RU2626371C1 - Method of processing metallurgical production waste - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: iron and zinc-containing dust, milling scale, carbonaceous reducing agent and slag forming components are mixed, agglomerated, dried and heat-treated in a rotary-hearth kiln. Zinc sublimations are captured, the exhaust gases are cooled. Oxidation and condensation of zinc oxide in the form of dust and trapping of dust containing zinc oxide are carried out. Granulated cast iron and slag are cooled and separated. The ratio of dust and scale is set to provide total iron content in the mixture of at least 50%. The slag forming components are introduced in an amount providing the basicity of CaO/SiO₂ in range of 0.6-1.6 and the sulfur content in cast iron is not more than 0.09. The carbonaceous reductant is introduced in an amount providing carbon content in the cast iron ranging from 1.0 to 4.5%. Heat treatment is carried out by two-stage heating: at 1200-1300°C, then at a temperature increased by 80-200°C.

EFFECT: increasing the content of zinc oxide in concentrate extracted from dust and scale, obtaining cast iron with metallic iron content of 94 percent or more, reducing the consumption of reducing agent and fuel.

3 cl, 1 dwg, 1 tbl, 1 ex

Description

The invention relates to ferrous and non-ferrous metallurgy and can be used to obtain a concentrate of zinc oxide and granular cast iron, by processing waste from metallurgical production, in particular iron and zinc-containing waste from steelmaking and rolling production.

Dust from electric steelmaking can be raw material for the production of pig iron and steel, as well as zinc concentrate, since this raw material contains a significant (for industrial raw materials) content of iron, zinc and zinc compounds. Also, in the rolling production of metallurgical enterprises, a large amount of iron oxide scale is formed, which is of limited use and is discharged into sludge collectors.

A known method of processing waste from metallurgical production, in which waste in the form of iron and zinc-containing sludge is thickened, dehydrated and dried to a moisture content of 6-10 wt. %, mixed with carbon-containing reducing agent and pelletized. Countercurrent treatment of pellets is carried out with products of combustion of gaseous or liquid fuels, distillation of zinc and capture of sublimates to produce zinc oxide. Dried iron and zinc-containing sludges are mixed with iron and zinc-containing dusts, oil-calcin-containing waste from rolling production is added to the mixture in an amount of 0.04-1.00 wt. hours for 1 wt. including mixtures, and to the resulting mixture - waste firing dolomite or waste production of lime and bentonite in amounts of 0.03-0.15 wt. hours and 0.006-0.009 wt. hours for 1 wt. hours mixture. The resulting raw material mass is pelletized to obtain pellets with a size of 10-25 mm and the pellets are processed with a coefficient of air consumption of 0.45-0.95 and a temperature of 1150-1450 ° C with a vacuum in the system of 15-160 Pa and a temperature of the waste products of processing 450-700 ° C (RU 2404271 dated 03.03.2009, C22B 7/00).

The main disadvantages of this method: the inability to obtain a highly liquid iron product with a low sulfur content, sophisticated technological equipment, ensuring the presence of vacuum in the system, and high energy costs.

There is a method of processing waste from metallurgical production, in which electric furnace dust is granulated together with crushed carbonaceous reducing agent and a binder in the form of pellets or briquettes. They are dried, heated and fired in a rotary kiln together with a lumpy solid reducing agent at a temperature of unloaded materials of 700-1000 ° C, gas cooling and trapping of dust containing zinc and lead sublimates from them. In this case, the dust of electric steel-smelting furnaces is preliminarily mixed with lime-containing material and ground carbon reducing agent before sintering in an amount exceeding the stoichiometrically necessary carbon content for the reduction of iron, zinc and lead oxides by 1.5-2.0 times. The mixture is moistened to a water content of 8-11%, aged for 1-3 hours, and the resulting pellets or briquettes are loaded into the furnace together with a lumpy solid carbon reducing agent with a grain size of 0-20 mm in an amount of 200-500 kg per ton of dust from electric steel furnaces ( RU 2484153 dated 08/09/2010, C22B 7/02).

