Strong magnetic separation

When you hear “strong magnetic separation,” the first thing that comes to mind is powerful magnets that rip out everything iron from the flow. But if everything were so simple, my work ten years ago would not have turned into a continuous trial with satisfied customers, who then wondered why the concentrate yield was lower than expected. The main mistake is to reduce the process only to the magnitude of magnetic induction, forgetting about the gradient, the design of the separator and, most importantly, the preparation of the material. Too strong a field sometimes does more harm than good, sintering small particles and clogging work areas. This is rarely written about in catalogues, but in practice you come across it all the time.

Where is the catch in ?power?

I remember one of the early projects on the enrichment of magnetite quartzites. The customer insisted on installing a separator with the highest possible induction at the poles - he thought this would ensure pure concentrate. They did. And the result? Yes, large grains of magnetite went perfectly. But the finely disseminated ore, the same one that causes the bulk of the losses, simply did not have time to “rip out” from the pulp flow - the feed rate is too high and the matrix configuration is incorrect. There was a strong field, but no effective gradient for small fractions. We had to revise the entire training scheme and add a classification stage. Conclusion: field strength without the correct geometry of the magnetic system is money down the drain.

Another nuance is magnetization reversal. In drum separators with permanent magnets based on rare earth elements, for example, NdFeB would seem to be ideal for strong separation. But if the food contains large pieces with residual magnetization, they create their own chaotic field that interferes with the process. I came across this during slag enrichment. Visually, everything works, but during measurements, the metal content in the tails is off the charts. The solution was not to strengthen the magnets, but to install an additional demagnetizing device before separation. Sometimes the problem is solved not by adding, but by removing “force”.

And of course, wear and tear. Strong magnetic fields require special solutions to protect the work area. Rubber linings of drums, which work well at medium inductions, with prolonged exposure to super-strong fields begin to quickly wear out with abrasive particles, because they are pressed against the surface with enormous force. We changed the lining on one line every six months until we switched to composite materials from a specific supplier. This is the case when the reliability of the system is determined by the weakest, non-magnetic link.

Experience and equipment: from theory to workshop

Here I cannot fail to mention our long-term contact withLONGI Corporation(https://www.ljmagnet.ru). Their approach has always been down-to-earth - first, long-term tests on our raw materials, and then recommendations on the separator model. They don't just sell hardware, but look at the process as a whole. Their engineers, knowing that the enterpriseLONGIlocated in Fushun and producing over 4,000 units per year, they clearly have experience with thousands of different configurations. This is felt in the dialogue. For example, they were the first to draw our attention to the problem of material wettability. It turns out that if the ore is too dry or, conversely, waterlogged, even the moststrong magnetic separationwill fail due to a violation of the conditions for transporting particles in the field action area.

At their test bench in China we "drove" samples of our skarn. We looked not only at the final concentrate, but also at the behavior of the pulp in the tray, at the formation of “beards”. on the matrix. Then we came to the conclusion that for our type of raw material, not a standard drum separator, but a rotary separator with alternating poles, produced by them, is better suited. The key point was with the gap adjustment - they showed how a millimeter adjustment changes the gradient and therefore selectivity for small classes. This is the very practice that is not in the manuals.

The aftertaste from that work is the understanding that a good technology supplier such asLONGI, this is not an equipment warehouse, but a partner who helps avoid dead-end decisions. Their argument was always supported by numbers from their own factory tests, and not by marketing brochures. It is especially valuable that they did not hide the limitations: they openly said where their separator could cope, and where pre-gravity or flotation was needed.

Case study: when everything went wrong

We had a project to extract wolframite from old tailings. Laboratory tests on a small magnetic carousel showed fantastic results -strong magnetic separationI had to get everything out. An industrial separator was launched. And we got... almost zero effect. Days passed, and the project's economics were bursting at the seams. They began to figure it out. It turned out that the laboratory sample was dried and ground, but in reality we were feeding old tailings with natural moisture, where the particles were cemented by clay deposits. The magnetic field acted only on the surface layer of the lumps, without penetrating inside.

We had to urgently build a disintegrator-moderator into the line. It was not a planned operation, additional costs, downtime. But it saved the project. Now, looking back, I understand that it is a classic mistake to transfer laboratory conditions to real production without modeling all parameters, especially the physical state of nutrition.Strong magnetic separationrequires no less strong attention to preparatory operations.

At the same facility, we were faced with the problem of matrix clogging with non-magnetic sludge. The field was so strong that it carried along the magnetic particles and sticky clay, which over time formed dense plugs. Regular pressure washing did not help. The recommendation of one of the technologists helped out - to supply a weak stream of hot steam to the separation zone. It reduced the viscosity of the sludge, and it was washed away. The solution is simple, but it was necessary to think of it while sitting on site, and not in the office.

Unobvious details that make all the difference

Temperature. Who would have thought that it affects magnetic enrichment? It turns out, yes. We worked in winter in an unheated workshop with separation of iron ore concentrate. In the morning, when the equipment and pulp were cold, extraction was 5-7% lower than planned. By lunchtime, when everything was warming up from the engines, the process reached its specified parameters. They started heating the water for the pulp - the problem went away. Apparently, the viscosity of the medium and the kinetics of particle movement strongly depend on temperature, and forstrong magnetic separationsmall classes are critical.

Matrix or drum material. It would seem like a minor detail. But if we are talking about working with abrasive materials, choosing stainless steel of a certain grade (say, 12Х18Н10Т versus 08Х13) can increase the overhaul period significantly. We learned this the hard way, changing drums once a season until we tested it with metal experts. Now this is a mandatory item in the technical specifications when ordering any separator.

And the last thing is the human factor. An experienced operator can detect by ear that a piece of non-magnetic rock has entered the power supply and is hitting the drum. Or, by a change in the engine hum, you can understand that the magnetization reversal of the core has begun. No automatic control system can replace this. Therefore, the implementation of complexstrong magnetic separationalways goes in parallel with the training of personnel who must feel the device. Without this, even the most advanced equipment from the sameLONGIwill not reveal even half of its potential.

Instead of a conclusion: thinking out loud

So what is itstrong magnetic separationin the end? For me now it is not a technology, but a technological complex. Where the magnetic system is only the heart, and the vessels and nerves are preparation, nutrition, transport, monitoring the condition of the material and competent maintenance. You can buy the most powerful magnet in the world, but if you don't pay attention to the little things? such as humidity, coarseness or temperature, the result will be disappointing.

Now, looking at new developments, for example, separators with controlled field strength in real time, I understand that the future lies in flexibility. So that one machine can operate in different modes depending on the variable composition of raw materials. And here again, it is not just strength that is important, but the ability to apply it accurately and targetedly. Experienced producers, the same ones who likeLONGI Corporation, has gone from a small enterprise created in 1993 to a large plant with a staff of 1,200 people, they are moving in this direction - towards intelligent systems. But the basis, the foundation, remains the same: a deep understanding of the physics of the process, supported by the bitter and sweet experience of real factories. Without this, all the talk about “strength?” - just words.