Magnetic separation has long been used to upgrade and beneficiate a wide variety of industrial minerals. Advances in both wet and dry magnetic separators over the years has broadened their use, and questions are often raised about which separation technique or equipment type is most appropriate for a particular operation. Minerals separation based on magnetic susceptibility differences in particles is accomplished wet or dry, at various intensities and in different basic machine configurations. The following types of industrial magnetic separators used in a modern mineral sands plant:
- Wet high-intensity electromagnetic separators (WHIMS)
- Wet low-intensity drum separators (LIMS)
- Dry high intensity induced roll magnetic separators (IRMS)
- Dry low intensity drum-type separators or ‚’scalper’‚ magnets
- Dry high-intensity rare-earth drum (RED) separators, and
- Dry high-intensity rare-earth roll (RER) separators
The selection of magnetic separation technology depends on many processing factors, including particle size, and the specific assemblage of minerals and grades as well as their corresponding magnetic susceptibility. Additionally, production and marketing factors must also be considered.
As operations always look to reduce drying requirements for obvious cost implications, employing wet magnetic separation early in a process can greatly benefit an operation if a low-grade final tailing, or a clean marketable product, can be produced, since it alleviates both drying and dry storage costs. While WHIMS use can be advantageous, a common drawback of conventional designs is entrapment of non-magnetics in the magnetics product, particularly when treating finer particles. Therefore WHIMS is normally used after conventional gravity concentration to remove a magnetic stream that can be upgraded easily to finished-product ilmenite. The resulting nonmagnetic fraction is then further upgraded by gravity concentration, and followed by conventional dry separation techniques to separate the higher value zircon and rutile products. This paper will provide a brief look at our experience in the induction and assimilation of wet high intensity magnetic separation technology for the bulk separation of up-graded heavy minerals before treating it for separation of individual minerals.
OPERATION OF THE WET MAGNET
Feed material is introduced into the distributor above the machine at a predetermined pulp density. This feed material is equally distributed to each of the stainless steel boil boxes positioned above the rotor and then passed into the rotor assembly at the ascending point of magnetic intensity. The magnetic particles contained in the feed are attracted to the serrations on the salient pole plates while the non-magnetic particles fall freely through into the catch box below. A regulated volume of water is provided to ensure the continuity of flow of the non-magnetics and free any particles, which may be trapped by the collection of the magnetics at the points of the serrated salient plates.
The magnetic fractions are transported to the midpoint of the ‘null’ zone located between two poles of identical polarity. Here they are scoured free from the salient poles by a pressurised volume of water and collected in their respective catch boxes located beneath the rotor. Three catch-box segments, with adjustable splitters, are provided for each separating zone to allow for maximum flexibility of operation and permit the selection of a middling fraction if required. The product from each catchbox is taken through rubber hoses to a collection box assembly secured beneath the machine.
EFFECT OF VARIABLES UPON PERFORMANCE
The Wet High Intensity Magnetic Separator has a number of operating variables, which relate to its performance. These variables may be defined into two distinct groups:
Machine Variables Feed Variables
- Coil amperes (magnetic intensity)
- Mineral composition
- Feed box position
- Particles size
- Non-magnetics wash water volume and position
- Feed rate
- Splitter positions
- Pulp density
The correct settings or limitations of any of the above variable quantities can be established by the carrying out of a test program upon a representative sample of ore.