RU2449023C2 - Manufacturing method of granulated metallic iron - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: during manufacture of granulated metallic iron there loaded is mixture of raw materials, which includes material containing iron oxide, carbon-bearing reducing agent and alkali metal compound, to furnace for thermal reduction. Mixture of raw materials is heated and molten and iron oxide is reduced so that metallic iron and slag is obtained as by-product. Coalescence of metallic iron to granules is provided at simultaneous separation of metallic iron from slag. Metallic iron is cooled and hardened. At that, mixture of raw materials includes at least Fe, Ca, Mg, Si and alkali metal as components. Obtained slag includes CaO, MgO, SiO₂ and alkali metal oxide. The latter represents at least one oxide chosen from Li₂O, Na₂O and K₂O. Alkali metal oxide meets at least one of the following conditions: Li₂O≥0.03%, Na₂O≥0.10% and K₂O≥0.10%. Basicity of slag is in the range of 1.3 to 2.3.

EFFECT: invention will allow providing high efficiency at manufacture of high-quality granulated metallic iron having low sulphur content.

22 cl, 5 dwg, 13 tbl

Description

Technical field

The present invention relates to a method for the production of granular metallic iron and, in particular, to a method for the production of granular metallic iron by heating a mixture of starting materials, including a substance containing iron oxide and a carbon-containing reducing agent, in a thermal reduction furnace for direct reduction.

State of the art

The process for producing iron in a shaft furnace is used primarily as a process for producing iron from a material containing iron oxide, such as iron ore or iron oxide. Currently, a promising process has been developed for the production of iron on a small scale by direct reduction, which is suitable for the production of small batches and products of a wide range.

In the process of producing iron by direct reduction, a mixture of starting materials is first obtained, comprising a material containing iron oxide and a carbon-containing reducing agent such as coal or coke (hereinafter also referred to as “carbon material”), alternatively, a simple pressed preform from the mixture or an extruded preform from a mixture containing carbon material, wherein the extruded preform containing carbon material has the form of a pellet or briquette. Then the mixture of starting materials is placed on the bottom of the furnace for thermal recovery (furnace for thermal recovery with a moving hearth, for example, a furnace with a rotating hearth). The mixture is heated by heat and thermal radiation from a heating burner while moving this mixture in a furnace, as a result of which iron oxide from a mixture of starting materials is subjected to direct reduction under the action of a carbon-containing reducing agent to produce metallic iron (reduced iron). The reduced iron is carbonized and melted. Then, the reduced iron undergoes coalescence into granules while simultaneously separating from the slag formed as a by-product. The reduced iron cools and hardens. Thus, granular metallic iron (reduced iron) is obtained, see, for example, Patent Documents 1-3).

The process of producing iron by direct reduction does not require large plants, such as a shaft furnace, and this process is intensively investigated to ensure its practical use. However, in order to realize it on an industrial scale, it is necessary to solve many problems related to quality, performance, stable functioning, cost, safety, etc., in the production of granular metallic iron (product).

One of the tasks is to prevent the inevitable sulfur pollution from coal having a high sulfur content, if coal is used, which is the most common material - a carbon-containing reducing agent.

The inventors of the present invention have found that upon thermal reduction of a raw material mixture including carbon as a carbon-containing reducing agent, approximately 70% or more mass percent of the sulfur contained in the coal is converted to granular metallic iron obtained by thermal reduction. In some cases, the sulfur content in the granular metallic iron (hereinafter, the sulfur content in the granular metallic iron is also referred to as [S], and the sulfur content in the slag is indicated as (S)) reaches 0.1 mass percent or more and 0.2 mass percent or more, depending on the type of coal used (hereinafter, the content in mass percent is also abbreviated as%). If metallic iron has such a high sulfur content, the value of the product is significantly reduced and, in addition, its scope is significantly limited. In the event that the granular metal iron produced by the direct reduction iron process is sent to existing steel plants, such as electric furnaces and converters, and used as a source of iron, it is desirable to reduce the sulfur content of the granular metal iron to a minimum.

As a way to reduce the sulfur content of granular metallic iron produced by direct reduction of iron production, Patent Document 4 describes the control of basicity ((CaO) / (SiO ₂ ) determined based on the content of CaO and SiO ₂ in the slag, which is a by-product resulting from the melting of metallic iron, where (CaO) and (SiO ₂ ) are respectively CaO and SiO ₂ in the slag. In addition, Patent Document 5 states that the basicity (([[CaO] + [ MgO]) / [SiO ₂ ]) slag-forming component calculated on the basis of CaO content, MgO content and SiO ₂ content in the starting material mixture are set in the range from 1.3 to 2.3, and that the MgO content in the slag-forming component is suitably controlled, where [CaO], [MgO] and [SiO ₂ ] are the contents of CaO, MgO and SiO ₂ , respectively, in the mixture of starting materials.

Patent Document 5 also indicates the following: (I) a basicity of (((CaO) + (MgO)) / (SiO ₂ )) of the resulting slag of 1.7 or more, as it increases, decreases the yield, such Thus, significantly reducing the ability for coalescence of small particles of reduced iron formed during the reduction of material containing iron oxide in a mixture of starting materials; (II) it is impossible in the production process to stably ensure a high yield of metallic iron with a large grain size due to a decrease in the ability to coalesce; (III) to increase said yield, it is sufficient to add a material containing CaF ₂ (for example, fluorspar), here (MgO) represents the MgO content in the slag.

Patent Document 1: Unexamined Japanese Patent Application No. 2-228411.

Patent Document 2: Unexamined Japanese Patent Application No. 2001-279313.

Patent Document 3: Unexamined Japanese Patent Application No. 2001-247920.

Patent Document 4: Unexamined Japanese Patent Application No. 2001-279315.

Patent Document 5: Unexamined Japanese Patent Application No. 2004-285399.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances. An object of the present invention is to provide a method for producing granular metallic iron having a low sulfur content, characterized by good productivity, this method being different from the methods described above. Another objective of the present invention is to provide slag as a by-product resulting from the implementation of the production method.

According to one aspect of the present invention, a method for the production of granular metallic iron comprises the following steps, in which:

load the starting material mixture, which includes material containing iron oxide, a carbon-containing reducing agent and an alkali metal compound, into a thermal reduction furnace, heating said mixture of starting materials and reducing the iron oxide contained in said iron oxide-containing material using a carbon-containing reducing agent with obtaining metallic iron and slag as a by-product, provide coalescence of metallic iron in granules while separating metal iron from slag, and cool the metal iron and allow it to harden,

wherein said starting material mixture contains at least Fe, Ca, Mg, Si and an alkali metal as constituent elements such that the slag contains CaO, MgO, SiO ₂ and an alkali metal oxide, and the alkali metal oxide is at least at least one oxide selected from Li ₂ O, Na ₂ O and K ₂ O,

alkali metal oxide satisfies at least one of the following expressions (1) to (3), and the basicity of the slag satisfies the following expression (4):

(1)(Li ₂ O) ≥0.03

(one)

(2)(Na ₂ O) ≥0.10

(2)

(3)(K ₂ O) ≥0.10

(3)

(4),1.3≤ ((CaO) + (MgO)) / (SiO ₂ ) ≤2.3

(four),

where in expressions (1) - (4) (Li ₂ O), (Na ₂ O), (K ₂ O), (CaO), (MgO) and (SiO ₂ ) are fractions (in mass percent) of Li ₂ O, Na ₂ O, K ₂ O, CaO, MgO, and SiO ₂ in slag, respectively.

According to another aspect of the present invention, a method for producing granular metallic iron comprises the following steps, wherein

load the alkali metal compound and a mixture of starting materials, which includes a material containing iron oxide and a carbon-containing reducing agent, in a furnace for thermal reduction, heating said mixture of starting materials and reducing the iron oxide contained in the said material containing iron oxide using a carbon-containing reducing agent with by obtaining metallic iron and slag as a by-product, provide coalescence of metallic iron into granules while pouring metallic iron from the slag, and cool the metallic iron and allow it to harden,

wherein said raw material mixture or alkali metal compound contains at least Fe, Ca, Mg, Si and an alkali metal as constituent elements such that the slag contains CaO, MgO, SiO _{2 an} alkali metal oxide, wherein the alkali metal oxide is at least one oxide selected from Li ₂ O, Na ₂ O and K ₂ O,

alkali metal oxide satisfied at least one of the above expressions (1) to (3), and the basicity of the slag satisfied the above expression (4).

According to a further aspect of the present invention, a method for producing granular metallic iron comprises the steps of loading a raw material mixture, which includes material containing iron oxide, and a carbon-containing reducing agent, into a furnace for thermal reduction, heating the raw material mixture, and reducing iron oxide contained in the material containing iron oxide, using a carbon-containing reducing agent to produce metallic iron and slag as a by-product, providing the coalescence of metallic iron into granules while separating metallic iron from slag, and cooling and solidification of metallic iron,

moreover, the said mixture of starting materials contains at least Fe, Ca, Mg and Si as constituent elements so that

the slag contained CaO, MgO and SiO ₂ , the basicity of the slag satisfied the expression (5) below, and the MgO content in the slag satisfied the expression (6) below:

(5)1.5≤ ((CaO) + (MgO)) / (SiO ₂ ) ≤2.2

(5)

(6),13 <(MgO) ≤25

(6)

where in expressions (5) and (6) (CaO), (MgO) and (SiO ₂ ) are the amounts (in mass percent) of CaO, MgO and SiO ₂ in the slag, respectively.

According to another aspect of the present invention, there is provided a slag formed as a by-product from the production methods described above.

The objectives, features, aspects and advantages of the present invention will become more apparent from the following detailed description and the attached drawings.

Brief Description of the Drawings

Figure 1 schematically shows an exemplary rotary hearth thermal reduction furnace.

Figure 2 is a graph illustrating the relationship between the basicity of the slag and the distribution coefficient of sulfur in Example a.

Figure 3 is a graph illustrating the relationship between the basicity of the slag and the distribution coefficient of sulfur in Example b.

4 is a graph illustrating the relationship between the basicity of the slag and the distribution coefficient of sulfur in Example c.

5 is a graph illustrating the relationship between the MgO content in the slag and the sulfur distribution coefficient in Example c.

Preferred Embodiments

First option

A first embodiment of the present invention will be described below.

To produce iron by direct reduction, an industrial rotary hearth thermal reduction furnace is typically used as an industrial thermal reduction furnace. In a rotary hearth thermal reduction furnace using a plurality of burners mounted above the rotary hearth, fuel gas, for example, natural gas, is burned. The resulting heat of combustion enters the raw material mixture placed on the hearth and serves as the heat needed for reduction with melting. The flue gas resulting from combustion contains oxidizing gases such as CO ₂ and H ₂ O. Oxidizing gases affect the composition of the gaseous atmosphere around the feed mixture. As a result, it is very difficult to maintain the reduction potential of the gaseous atmosphere in the furnace at a high level if oxidizing gases are not removed in a suitable manner. At the same time, in the case of a sufficiently high reduction potential of the gaseous atmosphere inside or around the mixture of starting materials, the sulfur contained in a carbon-containing reducing agent, such as coal or coke, included in the mixture of starting materials, is fixed in the form of CaS due to the presence of CaO in slag. CaS is separated from the mixture of starting materials together with slag. The inclusion of a fluorine-containing substance such as fluorspar (CaF ₂ ) in the composition of the starting material mixture further leads to the separation of sulfur in the starting material mixture from this mixture.

As for the method of removing oxidizing gases, a layer of carbon-containing powder (hereinafter referred to as the bedding layer), which is not shown, is preliminarily created on the hearth of the furnace A for thermal reduction shown in FIG. The mixture of starting materials is placed on the underlying layer and subjected to thermal recovery. The conditions for the targeted reduction reaction to be melted are efficiently created while the hearth of said thermal reduction furnace is rotated with a rotating hearth with a cycle of from about 8 to about 16 minutes. The recovery potential of the gas atmosphere in the immediate vicinity of the mixture of starting materials can be maintained at a high level. In addition, it is possible to some extent to increase the ability to desulfurize.

However, the inventors of the present invention have found that solely the above-described operation of creating an underlying layer is still insufficient to guarantee the production of granular metallic iron having a low sulfur content in a rotary hearth furnace used in practice. The use of the methods described in Patent Documents 4 and 5, which are indicated above, increases the guarantee of obtaining granular metallic iron having a reduced sulfur content. In the methods corresponding to these patent documents, the main focus is on the basicity of the slag. The explanation for this is outlined below.

In order to reduce the [S] sulfur content in the granular metallic iron (that is, to increase the observed degree of desulfurization), it is extremely important to maintain a stable level of (S) sulfur in the slag when it is fixed in the slag in the form of CaS, as well as to prevent the migration of sulfur in the direction of reduced gland. More specifically, it is necessary to maintain the recovery potential of the gas atmosphere at a high level and maximize the basicity of the resulting slag. In contrast to a conventional furnace for producing cast iron or steel using molten iron in the melting reduction method of the present invention, an atmosphere temperature in excess of 1550 ° C. is not preferable in terms of equipment and operation of a rotary thermal reduction furnace Pod. It is desirable to function while maintaining the temperature of the atmosphere at about 1550 ° C. or lower, and preferably 1500 ° C. or lower. However, if the basicity of the slag formed during the reduction stage during melting under the indicated temperature conditions begins to exceed approximately 1.7, the melting point of the slag rises, which slows its coalescence. In addition, the coalescence of reduced iron also slows down. This makes it difficult to ensure a high yield of metallic iron with a large piece size in the manufacturing process.

