removing impurities from water

When people talk about removing impurities from water, most people immediately think of household filters or industrial reverse osmosis systems. These are, of course, key methods, but the area is much broader and more capricious. A common mistake is to consider the process a purely mechanical separation of dirt. In fact, especially on an industrial scale, for example, in mining and processing processes, with which I worked a lot, water is an active medium, a carrier of reagents, and its purification is the control of chemical and physical states. Sometimes it is not necessary to filter the solid phase, but, on the contrary, to create conditions for its effective sedimentation or flotation. This is where the most interesting and difficult part begins.

Mining: where water is both a working tool and a problem

In my practice, related to the supply of equipment for mining plants, the issue of purifying process water is a pressing issue. After crushing and grinding the ore, pulp is obtained - a mixture of water and fine solid particles. The task is to separate the water for its reuse in the cycle (recycling water supply) and at the same time obtain a dehydrated concentrate. If the water is poorly purified from suspended matter and, critically, from residual reagents (collectors, foaming agents), the entire flotation in the next cycle goes awry. The economics of the process are going downhill.

This is where magnetic separators are often used to remove ferromagnetic impurities, which is especially important at iron ore enterprises. But not all particles are magnetic. For thin sludge and clay suspensions, coagulation and flocculation processes are often used - this is already a chemicalremoving impurities from water. You add a reagent, the smallest particles stick together into flakes, which can be deposited in settling tanks or removed from the surface. Calculating the dosage and choosing a reagent is always a field for experimentation right on site. I remember an incident at one of the plants in Kuzbass: standard polyacrylamide did not work, I had to select a combination of cationic and anionic flocculant, and only then the clarifier worked as it should. The water became clear.

This is about the fact that there are no universal solutions. The technological map, the type of ore, the composition of the formation water - everything has an impact. Sometimes it is easier and cheaper to build a cascade of settling ponds, where the water settles naturally for weeks, but this requires huge areas. Somewhere they install powerful centrifuges or filter presses. The choice is always a compromise between capital costs, process speed and cleaning quality.

Magnetic methods: not a panacea, but a powerful tool

In the context of my experience of cooperation with industrial equipment manufacturers, I would like to highlight magnetic separation. A company like LONJI Corporation (official website - https://www.ljmagnet.ru), with its many years of experience in the development of mining equipment, knows this firsthand. Theirimpurity removal equipmentThe magnetic method is often used to protect pumps and pipelines from metal scrap, as well as to extract magnetic iron ore from pulps. This is ?Shenyang LONGJI Scientific Electromagnetic Co., Ltd., established back in 1993, and their engineers are well aware that a magnetic separator is not just a magnet in a housing.

An important nuance that is rarely written about in catalogs: the efficiency of magnetic separation drops sharply if pulp that has not been cleared of large debris passes through the drum. Abrasive particles wear out the drum, and pieces of wood or rags can jam it. Therefore, there is almost always a screen or sieve in front of the separator. This seems obvious, but at new facilities they often forget about it, trying to save on “little things”. Then unscheduled stops, repairs... Real operation always makes adjustments.

Another point is to clean the working surface of the separator itself from adhering magnetic product. In older models, use a manual scraper. Modern ones, like LONGI, often use an automatic release system (for example, using compressed air or moving scrapers). But if the sludge is very viscous and wet, it may not be completely discharged; a “beard” is formed, which reduces the magnetic field strength on the surface. You have to monitor, sometimes even change the reset mode for a specific material. Such details only come with experience of observing a working line.

Process chemistry: fine tuning and control

Let's return to chemical methods. Coagulants and flocculants are not “set and forget”. Their effectiveness depends on the pH of the medium, water temperature, ionic composition, and mixing speed. At one of the gold mining plants in Siberia, they were faced with a seasonal problem: in summer, the water in the river where the intake came from was much warmer than in winter. The winter dose of flocculant stopped working in the summer - flakes did not form, the settling tank could not cope. We had to make adjustments to the seasonal regulations. This is an example of how the systemremoving impuritiesmust be adaptive.

Controlling the reagent injection point is also a science. If you introduce the flocculant too early, in the zone of turbulent flow, it will simply break into molecules and will not work. If it’s too late, it won’t have time to form flakes before the settling tank. Usually, special mixing chambers with adjustable rotation speed of the mixer are installed for this purpose. But even there, you need to empirically select the pulp retention time. Simple visual control often helps: you take a sample after the mixing chamber into a transparent glass and watch how flakes form. Primitive, but clear and fast.

And of course, the economy. Reagents are a fixed cost. Sometimes it is more profitable to invest in a more advanced mechanical dewatering apparatus (such as a chamber filter press with membrane extraction), which will produce a drier cake, even with less well-clarified water, than pouring tons of expensive flocculant. Calculating the total cost of ownership (TCO) for a water purification system is a mandatory step, which, unfortunately, is sometimes ignored, choosing a simple and cheap solution at the start.

Equipment and its vagaries: from practice

Any water purification equipment requires maintenance. Settling tanks (thickeners) must be regularly cleaned of accumulated sludge, otherwise their efficiency decreases. Pumps pumping abrasive suspensions have a limited service life of impellers and housings. We once supplied slurry pumps with wear-resistant linings to the site, but the client saved money and bought cheaper spare parts not from the original manufacturer. The resource has dropped threefold, constant downtime. My firm belief: at critical nodes, especially those associated with pumping media containing solidsimpurities in water, saving on materials and original spare parts almost always backfires.

Another painful point is automation. Modern reagent dosing systems with feedback from turbidity sensors are great. But in remote, dusty and cold industries, these sensors can become dirty and fail. And the operator switches to manual control “by eye”. Therefore, when designing, it is always necessary to include the possibility of simple, redundant manual control and easy access for cleaning and calibrating meters. Reliability is more important than “sophistication”.

LONGI Corporation, with its production capacity (area of ​​140,000 m2, more than 1,200 employees) and annual production of about 4,000 units of equipment, is one of those who understand the importance of reliability in harsh conditions. Their products, whether a magnetic separator or part of a processing line, are designed to last. But even the highest quality equipment requires competent integration into the technological chain and understanding on the part of the operating personnel.

Results: thinking out loud

So, back to the topicremoving impurities from waterin industry... It is never easy to “install a filter”. This is a complex problem at the intersection of mechanics, chemistry, hydrodynamics and economics. Success depends on an accurate understanding of the nature of the impurities, the characteristics of the water flow and a clear definition of the purpose of treatment: for recycling use, for discharge into a reservoir, or to obtain a marketable product.

Often the optimal solution is a hybrid solution: rough mechanical cleaning (grids, sieves), then magnetic separation (if there are ferromagnets), then a chemical precipitation stage and, finally, fine dewatering. But the circuit needs to be “adjusted” each time. for specific raw materials and conditions. There are few ready-made recipes.

The main conclusion that I made for myself: the best results come from close cooperation between the equipment manufacturer (like LONGI engineers who know the capabilities of their equipment) and on-site technologists who understand the nuances of their production. When these parties begin to speak the same language, a truly effective and resilient system is born. And water, purified from impurities, ceases to be a problem and becomes a valuable resource that works for the cycle, saving both money and natural reserves.