JP5458631B2 - Method for recovering molten metal - Google Patents

Description

  The present invention relates to a method for recovering molten metal, and more particularly, to a method for recovering metallic chromium from chromium-containing slag mainly using silicon in a chromium-containing cold iron source.

Conventionally, a large amount of slag is reduced to recover metal chromium. For example, slag generated in a converter or the like is heated by charging a slag into an electric furnace together with a cold iron source such as alloy iron or scrap, and chromium oxide (Cr _{2) in the} slag by carbon or silicon in the molten metal. O ₃ ) is reduced to recover metallic chromium. The recovered metal chromium is used as a raw material for stainless steel, for example.

  As a method of recovering such metal chromium, for example, in a method of recovering metal chromium from slag containing chromium oxide discharged from a refining process mainly for the manufacture of stainless steel, the slag discharged from the refining process is reduced. There has been proposed a method of charging in an electric furnace and reducing the state (for example, see Patent Document 1). In addition, for example, a method has been proposed in which converter slag generated in a steelmaking process is charged into an electric furnace in a molten state and metal in the slag is recovered (see, for example, Patent Document 2).

Special table 2003-502504 gazette JP-A-51-28502

  However, in the methods described in Patent Documents 1 and 2, the quantitative relationship between the reducing agent carbon and silicon and the reduced slag and the control of the balance between the reducing agent amount and the reduced slag amount are studied. Not. As described above, if the balance between the amount of carbon or silicon as a reducing agent and the amount of slag to be reduced is not appropriate, there are the following problems. That is, when the amount of the reducing agent is excessive, there is a problem that oxygen efficiency is lowered in a subsequent decarburization step or metal yield is lowered. On the other hand, when the amount of slag to be reduced is excessive, there is a problem that chromium cannot be sufficiently reduced or recovered, or the fluidity of slag deteriorates and cannot be discharged from the furnace. Even when fluidity can be secured, CO gas is generated and slag foaming occurs, and stable operation may not be possible.

  Therefore, the present invention has been made in view of such a problem, and in a molten metal recovery method for recovering metallic chromium from chromium-containing slag, mainly using silicon in a chromium-containing cold iron source, By controlling the amount of silicon to be reduced and the amount of slag to be reduced to an appropriate balance, chromium-containing slag can be reduced without excess and deficiency, and metal chromium can be fully recovered under stable operation. The purpose is to improve oxygen efficiency and metal yield in the decarburization process.

  In order to solve the above-mentioned problems, according to the present invention, in a method for recovering molten metal in which chromium-containing slag is reduced in a melting furnace and metal chromium is recovered, a chromium-containing cold iron source, and the chromium-containing cold iron source The chromium-containing slag in an amount of 90% by mass or less of the amount of the chromium-containing slag containing an equivalent amount of chromium oxide that reacts with silicon contained therein is charged into the melting furnace, and the chromium-containing cold iron source and the chromium-containing slag After the silicon is completely melted, the amount of silicon contained in the molten metal is measured, and the amount of the chromium-containing slag containing an equivalent amount of chromium oxide that reacts with the measured amount of silicon is added to the melting furnace. There is provided a method for recovering a molten metal, which is determined as an amount of the chromium-containing slag, and additionally adding the determined amount of the chromium-containing slag to the melting furnace.

  In this way, after adding the amount of slag added in a state that is insufficient relative to the amount of silicon in the cold iron source, the amount of silicon in the molten metal is analyzed, and the additional amount of slag added is determined based on the analysis result. By doing so, the amount of silicon as a reducing agent and the amount of slag to be reduced can be controlled to an appropriate balance.

  Here, when the chromium-containing cold iron source and the chromium-containing slag are charged into the melting furnace, after only the chromium-containing cold iron source is charged into the melting furnace, at least a part of the chromium-containing cold iron source In a molten state, the chromium-containing slag in an amount of 90% by mass or less of the chromium-containing slag containing an equivalent amount of chromium oxide that reacts with silicon in the chromium-containing cold iron source is charged into the melting furnace. preferable.

  In the molten metal recovery method, it is preferable that the chromium-containing slag that is initially charged into the melting furnace is continuously or intermittently charged from above the melting furnace.

  Further, in the molten metal recovery method, the chromium-containing slag to be additionally charged may be charged into a container in which the molten metal is discharged from the melting furnace.

Further, in the method for recovering molten metal, in place of part or all of the chromium-containing slag to be added additionally, one or more of chromium ore, iron ore, and chromium-containing scale are equivalent to react with silicon. The chromium oxide may be added so that the amount of the chromium oxide as a whole becomes the same as that of the chromium-containing slag .

  According to the present invention, in the molten metal recovery method for recovering metallic chromium from chromium-containing slag, mainly using silicon in the chromium-containing cold iron source, the amount of silicon as a reducing agent and the amount of slag to be reduced are reduced. It is possible to control the balance appropriately, thereby reducing chromium-containing slag without excess and deficiency, and recovering metal chromium sufficiently under stable operation, and oxygen in the decarburization process, which is a subsequent process. Efficiency and metal yield can be improved.

