Process for beneficiating low-grade bauxites

Abstract

The invention relates to the beneficiation of low-grade bauxites and can be used in aluminium production. The present process includes washing, crushing, drying, gravity separation to isolate four fractions, and subsequent electrostatic separation. Crushing is carried out to a particle size of 0.5 mm using a cone crusher in a swirling air flow. Drying is carried out in a rotary furnace for 40 minutes at a temperature of 750°С. Electrostatic separation is carried out at a voltage of 2000 V utilizing the difference in electrical conductivity between the SiO2 and Аl2ОЗ components of bauxites to bring about separation into fractions of different conductivity. Silicon oxide with negative conductivity is attracted to a separator cylinder and then removed, and aluminium oxide with positive conductivity is separated to a dedicated sector. The invention provides a process of converting low-grade bauxites that is simpler and more efficient.

Description

[0001] Method of enrichment of low-grade bauxite

[0002] The invention relates to non-ferrous and ferrous metallurgy and the refractory industry and is of practical interest for the production of alumina, iron pellets and mullite-siliceous products with preliminary enrichment of bauxite.

[0003] Prior art.

[0004] A method for processing bauxite is known (patent No. 2706907, application 2019116365, IPC class C22BZ / 00, published on 21.11.2019 in bulletin No. 33).

[0005] The method for processing bauxite includes a stage of their preliminary grinding, then includes a stage of mixing the ground bauxite with water treated with a magnetic field until it reaches the state of pulp, a stage of acting on the pulp in a reaction chamber with a rotating magnetic field formed by rotating ferromagnetic elements, wherein the action on the pulp is carried out in a vortex layer at a rotation speed of the ferromagnetic elements of at least 2800 rpm until a magnetostriction effect occurs, ensuring the reduction of metals and the production of metal oxides, after which a stage of separating the resulting mixture of metal oxides is carried out.

[0006] The disadvantage of the known method is the addition of existing enrichment methods (crushing, classification, pulp formation, centrifugal separation, drying, separation) with magnetostriction equipment and bringing the rotation frequency to a level of more than 2800 rpm. In this case, a combination of various physical phenomena occurs: acoustic waves, magnetic hydraulic impulse (impact), thermal energy, sound waves, mechanical cavitation, hydrodynamic cavitation, acoustic cavitation, mechanical impact force, mechanical friction force, ultrasound simultaneously affecting bauxite ore.

[0007] The disadvantage of the known method is that the complex structure of the formation of several types of energy requires various additional technical devices to obtain them, and the listed energies - mechanical, magnetic and wave - act separately, in connection with this, the implementation of this method is characterized by technical complexity.

[0008] A method for hydrochemical enrichment of high-carbonate bauxites for the production of alumina is known (patent No. 2752160, application No. 2021101156, C01F7 / 47, published on July 23, 2021 in bulletin No. 21).

[0009] A method for enriching high-carbonate bauxites involves mixing disodium ethylenediaminetetraacetic acid (EDTA) with bauxite, which selectively reacts with carbonate-containing minerals, converting them into a soluble state, wherein the amount of the solution of disodium ethylenediaminetetraacetic acid for dissolving carbonates is calculated according to stoichiometry, grinding is carried out and then maintained at a temperature preferably not lower than 70° C with stirring to reduce the concentration of carbonates in the bauxite to less than 0.5 wt.%, the pulp obtained after aging is filtered, the enriched bauxite with a reduced carbonate content is sent for the extraction of alumina, and the solution saturated with calcium salts is sent for the regeneration of disodium ethylenediaminetetraacetic acid.

[0010] The disadvantage of the known method is the complexity of the bauxite processing process, the cumbersomeness of the process flow diagrams, the use of various process devices that require the formation of various forces and energies, the need to use alkali in the process chain. In addition, a significant disadvantage of the known technical solutions is the production of a large amount of an environmentally unsafe by-product - red mud.