The main disadvantages of this method are as follows. Carrying out firing in a tube furnace involves obtaining an iron-containing product in the form of porous reduced iron of the DRI type (Direct Reduced Iron), which makes direct processing of the product in a steel furnace extremely difficult, due to the high degree of reverse oxidation of porous iron when heated in a steel furnace starting from 900 ° C. In addition, firing in a tube furnace is inherent to all its shortcomings, such as high gas flows, which leads to high dusting of the material and, as a result, to contamination of the resulting zinc oxide, as well as high energy consumption during the process.

A known method of processing waste from metallurgical production, in which the electric steel is first desalted, then mixed in a mixer with mill scale and a reducing agent (anthracite), the mixture is loaded into a rotary kiln. The basicity of the resulting slag (CaO + MgO) / SiO ₂ in the range of 1.0-1.4. The firing temperature in the furnace is 1100-1350 ° C. One of the products - zinc oxide - is captured and removed into cyclones, then collected in a hopper. Granular reduced iron is discharged into a container of water, cooled and placed in a warehouse (JP 58-045335 dated 03.16.1983, C22B 1/00).

The disadvantage of this method is the inability to obtain pure, without slag part, iron. Zinc oxide is obtained with a high degree of pollution due to firing in a tubular furnace, in which it is impossible to achieve low flow rates of exhaust gases contaminated with combustion products and dust particles. In addition, rotary kilns structurally have high energy costs.

The technical result of the present invention is to increase the content of zinc oxide in the concentrate released from dust and scale of metallurgical industries, not less than 60%, to ensure the separation of reduced iron (granular cast iron) and slag part, to obtain granular cast iron with a metal iron content of 94% and more, with a low sulfur content, not more than 0.09%, in reducing the consumption of reducing agent and fuel while increasing the environmental safety of the process.

The specified technical result is achieved by the fact that in the method of processing waste from metallurgical production, including:

mixing iron and zinc dust, mill scale, carbon reducing agent, slag-forming components,

agglomeration of the mixture, drying of the granulated material, heat treatment in a rotary hearth furnace, capture of zinc sublimates, cooling of exhaust gases, oxidation and condensation of zinc oxide in the form of dust and capture of dust containing zinc oxide, cooling and separation of heat treatment products of granular cast iron and slag,

according to the invention

the ratio of the specified dust and mill scale in an amount providing a total iron content (Fe ₂ O ₃ + FeO) in the mixture of at least 50%,

slag-forming components are introduced in an amount that ensures the basicity of CaO / SiO ₂ in the range of 0.6-1.6 and the sulfur content in granular cast iron is not more than 0.09%,

the carbonaceous reducing agent is introduced in an amount providing the carbon content in the granular iron, in the range from 1.0 to 4.5%,

heat treatment is carried out by two-stage heating: at a temperature of 1200-1300 ° C, then at a temperature increased by 80-200 ° C.

In the framework of the present invention, it is necessary to distinguish between the concepts of "reduced iron" - an intermediate product obtained after the first stage of heat treatment, and "granular cast iron" after the second stage of heat treatment.

The term "agglomeration" in the context of the claimed invention means the process of giving the initial mixture a certain shape in any way, in particular briquetting, pelletizing, pelletizing, etc.

The extraction of iron and zinc from the pulverized wastes of metallurgical production is based on the recovery of valuable components from their oxygen-containing forms with carbon-containing materials. Due to solid carbon, valuable elements from the charge are partially restored; this process plays a secondary role. The main reducing agent is CO, solid-phase carbon is involved in the decomposition of CO ₂ to produce carbon monoxide, which accelerates the production of elemental zinc. Under thermal exposure, CO reduces oxides to pure iron according to the scheme Fe ₂ O ₃ → Fe ₃ O ₄ → FeO → Fe. Part of the reduced iron combines with excess carbon and iron carbide Fe ₃ C is formed (i.e., carbonization of iron occurs and granular cast iron is formed).

часть цинка в пылях связана с железом в виде феррита ZnO⋅Fe₂O₃, который довольно хорошо восстанавливается моноксидом углерода: ZnO⋅Fe₂O₃+2CO=Zn↑+2FeO+2CO₂, ΔG°₁₂₇₃=-876,2 Дж/моль.Active reduction of zinc by carbon monoxide occurs at 906 ° C with its transition to the vapor state: Zn + СО = Zn ↑ + CO ₂ . The bulk of the zinc goes into a vapor state at 1100 ° C.

part of the zinc in dust is bound to iron in the form of ferrite ZnO⋅Fe ₂ O ₃ , which is rather well reduced by carbon monoxide: ZnO⋅Fe ₂ O ₃ + 2CO = Zn ↑ + 2FeO + 2CO ₂ , ΔG ° ₁₂₇₃ = -876.2 J / mol.

