in this paper has certain directive significance to the permanent magnetization of HGMS. |
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