magnetic separator characteristics

When you hear “magnetic separator characteristics”, numbers immediately come to mind: induction, productivity, power. But from experience, the essence is often lost behind these numbers. Many people, especially at the start, chase maximum values, not realizing that the key is balance and compliance with a specific task. For example, high induction on a drum separator is not always a good thing; it can also pick up useful material if the ore is complex. Or the story with the field gradient in roller separators - you can’t get away with just one number, the whole curve is important. I’ll try to break down what it usually looks like in practice and what I’ve encountered myself.

Basic parameters: what to look for in the data sheet

So, you open the documentation, for example, for a separator like PBM or SMB. The first thing I look at ismagnetic inductionin the work area. But not just a number, but at what working gap it is indicated. Because if the gap is 50 mm, and the ore flowed with pieces up to 80 - that’s it, the parameters go down. I have seen cases where a production facility installed a separator designed for finely crushed ore onto a flow from large overburden - and were surprised at the low recovery. It's not the separator that's bad, but the inconsistency.

Second point -magnetic field gradient. It is especially critical for weakly magnetic ores, such as manganese or oxidized iron. A high gradient allows you to capture small and weakly magnetic particles. But it is achieved by the design of the magnetic system - the shape of the poles, the use of polymagnetic inserts. Some manufacturers, by the way, modestly keep silent about this parameter in their passports and only write induction. This is a red flag.

And third is productivity. But not the one for “ideal ore?”, but with an indication of bulk density, feed size and humidity. I remember that a separator was delivered to one of the plants; its stated capacity was 100 t/h. But in reality they barely squeezed out 70. It turned out that the calculations took a density of 2.2 t/m3, but the real ore was 1.8 and still sticky. So now I always require it to be linked to specific conditions. By the way,LONGI Corporationin the technical descriptions for their separators (https://www.ljmagnet.ru) usually give graphs of productivity depending on size and humidity - this is practical.

Design features affecting performance

Here a lot depends on the magnetic system. Permanent magnets or electromagnets? For dry enrichment, recently they are more often using neodymium permanent magnets - stable, no power required, less heating. But there is a nuance: if the temperature in the workshop rises above 80-100°C (this happens near drying drums), an irreversible loss of magnetic properties may begin. I came across this at a factory in Kazakhstan - they moved the separator closer to the dryer, and after six months the induction dropped by 15%.

Drum or roller design. Shell thickness, material (non-magnetic steel, polyurethane). The thinner the wall, the higher the induction on the surface, but the shorter the service life with abrasive ore. You look for the optimal solution experimentally. LONGI, if we take their experience since 1993, some models use replaceable polyurethane casings - a solution for highly abrasive materials, this can be seen from their use in mining and processing plants.

Adjustment system. The ability to change the gap between the drum and the magnetic system, the angle of inclination, and the rotation speed are not just “nice options”, but tools for fine-tuning for changing raw materials. At one coal factory, it was precisely by adjusting the angle of inclination that it was possible to reduce the ash content of the concentrate by 2%, simply because the ore from the new section had a different granulometry.

Operational parameters: what is visible only in operation

Anycharacteristics of magnetic separator, stated in the passport, are laboratory conditions. The real test is on the shop floor. For example, sensitivity to uneven nutrition. If the feeding conveyor or chute does not produce a flow across the entire width of the drum, but with a hump in the center, then the edges work idle, and the overall extraction drops. It is necessary to install leveling dampers or vibrating feeders.

The effect of humidity on dry separators is a separate story. The material begins to stick together, clump, and flows poorly through the separation zone. This is especially true for thin classes, minus 1 mm. Sometimes a little heating of the air around the drum or preliminary dehydration helps, but these are additional costs. In one of the projects for the beneficiation of magnetite quartzites, it was even necessary to change the type of separator from dry to wet at the final stage due to the high natural moisture of the ore.

Maintainability and availability of components. The characteristic is also how long the separator maintains these parameters. How quickly can a worn shell or magnetic blocks be replaced? How accessible are bearing units? In this regard, I like the approach when the magnetic blocks are assembled into cassettes and bolted from the inside of the drum - there is no need to disassemble the entire shaft, as in old designs. Understanding of such details comes only with years of operation and repairs.

Case Study: Separator Setup for Complex Ore

We had a project in the Urals, polymetallic ore, with magnetite, but a lot of sulfides and clayey material. We installed a standard high-induction drum separator. The result for iron was good, but too many sulfides (pyrrhotite) went into the magnetic fraction, which then interfered with the flotation. It turned out that we were “remagnetizing”.

We started experimenting. They reduced the induction, changed the rotation speed of the drum to create a more dynamic field - pyrrhotite particles, which are weaker than magnetite, did not have time to be attracted and were thrown into the tails. Plus, an additional flow cutoff was installed to filter out medium-magnetic products. This was not described in the initial specifications; it had to be modified on the spot, almost at random.

As a result, we came to a two-stage scheme: the first stage with a higher induction for the extraction of pure magnetite, the second - with a lower one for additional extraction and dumping of the intermediate product. Efficiency has increased. This is to the question that passport data is the basis, and real work requires flexibility and understanding of the physics of the process.

Where to look when choosing: a short checklist from a practitioner

So, to summarize. When you evaluatemagnetic separator, don't get hung up on one star number. Ask yourself: 1) Under what specific ore conditions (size, humidity, magnetic susceptibility) are these characteristics given? 2) How is the declared field gradient ensured and maintained? 3) To what extent does the design allow adaptation to changes in the properties of raw materials (adjustments)? 4) What about the resource of critical nodes and their replacement?

It is very helpful to look at the manufacturer's experience in similar applications. The sameLONGI, with their history since 1993 and an area of 140,000 m2, has clearly gone through many cases in different mining enterprises. When a manufacturer has its own design bureaus and test benches (and more than 60% of their staff are specialists with higher education), this usually means that the technical characteristics will be closer to reality, and not taken from the air.

And one last thing. Always ask not just for a passport, but for a test report on similar raw materials or, ideally, the opportunity to conduct pilot tests at your site. Because none, even the most detailed,characteristics of magnetic separatorwill not replace the view of how the material behaves in a magnetic field on your conveyor. This is the most honest indicator.