wet magnetic separator

When they talk aboutwet magnetic separator, many people imagine just a rotating drum with magnets inside, and that’s all. But if everything were so simple, there would not be so many problems at processing plants with fine magnetite ores. The main mistake is to assume that the main work is done by the magnetic system. In fact, at least half of the success is the correct supply of pulp, the design of the unloading device and, oddly enough, water. The pulp is too thick - the magnet does not have time to “stick”, too liquid - it carries away non-magnetic particles. There is also a nuance with field strength. Everyone writes “high-gradient”, but for each fraction and each type of ore there is its own “high” grade. Sometimes 1500 Gauss is enough, but for thin slurries even 10,000 may not be enough if the flow rate is incorrectly calculated.

What does effectiveness actually consist of?

Let's go in order. The magnetic system is the heart of the device. Previously, ferrite magnets were often used, but for thin classes they were rather weak. Now the standard is rare earth (neodymium-iron-boron). But here’s what’s important: not just insert powerful magnets, but arrange them correctly into a pole system. The alternation of poles, the angle of coverage of the drum - this affects the “turning over”. particles and waste rock washing. We had a case at one of the factories in the Urals: they installed a separator with a supposed super system, but the extraction of magnetite into concentrate increased by only 2%. They began to look into it - it turned out that the poles are located in such a way that they create “dead zones”, where particles simply slip through. We redid the circuit on site, increased the coverage angle to 140 degrees - the result was +8% to recovery. This refers to the question that ready-made equipment always needs to be “customized?” for a specific ore.

The second key element is the tank and delivery system. The pulp must flow evenly along the entire length of the drum, otherwise in some sectors there will be an overload, and in others there will simply be an idle run of water. They often save on the distribution tray and make it from ordinary steel, which is quickly corroded by abrasive pulp. After six months, the flow profile is already distorted and efficiency drops. In our projects, we always insist on wear-resistant lining of the tray, although this increases the cost of the design. But it’s better to invest once than to stop the line for repairs every few months.

And the third point that is often overlooked is the flush system. It is not enough to simply have water nozzles. Their location relative to the unloading zone of the magnetic product is important. If the jet hits too early, it washes the not yet separated magnetite back into the tailings. If it’s too late, the concentrate is poorly washed from sludge. You have to select experimentally, sometimes directly on a working device, with a stopwatch and a sampler in your hands.

Experience and rake: when theory diverges from practice

I remember a project for a plant in Karelia. The ore is complex and finely disseminated. Customers wanted high recovery from the -0.1mm class. According to calculations and laboratory tests, ourwet magnetic separatorwith a high-gradient system it should have produced 92-93%. In practice, the industrial sample barely reached 87%. We started looking for the reason. It turned out that the laboratory used deslimed ore, but in a real flow the pulp contained a large amount of fine clay particles, which changed its viscosity and electrokinetic properties. These particles enveloped the magnetite grains, preventing them from being captured. We had to refine the preliminary classification scheme on the fly and introduce an additional desliming stage in front of the separator. This added costs, but without this the separator worked at half capacity.

Another common mistake is ignoring the influence of previous crushing and grinding stages. If the ore after the mill contains a lot of over-ground magnetite (the so-called “sludge?”), then even the best separator will not catch it - the particles are too small and their magnetic moment is weak. They will go to the tails. Therefore, sometimes it is more effective not to strengthen the magnetic field, but to optimize the grinding mode in order to minimize overgrinding. This is a systematic approach that is often forgotten when chasing the “magic” solution. setting up one device.

There was also a curious case with corrosion. At one of the Siberian enterprises, the separator, having worked for only a season, began to lose productivity. They opened it up and found loose brown deposits inside the tank and on the drum. The analysis showed the active development of iron bacteria in the circulating water. It turned out that the water was taken from a closed bypass channel, where ideal conditions for microflora were created. These bacteria literally “ate” magnetic field, creating an insulating layer. The solution was simple - we installed a UV sterilizer on the water supply line. The problem is gone. But who thinks about this at the design stage?

LONGI equipment in this context

Working with a variety of equipment, includingLONGI Corporation, you note their approach to consistency. They don't just sell a separator, but often offer to test your ore at their stand in Fushun. This is expensive and time-consuming, but it avoids many of the pitfalls I mentioned above. They have a model range where different configurations of magnetic systems and tank designs are used for different tasks - from primary enrichment of large classes to additional extraction of magnetite from tailings. This is important because a universal “separator for all occasions”? does not exist.

For example, their concentrate purification devices often have a two- or even three-stage wet magnetic separation scheme in one housing, with intermediate dilution and washing. This makes it possible to achieve a high iron content in the final concentrate with minimal losses. I saw their installations at one of the mining and processing plants in Kuzbass - they work stably, although the local ore is also not a gift, with a high clay content.

What impresses is their attention to detail in the design. The same lining with wear-resistant rubber at key points, dismountable units for easy replacement of magnets (this, by the way, is a sore spot for many manufacturers - to change the magnetic block, sometimes you need to disassemble almost the entire separator), well-thought-out hatches for inspection and cleaning. This suggests that the designers have been to factories themselves and know what problems operators face.

Thinking out loud about the future of technology

Where to go next? The increase in field strength probably has a limit. Rare earth magnets already produce huge values. I think the reserve lies in intelligent process control. Sensors that monitor pulp density, iron content in the feed and concentrate in real time, with automatic adjustment of drum speed, water flow and possibly even the angle of inclination of the magnetic system. So that the separator itself adapts to changes in the quality of incoming ore. This is no longer science fiction; the first such systems are appearing.

Another trend is combined devices. For example,wet magnetic separator, combined with a gravity jigger or flotation chamber for complex processing of complex ores. This will make it possible to extract both magnetic, weakly magnetic, and non-magnetic valuable components in one unit. It is still difficult to construct, but work is underway.

And of course, the fight for energy efficiency will always be relevant. The drum drive, water and pulp pumps are all energy consumers. New lightweight drum designs made of composite materials and more efficient motors mean direct savings for the enterprise. Sometimes the money saved on energy in a year can cover a good part of the cost of the device itself.

Instead of a conclusion: just a tool in a chain

As a result,wet magnetic separator- this is not a panacea and not a black box into which you poured ore and got a concentrate. This is a precision tool, the effectiveness of which is determined 30% by its design and 70% by how it fits into the process chain, whether the material is prepared for it, and whether the operators understand it. The most perfect device can be ruined by improper use. Conversely, an old separator, with proper adjustment and minor modifications, can show excellent results. The main thing is not to blindly believe the passport data, but to constantly analyze, experiment and listen to what is happening inside this rotating drum. This is precisely the job of a mineral processing engineer, not just pressing buttons on a remote control.