RU2164543C1 - Method of preparing low-carbon metals and alloys - Google Patents

Abstract

FIELD: pyrrometallurgy, more particularly reduction of metals with solid carbon from oxides thereof. SUBSTANCE: method comprises forming solvent melt based on alkaline-earth metal halides, creating ore thermal melting mode, continuously feeding the blend composed of oxide-containing material and solid carbon reducing agent, dissolving oxides in solvent melt, reducing thereof with solid carbon at preset temperature and fixed partial pressure of carbon oxide over melt, and separating the resulting metal from solvent melt. High concentration of dissolved oxides is constantly maintained in solvent melt by feeding continuously oxide-containing material, solid carbon reducing agent is fed separately in amount of less than stoichiometric amount, and height of solvent melt layer is maintained at level of at least four diameters of electrodes. Method makes it possible to prepare low-carbon metals and alloys by single stage process directly from ores, concentrates, semiproducts and metallurgical waste. EFFECT: more efficient preparation method. 4 ex, 1 tbl

Description

 The invention relates to pyrometallurgy, in particular to the recovery by solid carbon of metals from their oxides dissolved in a melt of halides of alkali and / or alkaline earth metals, and can be used for the single-stage production of low-carbon metals and alloys directly from ores, concentrates, intermediate products and metallurgical waste.

 Almost all known processes of reductive smelting of metal oxides, proceeding using solid carbon as a reducing agent, produce carburized metal as a target product, which is actually a "semi-finished product" and requires further processing.

 A known method of reducing iron ore in an ore-reducing electric furnace [1].

 In the known method, a charge consisting of a mixture of fluxed agglomerate or iron ore pellets with a carbon reducing agent (coke) is loaded into the furnace bath, and “synthetic” cast iron is obtained as the target product.

 The disadvantage of this method is the inability to obtain low-carbon iron and, accordingly, the need for further processing of cast iron containing 3-4% carbon.

 A known method of producing high-carbon ferrochrome in a closed electric furnace [2].

 In the known method, a mixture consisting of lump chromite ore and a carbon reducing agent (coke or semi-coke) is loaded into the furnace bath, and ferrochrome containing 7-8% carbon is obtained as the target product.

 The disadvantage of this method is the impossibility of obtaining low-carbon ferrochrome and, accordingly, the need for multi-stage processing of high-carbon ferrochrome.

The known method adopted for the prototype, the production of metals and alloys, including the formation of the reaction volume of an electric furnace based on halides of alkali and / or alkaline earth metals, the creation of an ore-thermal melting mode in the reaction volume, the dissolution of oxides in the melt, their recovery from solution with solid carbon and separation the obtained metal from the melt-solvent, characterized in that the oxides are reduced at a temperature of 950-1500 ^o C, as an additional reducing agent use a carbon lining serving as an electrode, while the partial pressure of carbon monoxide over the melt is maintained below equilibrium for the reduced oxide [3].

 In the known method, a charge consisting of an oxide-containing material (ores, concentrates, intermediate products, metallurgical waste) and a reducing agent, which is used as practically any solid carbonaceous material, is loaded into the furnace bath.

 The disadvantage of the method adopted for the prototype is the possibility of carburization of the target product.

 It is possible to prevent carburization of the target product by contact with the carbon lining of the furnace (mainly with the hearth) when using a water-cooled casing protected by a skull or a special device for the reduction of metal oxides as a furnace bath [4].

 However, when using a furnace bath without a carbon lining, the formation of a carbonized target product is possible. This occurs, firstly, because at a process temperature in some cases the metal oxide is reduced not only to the metal, but also to its carbide.

So, for example, the reduction of carbon oxides of chromium from a mixture by reactions:
2 / 3Cr ₂ O ₃ + 18 / 7C ---> 4 / 21Cr ₇ C ₃ + 2CO (1)
ΔG $\genfrac{}{}{0ex}{}{\text{0}}{\text{T}}$ = 121986-87.61 T cal
2 / 3Cr ₂ O ₃ + 2C ---> 4 / 3Cr + 2CO (2)
ΔG $\genfrac{}{}{0ex}{}{\text{0}}{\text{T}}$ = 130340-86.11 T cal
The chemical equilibrium temperature of reaction (1) is 1403 K (1130 ^o C), and reaction (2) is 1513 K (1240 ^o C). This means that, from the point of view of chemical thermodynamics, the reduction of chromium oxide to carbide is energetically more favorable and begins at a lower temperature than the reduction of chromium oxide to metal [5].

