Magnetic separation is often the best means for removing iron from industrial minerals products. Dry magnetic separators are generally used because they are inherently more efficient than equivalent wet magnetic separators (hydrodynamic drag forces compete with magnetic forces making it more difficult to influence particle movement in slurry systems). In some situations, processing these streams wet would make more sense in the grand scheme of the operation, but product quality concerns cause reluctance in considering processing alternatives. Recent studies show the more modern wet magnetic separators, coined VPHGMS because they are ‘vertically pulsating’ high gradient magnetic separators, just might solve this dilemma, Outotec reports in its latest Separation Solutions.
In many industrial minerals and related markets, Fe or Fe2O3 product specification requirements are stringent. The unwanted residual iron content can be associated with discrete iron-bearing minerals, iron-bearing inclusions within the desired mineral, particle coatings or surface staining, or a combination of one or more of these occurrences. To remove these trace contaminants, dry magnetic separation is most often the answer.
There are cases where wet magnetic separation would be advantageous, provided that the separation erformance is adequately efficient or exacting when considering the entire flowsheet. In some instances, dry magnetic separation equipment requirements could be reduced, and perhaps in rarer situations, eliminated altogether. Alternatively, from a quality perspective, the cumulative contribution of both wet and dry magnetic separation steps may allow for a cleaner final product.
If the mass rejection of unwanted magnetic minerals in the wet magnetic separation circuit is significant enough, drying costs savings may also be realised. In this situation, the same production goals are met by drying a smaller quantity of higher quality feed. Alternatively, excess dryer capacity would then be available as a means to gain incremental production.
There are also many industrial minerals processes where wet processing is used exclusively because the final product is sold damp, so the more efficient dry magnetic separation technologies can’t be employed. In these flowsheets, upgrades involving newer, more efficient wet magnetic separation circuits could have obvious advantages in reducing reliance on gravimetric and flotation based unit operations to achieve finished product quality objectives.
Modern advancements
Failings of traditional WHIMS designs, most notably matrix plugging, kept the separators from broad use in many operations. Today, the modern technological advances of the new VPHGMS units have allowed for their effective application in finer iron and similar ore processing operations, so their potential for greater use in industrial minerals operations is being revisited. (For more detail on the VPHGMS advancements, see Separation Solutions Issue 2, 2006.)