JP3432542B2 - Method for reducing and recovering valuable metals in slag with improved accuracy of molten steel components - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention reduces and recovers Fe, Mn, Cr, etc. suspended in a slag layer covering the surface of molten steel after refining into molten steel and enhances the accuracy of the composition of the resulting molten steel. A method for reducing and recovering valuable metals in slag.

[0002]

2. Description of the Related Art When decarburizing and blowing alloy steel such as stainless steel in a converter, a vacuum degassing device, etc., when carbon in molten steel reacts with blowing oxygen and becomes CO gas and is removed from molten steel. At the same time, some of useful components such as Cr, Fe and Mn are oxidized according to the following reaction. 4 [Cr] + 3O ₂ → 2 (Cr ₂ O ₃ ) 2 [Fe] + O ₂ → 2 (FeO) 2 [Mn] + O → 2 (MnO)

The metal elements such as Cr, Fe and Mn that have become oxides migrate to the slag floating on the surface of the molten steel. The metal element in the slag is reduced from the oxide to a metal state in the final stage of steel making, and is recovered as molten metal in the molten steel. The recovery is performed by utilizing that metal elements such as Cr, Fe and Mn are easily reduced to a metal state by Si, and for example, a predetermined amount of Si is added to the molten steel in the ladle during vacuum refining. . The reduction reaction with Si is as follows. 2 (Cr ₂ O ₃ ) + 3Si → 4 [Cr] +3 (SiO
₂ ) 2 (FeO) + Si → 2 [Fe] + (SiO ₂ ) 2 (MnO) + Si → 2 [Mn] + (SiO) Further, Al, Ti, etc., which have a greater oxygen affinity than Si, are used as reducing agents. At this time, Si in the slag can be transferred to metal.

Cr, Fe, Mn, etc. in the metallic state are taken into the molten steel and the composition of the molten steel is adjusted. In order to adjust the composition with high accuracy, it is necessary to quantitatively grasp the metal elements that migrate from the slag to the molten steel at the final stage. Recently, steel grades with extremely strict standards for Si content have begun to be used. In order to cope with such high-accuracy component adjustment and steel types in which the Si content is strictly controlled, it is necessary to accurately grasp the amount of reducing oxides reduced by Si contained in the slag. is necessary.
The oxygen content of the reducing oxide contained in the slag is Cr ₂
It is calculated from the oxygen concentration and the amount of slag in metal oxides such as O ₃ , FeO and MnO. The calculated oxygen amount serves as a reference for determining the amount of Si added as a reducing agent.

[0005]

A method of fluorescent X-ray analysis of a slag sample is known as a method for quantifying oxygen in a metal oxide. In fluorescent X-ray analysis, molten slag collected from a converter during smelting, a vacuum degassing device, etc. is prepared as an analytical sample by a glass bead method, a press molding method, or the like. In the glass bead method, for example, as shown in FIG.
After crushing the solidified slag, weigh it and slag 0.2g
Is placed in a platinum crucible together with 2.0 g of a flux such as sodium carbonate, and heated and stirred with a bead sampler to uniformly melt
Cooling. According to this method, it takes about 25 minutes to obtain a sample for analysis.

In the press molding method, an appropriate amount of the collected slag is filled in an aluminum cap and pressure-molded with a press of 15 to 20 tons to prepare a sample for analysis. The press molding method takes a shorter time to obtain a sample for analysis than the glass bead method, but requires two analyzes on the same sample in order to eliminate measurement errors due to variations in crushed particles. . Therefore, it takes about 20 minutes to obtain the analysis result. In both the glass bead method and the press molding method, the fluorescent X-ray analysis method requires 20 to 25 minutes from the sample weighing to the calculation of the analysis value. Moreover, it is assumed that the metal oxide contained in the sample has a single oxide form, and the quantitative value of the oxide is multiplied by the coefficient determined from the stoichiometric relationship between the metal and the oxide. The oxygen analysis value is calculated by. Therefore, a measurement error is inevitably generated in a sample containing Cr, Fe, Mn or the like in a metallic state, a sample containing a metal oxide having a different oxygen value, or the like.

In order to shorten the analysis time and suppress the analysis error, the inventors of the present invention determined the steelmaking slag based on the amount of oxygen discharged from the system due to the reaction between the sample collected from the steelmaking slag and the carbon source. A method for quantifying oxygen in reducing oxides such as Cr, Fe, and Mn contained therein was developed.
Filed as No. 19364. By this method, 10
It is possible to quantify oxygen in the slag in a short time within a minute and with the analysis error minimized. On the other hand, as a method of measuring the amount of slag, there is known a method of measuring the weight of the ladle for each tapped steel and slag and subtracting it from the total weight of the ladle including the molten steel and the slag weight. Is difficult to measure with high accuracy. Therefore, the present inventors have found that the total weight W _T , the molten metal weight W _M and the container weight W _{V of the} vacuum degassing container, the ladle, etc., which are easy to measure, and the slag weight W _S
We have developed a method to calculate. According to this method, the slag weight W _S is calculated as W _S = W _T − (W _M + W _V ).
In this method, the molten metal surface is detected and the molten metal weight W
It is required to know _M.

