RU2840418C1 - Method of preparing raw material for production of zinc oxide by waelz process - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to nonferrous metallurgy, particularly, to production of zinc oxide using Waelz process. At preparation of charge for production of zinc oxide by Waelz-process the components of charge containing zinc oxide, dust of particle board, flux and solid fuel, their mixing and pelletizing are carried out. Fuel used is a finely ground carbonaceous reducing agent with fraction content of less than 50 mcm of more than 90%, in an amount of not more than 75% of the total consumption of the carbonaceous reducing agent. Reducing agent contains at least 3 wt.% oxides of the following metals: Cr, Mn, Fe, Co, Ni, Cu, Zn. Carbon black from pyrolysis of industrial rubber articles or iron coke can be used as carbonaceous material.

EFFECT: higher efficiency of using solid fuel with simultaneous increase of strength of charge granules, which reduces dust emissions.

2 cl, 1 dwg, 7 tbl, 5 ex

Description

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

It is known that carbon fuel, such as coke breeze (coke) and coal, is used as a reducing agent in the Waelz process [Kozlov P.A. The Waelz Process, 2002, Moscow: Ore and Metals Publishing House, 176 p.]. In this case, up to 30% of the mass of carbon loaded into the furnace is consumed for reduction, and up to 40% is consumed for combustion with heat release. It is known that an increase in the rate of the reduction reaction can be achieved by increasing the specific surface area of the fuel, while the lower limit of the grain size of the Waelz process raw material is limited to 0.3 ... 0.7 mm. The combustion of solid carbon fuel is most effective when the content of the fraction less than 600 ... 50 μm is more than 90% [Babiy V.I. Combustion of coal dust and calculation of a pulverized coal torch / V.I. Babiy, Yu.F. Kuvaev. - M.: Energoatomizdat, 1986.]. Thus, the conditions for efficient combustion of carbon fuel and the requirements for the granulometric composition of raw materials for Waelz kiln differ significantly.

It is also known that for the production of zinc oxide by Waelz-furnace it is necessary to granulate the batch (raw material). Such preparation of the batch provides an increase in the sublimation of Zn into Waelz-oxide and a decrease in dust removal. Taking into account the need to ensure the required basicity modulus (up to 3.0 units), which affects the formation of scale in a rotary tube furnace, lime is used as a flux. Lime, in addition to the addition of CaO (fluxing), improves the ability of the batch to granulation [Kozlov P.A. et al. Processing of zinc-containing dust of electric arc furnaces. Magazine "Non-ferrous Metals", N7, Publishing House "Ore and Metals", 2009]. The addition of calcium oxide to lime also helps to increase the degree of extraction of valuable components into Waelz-oxide and solutions [RU 2484153].

A method for processing EAF dust is known according to patent RU 2653394, according to which EAF dust is mixed with a flux - limestone in the amount of 4-5% of the dust weight, to ensure the ratio CaO/SiO2 = 0.9-1.1 and coke (coke breeze). Coke consumption is 230-250 kg / t of dust. The batch is pelletized with a binder (lime, consumption 1-2%) and sent to Waelz I (temperature in the reaction zone of the furnace is 1250 ° C). Rough Waelz oxide (a mixture of ferrite and zinc oxide, with zinc and lead halides) is sent to Waelz II (temperature in the reaction zone of the furnace is 900-1000 ° C). In the process of Waelz II, halides and lead are converted into 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.

It is known from the state of the art that coke breeze or coal with the following parameters is used as fuel for Waelz kiln: total carbon content of at least 80%; content of fractions less than 5 mm more than 90%. The main disadvantage of such material is its explosiveness when crushed to an effective level of use (less than 50 µm), as well as an increase in dust carryover during Waelz kiln.

A patent is known [RU 2359045], which proposes to use a dust-like carbonaceous material with an activation energy of the carbon gasification reaction in the range of 56-209 kJ/mol, introduced as a reducing agent during the roasting-melting of a dry charge in a suspended state in an oxygen atmosphere to obtain a dispersed oxide melt. This patent uses the effect of finely dispersed solid fuel, but the invention cannot ensure the production of zinc oxide by the Waelz process.