It is a flowchart which shows the flow of operation of the recovery method of the molten metal which concerns on one Embodiment of this invention. It is explanatory drawing which shows the operation condition of the collection | recovery method of the molten metal which concerns on the same embodiment. It is explanatory drawing which shows the state which is adding the chromium-containing slag when pouring molten metal from the melting furnace to the ladle. It is explanatory drawing which shows the operation condition of the collection | recovery method of the molten metal in the comparative example 1. The relationship between the Cr ₂ O ₃ concentration and Si concentration in the melt in the slag after tapping in Examples and Comparative Examples of the present invention is a graph showing. The relationship between the Cr ₂ O ₃ concentration after pouring in Examples and Comparative Examples of the present invention the initial charge ratio (mass%) and slag (wt%) is a graph showing.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

[Examination of balance control method between reducing agent and slag]
First, before describing a preferred embodiment of the molten metal recovery method according to the present invention, in a method of recovering metal chromium by reducing slag containing chromium oxide (hereinafter referred to as “chromium-containing slag”), The results of the study by the present inventors will be described with respect to a method for controlling the amount of silicon as a reducing agent and the amount of slag to be reduced to an appropriate balance.

(Regarding the method for determining the total amount of chromium-containing slag based on the amount of silicon in the iron source)
As a method for controlling the amount of silicon as a reducing agent and the amount of slag to be reduced in an appropriate balance, the present inventors are in a cold iron source containing chromium (hereinafter referred to as “chromium-containing cold iron source”). The total amount of chromium-containing slag was determined based on the silicon content. First, based on the amount of silicon contained in the cold iron source charged into the melting furnace, the suitability of a system in which all of the chromium-containing slag containing an equivalent amount of chromium oxide that reacts with the silicon was introduced into the melting furnace at once was confirmed. As a result, the following was found.

<Regarding problems when the amount balance of reactants is not appropriate>
The reduction reaction of chromium oxide in the chromium-containing slag by silicon in the chromium-containing cold iron source is performed as shown in the following reaction formula A.
3Si + 2Cr ₂ O ₃ → 4Cr + 3SiO ₂ (Reaction Formula A)
In this reaction, the basicity (CaO / SiO ₂ mass ratio) is preferably in the range of 1.2 to 1.7. This is because when the basicity is less than 1.2, the reaction of the reaction formula A is not sufficiently performed, and it is difficult to sufficiently reduce chromium oxide. Moreover, when basicity exceeds 1.7, it is because the amount of quicklime to add increases, cost deteriorates, and it becomes difficult to maintain the molten state of slag, and reaction becomes easy to be inhibited.

  Here, when the entire amount of chromium-containing slag containing an equivalent amount of chromium oxide that reacts with silicon in the chromium-containing cold iron source is charged at once, the amount of reactants (that is, the amount of silicon as a reducing agent and reduction) When the balance of the amount of chromium oxide) is not appropriate, the following problems occur.

First, when the silicon amount is excessive relative to the chromium oxide amount, that is, when the molar concentration of silicon is [Si] and the molar concentration of chromium oxide is [Cr ₂ O ₃ ], [Si]> (2 / 3) In the case of [Cr ₂ O ₃ ], since the silicon concentration after the reduction reaction is high and the amount of oxygen used for the oxidation of excess silicon is increased in the decarburization process, which is a subsequent process, the oxygen efficiency decreases. To do. In addition, when the silicon concentration after the reduction reaction is high, the amount of slag (SiO ₂ and CaO added for adjusting the basicity) in the decarburization process, which is a subsequent process, increases, so that the metal yield decreases.

On the other hand, when the amount of silicon is insufficient with respect to the amount of chromium oxide, that is, when [Si] <(2/3) [Cr ₂ O ₃ ], the amount of reduced chromium oxide is large and the reducing agent Since the amount of silicon to be reduced is insufficient, the reduction reaction of chromium oxide does not proceed sufficiently, and a sufficient amount of metal chromium cannot be recovered. Moreover, since the chromium oxide density | concentration after reaction becomes high, the fluidity | liquidity of slag is bad and it may become difficult to discharge from the furnace which performs a reductive reaction. Furthermore, even when the chromium oxide concentration remaining after the reaction is relatively low and the fluidity of the slag can be secured, the chromium oxide remaining in the slag and the carbon in the molten metal react. Since CO gas is generated and slag foaming may occur, stable operation cannot be performed.

<Reasons for variation in the amount balance of reactants>
In addition, as a result of the study by the present inventors, when the entire amount of chromium-containing slag containing an equivalent amount of chromium oxide that reacts with silicon in the chromium-containing cold iron source is charged at once, the reaction product is caused by the following factors: It was found that the amount balance of silicon and chromium oxide, which is, varies, so that it is difficult to be appropriate.

  The cause of this may be the case where the silicon content varies and the case where the chromium oxide content varies. The silicon content varies depending on the type of iron scrap that is mainly used as a chromium-containing cold iron source (iron Since the composition ratio of the elements in the scrap is miscellaneous, there is a factor that the silicon content of the iron scrap cannot be accurately grasped. In this case, the amount of silicon varies when determining the amount of chromium-containing cold iron source to be added. In addition, during the melting of the cold iron source in the melting furnace, the silicon in the chromium-containing iron source is oxidized by air entering from the outside, oxygen for scrap cutting, oxygen in the auxiliary burner, etc. There is also a factor that the amount of silicon used in the reduction reaction is reduced. In this case, the amount of silicon to be oxidized varies depending on the dissolution conditions of the chromium-containing cold iron source, and therefore the silicon amount varies. On the other hand, when the amount of chromium oxide varies, there is a factor that the chromium-containing slag has a high melting point and is not a uniform melt when melted. Therefore, the analysis value of the chromium oxide component in the chrome-containing slag is not representative and the variation in the amount of chromium oxide increases.