The inventors of the present invention conducted in-depth studies in order to ensure as fast as possible the melting of slag-forming components with the formation of slag under conditions of heating a mixture of starting materials placed in a rotary hearth thermal reduction furnace, and, as a result, to enable coalescence of the resulting slag so that promote coalescence of the remaining reduced iron, which will increase the yield of granular metallic iron, as well as to reduce the proportion of sulfur, which inevitably pollutes the granular metallic iron obtained by such a process.

Based on these studies, the following was discovered: if the starting material mixture contains at least Fe, Ca, Mg, Si and an alkali metal as constituent elements so that the slag contains CaO, MgO, SiO ₂ and an alkali metal oxide, an alkaline oxide the metal was at least one oxide selected from Li ₂ O, Na ₂ O and K ₂ O, the alkali metal oxide satisfied at least one of the above expressions (1) to (3), and the basicity of the slag satisfying the above expression (4), then the sulfur distribution coefficient between receiving resulting from slag and the resulting granular metallic iron, i.e. (S) / [S] improves significantly, providing a marked reduction in the [S] sulfur content of the granular metallic iron, whereby a good yield of granular metallic iron having a low sulfur content can be ensured. This led to the creation of a method for the production of granular metallic iron, corresponding to the first embodiment of the present invention. The method for producing granular metallic iron according to the first embodiment of the present invention, as well as the production of slag as a by-product resulting from the implementation of said production method, will be described in detail below.

[Components of slag]

Slag formed during the usual process of producing iron by direct reduction contains CaO, MgO and SiO ₂ as components. The basicity of the slag (((CaO) + (MgO)) / (SiO ₂ )) is determined by the fractions of these components. The basicity of slag is closely related to the sulfur distribution coefficient (S) / [S] in the slag-metal reaction during the normal process for producing cast iron and steel.

At the same time, the slag formed in this embodiment of the present invention also contains alkali metal oxide as a component. The slag containing alkali metal oxide in addition to CaO, MgO and SiO ₂ provides a deeper desulfurization compared to conventional slag containing CaO, MgO and SiO ₂ .

The reason that the slag containing alkali metal oxide in addition to CaO, MgO and SiO ₂ provides excellent desulfurization remains to be theoretically explained. However, based on the experimental results described below, the following conclusion is made. Namely, it is assumed that a suitable control of the basicity of the slag produced as a by-product in the production of granular metallic iron and a suitable control of the content of alkali metal oxides in the slag lead to a decrease in the melting point of the slag, which is a by-product, of optimization of such physical properties as slag flow , and increase to a maximum the sulfur distribution coefficient (S) / [S] for slag, which is a by-product.

The type of alkali metal oxide in the slag is not particularly limited. If the alkali metal oxide is Na ₂ O, K ₂ O or Li ₂ O, the alkali metal oxide significantly affects the decrease in the melting temperature of the slag. As a consequence, the alkali metal oxide may be at least one oxide selected from the group consisting of Na ₂ O, K ₂ O and Li ₂ O.

[The content of Li ₂ O, Na ₂ O and K ₂ O in the slag]

The desulfurization effect is achieved when the content of alkali metal oxide in the slag is approximately 0.03 mass percent, if this oxide is Li ₂ O, about 0.10 mass percent, if this oxide is Na ₂ O, or about 0.10 mass percent, if this oxide is K ₂ O. The content of Li ₂ O in the resulting slag is preferably 0.1 mass percent or more, and more preferably 0.3 mass percent or more. The content of Na ₂ O in the resulting slag is preferably 0.2 mass percent or more, and more preferably 0.5 mass percent. The content of K ₂ O in the resulting slag is preferably 0.3 mass percent or more, and more preferably 0.7 mass percent.

The upper limit of the content of Li ₂ O in the resulting slag is preferably 12 mass percent. The upper limit of the content of Na ₂ O in the resulting slag is preferably 5 weight percent. The upper limit of the content of K ₂ O in the resulting slag is preferably 5 weight percent. Active inclusion of Li ₂ O, Na ₂ O or K ₂ O in the resulting slag leads to a decrease in the melting point of this slag, which is a by-product, and to an increase in the sulfur distribution coefficient for this slag. However, the too high content of Li ₂ O, Na ₂ O or K ₂ O in the slag causes their strong evaporation, as a result of which the evaporated Li ₂ O, Na ₂ O or K ₂ O reacts with refractory materials in the furnace, causing damage to the walls of this furnace. The content of Li ₂ O is preferably 11 mass percent or less, and more preferably 10 mass percent or less. The Na ₂ O content is preferably 4.5 weight percent or less, and more preferably 4 weight percent or less. The K ₂ O content is preferably 3 weight percent or less, and more preferably 2 weight percent or less. Slag may contain separately Li ₂ O, Na ₂ O or K ₂ O, or in combination of two or more of them.

[Alkali metal compound]

An alkali metal compound according to this embodiment of the present invention may be at least one compound selected from the group consisting of lithium compounds, sodium compounds and potassium compounds. That is, an alkali metal compound according to this embodiment of the present invention may be a lithium compound, a sodium compound or a potassium compound. Alternatively, the alkali metal compound of this embodiment of the present invention may be a combination of two or more compounds selected from the group consisting of lithium compounds, sodium compounds and potassium compounds. In addition, an alkali metal compound according to this embodiment of the present invention may also be a combination of any of said lithium compounds, sodium compounds and potassium compounds with an alkali metal compound different from said lithium compounds, sodium compounds and potassium compounds.

The starting material mixture may contain at least one compound selected from the group consisting of lithium compounds, sodium compounds and potassium compounds, as an alkali metal compound such that the alkali metal oxide in the slag satisfies at least one of the above expressions (1) - (3). As a consequence, the starting material mixture may contain an alkali metal compound such that the slag contains alkali metal oxide different from the aforementioned Li ₂ O, Na ₂ O or K ₂ O.

The type of lithium compound is not particularly limited. Examples thereof include lithium carbonate (Li ₂ CO ₃ ) and lithium oxide (Li ₂ O).

The type of sodium compound is not particularly limited. Examples thereof include sodium carbonate (Na ₂ CO ₃ ) and sodium oxide (Na ₂ O).

The type of sodium compound is not particularly limited. Examples thereof include potassium carbonate (K ₂ CO ₃ ) and potassium oxide (K ₂ O).

The alkali metal compound may be a compound that forms any two or more of the oxides Li ₂ O, Na ₂ O and K ₂ O in the slag. An example of a complex oxide based on M1-M2, in which the alkali metal oxide (M1) is simply mixed with the oxide of a chemical element (M2) other than alkali metals is Na ₂ O-Li ₂ O-SiO ₂ -CaO. An example of an alkali metal compound that forms Na ₂ O and K ₂ O in slag is nepheline [composition: (Na, K) (Al, Si) O ₄ ]. Note that nepheline also corresponds to the complex oxide described below, which has a melting point of 1400 ° C. or lower and contains an alkali metal.

The alkali metal compound is preferably a complex oxide that has a melting point of 1400 ° C. or lower and contains at least one alkali metal. As described above, a moving hearth thermal reduction furnace typically operates while maintaining the temperature (atmosphere temperature) therein at a level of from about 1450 ° C. to about 1550 ° C. Thus, heating a starting material mixture containing a complex oxide that has a melting point of 1400 ° C. or lower in said furnace leads to a rapid melting of this oxide. Its coalescence leads to the rapid formation of slag. The rapid formation of slag facilitates the coalescence of the remaining metallic iron to produce granules, which increases the yield of granular metallic iron. That is, the inclusion (addition from the outside) of a complex oxide having a low melting point in the mixture of starting materials leads to the rapid melting of this oxide under the influence of heat with the appearance of a state of preliminary melting, which increases the yield of granular metallic iron. As described in Example b below, the use of complex oxide as an alkali metal compound not only reduces the sulfur content of metallic iron, but also reduces the time required to melt the starting material mixture, compared to using simple alkali metal oxide, which further increases said yield.

Examples of alkali metals in the complex oxide include Li, Na and K, Li and Na are preferably used in terms of availability. The complex oxide described above may contain at least one alkali metal. For example, a complex oxide preferably contains at least one of the following metals: Li, Na and K.

The term "complex oxide containing at least one alkali metal" is used to indicate an oxide containing at least one chemical element selected from the group consisting of alkali metal chemical elements and containing at least , one chemical element other than alkali metals, based on an analysis of the chemical composition using, for example, inductively coupled plasma spectrometry (ICP, Inductively-Coupled Plasma) or atomic absorption spectrometry. More specifically, when analyzing the chemical composition of an oxide, for example, using inductively coupled plasma spectrometry or atomic absorption spectrometry, at least one alkali metal and one chemical element other than alkali metals are detected. The complex oxide contains an alkali metal oxide (e.g., Na ₂ O, Li ₂ O or K ₂ O) and an oxide of another chemical element (e.g., oxide of a slag-forming component) different from alkali metals, if it is assumed that each of the detected chemical elements is in as a simple oxide. That is, the complex oxide may contain at least one oxide selected from the group consisting of Na ₂ O, Li ₂ O and K ₂ O, and at least one oxide selected from the group consisting of MgO, CaO , BaO, MnO, FeO, B ₂ O ₃ , Al ₂ O ₃ and SiO ₂ .

The complex oxide can be prepared as follows: first, the material supplying the alkali metal is mixed with the material that supplies the chemical element other than alkali metals. Then, the resulting mixture is calcined. Alternatively, the mixture is melted and allowed to solidify. The resulting complex oxide may, if necessary, be pulverized to adjust particle size.

Examples of said alkali metal supplying material include sodium carbonate (Na ₂ CO ₃ ) as the material contributing Na; potassium carbonate (K ₂ CO ₃ ) as a material contributing K; and lithium carbonate (Li ₂ CO ₃ ) as the material contributing Li.

Examples of said material supplying a chemical element other than alkali metals are described below.

Examples thereof include SiO ₂ as a Si depositing material; calcined lime (CaO) and calcium carbonate (CaCO ₃ ) as a Ca depositing material; MgO and MgCO ₃ as a material contributing Mg; BaCO ₃ as Ba depositing material; MnCO ₃ as a material contributing Mn; FeO as a material contributing Fe; H ₃ BO ₃ as material contributing B; and Al ₂ O ₃ as the material contributing Al. These materials usually contain minor impurities.

An example of a material introducing Na, K and Si is nepheline [composition: (Na, K) (Al, Si) O ₄ ].

The complex oxide described above may further comprise another chemical element, until this element increases the melting temperature of the complex oxide over 1400 ° C. However, in the oxide based on M1-M2, the effect of reducing the melting time does not occur due to the fact that with simple mixing of M1 oxide with M2 oxide, the melting temperature of the resulting mixture does not decrease to 1400 ° C or less.

The starting material mixture may contain said complex oxide, which has a temperature of 1400 ° C. or lower and contains at least one alkali metal, as well as a simple alkali metal compound as an alkali metal compound. Examples of said simple alkali metal compound include alkali metal oxides and alkali metal carbonates.

In the case of using said complex oxide, which has a melting point of 1400 ° C or lower and contains at least one alkali metal, as an alkali metal compound, the complex oxide can be added to the mixture of starting materials so that the total fraction of simple oxides was 0.03 mass percent or more, preferably 0.05 mass percent or more, and more preferably 0.2 mass percent or more, if it is assumed that the chemical elements are alkali metals in slag in the form of simple oxides.

In addition, in the case of using said complex oxide, which has a melting point of 1400 ° C. or lower and contains at least one alkali metal, as an alkali metal compound, the complex oxide can be added to the mixture of starting materials so that the total the proportion of simple oxides was 15 weight percent or less, preferably 14.5 weight percent or less, and more preferably 13 weight percent or less, if the chemical elements are assumed to be alkali metal s are in the slag in the form of simple oxides. The rationale for this is as follows: as described above, the active incorporation of alkali metal oxide into the resulting slag leads to a decrease in the melting point of this slag, which is a by-product, and to an increase in the sulfur distribution coefficient for this slag. However, too high an alkali metal oxide content causes too much evaporation of the alkali metal in the furnace, as a result of which the evaporated alkali metal reacts with refractory materials in the furnace, causing damage to these materials.

The fact that the alkali metal chemical elements are supposed to be in the form of simple oxides indicates that when designating an alkali metal chemical element as M1, the oxide of this chemical alkali metal element contained in the slag is represented by the formula M1 ₂ O.

The proportions of simple oxides of chemical elements - alkali metals in the slag can be controlled by adjusting the amount of complex oxide added to the mixture of starting materials in accordance with its chemical composition. That is, the regulation of the amount of complex oxide added to the mixture of starting materials, in accordance with the chemical composition of this complex oxide, which contains at least one chemical element selected from the group consisting of alkali metal chemical elements, regulates the content of alkali metal oxides in slag.

