Olaf Drusche, HAZEMAG & EPR GmbH, describes the process of crushing and drying brucite ore at a Russian mine.

IntroductionVyazma Brucite LLC is a leading producer of brucite ore (Mg(OH)2) and magnesia products in Russia. The mining of the brucite ore takes place in an opencast mine in Kuldur, in Russia’s Jewish Autonomous region. The mine has more than 8 million t of proven reserves of raw materials. The Jewish Autonomous region is a federal subject of Russia, located in the Russian Far East,

bordering Khabarovsk Krai and Amur Oblast in Russia, and Heilongjiang province in China.

The run-of-mine (ROM) brucite ore is processed in a crushing and screening system with a capacity of up to 250 000 tpy. After primary crushing, the 60 – 200 mm fraction undergoes x-ray radiometric separation, where an enrichment process takes place. Innovative technologies

Tunguska River in the Jewish Autonomous Region in the Far East of Russia. Vyazma Brucite LLC’s mine is also located in the Jewish Autonomous Region, which borders Khabarovsk Krai and Amur Oblast in Russia, and Heilongjiang province in China.

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ensure stable quality of the concentrate, the properties of which are already very close to synthetic products. The newest equipment and technologies are used to perform processing operations.

The mine is located in the Far East of Russia, but further processing and beneficiation of the brucite ore into high-magnesia products takes place in Vyazma, Smolensk region, 200 km southwest of Moscow. For the processing of the ore, modern equipment is used, including energy-efficient HAZEMAG drying and grinding systems. Vyazma Brucite LLC recently bought a complete second drying/grinding system from the German company, containing the following components: a hot gas generator with a capacity of 750 kW, a HAZEMAG HGV 058 rotary gate valve, a single-rotor HAZEMAG HUM 1008 hammer mill, the material discharge device, and lastly the engineering of the complete plant.

Product mix and marketsBrucite is an uncommon mineral primarily known to mineral collectors and to specialists studying contact metamorphic and ultramafic rocks. It is environmentally friendly and flame retardant and is in commercial demand; it also represents a potential ore source for magnesium, which is itself in great demand. The present brucite market for flame-retardants is quite small, but it is increasing exponentially. Brucite has the advantage of not containing CO2; hence none is released during calcination, a positive feature in today’s society concerned with climate change. Given the demand for minerals and metals, high-grade brucite deposits may become hot exploration targets within the next few years.

Brucite is classified either as a magnesium metal ore or as an industrial mineral. In both instances, it has to compete for its share of the market with other materials. As an industrial mineral, brucite can be used in caustic and dead-burned magnesia production. It also has a variety of other industrial mineral applications, such as a functional filler in plastic compounds, fire and smoke retardant, electric wire insulation, and carpet backing. Brucite is also used in wastewater treatment. Other uses include agricultural feed, a dietary magnesium supplement, odour control, and in speciality cement preparations, as an additive to portland cements. The Russian Mining Chemical Co. and its subsidiary Europiren B.V., located in Rotterdam, serves the European, North and South American, and Asian markets in the aforementioned market segments.

Equipment selection processThe granulometric composition of the finished product depends only in part on the feed material’s crushing behaviour. The configuration of the grain structure is mainly influenced by the following machine-specific factors:

l The rotor circumferential speed, which may be chosen in the range of 25 – 100 m/sec., depending on the desired grain structure.

Figure 1. HAZEMAG HUM hammer mill cross section.

Figure 2. HAZEMAG HUM hammer mill.

Figure 3. HAZEMAG HUM hammer mill.

Figure 4. HAZEMAG hammer mill: disk rotor.

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l The gap width of the milling grates and/or perforated plates, which are in the lower area of the mill’s working space.

l The configuration, i.e. the length, of the grinding paths, which are also arranged in the lower area of the mill’s working space.

The rotor circumferential speed has the greatest influence on the fines produced in the finished product. The maximum admissible grain in the finished material is determined by the grate’s gap width or by the mesh aperture.

It is advisable to use a frequency converter for the regulation of the rotor circumferential speed. By means of the combination of frequency converter and milling grates with different gap widths, the HAZEMAG hammer mills provide efficient output of the desired grain size distribution.

For the correct dimensioning of the drive capacity, the power requirement for the idling, as well as for the actual crushing procedure of the material to be crushed, is referred to. The power requirement in idling depends on the dimensions of the rotor mass. It nearly increases with the square of the rotor circumferential speed.

Generally, the power requirement for the respective application is determined via tests in the in-house HAZEMAG pilot plant station or is derived from empirically determined characteristic values.

Taking into account the mineralogical-petrographic rock properties and the desired crushing ratios, the energy requirement of HAZEMAG hammer mills is in the range of 1 – 6 kWh/t. With good approximation, the drive capacity depends on the linear rate from the throughput rate. Therefore, the specific energy consumption is smaller, as the smaller the power requirement for the idling, the bigger the throughput rate is.

