JP5522133B2 - Regeneration method of slag - Google Patents

Description

  The present invention relates to a slag regeneration processing method.

  Conventionally, slag generated in a steelmaking process has been widely used as a civil engineering material such as a concrete aggregate and a roadbed material. However, the reduced slag generated in the desulfurization process using a desulfurizing agent containing CaO as a main component generally has the problem that unreacted CaO inevitably remains, which causes expansion and strong alkali. There are also difficult aspects.

  As a technique for utilizing slag for applications other than civil engineering materials, for example, Patent Document 1 relates to a so-called recycle method of reduced slag that occurs in the secondary refining process of an electric furnace steelmaking process, by bringing reduced slag into contact with water. A method of newly obtaining a faux former by performing a desulfurization treatment and further performing a carbonation treatment to obtain a solidified body is described.

In the method of Patent Document 1, slag generated in the secondary refining process, that is, slag generated in the desulfurization process of “molten steel” is brought into contact with water to perform desulfurization treatment of the slag (the following formula [Chemical Formula 1]). is there. In addition, in the following chemical formula, in accordance with the customary practice in the field of iron metallurgy, components existing in a solid solution state in slag are indicated with (), and dissolved components in molten iron are indicated with _. .

However, the desulfurization process of “molten steel” in the secondary refining process is performed at a high temperature around 1600 ° C., and in these desulfurization processes, the desulfurization reaction according to the following formula [Chemical Formula 2] proceeds, so in the secondary refining process, Sulfur present in the generated slag exists not in the form of solid CaS but in a dissolved state in the liquid phase slag as a dilute solution.

  On the other hand, the above [Chemical 1] is a reaction that controls the diffusion of sulfur in the solid slag, so that the slag produced by [Chemical 1] is present under the condition that sulfur exists in a dissolved state in the liquid phase slag. However, the desulfurization reaction did not proceed very slowly, and there was a problem of lack of practicality.

  In Patent Document 2, reduced slag having an increased sulfur content is placed in a heat treatment furnace, the inside of the furnace is set to a carbon dioxide gas atmosphere, and heated to 900 ° C. or higher for 1 hour or longer. In addition, a method is described in which a sulfur component is removed from the reduced slag without changing other components other than the sulfur component, thereby increasing the desulfurization capacity of the reduced slag so that it can be reused.

However, in many cases, CaO in the reduced slag is 2CaO · SiO ₂ having a low desulfurization capacity due to the inevitable mixing of SiO ₂ . Therefore, it is difficult to use it as a refining material by removing only sulfur in the reduced slag, and it is necessary to add a new CaO source to increase the desulfurization capacity. There is also a problem that the heat loss accompanying the increase in the amount of slag or the increase in cost is caused.

JP 2009-30101 A JP 2008-308754 A

  The object of the present invention is to solve the above-mentioned problems and to quickly remove sulfur in hot metal desulfurization slag as a technology for reusing hot metal desulfurization slag for the purpose of reducing the amount of hot metal desulfurization slag generated in the steelmaking process. It is intended to provide a technique capable of separating and recovering the desulfurization ability without newly adding a CaO source.

The slag regenerative treatment method of the present invention, which has been made to solve the above problems, comprises suspending hot metal desulfurization slag generated in the hot metal desulfurization treatment step in water and bringing it into contact with water containing carbon dioxide gas. The sulfur component contained therein is separated as H ₂ S gas by the following formula [Chemical Formula 3], and 2CaO · SiO ₂ inevitably contained in the hot metal desulfurization slag is converted into CaCO ₃ , SiO ₂ by the following formula [Chemical Formula 4], respectively. ₂ is settled and separated.

  The invention according to claim 2 is characterized in that in the slag regeneration treatment method according to claim 1, hot metal desulfurization slag classified to a particle size of less than 2 mm is suspended in water.

  A third aspect of the invention is characterized in that in the slag regeneration treatment method of the first aspect, hot metal desulfurization slag having a particle size of 2 mm or more is pulverized to less than 2 mm and suspended in water.

