RU2450065C2 - Method to process dust of metallurgical production - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: dust of metallurgical production is agglomerated jointly with a carbon reducer, the produced agglomerated materials are dried, heated and annealed, zinc is reduced and sublimated into a gas phase. Waste gas is cooled, zinc oxide is oxidised and condensed in the form of a finely dispersed dust, and dust containing zinc oxide is caught. In process of dust agglomeration, the material of main composition is added into the charge with the content of MgO of at least 70%, additionally, together with the agglomerated material, a carbon reducer is loaded into a furnace. Reduction annealing is carried out at the temperature of 1200-1400°C.

EFFECT: dezinced material discharged from a furnace is exposed to magnetic separation.

4 cl, 3 tbl, 1 ex

Description

The invention relates to methods for processing waste (dust) of metallurgical production and can be used in ferrous and non-ferrous metallurgy.

A well-known technical solution is a method of processing metallurgical waste (dust) by pelletizing (or briquetting) followed by metallization of the agglomerated material in rotary tube furnaces (Complex use of raw materials and waste. Ravich BM, Okladnikov VP, Lygach V.N. ., Menkovsky M.A. M.: Chemistry, 1988, p. 92). Raw pellets, according to a known method, are pre-screened for screening fines, drying and hardening heating in rotary kilns to 1100 ° C. Coke breeze or anthracite is used as a reducing agent in furnaces, and the reduction processes of iron and zinc oxides proceed due to the reducing agent carbon supplied to the furnace together with pellets.

The disadvantages of this method are:

- reduced zinc oxide content in the captured dust (less than 40%) due to pollution by coal and coke dust;

- the need for long exposure at a reduction temperature due to the fact that the gas penetrates from the surface of the pellet to the center by relatively slow diffusion through the pores.

There is a method of processing metallurgical waste (dust), in which more than 3% by weight of MgO or MgO-C products used are added to a rotary kiln with steelmaking wastes in order to slow down the process of destruction of the furnace lining, increase the softening temperature and melt the calcined product in a rotary kiln and to achieve a high rate of reductive evaporation of ZnO and PbO. The carbon-containing reducing agent (coke) is added to the furnace separately and can be partially or completely replaced by MgO-C products (JP 05-132723, C22B 7/02).

The disadvantages of this method are:

- a relatively low degree of sublimation of zinc and lead due to the undeveloped surface of the interaction of calcined waste and a reducing agent,

- low productivity of the process due to partial melting of the granules formed in the drying and heating zones of a rotary kiln, because magnesia additive, increasing the temperature of their melting, was not specially distributed over the volume of pelletized waste.

The closest technical solution to the claimed is a method of processing metallurgical waste (dust), in which the briquetting of waste is carried out together with a solid carbon-containing substance in the form of crushed stone or brown coal with a grain size of 3-5 mm Briquettes are fed into a direct-flow tube furnace heated from the fuel loading side by oxygen burners, while the temperature of the briquettes at the furnace outlet is maintained in the range of 700-1000 ° C. The filtration rate of the furnace gases in a direct-flow tube furnace, reduced to normal conditions: a temperature of 20 ° C and a pressure of 760 mm Hg, is set to 0.3-1.0 m / s. Waste before briquetting is preheated in a heating counter-current tube furnace to a temperature of 550-1000 ° C (RU 2240361, C22B 1/14).

The disadvantages of this method are:

- the absence of special conditions that prevent the formation of crusts on the lining of the furnace channel, which limits the possibility of raising the temperature to 1300 ° C, and the latter is necessary for the complete removal of zinc from dust from metallurgical production containing 5-17% Zn + ZnO;

- crusts are also formed due to the reduction of ferrites and zinc silicates, which are inevitably contained in the dust of metallurgical production, as well as wustite in the range of 1200-1250 ° C, which simultaneously prevents the release of zinc vapor and carbon monoxide with a corresponding decrease in the degree of sublimation of zinc and metallization;

- the necessary reduction potential for a high degree of metallization of iron is not formed and the content of metallic iron in the unloaded briquettes is not enough to use them for direct loading into steelmaking units, which reduces the consumer cost of the product.