[Slag basicity: 1.3-2.3]

The basicity of the slag (((CaO) + (MgO)) / (SiO ₂ )) is set in the range from 1.3 to 2.3. The presence of a higher proportion of CaO / MgO introducing material, which serves as the basicity regulating agent (material that forms CaO and MgO in the slag), such as limestone or dolomite ore, in the mixture of the starting materials leads to an increase in the CaO and MgO content obtained in The result is slag, thus increasing the basicity of the slag. The inclusion of an excess amount of CaO / MgO introducing material leads to the formation of slag having a basicity of more than 2.3. However, an excessively high slag basicity causes an increase in slag flowability, slowing down the coalescence of the reduced iron and, thus, making it difficult to obtain granular metallic iron with a preferred, mainly spherical shape. In addition, there is a tendency to reduce the yield of granular metallic iron. As a result, it is determined that the upper limit of slag basicity is 2.3. The slag basicity is preferably 2.2 or less, and more preferably 2.0 or less. Note that a higher basicity of the slag leads to a decrease in the melting temperature of the resulting slag.

At the same time, a slag basicity of less than 1.4 causes a decrease in the slag desulfurization ability, as a result of which the intended goal is not achieved, even if the atmospheric reduction potential is maintained at a sufficiently high level. As a result, it is determined that the lower limit of slag basicity is 1.4. The slag basicity is preferably 1.5 or more.

In this description, the term "slag basicity" is used to indicate the ratio of (CaO) + (MgO) to (SiO ₂ ), i.e. ((CaO) + (MgO)) / (SiO ₂ ), determined based on the amounts of CaO, MgO and SiO ₂ in slag, unless otherwise indicated.

[MgO content in slag: from 5 to 22 weight percent]

In an embodiment of the present invention, the slag preferably contains MgO at a level of 5 weight percent or more. This is due to the fact that even with a slag basicity of 2.3 or less, in fact, the ability to coalesce small particles of reduced iron formed during the reduction of material containing iron oxide in the mixture of starting materials gradually decreases with an increase in basicity in areas of relatively high levels, starting from 1.9 and above. That is, in the region of relatively high levels of basicity, the coalescence ability of the slag is significantly reduced, and the ability to coalesce the resulting reduced iron particles is also reduced, which makes it difficult to ensure high yield in the production of metallic iron with a large piece size, which is the goal in this embodiment of the present invention. As a result, in the region of relatively high levels of basicity, even when the basicity of the resulting slag is 2.3 or less, it is preferable that the slag contain 5 weight percent or more MgO from the point of view of providing economical operation in this embodiment of the present invention. This is due to the fact that the MgO content in the slag of less than 5 weight percent leads to the formation in the slag of a complex oxide represented by the formula 2CaO • SiO ₂ at normal operating temperature, causing a loss of slag flowability and a loss of coalescence ability. On the other hand, with a relatively high basicity of 1.9 or more, the MgO content in the slag in excess of 22 weight percent causes the release of pure MgO in the slag, making coalescence difficult. As a result, it is impossible to provide a high yield in the production of the target metallic iron with large piece sizes. Therefore, the MgO content in the slag is preferably 22 weight percent or less. In a more preferred case, the MgO content in the slag is 20 weight percent or less.

The basicity of the slag and the MgO content in the slag can be controlled by controlling the added amounts of the material containing iron oxide and the carbon-containing reducing agent. This is due to the fact that the material containing iron oxide and the carbon-containing reducing agent contain at least CaO, MgO and SiO ₂ . Iron ore, added as a material containing iron oxide, as well as coal or coke, added as a carbon-containing reducing agent, are natural products. Consequently, the fractions of CaO, MgO and SiO ₂ differ depending on their types. Therefore, it is difficult to uniquely determine the added quantities of these materials. It is preferable to appropriately adjust the amounts of the material containing iron oxide and the carbon-containing reducing agent, taking into account the chemical composition of the gangue contained, for example, in iron ore, added as the material containing iron oxide, and the chemical composition of the ash contained in coal or coke, added as a carbon-containing reducing agent.

The same is true for the added amount of complex oxide. It is difficult to unambiguously determine the amount of complex oxide due to the fact that the chemical composition varies depending on the type of oxide. Thus, the added amount of the complex oxide can be adjusted appropriately taking into account the chemical composition of this oxide.

For example, in the case of loading a carbon-containing powder used as a component forming the underlying layer, the basicity of the slag and the MgO content in the slag can be controlled by adjusting the added amounts of the material containing iron oxide and the carbon-containing reducing agent, taking into account the composition and amount of the loaded carbon-containing powder.

As described above, the main features of this embodiment of the present invention are as follows: the resulting slag contains alkali metal oxide; and set the content of Na ₂ O, the content of K ₂ O and the content of Li ₂ O, as well as the basicity of the slag. Accordingly, it is not always necessary to use a carbon-containing powder, which serves as a component that forms the underlying layer, which is placed on the hearth. However, the placement of a carbon-containing powder on the hearth, which serves as a component that forms the underlying layer, leads to a more significant increase in the reduction potential in the furnace, as a result of which it is possible to more effectively provide both the effect of increasing the degree of metallization and the effect of reducing the [S] sulfur content in metallic iron . In order to more reliably provide such effects from the component forming the underlying layer, it is desirable to place granular carbon-containing powder to obtain a layer having a thickness of about 2 mm or more. If the carbon-containing powder is placed as a component forming the underlying layer, so that the layer has a certain thickness, the underlying layer will serve as a buffer between the mixture of starting materials and the refractory material of the hearth or serve to protect the refractory material of the hearth from slag, which is a by-product thus increasing the service life of said hearth refractory material.

Too much thickness of the underlying layer, however, can cause an unfavorable retardation of recovery, allowing the mixture of starting materials to immerse in this underlying layer located on the hearth. As a consequence, the thickness of the underlying layer is preferably set at about 7.5 mm or less.

The type of carbon-containing powder used as a component forming the underlying layer is not particularly limited. Milled common coal or coke can be used. In the preferred case, you can use milled ordinary coal or coke, the grain size of which is controlled properly. In the case of coal, anthracite is suitable, which has a low fluidity, and also does not increase in size or stick to the hearth.

Both iron ore, which serves as a material containing iron oxide, and coal, which serves as a carbon-containing reducing agent, which are added to the starting material mixture, correspond to a material that introduces MgO (a material that introduces MgO into slag). As another MgO-introducing material, a material other than a material containing iron oxide, a carbon-containing reducing agent or an alkali metal compound may be added to the starting material mixture. Said other MgO-introducing material corresponds to an external additive compared to an iron oxide-containing material, a carbon-containing reducing agent and an alkali metal compound. In this case, the added amounts of said other MgO-introducing material, an iron oxide-containing material, a carbon-containing reducing agent and an alkali metal compound can be adjusted according to their chemical compositions so that the slag has a basicity of 1.3 to 2.3, and, as necessary, the MgO content is from 5 to 22 weight percent.

The type of other MgO contributing material mentioned is not particularly limited. Examples thereof include MgO powder, natural ore, Mg-containing materials extracted from sea water and the like, and magnesium carbonate (MgCO ₃ ).

Both iron ore, which serves as a material containing iron oxide, and coal, which serves as a carbon-containing reducing agent, which are added to the feed mixture, also correspond to a material that introduces CaO (a material that introduces CaO into slag). As another CaO-introducing material, a material other than a material containing iron oxide, a carbon-containing reducing agent or an alkali metal compound may be added to the starting material mixture. Said other CaO-introducing material corresponds to an external additive compared to an iron oxide-containing material, a carbon-containing reducing agent and an alkali metal compound. In this case, the added amounts of said other CaO-introducing material, an iron oxide-containing material, a carbon-containing reducing agent and an alkali metal compound can be adjusted according to their chemical compositions so that the slag has a basicity of 1.3 to 2.3, and, as necessary, a CaO content in a suitable range.

The type of other CaO contributing material mentioned is not particularly limited. Examples thereof include lime CaO and calcium carbonate (CaCO ₃ ).

For example, dolomite ore may be added to the feed mixture as a CaO / MgO depositing material.

The method of adding said other MgO contributing material and other CaO introducing material is not particularly limited. Instead of adding said other MgO-introducing material and another CaO-introducing material to the starting material mixture, said other MgO-introducing material and other CaO-introducing material can be pre-arranged on the rotating hearth together with the bedding component, or independently of it. Alternatively, said other MgO-introducing material and other CaO-introducing material may be loaded at the same time as the feed mixture is loaded, or may be loaded separately from above, after the feed mixture is loaded.

The starting material mixture may contain a small amount of a polysaccharide (e.g., starch from flour) as a binder.

Preferably, fluorspar is not added to the feed mixture for environmental safety reasons. According to the embodiment of the present invention described above, it is possible to sufficiently increase the desulfurization ability and the coalescence ability without adding fluorspar. However, the addition of fluorspar to the starting material mixture can further increase the aforementioned desulfurization and coalescence properties.

In this embodiment of the present invention, as described above, when performing work using a rotary hearth thermal reduction furnace, commonly used in practice, when the basicity of the resulting slag increases to approximately 2.3, provided that the material that controls basicity, serves as a material that introduces MgO, the slag can melt sufficiently at temperatures from a range of up to 1450 ° C, which differs from the current level of technology. This allows the production of granular metallic iron in a stable mode. In addition, it is possible to provide a distribution coefficient of sulfur between slag and metal, (S) / [S], equal to about 10 or more, and, in particular, 20 or more. As a result, although there are some differences depending on the type of coal that serves as a carbon-containing reducing agent, the component forming the underlying layer, and so on, the sulfur content in the resulting granular metallic iron can stably decrease to 0.080% or less and, in particular, to 0.05% or less. In the case of using said complex oxide, which has a melting point of 1400 ° C. or lower and contains at least one alkali metal, as an alkali metal compound, the sulfur content of the resulting granular metallic iron can be stably reduced to 0.05% or less, and in particular up to 0.01% or less.

As described above, in the case of using the most versatile gas burners for heating an industrial furnace, a decrease in the sulfur distribution coefficient (S) / [S] cannot be avoided due to a decrease in the reduction potential of the gas atmosphere. In this embodiment of the present invention, however, it is possible to prevent a decrease in the distribution coefficient of sulfur (S) / [S], since alkali metal oxide (eg, Li ₂ O, Na ₂ O and K ₂ O) in the slag satisfies at least , one of the above expressions (1) through (3), and since the basicity of the slag satisfies the above Equation (4).

The main characteristics of the rolling hearth thermal reduction furnace used in this embodiment of the present invention, the main characteristics of the granular metal iron production method using the thermal reduction furnace, and the granular metal iron production mechanism will be described in detail below with reference to FIG. The drawings are not limited to this embodiment of the present invention. They may be appropriately modified in accordance with the purposes indicated above and below in this description. All such changes are not outside the scope of the present invention.

Figure 1 schematically shows an example of the design of a rotary hearth thermal reduction furnace A, similar in type to rolling hearth thermal reduction furnaces. A partial section is shown to show the internal structure of the furnace.

A mixture of 1 starting materials, which includes a material containing iron oxide, a carbon-containing reducing agent and an alkali metal compound, is continuously fed to a rotary hearth 4 under a furnace A for thermal reduction with a rotary hearth through a material supply hopper 3. As the material containing iron oxide, iron ore, magnetic iron ore and the like are usually used. As a carbon-containing reducing agent, coal, coke and the like are usually used. As the alkali metal compound, sodium carbonate, nepheline and the like are usually used.

The shape of the feed mixture 1 of the starting materials is not specifically limited. Typically, a simple pressed preform is used from a mixture of starting materials, including a material containing iron oxide, a carbon-containing reducing agent, and an alkali metal compound. As an alternative, a pressed blank of a mixture of starting materials containing carbon material, which has the form of a pellet or briquette, is used. A mixture may be supplied in which material containing iron oxide, a carbon-containing reducing agent, an alkali metal compound, and the like are suitably mixed. In addition, granular carbon-containing powder 2 can be supplied together with a simple pressed preform or a pressed preform containing carbon material.

If necessary, a material (e.g., MgO-introducing material or CaO-introducing material) different from the starting material mixture may be loaded into the furnace A for thermal reduction. However, in a preferred case, the fluorine-containing desulfurizing agent is not loaded for environmental reasons.

The procedure for feeding the feed mixture 1 to the furnace A for thermal reduction will be more specifically described below. In a preferred case, a granular carbon-containing powder 2 is fed through a hopper 3 for supplying materials to a rotary under 4 to obtain a bed before feeding a mixture of 1 starting materials, and then a mixture of 1 starting materials is placed on it.

Figure 1 shows an example with a single hopper 3 of the material supply, which is used both for the supply of carbon-containing powder 2, and for feeding the mixture 1 of the starting materials. Alternatively, the carbon-containing powder 2 and the mixture 1 of the starting materials can be loaded individually using two or more silos. The carbon-containing powder 2 used to create the underlying layer (bed) is very useful not only from the point of view of increasing recovery efficiency, but also from the point of view of helping to reduce the sulfur content in granular metallic iron obtained by direct reduction. However, the supply of carbonaceous powder 2 can be excluded. The type of carbon-containing powder supplied to create a bed is not particularly limited. Examples thereof include coal and coke. The carbon-containing powder supplied to create a bed preferably has a lower sulfur content than the carbon-containing reducing agent added to the feed mixture.