CaO in the hot metal desulfurization slag is derived from blast furnace slag and is inevitably mixed with SiO ₂ , and many of them have low desulfurization ability 2CaO · SiO ₂ , but the slag regeneration treatment method according to the present invention is The hot metal desulfurization slag generated in the hot metal desulfurization treatment process is suspended in water, brought into contact with water containing carbon dioxide gas, and subjected to sedimentation separation as CaCO ₃ and SiO _{2 according} to [Chemical Formula 4], respectively. High CaCO ₃ can be recovered. At the same time, sulfur in the reduced slag can be quickly separated by [Chemical Formula 3]. That is, according to the present invention, sulfur in the hot metal desulfurization slag can be quickly separated and the desulfurization capacity can be recovered without newly adding a CaO source. Therefore, the recovered CaCO ₃ is desulfurized again. It can be effectively utilized as a substitute for limestone used in the agent, dephosphorizing agent, or iron making process, and it is possible to greatly reduce the out-of-system discharge of slag generated in the steel making process.

It is a schematic diagram of a reactor suitable for carrying out the present invention. It is an example of the basic experiment which leads to this invention, and the particle size distribution of the slag used for this method. It is a figure which shows the composition change of the slag in the process in the basic experiment which reaches this invention. It is the powder X-ray-diffraction data of the slag sample before a process in the basic experiment which reaches this invention, and a process after a process.

  Preferred embodiments of the present invention are shown below. FIG. 1 shows an apparatus for carrying out the method of the present invention by a so-called batch processing method. However, the method of the present invention is not limited to the batch processing method, and may be a continuous processing method.

A reaction vessel 1 shown in FIG. 1 contains water 3, and a gas 5 containing carbon dioxide gas is passed through to dissolve CO ₂ . Slag 2 (hereinafter referred to as hot metal desulfurization slag) generated by hot metal desulfurization treatment is put into water 3 in which CO ₂ is dissolved. Stirring is performed by the impeller 12 while continuously supplying a gas containing CO ₂ into the reaction vessel 1 charged with hot metal desulfurization slag.

The hot metal desulfurization slag to be treated in the present invention is slag generated when the hot metal desulfurization treatment is performed using a desulfurization agent containing CaO as a main component. In the hot metal desulfurization treatment step performed at a low temperature of about 1250 to 1400 ° C., the desulfurization reaction with solid CaO proceeds basically by the reaction of the following formula [Chemical Formula 5]. The desulfurization reaction with solid CaO is a reaction that generates solid CaS. Therefore, the slag produced by the reaction becomes a very non-uniform slag in which CaS containing a high concentration of sulfur exists locally.

  In the present invention, the reaction of [Chemical Formula 3] can be rapidly carried out by bringing the extremely heterogeneous hot metal desulfurization slag, in which CaS containing a high concentration of sulfur locally exists, into contact with water containing carbon dioxide. Progress is possible.

The H ₂ S that is the exhaust gas is guided to the H ₂ S recovery device 6 and recovered. Gas containing CO ₂ of unreacted separating CO ₂ in the CO ₂ separation device 7, is circulated back to the reaction vessel 1, the remaining gas is discharged out of the system from the exhaust tower 13.

In the hot metal desulfurization slag generated in the desulfurization process using a desulfurizing agent containing CaO as a main component, unreacted CaO generally remains unavoidably. Furthermore, the amount of CaO in the hot metal desulfurization slag cannot be ignored due to the SiO _{2 component} (derived from the blast furnace slag) inevitably mixed in the hot metal desulfurization slag. Calcium silicate is mainly composed of 2CaO · SiO ₂ . Therefore, even if only the sulfur in the hot metal desulfurization slag is removed, the CaO content in the hot metal desulfurization slag is 2CaO · SiO ₂ having a low dephosphorization and desulfurization ability, so the value of recycling is actually low. In such a case, it is necessary to newly add a CaO source in order to increase the dephosphorization and desulfurization ability of the slag. Therefore, the heat accompanying the increase in the amount of slag discharged outside the system or the increase in the slag amount. Loss increases and costs increase. Therefore, it is not sufficient to remove only the sulfur content in the hot metal desulfurization slag, and how to remove the SiO ₂ content in the hot metal desulfurization slag when regenerating a considerable amount of CaO and aiming for recycling. Becomes important.

In the present invention, hot metal desulfurization slag generated in the hot metal desulfurization treatment step is suspended in water, brought into contact with water containing carbon dioxide gas, and precipitated by CaCO ₃ and SiO _{2 according} to [Chemical Formula 4], respectively. The recovery of CaCO ₃ having a high desulfurization capacity is performed.