The technical result of the invention is to increase the degree of extraction of zinc from waste (dust) of metallurgical industries and to obtain a metallized product with a metallic iron content of more than 85%. This product can be loaded in steelmaking furnaces to replace parts of scrap metal or in blast furnaces as an iron-containing additive.

The specified technical result is achieved by the fact that a method for processing dust of metallurgical production is implemented, which consists in sintering dust together with a carbon reducing agent, drying the obtained agglomerated materials, heating and calcining them, recovering and sublimating zinc into the gas phase, cooling the exhaust gases, oxidizing and condensing zinc oxide in the form of fine dust and the collection of dust containing zinc oxide,

according to the claimed invention, when agglomerating dust, a material of the main composition with an MgO content of at least 70% is added to the charge,

additionally, together with the agglomerated material, a carbonaceous reducing agent is charged into the furnace,

wherein recovery firing is carried out at a temperature of 1200-1400 ° C,

the zinc-free material discharged from the furnace is subjected to magnetic separation.

When dusting the dust, the basic material with an MgO content of at least 70% is used in an amount of 20-50 kg per 1 ton of metallurgical dust, and a carbon reducing agent in an amount of 100-150 kg per 1 ton of metallurgical dust.

Dust agglomeration of metallurgical production together with the basic composition material and carbon reducing agent is carried out by the method of pelletizing, granulation or briquetting.

Carbon reducing agent, additionally loaded into the furnace together with the agglomerated material, is used in an amount of 200-400 kg per 1 ton of agglomerated material.

For processing by the claimed method, dust of metallurgical production can be used, in particular dust of electric steel-smelting, converter, blast furnace and open-hearth production, containing iron oxides (45-50%) and zinc (5-17%). The average chemical composition of various dust metallurgical production are given in table 2.

As a material of the main composition with an MgO content of at least 70%, the following can be used:

caustic magnesite powder obtained by collecting dust generated during the production of periclase powder,

periclase powder, magnesite powder obtained by firing (melting) of natural magnesia raw materials (magnesite, brucite),

periclase (magnesite) powder, calcined periclase powder obtained by high-temperature firing of natural magnesite and / or a mixture of natural magnesite with caustic.

As a carbon reducing agent can be used coke, coal, semi-coke, coke dust, anthracite.

The agglomerated material from a mixture of metallurgical dust, a carbon reducing agent and a basic composition material with an MgO content of at least 70% has a number of properties that contribute to the most complete removal of zinc and metallization of iron. In addition, the presence of a basic composition material with an MgO content of at least 70% prevents the formation of deposits (growths) in the furnace channel from fired products at a temperature that ensures sublimation of zinc.

The presence of a basic composition material with an MgO content of at least 70%, which has refractory properties and increases the temperature of the onset of melting of pelletized material, makes it possible to raise the calcination temperature to 1400 ° C without melting and loss of granule shape. The processes of reduction of zinc and iron oxides are intensively inside the agglomerated material due to the developed reaction surface, due to the direct contact of dust particles and products of gasification of the carbonaceous reducing agent while maintaining the porous structure of the agglomerated materials.

The content of the basic composition material with an MgO content of at least 70% in the agglomeration mixture below 20 kg per 1 ton of dust in metallurgical production does not provide universal contact between dust particles and magnesium oxide, local melting zones appear that reduce the gas permeability of the agglomerated material with an increase in the amount of zinc in the metallized product , which reduces the efficiency of the process of sublimation of zinc. An increase in the consumption of the basic composition material with an MgO content of at least 70% more than 50 kg per 1 ton of metallurgical dust slows down the sublimation process, requires an elevated temperature to maintain the integrity of the metallized briquette, and reduces the furnace productivity.

The consumption of crushed carbon material in the agglomeration mixture of less than 100 kg per 1 ton of metallurgical dust does not sufficiently intensify the reduction processes of zinc and iron oxides due to the fact that not all pores of the agglomerated material are filled with carbon gasification products. The increase in the content of carbonaceous reductant in excess of 150 kg leads to the fact that not all of it is spent on recovery processes with an average iron content in the waste of 45-50% and zinc 5-17%. Excess carbon does not react, which reduces the economic performance of the process, plays the role of a baking powder, preventing the compaction of the agglomerated material, and the strength of the calcined agglomerated material is reduced to a level that does not allow its effective further transportation and use in metallurgical units.