The range of machines from HAZEMAG’s machine portfolio considers all of the product-specific, process-technical, market-economic, and business requirements of the customer.

Equipment specificationsThe HAZEMAG hammer mills are versatile as their equipment may be adapted to the respective application. They have quickly rotating rotors in the working space, on which beaters (hammers) are flexibly mounted. Upon rotation, the latter are radially oriented by centrifugal forces. The material to be crushed, which is conveyed to the working space, is comminuted through impact and beaten as soon as the hammers strike it. During the impact procedure, the material knocks against the moving beaters, and the stroke crushing is effected between two solid surfaces at a high stress speed. With a corresponding hammer mass and rotor circumferential speed, the hammers maintain their extended position and only swivel out of this position in the case of large feed sizes and hard or uncrushable foreign bodies.

The fixed grinding tools may either consist of stepped grinding paths, milling grates, punched sheets, or a combination of these components. Depending on the machine type, the symmetrically-constructed mill casings may be opened manually or hydraulically. When opening the mill, the snap ring grooves in which the grinding path tools lie, are laid bare, thus enabling the mounting parts to be easily accessible and exchangeable. The rotors are disk rotors and are mounted in heavy antifriction bearings, which – depending on the construction size – are lubricated with grease or oil.

The torsion-free mill casing is protected against wear through screwed-on lateral plates of wear-resistant material. The mill casing is mounted on a base plate, which reduces dynamic loads as far as possible. Due to the machine’s relatively low weight, a trouble-free assembly of the complete unit is possible, even on lightweight basements and high steel platforms.

ConstructionThe drying and pulverising systems, which may be combined with HAZEMAG hammer mills, work according to the principle of short-time drying and are applied where a fine crushing and a simultaneous drying of the crushed material is required. Drying is effected per convection, i.e. a hot gas hits the material to be crushed and effects the vaporisation of the water. Normally, flue gases from a hot gas generator are used as hot gases; however, hot exhaust gases, which are available onsite, are also usable. Natural gas is utilised as a fuel for the hot gas generator. In combined drying and pulverising systems with HAZEMAG hammer mills, no drying with a dormant material layer is effected. Grinding and simultaneous drying happens at a hot gas speed of 20 – 40 m/sec.; hence the drying period is only a few seconds. Drying is effected according to the direct current principle, where the material is permanently in motion and is only marginally heated-up, which is of importance for the production of dry mortar, as too high material temperatures have a negative effect on the subsequent process steps.

Table 1. Technical data for the drying/grinding system.

Material Brucite

Feed grain size 5 – 100 mm

Bulk density 1.4 t/m³

Initial H2O content 3 wt%

Product H2O content ≤ 0.5 wt%

Product rate About 12 000 kg/hour

Product size 0 – 4 mm

Drying medium Hot gas generator

Gross heat capacity required About 750 kW

Hot gas temperature About 550°C

Off gas temperature About 130°C

Off gas volume flow rate About 7000 am³/hour

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In order to achieve a successful drying, the following points have to be complied with at the layout of a combined drying and pulverising system:

l A high temperature gradient between drying gas and material to be pulverised.

l A high difference in speed between hot gas and crushed material.

l A large specific surface area of the material to be crushed.

In doing so, thermal excessive stress of plant components –and especially dew point undercuts – have to be avoided during the cooling-down procedure in exhaust pipes and filters. Depending on size and design, the specific heat requirement of combined drying and pulverising systems may amount to 800 − 2000 kcal/kg water.

Crushing and drying compliment and support one another during the combined procedure. The material stresses being produced by the heat input, in the material to be crushed during the drying process, support the crushing process. The enlarged product grain surface, which results from the mechanical crushing in the hammer mill, permits the quick evaporation of the water that adheres to the product grain matrix. The selection of the hammer mill within a combined drying and pulverising system is effected on the basis of the feed quantity and the water content of the material feed, as well as of the required hot gas volume flow for drying.

Energy and environmentIn the past, the cost pressure caused increasingly high throughput rates of beneficiation plants at constant machine dimensions. This pressure will persist. Even larger beneficiation plants are to be expected in future, because the high-quality deposits have been exploited and, as a result, the raw materials quality in the ROM material is getting worse. The solution consists of the reduction of the ‘totex’ (total expenditures), that is in the use of smaller machine dimensions at the same or even a higher throughput rate with unchanged machine dimensions. The advantages of a higher performance level are the extension of the operating range and the development of new application fields. HAZEMAG hammer mills offer this advantage of a high performance level at comparably small dimensions, and are currently used across all sectors in different applications.

About the author After his raw materials and geotechnics studies in Bochum, at the Georg Agricola Technical University (1996 – 2000) with the focus on non-metallic mineral processing, opencast pit technology, beneficiation, and processing, Olaf Drusche has worked in different positions in sales, construction, and operations for various machine and plant construction companies. Since 2015, he has been working in the minerals division of HAZEMAG & EPR GmbH as the Senior Sales Manager.