RU2821973C1 - Method of producing zinc oxide by waelz process from zinc-containing dusts of electric arc furnaces - Google Patents

Abstract

FIELD: various technological processes.

SUBSTANCE: invention relates to production of zinc oxide using Waelz process. Dust of electric arc furnaces (EAF) is mixed with an additive in the form of dust of steel making in an amount which provides addition of calcium oxide to basicity of the entire charge to a given level of 3 units, and coke in amount of 1–2 % of the weight of dust. At that, steelmaking dust contains calcium oxide not less than 20 %, mainly in active form, with basicity CaO/SiO₂ higher than 1, by content of SiO₂+Al₂O₃ higher than 5 %, wherein not less than 80 % of dust volume is preliminarily crushed to the level of not less than 40 mcm. Then pelletizing and Waelz process are performed.

EFFECT: method increases strength of charge granules, which reduces dust emissions, and reduces consumption of mineral resources – limestone and lime.

1 cl, 3 tbl

Description

The invention relates to non-ferrous metallurgy, namely to the production of zinc oxide using the Waelz process.

It is known that during the Waelz process of zinc-containing materials, flux is added to the granules to provide the required silicate module (up to 3.0 units), which affects the formation of deposits in a rotary tubular kiln. Limestone or lime is used as fluxes. Lime, in addition to the addition of CaO (fluxing), further improves the ability of the charge to granulate [Kozlov P.A. and others. Processing of zinc-containing dust from electric arc furnaces. Magazine "Non-Ferrous Metals", N7, Publishing House "Ore and Metals", 2009.]. The addition of calcium oxide also helps to increase the degree of extraction of valuable components into Waelz oxide and solutions [RU2484153].

There is a known method for processing EAF dust according to patent RU2653394, according to which EAF dust is mixed with flux - limestone in an amount of 4÷5% of the weight of the dust, to ensure a CaO/SiO2 ratio of 0.9÷1.1 and coke (coke breeze). Coke consumption is 230-250 kg/t dust. The charge is rolled with a binder (lime, consumption 1÷2%) and sent to Waelz treatment I (temperature in the reaction zone of the furnace 1250°C). Rough Waelz oxide (a mixture of ferrite and zinc oxide, with zinc and lead halides) is sent to Waeltz treatment II (temperature in the reaction zone of the furnace 900-1000°C). During the Waelz process II, halides and lead pass into the sublimates, and a mixture of zinc oxide and ferrite remains in the clinker. The clinker is sent for hydrometallurgical processing with the extraction of zinc into solution.

The disadvantages of this method are:

- the use of mineral raw materials - limestone, or lime, the production of which requires costs.

- low strength of charge granules when using limestone.

There is a known solution according to patent RU2732817, which describes the processing of zinc-containing dust from electric arc furnaces, including the operations of mixing, pelletizing, adding coke breeze, Waelz, characterized in that the dust of electric arc furnaces is mixed and pelletized with a material containing aluminum oxide, providing the addition of aluminum oxide in an amount 8-12% of the content of calcium oxide in the dust, while waste from the production of zinc-aluminum alloys in the form of zinc-aluminium-containing dross is used as a material containing aluminum oxide. The analogue states that 8÷12% of the calcium oxide content in the dust is used. The description also states that it can go up to 14%. The disadvantage of this solution is that the additive does not increase the strength of the granules - it does not have the properties of a hydraulic binder.

Based on the prior art, a solution is known according to patent RU2104310, in which the actual basicity of the slag is CaO/SiO2 = 1.7, i.e. above 1. Also known from the prior art is a method for extracting metals by burning solid fuel in a melt [RU2009204], which describes the use of calcium oxides located in a mineral mixture that contains both active CaO and minerals with silicon and aluminum, while the content SiO2+Al2O3 is 5 - 55%. Grinding to a level of at least 80% class - 0.04 mm - is known in the art and is not an essential feature for achieving the stated result.

The closest in technical essence and achieved result (prototype) is the author. St. of the USSR No. 1731850A1, class. C22V 19/38, 06/05/90. publ. Bulletin No. 17 dated 05/07/1992, which describes a charge containing the following components, wt.%: zinc-lead-containing slag - 32-46; - calcium-containing tailings from wastewater treatment - 28-40; - solid carbonaceous reducing agent - the rest. The main disadvantage of this solution is that when implemented, Waelz sublimates (the final product of Waelz treatment) contain a significant amount of lead, which complicates further hydrometallurgical processing. In addition, calcium-containing wastewater treatment tailings do not have the properties of a hydraulic binder and therefore cannot improve the strength of the granules. Accordingly, since the granules will be fragile, a significant amount of dust will be released during Waeltzing of the charge, which contributes to an increased consumption of mineral raw materials, which includes calcium-containing tailings.