It is known the USSR A.S. No. 1731850A1, class C22B 19/38, 05.06.90, published, bulletin No. 17 of 07.05.1992, 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 it is implemented, Waelz sublimes (the final product of Waelzation) contain a significant amount of lead, which complicates further hydrometallurgical processing. In addition, calcium-containing tailings from wastewater treatment 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 the Waelz process, which will contribute to increased consumption of mineral raw materials, which include calcium-containing tailings.

In addition to those described, there are inventions [SU 358371, SU 342922, SU 1062288A1, SU 901315A1, SU 396412A1], in which finely ground carbonaceous reducing agent is added to the charge in an amount of no more than 75% of the total consumption of carbonaceous reducing agent.

The closest analogue is the patent [RU 2496895, published 27.10.2013], which describes a method for rolling zinc cakes, including mixing, pelletizing zinc cakes together with a solid carbon-containing material and Waelz-rolling the rounded material, characterized in that a mixture of calcium- and magnesium-containing materials is fed to the mixing stage with a magnesium oxide content in the mixture of 20-50% and a ratio in the batch of (CaO+MgO)/SiO2=2÷4, the mixture is pelletized together with a solid carbon-containing material with a size of less than 2 mm, and Waelz-rolling of the rounded material is carried out with the addition of a carbon-containing material with a size of more than 2 mm at a temperature of 1100°C.

The prototype proposes to use waste from the coal and oil refining industries as carbon-containing material. The size of the material is proposed to be kept at a level of more than 500 microns.

The technical result of the present invention consists in increasing the efficiency of using solid fuel while simultaneously increasing the strength of the charge granules, which reduces dust emissions.

The specified technical result is achieved due to the fact that a method is claimed for obtaining a charge for Waelz, obtaining a charge for obtaining zinc oxide by Waelz, including the operations of dosing, mixing and pelletizing (granulation), characterized in that a finely ground carbonaceous reducing agent with a fraction content of less than 50 μm more than 90% is fed into the charge, in an amount of no more than 75% of the total consumption of the carbonaceous reducing agent. At the same time, in order to increase the efficiency of carbon gasification according to the reaction C + Me _x O _y → CO + Me _x O _y-1, it is necessary that the solid fuel contain at least 3% by weight of oxides of the following metals: Cr, Mn, Fe, Co, Ni, Cu, Zn.

Preferably, carbon black from the pyrolysis of rubber products or iron coke is used as the carbon material.

Implementation of the invention

The claimed method for obtaining a charge for Waelz processing, obtaining a charge for obtaining zinc oxide by Waelz processing, includes the operations of dosing, mixing and pelletizing (granulation).

The new feature of the method is that finely ground carbonaceous reducing agent with a fraction content of less than 50 μm more than 90% is added to the charge in an amount of no more than 75% of the total consumption of carbonaceous reducing agent. At the same time, to increase the efficiency of carbon gasification by the reaction C + Me _x O _y → CO + Me _x O _y-1 , it is necessary that the solid fuel contain at least 3% by weight of oxides of the following metals: Cr, Mn, Fe, Co, Ni, Cu, Zn.

Preferably, carbon black from the pyrolysis of rubber products or iron coke is used as the carbon material.

The implementation of all the conditions specified in the declared method is linked to the need to:

- rolling the fine fraction of carbon fuel into granules (this requires a fuel fraction content of less than 50 µm of more than 90%, which ensures a specific surface area of interaction between carbon and charge components of 3000 ^cm2 /g or more);

- ensuring the presence of fuel not only in the granules, but also between them (for this, the amount of such fuel is no more than 75% of the mass of the carbonaceous reducing agent); if the content of the specified material is more than 75%, then some of the dust does not roll into the granules and is carried out of the furnace with the flue gases;

- ensuring rapid gasification of carbon by the reaction С+Me _x O _y →CO+Me _x O _y-1 (for this purpose, the solid fuel contained at least 3% (by weight) of oxides of the following metals: Cr, Mn, Fe, Co, Ni, Cu, Zn); if the content of oxides of the specified metals is less than 3% (by weight), their catalytic effect on gasification is sharply reduced, which is associated with ~25% gasification of carbon, the carbon content in the fuel is at least 70%, the ratio of the mass of one mole of carbon and one mole of the “lightest” oxide of the specified metals is 0.176; in this case, we get 0.7*0.25*0.176=0.03 or 3%.

