JP6954500B1 - Manufacturing method of slag products and slag products - Google Patents

Abstract

To provide a method for producing a slag product and a slag product in which the hydration and expansion of slag containing free MgO is suppressed. This is a method for manufacturing slag products using steel slag. When manufacturing slag products using slag obtained by cooling and solidifying molten steel slag as a raw material, the amount of free MgO contained in the steel slag is 100 parts by mass. Boron corresponding to 30 parts by mass or more in terms of boron oxide is added to the molten steel slag, the steel slag to which boron is added is mixed, and then the steel slag is cooled and solidified.

Description

The present invention relates to a method for producing a slag product and a slag product.

With the development of industry, the number of industrial by-products produced in various industries is steadily increasing. Recently, from the viewpoint of global environmental conservation, attempts have been made to effectively utilize such industrial by-products. As examples of industrial by-products, for example, steel slag such as blast furnace slag and steelmaking slag generated from steel mills, coal ash generated from thermal power plants, incineration ash of waste and sewage sludge, etc. are melted at high temperature and cooled and solidified. There are slags, etc. that have been made to work. These slags are appropriately adjusted in particle size and reused as civil engineering and construction materials such as roadbed materials and ground materials. In addition, for example, a steel slag hydrated solidified body, which is a material mainly composed of steelmaking slag and blast furnace slag fine powder, can be produced by using a kneading facility in the same manner as concrete. In addition, the steel slag hydrated solidified material may be used as an artificial stone material such as a harbor civil engineering material or a roadbed material. Civil engineering and construction materials and steel slag hydrated solidified products made from such slag are called slag products.

Since refractories used in the steelmaking process of steelworks are required to have heat resistance and erosion resistance, magnesium may be used. Further, in the steelmaking process, in order to prevent erosion and erosion of the refractory refractory, a required amount of magnesium oxide is usually added to the molten slag. Some of the MgO in the slag cooled from this state _{forms a composite oxide with CaO, Al 2} O ₃ , SiO _{2, and the} like, but the others exist in the state of MgO as they are.

The composite oxide formed from CaO, Al ₂ O ₃ , SiO _2, etc. and MgO is a stable compound that hardly reacts at room temperature. However, MgO (hereinafter, also referred to as free MgO) existing as a simple magnesium oxide phase that does not form a composite oxide reacts with water at room temperature to become Mg (OH) ₂ , which causes about twice the volume expansion. cause.
Therefore, slag containing a simple magnesium oxide phase may be pulverized due to volume expansion when used as a hydrated solidified steel slag, and cannot be effectively used.

In addition, CaO in the slag also causes volume expansion associated with the hydration reaction like MgO. As a technique for suppressing this, there are steam aging in which slag is steamed with steam at 100 ° C. and pressurized steam aging in which slag is steamed at 100 ° C. or higher (equivalent to 180 ° C. at 10 atm) in a high-pressure autoclave tank. .. All of these methods correspond to the accelerated aging described in JIS A 5015 “Road Steel Slag”. In the following, the volume expansion associated with hydration in MgO and CaO is also referred to as "hydration expansion".
Further, for example, Patent Document 1 proposes a method of suppressing pulverization due to γ transformation of _{2CaO · SiO 2} by setting the boron concentration to 0.010 to 0.050% by mass with respect to the molten slag. ing. This is a technique aimed at suppressing pulverization, and its upper limit corresponds to 0.16% when converted to boron oxide.

Japanese Unexamined Patent Publication No. 2005-272275

By the way, MgO has a lower hydration rate than CaO. Therefore, when trying to suppress the hydration expansion of MgO by using the above-mentioned steam aging or pressurized steam aging, a long-term aging treatment is required, which requires a large processing cost and time.
Further, in the method of Patent Document 1, as a result of investigation by the present inventor, it was confirmed that the hydration and expansion of free MgO may not be sufficiently suppressed for slag containing free MgO.

Therefore, the present invention has been made by paying attention to the above problems, and an object of the present invention is to provide a method for producing a slag product and a slag product in which the hydration and expansion of slag containing free MgO is suppressed. ..

According to one aspect of the present invention, in a method for producing a slag product using steel slag, when the slag product is produced using the slag obtained by cooling and solidifying the molten steel slag as a raw material, the above. After adding boron corresponding to 30 parts by mass or more in terms of boron oxide to 100 parts by mass of free MgO contained in the steel slag to the molten steel slag and mixing the steel slag to which the boron is added. , A method for producing a slag product, which cools and solidifies the steel slag, is provided.
According to one aspect of the present invention, it is a slag product manufactured by using steel slag, and the amount of boron contained is 30 parts by mass or more in terms of boron oxide with respect to 100 parts by mass of free MgO contained. Slag products are provided.