Rotating under 4 furnaces A for thermal reduction, shown in FIG. 1, rotates counterclockwise. The rotation speed varies depending on the size and operating parameters of the furnace A. The rotation cycle of the rotating hearth 4, as a rule, is from about 8 to about 16 minutes. A plurality of heating burners 5 are installed on the walls of the housing 8 of the furnace A for thermal restoration. It is heated by the heat of combustion or thermal radiation from the heating burners 5. The heating burners 5 can be installed on the roof of the furnace.

The mixture 1 of the starting materials, placed on a rotating hearth 4 made of refractory material, is heated due to the heat of combustion or thermal radiation coming from the heating burners 5, while the said mixture moves in a circumferential direction on the rotating hearth 4 in the furnace A for thermal recovery . Iron oxide contained in mixture 1 of the starting materials is reduced by passing through the heating zone in furnace A for thermal reduction. Then, the reduced iron is carbonized using the remaining carbon-containing reducing agent while simultaneously separating from the molten slag formed as a by-product, and coalesces into granular metal iron 10. The granular metal iron 10 solidifies upon cooling in the zone of the rotating hearth 4, which is further in the direction of movement, after which it is discharged from the hearth using an unloading device 6, such as a screw. This also discharges the slag formed as a by-product. The granular metal iron 10 and slag pass through a hopper 9, and then are separated into metal iron and slag using any separating means (e.g., sieves or magnetic separators). 1, reference numeral 7 denotes an exhaust gas channel.

In this embodiment of the present invention, as described above, in the slag, which was formed as a by-product of thermal reduction, the alkali metal oxide satisfies at least one of the above expressions (1) to (3), and the basicity of the slag satisfies the above above the expression (4). Thus, it is possible to appropriately control the melting point of the resulting slag and the sulfur distribution ratio (S) / [S], as well as to obtain granular metallic iron having a low sulfur content with high efficiency.

Examples

A method for producing granular metallic iron according to this embodiment of the present invention will be described below in more detail by way of examples. The present invention is not limited to the examples mentioned, which are discussed below. These examples may be duly modified in accordance with the purposes indicated above and below in this description. All such changes are not outside the scope of the present invention. The following examples describe the results of tests performed using a small experimental furnace for thermal reduction.

Example a

As the material containing iron oxide, iron ore was used. Coal was used as a carbon-containing reducing agent. They were mixed to form mixture M. Table 1 shows the chemical composition of iron ore. Table 2 shows the chemical composition of coal ("Other" in the Design Values indicates a carbon-containing solid).

Table 1 The chemical composition of iron ore, mass percent Amount Fe FeO SiO ₂ Cao MgO Al ₂ O ₃ S P 69.39 30.10 1.75 0.45 0.40 0.49 0,028 0.013

table 2 Coal Estimated value, mass percent The chemical composition of the ash, mass percent Volatiles Total ash Sulfur Other Fe ₂ O ₃ SiO ₂ Al ₂ O ₃ Cao MgO 15.8 4.3 0.61 79.29 13.84 43.09 27.57 4.95 1,54

Table 3 The chemical composition of dolomite ore, mass percent CO ₂ SiO ₂ Al ₂ O ₃ Cao MgO 47.60 1,02 0.21 30.08 21.09

In the mixture M, in addition to the material containing iron oxide and a carbon-containing reducing agent, a binder (flour) was added. To obtain the final mixture of the starting materials (hereinafter also referred to as the complex), auxiliary materials, regulating the basicity of the slag, such as calcium carbonate (CaCO ₃ ), which serves as the material making CaO, and dolomite ore (consisting mainly of from CaCO ₃ • MgCO ₃ , the detailed chemical composition of which is given in Table 3), which serves as a material, contributing CaO / MgO, sodium carbonate (Na ₂ CO ₃ ) as an alkali metal compound, sodium oxide (Na ₂ O), nepheline [composition : (Na, K) (Al, Si) O ₄ ], lithium carbonate (Li ₂ CO ₃ ) and under other. Table 4 shows the chemical composition of the complexes.

Table 4 The chemical composition of the complex, mass percent Test case Iron ore Coal Bunch CaCO ₃ Dolomite ore Na ₂ CO ₃ Nepheline Li ₂ CO ₃ a1 75.7 16,0 0.5 5.8 - - 2.0 - a2 77.7 16,0 1,0 0.7 3.8 0.8 - - a3 77.1 15,5 1,0 0.8 4.0 1,6 - - a4 77.8 15.6 1,0 3.6 1,0 1,0 - - a5 78.0 15.1 1,0 2.7 2,3 0.9 - - a6 77.3 15.4 1,0 3.0 2.0 1.3 - - a7 77.7 15,2 1,0 2.0 3.0 1,1 - - a8 77.3 15.4 1,0 3.0 2.0 1.3 - - a9 78.1 15.6 1,0 4.0 - 1.3 - - a10 79.1 15.8 1,0 3.0 1,0 0.1 - - a11 76.6 15.4 1,0 4.0 - 3.0 - - a12 73.7 14.9 1,0 5,4 - 5,0 - - a13 78.5 15.7 1,0 4.7 - - - 0.10 a14 77.6 15.6 1,0 5.7 - - - 0.10 a15 78,2 15.7 1,0 3,1 - - - 2.00 a16 77.8 15.6 1,0 4.0 - - - 1,60 a17 77.3 15,5 1,0 2.2 2.0 - - 2.00 a18 77.0 15.4 1,0 3.0 2.0 - - 1,60 a19 76.1 15.3 1,0 5,6 - - - 2.00 a20 79.0 15.8 1,0 3.0 1,2 - - 0.01 a21 73.9 14.6 1,0 - 6.5 - - 4.00 a22 78,4 15.4 1,0 2.7 1,5 0.5 - 0.50 a23 77.9 15.4 1,0 2.7 1,5 0.5 - 1.00 a24 75,5 15,2 1,0 5.2 1,0 2.1 - - a25 74.0 15.0 1,0 6.0 - - - 4.00 a26 80.5 15.8 1,0 1,5 1,2 - - 0.01 a27 81.7 17.3 1,0 - - - - - a28 79.0 15.0 1,0 3.0 2.0 - - - a29 84.0 15.0 1,0 - - - - - a30 81.0 15.0 1,0 1,5 1,5 - - - a31 81.7 14.9 1,0 1,2 1,2 - - - a32 81.0 14.8 1,0 1.7 1,5 - - - a33 80.6 14.7 1,0 2.2 1,5 - - - a34 79.7 15.1 1,0 2.7 1,5 - - -

Each of the resulting complexes was converted into pressed blanks from raw materials in the form of pellets. The resulting pressed preforms from the starting materials were loaded into a small experimental furnace for thermal reduction and subjected to thermal reduction. Before loading the pressed preforms from the starting materials, coal (carbon-containing powder) having the chemical composition shown in Table 2 was placed on the hearth to obtain a base layer having a thickness of approximately 5 mm. The temperature in the furnace was set equal to 1450 ° C.

Iron oxide in pressed preforms from raw materials located on the hearth of the furnace for thermal reduction was reduced by heating in the furnace for from about 10 to about 16 minutes, while maintaining the solid state of this oxide. The resulting reduced iron was carburized using the carbon-containing powder remaining after reduction, which led to a decrease in the melting point and coalescence of the reduced iron. At the same time, the slag formed as a by-product partially or completely melted and coalesced. In this case, the molten granular metallic iron was separated from the molten slag. Then, the molten granular metallic iron and molten slag were cooled to their melting points (namely, approximately 1100 ° C.) and solidified. Solid granular metallic iron and solid slag were discharged from the furnace.

Tables 5 and 6 show the chemical composition of granular metallic iron and slag in each test example. In addition, based on the CaO content, MgO content and SiO ₂ content in the slag, the basicity of the slag (((CaO) + (MgO)) / (SiO ₂ )) in each test example was calculated. Tables 5 and 6 also show the basicity of the slag in each test example.

In each test example, from the ratio of the mass of Fe (hereinafter also referred to as Fe1) of granular metallic iron formed by coalescence to the mass of Fe (hereinafter also referred to as Fe0) determined based on the calculation of the chemical composition, the degree of yield (Fe1 / Fe0) was calculated. The ability to coalesce in a test example with a yield exceeding 98% was rated as good (A). The ability to coalesce in a test example with a yield of 98% or less was rated as poor (B). Tables 5 and 6 also show the results of the evaluation in test examples. In Table 6, the coalescence ability “C” indicates that the granular metallic iron was not recovered since it did not separate from the slag.

In addition, in each test example, the ratio of sulfur content (S) in slag to sulfur content [S] in granular metallic iron was calculated (sulfur distribution coefficient (S) / [S]). Tables 5 and 6 also show the sulfur distribution coefficient in each test case.

In test example A1, shown in Table 5, as an alkali metal compound, an alkali metal compound, which is a sodium compound and a potassium compound, was added to the starting material mixture. The content of alkali metal oxides in the slag and the basicity of the slag satisfied the above expressions (2) - (4). Note that the alkali metal compound used in test example a1 also corresponds to said complex oxide, which has a melting point of 1400 ° C. or lower and contains at least one alkali metal. In each of test examples a2 through a12 shown in Table 5, only the sodium compound was added to the mixture of starting materials as an alkali metal compound. The content of alkali metal oxides in the slag and the basicity of the slag satisfied the above expressions (2) and (4). In each of the test examples a13 through a21 shown in Table 5, only a lithium compound was added to the mixture of starting materials as an alkali metal compound. The content of alkali metal oxides in the slag and the basicity of the slag satisfied the above expressions (1) and (4). In each of test examples a22 and a23 shown in Table 5, only the sodium compound and lithium compound were added to the mixture of starting materials as the alkali metal compound. The content of alkali metal oxides in the slag and the basicity of the slag satisfied the above expressions (1), (2) and (4). All test examples a1 through a23 shown in Table 5 were within the range corresponding to this embodiment of the present invention. MgO levels in the slag ranged from 5 to 22 weight percent.

In test example a26 shown in Table 6, although only a lithium compound was added to the mixture of starting materials as the alkali metal compound, the content of alkali metal oxides did not satisfy any of expressions (1) - (3). In each of the test examples a27 through a34 shown in Table 6, no alkali metal compound was added to the starting material mixture. The content of alkali metal oxides in the slag did not satisfy any of the expressions (1) - (3). All test examples a26-a34 shown in Table 6 were outside the range corresponding to this embodiment of the present invention.

Figure 2 shows the relationship between the basicity of each of the slags formed in test examples a1-a23 and a26-a34, and the sulfur distribution coefficient. In Fig.2, the basicity of the resulting slag is laid on the horizontal axis. The sulfur distribution coefficient is plotted on the vertical axis.

In Fig. 2, filled squares correspond to test examples a1-a12 shown in Table 5. Shaded triangles correspond to test examples a13-a21 shown in Table 5. Unfilled rhombuses correspond to test examples a22 and a23, shown in Table 5. Unfilled circles correspond to test examples a26-a34 shown in Table 6.

From Tables 5 and 6 it is clearly seen that in order to provide a sulfur content of granular metallic iron of 0.080% or less, it is necessary that the alkali metal oxide content in the slag and the slag basicity be in the range corresponding to this embodiment of the present invention. Due to this, a sulfur distribution coefficient of 10 or more can be guaranteed.

From Figure 2 it is clearly seen that the sulfur distribution coefficient (S) / [S] increases sharply with increasing slag basicity. In particular, slag basicity in excess of 1.4 leads to a substantial increase in sulfur distribution coefficient.

2 clearly shows that the distribution coefficient of sulfur (S) / [S] increases with increasing basicity, regardless of whether an alkali metal compound is added to the mixture of starting materials. However, in each test example in which an alkali metal compound is added to the starting material mixture and in which the content of alkali metal oxides in the slag satisfies at least one of the above expressions (1) to (3), the sulfur distribution coefficient (S) / [S] is higher than in those test examples in which the content of alkali metal oxide in the slag does not satisfy the above expressions (1) - (3).

Each test example, in which an alkali metal compound was not added to the starting material mixture, demonstrated that when the basicity of the resulting slag increased to approximately 1.7, the melting temperature of the slag increased, which caused difficulties in the coalescence of molten slag and prevent the formation of reduced iron. A large amount of granular metallic iron with a small grain size arose, which caused difficulties in providing a high yield of granular metallic iron with a large grain size.

In Example a, the slag basicity and MgO content in the slag are controlled by adding dolomite ore, which serves as the CaO / MgO depositing material. In each of the compositions of the complexes in Example a, the slag basicity and MgO content in the slag can be controlled within the ranges of basicity and MgO content specified in this embodiment of the present invention, controlling the dolomite ore content in the complex so that it is from about 0 to 6.5 weight percent.

As described above, Example a demonstrated that when a material containing iron oxide, a carbon-containing reducing agent, an alkali metal compound and the like was suitably added to the starting material mixture, the alkali metal oxide in the slag satisfied at least one of the above expressions (1) - (3), and the resulting basicity of the slag defined on the basis of the content of CaO, MgO content and content of SiO _2, satisfies the expression (4), the sulfur distribution ratio was 10 or more and comprises of [S] sulfur in the granular metallic iron was decreased to 0.080% or less even in the region where the slag basicity was 1.7 or more.

Example b

An example of a method for producing granular metallic iron using the complex oxide as an alkali metal compound, which has a melting point of 1400 ° C. or lower and contains at least one alkali metal, will be described below.

As the material containing iron oxide, the iron ore shown in Table 1 was used. The carbon shown in Table 2 was used as the carbon-containing reducing agent. They were mixed to form a mixture of N.