The influence of all the specified metals on the stated result is determined by the reactions:

C+ _Cr2O3 →CO+ _Cr

C+MnO→CO+Mn

C+FeO→CO+Fe

C+CoO→CO+Fe

C+NiO→CO+Ni

C+CuO→CO+Cu

C+ZnO→CO+Zn

The invention is used as follows.

The Waelz process is carried out in one stage.

The components of the batch for obtaining zinc oxide by Waelz are dosed, mixed and pelletized (granulated), while finely ground carbonaceous reducing agent with a fraction content of less than 50 μm more than 90% is used as fuel, in an amount of no more than 75% of the total consumption of carbonaceous reducing agent of solid fuel, which contains at least 3% (by weight) of oxides of the following metals: Cr, Mn, Fe, Co, Ni, Cu, Zn. Finely ground special iron coke, or preferably soot from the pyrolysis of rubber products, can be used as such material. When using soot, there is no need for grinding (it immediately meets the requirements).

The supply of this particular reducing agent allows:

- increase the rate of carbon reactions;

- increase the rate of zinc recovery in the charge layer;

- to obtain strong granules and thereby increase the efficiency of the Waelz process, including by reducing dust emission.

The limitation of the use of fine material according to the invention is due to the fact that at least 25% of the carbon material must be represented by coke fines and be located between the granules.

Increasing the speed of chemical reactions will ensure increased productivity, and the durable granules allow for 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 pelletizing and increased productivity) make up the difference from the closest analogue.

Thus, the prototype does not achieve an improvement in the strength of granules during pelletizing of the charge, and the effect of grinding the fuel is not realized.

The implementation of the claimed method has been tested. Below are examples of implementation proving the achievement of the claimed result.

Example 1

The following solid fuel ratio was used for the tests:

coke content 100% (prototype);

coke content 75%, soot - 25%;

coke content 50%, soot - 50%;

coke content 25%, soot - 75%;

soot content 100%;

Coke breeze does not meet the requirements of the invention, but soot does fully meet them.

Table 1 shows the determined properties of dust, flux and solid fuel before pelletizing.

Table 1. Properties of charge components

Name Chipboard dust Coke (-2 mm) Soot Lime dust Angle of natural slope, deg 36 36 39 39 Bulk density, t/ ^m3 0.785 0.567 0.184 0.624 Content of fraction less than 50 microns 65 12 97 13

Obtaining granules includes the following steps: water is added to the batch (fine spraying) in the amount necessary to form granules. After obtaining embryos of +1 to -2 mm in size, we add the batch and water to increase the size of the granules and form new ones. The ratio of components (chipboard dust: carbon fuel: lime dust) is the same in all experiments.

A composition with a soot content of 0% was selected as a prototype (highlighted in gray in the tables).

As a result of pelletizing the dust of batches with different soot content, the granulometric composition has the following form (Table 2). It is evident that the addition of soot reduces the amount of fine fraction (-2 mm).

Table 2. Granulometric composition of the obtained granules

The compressive strength of the obtained raw granules (after rolling) and then daily for 7 days of aging was determined.

Compressive strength is determined by the magnitude of the load acting on the granules, recorded at the moment of its destruction, and is calculated as the arithmetic mean of 10 determinations.

The drawing shows an example of compressive strength based on the weighted average value.

It can be seen from the drawing that granules with a carbon black content of 25% - 75% show a higher initial compressive strength and its rapid growth during the curing period (Fig. 1).

The results of Waelz kilning of these batches are given in Table 3.