According to one aspect of the present invention, there is provided a method for producing a slag product and a slag product in which the hydration and expansion of slag containing free MgO is suppressed.

In the embodiment, it is a graph showing the relationship between the mixing ratio of B ₂ O ₃ with respect to the rate and steel slag free MgO in steel slag.

In the following detailed description, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same or similar parts are designated by the same or similar reference numerals, and duplicate description will be omitted. Each drawing is schematic and may differ from the actual one. Further, the embodiments shown below exemplify devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention describes the materials, structures, arrangements, etc. of the components. It is not specific to the following. The technical idea of the present invention can be modified in various ways within the technical scope specified by the claims described in the claims.

<Manufacturing method of slag products>
The target slag in this embodiment is steel slag generated in various refining processes performed in refining equipment such as converters, electric furnaces, and melt reduction furnaces. Further, this steel slag contains free MgO. Free MgO is MgO that exists as a simple magnesium oxide phase that does not form a composite oxide, that is, MgO that is a mineral phase at room temperature, and is also called free magnesium oxide. Further, the steel slag may contain free MgO, and may contain other components (for example, _{basicity, which is the ratio of CaO concentration to SiO 2} concentration, or free CaO (mineral phase CaO at room temperature, free calcium oxide). The content rate, etc.) is not particularly limited.

The target steel slag in the present embodiment is preferably steel slag generated in a refining process including reduction refining used in the production of stainless steel and the like. Such steel slag has a higher content of MgO and free MgO and a lower content of free CaO than the steel slag generated in the refining process used in the production of general ordinary steel. For this reason, steel slag generated by refining processing including reduction refining has a lower effect of suppressing hydration and expansion due to steam aging and pressurized steam aging than other steel slags, and is therefore particularly applicable to slag products. It was difficult.

In the present embodiment, first, boron is added to the molten steel slag and mixed (addition step). In the addition step, boron is added according to the mass of free MgO of steel slag. Boron added is boric oxide _{(B 2 O} 3), boric acid _(H 3 _BO 3), boronic acid _(H 3 _BO 2), borinic acid _(H 3 BO), metaboric acid _(HBO 2), metaboric acid It is sodium (NaBO ₂ ) or sodium tetraborate (Na ₂ B ₄ O ₇ ). By adding any of these, it becomes possible to melt the boron source into steel slag. Is. At this time, boron corresponding to 30 parts by mass or more in terms of boron oxide is added to 100 parts by mass of free MgO. More preferably, boron corresponding to 45 parts by mass or more in terms of boron oxide is added to 100 parts by mass of free MgO. By adding boron in the above range, hydration of free MgO can be suppressed. The upper limit of the amount of boron added is not particularly limited, but it may be appropriately set according to the specifications and specifications of the target slag product.

The mass of free MgO in steel slag is determined based on the mass ratio (content rate) of free MgO in steel slag measured or estimated by the following method and the mass of steel slag.
When measuring the mass ratio of free MgO in steel slag, the measurement is performed by the following method. In the measurement of the mass ratio of free MgO, a part of the molten steel slag is sampled and cooled to prepare a sample. Next, the mass ratio of free MgO in this sample is measured. At this time, the measurement method described in "Development of free-MgO analysis technology in slag" (Iron and Steel, The Iron and Steel Institute of Japan, 2016, Vol.102, No.1, p.24-28) is used. In this measurement method, the mass ratio of free MgO is calculated by combining the dissolution of slag using ethylene glycol and _{the quantification of Mg (OH) 2 by the thermal weight measurement method.} In this measurement method, steel slag is collected at multiple points, and the steel slag is mixed and crushed to prepare a sample, thereby improving the reliability of measurement.

Further, when estimating the mass ratio of free MgO of steel slag, the estimation is performed by the following method. If the operating conditions are the same, it can be assumed that the steel slag has almost the same slag composition. Therefore, if a part of the sample is taken as needed and the mass ratio of free MgO is measured, the mass ratio of free MgO of steel slag generated under the same operating conditions can be estimated. Further, as the operating conditions used in estimating the mass ratio of free MgO, conditions that generally affect the slag composition can be used. For example, as operating conditions, conditions such as the type and amount of auxiliary raw materials (slag slag, etc.) used, the composition of components before and after the treatment of molten iron, and the mass of molten iron can be considered.

