RU2548840C1 - Method of processing of fine zinc containing metallurgical scrap - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes dosing of zinc containing metallurgical scraps, solid fuel, binding and flux additives, mixing and pelletisation of produced charge, drying and heat treatment of pellets. Dosing of charge components is performed ensuring carbon content is charge by 80-100% of stoichiometric necessary for direct iron and zinc recovery in the charge, and melt temperature of lean material and ash of solid fuel in slag 1400°C maximum. Heat treatment of the pellets is performed at temperature 1350-1450°C and heating rate 400-500°/min, for this metallised product is removed from slag.

EFFECT: increased efficiency of processing of zinc containing scram with production of metallised product in form of zinc-free cast iron pellets.

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Description

The invention relates to the field of ferrous and non-ferrous metallurgy and can be used in the processing of fine-grained zinc-containing wastes of metallurgical production with the production of granular cast iron and raw materials for non-ferrous metallurgy.

A known method of processing zinc-containing metallurgical sludge and dust by Waelz in rotary kilns in an overflowing ore-coal-flux layer [1].

Weltz products are zinc-containing dust, a metallized product in conglomerate with gangue and solid fuel ash.

Extraction of zinc in the gas phase does not exceed 93%, and iron in the metallized product reaches 90%. The degree of metallization is 95-97%.

Other disadvantages of this method are the high consumption of solid fuel, amounting to 35-55% of the mass of the charge, to prevent the formation of crusts in the furnace, the low productivity of the unit is 0.15-0.2 t / (m ³ day).

Closest to the proposed solution in terms of technical nature and the achieved result is a method of processing zinc-containing waste from metallurgical production, including dosing of zinc-containing waste, solid fuel, binder and fluxing additives, mixing and pelletizing the resulting mixture, drying, heat treatment of pellets for 6-12 minutes at temperatures 1250-1350 ° C.

The method allows to obtain a metallized product from metallurgical waste with the removal of zinc, lead and alkalis from the latter. As a reducing agent, ordinary grades of coal are used. Pellets are heat treated in an annular hearth furnace.

The disadvantage of this method is the low quality of the metallized product, which limits its consumption as scrap in steelmaking. The low iron content (up to 70%) with an average degree of metallization of 92% is due to the fact that in the metallized product remains waste rock and coke ash. For this reason, such a product is smelted mainly in blast furnaces with re-heating of waste rock and coke ash for conversion to slag.

The objective of the invention is to increase the efficiency of processing fine-grained zinc-containing wastes of metallurgical production to produce a metallized product in the form of granular cast iron by optimizing the process parameters when composing a charge from various metallurgical wastes and the temperature-time parameters of heat treatment of pellets that provide the melting temperature of waste rock mixed with ash solid fuel not higher than 1400 ° C and obtaining a metallized product, with free from zinc and easily separated from slag.

The problem is solved in that in the method of processing fine-grained zinc-containing wastes of metallurgical production, including dosing of zinc-containing wastes of metallurgical production, solid fuel, binder and fluxing additives, mixing and pelletizing the resulting mixture, drying and heat treatment of pellets, in contrast to the prototype, the components of the mixture are dosed providing the carbon content in the charge by 80-100% of the stoichiometric need for direct reduction of iron and zinc in the charge, and t mperatury fusion of gangue and ash of the solid fuel is not higher than 1,400 ° C, furthermore, the heating of pellets is carried out at a speed of 400-500 ° / min, and heat treating the pellets is carried out at temperatures of 1350-1450 ° C followed by separation of the metallized product slag.

A distinctive feature of the proposed method is that the component composition of the charge from various zinc-containing wastes of metallurgical production for producing pellets is formed on the basis of providing carbon with 80-100% of the stoichiometric need for direct reduction of iron and zinc in the charge and obtaining the chemical composition of slag from waste rock in mixtures with solid fuel ash with a melting point not higher than 1400 ° C.

The stoichiometric carbon demand for the direct reduction of iron and zinc can be estimated using expressions (1-3):

; $$F{e}_2{O}_3+3C=2Fe+3COC/Fe=0.321(\mathrm{one})$$

;

; $$FeO+C=Fe+COC/Fe=0.214(2)$$

;

. $$ZnO+C=Zn+COC/Zn=0.184(3)$$

.