  As described above, when the entire amount of chromium-containing slag containing an equivalent amount of chromium oxide that reacts with silicon in the chromium-containing cold iron source is charged at once, the amount balance between the reactant silicon and chromium oxide tends to vary. . Therefore, it has been found that the method of supplying the entire amount of chromium-containing slag containing an equivalent amount of chromium oxide that reacts with silicon in the chromium-containing cold iron source at a time is not appropriate.

[Method for recovering molten metal according to an embodiment of the present invention]
Therefore, as a result of further investigations, the present inventors found that the amount of chromium-containing slag added was insufficient in an amount equivalent to the amount of silicon that reacts with the amount of silicon in the chromium-containing cold iron source. Based on the analysis results, the amount of chromium-containing slag containing an equivalent amount of chromium oxide that reacts with the amount of silicon in the molten metal is determined as an additional input amount. The present inventors have found that the amount of slag and the amount of slag to be reduced can be controlled to an appropriate balance, and the present invention has been completed.

That is, the method for recovering molten metal according to the present invention includes the following steps (1) to (3) in a method for recovering metallic chromium by reducing chromium-containing slag in a melting furnace.
(1) Chromium-containing cold iron source and chromium-containing slag in an amount of 90% by mass or less of the amount of chromium-containing slag containing an equivalent amount of chromium oxide that reacts with silicon in the chromium-containing cold iron source throw into.
(2) After the chromium-containing cold iron source and the chromium-containing slag are completely melted, the amount of silicon contained in the molten metal is measured.
(3) The amount of chromium-containing slag containing an equivalent amount of chromium oxide that reacts with the measured amount of silicon is determined as the amount of chromium-containing slag that is additionally charged to the melting furnace.
(4) Add the amount of chromium-containing slag determined in (3) to the melting furnace.

  Here, in the present invention, the molten chromium oxide slag is not charged all at once, but melted in a state where the amount of chromium oxide to be reduced is insufficient with respect to the equivalent amount reacting with the silicon amount. The reason for measuring the amount of silicon in the molten metal and determining the amount of chromium-containing slag to be additionally introduced based on the measurement result is as follows.

  That is, when all of the expected amount of chromium-containing slag is charged into the melting furnace at once, the amount of silicon contained in the chromium-containing cold iron source is the type of iron scrap, etc. used as the chromium-containing cold iron source, and during melting Occasionally, there may be a case where the amount of the silicon oxide is less than the equivalent amount of the chromium oxide contained in the chromium-containing slag due to oxidation of silicon. In such a case, all of the silicon in the molten metal has been used for the reduction reaction of chromium oxide, so the amount of chromium oxide in the molten slag is analyzed, and an additional silicon source (in this embodiment) In principle, it is possible to calculate the amount of chromium-containing cold iron source. However, in reality, the composition analysis of slag is complicated and time-consuming to handle and analyze, such as once collecting molten slag, solidifying the slag and then pulverizing it before analysis. Therefore, it is very difficult to perform analysis during the operation of the slag reduction reaction. On the other hand, the composition analysis of the molten metal can be easily performed by the method described later.

  Therefore, an amount of chromium-containing slag in which the amount of chromium oxide to be reduced is always insufficient with respect to the amount of silicon as a reducing agent is first charged into the melting furnace, By completely melting the chromium-containing cold iron source, the amount of silicon in the molten metal can be analyzed. This makes it possible to calculate the amount of chromium-containing slag to be added additionally based on the analysis result of the silicon amount in the molten metal. Thus, by melting the chromium-containing slag and the chromium-containing cold iron source in a state where the silicon amount is always excessive with respect to the chromium oxide amount, the silicon always remains in the molten metal after the reduction reaction of the chromium oxide. It becomes. Therefore, by measuring the amount of silicon and determining the amount of chromium-containing slag to be added additionally based on the measured amount of silicon, the balance of the amount of chromium oxide to be reduced and the amount of silicon to be the reducing agent is appropriately adjusted. State.

  Hereinafter, a molten metal recovery method according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2. FIG. 1 is a flowchart showing the operation flow of the molten metal recovery method according to the present embodiment, and FIG. 2 is an explanatory diagram showing the operation status of the molten metal recovery method according to the present embodiment.

(Procedure (1))
In the molten metal recovery method according to the present embodiment, first, the chromium-containing cold iron source Ms is reacted with silicon in the chromium-containing cold iron source Ms based on the composition analysis value of the chromium-containing cold iron source Ms. The amount of chromium-containing slag Ss containing an equivalent amount of chromium oxide (hereinafter referred to as “the amount to be charged”) is 90% by mass or less, preferably 80% by mass or less, and the chromium-containing slag Ss is charged to the melting furnace 1. To do. As a charging method at this time, a method of charging the chromium-containing cold iron source Ms and the chromium-containing slag Ss at a time (S103 in FIG. 1), and a chromium-containing cold iron source Ms and the chromium-containing slag Ss are divided and charged. And a method (S105 to S115 in FIG. 1). In addition, as a chromium containing cold iron source Ms, iron scrap, alloy iron, etc. can be used, for example.