The mass of the steel slag can be obtained from the difference by measuring the mass of the slag pot before and after discharging the molten steel slag into the slag pot, which is a dedicated pot. Alternatively, more simply, in the operation of a converter, an electric furnace, a melt reduction furnace, etc. that generate steel slag, the mass of the generated steel slag may be obtained from the mass balance between the raw material to be added and the auxiliary raw material. ..
Then, by multiplying the obtained mass of the steel slag by the measured or estimated mass ratio of the free MgO, the mass of the free MgO in the target steel slag can be obtained.

Further, as a method of adding boron to the molten steel slag in the addition step, there are a method of adding it into the furnace of various smelting furnaces, a method of adding it to the steel slag transferred or stored in the slag pot, and the like. .. In the case of the method of adding in a furnace, boron is added in the furnace at the final stage of refining in the smelting furnace. The boron-added steel slag is mixed according to the refining process in the refining furnace. On the other hand, in the case of the method of adding to the steel slag to be transferred to the slag pot, when the steel slag is transferred from the smelting furnace to the slag pot, boron hits the steel slag discharged from the smelting pot. Added. In the case of the method of adding to the steel slag contained in the slag pot, after receiving the steel slag in the slag pot, boron is blown into the steel slag through a dipping nozzle, or the steel slag of the steel slag. Boron is added by spraying boron from above. Further, in the method of adding to the steel slag to be transferred or contained in the slag pot, after adding boron, the steel slag in the slag pot is transferred to another slag pot by repeating the process of transferring the slag to another slag pot. Mix steel slag. Boron-added steel slag becomes homogeneous slag when mixed.

After the addition step, the steel slag is cooled to solidify (cool and solidify) (cooling step). If necessary, the steel slag may be subjected to an aging treatment. For example, in the case of steel slag generated in a refining process including reduction refining used in the production of stainless steel, it is judged that the suppression of hydration expansion of free CaO is sufficient because the basicity of the steel slag is low. If so, the aging process may not be performed.

After the cooling process, slag products are manufactured from the cooled and solidified steel slag. At this time, the cooled and solidified steel slag may be pulverized and, if necessary, magnetically separated and then processed to a predetermined particle size (for example, 40 mm or less or 25 mm or less) as a raw material for the slag product. As a method for producing slag products from cooled and solidified steel slag, a well-known method for producing slag products such as civil engineering and construction materials and steel slag hydrated solidified products can be used. Since the hydration reaction of MgO is suppressed in the steel slag produced in this manner, for example, it can be used as an aggregate for a steel slag hydrated solidified body having less volume expansion.

<Slag products>
The slag product manufactured by the above method for manufacturing the slag product has the following features. The slag product according to the present embodiment is a slag product manufactured by using steel slag, and the amount of boron contained is 30 parts by mass or more in terms of boron oxide with respect to 100 parts by mass of free MgO contained. More preferably, the steel slag product contains 45 parts by mass or more of boron in terms of boron oxide with respect to 100 parts by mass of free MgO contained.

<Modification example>
Although the present invention has been described above with reference to specific embodiments, it is not intended to limit the invention by these descriptions. By reference to the description of the invention, one of ordinary skill in the art will appreciate other embodiments of the invention that include various modifications as well as the disclosed embodiments. Therefore, it should be understood that the embodiments of the invention described in the claims also include embodiments including these modifications described herein alone or in combination.

For example, in the above embodiment, when measuring the mass ratio of free MgO, the measurement is performed by a method using ethylene glycol and a thermogravimetric analysis method, but the present invention is not limited to such an example. As a method for measuring free MgO, a method of identifying a peak derived from free MgO from the X-ray peak of steel slag and quantifying the peak, or a method of embedding particulate steel slag in a resin or the like and polishing it is performed. Other methods such as a method of identifying the MgO mineral phase with an electron probe microanalyzer (EPMA method) and calculating the weight ratio from the area ratio may be used. In the method using X-ray peaks, steel slag is collected at multiple points, and the steel slag is mixed and crushed to prepare a sample, thereby improving the reliability of measurement. Further, in the method using EPMA, if steel slag is similarly collected at multiple points, several to several slag particles are measured, and the average value of their free MgO phase area ratios is obtained, the measurement reliability is improved. improves. From the viewpoint of measurement accuracy, the method for measuring the mass ratio of free MgO is preferably a measurement method using ethylene glycol and a thermogravimetric measurement method, as in the above embodiment.

