wet magnetic separation of iron ores

When you hear “wet magnetic separation,” many people imagine just a drum with magnets filled with pulp. In fact, this is a whole philosophy of getting rich, where little things decide everything. They often mistakenly focus only on field strength, forgetting about particle size distribution, pulp viscosity or even water temperature. I myself worked at several factories where, due to such a simplified approach, up to 15% of magnetite was lost into tailings. I’ll try to break down what it looks like from the inside, without the gloss.

From theory to practice: where the main losses lie

In textbooks, the process looks ideal: ore pulp enters the separator, magnetic particles are attracted, non-magnetic particles are carried away. Reality is harsher. One of the main problems iswet magnetic separationfinely disseminated ores. If large fractions of magnetite (0.1 mm and above) flow away relatively cleanly, then thin slurries (minus 0.044 mm) are often carried away by the water flow, even having magnetic properties. This is not due to a lack of magnetic force, but due to hydrodynamics. Flow speed, slurry feed angle, clearance between drum and tank - all these are parameters that are adjusted empirically, often right on site.

I remember at one of the old plants in the 2010s they tried to increase recovery by simply increasing the drum speed. Result? The more turbulent flow began to wash away even medium-grained concentrate, plus the wear of the lining increased. We had to return to the old settings and change the approach - we began to pre-classify the pulp in hydrocyclones, sending a product that was more uniform in size for separation. This gave an increase, but added operating costs. This is the balance.

Another nuance is the quality of water. Hard water with a high salt content can lead to “sticking?” fine particles, the formation of agglomerates that behave unpredictably in the separator. In Siberia, at one field, they encountered seasonal changes in the composition of the water from the river that was used in the process. In winter, extraction dropped by 3-5%, until they decided to conduct a chemical analysis and began adding simple dispersants. It's a small thing, but it has an impact.

Equipment: All that glitters is not gold

The market is flooded with proposals, but reliability and maintainability are often more important than passport specifications. He worked a lot with devices of different generations - from Soviet PBMs to modern series. The key element is the magnetic system itself. Rare earth permanent magnets (NdFeB) are certainly a breakthrough compared to ferrite or electromagnetic systems. They provide a stable field, do not require energy for magnetization, and heat up less. But they also have an Achilles heel - fragility and sensitivity to temperature changes. In the north, at -40, the drum body can develop a microcrack, moisture gets on the magnetic blocks - and corrosion begins, causing an irreversible loss of strength.

It is worth noting here that some manufacturers have learned to deal with this. For example, in equipment fromLONGI Corporation(their website ishttps://www.ljmagnet.ru) saw the use of multi-layer sealing of magnetic blocks in drums. This company?Shenyang Scientific Electromagnetic Co., Ltd. LONGJI?, has been in business since 1993 and has grown into a major player in the mining equipment market. Their production base in Fushun is impressive in scale - 140 thousand m2, more than 1200 employees, most of whom are engineers. They rely on adapting equipment to the specific conditions of the customer, which forwet magnetic separationcritically important. Not just sell the unit, but design it for a specific ore, and provide for the possibility of modernization.

But even with good equipment, incidents happen. Once a new separator with a high declared productivity was installed at the factory. And the supply of the pulp was left with old worn-out pumps that could not provide uniform pressure. As a result, the device worked in constant overload and “starvation” mode, the result was worse than the old one. I had to change the entire feed system. Conclusion: a separator is not a magic box, but part of a technological chain.

Recovery and concentrate quality: the eternal compromise

The main KPI is the percentage of extraction of the magnetic fraction. But chasing 99% is a utopia and economically unprofitable. With each additional percentage of recovery, the costs of tailings processing rise sharply, and the quality of the concentrate decreases due to the capture of aggregates and impurities. The sweet spot is usually somewhere between 92% and 96% for run-of-the-mill magnetite ores. It is determined not only technologically, but also economically—the cost of iron ore concentrate, electricity tariffs, and water.

The quality of the concentrate is a separate pain. The iron content is one thing, but the content of silica, sulfur, and phosphorus is also important.Wet magnetic separationIt removes free non-magnetic minerals well, but if apatite or pyrrhotite is in close intergrowth with magnetite, they will go into concentrate. To combat this, additional operations are sometimes used - for example, reverse flotation of a magnetic concentrate. But that’s another story and different investments.

There was an interesting experience at one of the processing plants in the Urals. The ore had a high manganese content. Magnetite and braunite (manganese mineral) have different magnetic susceptibility, but in the range of operating fields of the separator they were both recovered. The result was a concentrate with increased Mn, which metallurgists were not very fond of. I had to experiment with field strength and gradient to find a regime where the magnetite was extracted as much as possible, and the brownite, if possible, remained in the tailings. It was not possible to completely solve the problem, but the Mn content was reduced by a third. Sometimes success is not an ideal, but an acceptable compromise.

Prospects and dead ends: where technology should go

It would seem that the technology is old, what can be invented here? But there is progress. These include new designs of separators with polygradient magnetic systems, which create a non-uniform field for better capture of thin and weakly magnetic particles. These are automatic monitoring and control systems based on density sensors and magnetic susceptibility of the pulp in real time. Allows you to quickly adjust the regime, save water and reagents.

But there are also dead-end branches. For example, attempts to usewet magnetic separationfor deep enrichment of oxidized iron ores (hematite, hydrogoethite) without magnetizing roasting. Direct separation of weakly magnetic oxides in low-intensity fields gives scanty recovery. I have seen projects where magnetite weighting material or ferrosilicon was added to the pulp in an attempt to create an artificial magnetic environment. Technically it worked in the laboratory, but on an industrial scale it turned out to be terribly expensive and difficult to manage. Investors were disappointed.

Now, in my opinion, the most promising vector is not the creation of a “supermagnet”, but the intellectualization of the entire process. An integrated approach from crushing and grinding to separation, where the parameters of each previous stage are optimized for the final goal. And here is the experience of such manufacturers asLONGI, which deal not only with separators, but also with other mining and processing equipment, may be key. Their ability to design turnkey complexes allows you to build a more harmonious technological chain, wherewet separationwill not be a separate node, but a logically built-in element.

Instead of a conclusion: thinking out loud

So, to summarize... It's unlikely to work. Because every ore, every quarry, every plant is a unique case. There are no ready-made recipes. There are basic principles, the physics of the process, that are unchanged. And everything else is constant adjustment, observation, analysis of sludge and samples, sometimes a step back in order to take two steps forward.Wet magnetic separation of iron oresis a craft based on science. You can buy the most expensive equipment, but without understanding these nuances, without specialists who understand the process, you cannot achieve high results. The technology is alive and will live as long as there are magnetic ores. It just requires not blindly following instructions, but a thoughtful, almost intuitive approach. Which, however, makes the work interesting.