 In addition, the formation of metal carbide is possible when droplets of the reduced metal come into contact with a solid carbon reducing agent floating on the surface of the melt (metal drops form on the reducing agent, which then come off and fall onto the bottom of the furnace bath).

So, for example, drops of reduced iron in contact with a reducing agent form iron carbide by the reaction:
3Fe + C ---> Fe ₃ C (3)
ΔZ _1115-1808K = 2475-2.43T [6]
The temperature of the onset of reaction (3) is 1019 K (745 ^° C.).

 Thus, when using a carbon-free bath of the furnace, the formation of a carbonized target product is possible.

 The objective of the invention is to obtain low carbon metals and alloys during the recovery of solid carbon metal oxides dissolved in a melt of alkaline earth metal halides.

The solution to the problem is due to the fact that, under certain conditions, all metal carbides are reducing agents for the oxides of these metals by the reaction:
MeO + MeC ---> 2Me + CO (4)
Since metal oxides dissolved in it are present in the melt-solvent, metal carbides, falling to the bottom of the furnace bath through the melt-solvent, inevitably give carbon to the reduction of the oxides of these metals. Carbon, combining with oxygen, leaves the melt in the form of carbon monoxide and burns over the bathtub of the furnace. For the complete reaction (4) to occur, it is necessary that the melt-solvent be sufficiently saturated with the dissolved metal oxides in it, the height of the layer of the melt-solvent is sufficient so that the metal carbides have continuous contact with the solution of metal oxides, and the process temperature is sufficient for the progress of reaction (4).

 The specified technical result is achieved by the fact that in the method for producing low-carbon metals and alloys, including the formation of a melt-solvent based on fluorspar, the creation of an ore-thermal melting mode, the continuous loading of a charge consisting of an oxide-containing material and a solid carbon reducing agent, the dissolution of oxides in the melt, their recovery with solid carbon at a given temperature and a fixed partial pressure of carbon monoxide over the melt, separation of the obtained metal from The solvent alloy according to the invention in a solvent melt constantly maintains a high concentration of dissolved oxides by continuously loading an oxide-containing material, the solid carbon reducing agent is separately charged in an amount less than stoichiometric, and the height of the solvent melt layer is maintained at least four electrode diameters.

 The method is as follows.

 A halide, mainly fluorspar, is loaded into a bath of an ore-reducing electric furnace, representing a water-cooled metal casing or a special device for the reduction of metal oxides [4], melted in an arc mode and brought into a liquid-mobile state in an ore-thermal mode. A mixture consisting of reducible oxides is loaded into the furnace bath, which dissolves when it enters the melt. Then, a solid carbon reducing agent in an amount less than stoichiometric is loaded into the furnace bath. Solid carbon floating on the surface of the melt-solvent reduces the dissolved oxides to both metals and their carbides, while the resulting metal alloy is lowered onto the hearth of the furnace and, passing through the melt saturated with dissolved oxides, gives up carbon for their reduction. It was experimentally established that, for complete decarburization of the alloy, the height of the melt-solvent layer should be at least four electrode diameters.

 The cycle of loading the charge into the melt — loading the reducing agent into the melt — reduction is repeated many times, while a high concentration of dissolved oxides is constantly maintained in the melt-solvent. The resulting target product remains in the furnace (smelting per block) or is removed through an eccentric bottom outlet.

 Examples of the method.

 Example 1 (prototype).

