22-08-2012, 04:59 PM
Low intensity magnetic separator
1Low intensity.doc (Size: 174 KB / Downloads: 43)
Low intensity magnetic separator is maily used for ferromagnetic materials ans paramagnetic materials of high susceptibility. L.I.M. separators employ either electromagnet or permanent magnets. Electromagnet provide high magnetic field. It is mainly used for concentration of coarser size sand particles. This process is called cobbing. It is used for relatively coarser size. If the size of particle is below 0.5cm then it is replaced by wet L.I.M magnetic separartor.
Working principle
Dry drum separator is the most common type in use nowadays. Typically the rotating drum contains from three up to ten magnets of alternate polarity. These are arranged radially on the shaft covering approximately 180° of the drum. Initially the magnets were electromagnets but now have all been replaced in designs by permanent magnets using,
The drum cover is non-magnetic, and the drum rotates about the hub at typically 40 rpm. Material is fed onto the top of the drum and separated The alternating polarity aids the rotation of magnetic particles and the release of non-magnetic particles.
Typical uses for this type of separator includes upgrading of blast furnace slag, iron ore, and sponge iron and commercial separators are available over a wide range of sizes. Drum diameters vary from 300 to 1500mm and drum lengths from 300 to 4000mm. The performance of a drum dry low intensity magnetic separator can be predicted by the use of four parameters – magnetic field at the drum surface, angular spacing between the magnets, drum radius and the revolution rate. Dry low intensity magnetic separation is mainly applied to strongly magnetic coarse sands, typically 5 – 8mm material economic feed rates of 150 tph per metre of length can be obtained.
In other forms dry low intensity magnetic separators are often used as pulleys installed over the end of conveyor belts which draw the tramp iron from the material and carry it to the underside of the conveyor to be discharged. Over band separators and suspension magnets are installed over conveyor belts to remove tramp iron. Suspension magnets are used to extract iron form the material being transported and are used on conveyor widths up to 2200mm with an operating gap up to 850mm.
Wet low intensity magnetic separators
This is today by far the most widely used type of magnetic separation. But it can only be used for strongly magnetic minerals, so its primary use is for magnetite and ferrosilicon recovery in dense media circuits. Other applications include iron ore concentration and removal of highly magnetic material prior to high intensity wet magnetic separation. Other low intensity wet magnetic separations take the form of matrices through which the product percolates, such as clayslip in order to remove any ferrous contaminants.
There are three basic designs of wet low intensity magnetic separation – concurrent, countercurrent and counter rotation.
Wet low-intensity drum magnetic separators
Drum separator is the most commonly use magnetic separator mostly used for separation of iron ore. A wet low-intensity drum magnetic separator consists of a drum. The drum itself cannot be magnetized (often made from stainless steel or reinforced plastics). It consists of 3-6 permanent magnets of alternating polarity.. The magnetic particle is collected by the magnet and is pinned in the drum and carried out of the field. Where is the gangue remaining in the tailing. Inside the drum there is an adjustable array of permanent magnets
Concurrent
This type of drum separator is almost exclusively used for the treatment of particles of 5mm and below. The ore is carried forward by the drum since it flows in the same direction as the drum rotation. It then passes through a gap where it is compressed and dewatered before leaving the separator. Magnetic material is picked up by the drum and the non-magnetics are discharged at the bottom of the tank. This method is widely used in heavy media recovery systems since it offers a magnetic concentrate from relatively coarse material with high throughput rates.
Counter rotation
In the counter rotation design of wet low intensity magnetic separation the feed flows in the opposite direction to the drum rotation. This type is often used in roughing operations where occasional surges in feed must be accommodated without a minimum loss of magnetic material and where a high quality concentrate is of secondary importance. This is because the tailings flow along the entire magnetic arc of the drum. The feed size for a counter rotation drum separator is nominally less than 1mm for optimum results.
Counter current
The term counter current is derived from the fact that the tailings flow counter to the rotation of the drum when leaving the tank. Sometimes known as the Steffenson Tank the separator is often used for the separation of finely ground particles of approximately 100µ and less in size. Coarser ores cause settling problems. The feed is introduced near the bottom of the drum and the magnetic particles are picked up by the drum and agitated by wash water jets. The tailings discharge through an overflow at the opposite end of the tank, which also acts as a pulp level control. The counter current design ensures a high recovery of magnetic material and a high quality concentrate.