In addition to the material containing iron oxide and the carbon-containing reducing agent, a binder was added to mixture N. To obtain the final mixture of the starting materials (complex), auxiliary materials, regulating the basicity of the slag, and an alkali metal compound (complex oxide, simple oxide, or carbonate) were added, as needed.

Flour was added as a binder. As auxiliary materials regulating the basicity of the slag, calcium carbonate (CaCO ₃ ) was added, which serves as the CaO depositor, and dolomite ore, the CaO / MgO depositor, shown in Table 3.

Table 7 shows the chemical composition of complex oxides and simple oxide. The types A-F shown in Table 7 are examples in which complex oxides are used as alkali metal compounds. The type G shown in Table 7 is an example in which a simple oxide (alkali metal oxide) is used as the alkali metal compound. Table 7 shows the chemical compositions of complex oxides and simple oxide, for which the oxide content was calculated using inductively coupled plasma spectrometry or atomic absorption spectrometry.

Table 7 The chemical composition of complex oxide and simple oxide, mass percent Melting point, ° С Type of SiO ₂ Cao Na ₂ O Li ₂ O A 55.0 - - 45.0 1024 B 59.1 24.8 - 16.1 1090 C 38.7 50,0 - 11.3 1050 D 50.9 31.6 17.5 - 1284 E 51.0 15.6 33,4 - 1200 F 50,0 43.0 7.0 - 1400 G - - - one hundred 1570

The complex oxides of types AF shown in Table 7 were prepared by maintaining the molten state of SiO ₂ , CaCO ₃ , Na ₂ CO ₃ and Li ₂ CO ₃ at 1500 ° C for 1-2 hours and performing grinding in this way so that the average grain size is 100 μm or less. Table 7 also lists the melting points of the oxides.

Carbonate was that alkali metal compound used in conjunction with a complex oxide that is different from coplex oxide. As a lithium compound, lithium carbonate (Li ₂ CO ₃ ) was added.

Table 8 shows the chemical compositions of the complexes.

Table 8 The chemical composition of the complex, mass percent Test case Iron ore Coal CaCO ₃ Dolomite ore Oxide Li ₂ CO ₃ Bunch Type of Content b1 81.7 17.3 - - - - - one b2 79 fifteen 3.0 2 - - - one b3 84 fifteen - - - - - one b4 81 fifteen 1,5 1,5 - - - one b5 81.7 14.9 1,2 1,2 - - - one b6 81 14.8 1.7 1,5 - - - one b7 79.7 15.1 2.7 1,5 - - - one b8 80.6 14.7 2.2 1,5 - - - one b9 66 13.5 8.5 6 BUT 5 - one b10 68.5 fourteen 6.5 5 BUT 5 - one b11 70.1 14,4 5,0 4,5 BUT 5 - one b12 72.1 15.8 3,5 3.9 B 2 1.7 one b13 73.5 16,2 2.1 3,5 C 2 1.7 one b14 71 15.6 4,5 2.2 C four 1.7 one b15 69.8 14,4 6.3 5.5 B 3 - one b16 72.3 14.7 5,0 four B 3 - one b17 75 15,2 3.0 2,8 B 3 - one b18 75.6 15.4 2.5 2.5 B 3 - one b19 76.9 15.4 4.1 2.5 B 0.1 - one b20 78,2 15.7 3.0 2 B 0.1 - one b21 80 15.9 1,5 1,5 B 0.1 - one b22 80.3 16.1 1,5 one B 0.1 - one b23 79.05 15.9 2.0 2 B 0.05 - one b24 79.08 15.9 2.0 2 B 0.02 - one b25 79.09 15.9 2.0 2 B 0.01 - one b26 73.5 16.1 3,5 3.9 D 2 - one b27 73.5 16.1 3,5 3.9 E 2 - one b28 74 15.6 3,5 3.9 F 2 - one b29 77.5 16.1 2,4 2 G one - one

Each of the resulting complexes was converted into pressed blanks from raw materials in the form of pellets. The resulting pressed preforms from the starting materials were loaded into a small experimental furnace for thermal reduction and subjected to thermal reduction. Before loading the pressed preforms from the starting materials, coal (carbon-containing powder) having the chemical composition shown in Table 2 was placed on the hearth to obtain a base layer having a thickness of approximately 5 mm. The temperature in the furnace was set equal to 1450 ° C.

Iron oxide in pressed preforms from raw materials located on the hearth of the furnace for thermal reduction was reduced by heating in the furnace for from about 10 to about 16 minutes, while maintaining the solid state of this oxide. The resulting reduced iron was carburized using the carbon-containing powder remaining after the reduction, which resulted in a decrease in the melting point and, as a result, in the coalescence of the reduced iron. At the same time, the slag, which is a by-product, partially or completely melted and coalesced. In this case, the molten granular metallic iron was separated from the molten slag. Then, the molten granular metallic iron and molten slag were cooled to their melting points (namely, approximately 1100 ° C.) and solidified. Solid granular metallic iron and solid slag were discharged from the furnace.

After loading the pressed blanks from the starting materials into the experimental furnace for thermal reduction, the state inside this furnace was visually monitored. The time required to melt all the pressed billets in view was measured. Table 9 shows the time for complete melting, measured in each test example. A full melting time of 14 minutes or less was rated acceptable.

Table 9 Sulfur distribution coefficient Full melting time Test case Basicity Value Rating Minutes Rating b1 0.39 0.34 Unacceptably 9.5 Acceptable b2 1.95 9.59 Unacceptably 14.75 Unacceptably b3 0.33 0.27 Unacceptably 9.5 Acceptable b4 1.21 2.90 Unacceptably 10.75 Acceptable b5 1.21 1,56 Unacceptably 10.75 Acceptable b6 1.45 2.95 Unacceptably 12.00 Acceptable b7 1.70 5.05 Unacceptably 13.25 Acceptable b8 1,52 3.75 Unacceptably 12.50 Acceptable b9 1.95 1109,0 Acceptable 11.00 Acceptable b10 1,57 257.5 Acceptable 11.00 Acceptable b11 1.31 41.2 Acceptable 10.00 Acceptable b12 1,64 187.6 Acceptable 11.50 Acceptable b13 1.79 211.6 Acceptable 11.25 Acceptable b14 1.82 418.5 Acceptable 11.00 Acceptable b15 2.27 152.1 Acceptable 11.75 Acceptable b16 1.83 58.1 Acceptable 11.50 Acceptable b17 1.32 18.1 Acceptable 10.50 Acceptable b18 1.19 9.0 Unacceptably 10.25 Acceptable b19 No coalescence b20 1.93 31.5 Acceptable 11.75 Acceptable b21 1.31 12.3 Acceptable 10.50 Acceptable b22 1.17 7.5 Unacceptably 10.25 Acceptable b23 1,64 19.7 Acceptable 10.50 Acceptable b24 1.65 12.5 Acceptable 10.50 Acceptable b25 1.65 6.7 Unacceptably 11.00 Acceptable b26 1.96 277.8 Acceptable 11.50 Acceptable b27 1.83 162.0 Acceptable 11.00 Acceptable b28 1.99 57.8 Acceptable 12.00 Acceptable b29 1.91 35,4 Acceptable 13.75 Acceptable

Table 10 shows the chemical composition of granular metallic iron and slag in each test example. In addition, based on the CaO content, MgO content and SiO ₂ content in the slag, the basicity of the slag (((CaO) + (MgO)) / (SiO ₂ )) in each test example was calculated. The slag basicity for each test example is shown in Table 9. In test example b19 shown in Table 10, the slag basicity was adjusted so that it was approximately 2.4, so that coalescence did not occur.

In addition, in each test example, the ratio of sulfur content (S) in slag to sulfur content [S] in granular metallic iron was calculated (sulfur distribution coefficient (S) / [S]). Table 9 also shows the sulfur distribution coefficient in each test case.

In each of test examples b9-b17, b20, b21, b23, b24 and b29 shown in Table 10, one or two lithium compounds were added to the mixture of starting materials as an alkali metal compound. The content of alkali metal oxides in the slag and the basicity of the slag satisfied the above expressions (1) and (4). In each of test examples b9-b17, b20, b21, b23 and b24 shown in Table 10, a complex oxide was added as an alkali metal compound. In test example b29, a simple oxide was added as an alkali metal compound. In each of the test examples b26-b28 shown in Table 10, a sodium compound corresponding to the complex oxide was added to the mixture of starting materials as an alkali metal compound. The content of alkali metal oxides in the slag and the basicity of the slag satisfied the above expressions (2) and (4). All test examples b9-b17, b20, b21, b23, b24 and b26-b29 shown in Table 10 were in the range corresponding to this embodiment of the present invention. The MgO content in the slag was in the range of 5-22 weight percent.

In each of the test examples b1-b8 shown in Table 10, no alkali metal compound was added to the starting material mixture. The content of alkali metal oxides in the slag did not satisfy any of the expressions (1) - (3). In each of test examples b18 and b22 shown in Table 10, a lithium compound was added to the mixture of starting materials as an alkali metal compound. Although the content of alkali metal oxides in the slag satisfied the above expression (1), the basicity of the slag did not satisfy the above expression (4). In test example b25 shown in Table 10, although a lithium compound was added to the mixture of starting materials as an alkali metal compound, the content of alkali metal oxides in the slag did not satisfy any of the above expressions (1) - (3). All test examples b1-b8, b18, b22, and b25 shown in Table 10 were outside the range corresponding to this embodiment of the present invention.

Figure 3 shows the relationship between the basicity of each of the slags formed in test examples b1-b18 and b20-b29, and the distribution coefficient of sulfur. In Fig. 3, the basicity of the formed slag is plotted along the horizontal axis. The sulfur distribution coefficient is plotted on the vertical axis.

In Fig. 3, filled diamonds correspond to test examples b1 to b8. Unfilled circles correspond to test examples b9 - b17, b20, b21, b23 and b24. The filled circles correspond to test examples b18, b22 and b25. Unfilled diamonds correspond to test examples b26 and b28.

As can be seen from Table 9, the complete melting time in each of test examples b9-b17, b20, b21, b23, b24 and b26-b29, which are within the range corresponding to this embodiment of the present invention, is estimated as acceptable. The full melting time in each of test examples b9-b17, b20, b21, b23, b24 and b26-b28, in which the mentioned complex oxides are added as alkali metal compounds, each of which has a melting point of 1400 ° C or lower and contains at least one alkali metal is reduced to 13.5 minutes or less. Thus, by adding the complex oxide as an alkali metal compound, which has a melting point of 1400 ° C. or lower and contains at least one alkali metal, it is possible to increase the yield compared to the case of adding the said alkali metal compound, such as a simple oxide or carbonate, different from complex oxide.

From Tables 8 and 9 it is clearly seen that in order to ensure the sulfur content in the granular metallic iron at a level of 0.05% or less, it is necessary that the alkali oxide content in the slag and the slag basicity be in the range corresponding to this embodiment of the present invention. Due to this, a sulfur distribution coefficient of 10 or more can be guaranteed.

From Figure 3 it is clearly seen that the distribution coefficient of sulfur (S) / [S] increases sharply with increasing basicity of the slag.

From Table 8 and Figure 3 it is clearly seen that the sulfur distribution coefficient (S) / [S] increases with increasing basicity of the slag, regardless of whether an alkali metal compound is added to the raw material mixture or not. However, in each of test examples b9-b17, b20, b21, b23, b24 and b26-b28, in which alkali metal compounds are added to the mixture of starting materials, and in which the content of alkali metal oxides in the slag satisfies at least one of the above expressions (1) to (3), the sulfur distribution coefficient (S) / [S] is 10 or more. That is, the sulfur distribution coefficient (S) / [S] is higher than in test examples b1-b8, in which the content of alkali metal oxide in the slag does not satisfy the expressions (1) - (3).

In Example b, the slag basicity and MgO content in the slag are controlled by adding dolomite ore, which serves as an auxiliary material for regulating the slag basicity.

As described above, Example b demonstrated that when a material containing iron oxide, a carbon-containing reducing agent, an alkali metal compound and the like was suitably added to the starting material mixture, the alkali metal oxide in the slag satisfied at least one of the above expressions (1) - (3), and the resulting basicity of the slag defined on the basis of the content of CaO, MgO content and content of SiO _2, satisfies the expression (4), the sulfur distribution ratio is 10 or more (up to 1109.0), content [S] of sulfur in the granular metallic iron was reduced to 0.05% by weight percent or less even in the region where the slag basicity was 1.7 or more.

Second option

A method for producing granular metallic iron according to a second embodiment of the present invention will be described.

A method for producing granular metallic iron according to this embodiment of the present invention includes the steps of loading an alkali metal compound and a mixture of starting materials, which includes a material containing iron oxide and a carbon-containing reducing agent, in a furnace for thermal reduction, heating the mixture of starting materials and reducing iron oxide contained in the material containing iron oxide, using a carbon-containing reducing agent to obtain metallic iron slag as a byproduct ensure coalescence of metallic iron to granules while separation of metallic iron from slag, and cooling and solidifying the metallic iron.