Table 3. Results of Waelz testing according to example 1

As can be seen from the obtained data, the use of the proposed method improves not only the quality of the granules, but also the indicators of the Waelz process. It is also clear from this example that increasing the soot dosage above 75% leads to deterioration of the process parameters.

Example 2

To assess the influence of individual components of the invention formula, an experiment similar to Example 1 was conducted. In this case, the soot was replaced by a carbon product of similar size, but it contained less than 3% of metal oxides (Cr, Mn, Fe, Co, Ni, Cu, Zn). The result is given in Table 4.

Table 4. Results of Waelz testing for Example 2

As can be seen from the data obtained, the refusal to comply with the requirement for the content of metal oxides (Cr, Mn, Fe, Co, Ni, Cu, Zn) led to a decrease in the efficiency of gasification and a deterioration in the performance of the Waelz process.

Thus, only the implementation of the invention formula as a whole allows achieving the stated effect.

Example 3

Experimental studies were conducted to confirm the selected fuel parameters (content of the carbonaceous reducing agent fraction less than 50 μm more than 90%). For this purpose, a charge was produced using the presented invention with varying fuel size and fraction ratio, with an assessment of the effect on granule strength, dust removal and fuel utilization. The results of the study are given in Table 5.

Table 5. Results of the study of the influence of fuel size on the Waelz indicators

Granule strength at 100% - 7 kg, at 0% - 0 kg; dust removal at 100% - 120 kg/t, at 0% 0 kg/t; fuel utilization rate at 100% - complete combustion of carbon to CO ₂ .

The experiments were conducted in a laboratory setup of the "tubular rotary kiln" type, the scheme and operating methodology of which are given in the work [Influence of the specific surface area of the concentrate on the process of roasting iron ore pellets in a pouring layer Steel I.S. Bersenev, V.A. Gorbachev, Yu.S. Zhukov, E.G. Podkovyrkin, T.V. Sapozhnikova, 2014, No. 8, pp. 22-24]. During the study, the compressive strength of the granules was determined using an IPG-1 device; dust removal was determined by the mass of dust captured in the gas cleaning device of the laboratory setup; the degree of fuel utilization was determined as the proportion of carbon burned to CO ₂ . The fuel utilization rate was determined as follows: the flue gas flow rate and _CO2 content in it were measured, then the mass of _CO2 was calculated using the formula M1=Vg* _CO2 *1.96 kg, where Vg is the volume of flue gases, m3/h, _CO2 is the proportion of CO2 in flue gases, in proportions. Next, the mass of _CO2 formed during complete combustion of fuel carbon to _CO2 was determined using the formula M2=C*3.67, where C is the mass of fuel carbon, kg. The fuel utilization rate was determined as M1/M2.

The results show that in terms of fuel utilization and granule strength, there is a limited (optimal) range of fuel size and dosage. It is highlighted in the table with a gray fill. It is clear that when the content of the 50 µm fraction in the fuel is less than 90%, the granule strength and fuel combustion efficiency decrease. This leads to increased dust removal.

It is also noticeable that when using fine fuel (less than 50 microns) in a dosage of more than 75% of the total consumption of carbon fuel, the completeness of fuel combustion decreases due to the removal of some of the combustible components from the working space.

Thus, the requirements for fuel stated by the invention are confirmed. Simultaneous fulfillment of the requirements for increasing the strength of granules, reducing dust emission and increasing the completeness of fuel use is achieved only under conditions corresponding to the stated invention.

Example 4

To clarify the requirements for the dosage of fine fractions (“finely ground carbonaceous reducing agent with a fraction content of less than 50 microns of more than 90% is used as fuel, in an amount of no more than 75% of the total consumption of carbonaceous reducing agent”), additional studies were conducted.

For this purpose, the dosage of fine fuel (with a fraction content of less than 50 microns more than 90%) was changed in the range of 0% - 100% with a step of 5%. The initial data and raw materials are similar to Examples 1-3.

The results are shown in Table 6.