  The batch charging method is to start heating (energization) after charging the chromium-containing cold iron source Ms and the chromium-containing slag Ss with a scrap bucket or the like (S103). This method has the advantage that the operation is simple because the chromium-containing slag Ss is not charged during heating (energization), and can be carried out even when there is no on-furnace charging facility for the chromium-containing slag Ss.

  On the other hand, the method of dividing and feeding will be described in detail with reference to FIGS. First, as shown to (a1) of FIG. 2, only the chromium-containing cold iron source Ms is thrown into the melting furnace 1 (S105 of FIG. 1). That is, at this time, the chromium-containing slag Ss is not charged into the melting furnace 1 but is held in the raw material charging hopper 2 in which the charging valve 3 is closed. Next, energization of the electrode 4 of the melting furnace 1 is started, and the chromium-containing cold iron source Ms charged into the melting furnace 1 is melted (S107 in FIG. 1).

  Then, as shown in FIG. 2 (a2), at least a part of the chromium-containing cold iron source Ms is melted, that is, a part of the solid chromium-containing cold iron source Ms remains undissolved in the molten metal Mm. In this state, the charging valve 3 is opened, and chrome-containing slag Ss in an amount of 90% by mass or less, preferably 80% by mass or less of the pre-calculated estimated amount is charged into the melting furnace 1 (S109 in FIG. 1). ).

  In the latter method, the chromium-containing slag Ss is introduced into a metal bath in which at least a part of the chromium-containing cold iron source Ms is melted. There is an advantage that it can be dissolved. However, if there is no on-furnace charging facility for chromium-containing slag Ss, heating is interrupted halfway and the chromium-containing slag Ss is charged by a bucket or the like. There are cases in which smoke or the like becomes a problem as compared with the method of throwing in at once. Therefore, it is desirable to select either a batch charging method or a split charging method depending on the equipment configuration to be used.

  Here, the amount of chromium-containing slag Ss initially charged into the melting furnace 1 (hereinafter referred to as “the initial amount of chromium-containing slag Ss”) is 90% by mass or less, preferably 80% by mass or less of the planned charging amount. The reason is as follows. That is, as will be described in the examples described later, when the initial charging amount is 100% by mass of the planned charging amount (that is, when the entire amount of the chromium-containing slag Ss of the planned charging amount is charged at one time), As shown in the figure, the variation of chromium oxide concentration in the slag after tapping is large, but when the initial charging amount is 90% by mass of the planned charging amount, the chromium oxide concentration in the slag after tapping is stable at a low level. This is because In addition, when the initial charging amount is 80% by mass or less of the planned charging amount, the chromium oxide concentration in the slag after tapping is stabilized to a lower level than in the case of 90% by mass. When the initial charging amount is set to 80% by mass or less of the planned charging amount, the chromium oxide concentration in the slag after pouring can be more reliably stabilized at a low level.

  Even if the initial charging amount of the chrome-containing slag Ss is set to 70% by mass or less of the planned charging amount, the effect of lowering the chromium oxide concentration in the slag after tapping is saturated, but the initial charging amount of the chromium-containing slag Ss is If the amount is too small, the amount of additional chromium-containing slag Ss increases, so the variation in the amount of chromium oxide in the slag increases, making it difficult to maintain an appropriate balance of the reactants. It becomes difficult to carry out the embodiment of adding the chrome-containing slag Ss into the ladle that is being used. Therefore, the lower limit is preferably 50%.

  In addition, when the chromium-containing slag Ss is charged, it is preferable that the chromium-containing slag Ss is continuously or intermittently charged from the top of the melting furnace 1. That is, the chromium-containing cold iron source Ms previously charged into the melting furnace 1 is melted by a predetermined amount without first supplying the chromium-containing slag Ss initially charged before the start of energization of the melting furnace 1 simultaneously with the chromium-containing cold iron source Ms. In this state, it is preferable to continuously or intermittently add the chrome-containing slag Ss from the furnace of the melting furnace 1 as needed. Thereby, it can suppress that the supplied chromium-containing slag Ss is agglomerated on the molten metal surface around the furnace.

(Procedure (2))
Next, as shown in (a3) of FIG. 2, the chromium-containing cold iron source Ms and the chromium-containing slag Ss charged into the melting furnace 1 are completely melted (S111 in FIG. 1). The amount of silicon contained in the molten metal Mm in a state where the chromium-containing cold iron source Ms and the chromium-containing slag Ss are completely melted, that is, in a state where only the molten metal Mm and the molten slag Ss exist in the melting furnace 1. Is measured (S113 in FIG. 1). As shown in FIG. 2 (a3), the silicon content is measured by sampling the molten metal Mm using a handle 5 or the like, and measuring the silicon content contained in the sample by, for example, an emission spectrometer. The amount of silicon contained in the molten metal Mm in the melting furnace 1 is calculated from the measured value. Alternatively, the surface of the molten metal Mm in the melting furnace 1 is irradiated with a laser, and as a result, the peak position of the excitation light emitted from the molten metal surface Mm is analyzed. The silicon concentration contained in the molten metal Mm in the melting furnace 1 may be directly measured by a sampling method.