According to the method developed by the present inventors, when the level of the molten metal surface under the slag is detected by the eddy current sensor,
An alternating current of a specific frequency is supplied to the oscillation coil of the eddy current sensor. The high-frequency current of 0.5 to 500 kHz suppresses the error factor due to the eddy current caused by the metal droplets suspended in the slag layer from being taken into the receiving coil of the eddy current sensor, and the molten metal surface below the slag. It has become possible to detect the level with high accuracy. The required addition amount of the reducing agent is calculated from the oxygen amount of the reducing oxide in the slag and the weight of the slag thus obtained. When the reducing agent is added in this addition amount, the reducing oxide in the slag is reduced and recovered in molten steel in the molten steel. Also,
Since an excessive reducing agent is not added, the reducing agent also brought into the molten steel can be reduced. That is, according to the present invention, by adding a reducing agent in an amount determined based on the composition and weight of the slag, the reducing agent such as Si and Al is not brought into the molten steel in a large amount, and Mn,
The purpose of the present invention is to obtain molten steel in which the content of alloy components such as Cr is appropriate and the precision is improved.

[0009]

In order to achieve the object, the method of recovering valuable metals of the present invention reduces and recovers valuable metals in reducing oxides from the slag floating on the surface of molten steel to the molten steel. At this time, while measuring the oxygen content of the reducing oxide contained in the slag by reducing the sample collected from the slag with carbon, the surface position of the molten steel is detected, from the bottom surface of the container to the molten metal surface. Obtain the weight of the slag from the weight of the molten steel calculated based on the molten steel volume calculated by integrating the internal cross-sectional area of the container, the required addition of a reducing agent from the content of the reducing oxide and the weight of the slag The amount of the reducing agent is calculated, and the reducing agent is added to the slag according to the calculated addition amount. When Si or ferrosilicon is used as the reducing agent, reducing oxides such as Fe, Mn and Cr are reduced and recovered from the slag into molten steel. As a reducing agent, A, which has a greater oxygen affinity than Si or ferrosilicon
When using l, Ti, Ca, Mg alloys, etc.,
Si in the slag is also reduced and recovered in molten steel. In any case, the amount of reducing agent added is determined by the amount of oxygen in the reducing oxide in the slag and the weight of the slag. Can be obtained at.

-Oxygen determination of reducing oxide in slag-The oxygen content of reducing oxide in slag is determined by reacting with a carbon source while continuously heating a sample collected from slag in an inert atmosphere. It can be quantified by measuring the amount of oxygen bound to carbon and discharged to the outside of the system in a time series. For example, when a slag sample is placed in a graphite crucible together with a carbon source such as activated carbon or carbide and the temperature is continuously raised in an inert atmosphere, CO gas is generated by the reaction between the reducing oxide and carbon. The easily reducing oxides such as Cr, Fe and Mn contained in the sample start the reduction reaction at a relatively low temperature,
Oxygen separated from the metal element is extracted. On the other hand, Ca,
The hard-to-reduce oxides such as Mg and Si are Cr ₂ O ₃ and Fe.
Since it has a stronger oxygen affinity than the easily reducing oxides such as O and MnO, the reduction reaction starts at a high temperature. That is, after the oxygen extraction from the easily reducing oxide is completed, the oxygen extraction from the hardly reducing oxide is started.

C generated by carbon reduction of sample slag
When the O gas is continuously quantified by the infrared absorption method, an oxygen extraction curve as shown in FIG. 2 is obtained. The oxygen extraction curve rises with the analysis time and the heating temperature, but once drops at the temperature T ₁ near 1800 ° C. reaching the time point t ₁ and then rises again, the oxygen intensity becomes 0 at the time point t ₂ . Minimum value I ₁ of the analytical oxygen intensity at time t ₁ is clearly detected, and a reduction reaction of the reduction reaction and irreducible oxides reducible oxide can be clearly distinguished.