Zinc from zinc ferrite is reduced faster than from pure zinc oxide at a lower temperature, and the process proceeds stepwise, but zinc oxide is restored only after complete reduction of iron from iron oxide, while ZnO can be reduced by formed elemental iron.

It has been experimentally established that the ratio of iron and zinc dust and mill scale is determined in an amount providing a total iron content (Fe ₂ O ₃ + FeO) in the mixture of at least 50%, preferably 60% or more. With a total iron content of less than 50%, it is not possible to obtain a good separation of the reduced iron with the slag component.

As the slag-forming components used are silicon oxide (SiO ₂ ) and calcium-containing components, in particular calcium oxide (CaO), hydrated lime [Ca (OH) ₂ ], calcium carbonate (CaCO ₃ ), particle size less than 0.1 mm in quantity, sufficient to control the basicity of the slag components in the agglomerated material, i.e. CaO / SiO ₂ , in the range from 0.6 to 1.6, and the sulfur content in granular cast iron not more than 0.09%.

It is believed that a decrease in sulfur content occurs when the sulfur contained in the agglomerated material makes it possible to interact with CaO and, thus, fix it in the form of CaS (CaO + S = CaS). Experimental work has confirmed that the CaO in the slag traps sulfur when the reduced iron melts, forms granules and is separated from the slag due to carburization caused by the residual carbon in the reduced metal, and therefore the sulfur content in the obtained metallic iron granules can be significantly reduced.

The presented mechanism for reducing the sulfur content differs from the usual desulfurization of liquid metal using slag containing CaO, and is considered as a reaction similar to the above process. Of course, if the carburized and molten reduced iron is sufficiently brought into contact with the molten by-product slag under appropriate heating conditions, then the reaction of a liquid with a liquid (molten iron with molten slag) can determine the ratio of sulfur content in slag (S%) to S content in metallic iron granules [S%], i.e. sulfur distribution coefficient (S%) / [S%]. However, the contact area of the slag-metal obtained molten iron and the resulting slag is small. Thus, it is impossible to expect a large decrease in sulfur content as a result of the equilibrium reaction of slag with the metal after carburization, melting, and cohesion of reduced iron. Accordingly, it can be assumed that the desulfurization mechanism with the intentional addition of CaO includes a sulfur capture reaction peculiar only to CaO during the carburization, melting and cohesion of reduced iron, while the sulfur capture reaction prevents the sulfurization of metallic iron granules.

The amount of CaO added to control the basicity should be determined based on the amount and composition of the porous component (impurity) contained in the feed (iron and zinc dust and mill scale), and the amount of carbon-containing substance added to the material. The amount of CaO required to control the basicity of the entire slag component in the above range of 0.6-1.6 in terms of pure CaO is from 2.0 to 7.0%, and more preferably from 3.0 to 5.0% CaO . When using slaked lime [Ca (OH) ₂ ] or calcium carbonate (CaCO ₃ ), its amount should be converted to CaO. It was confirmed that when the agglomerated material contained 4% CaCO ₃ to control the basicity of the slag component to a value of about 0.9 to 1.1, an apparent desulfurization coefficient of 45-50% was obtained. The apparent desulfurization coefficient was determined by the equation below. When 6% CaCO _{3 was} contained in the agglomerated material to control the basicity of the slag component to a value of about 1.2 to 1.5, an apparent desulfurization coefficient of 70-80% was obtained.

The apparent desulfurization coefficient (%) = [content of S (%) in the granules of metallic iron obtained from the agglomerated material with the addition of CaO / content of S (%) in the granules of metallic iron obtained from the agglomerated material without the use of CaO] × 100.

As a carbon reducing agent, coal and / or brown coal and / or coal coke can be used. As shown by the pilot work, in the case of using coal as a reducing agent, having in its composition volatile more than 30%, it is possible to carry out briquetting without the use of a binder.