(Procedure (3))
Next, based on the amount of silicon in the molten metal Mm measured as described above, the amount of chrome-containing slag Ss to be added to the melting furnace 1 is determined. The amount of the chromium-containing slag Ss added in addition may be an amount containing an equivalent amount of chromium oxide that reacts with silicon in the molten metal Mm. Then, the amount of chromium-containing slag Ss determined in this way is additionally charged into the melting furnace 1 as shown in FIG. 2 (a4) (S115 in FIG. 1).

  Here, as a method of adding the chrome-containing slag Ss to be added to the melting furnace 1 additionally, instead of charging the chromium-containing slag Ss into the melting furnace 1, a ladle that discharges molten metal Mm from the melting furnace 1. You may throw in in molten metal containers, such as. The reason for this will be described with reference to FIG. FIG. 3 is an explanatory view showing a state in which chrome-containing slag is additionally charged when molten metal is poured from a melting furnace into a ladle.

  When the molten metal Mm is discharged from the melting furnace 1 to the ladle 6, the molten metal in the ladle 6 is in a state of being vigorously stirred. If chromium-containing slag Ss is additionally added to the ladle 6 in this state, it can be melted and reacted in a short time by its strong stirring force. However, since there is no heating source at the time of additional charging, it is preferable that the amount of chromium-containing slag Ss initially charged is 70% by mass or more of the planned charging amount.

  Further, in the molten metal recovery method according to the present embodiment, one or more of chrome ore, iron ore, and chrome-containing scale are added instead of part or all of the chrome-containing slag Ss to be additionally input. Also good. Since chromium ore and chromium-containing scale contain chromium oxide, these can be used as a chromium oxide source. On the other hand, since iron ore does not contain chromium oxide, it cannot be used as a source of chromium oxide. However, iron oxide, which is the main component, adds an equivalent amount of iron oxide that reacts with the amount of silicon in the molten metal. By doing so, the problem when the amount balance of the reactants is not appropriate as in the prior art can be solved.

  After adding the additional chromium-containing slag Ss as described above, the chromium-containing slag Ss is melted as shown in FIG. 2 (a5), and the molten metal recovery method according to this embodiment is completed.

(About the effects)
According to the molten metal recovery method according to the present embodiment described above, the balance of the amount of chromium oxide to be reduced and silicon as a reducing agent can be brought into an appropriate state. Thus, a sufficient amount of metallic chromium can be recovered.

  In addition, according to the method for recovering molten metal according to the present embodiment, the balance of the amount of chromium oxide to be reduced and silicon as a reducing agent can be in an appropriate state. There is almost no silicon present. Therefore, since the amount of oxygen used for silicon oxidation is hardly increased in the decarburization step which is a subsequent step, it is possible to prevent the oxygen efficiency from being lowered. Moreover, since there is almost no increase in the amount of slag accompanying the oxidation of silicon, it is possible to suppress a decrease in metal yield.

  Further, there is almost no excess chromium oxide after the reduction reaction of chromium oxide. Therefore, deterioration of the fluidity of the slag due to the presence of chromium oxide can be prevented. Furthermore, since almost no chromium oxide remains in the slag, it is possible to suppress the generation of CO gas due to the reaction between chromium oxide in the slag and carbon in the molten metal, and stable operation can be performed.

  The preferred embodiment of the method for recovering molten metal according to the present invention has been described in detail above. Subsequently, the method for recovering molten metal according to the present invention will be described more specifically with reference to examples. In the examples and comparative examples described below, the chromium-containing slag charging method is changed, the slag reduction reaction is performed in an electric furnace with an actual machine, the component analysis of the slag and the molten metal (molten metal) after tapping The operation status was observed.

Example 1
In this example, the reduction reaction of slag was performed using an AC arc electric furnace having the same structure as the melting furnace 1 shown in FIG. 2 as the melting furnace. Specifically, 51.5 tons of ferrochrome, 39 tons of stainless steel scraps (12 tons, 16 tons and 11 tons of three types of scrap, respectively), 30% by mass of chromium oxide (Cr ₂ O ₃ ) and iron oxide 14.6 tons of slag containing 6 mass% of (FeO) and a total of 105.1 tons were charged into a 90-ton capacity melting furnace, and melting (energization) was started. In order to adjust the basicity of the slag, quick lime was divided into 6 parts each about 1 ton from 30 minutes after the start of energization, and was added at intervals of about 10 minutes.

  The initial input amount of 14.6 tons of slag was determined as follows.

<Determination method of initial input amount of slag>
First, the amount of silicon (Si) contained in ferrochrome and stainless steel scrap was calculated from the amount of ferrochrome and stainless steel scrap used and their Si component values as follows. The Si component values are: ferrochrome: 4.3 mass%, stainless steel scrap (A): 0.4 mass%, stainless steel scrap (B): 0.4 mass%, stainless steel scrap (C): 0.3 mass% %Met.
-Si amount contained in ferrochrome = 51.5 tons x (4.3 mass% / 100 mass%) = 2.215 tons-Si amount contained in stainless steel scrap (A) = 12 tons x (0.4 mass % / 100 mass%) = 0.048 tons ・ Si content in stainless steel scrap (B) = 16 tons × (0.4 mass% / 100 mass%) = 0.064 tons ・ Stainless steel scrap (C) Amount of Si contained in = 11 tons × (0.3 mass% / 100 mass%) = 0.033 tons As a result of the above calculation, the amount of Si contained in ferrochrome and stainless steel scrap was 2.36 tons. .