At the same time, carbon can participate in reduction processes many times, since CO also participates in indirect reduction by reactions (4-6):

; $$F{e}_2{O}_3+CO=2FeO+C{O}_2(\mathrm{four})$$

;

; $$FeO+CO=Fe+C{O}_2(5)$$

;

. $$ZnO+CO=Zn+C{O}_2(6)$$

.

It is impossible to fully realize the potential of carbon in the reduction processes, since part of the CO leaves the reaction zone before reacting, but protecting the surface layers of the pellets from oxidation of the metallized product. Part of the carbon goes into the metal in the form of cementite (Fe ₃ C). As the experimental results show, due to the development of indirect reduction, the completeness of the metallization process can be achieved at a carbon consumption in the range of 80-100% of the stoichiometric need for direct reduction, while allowing control of the carbon content in granular cast iron. With a further decrease in carbon consumption, the metallization degree decreases due to excessive dispersal of carbon in the mass of pellets, and a decrease in the number of carbon contacts with iron oxides. An increase in carbon consumption above the stoichiometric need for direct reduction worsens the technical and economic performance of the metallization process due to the unjustified overspending of the reducing agent.

Knowing the consumption of zinc-containing waste and solid fuel for metallization, the weighted average chemical composition of the slag-forming components of waste rock ore and solid fuel ash is calculated, and using the state diagrams of slags [3], solving the system of equations, they find the flow rate of the necessary fluxing agent, which ensures the formation of slag with the melting temperature no higher than 1400 ° C, which makes it easy to separate the metal from the slag. Exceeding this temperature leads to the fact that solid and viscous slag-forming compounds of waste rock and solid fuel ash, being in close contact with iron and zinc oxides, complicate the course of recovery processes, on the one hand. On the other hand, these compounds remain in the conglomerate together with the metallized product, reducing the content of the latter in the final product.

Another difference of the proposed technical solution is the optimization of the temperature-time parameters of heat treatment of pellets from zinc-containing waste.

Heat treatment of pellets at temperatures below 1350 ° C does not allow melt to be obtained from reduced iron. The final product of heat treatment in this mode is a conglomerate of reduced iron and slag. During heat treatment at temperatures above 1350 ° C, favorable conditions are created for the formation of cementite by reactions (7, 8):

; $$3Fe+C=F{e}_{3}C(7)$$

;

; $$3Fe+2CO=F{e}_{3}C+CO(8)$$

;

In turn, cementite is well soluble in iron, lowering its melting point. Thus, the heat treatment of pellets in the temperature range from 1350 to 1450 ° C favorably affects the formation of two phases of cast iron and slag in liquid form, which allows them to be separated from each other by magnetic separation at the final stage. Conducting heat treatment of pellets at temperatures above 1450 ° C leads to an increase in gas consumption for heating the pellets and a decrease in the resistance of refractory masonry in units for heat treatment of pellets. In the indicated temperature range, as in the known solutions, zinc is completely reduced by diffusing into the gas phase, where it is again oxidized to zincite (ZnO), and then settles in dust collecting units. Caught dust is a raw material for enterprises producing zinc.

In the process of heating the pellets, carbon oxidation processes occur, starting from the ignition temperature of solid fuel (600-700 ° C) according to reactions (9-11):

; $$C+O_2=C{O}_2(9)$$

;

; $$2CO+O_2=2C{O}_2(10)$$

;

. $$2C+O_2=2CO(\mathrm{eleven})$$

.

A restriction can be imposed on the development of these reactions by varying the heating rate of pellets from 400 to 500 ° C / min to the temperatures reached by heating the pellets when recovery processes involving the reaction (12) are developed:

. $$C{O}_2+C=2CO(12)$$

.

Heating the pellets at a rate of less than 400 ° C / min expands the time range for their stay at temperatures for reactions 9-11, leading to a decrease in the efficiency of carbon utilization and an increase in the total duration of the heat treatment period. Carrying out the heating rate of pellets at a rate of more than 500 ° C / min is associated with unjustified overspending of gas for this technological operation and uneven heating of the pellets.

Thus, the high-temperature reduction of iron to a metallic state and then a molten state to break the chemical bond between iron oxides and gaseous oxides in combination with a low melting point of slags makes it easy to separate the metallized product from slag.

The proposed method is as follows.