The use of a carbon reducing agent only in the form rolled into agglomerated material, briquettes or granules does not allow creating an atmosphere in a furnace with a high reducing potential. After the initial stage of reduction of zinc and iron oxides, which proceeds at a high partial pressure of gases inside the agglomerated material, oxidizing gases, which are the products of burning natural gas supplied to burners, begin to penetrate into the pores of pellets, briquettes, or granules. Zinc evaporated at the initial stage of active reduction is removed, and metallic iron is oxidized by carbon dioxide and water vapor, which reduces the degree of metallization of the pelletized product. To achieve high degrees of sublimation of zinc and metallization of iron, a carbonaceous reducing agent, for example, in the form of coke or coal, is loaded together with the agglomerated material. The carbon of a solid reducing agent is gasified by carbon dioxide by the Boudoir reaction and water vapor by the reaction of water gas. The resulting carbon monoxide and hydrogen have a high reducing potential and provide almost complete sublimation of zinc in metallurgical dust rich in this element and metallization of iron. In addition, the presence of lumpy coke or coal in the furnace space will provide advanced oxidation (burning) of oxygen in the air, penetrating through leaks in the docking unit of the fixed heads and the rotary drum of the tube furnace. The absence of oxygen both in the depth of the overgrowing layer and on its surface is a guarantee of the preservation of metallic iron in the calcined material discharged from the furnace.

The loading of lumpy carbon reducing agent in an amount of less than 200 kg per 1 ton of agglomerated material is not sufficient to burn all the oxygen generated in the furnace space of a rotary kiln, and will lead to a decrease in the degree of metallization of iron. The introduction of lumpy carbonaceous reducing agent of more than 400 kg per 1 ton of agglomerated material is not required to maintain a high reduction potential of the gas phase and is not advisable due to additional costs.

Carbon thermal reduction at temperatures up to 1400 ° C allows you to transfer to a gaseous state and then trap zinc, not only zincite, but also difficult to reduce silicates and zinc ferrites, which are present in zinc-enriched dust of metallurgical production, raising the quality of both sublimates and metallized products.

The claimed method allows the most efficient in terms of specific consumption of reducing agent to use the latter to extract the target product from metallurgical dust.

An example implementation of the claimed method. Dust of metallurgical production (the average chemical composition of dust is presented in Table 2), coke in the amount of 130 kg per ton of dust and magnesite powder (or other material indicated in table 3) in the amount of 30 kg per ton of dust are mixed, moistened if necessary , then the mixture is fed to the agglomeration site. A rotary kiln of cement production is used as a tube furnace. The obtained agglomerated material, as well as coke in an amount of 300 kg per ton of agglomerated material, is fed into a rotary kiln. Recovery firing in a rotary kiln is carried out at a temperature in the zone of reduction of zinc oxide and sublimation of zinc 1200-1400 ° C. In the furnace, zinc is reduced by carbon and carbon monoxide, metallic zinc is sublimated into the gas phase and then, when gases are cooled in ducts, coolers and dust collectors, zinc is oxidized by atmospheric oxygen. The resulting zinc oxide condenses in the form of fine dust and is captured by filters, forming an intermediate with a high concentration of zinc oxide, which is a raw material - a concentrate for further processing.

The zinc-free material discharged from the furnace is cooled, and then subjected to dry magnetic separation with the release of a carbon reducing agent, ash and slag components into a non-magnetic fraction, and the metallized product into a magnetic part. The non-magnetic fraction is classified with separation into the dump of fines and unburned reducing agent, the magnetic part is crushed and re-separated in magnetic fields with the release of the purified metal product into the magnetic fraction. The carbonaceous reducing agent recovered during dry magnetic separation is charged back into the furnace together with the agglomerated dust.