[0011] There are many technological (chemical) methods of processing (enrichment) of bauxites. These are acid, alkaline, acid-alkaline technologies. Various acids and alkalis, as well as their combinations, are used. All these methods require very expensive equipment, expensive preparations, and all are used only for rich ores. It can be said that the potential of chemical methods is exhausted today. A chemical method (economically justified) for processing "poor" ores has not yet been found.

[0012] A method for processing sulphide gold-bearing ore is known (patent No. 2198948, application No. 2001104295, IPC class C22B11 / 00, published 20.02.2003, bulletin No. 5).

[0013] The method includes grinding, classification and multi-stage separation into gold-containing product and tailings. Multi-stage separation is carried out by electrical separation. The gold-containing product isolated after electrical separation is subjected to additional enrichment by further grinding, classification and subsequent separation of the granular fraction.

[0014] The disadvantage of the known method is that it has not been applied to other ores, such as bauxite.

[0015] There are several types of aluminum ores in the world, but the main raw material for the production of this metal is bauxite. This is a rock consisting mainly of aluminum oxide with an admixture of other minerals. Bauxite is considered high-quality if it contains more than 50% aluminum oxide.

[0016] Bauxites are processed into alumina - this is aluminum oxide Al2O3, which is a white crumbly powder. The main method for obtaining alumina in the world is the Bayer method, discovered more than a hundred years ago, but is still relevant - about 90% of alumina in the world is produced in this way. This method is very economical, but it can only be used when processing high-quality bauxites with a relatively low content of impurities - primarily silica.

[0017] The issue of processing low-quality bauxite and the search for effective and inexpensive technologies for processing bauxite is relevant.

[0018] The technical result is to simplify the process of processing low-quality bauxite and increase its efficiency.

[0019] Disclosure of the invention and description of the drawings.

[0020] A method for enriching low-quality bauxites is proposed, including washing, crushing, drying, gravity separation with the allocation of four fractions and subsequent electrostatic separation. The difference is that crushing using a conical crusher is carried out until a particle size of 0.5 mm is obtained, then drying is carried out in a rotary kiln for 40 minutes at a temperature of 750 ° C, electrostatic separation is carried out under a voltage of 2000 volts, using different specific electrical conductivity of SiO2 and Al2O3 elements of bauxites, under the influence of which separation into fractions with different specific electrical conductivity occurs, silicon oxide with negative electrical conductivity is attracted to the separator cylinder and then removed, and aluminum oxide with positive electrical conductivity is separated into a dedicated sector.

[0021] The essence of the proposed method is shown in Fig. 1 and Fig. 2, Fig. 3, where Fig. 1 shows a diagram of the method, Fig. 2 shows the process of separation into fractions with different specific electrical conductivity, Fig. 3 shows different enrichment modes under different voltages.

[0022] To obtain alumina (raw material for aluminum production), bauxites with the following parameters are used: Al2O3 over 50%, SiO2 less than 8%. The quality of bauxites is determined by the silicon modulus. It is better if there is no silicon oxide at all, and Al2O3 is as high as possible. (Silicon modulus p si = Al2O3(%) / SiO2(%). If ρ si > 8 - the Bayer method, if p si < 8 - the sintering method).

[0023] Chemical composition of bauxites from the Barzas deposit:

[0024] A12O3 SiO2 Fe2O3 TiO2

[0025] 33.6% 23.4% 21.5% 4.9%.

[0026] Thus, it is necessary to bring bauxite to the level of commodity items - bauxite concentrate for delivery to alumina production plants to the level of commodity items - bauxite concentrate for delivery to alumina production plants.

[0027] The stated goal is achieved by the fact that in the known method of bauxite enrichment, including crushing and classification, classification is carried out using gravity separation methods and electrostatic separation (dry enrichment method).

[0028] Gravity separation of crushed bauxite allows the product to be divided into four fractions by specific gravity. The mineral composition of the ore is gibbsite (aluminum hydroxide), hematite (iron oxide) and kaolinite (clay material from the group of hydrous aluminum silicates).