Calcium-containing tailings cannot provide increased granule strength because the calcium oxide in them is in hydrated (CaOH ₂ ) or carbonate form (CaCO ₃ ), which cannot improve granulation and increase granule strength. Calcium-containing wastewater tailings can act as a flux, but cannot provide high-quality charge granules.

The objective of the invention is to solve these problems.

The technical result of the invention is to increase the strength of charge granules, which reduces dust emissions, and also helps to reduce the cost of mineral resources - limestone and lime.

The specified technical result is achieved due to the fact that a method for producing zinc oxide is claimed, which includes mixing electric arc furnace (EAF) dust with an additive in the form of steelmaking dust in an amount ensuring the addition of calcium oxide to the basicity of the entire charge to a given level of 3 units, and coke in an amount of 1-2% by weight of dust, and also including rounding and Waeltzing, characterized in that the mixture contains an additive of steelmaking dust, which contains at least 20% calcium oxide, mainly in the active form, basicity (CaO/SiO ₂ ) above 1, in terms of SiO ₂ +Al ₂ O ₃ content above 5%, and at least 80% of the dust volume is pre-ground to a level of at least 40 microns.

Carrying out the invention

The claimed method for producing zinc oxide using the Waelz process from zinc-containing dust from electric arc furnaces is based on mixing electric arc furnace dust with an additive that:

A) contains calcium oxide in the form of CaO for fluxing in an amount of at least 20% and a basicity (CaO/SiO2) above 1 (for adding CaO to the charge), while calcium oxide is in the form of active CaO;

B) is a production waste (to reduce the consumption of mineral resources);

C) calcium oxides are in a mineral mixture that contains both active CaO and minerals with silicon and aluminum (to ensure the binding properties of the additive), and the content of SiO ₂ +Al ₂ O ₃ should not be lower than 5%.

D) crushed to a level of at least 80% class - 40 microns (to activate silicates and calcium aluminosilicates).

Implementation of these conditions separately does not allow achieving the effect. Thus, if condition A is not met, then the material cannot be a flux and cannot provide an increase in the strength of the granules.

If the condition for using production waste (B) is not met, then limestone, lime or other CaO-containing material extracted from the subsoil is added to the charge as a flux.

If condition B is not realized, then the material will not have binding properties and the granules will not be strong for a long enough time. This is due to the fact that calcium silicates and aluminosilicates react with water to form a hardening cement mixture. The addition of such a mixture to the composition of the raw material for Waelzation allows increasing the strength of the granules (due to hardening). If the content of the sum of SiO ₂ +Al ₂ O ₃ oxides is below the specified level, then the content of calcium silicates and aluminosilicates will not be enough to form the strength of the granules.

The implementation of condition D is required to activate the compounds of calcium, silicon and aluminum, which will be binders in the granules. The degree of grinding meets the requirements for the cement industry.

Thus, the implementation of the claimed method is possible only in combination with the declared features. As such an additive, it is possible to use steelmaking dust that meets all these conditions.

The Waelzation process is carried out in one stage.

The method is carried out as follows.

EAF dust is mixed with an additive (steelmaking dust) in an amount, the addition of calcium oxide to make the entire charge basic to a given level (up to 3 units), and coke in an amount of 1-2% by weight of the dust. The additive is crushed before use to activate the binders. The resulting mixture is fed into a disc granulator, into which water is supplied to ensure the moisture content of the granules is 12-14%. The granules are loaded into a Waelz kiln. Waelzation is carried out at a temperature in the reaction zone of 900-1000°C. The clinker is unloaded from the kiln and then transported to zinc leaching.

The supply of the additive allows:

- reduce the consumption of limestone and lime;

- obtain strong granules and thereby increase the efficiency of the Waelz process.

Reduced consumption of limestone and lime reduces the cost of mineral resources, and durable granules allow the Waelz process to be carried out efficiently with minimal dust emissions. These distinctive features together and the effect they achieve (which is expressed in improved pelletization and reduced consumption of calcium-containing products) constitute a difference from the closest analogue.

Thus, in the prototype, the improvement in the strength of the granules during pelletization of the charge is not achieved, and the effect of the astringent properties of the additive is not realized. This is due to the fact that calcium-containing wastewater treatment tailings contain calcium in the form of hydrates or carbonates, and its addition increases the basicity of the charge, but does not improve the properties of the granules. In addition, none of the close analogues provides the technical effect of the patented method - increasing the strength of the charge granules.

An example of the method implementation.

The following materials were used for research:

1) chipboard dust;

2) dust from steelmaking;

3) flux (lime and a mixture of limestone and lime).