The optimal carbon content in the final product - granular cast iron - should be in the range from 1.0 to 4.5%. A carbon content of less than 1% is not sufficient for complete reduced iron in the solid state, with a carbon content of more than 4.5%, the process of subsequent separation of granular iron and slag is difficult.

The final carbon content is essentially determined by the amount of carbon-containing substance (carbon reducing agent) used in the preparation of the briquettes of the material, and by controlling the atmosphere during the solid recovery period. The lower carbon limit is determined by the residual carbon content of the reduced iron during the final stage of solid state reduction and the retention time (degree of carbonization) during the period following the solid state reduction period.

To maintain the solid state of the agglomerated material supplied to the furnace, and to recover and evaporate zinc and iron to a degree of reduction (oxygen removal rate) of 94% or more, the furnace temperature is maintained in the range from 1200 to 1300 ° C, and then to restore the remaining iron oxide is increased by 80-200 ° C, while allowing the resulting reduced iron to form granules by carburization and melting. For smooth and efficient implementation of the solid state reduction process, carburization and melting, the temperature during carburization and melting is higher than the temperature during solid state reduction.

According to this two-stage heating process, granules of metallic iron, granular cast iron, having a high degree of purity Fe can be reliably and efficiently obtained.

The inventive method is implemented using a rotary hearth furnace, to explain the invention in FIG. 1 is a schematic illustration of the indicated furnace.

The furnace has a movable under 1 under the housing 2. In order to control the temperature and composition of the gaseous atmosphere inside the furnace in accordance with the course of the reduction smelting, the furnace is divided into at least two zones in the direction of movement of the hearth 1 of the furnace using a partition 3. First zone (along the length of the hearth furnace) has such a configuration that it can serve as a zone for the reduction in the solid state of iron, reduction and evaporation of zinc. The zone that follows the first one has such dimensions along the furnace hearth that it can serve as a zone for carburization, melting, and cohesion so that the temperature and composition of the gaseous atmosphere of each zone can be separately controlled. The number of zones can be adjusted in such a way that it meets the conditions for the entire process of iron reduction, reduction and evaporation of zinc, and subsequent cooling to solidify granular iron and the resulting slag.

The fumed material, having a diameter of 19 to 30 mm, containing a mixture of iron and zinc dust and mill scale as a source of iron oxide, and coal as a carbon-containing reducing agent, is fed to a rotary hearth furnace having an atmosphere temperature of 1200-1300 ° C in order to carry out the recovery of the agglomerated material in the solid state until zinc is reduced and vaporized and a degree of iron reduction of 100% is achieved (the degree of removal of oxygen from the iron oxide contained in the agglomerated ohm material), and then the obtained reduced iron is fed into the melting zone with a temperature above the temperature during reduction by 80-200 ° C in order to melt the obtained reduced iron, the particles of which coagulate to form granular cast iron.

During the solid recovery period, the source of iron oxide (a mixture of iron and zinc dust and mill scale) and the carbonaceous reducing agent in the form of agglomerated material fed to the furnace interact with each other to produce a large amount of CO gas and a small amount of CO ₂ gas. Accordingly, the region adjacent to the agglomerated material is maintained in a sufficiently reducing atmosphere as a result of the screening effect of CO gas extracted from the carbon-containing materials of the briquettes themselves. However, during the later stage and the final stage of the solid reduction period, the amount of CO gas decreases rapidly, which reduces the effect of self-shielding. Accordingly, the reduced iron becomes susceptible to flue gas, i.e. oxidizing gas, such as CO ₂ and H ₂ O, obtained by heating, and therefore, reoxidation of the reduced metallic iron may occur. In addition, after solid state reduction is completed due to carburization of the reduced iron using residual carbon in the agglomerated material and a decrease in the melting temperature as a result of carburization, melting and cohesion of small particles of reduced iron occurs. During this step, due to the poor self-shielding effect, reoxidation of the reduced iron can also easily occur.

To prevent re-oxidation of Fe as much as possible, the composition of the gaseous atmosphere in the areas of carburization and melting is optimized. To maintain a reducing atmosphere, any material is used as an atmospheric regulator as long as it emits CO, in particular the designated carbonaceous reducing agent. The atmospheric regulator can be laid in a layer on the underneath the furnace before feeding the agglomerated material. In this case, the atmospheric regulator also has the function of protecting the hearth refractories from slag leakage during the reduction smelting process. However, since the atmospheric regulator exerts its influence during the period of carburization, melting, and cohesion after reduction in the solid state, it is also effective to disperse the atmospheric regulator over the furnace hearth immediately before the carburization and melting of the agglomerated material begins.