[0029] Kaolinite with a hardness of 1.0 (Mohs) passes into the sludge fraction and is destroyed faster than gibbsite, hematite and magnetite with a hardness of 3 to 5-6 Mohs). Therefore, during gravitational separation, the concentration of both iron oxide (up to 30%) and silicon oxide (up to 12.77%) increases.

[0030] Dry desliming by fractions of - 0.5 mm is recommended to be performed in air vortex modes - dry cyclones, air classifiers and bag filters. In gravitational separation, the difference in friction coefficients of particles of different sizes is used. The use of air vortex mode allows the desliming process to be carried out most effectively.

[0031] Kaolinite with a hardness of 1.0 (Mohs) passes into the sludge fraction and is destroyed faster than gibbsite, hematite and magnetite with a hardness of 3 to 5-6 Mohs). Therefore, during gravitational separation, the concentration of both iron oxide (up to 30%) and silicon oxide (up to 12.77%) increases.

[0032] The use of electrostatic separation allows increasing the concentration of the extracted aluminum oxide and reducing the concentration of silicon oxide, the process of desiliconization of raw materials in one of the fractions is carried out due to the difference in the specific electrical conductivity of the product, i.e. different behavior of particles is used, which is determined by the different ratio of electrical and mechanical forces acting on them, separation is realized by the ability of particles to receive a positive and negative charge. To implement electrostatic separation, a high-intensity electric field is required. Fig. 3 shows a graph using different voltage for enrichment. The concentration of aluminum oxide is shown as 1, the concentration of iron oxide is shown as 2. The graph shows that with an increase in voltage, the concentration of aluminum oxide increases, and the concentration of iron oxide decreases slightly. The optimal voltage when using the claimed method is 2000 volts.

[0033] Thermal treatment at a temperature of 750°C is of great importance in the preparation of ore. The optimum temperature in this case was selected experimentally.

[0034] This allows obtaining a high-quality product - bauxite concentrate, suitable for use in the alumina industry. During electrostatic separation, hematite in association with gibbsite has increased sludge formation, covers all neighboring particles of separated minerals with a thin film, levels out the contrast of conductors (hematite and magnetite) and dielectrics (gibbsite, calcite and kaolinite).

[0035] Electrostatic separation is usually used for enrichment, classification and dust removal of granular bulk materials with a size of less than 5 mm, the processing of which by other methods is ineffective or unprofitable from an economic point of view. For example, corona electrostatic separators SE-70 / 140 are used for electrostatic separation. They are designed to separate elements by electrical conductivity.

[0036] Desliming is a preliminary material processing operation during mineral enrichment, which involves removing sludge.

[0037] It has been established that crushing of a solid rocky product before electrostatic separation must be carried out to a grain size of 0.5 mm. With an increase in grain size, the influence of electrostatic separation decreases, the effect decreases.

[0038] Thus, the proposed method allows to obtain high-quality products from previously unused raw materials: bauxite concentrate used in the production of alumina, iron oxide used to produce pigments and iron pellets, titanium oxide. The proposed method allows for the comprehensive use of raw materials, the proposed technology is waste-free. In addition, compared to the prototype, the quality of bauxite in terms of Al2O3 and SiO2 content is sharply increased due to deeper enrichment using the electrostatic separation method. Thus, when using the proposed invention, not only is the technological process simplified, but the effect is also increased.

[0039] The authors are not aware of the use of the claimed set of features for the stated purpose, which allows us to conclude that the proposed solution complies with the criterion of “significant differences”.

[0040] The drawing in Fig. 1 shows a diagram of the enrichment of low-quality bauxites using the proposed method.

[0041] The stated goal is achieved by the fact that in the known method of bauxite enrichment, including crushing and classification, classification is carried out using gravity separation methods and electrostatic separation, which significantly simplifies the production process in comparison with known analogues.