<Effect of embodiment>
(1) The method for producing a slag product according to one aspect of the present invention is a method for producing a slag product using steel slag, wherein the slag product is made from slag obtained by cooling and solidifying molten steel slag. At the time of production, boron corresponding to 30 parts by mass or more in terms of boron oxide with respect to 100 parts by mass of free MgO contained in the steel slag is added to the molten steel slag, and the steel slag to which boron is added is mixed. After that, the steel slag is cooled and solidified.

According to the configuration of (1) above, the added boron suppresses the hydration expansion of free MgO in the steel slag. This is because when the steel slag is exposed to an environment containing water, a layer containing boron is formed on the surface of the free MgO in the steel slag, and this layer suppresses the contact between the free MgO and water. Presumed. Further, in the configuration of (1) above, since it is only necessary to add boron to the molten steel slag and mix it, the hydration expansion of free MgO can be suppressed easily and in a short time.

(2) The slag product according to one aspect of the present invention is a slag product manufactured using steel slag, and the amount of boron contained is 30 parts by mass in terms of boron oxide with respect to 100 parts by mass of free MgO contained. It is more than a part.
According to the configuration of the above (2), the same effect as the above (1) can be obtained.

Next, the examples carried out by the present inventors will be described. In the examples, the mass ratio of free MgO of various steel slags generated in a steel mill was investigated. Further, the mass ratio of the free MgO was calculated by a method using ethylene glycol and a thermogravimetric analysis method. _{Table 1 shows the measurement results of the basicity (CaO / SiO 2} ), the mass ratio of MgO, and the mass ratio of free MgO of the six types of steel slags A to D investigated. Further, a predetermined amount of boron oxide B ₂ O ₃ was put into each steel slag into the refining furnace at the final stage of refining. Then, the obtained steel slag was cooled and solidified and crushed to have a size of 25 mm under. Then, the following expansion measurement was performed on the obtained steel slag.

In the expansion measurement, first, the obtained steel slag was crushed and sieved to 2 mm and 1.2 mm. Next, 15 g of 2 to 1.2 mm steel slag and 15 g of 1.2 to 0 mm steel slag were mixed to prepare 3 samples per condition. Further, each sample was compression-molded into a cylinder having a diameter of 25 mm. Then, each compression-molded sample was immersed in water at 80 ° C., and the amount of expansion was measured for 10 days. As a result of the expansion measurement, the expansion rate tended to decrease as the amount of boron added increased.

Further, in the example, a steel slag hydrated solidified body was prepared using the same steel slag. After that, the obtained solidified body is immersed in water at 80 ° C., and the specimen is observed after 30 days, and the one that cracks is "bad" and the one that produces a very slight pop-out within 10 mm in diameter. Was evaluated as "good", and a healthy one with no abnormality in appearance was evaluated as "excellent". The results are shown in Table 2 and FIG. In FIG. 1, the evaluation results of bad, good, and excellent are indicated by Δ, ◇, and ◯, respectively. As shown in Table 2, in Examples 1 to 18 in which the amount of boron corresponding to 30% by mass or more in terms of boron oxide was added to the mass of free MgO, the specimen did not crack and remained healthy. rice field.
From the viewpoint of suppressing pulverization associated with the γ transformation of 2CaO · SiO _2, the amount of boron oxide added at the ratio of this example is sufficient. When the appearance of the slag of this example was observed when it was crushed to 25 mm under, no powdery slag was observed. Moreover, when the mineral phase was confirmed by X-ray, _{neither 2CaO / SiO 2 in the} γ form was confirmed at all.

Claims (2)

A method for manufacturing slag products using steel slag.
When manufacturing the slag product using the slag obtained by cooling and solidifying the molten steel slag as a raw material,
Boron corresponding to 30 parts by mass or more in terms of boron oxide with respect to 100 parts by mass of free MgO contained in the steel slag was added to the molten steel slag.
A method for producing a slag product, in which the steel slag to which boron is added is mixed and then the steel slag is cooled and solidified. A slag product manufactured using steel slag.
A slag product in which the amount of boron contained is 30 parts by mass or more in terms of boron oxide with respect to 100 parts by mass of free MgO contained.

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