An electric furnace was used in the experiment, equipped with two graphite electrodes with a diameter of 50 mm, powered by an AC transformer with a power of 100 kVA (power consumption - 50 V, current strength 1.0-1.5 kAm). The furnace bath was a rectangular water-cooled metal casing measuring 350x200x400 mm with the possibility of a skull on the bottom and walls of the bathtub. 25 kg of fluorspar was loaded into the furnace bath, which was melted by an open electric arc and brought to a liquid-mobile state within 25-30 minutes, after which the furnace switched to the electrical resistance mode. Then, a mixture consisting of 30 kg of screenings of chrome ore with a grain size of 2.5 mm and 4 kg of reducing agent (graphite powder) was continuously charged into the solution-solvent based on fluorspar, having a temperature of 1500-1600 ^° C. The process of reduction of chromium, iron, and silicon oxides proceeded both during the charge loading and at the end of loading (within 40 min), which was recorded by the combustion of carbon monoxide over the furnace bath. At the end of the reduction smelting, the furnace was frozen. As a result of melting, a conglomerate of large (up to 100 mm in diameter) metal beads formed on the bottom of the furnace. Analysis of the metal alloy showed that it is a ferrochrome of the following chemical composition (%):
Cr - 60.0; Fe - 31.5; C 8.9; Si - 0.9; P is 0.03.

 In the above example, the melt-solvent layer had a height of 200 mm, which was 4 electrode diameters, however, the reducing agent was taken in excess. When the content of chromium oxide in the ore is 40%, or 12 kg, 2.85 kg of carbon was required for its reduction to chromium by reaction (2). The remaining 1.15 kg of reducing agent (graphite) was spent on the formation of chromium carbide by reaction (1).

 Example 2 (by the proposed method).

 For the experiment, a two-electrode ore-thermal furnace with a capacity of 100 kVA (electrode diameter 75 mm) was used. The furnace bath was a water-cooled metal casing with a volume of 50 liters with a cooled magnesite brick hearth.

For the experiment, 25 kg of ChDA grade chromium oxide with a particle size of 0.05 mm and 25 kg of chromium ore enriched with a particle size of 0.2 mm were prepared with the following chemical composition (%): Cr ₂ O ₃ - 59.2; FeO - 14.0; Al ₂ O ₃ - 8.7; MgO - 16.2; SiO ₂ - 1.8.

During the experiment, 75 kg of fluorspar in the form of a powder (flotation concentrate containing 85% CaF ₂ ) was initially loaded into the furnace bath, melted by an open arc and brought into a liquid-thermal regime with a melt temperature of 1600 ^o C.

Then, 15 kg of pure chromium oxide Cr ₂ O ₃ and 15 kg of enriched chromium ore were loaded into the furnace bath for 45 minutes. The reduction of iron oxide from chromium ore was supposed to lead to the formation of ferrochrome with a relatively low melting point (pure chromium melts at a temperature of 1857 ^o C - unattainable in laboratory conditions). After loading the mixture into the furnace bath, 2 kg of reducing agent (powdered graphite) was loaded. The low side voltage was 50 V, the current strength was 1400-1600 A. The course of the reduction process was recorded by the combustion of carbon monoxide over the melt surface. Recovery took place within 30 minutes until the reducing agent was completely consumed. Then the melting was frozen.

 As a result of cutting the smelting, it was found that ~ 40 kg of slag is saturated with metallic chromium in a dispersed state - chromium oxide was restored, but the obtained chromium could not be melted due to the low power of the laboratory furnace.

 It was also found about 2 kg of an alloy of the following chemical composition (%): Cr - 53.6; Fe - 40.0; C is 3.3. Although the alloy does not meet standard ferrochrome in terms of chromium content (60-65% Cr), in terms of carbon content it is quite consistent with medium-carbon ferrochrome (1-4% C).

 In the above example, the reducing agent was taken in an amount less than stoichiometric, but the height of the melt layer was 200 mm, i.e., less than three electrode diameters. The chromium carbide formed as a result of the reduction fell to the bottom of the furnace bath, not having time to completely react with chromium oxide dissolved in the melt-solvent.

 Example 3 (by the proposed method).

 The experiment used a three-phase electric arc furnace ДС-6Н1 with a capacity of 4000 kVA with an electrode diameter of 350 mm. Especially for the experiment, a furnace bath was made, representing a water-cooled metal casing. Protection of the casing from the melt was carried out by means of a skull, the thickness of which reached 30-50 mm. The hearth of the furnace bath was made of magnesite brick. 1100 kg of fluorspar was loaded into the furnace bath, melted with an open arc, and brought into a fluid flow state in the ore-thermal regime. The height of the melt-solvent layer was 1400 mm.

