JP7131534B2 - Aggregate manufacturing method, coarse aggregate and fine aggregate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing aggregate using by-products generated in a metal manufacturing process as a raw material, and coarse aggregate and fine aggregate produced by the method.

In the metal refining process, a large amount of slag and dust are generated because the impurities in the raw material are separated from the metal content at high temperatures. In addition, the metal refining process requires containers for holding high-temperature metal and slag, and the refractories used in these containers are discarded as they deteriorate over time and become used refractories. Furthermore, steel slabs and ingots of various metals produced in the metal refining process are subjected to appropriate rolling, processing, surface treatment, etc. when processed into products. Sludge containing and separated substances is generated. In addition, in coal-fired power plants and the like, ash in fuel remains after combustion and is collected as fly ash.

By-products such as slag, dust, used refractories, and sludge generated in the metal manufacturing process are all mainly composed of metal oxides such as SiO ₂ , Al ₂ O ₃ , CaO, and MgO, and are used in crushed stone and concrete. It is expected to be used as a raw material. However, depending on the composition of these by-products, for example, those containing a large amount of CaO or MgO may expand or pulverize over time, or the metal components may be eluted, albeit minutely. There were quite a few things that could not be used effectively.

To address this problem, Patent Document 1 discloses adding a _SiO2 -containing substance and a reducing agent to molten steelmaking slag, and using waste plastics that meet special conditions as part or all of the reducing agent. A technique for melting and reforming is disclosed. Patent Document 1 discloses, as a specific means, blowing a SiO ₂ -containing substance and oxygen from an immersion lance into molten converter slag held in a slag ladle and blowing a reducing substance. there is

JP 2009-114023 A

The technology disclosed in Patent Document 1 is applied to molten steelmaking slag, but the slag generated in the metal refining process is molten immediately after generation, but cools over time to a solid state. Most of them are things, and there are not many opportunities to effectively implement the technology disclosed in Patent Document 1. Furthermore, since the dust generated in the metal refining process is produced in a solid state, it cannot be treated by the technique disclosed in Patent Document 1.

The present invention has been made in view of such problems of the prior art, and its object is to separate and cool the metal and oxide by melting the by-product at room temperature, and cool the oxide after cooling. It is to provide a method for producing aggregates that can be used for roadbed materials, concrete, etc., and coarse aggregates and fine aggregates produced by the production method.

Means for solving the above problems are as follows.
(1) A method for producing an aggregate by heating a by-product generated in a metal production process to separate the by-product into a metal and an oxide, and producing an aggregate using the separated oxide. , The by-product is one or more selected from slag, dust, sludge and used refractories, and a raw material containing a reducing agent is added to the by-product and heated to 1300 ° C. or higher using an electric furnace. The chemical composition of the oxide is CaO: 17% by mass to 59% by mass, SiO ₂ : 17% by mass to 53% by mass, Al ₂ O ₃ : 5% by mass to 45% by mass _, MgO: 2 % by mass or more and 20% by mass or less, basicity (CaO/SiO ₂ ): 0.7 or more and 2.0 or less, and cooled so that 90% by volume or more of the oxide heated to 1300 ° C. or more is crystallized. A method for producing an aggregate, wherein the cooled oxide is made to have a particle size of 40 mm or less.
(2) The aggregate according to (1), wherein the by-product contains a total of 1% by mass or more of one or more selected from metals and free carbon, and the electric furnace is a resistance heating electric furnace. Production method.
(3) The method for producing an aggregate according to (1) or (2), wherein the basicity (CaO/SiO ₂ ) is 0.7 or more and 1.6 or less.
(4) The method for producing an aggregate according to any one of (1) to (3), wherein the slag and the used refractory contain a reducing material.
(5) The aggregate according to any one of (1) to (4), wherein the raw material containing the reducing material is one or more selected from coal, coke, papermaking sludge, waste tires and waste plastics. manufacturing method.
(6) The method for producing an aggregate according to any one of (1) to (5), wherein a raw material for adjusting the chemical composition of the oxide is further added to the by-product and heated.
(7) The method for producing an aggregate according to (6), wherein the raw material for adjusting the chemical composition of the oxide is one or more selected from fly ash, sand and gravel.
(8) A powdering rate of 1.0% or less, an absolute dry density of 2.5 g/cm ³ or more, a water absorption of 3.0% or less, and a loss mass fraction of 12 in a stability test. % or less and the abrasion weight loss is 40% or less.
(9) A powdering rate of 1.0% or less, an absolute dry density of 2.5 g/cm ³ or more, a water absorption of 3.0% or less, and a loss mass fraction of 10 in a stability test. % or less and a water retention amount of 3% by mass or more.

