Dry Magnetic Separator

Dry drum separators have been developed mainly for dry separation of ferromagnetic ores with particle sizes finer than 20 mm. In addition to this conventional application, the dry drum separator has found a wide range of other applications such as:
Iron and steel slag treatment
Reduced pyrite ash separation
Calcined ilmenite production
Metal powder production
Super-grade magnetic concentrate production
Removal of ferromagnetic particles prior to High Intensity Magnetic Separation
Control of iron contamination in glass sand production

Efficient separation can be obtained with particle sizes in the range of 0.01 to 25 mm. By utilizing separators with different drum speeds, it is often possible to obtain a high grade concentrate with middlings and tailings as separate products.

Often, dry magnetic separator can be more flexible than conventional wet magnetic separation and can provide large savings in grinding costs by recovering the valuable minerals at an early process stage.

Design:
The dry drum separator consists of a stationary magnetic yoke with a number of permanent magnets placed inside a rotating drum of non-magnetic material. The magnets have alternating polarity and are normally of strontium-ferrite. The revolving drum is made in two versions:
1) for low speed, stainless steel with a replaceable wear cover of rubber, polyurethane or stainless steel etc
2) for high speed,  reinforced plastic with rubber or polyurethane wear protection.
The magnetic drum assembly is contained in a dust proof housing with an opening at the bottom for discharge of both magnetic and non-magnetic products. These products are separated by means of a splitter placed under the drum inside of the housing. The whole unit can be dust vented by connecting the plant exhaust system to the outlet provided on the housing. Parts of the housing exposed to wear are normally protected by replaceable rubber or steel wear plates. Inspection of the drum and housing is made through inspection hatches. The housing is easily dismantled for erection and maintenance.
The feed arrangement is dependant upon local conditions. For run-of-mine fines, a belt feeder is recommended. For other materials, a vibrating feeder, (or in the case of dusty material, completely covered drum feeders) can be used. The housing is equipped with a standard replaceable feed chute
To meet the various requirements the separators are manufactured with two different drum diameters; i.e. 916 and 1200 mm and drum lengths from 300 mm to 3000 mm in. The separator design allows for an easy combination of drums into double- or triple- drum units.
The drive is normally comprised of a speed reducer, V-belts, pulleys, and motor. The adjustment of the separator drum speed is easily achieved by changing V-belt pulleys when the change is reasonably small. Normally the drum peripheral is set between 1 and 6 m/s but applications with speeds up to 9 m/s exist. Optionally, the separators can be supplied with a variable speed drive.
Product chutes under the drum housing are normally not provided as these are often designed to fit local conditions.

Operation principles
The material to be separated is fed on top of the moving drum and accelerated by the drum. The non-magnetic are thrown off by the centripetal force while the attached magnetics form clusters in the magnetic field which covers 50% of the circumference of the drum. The clusters follow the rotating drum to the discharge point and are discharged in the concentrate chute.
The material to be separated is fed on top of the moving drum and accelerated by the drum. The non-magnetics are thrown off by the centripetal force while the attached magnetics form clusters in the magnetic field which covers 50% of the circumference of the drum. The clusters follow the rotating drum to the discharge point and are discharged in the concentrate chute. The alternating polarity of the magnets causes the clusters to rotate and entrapped non-magnetics and middlings are released and thrown off. By varying the drum speed, particles of different grades can be separated. At low speed, pre-concentrate and barren tailings can be produced on a single drum. The pre-concentrate can then be cleaned on a second drum with a higher speed to produce a high-grade concentrate and middlings

Capacity:
The capacity per meter of drum length varies from about 10 to 200 metric tons per hour depending on the particle size of the feed and its magnetic properties. The use of multiple drum units will generally increase the overall.
Prior to final selection of equipment, it is recommended that careful laboratory and pilot plant studies of the ore to be treated be performed to determine optimum selection of equipment.

Selection of pole-pitch:
The pitch of the magnetic poles is of great importance and is chosen to suit the particle size and magnetic susceptibility of the material to be handled. Standard separators can be supplied with magnet assemblies having 25, 45, 65, 100 and 165 mm pole pitch. The final selection of pitch may differ.
If only a two product split is required, the separation is usually made on one drum. This is often the case in cobbing of magnetite, cleaning of feed to High Intensity Magnetic Separators, and extracting metal from slag. Pre-concentrate is cleaned on a second drum at higher speed where a final concentrate and middlings are obtained.
In a three-drum separator system, the first drum is run and middlings. The medium grade product is cleaned on a high speed drum to produce high grade and middlings. The three drum arrangement is recommended whenever good control of all three products is required. The typical flow-sheet is shown in the above figure, which also depicts a middlings processing stage.

Technical Parameters