EFFICIENCY OF VERMICULITE ORES ENRICHMENT IN AIR FILTER

ABSTRACT

The mineralogical and technological properties of vermiculite raw materials are analyzed in the article, the main properties of natural vermiculite are studied. As a result of the tests, a technological scheme for dry beneficiation of vermiculite ores was developed. The output of vermiculite concentrate by fractions is 10.57%, its amount in enrichment is 85%, the separation of vermiculite in enrichment is 95.95%.

АННОТАЦИЯ

В статье проанализированы минерало-технологические свойства вермикулитового сырья, изучены основные свойства природного вермикулита. В результате испытаний разработана технологическая схема сухого обогащения вермикулитовых руд. Выход вермикулитового концентрата по фракциям составляет 10,57%, его содержание в концентрате 85%, извлечение  вермикулита при обогащении 95,95 %.

Keywords: vermiculite, ore, enrichment, mineralogical composition, chemical composition, air separator, yield, recovery.

Ключевые слова: вермикулит, руда, обогащение, минералогический состав, химический состав, воздушная сепарация, выход, извлечение.

The production of vermiculite and materials based on it has just begun to develop in the Republic of Uzbekistan. high porosity, low density and low thermal conductivity, as well as high fire resistance and stability of the mineral content made it widely used among other heat-insulating materials. Dry building mixes are made from it, fire-resistant boards and paints are produced, it is widely used in insulation of heating devices and soundproofing of rooms, steel casting [1].

Currently, 500-600 thousand tons of vermiculite is produced annually worldwide, about 80% of which is mined in the USA and the Republic of South Africa, and the rest in Brazil, Argentina, China, India, Egypt, Kenya and Russia [2]. More than one hundred types of vermiculite products are produced in economically developed countries [3]. In most countries, the use of vermiculite is still limited due to the fact that the building materials production industry is not equipped with modern energy and resource-saving technologies [7-8]. Expanded vermiculite is widely used as an effective thermal and sound insulation material, porous filler for lightweight concrete and plastering admixtures, and other purposes [4].

Vermiculite is widely used in steel casting, water filtration, as an adsorbent of smoke and toxic gases, as an anti-radiation material, in wastewater treatment, in oil spill recovery, and in reducing soil nitrate pollution [2]. Agro vermiculite is widely used in horticulture and floriculture in developed countries with high agricultural culture [6].

In the steel and iron-based alloy casting industry, the melting of any metal is always associated with high temperatures, so a reliable refractory material is required to ensure the operability of the technological processes and to protect the equipment. Vermiculite can withstand temperatures above 1300⁰C and provides low thermal conductivity. Excellent adsorption properties of vermiculite are used in cases of disruption of technological processes in the production of chemical reagents, alkalis and acids

When it comes to the use of vermiculite in the energy industry, it is primarily used in atomic energy due to its ability to reflect gamma radiation and absorb the destructive radiation of radioactive isotopes including strontium, cesium, cobalt, and others. It is also used to create fire-resistant protection for high-voltage electric cables and distribution boxes, to organize fire barriers in energy complex facilities. The process of applying vermiculite to many branches of the engineering industry began: in the automotive industry, it is one of the main components in the production of brake pads and other friction products, effectively reducing the temperature that occurs during high-speed friction allows (has high physical and mechanical properties), as a result, the service life increases [2]. In the aircraft industry, based on the fire-resistant properties of vermiculite, special coatings have been created for runways that have the ability to quickly extinguish (reduce) the temperature during braking. In shipbuilding, vermiculite is included in the coatings used for the underwater part of ships. This prevents the growth of molluscs on the ship's hull. Fire-resistant parts and thermal insulation in ships and cars are also produced on the basis of vermiculite [2].

