removal of coarse impurities

When they talk aboutremoval of coarse impurities, many immediately imagine ordinary nets or sedimentation tanks. But in practice, especially in mining and processing, this is a whole science. A common mistake is to underestimate the abrasive effect of these same impurities on subsequent equipment. I have seen more than once how, due to a poorly designed first stage of cleaning, pumps quickly wore out or heat exchangers became clogged. Here it is important not just to “weed out the large ones,” but to understand the particle size distribution, particle density and their shape. The choice of method depends on this: screening, hydrocycloning or, say, magnetic separation, if we are talking about ferromagnetic inclusions.

Screening: the first frontier and its pitfalls

It all usually starts with rumblings. It would seem, what could be simpler? But here’s a caveat: the efficiency of screening drops significantly with high humidity of the material or the presence of clay fractions, which simply stick to the sieves. I remember an incident at one of the iron ore processing factories. They installed standard vibrating screens, and after a couple of weeks the productivity dropped by half. It turned out that the ore was heavily watered, plus the overburden rocks produced a lot of fine clay. The Sith stuck together into a monolith, and the entire system stopped. It was necessary to urgently introduce a preliminary dehydration stage and switch to sieves with a ball cleaning system or ultrasonic release. This is the very moment when theory diverges from practice - on paper the fractional composition is ideal for screening, but in reality the process does not work.

Another point is the choice of cell size. Often the technologist, trying to purify the product as much as possible, uses a mesh that is too fine. This leads not only to over-grinding of useful component particles, but also to a sharp increase in the load on the screen, its overheating and frequent breakdowns of bearing units. The optimal size is always a compromise between product purity and equipment life. Sometimes it is more economically profitable to skip some of the medium-disperse impurities at this stage and retain them later, for example, in hydrocyclones.

Here, by the way, screens from some trusted manufacturers perform well, taking into account such nuances in the design. For example, in equipment that suppliesLONGI Corporation (https://www.ljmagnet.ru), it is often possible to quickly change sieves and adjust the vibration amplitude for different types of wet or sticky materials. This is not an advertisement, but an observation - when a company like LONGIE has been operating since 1993 and produces thousands of pieces of mining equipment per year, they usually already have experience from such “field” in their decisions. problems.

Hydrocyclones: when water becomes a tool

If screening is a dry or semi-dry method, then hydrocyclones are already a wet classic. The principle is simple: centrifugal force separates heavy large particles. But simply installing a cyclone is not enough. The key parameter is the inlet pressure. Too low - it will not create the desired vortex, the large fraction will not separate. Too high - the wear of the sand nozzle and abrasive wear of the body itself will increase. We had an experiment in the desliming section: we increased the pressure to improveremoval of coarse impuritiessand The efficiency really increased, but after a month of work the lining of the cyclone and the nozzle had to be changed - they were worn down almost to holes. They considered the economy - the gain in quality did not cover the costs of spare parts and downtime.

The design of the hydrocyclone itself is also variable. The taper angle, the diameter of the sand and drain pipes - everything is selected for a specific task. For very coarse and heavy impurities, short-cone cyclones with a large diameter are sometimes used. But they are generally less effective for fine separation. It's always a balance.

Pulp preparation is often forgotten. If the density or viscosity of the suspension “walks”, the operation of the cyclones becomes unstable. We need constant measurements and, preferably, automatic adjustment. Without this, you can end up with either an overloaded sand product with a mass of small valuable particles, or, on the contrary, a dirty drain with pieces of rock that should have gone into the sand.

Magnetic separators: for special cases

This is a more specific method, but in the context of removing impurities from, for example, iron ore concentrate or when processing slag, it is irreplaceable. We are talking about removing random ferromagnetic inclusions - fragments of support and tools that got into the ore during mining. These inclusions are typical coarse impurities, but with special properties.

This is where the type of separator is often mistaken. To remove large pieces of metal (several millimeters in size), drum separators with a self-discharging belt or suspended separators above the belt are suitable. But if the metal is small but still ferromagnetic, separation at higher magnetic field gradients may be required. Once I had to deal with the increased iron content in a non-metallic concentrate. We installed a standard drum separator - it did not help. It turned out that the impurity was fine magnetite dust that had settled on particles of a useful mineral. The problem was solved by introducing a wet magnetic separation stage with finer tuning.

Companies with deep expertise in electromagnetic technology are particularly noticeable in this segment. SameLONGI Corporation, being originally a scientific electromagnetic company, often offers solutions where magnetic separation is integrated into the overall circuitremoval of coarse impuritiesnot as a separate operation, but as a logical addition to screening or classification. This is an approach that comes from experience in complex equipment design.

Practical pitfalls and process integration

The biggest mistake is to consider the stage of removing coarse impurities in isolation. This is a link in the chain. For example, if after screening the material goes into a ball mill, then the large pieces of waste rock that have not been removed not only waste the grinding media, but can also become a source of that same metal scrap (when the lining and balls wear out), which will then be a problem at the stage of magnetic separation. It turns out to be a vicious circle.

Therefore, it is important to have feedback between stages. A simple example: if the operator notices an increase in large particles in the drain of hydrocyclones, this is a signal of either a drop in supply pressure or wear of the sand nozzle. You need to react quickly, otherwise the entire subsequent technological chain will lead to defects.

Another trap is changing the properties of the feedstock. There is only one deposit, but different parts of it can produce ore with different propensities for decay, hardness, and clay content. What worked yesterday may not be effective today. A certain flexibility of the circuit is needed and, what is important, trained personnel who understand the essence of the processes, and do not just monitor the readings of the sensors.

Instead of a conclusion: thinking out loud

So,removal of coarse impurities- this is far from simple “filtration”. This is the first and critical barrier to raw materials being processed. The wear and tear of all equipment, the consumption of flotation reagents, the quality of the final concentrate and, ultimately, the economy of the entire enterprise depend on its efficiency. The methods are as old as the hills, but the subtleties of their application have been honed over the years, often through trial and error. And the key to success is not in the ideal equipment from the catalog, but in a correctly selected and adapted scheme for specific, always slightly unique, conditions. That is why cooperation with manufacturers who are themselves immersed in the industry and have dozens of completed projects behind them, like LONGI with its more than 1,200 employees and its own production, often gives a more reliable result than buying a “universal” one. solutions. Because they have most likely already gone through these mistakes over the 30-odd years of work and know where the weak points in the process may be.