  Next, the amount of Si oxidized by the air from the outside during melting of the cold iron source (ferrochrome and stainless steel scrap) is set to 0.5 mass% of 90.5 tons of the supplied cold iron source, that is, 0.45. Set with tons. In addition, since the value of 0.5 mass% is a general and empirical value of Si content that is oxidized (oxidation loss) when ferrochrome and stainless steel scrap are melted by a normal electric furnace, Values were used.

Further, in order to economically stabilize the value of Cr ₂ O ₃ in the slag, the target concentration of the Si component in the tapping metal (molten ferrochrome and stainless steel scrap) was set to about 0.4% by mass. The relationship between the Cr ₂ O ₃ concentration in the slag and the Si concentration in the molten metal is described in known literature (eg, Steel Handbook III, Steelmaking / Steel Making, P.705). _{The 2} O ₃ concentration can be controlled. Specifically, even if the Si concentration is larger than 0.4 mass%, the decrease in the concentration of Cr ₂ O _{3 in} the slag is not significant, and Si cannot be effectively used for the reduction of Cr ₂ O _3. So it is irrational. On the other hand, if the Si concentration is less than 0.4% by mass, the Cr ₂ O ₃ concentration in the slag increases, and the reduction and recovery of chromium (Cr) becomes insufficient. From the above, the target concentration of the Si component in the tapping metal was set to 0.4% by mass. The amount of tapping metal is determined from the input metal (cold iron source) in consideration of the increase in slag reduction reaction and dust loss, but as an approximation, we can use the input metal amount. Have confirmed. Accordingly, the amount of residual Si in the tapping metal (molten metal) is equivalent to 0.4% by mass of the amount of metal added, 90.5 tons, that is, 0.36 tons.

From the above, the amount of Si that can be used for the reduction of Cr ₂ O ₃ and FeO in the slag is 2.36 tons−0.45 tons−0.36 tons = 1.60 tons. The reduction reaction is represented by the following formula, and the target concentration of Cr ₂ O ₃ after the reaction is 2% by mass and the target concentration of FeO is 1% by mass. The relationship between the Si concentration in the molten metal at 1650 ° C., the Cr ₂ O ₃ concentration in the slag, and the FeO concentration was previously investigated by a small laboratory dissolution test. From the results, the Si concentration was 0.4%. It was set as the value equilibrated to.
2Cr ₂ O ₃ + 3Si → 4Cr + 3SiO ₂ (Reaction Formula A)
(304) (84) (208) (180)
2FeO + Si → 2Fe + SiO ₂ (Reaction Formula B)
(136) (28) (112) (60)
* Numbers in parentheses indicate the formula weight of each substance.

If the amount of slag containing the equivalent amount of Cr ₂ O ₃ that reacts with the amount of Si contained in the cold iron source charged into the melting furnace is X ton, the amount of Si and Cr ₂ O ₃ is balanced The following formula (1) was established, and X = 18.3 was calculated. Therefore, 80 mass% of the scheduled slag charge amount of 18.3 tons, that is, 14.6 tons, was set as the initial slag charge amount (X ₁ ). As described above, _Cr 2 _{O 3} content in the slag is 30% by weight, FeO content was 6 wt%.

  After 80 minutes from the start of energization, energization was temporarily stopped, and the temperature of the molten metal was measured with a thermocouple, and the molten metal was sampled with a handle. As a result, the molten metal temperature was 1650 ° C. Moreover, about the molten metal sample, as a result of implementing a component analysis with the emission-spectral-analysis apparatus, Si component value was 0.5 mass%.

After completion of temperature measurement and component analysis of the molten metal, energization of the melting furnace is resumed, and the slag amount (X ₂ ) to be added to the melting furnace is added based on the Si component value obtained as a result of the above component analysis. It was determined by the same method as the determination of the planned amount (X). That is, from the quantity balance of Si and Cr ₂ O ₃ , the following formula (2) was established and X ₂ = 1.0 was calculated. Therefore, 1.0 ton of slag was added to the melting furnace.

After 15 minutes from the resumption of energization, the energization was terminated, the melting furnace was tilted and the hot water was discharged into the ladle under the furnace. In addition, the slag in the melting furnace always maintained fluidity, and no slag forming was observed, and stable operation was possible from start to finish. Then, the temperature measurement of the molten metal in the ladle, the sampling of the molten metal, and the sampling of slag were performed. The temperature of the molten metal was 1650 ° C. Moreover, the molten metal component and the slag component are as shown in Table 1 below, and the concentration of Cr ₂ O ₃ was low, and the reduction reaction could be sufficiently advanced.