By carrying out the method for treating by-products according to the present invention, it is possible to separate the room-temperature by-products into metals and oxides, and to produce aggregates used in roadbed materials, concrete, etc. from the oxides. As a result, by-products generated in the metal refining process, which have been difficult to effectively utilize, can be effectively utilized as raw materials for roadbed materials, aggregates used in concrete, etc., so that the amount of waste can be reduced.

1 is a cross-sectional view of a cylindrical container 10 used for measuring water retention. FIG. FIG. 2 is an image diagram of water 22 retained in aggregate 20 measured in the measurement of the amount of retained water.

The present inventors focused on the chemical composition of slag, dust, sludge, and post-use refractories generated in the metal manufacturing process, which are difficult to effectively utilize, and by optimizing the chemical composition, the by-products were reduced to oxides and metals. The aggregates (coarse aggregates and fine aggregates) used for roadbed materials and concrete are produced by making it easier to separate from the oxides and further cooling so that 90% by volume or more of the separated oxides crystallize. The present invention was completed by discovering that it can be done. Hereinafter, the present invention will be described through embodiments of the invention.

In the aggregate manufacturing method according to the present embodiment, the by-product is heated to 1300° C. or higher using an electric furnace. By heating the by-products to 1300° C. or higher, the by-products can be melted and separated into metals and oxides. On the other hand, if the heating temperature is less than 1300° C., the by-product cannot be melted and the by-product cannot be separated into an oxide and a metal. The oxide and metal cannot be sufficiently separated, and a large amount of metal remains in the oxide.

The higher the temperature of the molten oxide, the lower the viscosity and the easier it is to separate the oxide and the metal. is no problem. For heating the by-product, it is preferable to use an electric furnace which can input a large amount of energy and which is easy to control the temperature. Various electric furnaces such as a resistance heating electric furnace, an arc furnace and an induction heating electric furnace can be used as the electric furnace. When an arc furnace or an induction heating electric furnace is used, molten metal such as hot metal or scrap metal can be added to the by-products for treatment.

Among these electric furnaces, it is preferable to use a resistance heating electric furnace. For example, in an arc furnace, it is necessary to perform arc discharge between electrodes and transfer the heat generated by the arc discharge to a by-product to melt it. On the other hand, if the by-products such as slag and dust contain a total of 1% by mass or more of metal or free carbon, a resistance heating electric furnace can be used to convert the metal and free carbon into electricity. flows to generate resistance heat, and this heat is directly transferred to the by-products, so heat transfer to the by-products is performed efficiently. Therefore, the temperature of the by-product can be raised to a predetermined temperature in about one-fifth of the time required for heating in an arc furnace. The by-product in the present embodiment is one or more selected from slag, dust, sludge, and used refractories generated in the metal manufacturing process. In the following description, a resistance heating electric furnace is used as the electric furnace, and slag and dust are used as by-products.

Slag and dust, which are by-products, are charged into a resistance heating electric furnace. An electrode is inserted into the furnace where slag and dust are deposited, and a voltage is applied. At this time, the presence of a total of 1% by mass or more of metal and free carbon in the slag or dust causes current to partially flow through the slag or dust, thereby generating resistance heat and raising the temperature of the slag or dust.

Since the main component of slag and dust is metal oxide, it has electrical conductivity in the molten state. Therefore, when the slag or dust itself melts due to temperature rise, the amount of current flowing also increases. As a result, the calorific value also increases, and by raising the temperature to 1300° C. or higher, the slag and dust charged into the furnace can be entirely melted. If the slag and dust can be melted as a whole, metals such as iron, copper, and nickel contained in the slag and dust will be melted and agglomerated, so that metals and oxides can be separated.