The claimed method allows to obtain a concentrate with a ZnO content of 50-70%, suitable for zinc production, as well as a finished metal product - metallized pellets with Fe content _total. more than 85% with a metallization degree of more than 95%, corresponding to the requirements for iron-containing raw materials for steelmaking.

Comparison of process indicators in the present method and prototype are shown in table 1.

From the presented table it is obvious that the inventive method allows the processing of dust from metallurgical production with significantly higher efficiency of the use of a reducing agent per ton of extracted zinc oxide and with a more efficiently organized process of iron reduction, characterized by the degree of metallization. Moreover, both in the prototype and in the claimed method, zinc is practically absent in metallized products of firing.

Table 1 Comparative indicators of the prototype and the proposed method Prototype
(RU 2240361) The claimed method Fe (total) - charge,% fifty fifty Fe (meth) - finished product,% 75 80 ZnO (charge),% 0.6 5-17 ZnO (metallized product) 0.01 0.01 Specific consumption of natural gas, m ³ / t of charge fifty fifty Specific consumption of solid reducing agent, kg / t of charge 100 (coal) 350 The content in the dust captured from the gases leaving the furnace, zinc oxide,% fifty 55-70 Loss of material with return during waste processing,% 5 5

table 2 Averaged chemical composition of dust in metallurgical industries No. p / p Type of dust metallurgical production of various enterprises Fe _commonly FeO Fe ₂ O ₃ Cao SiO ₂ MgO Zno Pbo S ^total With _tv PMP MnO Σ _ox one Blast furnace slurry 44.5 8.9 53.7 6.6 5.7 1,2 5.2 0.02 0.40 10.9 - 0.4 91.2 2 Blast furnace slurry 29.7 13.3 49.6 15.7 11.5 1.8 5.7. - - - 16.1 - 90.7 5 Open-hearth dust 53,2 0.5 75,4 od 0.6 0.8 7.0 0.5 2.2 0.1 - 1.3 88.5 four DSP-80 electric steel smelting dust and ladle furnace 43.7 3,5 58.5 8.2 10.0 2.5 6.7 - 0.6 1,0 3.3 - 94.3 5 Electric steel dust 23,4 1,1 52,2 8.4 10.0 1,2 25.7 0.05 0.8 1.4 13.3 - 91.3 6 Electric steel dust 27.5 5.1 50,5 11.1 12.0 1.7 20.3 - 0.9 2.6 9.11 - 81.1

Table 3 The chemical composition of basic materials with an MgO content of at least 70% Basic materials The chemical composition, mass. share,% MgO CaO SiO ₂ Fe ₂ O ₃ Δm _prk caustic magnesite powder 82.1 4.20 1.93 2.60 7.7 periclase powder 86.3 2.06 1.39 1.87 6.9 periclase (magnesite) powder 88.9 3,5 1.8 2.2 3.3 calcined periclase powder 92.3 2.2 2.0 1,62 0.6

Claims (4)

1. A method of processing dust of metallurgical production, including dust agglomeration together with a carbon reducing agent, drying the obtained agglomerated materials, heating and calcining them, recovering and sublimating zinc into the gas phase, cooling the exhaust gases, oxidizing and condensing zinc oxide in the form of fine dust, and collecting dust containing zinc oxide, characterized in that when the dust is agglomerated, a material of the main composition with an MgO content of at least 70% is added to the charge, additionally together with the agglomerated material The carbonaceous reducing agent is charged with scrap in the furnace, while reducing firing is carried out at a temperature of 1200-1400 ° C, and the de-galvanized material discharged from the furnace is subjected to magnetic separation. 2. The method according to claim 1, characterized in that when dusting the material of the basic composition with an MgO content of at least 70% is used in an amount of 20-50 kg per ton of dust of metallurgical production, and a carbon reducing agent in an amount of 100-150 kg per one ton of metallurgical dust. 3. The method according to claim 1, characterized in that the dust agglomeration together with the basic composition material with an MgO content of at least 70% and a carbonaceous reducing agent is produced by pelletizing, granulation or briquetting. 4. The method according to claim 1, characterized in that the carbonaceous reducing agent, additionally loaded into the furnace together with the agglomerated material, is used in an amount of 200-400 kg per ton of agglomerated material.