Control the chemical composition of the components of the mixture for the production of pellets. Depending on the required carbon content in cast iron, they are set by the consumption of carbon in the charge in the range from 80 to 100% of its stoichiometric need for direct reduction of iron and zinc. Knowing the consumption of zinc-containing waste, binder, and solid fuel for recovery, the weighted average chemical composition of the slag-forming compounds is estimated. By calculation, using information on the melting point of slag from the state diagrams in the CaO-MgO-SiO ₂ -Al ₂ O _{3 system} [3], if necessary, the fluxing agent consumption is determined to achieve a slag melting point of no higher than 1400 ° C.

Further dosing of the charge components, its mixing and pelletizing, as well as drying and heat treatment of the pellets, is carried out in a known manner, with the difference that the pellets are heated at a rate of 400-500 ° C / min, and the heat treatment of the pellets is carried out in the range from 1350 to 1450 ° C followed by separation of the metallized product from the slag by magnetic separation. Studies on the processing of zinc-containing waste to produce a metallized product in the form of granular cast iron were carried out in a Nabertherm chamber heating furnace, which made it possible to control the set heating rate to 1800 ° C with the required exposure at a given temperature. If necessary, the change in the component composition of the slag-forming compounds in the initial charge was controlled by the quartzite flow rate to achieve slag melting temperatures not exceeding 1400 ° C using slag state diagrams in the CaO-MgO-SiO ₂ -Al ₂ O _{3 system} .

The research results are shown in tables 1-4:

table 1 - characteristics of metallurgical waste;

Table 2 - carbon and flux consumption for metallization of metallurgical waste;

Table 3 - the effect of the temperature-time parameters of heat treatment on the metallization indices of zinc-containing wastes (carbon consumption corresponds to the stoichiometric need for direct reduction of Fe and Zn);

table 4 - the effect of carbon consumption on the metallization of zinc-containing waste (the temperature of the heat treatment of pellets in the method "A-proposed method" - 1400 ° C, in the method "B-prototype" - 1300 ° C).

An analysis of the data in Tables 1 and 2 shows that blast furnace dust and blast furnace slurry do not require any flux additives, since the melting point of gangue and solid fuel ash does not exceed 1300 ° C. To reduce the temperature of the slag in the case of using ESPC dust and converter sludge, it is necessary to introduce quartzite into the charge. The blast furnace dust contains enough carbon to satisfy the stoichiometric demand for it of 100% or more for the direct reduction of Fe and Zn. Blast furnace slurry covers such needs by 91%.

The data shown in tables 3 and 4 indicate that the heat treatment of pellets at temperatures below 1350 ° C and at heating rates less than 400 ° C / min, as well as at a carbon consumption of less than 80% of the stoichiometric need for direct reduction of Fe and Zn leads to a decrease in the degree of metallization of the final product and to a decrease in the degree of removal of Zn from it. Exceeding the values of the declared parameters leads to an unjustified increase in energy costs for heating the unit for heat treatment of pellets, as well as to excessive consumption of solid fuel without improving the degree of metallization and the degree of removal of Zn.

Thus, the proposed technical solution allows to obtain a new metallized product during the processing of fine-grained wastes of metallurgical production - granular cast iron, as a substitute for scrap metal in steelmaking, slag with a grain size of 0-20 mm, as raw material in road construction, cement and concrete production, as well as Zn- containing dust as a raw material for enterprises producing zinc.

There are other important advantages of the proposed solution compared to the known solutions:

- waste rock is heated once to the melting temperature of the slag;

- eliminates the cost of servicing fire-liquid slag obtained from waste rock and solid fuel ash.

Information sources

1. Lisin B.C., Skorokhodov V.N., Kurunov I.O., Chizhikova V.M. Current status and prospects of recycling zinc-containing wastes of metallurgical production. // BNTI Ferrous metallurgy. 2001. Appendix 6, 32 p.

2. Jimbo J., Tanaka H., Ruwata Y. New coal-based ironmaking Fastmet / Fastmelt // Proceedings of the 4-th European Coke and Ironmaking Congress, June 19-22, 2000. Paris, France. V.2. P / 492-498.