In the method for producing an aggregate according to the present embodiment, the chemical composition of the oxide is CaO: 17% by mass or more and 59% by mass or less, SiO ₂ : 17% by mass or more and 53% by mass or less, and Al ₂ O ₃ : 5% by mass or more. 45 mass % or less _, MgO: 2 mass % or more and 20 mass % or less, basicity (CaO/SiO ₂ ): 0.7 or more and 2.0 or less. By setting the chemical composition of the oxide within the above range, the viscosity of the molten oxide is within a preferable range for separation from the molten metal, and the metal and oxide contained in the by-product can be easily separated. Furthermore, by setting the chemical composition of the oxide within the above range, the expansion of the oxide by hydration is suppressed, and the material becomes useful as a roadbed material, aggregate for concrete, and the like. On the other hand, when the basicity (CaO/SiO ₂ ) of the oxide is higher than 2.0, the viscosity of the molten oxide increases, making it difficult to separate the metal and the oxide, and the metal mixed into the oxide after separation becomes become more. In addition, when the basicity (CaO/SiO ₂ ) of the oxide is higher than 2.0 or the content of MgO is higher than 20% by mass, f-CaO and f-MgO are likely to precipitate from the oxide, leading to hydration expansion. occurs.

The basicity (CaO/SiO ₂ ) of the oxide is preferably 0.7 or more and 1.6 or less. By setting the basicity (CaO/SiO ₂ ) of the oxide to 0.7 or more and 1.6 or less, the viscosity of the molten oxide is lowered and the metal and the oxide are more easily separated. Furthermore, the volume change of the oxide during the cooling process of the oxide and the precipitation of f-CaO and f-MgO from the oxide are suppressed, thereby suppressing the powdering of the oxide and further suppressing hydration expansion. can.

On the other hand, when the basicity (CaO/SiO ₂ ) of the oxide is higher than 1.6, the crystal transition of 2CaO SiO ₂ (transition from α' type or β type to γ type) during the cooling process of the oxide causes The volume begins to change, which is undesirable as it pulverizes the oxide.

For the chemical composition of the oxide, check the chemical composition of the slag, dust, sludge and used refractory to be charged into the resistance heating electric furnace in advance. Control by adjusting the ratio. In addition, as a raw material for adjusting the chemical composition of the oxide, one or more selected from fly ash, sand and gravel may be further added, and by adding these, the chemical composition of the oxide is adjusted to the target range. may be controlled.

Here, some of the dust has the effect of increasing the basicity of the oxide and increasing the particle size of the collected dust to make it easier to collect. Some sludges have the effect of increasing the base content of oxides while reducing them. Some post-use refractories have the effect of reducing the basicity of oxides while reducing them. Some fly ash, sand and gravel have the effect of reducing the basicity of oxides. Considering these effects, by adjusting the mixing ratio of each raw material and controlling the chemical composition of the oxide within the above range, the expansion source is eliminated from the oxide, and the oxide is used for roadbed materials and concrete. It is possible to manufacture aggregates that can be used for aggregates such as

In addition, raw materials containing reducing agents are added to by-products such as slag, dust, sludge, post-consumer refractories and fly ash. If the reducing material exists in a state where the by-products are completely melted, part of the metal oxide is reduced, and the amount of metal oxide remaining in the oxide can be reduced, and the amount of metal that can be separated and recovered. increases. As the raw material containing the reducing material, for example, one or more selected from coal, coke, papermaking sludge, waste tires and waste plastics may be used. When slag or used refractories are used as by-products, it is preferable to use slag or used refractories containing a reducing agent. By using a slag containing a reducing agent or a used refractory, it is possible to reduce the amount of the reducing agent that is externally added to reduce the oxide.

In charging the raw materials into the resistance heating electric furnace, the raw materials containing FeO, MnO, and Al ₂ O ₃ that form a melt at a low temperature are first charged into the resistance heating electric furnace, and a voltage is applied. After melting, it is preferable to sequentially charge other raw materials. This allows the overall melting of the by-products with high efficiency. Furthermore, in addition to the raw material that produces the melt at the lowest temperature, a raw material that lowers the melting point of the entire raw material may be charged first.

Further, in order to protect the furnace wall refractories of the resistance heating electric furnace, the operation may be performed so that the by-products in the vicinity of the furnace wall are not melted, instead of melting all the charged by-products. For example, the electrodes of a resistance-heated electric furnace may be operated with a centered electrode so that all of the by-products are not dissolved, which results in less erosion of the refractory forming the self-lining layer, resulting in , longer furnace life. In addition, when the operation is performed so that the entire amount of the by-products is not dissolved, it is necessary to prevent the undissolved portion from being mixed when the molten slag is discharged out of the furnace.