Table 6. Results of experiments for Example 4

Fine fuel content, % Dust removal, % 100 14.0 95 13.0 90 12.9 85 12.7 80 12.5 75 10.0 70 10.2 65 10.5 60 10.9 55 10.3 50 11.0 45 11.3 40 11.3 35 11.1 30 11.3 25 11.0 20 11.1 15 11.6 10 11.4 5 11.5 0 (base value) 12.0

The obtained data show that dust removal increases above the base value with a fine fraction share of more than 75%. In the range of fine fraction fuel content from 0% to 75% (by weight), the use of the claimed invention is effective. This is due to the fact that fine fuel is granulated inside the lumps of the charge, and large components of the fuel remain in the intergranular space. When dosing the fine fraction (according to the claimed method) in an amount of more than 75%, the granules are unable to assimilate the fine fraction of the fuel and during further Waelz-making this dust is removed from the working space of the furnace, contributing to an increase in dust removal.

Thus, the dosage of fuel according to the invention should not exceed 75% of the total mass of solid fuel.

Example 5

To assess the effect of the reducing agent composition, experiments similar to examples 1-4 were conducted, with soot and oxides of Cr, Mn, Fe, Co, Ni, Cu, Zn (chemically pure grade) used as fuel. The purpose of the experiment was to show that the content of the specified oxides. Table 7 shows the experimental results.

Table 7. Results of experiments for Example 5

No.
experience Content of metal oxides in fuel Fuel efficiency, % Cr Mn Fe Co Ni Cu Zn 1 1 0 0 0 0 0 0 69.9 2 0 1 0 0 0 0 0 70.9 3 0 0 1 0 0 0 0 71.2 4 0 0 0 1 0 0 0 70.6 5 0 0 0 0 1 0 0 70.2 6 0 0 0 0 0 1 0 71.9 7 0 0 0 0 0 0 1 72.8 8 2 0 0 0 0 0 0 74.1 9 0 2 0 0 0 0 0 73.2 10 0 0 2 0 0 0 0 73.5 11 0 0 0 2 0 0 0 72.5 12 0 0 0 0 2 0 0 73.1 13 0 0 0 0 0 2 0 75.1 14 0 0 0 0 0 0 2 74.4 15 3 0 0 0 0 0 0 78.8 16 0 3 0 0 0 0 0 77.9 17 0 0 3 0 0 0 0 78.1 18 0 0 0 3 0 0 0 79.3 19 0 0 0 0 3 0 0 80.1 20 0 0 0 0 0 3 0 81.3 21 0 0 0 0 0 0 3 81.7 22 4 0 0 0 0 0 0 80.9 23 0 4 0 0 0 0 0 79.6 24 0 0 4 0 0 0 0 79.6 25 0 0 0 4 0 0 0 82.0 26 0 0 0 0 4 0 0 83.0 27 0 0 0 0 0 4 0 79.9 28 0 0 0 0 0 0 4 81.3 29 5 0 0 0 0 0 0 82.7 30 0 5 0 0 0 0 0 81.2 31 0 0 5 0 0 0 0 83.0 32 0 0 0 5 0 0 0 82.4 33 0 0 0 0 5 0 0 79.9 34 0 0 0 0 0 5 0 81.2 35 0 0 0 0 0 0 5 81.1 36 0.3 0.5 0.6 0 0 1.4 1,1 80 and above

The obtained data confirm that with the amount of oxides of the specified metals at the declared level (3%), the effect in terms of the degree of utilization is achieved: in experiments 1-14, the degree of fuel utilization is lower than in experiments 15-35.

Claims (2)

1. A method for preparing a charge for producing zinc oxide by the Waelz process, including dosing the components of the charge containing zinc oxide, chipboard dust, flux and solid fuel, mixing and pelletizing them, characterized in that a finely ground carbonaceous reducing agent with a content of a fraction of less than 50 μm greater than 90% is used as fuel, in an amount of no more than 75% of the total consumption of the carbonaceous reducing agent, while the reducing agent contains at least 3% by weight of oxides of the following metals: Cr, Mn, Fe, Co, Ni, Cu, Zn. 2. The method according to item 1, characterized in that the carbon material used is soot from the pyrolysis of rubber products or iron coke.