A value obtained by integrating the oxygen intensity from the start of analysis to time t ₁ , in other words, the area of the shaded region in FIG. 2 corresponds to the amount of oxygen extracted from the reducing oxide. The oxygen content of the reducing oxide contained in the slag is calculated from the oxygen content thus obtained, and the necessary addition amount of the reducing agent is calculated accordingly. In addition, since the reducing agent is added in an appropriate amount to the slag whose composition has been identified, the valuable metal recovered from the slag into the molten steel is also quantitatively controlled, and unreacted reducing agent is brought into the molten steel. The increase in Si content is suppressed. The carbon reduction method is used when quantifying reducing oxides such as Fe, Mn, and Cr that are reduced by Si. By combining the carbon reduction method with the fluorescent X-ray analysis method, Al, T having a larger oxygen affinity can be obtained.
Non-reducible oxides reduced by i, Ca, Mg, that is, metal oxides having a larger oxygen affinity than Cr, Fe, Mn, etc. and a smaller oxygen affinity than the reducing agent described above are also quantified. For example, when Al is used as a reducing agent, oxygen in SiO ₂ , TiO _2, etc. is quantitatively determined.

-Measurement of Slag Weight- Metal particles are suspended in the slag layer floating on the molten steel surface, and the suspended amount of the metal particles is also varying. Therefore, the slag weight cannot be simply obtained by converting the slag layer thickness into a specific gravity. Therefore, in the present invention, the slag weight is calculated by subtracting the weights of the molten steel and the container itself from the total weight. In containers such as converters and vacuum degassing devices that contain molten steel, the refractory lining is eroded by the molten steel, and the internal cross-sectional area changes with each charge.
In order to accurately obtain the weight W _{M of} the molten steel contained in such a container, the molten steel volume is calculated by detecting the molten metal level and integrating the internal cross-sectional area of the container from the bottom surface of the container to the molten metal level. By multiplying the obtained molten steel volume by the specific gravity,
The weight W _{M of} molten steel is obtained.

On the other hand, the total weight W _{T of the} container containing the molten steel and the slag can be easily measured by a load cell or the like. Also, the weight W _{V of the} container itself can be easily obtained by weighing the container before or after charging. Therefore, the slag weight W _S is calculated by the formula W _S
= W _T - it is calculated from (W _M + W _V). In order to measure the level of molten steel, it is preferable to use an eddy current sensor supplied with a high frequency alternating current of 0.5 to 500 kHz.
The high frequency alternating current of 0.5 to 500 kHz suppresses the error factor caused by the eddy current generated in the metal droplets floating in the slag, and accurately detects the molten steel level. For example,
As shown in FIG. 3, even with a slag in which conductive metal droplets are suspended to about 50%, the molten metal surface position is measured with high accuracy without being affected by the metal droplets in the slag. be able to.

-Calculation of Required Addition Amount of Reducing Agent-Distance D from the molten metal surface to the eddy current sensor by an optical system.
Was measured, and the molten steel surface covered with the slag was measured by the eddy current sensor at the distance D. The molten metal surface position d ₁ when the molten steel surface was covered with slag and the molten metal surface position d ₂ without the slag were measured by the eddy current sensor while changing the measured distance D. Then, the measurement error δD is
It was defined as (d ₁ −d ₂ ) / D. When the relationship between the amount of metal particles suspended in the slag and the measurement error δD was investigated,
The relationship shown in FIG. 3 was established between the two. From this relationship, it is understood that the molten metal surface position can be detected with high accuracy by the eddy current sensor.

-Calculation of Reducing Oxide- The required addition amount of the reducing agent is determined according to the flow shown in FIG. The total weight of the ladle containing the molten steel and the slag is measured and the amount of oxygen contained in the slag is determined. The weight of the ladle in the empty state is obtained in advance. The weight of the molten steel contained in the ladle is calculated from the molten metal surface position measured by the eddy current sensor. Therefore, the slag amount is obtained by subtracting the ladle weight and the molten steel weight from the total weight of the ladle containing the molten steel and the slag. By multiplying this slag amount with the oxygen amount contained in the slag collected from the molten steel ladle, the total oxygen amount of the slag in the molten steel ladle can be obtained. The amount of the reducing agent required for the reduction is determined according to this total oxygen amount. In this way, by adding the adjusted amount of the reducing agent, the amount of F in the reducing oxide can be changed from the slag to the molten steel in a predetermined amount.
e, Mn, Cr, etc. are recovered, and the introduced reducing agent is not excessively mixed into the molten steel. as a result,
Not only can the reducing agent be efficiently consumed, but the appropriateness of the components of the molten steel after melting can be improved. In particular, S derived from a reducing agent
It becomes possible to accurately manufacture steel grades that require strict control regarding the contents of i, Al, and the like.