In the aggregate manufacturing method according to the present embodiment, the by-product is melted and separated into metal and oxide, and then cooled so that 90% by volume or more of the oxide is crystallized. In this way, by crystallizing 90% by volume or more of the oxide, it is possible to produce a dense aggregate that is less likely to be distorted and that is excellent in water retentivity from the oxide. An oxide in which 90% by volume or more is crystallized can be obtained by adjusting the cooling rate from the molten state to 700°C. The cooling rate from the molten state at which 90% by volume or more can be crystallized to 700° C. varies depending on the composition of the oxide. For example, in the case of an oxide having a basicity (CaO/SiO ₂ ) of 1.3, the cooling rate from the molten state to 700° C. is set to 20° C./sec or less, whereby 90% by volume or more of the oxide is crystallized. can get.

In this embodiment, the crystallization rate (% by volume) of the oxide is calculated by the following procedure.
1. Oxide is embedded in resin and a polished sample is created.
2. A sample is observed under a microscope, and the ratio of amorphous and crystalline areas is calculated.
3. The ratio of the crystalline area is calculated from the crystalline area/(amorphous area+crystalline area), and the crystallization rate (volume %) of the oxide is calculated from this.

In the method for producing an aggregate according to the present embodiment, the grain size of 90% by volume or more of the crystallized oxide is reduced to 40 mm or less. Since the maximum size of coarse aggregate is 40 mm at the largest, the meaning of reducing the particle size of oxides to 40 mm or less is to use a sieve with a predetermined mesh size of 40 mm or less to obtain coarse aggregate and fine aggregate. It means to adjust the particle size distribution. The particle size distribution required for coarse aggregate and fine aggregate is specified in JIS A 5005 "Crushed Stone and Crushed Sand for Concrete". As a result, aggregates (coarse aggregates and fine aggregates) suitable for use in concrete and roadbed materials can be produced.

The aggregates manufactured by the method for manufacturing aggregates according to the present embodiment are coarse aggregates or fine aggregates. When the aggregate is coarse aggregate, the coarse aggregate has a pulverization rate of 1.0% or less, an absolute dry density of 2.5 g/cm ³ or more, and a water absorption rate of 3.0% or less. , the loss mass fraction in the stability test is 12% or less, and the abrasion weight loss is 40% or less.

Further, when the aggregate is fine aggregate, the fine aggregate has a pulverization rate of 1.0% or less, an absolute dry density of 2.5 g/cm ³ or more, and a water absorption rate of 3.0. %, the loss mass fraction in the stability test is 10% or less, and the water retention amount is 3% by mass or more. These values are values specified in JIS A 5005.

Here, the pulverization rate is based on Coastal Technology Library No. 28 "Technical Manual for Iron and Steel Slag Hydrated Solids" Appendix 3, "Steelmaking Slag Pulverization Rate Measurement Test Method". By using coarse aggregates and fine aggregates with a pulverization rate of 1.0% or less for concrete, the concrete is excellent in durability that is not affected by the expansion of the aggregates.

Coarse aggregate with absolute dry density of 2.5 g/cm ³ or more, water absorption of 3.0% or less, loss mass fraction in stability test of 12% or less, and abrasion loss of 40% or less shall be used in concrete. results in concrete with good fresh and cured properties. Good fresh properties are defined by the slump value (see JIS A 1101 Concrete Slump Test Method) and air content (see JIS A 1116 Fresh Concrete Unit Volume Mass Test Method and Air Volume Mass Test Method). Concrete is easy to place according to the value, and bleeding is appropriate, so it means that finishing is easy. Good properties after curing mean that the strength is as set, the drying shrinkage (see JIS A 1129 Mortar and Concrete Length Change Measurement Method) is small, and the fire resistance is excellent. Therefore, the coarse aggregate that satisfies the above criteria is suitable for roadbed materials and concrete.

Similarly, the absolute dry density is 2.5 g / cm ³ or more, the water absorption is 3.0% or less, the loss mass fraction in the stability test is 10% or less, and the water retention amount is 3% by mass or more. The use of certain fine aggregates in concrete results in concrete with good fresh and hardened properties. Therefore, fine aggregate satisfying the above criteria is suitable for roadbed materials and concrete.

The absolute dry density and water absorption are measured according to JIS A 1109 "Determination of Coarse Aggregate Density and Water Absorption" or JIS A 1110 "Determination of Coarse Aggregate Density and Water Absorption". The loss mass fraction in the stability test is measured according to JIS A 1112 "Stability test method for aggregates using sodium sulfate". Abrasion weight loss is measured according to JIS A 1121 "Abrasion test method for coarse aggregate by Los Angeles tester".