(Example 2)
In this example, the reduction reaction of slag was performed using an AC arc electric furnace having the same structure as the melting furnace 1 shown in FIG. 2 as the melting furnace. Specifically, 51.5 tons of ferrochrome and 39 tons of stainless steel scrap (3 types of scrap, 12 tons, 16 tons, and 11 tons, respectively), a total of 90.5 tons, was put into a 90-ton capacity melting furnace. , Started energization. From 25 minutes after the start of energization (from the time when the chromium-containing cold iron source begins to melt partially), slag containing 30% by mass of chromium oxide (Cr ₂ O ₃ ) and 6% by mass of iron oxide (FeO) 14. 6 tons were divided into 7 portions by about 2 tons and charged at intervals of 5 minutes. Moreover, in order to adjust the basicity of slag, quick lime was divided | segmented into 6 times about 1 ton, and a total of 6.4 tons was thrown in between slag throwing. Hereinafter, operation was performed in the same manner and method as in Example 1, and the amount of chromium-containing slag (X ₂ ) to be added to the melting furnace was calculated to be 0.7 tons, so 0.7 tons of slag was dissolved. Added to the furnace. As a result, as in Example 1, the operation was stable from start to finish, and the Cr ₂ O ₃ concentration in the ladle after tapping was also low as shown in Table 3 below, and the reduction reaction was sufficiently advanced. did it.

(Example 3)
In this example, the amount of chromium-containing slag to be added (X ₂ ) was calculated to be 1.2 tons based on the same concept as in Examples 1 and ₂ . Therefore, an additional amount of chromium-containing slag was introduced into the ladle in the tapping bath under the furnace. Specifically, the AC arc electric furnace, which is a melting furnace having a structure similar to that of the melting furnace 1, is poured into the ladle in 5 minutes. On the other hand, the addition of chromium-containing slag is 30 seconds after the start of the pouring. During 4 minutes from the start of the hot water, it was continuously charged. As a result, the forming due to the addition of chromium-containing slag was stable and was not observed. Further, Cr ₂ O ₃ concentration in the ladle after tapping is also shown below in Table 3, a low, it was possible to proceed sufficiently reduction reaction. Furthermore, after taking out hot water from the ladle, when the bottom part of the ladle was confirmed, the adhering of the additional slag to the ladle bottom part was not seen.

(Comparative example)
In this comparative example, the slag reduction reaction was performed using the melting furnace 1 shown in FIG. Specifically, as shown in FIG. 4 (b1), as the cold iron source Ms, 51.5 tons of ferrochrome, 39 tons of stainless steel scrap (three types of scrap are respectively 12 tons, 16 tons, and 11 tons). ) A total of 90.5 tons was put into the melting furnace 1 having a capacity of 90 tons, and energization was started. From 25 minutes after the start of energization (from the time when the cold iron source Ms starts to partially melt as shown in FIG. 4 (b2)), as shown in FIG. 4 (b3), chromium oxide (Cr ₂ O ₃ ) A total of 18.3 tons of slag Ss containing 30% by mass and 6% by mass of iron oxide (FeO) was charged from the top of the melting furnace 1. At this time, the slag Ss was divided into 9 parts by about 2 tons and charged at intervals of 5 minutes. Moreover, in order to adjust the basicity of slag, quick lime was divided | segmented into 6 times about 1 ton, and a total of 6.4 tons was thrown in between the injection | throwing-in of slag Ss. The amount of slag Ss input is determined by the calculation method described in the above-described embodiment, and the slag includes an equivalent amount of Cr ₂ O ₃ that reacts with the amount of Si included in the cold iron source Ms input to the melting furnace 1. The amount of Ss was 18.3 tons.

After 30 minutes from the end of the slag Ss input (95 minutes after the start of energization), the cold iron source Ms and the slag Ss were completely melted as shown in (b4) of FIG. 1 was tilted and the hot water was poured into the ladle under the furnace. In addition, in the melting furnace 1 in operation, the fluidity of the slag Sm decreased from the latter half of the operation, and the entire amount could not be discharged at the time of tapping, and a part of the slag Sm remained in the melting furnace 1. Thereafter, temperature measurement of the molten metal Mm in the ladle, sampling of the molten metal Mm, and sampling of the slag Sm were performed. The temperature of the molten metal Mm was 1653 ° C. Further, components of the components and slag Ss of the molten metal Mm are as shown in Table 2, the concentration of Cr ₂ O ₃ is high, the reduction reaction is insufficient. The cause of this is that the types of stainless steel scrap used as the cold iron source Ms are miscellaneous, so the amount of Si in the scrap cannot be accurately grasped, and the melting point of slag Ss is high, so Cr ₂ O ₃ It is conceivable that the representativeness of the component analysis values is poor.

(Comparison of implementation results of Examples and Comparative Examples)
Table 3 and FIG. 5 show the results of performing Example 1 and Example 3 of the present invention once, Example 2 multiple times, and Comparative Example multiple times according to the method described above. FIG. 5 is a graph showing the relationship between the Cr ₂ O ₃ concentration in the slag after tapping and the Si concentration in the melt in the examples and comparative examples of the present invention. In FIG. 5, the vertical axis indicates the Cr ₂ O ₃ concentration in the slag, and the horizontal axis indicates the Si concentration in the molten metal.