Adsorption properties of vermiculite open a wide way for its use in the food industry. The natural origin of this material makes it possible to use it for filtering water and all kinds of suspensions (sugar syrup, starch and molasses-based products, vegetable oils, alcohol products and beer, fruit and vegetable juices). In addition, vermiculite serves as insulation in food storage in industrial refrigerators. Expanded vermiculite is used for thermal insulation of walls, floors, foundations, and sound insulation of buildings.

The purpose of beneficiating vermiculite is to separate it from loose non-expandable rock and weakly expandable micas. This process is the most complex and expensive in the production of expanding vermiculite. The next stages of raw material processing - crushing and burning are performed with less labor and costs. Their presence in the final product has almost no effect on the quality of expanding vermiculite, because currently there are methods of waste and enrichment processing that allow the complete separation of biotite and phlogopite particles directly as a result of the incineration process [2].

In Uzbekistan, the production of vermiculite and materials based on it began to develop in the last five years. Instead of the technology of enrichment based on combustion, which is widely used in world practice, in the conditions of today's constant increase in the price of oil and gas products and their shortage, as well as increasing environmental requirements, increasing requirements for its quality, saving energy and resourcesand in the conditions of industrial safety, there was a need to develop production in new directions, vermiculite enrichments and conglomerate (from the Latin conglomeratus - crowded, compressed, a mixture of various dissimilar things, irregular addition, assorted) sets the task of creating a new concept of processing technological systems [1]. In beneficiation of vermiculite ores, sedimentation and dry magnetic separation processes are used. At the Kovdor beneficiation plant (Russia), ore is successively beneficiated by grinding, sorting, and separated into finished product (vermiculite), waste and intermediate products. Developed a technology for extracting expanding vermiculite from under-enriched vermiculite ore by incineration in a specialized electric furnace and simultaneous separation of inert material [2].

The highest quality vermiculite enrichment is obtained from the Kovdor vermiculite mine, which is a product of hydration. Technologies for beneficiation of Potanin, Altintas, Karatas, Barchin, Sholak-Kayraktan mines (Russia) have also been developed. The ores of a number of mines were tested in pilot-industrial conditions and included in the state reserve based on the proposed solutions for their processing [2].

Vermiculite can be burned in different furnaces (gaseous or liquid-fueled tower, rotary tube, etc.). The most effective way to burn vermiculite is in a fluidized bed furnace. Tower furnaces overcome this condition, providing intensive heating of vermiculite grains and their short stay in the high temperature zone. The impossibility of separating waste rocks is an important drawback of the incineration process [3].

While the main process in the production of vermiculite is incineration, experience shows that it is most effective to use a set of technologies that include pre-incineration and post-processing of the material to obtain high-quality products.

Modern vermiculite processing complexes should become the main element of modern enterprises (shops, plots) specializing in the production of vermiculite and products based on vermiculite. To implement the new concept, it is necessary to model and synthesize energy and resource-saving technologies, technological processing systems aimed at solving major scientific and technical problems of great national economic importance. Among such wastes, there are up to 52% vermiculites in the composition of vermiculite conglomerates, which are a mechanical mixture of various mineral particles.

The disadvantage of the method of processing vermiculite ores burned by exposing the processed material to an air flow and an electric field is the relatively low efficiency of the separation process. Aimed to increase the efficiency of the separation process by increasing the charge difference between mica and other rocks. The ore is heated to a temperature of 50-300⁰C (in which the charge difference between mica and other rocks increases), then separated in an electric field and air flow [3].

The granulometric composition of the vermiculite ores of the Tebinbulok mine is presented in table 1. The share of particles with a size of less than 5 mm prevails (from 55 to 98%, on average 83%)

Table 1.