  Since the calcium carbonate 10 having a high sedimentation rate is quickly precipitated in the reaction vessel, it is collected through the gate valve 8.

The SiO ₂ 11 having a slow sedimentation speed is guided to the sedimentation tank 9 while being colloidally present in water, and is settled and separated over time. The separated water is returned to the reaction vessel. Water for the evaporation loss is newly introduced and processing is performed for a predetermined time. Here, in order to promote sedimentation of SiO ₂ , air blowing by an ultrasonic transmitter or a microbubble generator may be performed.

  Note that the hot metal desulfurization slag may be slag used repeatedly. Furthermore, as a method of reusing calcium carbonate recovered by this method, for example, as shown in the example of Japanese Patent Laid-Open No. 2-200717, the bottom blowing powder of a hot metal dephosphorization furnace of the powder bottom blowing converter type It can be used as a body. Further, as disclosed in JP 59-53611 A, the hot metal can be reused as a desulfurization agent. It can also be used as an alternative to limestone used in the iron making process. In this case, since sulfur is removed, the sulfur can be reused in the sintering process without increasing the load of desulfurization of flue gas which is a problem in the sintering process.

In the basic experiment leading to the present invention, the inventors of the present application blow H ₂ S by blowing carbon dioxide gas in a state where the hot metal desulfurization slag having the composition shown in Table 1 and the particle size distribution shown in FIG. 2 is suspended in water. Attempts were made to remove sulfur and to separate and recover CaCO ₃ . That is, when CO ₂ gas was blown and sulfur was almost lost, solid-liquid filtration was performed and the components of the solid phase were examined. As a result, it was found that most of the components were CaCO ₃ . Further, when the liquid side was allowed to stand, SiO ₂ was precipitated and separated. This is probably because the SiO ₂ precipitation separation rate is slower than the CaCO ₃ precipitation separation. Note that the sedimentation rate of the SiO ₂ is low, is believed to be due to present as fine particles. On the other hand, CaCO ₃ particles grow with the progress of the carbonation reaction, and it seems that they settle relatively quickly because the particle size increases. The present invention has been made based on the experiment.

When the particle size of the hot metal desulfurization slag is less than 2 mm, the surface of the slag becomes large, so that [Chemical Formula 3] and [Chemical Formula 4] reactions tend to proceed, and fine SiO ₂ is preferable because colloid is easily generated in water. If the particle size of the slag is 2 mm or more, pulverization to 2 mm or less is preferable in order to disperse the fine colloidal SiO ₂ in water. Here, the slag particle size of less than 2 mm is slag particles having a sieve mesh of 2 mm, and the slag particle size of 2 mm or more means slag particles having a sieve mesh of not passing 2 mm.

  In this basic experiment, a 500 mL beaker is used, 250 mL of distilled water is filled, carbon dioxide is blown in while impeller stirring is performed, and a particle size of 32 μm to 75 μm is selected from hot metal desulfurization slag, and 15 g is added. did. Thereafter, after elapse of a predetermined time, the liquid and the solid were separated with a filter paper. After the solid was dried, its components were analyzed and powder X-ray diffraction was performed. A portion of the composition of water was analyzed, and the mixture was allowed to stand for about 8 hours, and the precipitated water was analyzed. FIG. 3 shows the change over time in the composition of the solid sample after carbonation for a predetermined time and after separation into solid and water, and FIG. 4 shows the powder X-ray diffraction results of the solid after 240 minutes of treatment. Show. The X-ray diffraction measurement conditions were as shown in [Table 2].

The hot metal desulfurization slag contains SiO ₂ , which originates from blast furnace slag that is inevitably mixed in the desulfurization process. This SiO ₂ component was found to be mostly γ2CaO · SiO ₂ by the powder X-ray diffraction method of the pre-treatment slag shown in FIG. γ2CaO · SiO ₂ seems to have transformed from the α phase with cooling. In this case, the particle size of the slag has become finer due to powdering accompanying the phase transformation (generally called dusting). Seem. In this case, the specific surface area of the reaction can be increased, which is advantageous as an object of the present invention.

As shown in FIG. 3, during the treatment, not only the sulfur concentration was lowered but also the SiO ₂ concentration was lowered, and the CaO / SiO ₂ concentration ratio was about 2.4 before the treatment, Increased to a degree and reusable value as dephosphorization and desulfurization agent. Further, as shown in FIG. 4, the main components of the pretreatment was the γ2CaO · SiO _2, the major components after treatment was confirmed that changes in the calcium carbonate.

