Method for producing zinc oxide

Abstract

The invention relates to metallurgical technologies, and more particularly to the treatment of zinc-containing electric arc furnace dust using the Waelz process. The technical result is achieved in that the reduction process is carried out under controlled addition of anthracite, permitting the complete combustion of carbon in the reduction process, optimal rotation of the furnace, and also a controlled supply of CaO to obtain the desired slag basicity. A maximally efficient reduction process is achieved in the furnace, with the complete combustion of carbon, the basicity of the slag is controlled in addition to the fluidity thereof for complete removal, and a completely closed and safe cycle is provided which makes it possible to obtain waelz oxide without the uncontrolled release of heavy metals, such as mercury, dioxins and furans, and Cl and SOx gases into the atmosphere, thus rendering the present technology completely environmentally friendly.

Description

[0001]The invention relates to metallurgical technologies, specifically to the processing of zinc-containing dust from electric arc furnaces using the rolling method. Patent RU 2340 403 C2, dated June 20, 2007, "Method for processing zinc-containing dust and sludge from metallurgical and mining production," is known., where the processing of sludge in ash ponds and its recycling is accomplished by disintegrating the feedstock in a continuous rotary-pulsation-cavitation apparatus at a solid-to-liquid ratio of 1:4 and an excess pressure of 5 atmospheres at the apparatus inlet. The material is then fed to a flotation machine, where zinc is separated as a harmful impurity into the froth product, and the chamber product is sent for gravity classification, where fine and coarse fractions are separated, and these are sent separately for wet magnetic separation in permanent magnet separators to produce a concentrated iron-containing concentrate, free of zinc and tailings. A disadvantage of this method is the lack of technology for further zinc extraction from the froth product. Patent RU 2588218 C2 “Method for hydrometallurgical processing of zinc-containing dust from metallurgical production” is known., where the processing of zinc-containing dust is carried out by leaching with a sulfuric acid solution with the dissolution of non-ferrous metal compounds in the form of sulfates, separating the iron-containing precipitate to obtain a solution containing non-ferrous metals, characterized in that the leaching is carried out in autoclave conditions, at a temperature of 140 to 200 ° C, with a sulfuric acid concentration of 220 to 250 g / l and a holding time of 2 hours, ensuring the extraction of zinc and cadmium into the solution up to 95-98%. The disadvantage of this technology is its irrelevance for industrial use from primary raw materials (metallurgical dust), due to the need to use significant volumes of sulfuric acid as a consumable and to meet all the requirements for its storage, transportation, operation. Author's certificate SU 789619 dated 23.12.1980 "Method for processing zinc-containing dusts from blast furnace and steelmaking production" is known.In order to simplify the production of metallic iron and eliminate sulfur contamination, reduction is carried out on the surface of an iron-carbon melt with zinc-to-sulfur ratios in the dust ranging from 2-20:1 and dust-to-iron-carbon melt ratios ranging from 0.01-0.1:1, and the melt is purged with gas for 1-5 minutes. A disadvantage of this method is that zinc cannot be extracted from the zinc-containing dust. Known is patent RU 2653394 C1 "Method for processing zinc-containing dust from electric arc furnaces", where the operations of mixing, pelletizing, Waelz-forming, and hydrometallurgical processing of zinc-containing clinker are distinguished in that the dust from electric arc furnaces is mixed before pelletizing with a material containing calcium oxide in an amount that provides the addition of calcium oxide in an amount of 70-110% of the content of iron oxide (Fe2O3) in the dust, which is part of zinc ferrite (ZnO×Fe2O3), and coke in an amount of 1-2% by weight of the said dust.A disadvantage of this invention is that the introduction of calcium oxide at a level of 70-110% of the iron oxide (Fe2O3) dust content will result in a basicity insufficient to achieve the required reduction in liquid phase. Author's Certificate SU 831833, "Method for Processing Zinc-Containing Dusts and Sublimates," is known, which involves roasting with sulfur-containing materials and subsequent leaching with sulfuric acid solutions. To reduce the concentration of fluorine and chlorine in the cinder and lower the process temperature, roasting of Waelz oxides is carried out with a sulfide material consumption of 5-15% of the Waelz oxides' weight in the presence of steam at a blast temperature of 500-600°C. The disadvantage of this method is that it does not cover the process of obtaining the Waelz oxide itself, but only its subsequent calcination, and that the use of superheated steam at the specified temperatures leads to corrosion at the chemical level, which significantly reduces the service life of the Waelz kiln elements.Patent WO9804755A1 1998-02-05 "Waelz Furnace Process for the Production of Zinc-Containing Bouletes," is known, where a charge is produced from zinc-containing material, a powdered solid fuel component, and an activator in a ratio of 8-12:2.5-7:0.8-1.5. The charge is mixed and granulated. The produced pellets, 1-30 mm in diameter and 16-18% moisture content, and the remaining solid fuel required for the process, are dosed according to a specified process mode, in a ratio of 3:1, and fed to the Waelz furnace. Oxygen in an amount of 3-12 m3. 