Granulometric composition of Tebinbulok mine ores

The main mineral in the ore is vermiculite, it also contains amphibole-Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂, carbonate, titanomagnetite-Fe₂TiO₄, iddingsite-MgFe₂ Si₃O10·₄(H₂O), montmorillonite-(Na,Ca)_0.33(Al,Mg)₂(Si₄O₁₀)(OH)₂·nH₂O, chrysotile-asbestos 3MgO·2SiO₂·2H₂O, gypsum- (CaSO₄ ·2H₂O), there are iron oxides Fe₂O₃, FeO, Fe₃O₄ [2]. The chemical composition of the ore mainly consists of ore-forming natural rocks, %: SiO₂ - 41.13, TiO₂ - 1.11, Al₂O₃ - 6.25, Fe₂O₃ - 7.36, FeO - 3.76, MnO - 15.04, CaO - 17.7, Na₂O - 1.0, K₂O - 0.62, P₂O₅ - 0.03, SO₃ - 0.29, Cl₂O - 1.31, CO₂ - 2.55.

According to the content of vermiculite, ores can be conditionally divided into 3 types: poor, medium (10-20%) and rich ores (more than 20%) containing 5-10% vermiculite. Taking into account the relatively low amount of vermiculite in the ore, laboratory tests were conducted to determine the possibility of preliminary beneficiation in a sedimentation machine. Tests were conducted on samples with vermiculite content of 8.12% and 11.62%. The amount of vermiculite in the obtained enrichments (in light fractions) was 18.49% and 28.35%, respectively, the yield of enrichment was 25.7% and 27.6%. The degree of separation of vermiculite into enrichment is               58-67%, the volume density of expanded vermiculite is 166-178 kg/m³.

The ore is crushed to separate the +4 mm fraction, the fraction larger than 4 mm is fed to the crusher for grinding, and then the crushed product is returned to the smelter. Vermiculite grains are easily opened along the cracks along the cleavage planes under mechanical action, forming very soft, weakly swollen layers. Therefore, excessive fragmentation of vermiculite during grinding should be avoided.

According to its structure and properties, vermiculite is significantly different from other natural rocks, which can be effectively crushed in hammer, jaw and jaw crushers. The ability of vermiculite to separate into thin layers and high viscosity do not allow using existing grinders to grind it in some cases. Physical properties of vermiculite, the above requirements for crushed material require vermiculite to be crushed by cutting or simultaneous cutting and impacting rather than by impact or crushing action. in the process of crushing vermiculite ore from Karauzyak mine, it was carried out in order to study the crushing parameters in jaw, jaw and hammer crushers.

Studies on vermiculite grinding showed good results using hammer mills with cutting blades [1]. Their use allows to reduce the degree of crushing, to increase the thickness of crushed vermiculite grains, thereby increasing the specific crushing efficiency. It is dried in cyclone drying drums at a temperature of 150⁰C to remove moisture. the removal of non-ferrous metals is carried out using a separator-sorter in an electromagnetic field, from where the vermiculite product is classified in sieves for sorting into -4+2 mm, -2+1 mm and -1 mm fractions.

In addition, dry sorting of vermiculite ores was carried out in air separators. each size class was separated separately to improve the enrichment performance and the efficiency of the separator. The experiments were carried out in a CAD-4 air separator with changes in the air flow rate. In the separation of vermiculite ores, minerals were separated by specific gravity. minerals with a high specific gravity fall into the first receiving hopper, while vermiculite has a low specific density. Compared to other minerals in the ore, it is carried away by air currents and enters a distant receiver. research results show that the initial speed of the main air flow should be in the range of 25-30 m/s to separate the vermiculite particles from the waste rock. The results of the conducted experiments are presented in Table 2.

Table 2.

Distribution of vermiculite enrichments by fractions

Conclusion. As a result of the tests, an effective technological scheme of dry beneficiation of vermiculite ores was developed. The yield of vermiculite enrichment by fractions is 3.5-4%. As a result of the studies carried out according to the developed scheme of vermiculite enrichment, the output of vermiculite enrichment for fractions -4+2mm, -2+1mm and -1mm was 11.47%, the amount of vermiculite in enrichment was 85%, and the degree of separation of vermiculite in enrichment was 95.95% organized. From the results of the conducted experiments, it was found that the dry beneficiation of vermiculite ores according to the proposed scheme is effective enough.

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