To increase the reliability of preventing re-oxidation during carburization, melting and cohesion, it is advisable to grind the atmospheric regulator to obtain a powder with a diameter of up to 3 mm, preferably from 0.3 to 1.5 mm. Strict restrictions are not imposed on the thickness of the layer of the atmospheric regulator, but, preferably, the layer thickness may be at least 2 mm-3 mm and not more than 6-7 mm.

An example embodiment of the invention. The starting components (iron and zinc containing steelmaking dust, mill scale, coal as a carbon reducing agent, calcium oxide and silicon oxide as slag-forming components and a binder) were mixed in the required amount (table 1) and then pelletized by pressing to obtain briquettes. Briquetted material was dried in a drying chamber at a temperature of 140-250 ° C, then loaded into a rotary hearth furnace. Heat treatment was carried out at a temperature in the first stage of 1200-1300 ° C and in the second stage of 1380-1450 ° C. Briquetted material placed on a rotating underneath is heated. The metal oxide contained in it is reduced while maintaining its solid state due to the presence of a carbon reducing agent in the briquetted material and carbon monoxide obtained by burning the carbon reducing agent. The zinc contained in the briquetted material is removed by evaporation after reduction, and the material with pre-reduced iron is continued to be heated in a reducing atmosphere in order to carburize and melt the reduced iron and at the same time provide the possibility of separating the reduced iron from the by-product slag (slag) and formation granules of cast iron. The obtained cast iron granules are cooled (preferably in water), the by-product of the slag is separated from the granulated cast iron by any suitable separation means (for example, a magnetic separation device). The exhaust gases are also cooled, the zinc oxide is oxidized and condensed in the form of dust, and the dust containing zinc oxide is captured.

The conditions and results of pilot tests for the production of granular cast iron and zinc concentrate are shown in table 1.

As a result of the implementation of the present invention, two target products are obtained, a zinc oxide concentrate with a zinc content of at least 60%, and granular cast iron. Granular cast iron obtained by this method does not contain a slag component and has a purity of Fe of 94-97%, a carbon content of 1.0 to 4.5% and a low sulfur content of up to 0.09% or less. The diameter of the obtained granular iron can be in the range from 1 to 30 mm. The quality of the obtained granulated cast iron corresponds to nodular cast iron and can be used as a source of iron in steel mills, such as the automotive industry, or for high-quality casting of critical parts of machine-building industries.

The zinc oxide concentrate obtained by the claimed method has a high zinc oxide content of more than 60% and, after the subsequent stage of purification from halides, has an advantage over enriched zinc concentrates in the content of zinc oxide of more than 65% and is a valuable raw material for the production of metallic zinc.

Claims (3)

1. A method for processing metallurgical waste, including mixing iron and zinc dust, mill scale, carbon reducing agent, slag-forming components, agglomerating the mixture, drying the agglomerated material, heat treatment in a rotary hearth furnace, trapping zinc sublimates, cooling the exhaust gases, oxidizing and condensing zinc oxide in the form of dust and the collection of dust containing zinc oxide, cooling and separation of heat treatment products in the form of granular cast iron and slag, I distinguish in that the total content of iron (Fe ₂ O ₃ + FeO) in the mixture by the ratio of the specified dust and mill scale provides at least 50%, slag-forming components are introduced in an amount that ensures the basicity of CaO / SiO ₂ in the agglomerated material within 0.6- 1.6 and the sulfur content in granular cast iron not more than 0.09, and the carbonaceous reducing agent is introduced in an amount providing a carbon content in granulated cast iron in the range from 1.0 to 4.5%, while the heat treatment is carried out in two stages by heating at a temperature of 1200 -1300 ° C and then at Temperature increased by 80-200 ° C. 2. A method of processing waste from metallurgical production according to claim 1, characterized in that the atmosphere regulator is additionally introduced. 3. The method of processing waste from metallurgical production according to claim 2, characterized in that coal, and / or coke, and / or charcoal are used as an atmosphere regulator.

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