A charge consisting of 1800 kg of class 30 hematite iron ore of the following chemical composition%: Fe _total — 56.28; was continuously charged into the melt, having a temperature of about 1600 ^° C, for three hours. FeO - 2.78; CaO - 0.54; MgO - 0.17; SiO ₂ - 12.85; S 0.155; P is 0.01; p.p.p. - 4.08. The reducing agent was a coke grade of 10 mm, containing 0.545% sulfur in an amount of 300 kg. The reduction took place on the surface of the melt, carbon monoxide burned over the bath of the furnace. Immediately after loading, the melt was frozen.

 As a result of reduction melting, 635 kg of metal was obtained.

 Chemical analysis (%) of metal and slag is presented in the table.

 The results of the experiment showed that the absence of a carbon lining of the furnace bath allowed the metal sinking to the bottom not to accumulate carbon, while carbon passing through the oxide-saturated melt, the carbon was completely spent on the reduction of oxides. All this contributed to the production of iron with a very low carbon content. The high sulfur content in the resulting iron is due to its conversion to metal from the reducing agent. To avoid sulfur contamination of metal, low-sulfur reducing agents should be used - waste from the lining of aluminum electrolysis cells.

 Example 4 (by the proposed method).

 The experiment used a three-phase electric arc furnace ДС-6Н1 with a capacity of 4000 kVA with an electrode diameter of 350 mm. The standard furnace bath was specially converted for the experiment: the hearth was made of magnesite brick, and the walls were made of graphite blocks with a castle made of hearth mass. Water cooling was mounted on the outside of the furnace bath, so that the internal graphite walls of the bath were protected by a skull and the melt did not touch.

 5300 kg of fluorspar was loaded into the furnace bath, melted by an open arc, and brought into a fluid flow state in the ore-thermal regime. The height of the melt-solvent layer was 1300 mm. Then, mill scale (consisting mainly of FeO) in an amount of 10,000 kg and carbon reducing agent (crushed waste from the lining of aluminum electrolysis cells) in an amount of 1,500 kg were cyclically loaded into the furnace bath. The recovery process was recorded by the combustion of carbon monoxide over the bath furnace. After the recovery process, the melt was frozen.

 As a result of smelting, about 6000 kg of metal of the following chemical composition (%) was obtained: Fe - 98.5; Si 0.04; Mn - 0.025; Cr - 0.05; Mo - 0.18; Ni is 1.1; C is 0.10.

 In the above example, despite the use of a carbon material for lining the walls of the furnace bath, it was possible to obtain a low-carbon alloy due to the prevention of contact between the walls of the bath and the melt due to the skull, the creation of a layer of melt-solvent of the required height, maintaining a high concentration of dissolved metal oxides in this melt.

 Thus, according to the proposed method, it is possible to obtain low-carbon metals and alloys.

Sources of information
1. Gasik M.I., Lyakishev N.P., Emlin B.I. Theory and technology for the production of ferroalloys. - M.: Metallurgy, 1988, p. 571.

 2. Ibid., P. 323-328.

 3. The method of producing metals and alloys // RF Patent N 2130500 according to the application N 98111174 from 06/08/98 (Prototype).

 4. Device for the reduction of metal oxides // RF Patent N 2133291 according to the application N 98107374 from 04/15/98.

 5. Gasik M.I., Lyakishev N.P., Emlin B.I. Theory and technology for the production of ferroalloys. -M .: Metallurgy, 1988, p. 323-328.

Claims (1)

 A method for producing low-carbon metals and alloys, including the formation of a melt-solvent based on fluorspar, the creation of an ore-thermal melting mode, the continuous loading of a charge consisting of an oxide-containing material and a solid carbon reducing agent, the dissolution of oxides in a melt-solvent, their reduction with solid carbon at a given carbon temperature and a fixed partial pressure of carbon monoxide over the melt, the separation of the obtained metal from the melt-solvent, characterized in that In a melt-solvent, a high concentration of dissolved oxides is constantly maintained by continuously loading an oxide-containing material, the solid carbon reducing agent is separately charged in an amount less than stoichiometric, and the height of the layer of the melt-solvent is maintained at least four electrode diameters.

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