3 / t of processed charge is blown into the discharge end of the furnaces. The gases leaving the furnaces, containing non-ferrous metals, are cooled and undergo two-stage filtration in filter equipment. The dust load of the exhaust gases after the first stage is up to 350 mg / Nm. 3and after the second stage - below 10 mg / Nm <3> The metal oxides collected in the filters are granulated into granules with a diameter of 2-6 mm and a moisture content of 13.6-16%, and then sent for heat treatment in a tubular furnace, at the outlet of which oxygen is blown in an amount of 5-12 m 3 / t of oxides. The resulting roasted metal oxides undergo further hydrometallurgical processing, the furnace gases are cooled, passed through filtering equipment, and the collected metal oxides are sent for further purification and recovery, where the exhaust gases contain 4-8 mg / Nm 3dust. The disadvantage of this method is that it requires additional cleaning equipment with two independent processing cycles. According to the description in source [7], the process of iron reduction from oxides occurs stepwise according to the following scheme: at temperatures above 560°C Fe2O3→Fe3O4→FeO→Fe, below 560°C magnetite is reduced to metallic iron, bypassing wustite Fe2O3→Fe3O4→Fe. The disadvantage of this method is the lack of extraction of heavy metals from zinc, as well as the formation of high pressure zinc vapor, which does not exclude their release into the atmosphere, also, Angren brown coal was used as a reducing agent, due to the low concentration of carbon in which it is difficult to regulate the complete process of reduction and complete combustion of carbon.The prototype (the closest analogue) for the proposed invention is Japanese patent JP2002241850A, where the removal of zinc from zinc-containing iron oxide is carried out using a rotary furnace, by means of which the formation of a ring is prevented and the solid reduction of iron oxide is performed by separating zinc from zinc-containing iron oxide in a shorter time than in the conventional method, and the productivity can be improved. In the method for removing zinc from zinc-containing iron oxide using a rotary furnace 12, by means of which zinc-containing iron oxide is heated in a furnace 24 of the rotary furnace 12 and zinc is separated from the zinc-containing iron oxide and then the iron oxide is reduced to obtain an iron-containing material 25, a mixture of raw materials 11, consisting essentially of zinc-containing iron oxide and a carbonaceous material for the reduction of zinc oxide in zinc-containing iron oxide and iron oxide.A mixture of raw materials 11 is loaded into a furnace 24 of a rotary kiln 12 having an air temperature of ≥1100°C in the furnace, and zinc oxide in the zinc-containing iron oxide is reduced with a carbonaceous material and then evaporated to obtain an iron-containing material 25 loaded into the reduction furnace. A disadvantage of this invention is that the zinc oxide is evaporated before drying, and during the evaporation process, heavy metals may also be present in the furnace gas, which complicates their subsequent extraction. The technical result, which the proposed invention is aimed at achieving, is: obtaining a product (Walz oxide) in a single processing cycle in a Waelz kiln, as well as the ability to regulate the process in each zone by varying the concentration and granulation of carbon-containing products and slag-forming mixtures. The technical result is achieved due to the fact that the rotary Waelz kiln has 5 zones (FIG. 1): 1.Drying zone, where moisture and partially crystallized water are removed from granulated Waelz oxide (zone temperature 750-850°C). H2O (l) ↔ H2O (g) 2. Preheating zone, where an endothermic reaction with semi-combustion of anthracite occurs, while in the furnace atmosphere due to the reaction, thermal energy is generated (furnace zone temperature 850-1000°C). CO + ½ O2 ↔ CO2 + Q 3. Prereaction zone, where volatile oxides evaporate, and some stable iron oxides begin to be reduced (furnace zone temperature 1000-1300°C). CdO + C. O↔ Cd+ CO2CuO + CO ↔ Cu + CO2 Fe2O3 + CO↔ 2 FeO + CO2 Fe3O4+ CO ↔ 3 FeO + CO2C + CO2 ↔ 2 CO CO+ ½ O2 ↔ CO2 + Q 4. The main reaction zone, where zinc and lead oxide are reduced to metallic zinc and lead. The remaining iron oxides, in the form of wustite (FeO – Fe0.83O), are reduced to metallic iron. (furnace zone temperature (approx. 1200°C) ZnO + CO ↔ Zn + CO2 PbO + CO ↔ Pb + CO2 FeO + CO ↔ Fe + CO2 C + CO2(g) ↔ 2 CO(g) ZnO∙Fe2O3 + CO ↔ 2 FeO + ZnO + CO2 ZnO∙SiO2 + CO ↔ Zn + SiO2 + CO2 To reoxidize metallic lead, zinc, and iron condensed in the furnace atmosphere, air is blown from the furnace head onto the solid Waelz slag using an oxidizing lance. Zn + ½ O2(g) ↔ ZnO Pb + ½ O2↔ PbO CO + ½ O2 ↔ CO2+Q\ Metallic lead and zinc are oxidized and condensed as a dust cloud Lead oxide and zinc oxide are released into the kiln atmosphere and returned to dust. Water is sprayed in for further cooling and hardening (the temperature is reduced to 300-350°C).The gas is then cooled to 150°C in the outlet heat exchanger and collected in the filter as Waelz oxide. Heavy metals such as dioxin, furan, mercury, micropollutants, and gases such as Cl and SO are removed. XIn the exhaust gases, passing through a reactor with activated carbon and a second absorption filter, they are filtered and are not released into the atmosphere, where clean air is released. 5. The slag formation zone, where the reduced iron in the main reaction zone combines with oxygen from the oxidation tuyere, again becomes iron oxide and mixes with slag. Air supplied from the oxidation tuyere minimizes the temperature generated during the combustion of anthracite, causing the slag to leave the furnace at a temperature of 900-800 ° C. To increase the basicity of the slag, quicklime is supplied with a ratio of (CaO + MgO) / SiO2 > 1.5. To optimize the operation of the furnace and complete reduction (complete combustion of carbon in anthracite), a rotation speed of n = 0.8-1.2 rpm is used. Also, after the entire process has been completed, it is possible to additionally calcinate the Waelz oxide to obtain a concentrate with a higher content of pure zinc due to the removal of lead and chlorine.The use of this technology makes it possible to obtain Waelz oxide of the chemical composition indicated in Table 1:. Thus, the technical result is achieved, consisting in obtaining Waelz oxide in a single processing cycle in a Waelz kiln, with an optimal operating mode in terms of temperature and time parameters, allowing both to carry out controlled reduction with complete combustion of carbon, and to obtain optimal slag fluidity, due to controlled basicity with the addition of CaO + MgO. The essence of the invention is explained in the drawing, where: - in FIG. 1 Waelz kiln zones; The use of the proposed technology will allow: - To create the most efficient reduction process in the kiln, with complete combustion of carbon, due to controlled kiln temperature, concentration flow and anthracite granulation. - To create coordination between the kiln operating modes in the kiln zones by optimizing the kiln rotation. - To control the basicity and fluidity of slag for its complete removal due to controlled lime supply.- By using controlled temperature and time parameters, achieve maximum productivity during the entire process - By using autonomous operating modes, achieve a completely closed and safe cycle that will ensure the production of Waelz oxide without uncontrolled emissions of heavy metals such as dioxin, furan, mercury, and Cl, SOx gases into the atmosphere, making this technology completely environmentally friendly.