[0017]

[Example] 80 tons of molten steel that had been subjected to converter smelting was poured into a vacuum degassing vessel, and 2 minutes later, a sample slag was sampled from the slag layer floating on the surface of the molten steel, and an eddy current sensor was used. The position of the molten metal surface was detected. Oxygen determination of the sample slag by the carbon reduction method revealed that the amount of oxygen was 15.3%. From this composition, the amount of the reducing agent Si necessary for reducing the reducing oxide is determined by the unit weight g of the slag.
It was calculated to be 0.13 g per unit. From the molten metal surface position detected by the eddy current sensor, the slag weight was calculated to be 2 tons. Therefore, MnO, Cr ₂ O ₃ , Fe in the slag
In order to reduce O and the like and recover Mn, Cr, Fe and the like in molten steel, 268 kg of ferrosilicon in terms of Si was added as a reducing agent. After 5 minutes from the introduction of ferrosilicon, the slag was sampled again to measure the oxygen content. As a result, it was found that it was reduced to 0.08%. On the other hand, the composition of molten steel is shown in Table 1 before and after deoxidizing silicon.
It was as shown in. As is clear from Table 1, S in molten steel is derived from ferrosilicon added as a reducing agent.
The tendency for the i content to increase was small. Also,
Since the reducing oxide in the slag was reduced and recovered by the molten steel, the Mn content and the Cr content in the treated molten steel were increased.

[Table 1]

Table 2 shows the results of separately analyzing the composition of the reducing oxide contained in the slag collected before and after the Si deoxidation by the wet analysis method. From the analysis results in Table 2, it was confirmed that the reducing oxide was reduced and recovered. In Table 1, Mn and C in the molten steel after deoxidation treatment
Table 2 also shows the recovery rate calculated assuming that the increased amount of r is derived from the reducing oxide in the slag.

[Table 2]

As described above, in this embodiment, by adding the optimum amount of the Si-based reducing agent, the reducing oxides such as Fe, Mn, and Cr in the slag are reduced to the metal state to form the metal. I am migrating. As a result, Fe, Mn,
Valuable metals such as Cr are efficiently recovered, and an increase in Si content due to the Si-based reducing agent is suppressed even in the molten steel after the treatment. In the above examples, the case where Fe, Mn, Cr and the like are reduced and recovered by using the Si-based reducing agent has been described. However, the present invention is not limited to this, and it is possible to use other reducing agents such as Al and Ti. For example, when using an Al-based reducing agent having a higher oxygen affinity than Si, Si contained in the slag is also reduced and recovered into metal. In this case, Si and Ti
The oxygen content of the slag is determined in the form containing the oxide of.

[0020]

As described above, in the present invention, by adding the reducing agent in the optimum amount, the reducing oxides such as Fe, Mn and Cr contained in the slag are converted into the metallic state. While reducing and recovering in molten steel, the increase in Si content, Al content, etc. in the molten steel after the treatment due to the reducing agent is suppressed. As a result, it is possible to produce molten steel having a high appropriate ratio to the target composition. Moreover, since the consumption amount of the reducing agent can be set to the necessary minimum, the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a flow showing a method for quantifying oxygen in a metal oxide.

FIG. 2 is a diagram for explaining oxygen determination by a carbon reduction method developed by the present inventors.

Fig. 3 Effect of metal droplets in slag on measurement error when measuring melt level using eddy current sensor

FIG. 4 is a flow chart showing a smelting method according to the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomiya Fukuda 11-11 Showa-cho, Kure-shi, Hiroshima Nisshin Steel Co., Ltd. Steel Research Laboratory (56) References JP-A-61-223117 (JP, A) JP-A-6-122917 (JP, A) JP-A-62-190819 (JP, A) JP-A-6-148167 (JP, A) JP-A-61-272604 (JP, A) JP-A-5-51625 (JP, A) JP 5-239527 (JP, A) JP 6-235017 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C21C 7/00

Claims (4)

(57) [Claims] 1. When the valuable metal in the reducing oxide is reduced and recovered to the molten steel from the slag floating on the surface of the molten steel,
The sample taken from the slag is carbon-reduced to measure the content of reducing oxides contained in the slag, the surface position of the molten steel is detected , and the bottom surface of the container is used as a molten metal.
Calculated by adding up the internal cross-sectional area of the container
Obtain the weight of the slag from the weight of the molten steel calculated based on the volume of molten steel, calculate the required addition amount of the reducing agent from the content of the reducing oxide and the weight of the slag, the addition amount of the calculation result A method for recovering valuable metals in slag with improved accuracy of appropriateness of molten steel composition, characterized by adding a reducing agent to the slag. 2. The reducing oxide according to claim 1 is Fe, M.
A method for reducing and recovering valuable metals in slag, which is an oxide of n and Cr, and whose reducing agent is Si or ferrosilicon, and which has improved the precision of suitability for molten steel components. 3. The reducing oxide according to claim 1 is Fe, M.
n, Cr and Si oxides, the reducing agent is Al, T
A method for reducing and recovering valuable metals in slag with improved precision of molten steel composition, which is i, Ca, Mg or alloys thereof. 4. The reducing oxide according to claim 1 is Fe, M.
It is an oxide of n, Cr, Si and Ti, and the reducing agent is A
A method for reducing and recovering valuable metals in slag with improved precision of molten steel composition, characterized by being 1, 1, Ca, Mg or alloys thereof.