3. The formation and properties of blast furnace slag. Zhilo N.L. M., "Metallurgy", 1974, 120 pp.

Table 1 Characteristics of metallurgical waste Type of waste Content% Zn Fe C FeO Fe ₂ O ₃ SiO ₂ Al ₂ O ₃ Cao MgO S p.p.p. Blast furnace dust 0.17 44.6 19.6 10.1 52.6 8.26 1.97 3.22 1.29 0,300 21.6 Blast furnace slurry 1.23 48.8 13.7 10.6 58.0 6.70 1.88 3.21 1.31 0.410 15.8 ESPC dust 1.65 41.5 - 16,4 38.9 8.76 1.65 18.50 2.70 0.210 4,51 Converter sludge 1,02 52.8 - 44,4 14.1 3.00 0.67 14.80 7.10 0,094 5.2

table 2 The consumption of carbon and flux for metallization of metallurgical waste No pp Waste consumption Receipt with waste, kg P _article, kg Quartzite consumption, kg _Mp slag, ° C [3] type of waste kg Fe ⁺² Fe ⁺³ C Zn BUT B BUT B one Blast furnace dust one hundred 7.86 36.82 19.6 0.18 13.53 - - 1300 1300 2 Blast furnace slurry one hundred 8.24 40,4 13.7 1.23 15.02 - - 1300 1300 3 ESPC dust one hundred 12.76 27.23 - 1.65 11.77 9,4 - 1400 2000 four Converter sludge one hundred 34.53 9.87 - 1,02 10.75 15,5 - 1400 2300 Note: P _article - stoichiometric carbon demand for direct reduction of Fe and Zn; T _PL - melting point.

Table 3 The influence of the temperature-time parameters of heat treatment on the metallization of zinc-containing waste (carbon consumption corresponds to the stoichiometric need for direct reduction of Fe and Zn) Indicators Heat treatment temperature, ° C BUT B 1300 1350 1400 1450 1500 1300 Pellet heating rate, ° C / min 350 400-500 550 350 400-500 550 350 400-500 550 350 400-500 550 350 400-500 550 350 The total duration of heat treatment, min 12.0 10.9-11.5 10.6 12.1 11.0-11.6 10.7 12,2 11.1-11.8 10.8 12,4 11.2-11.6 10.9 12.5 11.3-12.0 11.0 12.0 Duration of heating, min 3,7 2.6-3.2 2,3 3.8 2.7-3.3 2,4 3.9 2.8-3.5 2,5 4.1 2.9-3.3 2.6 4.2 3.0-3.7 2.7 3,7 The degree of removal of zinc,% 92.0 92.5-93.0 93.0 94.0 95.0-97.0 96.0 96.0 98.0-99.0 97.0 98.0 99.6 99.5 98.0 99.6 99.5 92.0 The degree of metallization,% 90.0 90.5-91.0 89.0 91.0 95.0-95.9 96.0 96.00 98.0-99.0 99.0 99,4 99.5-99.6 99.5 99.5 99.5-99.6 99.5 90.0

Table 4 The effect of carbon consumption on the metallization of zinc-containing waste Indicators Security in carbon from stoichiometric demand for it for direct reduction of Fe and Zn,% BUT B 70 80 90 one hundred 110 one hundred Pellet heating rate, ° C / min 350 400-500 550 350 400-500 550 350 400-500 550 350 400-500 550 350 400-500 550 350 The degree of removal of zinc,% 90.6 91.0-91.2 91.3 96.2 99.1-99.4 99.3 47.0 99.4-99.5 99,4 98.0 99.6 99.1 99.1 99.6 99.5 92.0 The degree of metallization,% 78.1 79.3-80.5 81.0 91.5 98.2-99.0 98.5 97.2 98.9-99.1 98.8 99,4 99.5-99.6 99.5 99,4 99.5-99.6 99.5 90.0

Claims (1)

A method of processing fine-grained zinc-containing wastes of metallurgical production, including dosing of zinc-containing wastes of metallurgical production, solid fuel, binder and fluxing additives, mixing and pelletizing the resulting mixture, drying and heat treatment of the pellets, characterized in that the components of the mixture are dosed with the carbon content in the charge on 80-100% of the stoichiometrically necessary for direct reduction of iron and zinc in the mixture and the melting point of waste rock and s of solid fuel in the slag is not above 1400 ° C, wherein the heat treatment is conducted at a temperature of pellets 1350-1450 ° C and a heating rate of 400-500 ° / min, after which the sintered product is separated from the slag.