As shown in Table 3 and FIG. 5, in the comparative example, the concentration of Cr ₂ O _{3 in} the slag after the hot water fluctuates in relation to the Si concentration in the molten metal, and is not stable at a low level with good reproducibility. In addition, when the Si concentration is low and the Cr ₂ O ₃ concentration is high, carbon in the molten metal reacts with Cr ₂ O ₃ at the end of the operation to generate CO gas, slag forming occurs, and stable operation is achieved. I could not. In addition, when the Cr ₂ O ₃ concentration is 4% by mass or more, the melting point of the slag is increased and the fluidity is deteriorated, so that forming does not occur, but the exhaustability from the melting furnace is poor. Slag remained in the furnace. On the other hand, in the examples of the present invention, the Cr ₂ O ₃ concentration was stable at a low level, no forming occurred, the evacuation property was good, and stable operation was always possible.

(Examination of initial slag input)
Next, the examination result of the initial charging rate of slag into the melting furnace performed by the present inventors will be described. The slag initial charging rate is 90% by mass and 70% by mass of the amount of slag containing an equivalent amount of Cr ₂ O ₃ that reacts with Si in the cold iron source, and slag is produced in the same manner as in the above-described embodiment. The reduction reaction was conducted. For the examples already shown (initial charge ratio: 80% by weight), comparative examples (initial charge ratio: 100% by weight), and the results of the above operations (initial charge ratios: 90% by weight, 70% by weight), The relationship between the Cr ₂ O ₃ concentration and the initial charging rate of slag was examined. The result is shown in FIG. FIG. 6 is a graph showing the relationship between the Cr ₂ O ₃ concentration (mass%) after pouring and the initial charging rate (mass%) of slag in the examples and comparative examples of the present invention. In FIG. 6, the vertical axis represents the Cr ₂ O ₃ concentration after tapping, and the horizontal axis represents the initial charging rate of slag.

As shown in FIG. 6, when the initial charging rate of slag is 100% by mass (the method of the comparative example), the initial charging rate is set to 90% by mass, so that Cr ₂ O _{3 in} the slag after hot water is poured. The concentration was stabilized at a low level, and it was found that the concentration was further stabilized at an initial charging rate of 80% by mass. It was also found that the effect of lowering the stability was saturated when the initial charging rate was 70% by mass. Based on the above results, in the present invention, the initial charging rate is 90% by mass or less, preferably 80% by mass or less.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  For example, in the above-described embodiment, the case where the chromium-containing slag Ss initially charged into the melting furnace 1 is charged in a state where a part of the chromium-containing cold iron source Ms remains unmelted has been described. The chromium-containing slag Ss initially charged into the melting furnace 1 may be charged into the melting furnace 1 after the chromium-containing cold iron source Ms is completely melted.

  Moreover, although the example which used the alternating current arc type electric furnace as an example of a melting furnace is shown in the Example mentioned above, as a melting furnace used for the recovery method of the molten metal which concerns on this invention, a direct current arc furnace, induction | guidance | derivation In addition to an electric furnace such as a heating furnace or an electric resistance heating furnace, a fossil fuel burner or oxygen may be used as an auxiliary.

DESCRIPTION OF SYMBOLS 1 Melting furnace 2 Raw material charging hopper 3 Charge valve 4 Electrode 5 Sampling handle 6 Ladle Ss Chrome-containing slag Sm Molten slag Ms Chrome-containing cold iron source Mm Molten metal

Claims (5)

In the molten metal recovery method of recovering metallic chromium by reducing chromium-containing slag in a melting furnace,
Chromium-containing cold iron source and 90% by mass or less of the chromium-containing slag containing an equivalent amount of chromium oxide that reacts with silicon in the chromium-containing cold iron source is charged into the melting furnace. And
Measuring the amount of silicon contained in the molten metal after the chromium-containing cold iron source and the chromium-containing slag are completely melted,
The amount of the chromium-containing slag containing an equivalent amount of chromium oxide that reacts with the measured amount of silicon is determined as the amount of the chromium-containing slag added to the melting furnace, and the determined amount of the chromium-containing slag is determined. A method for recovering molten metal, wherein slag is additionally charged into the melting furnace.   When the chromium-containing cold iron source and the chromium-containing slag were charged into the melting furnace, only the chromium-containing cold iron source was charged into the melting furnace, and then at least a part of the chromium-containing cold iron source was melted. The chromium-containing slag in an amount of 90% by mass or less of the chromium-containing slag containing an equivalent amount of chromium oxide that reacts with silicon in the chromium-containing cold iron source is charged into the melting furnace. The method for recovering molten metal according to claim 1.   The method for recovering molten metal according to claim 2, wherein the chromium-containing slag that is initially charged into the melting furnace is continuously or intermittently charged from above the melting furnace.   The method for recovering a molten metal according to any one of claims 1 to 3, wherein the chromium-containing slag to be additionally added is introduced into a container in which the molten metal is discharged from the melting furnace. Instead of part or all of the chromium-containing slag to be added additionally, one or more of chromium ore, iron ore, and a chromium-containing scale are replaced with an equivalent amount of chromium oxide that reacts with silicon by the chromium-containing slag. The method for recovering a molten metal according to any one of claims 1 to 4, wherein the amount of the chromium oxide as a whole is the same as that of the additional addition .

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