Tables 1 and 2 show the chemical and granulometric compositions of the materials, respectively.

Table 1. Chemical composition of materials. Dust name W, % Chemical composition, % B3 Fe _{SiO2 Al2O3 ​} CaO F MgO S Zn Cl Pb WITH Chipboard dust 0.54 28.73 4.55 1.06 9.37 0.11 1.79 0.9 22.42 3.71 2.68 0.2 2.45 steelmaking dust 0.48 19.2 7.25 3.09 22.26 0.04 26.99 1.79 3.27 0.19 0.16 0.2 6.79 Lime dust 0.45 2.29 3.45 83.49 3.04 Limestone dust 0.09 3.04 0.32 66.14 3.15

Table 2. Granulometric composition of dust, %. No. Particle size, microns Chipboard dust steelmaking dust 1 < 1 0.00 0.00 2 1-2 34.35 33.60 3 2-3 21.20 20.65 4 3-5 13.10 12.55 5 5-10 5.95 6.05 6 10-15 8.55 8.60 7 15-20 3.60 3.60 8 20-30 2.35 2.20 9 30-40 0.55 0.60 10 40-45 0.25 0.25 eleven 45-50 0.45 0.45 12 50-56 0.70 0.80 13 56-60 0.40 0.50 14 60-70 0.80 1.25 15 70-71 0.00 0.05 16 71-80 0.55 0.95 17 80-100 1.40 2.00 18 100-150 3.85 4.05 19 150-200 1.60 1.50 20 200-250 0.35 0.35 21 250-300 0.00 0.00

The content of particles up to 40 microns (lines 1 to 9 of Table 1) in dust from chipboards and steelmaking is 89.65% and 87.85%, respectively. The content of active calcium oxide in the additive (steelmaking dust) is 11.2%.

An experiment was conducted to obtain granules from these materials. The basicity of charge B3 was 3 units. The composition of the research batch is given in Table 3.

Table 3. No. Dust Experience Blend composition, % B ₃ Dust Koksik lime limestone dust Steel dust 1 Chipboard dust with lime dust 1 88.40 8.84 2.76 0 0 3.0 2 Chipboard dust with limestone dust 2 87.61 8.76 0 3.63 0 3.0 3 Chipboard dust with steelmaking dust 3 83.99 8.40 0 0 7.61 3.0

Flux consumption depends on the content of calcium oxides in it. At the same time, the use of steelmaking dust (experiment 3) makes it possible to abandon the use of lime and limestone, completely replacing them with production waste. This confirms the effect of saving material resources, and in particular, limestone and lime.

The granulation experiment was carried out in a laboratory bowl granulator (tilt angle 48°, ∅ = 0.8 m). The preparation of the mixture consisted of dosing materials, mixing and holding the mixture for 15 minutes to evenly distribute the particles of its components. The weight of the charge for each experiment was ~5 kg. The mixture was loaded into a granulator and moistened by supplying water in the amount necessary for the formation of granules. The resulting granules were classified on laboratory sieves of 2, 3, 4, 5 mm. To determine the physical characteristics of the pellets, granules with sizes of ~2-3 mm, 3-4 mm, 4-5 mm were used.

The rotation speed of the pelletizer is 22 rpm in accordance with GOST 12764-73.

The drop resistance of wet granules was determined by dropping them onto a metal surface from a height of 1000 mm. Compressive strength was determined using an IPG-1 sample. The results are shown in Table 4.

Table 4. Strength of granules. No.
experience Dropping strength (after 1 hour), times Dropping strength (after 1 day), times Compressive strength (after 1 hour), kg Compressive strength (after 1 day), kg 1 5.1 6.1 0.042 0.056 2 4.9 4.2 0.035 0.051 3 5.1 6.3 0.045 0.055

According to the data obtained, experiment 3 shows that the claimed method allows increasing strength after aging for one day due to the activation of silicates and calcium aluminosilicates. This confirms the effect of increasing the strength of the granules.

Claims (1)

A method for producing zinc oxide, including mixing electric arc furnace (EAF) dust with an additive in the form of steelmaking dust in an amount ensuring the addition of calcium oxide to the basicity of the entire charge to a given level of 3 units, and coke in an amount of 1-2% by weight of the dust, and also including pelletizing and Waeltzing, characterized in that the charge is supplied with an additive of steelmaking dust, which contains calcium oxide of at least 20%, mainly in the active form, with a basicity of CaO/SiO ₂ above 1, in terms of the content of SiO ₂ +Al ₂ O ₃ above 5%, and at least 80% of the dust volume is pre-crushed to a level of at least 40 microns.