dry magnetic separation

When you hear “dry magnetic separation”, the first thing that comes to mind is a powerful magnet and a flow of dry material. But in practice, everything comes down to subtleties that are often omitted in textbooks. Many people think that the main thing is the field strength, and then they wonder why the output concentrate is clogged or the separator is constantly clogged. I went through this myself.

Where theory diverges from shop reality

In theory, everything is simple: dry ore or sand is supplied, magnetic particles are attracted, non-magnetic particles go into the dump. But try to ensure this “dryness?” in conditions of a northern warehouse in winter or when processing material with a residual moisture content of even 2-3%. Everything starts to stick, the drum becomes overgrown, and efficiency drops significantly. I have repeatedly seen how facilities ignore this point at the design stage, and then struggle with the consequences for months.

Another nuance is the granulometric composition. For effectivedry magnetic separationa fairly homogeneous fraction is needed. If the food contains both dust and large pieces, separation occurs unevenly. Small particles, especially dusty ones, create an aerodynamic effect and are carried away by the air flow from the drum, even if they are magnetic. And large pieces may simply not have time to be magnetized in the area of ​​the field, especially if the rotation or feed speed is calculated incorrectly.

Therefore, the first thing I always look at a facility is not the separator itself, but the feed preparation system: dryers, screens, classifiers. Without them, even the most advanced magnetic device turns into an expensive toy. By the way,LONGI Corporationin their complexes they always focus on this, offering not just equipment, but a technological chain. On their websiteljmagnet.ruit is clear that they just grew out of practice, and not just from drawings.

Equipment: what is important besides the magnetic system

The heart of the separator is the magnetic system. Previously, we worked a lot with ferrite materials, then we switched to rare earth materials, and now we are increasingly talking about systems with an adjustable gradient. But there is a trap here: the desire for the maximum field is sometimes excessive. For many ores, especially ferruginous quartzites, what is more important is not the peak induction, but the correct field configuration and the stability of its operation under conditions of vibration and heating.

The design of the drum and hopper is a different story. Smooth versus corrugated drum, angle of inclination, method of removing the magnetic product - every detail affects. I remember an incident at one of the factories for the enrichment of magnetite sands: they installed a separator with a beautiful smooth drum, but the product was not removed, it stuck and the line had to be stopped for cleaning. It turned out that minimal corrugation and a different scraper were needed. A trifle, but downtime amounts to thousands of tons.

The aspiration system is a mandatory element that is often underfunded. Whendry magnetic separationA lot of dust is generated, which is not only harmful to personnel, but also impairs the visibility of the process, settles on the mechanisms, and creates an explosive environment. Good aspiration is not just an exhaust hood, it is a calculation of air flows so as not to carry away small magnetic particles.

From practice: examples and failures

Worked on a project to extract magnetite from old tailings. The material was finely dispersed, with high residual moisture after the tailings dump. The first thought is to dry it. But the economy has shown that drying costs eat up all profits. They began to experiment with preliminary granulation of the material and separation in “semi-dry” conditions. condition on a device with a special configuration of a rotating drum. Not ideal, but economically justified. This is the case when we had to move away from the canonical “dryness”.

But failure. We tried to use dry separation to refine chromite concentrate. The material seemed dry; the magnetic properties of pyrrhotite and magnetite-chromite were different. But in reality, due to electrostatics, the particles were magnetized chaotically, and the separation was unclear. We took the time to understand that a wet system is better suited for this type of ore, despite all its difficulties with water circulation. Conclusion: magnetic properties are not the only factor; surface properties are also important.

In catalogues, for example, the sameLONGI Corporation, you see models of separators for different tasks - from removing iron from quartz sand to extracting weakly magnetic minerals. For their simple description ?for dry separation? there are a lot of engineering solutions adapted for a specific ore. Their experience since 1993 in the development of mining equipment is felt precisely in such details that are not evident at first glance at the unit.

Key settings and controls

Drum rotation speed and material feed rate are a balance. If you increase the feed, you will increase productivity, but reduce extraction. If you do it slower, you will get a pure concentrate, but low throughput. There is no universal recipe; each time it is selected on the spot, often by trial. It’s good when the separator allows you to smoothly change these parameters without stopping.

The gap between the drum and the feed tray or dispenser. It would seem like a small thing. But this gap determines the thickness of the material layer. Too thin a layer - inefficient use of the working area, too thick - the lower layers are not properly exposed to the field. Often this adjustment is done manually, and its quality depends on the operator's experience.

Product quality control. Ideally, operational, on line. But many older factories still take samples once per shift and take them to the laboratory. While you are waiting for the result, you can lose tons of product. Current trends are the installation of sensors on output flows (for example, to measure magnetic susceptibility) for fast feedback and automatic adjustment of parameters. This is the next level to which our production still needs to grow and grow.

Looking Ahead and Final Thoughts

Where is it heading?dry magnetic separation? There is a trend toward intellectualization. Not just a device, but a system with sensors that itself adapts to changes in the composition of the food supply. Reducing power consumption is also important, especially for high-power systems with electromagnets. And, of course, materials: wear-resistant drum coatings, more heat-resistant and powerful permanent magnets.

For an engineer or technologist, the main thing is not to focus on equipment as a magic box. This is just one node in the chain. Its effectiveness is determined 50% by proper preparation of the power supply and 50% by proper operation and configuration. You can buy the best separator from a trusted manufacturer like LONGI, but install it in the wrong place or have it installed by an operator without understanding the process, and the results will be mediocre.

Ultimately, dry magnetic separation remains a powerful and relatively cost-effective tool, especially where water is scarce or uneconomical to use. But its success is always a compromise between theory, equipment capabilities and the harsh reality of the processing plant. And this compromise is not found in catalogs, but on the production site.