Magnetic Separation

Magnetic separators used for titanium, tantalum and tin minerals processing can be split into wet and dry, low and high intensity, and electro and rare earth magnets and listed as follows:

Wet high intensity magnetic separators (WHIMS) Wet / dry low intensity magnetic drums (LIMS) Induced roll magnetic separators (IRM) Lift roll magnetic separators Cross belt magnetic separators Disc magnetic separators Rare earth magnetic drums (RED) Rare earth magnetic rolls (RER)

Wet high intensity magnetic separators (WHIMS)Examples of these separators are the Readings www.rochemt.com.au and Eriez www.eriez.com . They are commonly used to recover / reject ilmenite from HMC ahead of dry separation. The ilmenite generally needs to be of a low TiO2 content (around 50%), so the magnetic susceptibility is high.

The Readings unit consists of a rotating carousel, which has vertically inclined salient plates through which feed slurry is passed. As the carousel rotates it passes through fields of magnetic influence generated by surrounding electromagnets, followed by fields of no magnetic influence. The magnetic grains are initially held up in the plates while the non magnetic grains are washed through into a launder below. When the plates are in the non magnetic field the magnetic grains are then wash off into a separate launder below.

In order to operate successfully the WHIMS needs to be:

Free of magnetite (which would hang up in the plates / matrix) Free of +1mm grains (which would block the plates / matrix) Have a clean constant supply of high pressure water Steady feed rate and density

The Readings WHIMS operating variables are:

Field strength (measured indirectly and controlled by amp adjustment of the electromagnet) typically up to 15,000 gauss.

Wash water position and flow Plate gap (typically 2mm) Product splitters position Feed rate is typically 25 -30tph for 16 pole unit

Wet / dry low intensity magnetic drums (LIMS)Examples of these separators are manufactured by Eriez www.eriez.com and Multotec www.multotec.com . They are commonly used to recover / reject magnetite from HMC ahead of high intensity wet or dry magnetic separation.

For the wet LIMS there are two models, counter-current and co-current flow. All LIMS consist of a rotating drum within which a fixed permanent magnet is located. Feed is presented to the drum and depending on the magnetic susceptibility of the grains is either attracted by the magnetic field and held to the drum surface or discharged by gravity / centrifugal throw. As the drum rotates the magnetic grains leave the magnet field and are discharged separately usually with the aid of a scraper / brush (and spray water for the wet LIMS).

The speed of drum rotation, magnet and splitter position are the variables used in the dry LIMS

The level of the slurry bath and magnet position are the variables used in the wet LIMS

As the names suggest the counter and co- current wet LIMS remove the products at different points in relation to the direction of the feed flow. The later is more suited to cleaning duties.

For the dry LIMS feed is distributed across the drum at the top, and as the drum rotates enters the magnetic field of a permanent magnet, with the non magnet grains

being unaffected and thrown off by centrifugal force, while the magnetic grains are held to the drum surface until they leave the magnetic field and either fall or are scraped off separately.

Operating variables:

Drum speed Splitter position Magnet position

Induced roll magnetic separators (IRM)Examples of these separators are the Readings and Carpco. They are commonly used to separate ilmenite from less magnetic and non magnetic in dry mills.

The Readings IRM consists of an electromagnet which induces a magnetic field onto a serrated rotating roll via a cast iron pole located a short distance away. Dry feed is distributed across and onto the surface of the roll at top, where depending on the magnetic susceptibility of the grains is either held to the roll or discharges off due to the centrifugal motion of the roll. The machine has two parallel feed points, each with two rolls which are mounted vertically above each other, with the lower roll operating as a non magnetic cleaner.

Operating variables are:

Field strength (measured indirectly and controlled by amp adjustment of the electromagnet) typically up to 15,000 gauss.

Pole gap (closer the gap higher the field strength), typically 2mm. Roll speed ( normally fixed and only adjusted by pulley and belt changes) Splitter position (determined by visual observation of the fan) Feed temperature will affect magnetic susceptibility Feed rate typically 2.5tph

Lift roll magnetic separatorsExamples of these separators are the Readings. They reverse the effect of grain size (coarse magnetic grains with non magnetic grains) due to the centrifugal action of the IRM, as in this case the magnetic grains are lifted onto a rotating roll from a moving feed prior to separate discharge from the non magnetic grains which are unaffected.

Cross belt magnetic separatorsExamples of these separators are the Readings. The cross belt consists of a single belt upon which the feed is distributed across and is transported slowly underneath a series of five electromagnets, the magnetic fields of which lift the magnetic grains off the belt depending on their susceptibility. Underneath each magnet is a smaller faster moving belt across the main belt at right angles which picks up the magnetic grains and transports them away from the magnetic field to discharge into launders. Non

magnetic grains unaffected by the magnetic fields remain on the main belt and discharge off the end.

Operating variables include:

Field strength (measured indirectly and controlled by amp adjustment of the electromagnet) typically up to 15,000 gauss.

Pole gap (distance between the poles and the belt) Typical feed rate 1.5tph

Disc magnetic separatorsThese separators are similar to cross belts, except that instead of using belts to transport magnetic material they employ rotating discs. Operating variables are similar.

Rare earth magnetic drums (RED)Examples of these separators are manufactured by Eriez. They are similar to the dry LIMS except that they employ an exotic permanent magnet capable of producing much higher intensity magnetic field. This magnet is positioned inside a large diameter drum.

Operating variables include:

Drum speed Magnet position Splitter position

Rare earth magnetic rolls (RER)Examples of these separators are manufactured by Eriez. They differ from REDs in that they have two smaller diameter rolls between and around which a belt tracks. Feed material is distributed onto the belt which transports it to the end roll which contains an exotic permanent magnet similar to the RED. The rolls and belt move at high speed and the trajectory of the grains discharging from the belt depends on their magnetic susceptibility and the following operating variables:

Belt speed Belt thickness Splitter position