FIG. 1 is a cross-sectional view of a cylindrical container 10 used for measuring water retention. The cylindrical container 10 is composed of a cylindrical portion 12 having a diameter of 100 mm and a height of 100 mm, a bottom portion 14 having a funnel shape, and a perforated plate 16 . The water retention capacity of fine aggregate is measured by the following procedure using the cylindrical container 10 shown in FIG.
1. The water absorption rate (Q) of the aggregate is determined according to JIS A 1109 "Determination of Density and Water Absorption Rate of Fine Aggregate".
2. A surface dry saturated aggregate is prepared.
3. A cylindrical container 10 having an inner diameter of 100 mm and a height of 100 mm shown in FIG. Fill with aggregate and smooth the surface.
4. Spray the container with water from the top until the bottom drains well.
5. Cover the top of the container to prevent the water from evaporating.
6. Collect the aggregate after 24 hours, and measure the mass of the collected aggregate (W ₁ ).
7. 5. in a dryer at about 110°C. Add aggregate and dry until absolutely dry.
8. Measure the mass of the bone dry aggregate ₍ W2).
9. The water retention amount is calculated using the following formula (1).

R ₌ (W1 _- W2 _- W2×Q/100) ×100/W2 ( ₁ )
In the above formula (1), R is the amount of water retention (% by mass), W ₁ is the amount of bone material in the water-retained state (g), W ₂ is the amount of bone material in the absolutely dry state (g), and Q is the water absorption rate (% by mass).

FIG. 2 is an image diagram of the water 22 retained in the aggregate 20 measured in the measurement of the retained water amount. The aggregate 20 retains not only the water 22 around the aggregate 20 but also the water permeating the pores of the aggregate. In the present embodiment, the water permeating through the pores (water corresponding to the water absorption rate determined by JIS A 1109 “Method for testing the density and water absorption rate of fine aggregates”) is not included in the water retained by the aggregate 20. , not subject to water retention measurement.

As described above, in the aggregate manufacturing method according to the present embodiment, by-products such as slag and dust at room temperature are heated to 1300° C. or higher to separate oxides and metals of predetermined chemical components. Then, it is cooled so that 90% by volume or more of the oxide at 1300° C. or higher is crystallized, and the cooled oxide is reduced to a grain size of 40 mm or less, which is required for coarse aggregate or fine aggregate. As a result, it is possible to recover metals from the by-products generated in the metal manufacturing process, which have been difficult to effectively utilize, and to manufacture aggregates used in roadbed materials, concrete, etc. from the separated oxides, thereby reducing the amount of waste. can be less.

Next, an example of the method for producing an aggregate according to the present invention will be described. First, 20 kg of room-temperature by-products were charged into a 100 kVA resistance-heating electric furnace, and energization was started. After confirming the melting of the by-product between the electrodes, the raw material was added. After 200 kg of the by-product was charged, the temperature was maintained at 1550°C for 1 hour, and then 700°C at 10°C/min. After that, it was allowed to cool naturally (heat treatment condition A). Table 1 shows the chemical composition of each raw material used. In Table 1, steelmaking slag B is a raw material that produces a melt at a low temperature. Fly ash and blast furnace gutter refractory waste are raw materials that lower the melting point of the entire raw material. Cr ore smelting reduction furnace slag, SUS dust, cold-rolled sludge, and fly ash are raw materials containing reducing agents. Silicon carbide (SiC) is the reducing material contained in the spent refractory. "<0.1" in Table 1 indicates that the content is less than 0.1% by mass, and "<1" indicates that the content is less than 1% by mass. In addition, in Table 1, the sum of chemical compositions of some materials is less than 100. This is because the raw materials shown in Table 1 contain components other than the chemical components concerned.

Table 2 shows the mixing ratio of each raw material in Examples 1 to 6. Similarly, Table 3 shows the mixing ratio of each raw material in Comparative Examples 1 to 6. Coke, papermaking sludge and waste tires in Tables 2 and 3 are all raw materials containing reducing agents. In Comparative Example 4, 20 kg of room-temperature by-products were charged into a 100 kVA resistance heating electric furnace, and energization was started. After confirming the melting of the by-product between the electrodes, the raw material was added. After 200 kg of the by-product was charged, the temperature was maintained at 1250°C for 1 hour, and then 700°C at 10°C/min. After that, it was allowed to cool naturally (heat treatment condition B).