A mixture of starting materials or an alkali metal compound contains at least Fe, Ca, Mg, Si and an alkali metal as constituent elements so that the slag contains CaO, MgO, SiO ₂ and an alkali metal oxide, wherein the alkali metal oxide is at least one oxide selected from Li ₂ O, Na ₂ O and K ₂ O, wherein the alkali metal oxide satisfies at least one of the above expressions (1) to (3), and the basicity of the slag satisfies the specified above the expression (4).

That is, this method is similar to the method of producing granular metallic iron according to the first embodiment of the present invention, except that the alkali metal compound is not contained in the mixture of starting materials, but is directly loaded into the furnace for thermal reduction.

In this embodiment, when loading (adding) a mixture of starting materials and an alkali metal compound into a furnace for thermal reduction, the outer surface of the mixture of starting materials begins to contact the outer surface of the alkali metal compound. In the contact area under the influence of heat in the furnace for thermal recovery, the same reaction occurs as in the first embodiment of the present invention. That is, it is assumed that in the case where the basicity of the slag formed as a by-product in the production of granular metallic iron is controlled in such a way that it satisfies the above expression (4), and when the alkali metal oxide content in the slag is controlled so that it satisfies at least one of the above expressions (1) to (3), the melting point of the slag formed as a by-product is reduced, physical properties such as slag fluidity are optimized and The sulfur distribution coefficient (S) / [S] for slag, which is a by-product, is maximized. In this embodiment of the present invention, it is also possible during production to provide a good yield of granular metallic iron having a low sulfur content.

The method for loading an alkali metal compound is not particularly limited. As a method for adding an alkali metal compound to a mixture of starting materials, for example, loading an alkali metal compound together with a bedding component can be used. The alkali metal compound can be pre-positioned on a rotating hearth, irrespective of the component forming the underlying layer. Alternatively, the alkali metal compound may be charged at the same time as the mixture of starting materials is loaded, or may be loaded separately from above, after loading the mixture of starting materials. In addition, you can use several loading methods in combination. The effect of this embodiment of the present invention is provided with any loading method.

Third option

A third embodiment of the present invention will be described below.

To solve the problem of the present invention, the authors conducted in-depth studies, in particular, based on the technology described in the above Patent Document 5: slag basicity regulation (((CaO) + (MgO)) / (SiO ₂ )); and reducing the sulfur content in the reduced iron by controlling the MgO content in the slag. In particular, in a third embodiment of the present invention, environmental safety is a priority. Particular attention is paid to the aforementioned process for producing iron by direct reduction using a mixture of starting materials that does not contain fluorspar.

The inventors of the present invention have found that, from the point of view of the aforementioned environmental safety, in the case where the basicity of the slag is controlled so that it is essentially in the same range as specified in Patent Document 5, and when the MgO content in the slag is regulated so that it is in the aforementioned range from more than 13 weight percent to 25 weight percent or less, outside the range specified in Patent Document 5, it is possible to obtain reduced iron, which has low sulfur content and can be used as a source of iron for electric furnaces and converters. The discovered information led to the creation of a method for the production of granular metallic iron, corresponding to the third embodiment of the present invention. That is, in the case when the mixture of starting materials contains at least Fe, Ca, Mg and Si as constituent elements so that the slag contains CaO, MgO and SiO ₂ , the basicity of the slag satisfies the above expression (5), and the MgO content in the slag satisfies the above expression (6), it is possible to ensure a good yield of granular metallic iron having a low sulfur content during production. A method for producing granular metallic iron according to a third embodiment of the present invention, as well as slag generated as a by-product of this method, will be described in detail below.

A common feature of Patent Document 5 and this embodiment of the present invention is that the sulfur content of the reduced iron is reduced by controlling the basicity of the slag and the MgO content of the slag. However, they differ in the range of MgO content, which is mainly due to their tasks. Namely, Patent Document 5 states that the main priority is to further reduce the sulfur content. The upper limit of the MgO content in the slag is set at 13 weight percent to provide a target level corresponding to this Patent Document 5 (sulfur distribution coefficient is 25 or more, and the sulfur content in the reduced iron is 0.050 mass percent or less). In contrast, the main priority of this embodiment of the present invention is environmental safety. The upper limit of the MgO content is set at 25 mass percent in order to provide a technology that allows for a low level of sulfur content (the distribution ratio of sulfur is 10 or more, and the sulfur content in metallic iron is 0.080 mass percent or less) to use the resulting iron as the source material for converters, although this is worse compared to the target level of Patent Document 5.

For example, when considering the presence or absence of fluorspar, in Patent Document 5, it is recommended to add fluorspar in the range when the slag basicity is ≥1.7. It is indicated that this prevents a significant decrease in the ability of fine particles of reduced iron to coalesce and increases the yield. In contrast, in this embodiment of the present invention, it is possible to produce reduced iron having a low sulfur content without the use of fluorspar, as long as the slag basicity is within the range of 1.5 to 2.2 (see Example c discussed below).

[Slag basicity: 1.5-2.2]

The significance of the slag basicity in this embodiment of the present invention is essentially the same as in Patent Document 5. That is, the slag basicity is a parameter that contributes to an increase in the yield of granular metallic iron and a decrease in the proportion of [S] sulfur that contaminates this iron . Thus, its lower limit is set equal to 1.5. A slag basicity of less than 1.5 causes a decrease in the desulfurization ability of the slag. When implementing this option in practice, the basicity of the slag is preferably 1.6 or more. However, a higher slag basicity causes an increase in slag flowability, slowing down the coalescence of the reduced iron and, thus, making it difficult to obtain granular metallic iron with a preferred substantially spherical shape. In addition, there is a tendency to reduce the yield of granular metallic iron. As a result, it is determined that the upper limit of slag basicity is 2.2. The slag basicity is preferably 2.1 or less, and more preferably 2.0 or less. The basicity of the slag can be adjusted within the above range.

[MgO content in slag: more than 13 weight percent and up to 25 weight percent]

The significance of said MgO content in the slag in this embodiment is essentially the same as Patent Document 5. That is, the content is set in such a way as to provide a satisfactory sulfur distribution ratio (S) / [S]. However, in Patent Document 5, the main priority is said significant reduction in sulfur content. As defined, the upper limit of the MgO content should be 13 weight percent in terms of providing a sulfur distribution coefficient of 25 or more. In contrast, in this embodiment of the present invention, it is determined that the lower limit of the MgO content should be more than 13 weight percent, and its upper limit should be 25 weight percent in terms of ensuring a low sulfur content (sulfur distribution coefficient of 10 or more, and the sulfur content in metallic iron is 0.080 mass percent or less) for the possibility of using the resulting iron as a starting material for converters, although this is worse in terms of vneny with a target level in Patent Document 5. In this embodiment of the present invention can be guaranteed to provide a target level of this embodiment without the use of fluorspar. A lower MgO content is preferable from the point of view of further reducing the sulfur content. The upper limit of the MgO content is set equal to 20 weight percent.

The melting point of the slag formed as a by-product can be set from about 1350 ° C to about 1550 ° C by adjusting the components of the starting materials so that the resulting slag satisfies the above expressions (5) and (6). The temperature is below about 1550 ° C, which is a typical temperature when operating a moving hearth thermal reduction furnace. As a result, when a mixture of starting materials is heated in a furnace for thermal reduction with a moving hearth, including components whose quantity is adjusted so that the resulting slag meets the above requirement, the slag-forming components melt and coalesce with rapid formation of slag. The rapid formation of slag promotes coalescence in the granules of the remaining metallic iron, which leads to an increase in the yield of granular metallic iron.

The sulfur distribution coefficient (S) / [S] between the resulting slag and the resulting granular metallic iron is significantly improved by adjusting the components of the starting materials so that the resulting slag satisfies the above expressions (5) and (6). This leads to a significant reduction in the sulfur content in the granular metallic iron.

In order to adjust the melting point of the slag formed as a by-product so that it is from about 1350 ° C to about 1550 ° C, the components of the starting materials can be adjusted so that the slag satisfies the above expressions (5) and (6). In a preferred case, the proportions of other oxides contained in the slag are also regulated (for example, CaO content, Al ₂ O ₃ content and SiO ₂ content), since the melting point of the slag also depends to some extent on the proportion of these oxides. The CaO content can be set at a level of from about 20 to about 50 weight percent. The content of Al ₂ O ₃ can be set at a level of approximately less than 20 weight percent. The content of SiO ₂ can be set at a level of approximately less than 40 weight percent.

The above expressions (5) and (6) can be met by appropriately controlling the added amounts of the material containing iron oxide and the carbon-containing reducing agent serving as starting materials. This is because the iron oxide-containing material and the carbon-containing reducing agent usually contain waste rock components such as CaO, MgO and SiO ₂ , and thus serve as the CaO-introducing material, the MgO-introducing material, and SiO ₂ -containing material (material that forms SiO ₂ in the slag). Iron ore, commonly used as a material containing carbon monoxide, and coal or coke, commonly used as a carbon-containing reducing agent, are natural products. Consequently, the fractions of CaO, MgO and SiO ₂ differ depending on their types. Therefore, it is difficult to uniquely determine the added quantities of these materials. Advantageously, it is preferable to adjust the added amounts according to the chemical composition of iron ore and the like, as well as the chemical composition of coal and the like. In the case of loading a carbon-containing powder used as a component forming the underlying layer, the basicity of the slag and the MgO content in the slag can be controlled by adjusting the added amounts of material containing iron oxide and a carbon-containing reducing agent, taking into account the composition and amount of the carbon-containing powder.

The raw material mixture used in this embodiment of the present invention may contain said other MgO-contributing material (external additive compared to the iron oxide-containing material and the carbon-containing reducing agent), which is different from the iron-oxide-containing material and the carbon-containing reducing agent, in addition to the last two materials mentioned. In this case, the amounts of the material containing iron oxide and the carbon-containing reducing agent are controlled taking into account the chemical composition and the added amount of the other MgO-introducing material, which makes it possible to control the basicity of the slag and the MgO content in the slag.

The type of other MgO contributing material mentioned is not particularly limited. Examples thereof include MgO powder, natural ore, Mg-containing materials extracted from sea water and the like, and magnesium carbonate (MgCO ₃ ).

In addition, the starting material mixture used in this embodiment of the present invention may contain said other CaO contributing material (external additive compared to the iron oxide containing material and the carbonaceous reducing agent), which is different from the iron containing material, and carbon-containing reducing agent, in addition to the last two materials mentioned. In this case, the amounts of the material containing iron oxide and the carbon-containing reducing agent are controlled taking into account the chemical composition and the added amount of the other CaO-introducing material, which makes it possible to control the basicity of the slag and the CaO content in the slag.

The type of other CaO contributing material mentioned is not particularly limited. Examples thereof include lime (CaO) and calcium carbonate (CaCO ₃ ).

An example of a material serving as the other MgO contributing material and other CaO contributing material is dolomite ore. Dolomite ore may be added.

Preferably, fluorspar is not added to the feed mixture for environmental reasons. According to this embodiment of the present invention, it is possible to substantially improve the desulfurization ability and the coalescence ability without adding fluorspar. However, adding fluorspar to the starting material mixture can further improve the desulfurization ability and coalescence ability.

A method for producing granular metallic iron using a moving hearth thermal reduction furnace, which corresponds to this embodiment of the present invention, will be described in detail below with reference to FIG. Figure 1 shows a non-limiting example of a moving hearth furnace for thermal reduction, which can suitably be used in the production method of this embodiment of the present invention.

Figure 1 schematically shows an example of the design of a furnace A for rolling stock thermal reduction, similar in type to rolling hearth reduction furnaces. A partial section is shown to show the internal structure of the furnace.

A mixture of 1 starting materials, which includes a material containing iron oxide and a carbon-containing reducing agent, is continuously fed to a rotary hearth 4 under a furnace A for thermal reduction with a rotary hearth through a material feed hopper 3. As the material containing iron oxide, iron ore, magnetic iron ore and the like are usually used. As a carbon-containing reducing agent, coal, coke and the like are usually used.

The shape of the feed mixture 1 of the starting materials is not specifically limited. Typically, a simple pressed blank of a mixture of starting materials is used, which includes a material containing iron oxide and a carbon-containing reducing agent. As an alternative, a pressed blank of a mixture of starting materials containing carbon material, which has the form of a pellet or briquette, is used. A mixture may be supplied in which material containing iron oxide, a carbonaceous reducing agent and the like are suitably mixed. In addition, granular carbon-containing powder 2 can be supplied together with a simple pressed preform or a pressed preform containing carbon material.

In this embodiment of the present invention, if necessary, material (for example, MgO-introducing material or CaO-introducing material) may be loaded, different from the starting material mixture.

The procedure for feeding the feed mixture 1 to the furnace A for thermal reduction will be more specifically described below. In a preferred case, a granular carbon-containing powder 2 is fed through a hopper 3 for supplying materials to a rotating one under 4 to obtain a bed before feeding the mixture 1 of the starting materials, and then the mixture 1 of the starting materials is placed on it.

The method of adding MgO-introducing material and CaO-introducing material that can be added in addition to the carbon monoxide-containing material and the carbon-containing reducing agent is not particularly limited. Suitably, the following methods can be used: for example, an MgO-introducing material and a CaO-introducing material can be added at the stage of preparing the starting material mixture. The MgO introducing material and the CaO introducing material may be pre-arranged on the rotating hearth, together with or independently of the component forming the underlying layer. Alternatively, the MgO-introducing material and the CaO-introducing material may be loaded at the same time as the mixture of starting materials are loaded, or may be separately loaded from above after loading the mixture of starting materials.