Claims

Claim 1. A method for producing zinc oxide containing 40-60% zinc; 3-9% lead; 1-5% calcium; 0.1-1.5% silicon; 0.1-3% iron; 0.1-2% sulfur; 0.1-1% cadmium; 0.1-5% manganese; 0.1-2% potassium; 0.1-2% sodium; 3-8% chlorine; 0.1-0.5% fluorine; the rest is oxygen, wherein zinc production occurs in a rotary Waelz kiln, characterized in that the reduction process uses controlled addition of anthracite, which allows for the reduction process to be carried out with complete combustion of carbon and optimal rotation of the kiln, as well as controlled supply of CaO, to obtain the required slag basicity.

2. The method according to claim 1, characterized in that in order to regulate the slag basicity level, MgO can be supplied together with CaO, wherein (CaO + MgO) / SiO2 > 1.

5.

3. The method according to claim 1, characterized in that heavy metals such as dioxin, furan, mercury, micropollutants and Cl, SOX gases remain in the gases and are filtered in reactors with activated carbon and absorption filters.

4. The method according to claim1, characterized in that the rotation frequency of the Waelz kiln is n = 0.8-1.2 rpm.

5. The method according to claims 1 and 4, characterized in that for the re-oxidation of metallic lead, zinc and iron condensed in the furnace atmosphere, air is blown from the furnace head onto the solid Waelz slag using an oxidizing tuyere.

6. The method according to claim 2, characterized in that it is possible, due to further calcination in the hardening furnace, to remove impurities and obtain technically pure zinc oxide containing 55-70% zinc; 0.5-1.5% lead; 1-5% calcium; 0.1-1.5% silicon; 0.1-3% iron; 0.1-2% sulfur; 0.1-1% cadmium; 0.1-3% manganese; 0.1-2% potassium; 0.1-2% sodium; 0.1-0.3% chlorine; 0.1-0.3% fluorine; the rest is oxygen.

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