[0042] Industrial testing of the proposed method was carried out.

[0043] For the research, a 10 kg sample of bauxite No. 980 was selected with the following chemical composition, %:

[0044] N samples A12OZ SiO2 Fe2O3 TiO2 980 12.9 3.93 41.69 11.52

[0045] This bauxite was processed according to the proposed method and the prototype. According to the proposed method, dry classification was carried out for the 500 µm class, classification was carried out into 4 fractions, the fraction with aluminum oxide was subjected to double gravitational and electrostatic separation with a working voltage of direct current of 2,000 volts.

[0046] The results of enrichment using the proposed method (982 and 983) and the prototype are given in Table 1.

[0047] N samples A12O3 SiO2 Fe2O3 TiO2

[0048] 980 12.9 3.93 41.69 11.52

[0049] 981 32.1 6.16 31.1 3.56

[0050] 982 42.57 6.26 19.42 4.11

[0051] 983 52.14 10.27 5.36 2.73

[0052] When enriching the original bauxite using the proposed method, useful products are obtained: Al2O3 used in the production of alumina, Fe2O3 used for the production of pigments and iron pellets, SiO2 used for the production of abrasives and "white" soot, TiO2 used in the production of titanium white and titanium, the enrichment technology is waste-free.

[0053] Bauxite enriched by the proposed method has a quality corresponding to bauxite grades B-00, B-0 and B-1 according to GOST 972-74. In practice, it has been proven that increasing the size of bauxite to 1-3 mm reduces the efficiency of electrostatic separation.

[0054] - the optimal size of bauxite according to research results is 0.5 mm.

[0055] The proposed method of enriching low-quality bauxite allows:

[0056] - to increase the complexity of using raw materials by obtaining high-quality products for the production of alumina, pigments and iron pellets, abrasives and “white” carbon black, titanium white and titanium.

[0057] - develop a waste-free and environmentally friendly technology for the enrichment of bauxite

[0058] Industrial testing of the proposed method (variants for implementing the invention):

[0059] The tests were conducted in a production laboratory. The processing method using magnetic separation was compared with the method using electrostatic separation at the same specified parameters of other enrichment stages.

[0060] The study of the possibility of separating gibbsite and hematite was carried out in VSMS operations into fractions of -0.315+0.063 mm with a strength of ~400 Ers, while a small part (up to 2.76% by output) of the magnetic fraction with an iron content of 35.8% was obtained, which determines the hematite content in this product at ~51% and gibbsite -38%. With corona electrical separation by conductivity, it was possible to increase the Peobshch content to ~42%, which in recalculation gives a hematite content of -60%. These experiments on the completed volume showed the fundamental possibility of dry separation of hematite from gibbsite. When using a dry enrichment cycle and temperature dehydration operations in processing bauxite ores of the Barzas deposit, concentrates A12OZ with concentration indicators from 50% to 76% can be obtained, the yield will be 32%.Thus, the declared technical result has been confirmed, the technological process of processing low-quality bauxite has been simplified, and an increase in its efficiency in the enrichment of low-quality bauxite ores has been confirmed.

Claims

Invention formula A METHOD FOR BENEFICIATION OF LOW-QUALITY BAUXITES, including washing, crushing, drying, gravitational separation with the allocation of four fractions and subsequent electrostatic separation, characterized in that crushing using a conical crusher in an air vortex flow is carried out until a particle size of 0.5 mm is obtained, then drying is carried out in a rotary furnace for 40 minutes at a temperature of 750 ° C, electrostatic separation is carried out under a voltage of 2000 volts, using different specific electrical conductivity of SiO2 and Al2O3 elements of bauxite, under the influence of which separation into fractions with different specific electrical conductivity occurs, silicon oxide with negative electrical conductivity is attracted to the separator cylinder and then removed, and aluminum oxide with positive electrical conductivity is separated into a selected sector.

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