The feed mixture may contain a small amount of polysaccharide (e.g., flour starch) as a binder.

Figure 1 shows an example with a single hopper 3 of the material supply, which is used both for the supply of carbon-containing powder 2, and for feeding the mixture 1 of the starting materials. Alternatively, the carbon-containing powder 2 and the mixture 1 of the starting materials can be loaded individually using two or more silos.

Note that it is not always necessary to use a carbon-containing powder, which serves as a component forming the underlying layer, which is placed on the hearth. The loading of carbonaceous powder can be eliminated. However, the placement on the hearth of a carbon-containing powder, which serves as a component forming the underlying layer, leads to a more significant increase in the reduction potential in the furnace, as a result of which it is possible to more effectively provide both the effect of increasing the degree of metallization and the effect of reducing the sulfur content in metallic iron, which is preferred. In order to more reliably provide such effects from the component forming the underlying layer, it is desirable to place granular carbon-containing powder to obtain a layer having a thickness of about 2 mm or more. If the carbon-containing powder is placed as a component forming the underlying layer, so that the layer has a certain thickness, the underlying layer will serve as a buffer between the mixture of starting materials and the refractory material of the hearth or serve to protect the refractory material of the hearth from slag, which is a by-product thus increasing the service life of said hearth refractory material.

Too much thickness of the underlying layer, however, can cause an unfavorable retardation of recovery, allowing the mixture of starting materials to immerse in this underlying layer located on the hearth. As a consequence, the thickness of the underlying layer is preferably set at about 7.5 mm or less.

The type of carbon-containing powder used as a component forming the underlying layer is not particularly limited. Milled common coal or coke can be used. In the preferred case, you can use milled ordinary coal or coke, the grain size of which is controlled properly. In the case of coal, anthracite is suitable, which has a low fluidity, and also does not increase in size or stick to the hearth. The carbonaceous powder supplied to make the bed preferably has a lower sulfur content than the carbonaceous reducing agent added to the mixture 1 of the starting materials.

Rotating under 4 furnaces A for thermal reduction, shown in FIG. 1, rotates counterclockwise. The rotation speed of the rotating hearth 4 varies depending on the size and operating parameters of the furnace A. The rotation cycle of the rotating hearth 4, as a rule, is from about 8 to about 16 minutes. A plurality of heating burners 5 are installed on the walls of the housing 8 of the furnace A for thermal restoration. It is heated by the heat of combustion or thermal radiation from the heating burners 5. The heating burners 5 can be installed on the roof of the furnace.

The mixture 1 of the starting materials, placed on a rotating hearth 4 made of refractory material, is heated due to the heat of combustion or thermal radiation coming from the heating burners 5, while the said mixture moves in a circumferential direction on the rotating hearth 4 in the furnace A for thermal recovery . Iron oxide contained in mixture 1 of the starting materials is reduced by passing through the heating zone in furnace A for thermal reduction. Then, the reduced iron is carbonized using the remaining carbon-containing reducing agent while simultaneously separating from the molten slag formed as a by-product, and coalesces into granular metal iron 10. The granular metal iron 10 solidifies upon cooling in the zone of the rotating hearth 4, which is further in the direction of movement, after which it is discharged from the hearth using an unloading device 6, such as a screw. This also discharges the slag formed as a by-product. The granular metal iron 10 and slag pass through a hopper 9, and then are separated into metal iron and slag using any separating means (e.g., sieves or magnetic separators). 1, reference numeral 7 denotes an exhaust gas channel.

In this embodiment of the present invention, as described above, for the slag, which was formed as a by-product of thermal reduction, the slag basicity and MgO content in the slag are controlled so that they satisfy the above expressions (5) and (6), as a result which suitably control the melting point of the resulting slag and the sulfur distribution ratio (S) / [S], which allows efficiently guaranteed to obtain granular metallic iron having a low sulfur content.

Example

A method for producing granular metallic iron according to this embodiment of the present invention will be described below in more detail by way of examples. The present invention is not limited to the examples mentioned, which are discussed below. These examples may be duly modified in accordance with the purposes indicated above and below in this description. All such changes are within the scope of this embodiment of the present invention. The following examples describe the results of tests performed using a small experimental furnace for thermal reduction.

Example with

As the material containing iron oxide, iron ore was used, the characteristics of which are shown in Table 11. As a carbon-containing reducing agent, coal was used, the characteristics of which are shown in Table 2. They were mixed to form a mixture. Table 11 shows the chemical composition of iron ore.

Table 11 The chemical composition of iron ore, mass percent Amount Fe FeO SiO ₂ Cao MgO Al ₂ O ₃ S P 69.33 29.92 1,64 0.42 0.41 0.45 0.013 0.014

A binder was added to the mixture, in addition to the material containing iron oxide and the carbon-containing reducing agent. To obtain the final mixture of the starting materials (complex), auxiliary materials, which regulate the basicity of the slag, were added, as necessary. Flour was added as the binder mentioned.

As auxiliary materials that regulate the basicity of the slag, calcium carbonate (CaCO ₃ ) was added, which serves as a CaO-contributing material, and dolomite ore, which serves as a CaO / MgO-contributing material, the characteristics of which are shown in Table 3. Table 12 shows the chemical composition of the complexes .

Table 12 The chemical composition of the complex, mass percent Test case Iron ore Coal Bunch MgO CaCO ₃ Dolomite ore s1 79.7 16.5 1,0 0.8 2.0 c2 79.1 16.3 1,0 1.3 2,3 c3 78.5 16,2 1,0 1.8 2.5 c4 80.0 15.0 1,0 1,5 2.5 c5 80.8 16,2 1,0 1,1 0.9 c6 80.6 16.1 1,0 0.6 1.7 c7 80.2 16.1 1,0 1,0 1.7 c8 81.7 17.3 1,0 s9 79.0 15.0 1,0 3.0 2.0 s10 84.0 15.0 1,0 s11 81.0 15.0 1,0 1,5 1,5 s12 81.7 14.9 1,0 1,2 1,2

Each of the resulting complexes was converted into pressed blanks from raw materials in the form of pellets. The resulting pressed preforms from the starting materials were loaded into a small experimental furnace for thermal reduction and subjected to thermal reduction. Before loading the pressed preforms from the starting materials, coal (carbon-containing powder) having the chemical composition shown in Table 2 was placed on the hearth to obtain a base layer having a thickness of approximately 5 mm. The temperature in the furnace was set equal to 1450 ° C.

Iron oxide in pressed preforms from raw materials located on the hearth of the furnace for thermal reduction was reduced by heating in the furnace for from about 10 to about 16 minutes, while maintaining the solid state of this oxide. The resulting reduced iron was carburized using the carbon-containing powder remaining after the reduction, which resulted in a decrease in the melting point and, as a result, in the coalescence of the reduced iron. At the same time, the slag formed as a by-product partially or completely melted and coalesced. In this case, the molten granular metallic iron was separated from the molten slag. Then, the molten granular metallic iron and molten slag were cooled to their melting points (namely, approximately 1100 ° C.) and solidified. Solid granular metallic iron and solid slag were discharged from the furnace.

Table 13 shows the chemical composition of the granular metallic iron and slag in each test example. In addition, based on the CaO content, MgO content and SiO ₂ content in the slag, the basicity of the slag (((CaO) + (MgO)) / (SiO ₂ )) in each test example was calculated. Table 13 also shows the basicity of the slag in each test example.

In addition, in each test example, the ratio of sulfur content (S) in slag to sulfur content [S] in granular metallic iron was calculated (sulfur distribution coefficient (S) / [S]). Table 13 also shows the sulfur distribution coefficient in each test case.

In each of the test examples c1-c4 shown in Table 13, the slag basicity and MgO content in the slag satisfied the above expressions (5) and (6). All test examples c1-c4 were in the range corresponding to this embodiment of the present invention.

In each of the test examples c5, c6, c8 and c10-c12 shown in Table 5, the basicity of the slag did not satisfy expression (5). In each of the test examples c7 and c9 shown in Table 13, although the basicity of the slag satisfied the expression (5), the MgO content in the slag did not satisfy the expression (6). All test examples c5-c12 shown in Table 13 were outside the range corresponding to this embodiment of the present invention.

Figure 4 shows the relationship between the basicity of each of the slags formed in test examples c1-c12, and the distribution coefficient of sulfur. In Fig. 3, the basicity of the formed slag is plotted along the horizontal axis. The sulfur distribution coefficient is plotted on the vertical axis. In Fig. 4, unfilled diamonds correspond to test examples c1-c4 shown in Table 13. Filled triangles correspond to test examples c5-c12 shown in Table 13.

Figure 5 shows the relationship between the MgO content in each of the slags formed in test examples c1-c12 and the sulfur distribution coefficient. In Fig. 5, the MgO content (in mass percent) in the resulting slag is plotted along the horizontal axis. The sulfur distribution coefficient is plotted on the vertical axis. In Fig. 5, unfilled diamonds correspond to test examples c1-c4 shown in Table 13. Filled triangles correspond to test examples c5-c12 shown in Table 13.

In each test example, the ratio of the yield (Fe1 / Fe0) was calculated from the ratio of the mass of Fe (Fe1) of granular metallic iron formed by coalescence to the mass of Fe (Fe0) determined by calculating the chemical composition. The ability to coalesce in a test example with a degree of yield exceeding 95% was rated as acceptable. The ability to coalesce in a test example with a yield of less than 95% was rated as unacceptable. Table 13 also summarizes these evaluation results.

From Table 13, as well as FIGS. 4 and 5, it is clearly seen that in the case where the slag basicity and MgO content are within the ranges corresponding to this embodiment of the present invention (i.e., the slag basicity and MgO content satisfy expressions (5) and ( 6)), it is possible to guarantee a sulfur distribution coefficient (S) / [S] of 10 or more, and provide a sulfur content in the granular metallic iron of 0.080 weight percent or less.

From Table 13 it is clearly seen that when the MgO content is within the range corresponding to this embodiment of the present invention, it is possible to increase the yield of granular metallic iron to 99.0% or more.

As discussed above, Example c demonstrated that in the case when a material containing iron oxide, a carbon-containing reducing agent and the like was appropriately added to the mixture of starting materials, and when the basicity of the slag and the MgO content in the slag satisfy expressions (5) and (6), the sulfur distribution coefficient was 10 or more, and the [S] sulfur content of the granular metallic iron was reduced to 0.080 weight percent or less.

As described in detail above, according to one aspect of the present invention, a method for producing granular metallic iron comprises the following steps, in which:

load the starting material mixture, which includes material containing iron oxide, a carbon-containing reducing agent and an alkali metal compound, into a thermal reduction furnace, heating said mixture of starting materials and reducing the iron oxide contained in said iron oxide-containing material using a carbon-containing reducing agent with obtaining metallic iron and slag as a by-product, provide coalescence of metallic iron in granules while separating metal iron from slag, and cool the metal iron and allow it to harden,

moreover, the aforementioned mixture of starting materials contains at least Fe, Ca, Mg, Si and an alkali metal as constituent elements so that the slag contains CaO, MgO, SiO ₂ and an alkali metal oxide, wherein the alkali metal oxide is at least one oxide selected from Li ₂ O, Na ₂ O and K ₂ O,

alkali metal oxide satisfies at least one of the following expressions (1) to (3), and the basicity of the slag satisfies the following expression (4):

(1)(Li ₂ O) ≥0.03

(one)

(2)(Na ₂ O) ≥0.10

(2)

(3)(K ₂ O) ≥0.10

(3)

(4),1.3≤ (CaO) + (MgO)) / (SiO ₂ ) ≤2.3

(four),

where in expressions (1) - (4) (Li ₂ O), (Na ₂ O), (K ₂ O), (CaO), (MgO) and (SiO ₂ ) are fractions (in mass percent) of Li ₂ O, Na ₂ O, K ₂ O, CaO, MgO, and SiO ₂ in slag, respectively.

According to this method, the mixture of starting materials contains at least Fe, Ca, Mg, Si and an alkali metal as constituent elements so that the slag contains CaO, MgO, SiO ₂ and an alkali metal oxide, the alkali metal oxide is, at least one oxide selected from Li ₂ O, Na ₂ O and K ₂ O, an alkali metal oxide satisfied at least one of the above expressions (1) to (3), and the basicity of the slag satisfied the above expression (four). As a result, even in the case of using a carbon-containing reducing agent such as coal or coke having a high sulfur content, it is possible to reduce the proportion of sulfur that contaminates the granular metallic iron, even in an area where the basicity of the slag was 1.7 or more. It is possible to produce granular metallic iron having a sulfur content of 0.080 mass percent or less, with a yield exceeding 98%, that is, during the manufacturing process, it is possible to provide a high yield of granular metallic iron having a reduced sulfur content.

In this production method, the mixture of starting materials as an alkali metal compound may contain, for example, at least one compound selected from Na ₂ O and sodium carbonate, at least one compound selected from K ₂ O and potassium carbonate, and at least one compound selected from Li ₂ O and lithium carbonate, or nepheline.

In this case, it is preferable that the starting material mixture further comprises a complex oxide as an alkali metal compound, which has a melting point of 1400 ° C. or lower and contains at least one alkali metal. The inclusion of a complex oxide serving as an alkali metal compound that has a melting point of 1400 ° C. or lower and contains at least one alkali metal, in addition to the alkali metal oxide and alkali metal carbonate, further reduces the sulfur content of the granular metallic iron.

