Wet drum magnetic separator

When you hear 'wet drum magnetic separator', many people, especially those new to beneficiation, think of just a rotating drum with magnets inside. In fact, if it were that simple, there wouldn't be so many tweaks that decide whether you'll lose valuable magnetite in the tailings or not. I myself have worked with these units for more than ten years, and I will say that the key here is not even the magnetic system itself, but precisely the interaction of the pulp flow, the drum design and the field strength at a specific point. A common mistake is to assume that the more powerful the magnet, the better. For thin classes, it happens that excessive force only worsens selectivity and many joints are captured. This is what I want to talk about, based on practice.

Design: where the pitfalls lie

If you disassemble the separator by stones, then the base is, of course, the drum. But not just anyone. The thickness of the shell, the material (non-magnetic stainless steel is a must), the gap between it and the magnetic system - these are parameters that seem trivial on paper, but in production result in recovery percentages. I remember that at one of the factories they were faced with rapid wear of the shell. Local mechanics blamed the abrasiveness of the pulp, but upon closer inspection it turned out that the magnetic blocks inside were displaced and in places “attracted” the drum, creating local friction. After reassembly and fine adjustment, the problem went away.

The magnetic system is a different matter. Previously, ferrite magnets were often used, but their strength was not enough for fine ores. Now the standard is neodymium assemblies. But there is a nuance here: the configuration of the poles. Alternating 'north-south' along the length of the drum or around the circumference? The first scheme is suitable for coarse sands, and for fine slurries, where particles need to be retained for a long time in the field action zone, the second scheme is often more effective. This is not a dogma; it needs to be tested on specific material.

And the most underrated element is the tank and feed system. Shape of the concave, position of the supply pipe, flow rate. If the flow is too turbulent, the particles do not have time to 'sink' and fly past the magnets' zone of action. I saw installations where they simply lowered the pipe 15 cm deeper and distributed the flow more evenly across the width of the drum - extraction increased by 3%. It would seem nonsense, but on a yearly scale - thousands of tons of concentrate.

Field tuning: from theory to practice

Data sheets are good, but the real work begins when the separator is integrated into the process chain. The main adjustable parameters are: drum rotation speed, pulp level in the tank and its density. Their interconnection is an art. High rotation speed means higher centrifugal force, which can “break off” large particles. But for thin sludge, sometimes a high speed is needed in order to create more active cleaning on the surface of the drum and remove non-magnetic impurities.

Pulp density is a critical parameter. Too thick - the magnets “suffocate”, cannot penetrate the layer of particles, and separation deteriorates. Too liquid - performance decreases and wear increases. Rule of thumb: For most iron ore slurries, the optimum density is in the region of 25-35% solids. But this is a rule, not a law. At one of the deposits in Karelia we had to work with a density of 40%, because the ore was specific, very light in slurry, otherwise we lost weight. I had to adjust the angle of inclination of the magnetic system.

Water quality is often forgotten. Hard water with salts can cause fine particles to 'stick together', forming agglomerates, which the separator perceives as large magnetic grains. This leads to contamination of the concentrate. There was a case when the factory changed the source of water supply, and suddenly the quality of the concentrate dropped. For a month they looked for the reason in mechanics, but it turned out to be in water chemistry. I had to install a simple softening system.

Typical problems and 'rake' that people step on

From practice, the most common breakdowns and failures are rarely associated with magnets. They last for years. The main headache is the drum shaft seals. Constant contact with abrasive pulp, even with seals and seals, leads to leaks. The solution is regular inspection and the use of wear-resistant materials. Some plants are switching to mechanical seals with a clean water supply under pressure - more expensive to install, but saving tons of concentrate that is not lost with leaking slurry.

Another “rake” is the uniformity of nutrition. If different amounts of pulp enter at different points along the length of the drum, then somewhere there is an overload, and somewhere there is an underload. This can be seen visually by the uneven layer of concentrate on the drum. The solution is to install a distribution tray or calibrate the dampers. Major repairs are not needed, but the effect is significant.

Corrosion. Even stainless steel can suffer in the aggressive environment of mine waters. Especially in weld areas. Regular inspection, especially after stops, is mandatory. One small pitting corrosion can turn into a through hole within a season, and then instead of separation you will have a constant air leak and a violation of the regime.

Experience with equipment from LONGI

In the context of talking about reliability and engineering solutions, it is worth mentioning the experience of working with separators fromLONGI Corporation. The company is not well known to everyone, but it is known among the professional community.'Shenyang Scientific Electromagnetic Co., Ltd. LONGJI', created back in 1993, over decades has accumulated solid experience in mining and processing equipment. Their factory in Fushun is not a handicraft workshop, but an enterprise with an area of ​​140,000 m2 and a team of over 1,200 people, which indicates a serious scale of production.

Specifically themwet drum separatorsWhat distinguishes it, in my opinion, is the thoughtfulness of the basic design. For example, they often use a cast (rather than welded) drum shell made of a special non-magnetic alloy, which immediately eliminates the issue of seam corrosion. The magnetic system is assembled on powerful neodymium magnets with a clear pole geometry, which gives a stable and deep field. I noticed that their standard configuration already includes a system for adjusting the angle of the magnetic block relative to the vertical - a small thing, but it saves the adjuster a lot of time on site.

I worked with their CTS series separator at one processing site for the enrichment of iron ore technogenic dumps. The material was complex, thin, with a high content of sludge. The device proved to be stable. What is important is that it was possible to achieve stable extraction of magnetite in the -0.05 mm class, which is a problem area for many separators. Of course, there were some on-site adjustments to the concentrate unloading system, but the base was solid. For those looking for information, details about their design approach can be found on their websitehttps://www.ljmagnet.ru. It shows that the emphasis is on engineering calculations for a specific ore, and not on selling a 'box with a drum'.

Thoughts out loud about the future of such separators

Where is technology heading? There are several growth points visible. The first is intelligent control systems. Sensors that monitor the thickness of the concentrate layer on the drum in real time, and automatic adjustment of rotation speed or pulp level. This is no longer science fiction, there are pilot projects. The second is materials. The emergence of more wear-resistant and at the same time non-magnetic coatings for drums can significantly increase their service life.

Third, and perhaps most important, is hybridization.Wet drum magnetic separatorrarely works under ideal conditions on clean material. Often he is faced with the task of 'scooping' magnetite out of a complex mixture. Therefore, more and more often I see schemes where a drum separator works in tandem, for example, with a gravitational concentrator or a high-intensity separator for finishing. In itself, it is a powerful and reliable workhorse, but it produces maximum effect in a properly structured technological chain.

In the end, back to the beginning.Wet drum magnetic separator- This is far from a primitive unit. This is the result of a balance between magnetic physics, fluid dynamics and practical enrichment experience. Its effectiveness is not only the data from the catalog, but also the ability to hear and see how it works here and now, with this particular pulp. And it is precisely this practical experience, full of bumps and solutions found, that is the most valuable part of knowledge about this seemingly classical technology.