In addition, from the results of this basic experiment, it became clear that the generation of H ₂ S is remarkably promoted when the pH of water falls below 7 after the start of blowing CO ₂ gas.

Removal of sulfur as H ₂ S and separation of CaCO ₃ by blowing carbon dioxide gas in a state where the hot metal desulfurization slag having the particle size distribution of [Table 3] and the composition of [Table 4] is suspended in water Recovery was attempted (Examples 1 to 3, Comparative Examples 1 and 2).

In this example and the comparative example, a tank having an internal volume of 6 m ³ was used as the reaction vessel 1 in FIG. The tank was charged with ³ m ³ of water in advance, and stirring with an impeller was started, and carbon dioxide blowing was started from a nozzle provided at the bottom. Furthermore, after throwing in the slag, processing for a predetermined time was performed. During the treatment, water was circulated and SiO ₂ was precipitated with a thickener. From the bottom of the reaction vessel, the precipitate (precipitate A) in the tank was appropriately extracted. After the treatment, all the water was transferred to a sedimentation separator, and the precipitate was further separated. The produced precipitate mainly composed of CaCO ₃ was dried with hot air and reused as a refining agent for bottom blowing injection in the steelmaking process. The precipitate mainly containing silicic acid recovered from the upper part of the reaction vessel (precipitate B) was effectively used as a SiO ₂ source after drying. [Table 5] shows the main components of the precipitate A, the precipitate B, and the recovered gas.

In Example 1, the hot metal desulfurization slag shown as slag 1 in [Table 3] is used as it is. The treatment for 240 minutes was performed, and the precipitate mainly composed of CaCO ₃ and the precipitate mainly composed of SiO ₂ could be recovered separately. When the precipitate containing CaCO ₃ as a main component was analyzed after drying, CaO / SiO ₂ was 4.5, which was sufficiently higher than 2.3 of the raw material slag. It was found that the sulfur concentration was sufficiently low at 0.2% and could be reused as a refining agent.

  In Example 2, the portion under 2 mm was similarly processed from the slag 1 of [Table 3] by sieving. In this example, the same effect was obtained in half the processing time as compared with Example 1.

  Example 3 is an example in which the slag 1 was crushed into [Table 3] and all were under 2 mm, but the same effect was obtained in half the processing time as compared with Example 1. .

In Comparative Example 1, the slag 1 was pulverized in [Table 3] and all were under 2 mm, but the slag 1 was processed according to the method disclosed in JP2009-30101A. That is, after removing sulfur by contacting with steam, carbonation was performed by aeration by contacting with CO ₂ . Removal of sulfur was possible, but because it was not possible separation of SiO2, could only recover those low CaO / SiO _2.

Comparative Example 2 is an example in which slag 1 was pulverized into [Table 3] and all made under 2 mm as in the case of Example 3 as a processing target. In this case, since N ₂ gas was blown without blowing CO ₂ gas, sulfur was slightly dissolved in water, and there was almost no effect of removing S and SiO ₂ .

1 Reaction vessel 2 Hot metal desulfurization slag 3 Water
4 makeup water 5 gas 6 H ₂ S recovery device 7 CO ₂ separation device 8 gate valve 9 sedimentation tank 10 calcium carbonate
11 SiO ₂
12 Impeller 13 Exhaust tower

Claims (3)

The hot metal desulfurization slag generated in the hot metal desulfurization treatment process is suspended in water and brought into contact with water containing carbon dioxide, and the sulfur component in the hot metal desulfurization slag is separated as H ₂ S gas by the following formula [Chemical Formula 1]. In addition, a method for regenerating slag, characterized in that 2CaO · SiO ₂ inevitably contained in the hot metal desulfurization slag is precipitated and separated as CaCO ₃ and SiO ₂ by the following formula [Chemical Formula 2], respectively.
  2. The method for regenerating slag according to claim 1, wherein hot metal desulfurization slag classified to a particle size of less than 2 mm is suspended in water.   The method for regenerating slag according to claim 1, wherein hot metal desulfurization slag having a particle size of 2 mm or more is pulverized to less than 2 mm and suspended in water.