In this production method, the alkali metal compound is preferably a complex oxide that has a melting point of 1400 ° C. or lower and contains at least one alkali metal. According to this method, the starting material mixture contains a complex oxide that has a melting point of 1400 ° C. or lower and contains at least one alkali metal. As a result, when a mixture of starting materials is heated in a furnace for thermal reduction, the complex oxide easily melts with rapid formation of slag. As a result, the starting material mixture can be melted in 13.5 minutes or less, which further improves productivity.

In this production method, the slag preferably has an MgO content of 5 to 22 weight percent. Since the slag has an MgO content of 5 to 22 weight percent, the coalescence ability of the reduced iron particles can be maintained at a high level, even when the work is carried out with a high slag basicity. As a result, in the production process, it is possible to provide a high yield of metallic iron with a large grain size.

In this production method, it is preferable that the mixture of starting materials additionally contains at least one compound selected from dolomite ore, MgO and magnesium carbonate, or at least one compound selected from CaO and calcium carbonate. Iron ore, added as a material containing iron oxide, as well as coal or coke, added as a carbon-containing reducing agent, are natural products. Consequently, the CaO content and MgO content vary depending on their types. According to this method, dolomite ore, MgO, magnesium carbonate, CaO or calcium carbonate are added to the starting material mixture according to changes in the CaO content and MgO content in the material containing iron oxide and the carbon-containing reducing agent, thereby controlling the CaO content and content MgO in slag and slag basicity. As a result, it is possible to provide good performance in the production of granular metallic iron having a reduced sulfur content.

According to another aspect of the present invention, a method for producing granular metallic iron comprises the following steps, in which:

load the alkali metal compound and a mixture of starting materials, which includes a material containing iron oxide and a carbon-containing reducing agent, in a furnace for thermal reduction, heating said mixture of starting materials and reducing the iron oxide contained in the said material containing iron oxide using a carbon-containing reducing agent with by obtaining metallic iron and slag as a by-product, provide coalescence of metallic iron into granules while pouring metallic iron from the slag, and cool the metallic iron and allow it to harden,

wherein said starting material mixture or alkali metal compound contains at least Fe, Ca, Mg, Si and an alkali metal as constituent elements such that the slag contains CaO, MgO, SiO ₂ and an alkali metal oxide, the alkali metal oxide is at least one oxide selected from Li ₂ O, Na ₂ O and K ₂ O,

alkali metal oxide satisfies at least one of the following expressions (1) to (3), and the basicity of the slag satisfies the following expression (4):

(1)(Li ₂ O) ≥0.03

(one)

(2)(Na ₂ O) ≥0.10

(2)

(3)(K ₂ O) ≥0.10

(3)

(4),1.3≤ ((CaO) + (MgO)) / (SiO ₂ ) ≤2.3

(four),

where in the expressions (1) - (4) (Li ₂ O), (Na ₂ O), (K ₂ O), (CaO), (MgO) and (SiO ₂ ) are amounts (in mass percent) of Li ₂ O, Na ₂ O, K ₂ O, CaO, MgO, and SiO ₂ in slag, respectively.

According to this method, a mixture of starting materials or an alkali metal compound contains at least Fe, Ca, Mg, Si and an alkali metal as constituent elements so that the slag contains CaO, MgO, SiO ₂ and an alkali metal oxide, an alkali oxide the metal is at least one oxide selected from Li ₂ O, Na ₂ O and K ₂ O, and the alkali metal oxide satisfies at least one of the above expressions (1) to (3), moreover, the basicity of the slag satisfied the above expression (4). As a result, during the production process, it is possible to provide a good yield of granular metallic iron having a reduced sulfur content.

According to a further aspect of the present invention, a method for producing granular metallic iron comprises the steps of loading a raw material mixture, which includes material containing iron oxide, and a carbon-containing reducing agent, into a furnace for thermal reduction, heating the raw material mixture, and reducing iron oxide contained in the material containing iron oxide, using a carbon-containing reducing agent to produce metallic iron and slag as a by-product, providing coalescence of metallic iron into granules while separating metallic iron from slag, and cooling and solidification of metallic iron, said mixture of starting materials containing at least Fe, Ca, Mg and Si as constituent elements so that the slag contains CaO, MgO and SiO ₂ , the basicity of the slag satisfies the expression (5) below, and the MgO content in the slag satisfies the expression (6) below:

(5)1.5≤ ((CaO) + (MgO)) / (SiO ₂ ) ≤2.2

(5)

(6),13 <MgO≤25

(6)

where in expressions (5) and (6) (CaO), (MgO) and (SiO ₂ ) are the amounts (in mass percent) of CaO, MgO and SiO ₂ in the slag, respectively.

According to this method, the slag contains CaO, MgO and SiO ₂ , the basicity of the slag satisfies the above expression (5), and the MgO content in the slag satisfies the above expression (6). As a result, it is possible to reduce the proportion of sulfur that contaminates the granular metallic iron, even in an area where the basicity of the slag is 1.7 or more. It is possible to produce granular metallic iron having a sulfur content of 0.080 mass percent or less, with a yield exceeding 95%, that is, it is possible to provide high productivity in the production of granular metallic iron having a reduced sulfur content.

In this production method, it is preferable that the mixture of starting materials additionally contains at least one compound selected from dolomite ore, MgO and magnesium carbonate, or at least one compound selected from CaO and calcium carbonate. Iron ore, added as a material containing iron oxide, as well as coal or coke, added as a carbon-containing reducing agent, are natural products. Consequently, the CaO content and MgO content vary depending on their types. According to this method, dolomite ore, MgO, magnesium carbonate, CaO or calcium carbonate are added to the starting material mixture according to changes in the CaO content and MgO content in the material containing iron oxide and the carbon-containing reducing agent, thereby controlling the CaO content and content MgO in slag and slag basicity. As a result, it is possible to provide good performance in the production of granular metallic iron having a reduced sulfur content.

According to yet another aspect of the present invention, there is provided a slag formed as a by-product from any of the production methods described above. The slag formed as a by-product of the above-mentioned production method has a high alkali metal oxide content or a high MgO content compared to conventional slag. Thus, an analysis of the chemical composition of the slag reveals whether this slag was produced by the granular metallic iron production method of the present invention or not.

Industrial applicability

By using the granular metallic iron production method of the present invention, it is possible to provide good productivity in the production of granular metallic iron having a reduced sulfur content.

Claims (22)

1. A method for the production of granular metallic iron, comprising the steps of loading a mixture of starting materials, which includes a material containing iron oxide, a carbon-containing reducing agent and an alkali metal compound, into a thermal reduction furnace, heating said raw material mixture and reducing iron oxide contained in said material containing iron oxide by means of a carbon-containing reducing agent to obtain metallic iron and slag as full-time product, provide coalescence of metallic iron into granules while separating metallic iron from slag, cool metallic iron and provide solidification, said mixture of starting materials containing at least Fe, Ca, Mg, Si and an alkali metal as constituent elements so that the slag contains CaO, MgO, SiO ₂ and an alkali metal oxide, the alkali metal oxide is at least one oxide selected from Li ₂ O, Na ₂ O and K ₂ O, the alkali metal oxide satisfies at least one of the following expressions (1) - (3) and the basicity of the slag satisfies the above expression (4):
Li ₂ O≥0.03; (one)
Na ₂ O≥0.10; (2)
K ₂ O≥0.10; (3)
1.3≤ (CaO + MgO) / SiO ₂ ≤2.3 (4),
where in the expressions (1) - (4) Li ₂ O, Na ₂ O, K ₂ O, CaO, MgO and SiO ₂ represent the amount, wt.%, in the slag, respectively. 2. The method according to claim 1, wherein the mixture of starting materials as an alkali metal compound contains at least one compound selected from Na ₂ O and sodium carbonate. 3. The method according to claim 1, in which the mixture of starting materials as an alkali metal compound contains at least one compound selected from K ₂ O and potassium carbonate. 4. The method according to any one of claims 1 to 3, in which the mixture of starting materials as an alkali metal compound contains at least one compound selected from Li ₂ O and lithium carbonate. 5. The method according to any one of claims 1 to 3, in which the mixture of starting materials as an alkali metal compound contains nepheline. 6. The method according to claim 1, in which the alkali metal compound is a complex oxide, which has a melting point of 1400 ° C or lower and contains at least one alkali metal. 7. The method according to any one of claims 1 to 3, in which the mixture of starting materials as an alkali metal compound contains a complex oxide that has a melting point of 1400 ° C or lower and contains at least one alkali metal. 8. The method according to any one of claims 1 to 3, in which the MgO content in the slag is from 5 to 22 wt.%. 9. The method according to any one of claims 1 to 3, in which the mixture of raw materials further comprises dolomite ore. 10. The method according to any one of claims 1 to 3, in which the mixture of starting materials further comprises at least one compound selected from MgO and magnesium carbonate. 11. The method according to any one of claims 1 to 3, in which the mixture of starting materials further comprises at least one compound selected from CaO and calcium carbonate. 12. A method for producing granular metallic iron, comprising the steps of loading an alkali metal compound and a mixture of starting materials, which includes a material containing iron oxide and a carbon-containing reducing agent, into a thermal reduction furnace, heating and melting said mixture of starting materials and reducing iron oxide contained in said material containing iron oxide, using a carbon-containing reducing agent to obtain metallic iron and slag as of the by-product, provide coalescence of metallic iron into granules while separating metallic iron from slag, cool metallic iron and provide its solidification, wherein said mixture of starting materials and an alkali metal compound contain at least Fe, Ca, Mg as constituent elements, Si and alkaline metal, so that the slag comprises CaO, MgO, SiO ₂ and alkali metal oxide, alkali metal oxide is at least one oxide selected from Li ₂ O, Na ₂ O and K ₂ O, ox d alkali metal satisfy at least one of the expressions (1) - (3), and the basicity of slag satisfies the expression (4):
Li ₂ O≥0.03; (one)
Na ₂ O≥0.10; (2)
K ₂ O≥0.10; (3)
1.3≤ (CaO + MgO) / SiO ₂ ≤2.3 (4),
where in the expressions (1) - (4) Li ₂ O, Na ₂ O, K ₂ O, CaO, MgO and SiO ₂ represent the amount, wt.%, in the slag, respectively. 13. The method according to item 12, in which the content of MgO in the slag is from 5 to 22 wt.%. 14. The method according to item 12, in which the mixture of raw materials further comprises dolomite ore. 15. The method according to any one of paragraphs.12-14, in which the mixture of starting materials further comprises at least one compound selected from MgO and magnesium carbonate. 16. The method according to any one of claims 12-14, wherein the mixture of starting materials further comprises at least one compound selected from CaO and calcium carbonate. 17. A method for the production of granular metallic iron, comprising the steps of loading a mixture of starting materials, which includes a material containing iron oxide and a carbon-containing reducing agent, into a furnace for thermal reduction, heating and melting said mixture of starting materials and reducing iron oxide contained in said a material containing iron oxide, using a carbon-containing reducing agent to obtain metallic iron and slag as a by-product, provide coalescence of metallic iron into granules while separating metallic iron from slag, cool metallic iron and provide its solidification, said mixture of starting materials containing at least Fe, Ca, Mg and Si as constituent elements, so that the slag contains CaO, MgO and SiO ₂ , the basicity of the slag satisfies the above expression (5) and the MgO content in the slag satisfies the above expression (6):
1.5 ((CaO + MgO) / SiO _{2 2} 2.2 (5);
13 <MgO≤25 (6),
where in the expressions (5) and (6), CaO, MgO and SiO ₂ represent the proportion, wt.%, in the slag, respectively. 18. The method according to 17, in which the mixture of raw materials further comprises dolomite ore. 19. The method according to 17, in which the mixture of starting materials further comprises at least one compound selected from MgO and magnesium carbonate. 20. The method according to any one of paragraphs.17-19, in which the mixture of starting materials further comprises at least one compound selected from CaO and calcium carbonate. 21. Slag obtained as a by-product of the process according to any one of claims 1-16, wherein the slag contains CaO, MgO, SiO ₂ and an alkali metal oxide, the alkali metal oxide is at least one oxide selected from Li ₂ O, Na ₂ O and K ₂ O, alkali metal oxide satisfies at least one of the above expressions (1) - (3) and the basicity of the slag satisfies the above expression (4)
Li ₂ O≥0.03; (one)
Na ₂ O≥0.10; (2)
K ₂ O≥0.10; (3)
1.3≤ (CaO + MgO) / SiO ₂ ≤2.3, (4)
where in the expressions (1) - (4) Li ₂ O, Na ₂ O, K ₂ O, CaO, MgO and SiO ₂ represent the amount, wt.%, in the slag, respectively. 22. Slag obtained as a by-product when performing the method according to any one of claims 17-20, wherein the slag contains CaO, MgO and SiO ₂ , the basicity of the slag satisfies the above expression (5) and the MgO content in the slag satisfies the above expression (6) ;
1.5 ((CaO + MgO) / SiO _{2 2} 2.2 (5);
13 <MgO≤25 (6),
where in the expressions (5) and (6), CaO, MgO and SiO ₂ represent the proportion, wt.%, in the slag, respectively.

Images