principle of operation of a magnetic separator

When they talk about the principle of operation of a magnetic separator, many people immediately imagine just a magnet that attracts iron. But in real work, especially at processing plants, everything is much more complicated and interesting. A common mistake is to assume that the main thing is the strength of the magnet. Strength is important, but if you do not take into account the nature of the feed, the granulometric composition of the material, humidity and even the speed of the belt, you can end up with either a pure concentrate with a bunch of waste rock, or, conversely, the loss of half of the valuable magnetic product. I myself have encountered situations where a formally powerful separator was running idle due to an incorrectly adjusted gap or because the material was coming out like a “sandwich”, in layers of different sizes.

Basics: the physics of the separation process

If we discard complex formulas, then the point is to create a non-uniform magnetic field. It is heterogeneity that is the key. A uniform field will simply magnetize the particle, while a non-uniform field will create a force that will move it to a zone with higher intensity. In drum separators, for example, this zone is the surface of the drum. Particles with high magnetic susceptibility (magnetite, for example) “stick?” to the drum and are removed with a scraper already behind the unloading zone of the non-magnetic product. But weakly magnetic materials, such as some iron ores or slags, require separators based on powerful permanent magnets made of rare earth metals or even high-tension electromagnets.

Here it is important to understand the difference between the strength of the magnetic field (intensity) and the gradient (the degree of its heterogeneity). For coarse, highly magnetic fractions, a high voltage is often sufficient. But for thin, weakly magnetic slurries, it is the high gradient that becomes decisive. This is precisely the area where separators with ferromagnetic wire matrices or gratings perform well. The particle gets stuck at the tip, where the gradient is maximum.

In practice, the choice between permanent magnets and electromagnets is always a compromise. Constant ones, especially neodymium ones, provide a stable field without energy consumption, but they are difficult to “turn off?” for cleaning from random ferromagnetic blockages. The electromagnets are controllable, the field can be adjusted within wide limits, but there is also power consumption and a cooling system. I remember that at one of the old sites there was a problem with overheating of the electromagnet windings during the summer shift - productivity dropped until an additional fan was installed. It's a small thing, but it has an impact.

Design nuances that decide everything

The drum is a classic. But even here there are dozens of options. The location of the magnets inside the drum (single-pole or multi-pole system) determines the nature of the movement of the magnetic particles. The multipolar system causes them to flip (reverse polarity?) when moving along an arc, which makes it possible to weed out weaker magnetic inclusions that will not hold up during such shaking. This is critical for obtaining high-grade concentrate.

But belt separators, where the magnetic system is stationary and the belt with the material moves above it, are good for removing random ferromagnetic impurities from bulk products, for example, in the food or chemical industry. But if the material is wet or sticky, the tape begins to become dirty and efficiency drops dramatically. You have to install cleaning rollers, increase the angle of inclination - in general, adjust.

Dry magnetic separation is a separate story. It would seem simpler: no pulp, no problems with water. But no. Dust is the main enemy. It clogs the working gaps, isolates particles from the action of the field, and is harmful for personnel. We have to organize aspiration and seal the nodes. I saw how in one production, due to poor aspiration, a thin magnetic fraction was simply carried away into the dust collection system along with the tailings - direct losses.

Practical pitfalls and how to avoid them

One of the most insidious problems is clogging. Not because it’s magnetic, but because it’s non-magnetic, but large. A stone or piece of wood can stand across the chute, change the flow of material, and the separation will go awry. Regular visual inspection of feed trays is a mandatory procedure, which, alas, is often ignored in the pursuit of fulfilling the plan. Another point is wear and tear. The drum lining, the belt itself, scrapers - all these are consumables. If the scraper is worn out and does not remove the concentrate cleanly, it begins to wrap around the drum, and after a couple of hours you can have a serious accident with the line stopping.

Adjusting the gap between the feeder and the drum or belt is almost an art. Too large - large heavy magnetic particles may not have time to be “picked up?” field and fall into the tails. Too small - the material will not have time to be fed, and a jam will occur. Often the optimal gap is found experimentally for a specific ore, and then simply fixed. But if the ore came from another quarry, even with the same general magnetism, but a different granulometric composition, the settings may “float away”. You need to be prepared for operational adjustments.

And about water. In wet separation, pulp density and viscosity are parameters No. 1. Too thick - the particles will interfere with each other, the magnetic ones will not be able to move freely to the drum. Too liquid - the load on the circulating water supply system will increase, plus there is a risk of entrainment of small magnetic particles. Controlling pulp density is a routine, but you can’t do without it.

Equipment in action: a view from the production side

There are many players in the market, and the choice often depends on the traditions of the enterprise and the specific technological task. If we talk about integrated solutions for the mining and processing complex, we can pay attention to the experience of such manufacturers asLONGI Corporation. The company, founded back in 1993, has accumulated serious experience over decades in the development and production of mining equipment. Their production base in Fushun with an area of ​​140,000 m2 and a staff of engineers (more than 60% of employees with higher education) allows us to talk about deep design development. The annual production of 4,000 units of equipment is a figure that speaks of the scale and, importantly, the possibility of replicating proven solutions.

For themprinciple of operation of a magnetic separator- not an abstraction, but a basis for engineering improvements. For example, in designs for processing highly magnetic ores, special layouts of magnetic systems can be used, which increase the length of the separation zone without increasing the dimensions of the apparatus itself. Or solutions for quickly replacing permanent magnet blocks to convert the separator to another type of raw material. These are the parts that are born not in a catalog, but in real production after analyzing feedback from existing factories.

An important point is adaptation to the customer’s conditions. Not every producer will understand why ore behaves differently in the Urals than in Kuzbass. But if the enterprise has its own scientific and technical base and a staff of engineers, like the mentioned corporation, then they are often ready to conduct tests on customer ore samples and make adjustments to the standard design. This may apply to the choice of steel grade for the drum (abrasive resistance) and the design of the unloading unit. More details about their approach can be found athttps://www.ljmagnet.ru.

Thoughts out loud about the future of separation

Where is everything going? The trend is intellectualization. Not just a pulp level sensor in the tank, but systems that, based on indirect signs (current consumption of the drum drive, bearing temperature, change in operating noise) can predict wear or the onset of clogging. While this is often the prerogative of very expensive Western lines, local manufacturers are also beginning to introduce IoT elements into their new models.

The second is materials. The development of sintered neodymium magnet technology with improved thermal stability paves the way for more compact and powerful separators for dry separation. This could revolutionize the approach to enrichment in arid regions where water is scarce.

And yet, despite all the technology, the last word often remains with the operator, who hears how the machine works and sees how the product flows.Operating principleremains unchanged - you can’t fool physics. But understanding of this principle should not be at the level of a textbook, but at the level of tactile sensations and accumulated visual skills. It is this combination - deep knowledge of theory and bitter experience of practical failures - that gives rise to that most effective work, when the separator does not just “buzz”, but actually brings an economic effect, clearly separating the valuable from the empty.