Table 4 shows the chemical composition of the oxide after separation, the presence or absence of reduction, the state of separation between the oxide and the metal, and the crystallization rate in Examples 1 to 6 and Comparative Examples 1 to 6. In this example, when Fe + Fe ₂ O ₃ in the oxide is 4% by mass or less and Cr ₂ O ₃ is less than 1% by mass, it is judged that the reduction is good, and “○” is entered in the “Reduction” column of Table 4. did. With this amount, the aggregate produced using the oxide is an aggregate that satisfies environmental standards. On the other hand, when Fe + Fe ₂ O ₃ is more than 4% by mass or Cr ₂ O ₃ is 1% by mass or more, the reduction is not good, and "x" is entered in the "Reduction" column of Table 4. In addition, when the amount of metal mixed in the oxide was 10% by mass or less, the separation was judged to be good, and "○" was entered in the "Separation" column of Table 4. On the other hand, when the amount of metal mixed into the oxide was more than 10% by mass, the separation was not good, and "X" was entered in the "Separation" column of Table 4.

The oxides obtained in Invention Examples 1 to 6 and Comparative Examples 1 to 6 are pulverized and sieved, and coarse aggregate corresponding to crushed stone 4005 and crushed stone 2005 in JIS A 5005 "crushed stone and crushed sand for concrete", or Fine aggregate equivalent to crushed sand was produced. In addition, in invention examples 1 and 3, both fine aggregate and coarse aggregate were produced. The pulverization rate, absolute dry density, water absorption, mass loss, wear loss, and water retention of these aggregates were measured. Table 5 shows these measurement results.

The aggregates of Invention Examples 1 to 6 had a pulverization rate of 0.5% or less. From this result, it can be seen that concrete with excellent durability and aggregate for roadbed materials can be produced. In addition, the aggregate of Invention Example 1-6 satisfies the required values for absolute dry density, water absorption, mass loss in stability tests, and abrasion loss specified in JIS A 5005, and is suitably used for roadbed materials and concrete. It was confirmed that aggregate (coarse aggregate/fine aggregate) can be produced.

On the other hand, in Comparative Example 1, since the amount of SiO ₂ was small, the viscosity of the oxide became high, and the oxide and the metal could not be separated satisfactorily. If the aggregate contains a large amount of Fe or Cr, these metals may oxidize during use, and rust juice may flow out, impairing the appearance of the aggregate. Therefore, from Comparative Example 1, it was not possible to produce an aggregate suitably used for a roadbed material or concrete.

In Comparative Example 2, only copper slag was used as a by-product and no reducing agent was included, so FeO, Fe ₂ O ₃ and Cr ₂ O ₃ remained in the oxide without being reduced. . Aggregates containing a large amount of FeO, Fe ₂ O ₃ , and Cr ₂ O ₃ are not preferable for use in roadbed materials or concrete because these metals may flow out during use. Therefore, from Comparative Example 2, it was not possible to produce an aggregate suitable for use as a roadbed material or concrete.

In Comparative Example 3, since the basicity was high, the viscosity of the oxide was high, and the oxide and the metal could not be separated satisfactorily. For this reason, the produced aggregates contained a large amount of metal, and from Comparative Example 3, it was not possible to produce aggregates suitable for roadbed materials and concrete.

In Comparative Example 4, the heat treatment temperature was low, resulting in incomplete melting, and the oxide and metal could not be separated satisfactorily. For this reason, the aggregate produced from Comparative Example 4 contained a large amount of metal, and it was not possible to produce an aggregate suitably used for roadbed materials and concrete. In addition, when the oxide of Comparative Example 4 was pulverized to a level equivalent to crushed sand to obtain fine aggregate, the water retention amount was less than 3%, and the fine aggregate was not capable of producing concrete having good properties fresh and after hardening. .

In Comparative Example 5, since the basicity was high, the viscosity of the oxide was high, and the oxide and the metal could not be separated satisfactorily. For this reason, the aggregate produced from Comparative Example 5 contained a large amount of metal, and it was not possible to produce an aggregate suitably used for roadbed materials and concrete. Furthermore, since the oxide of Comparative Example 5 was pulverized during the cooling process, the particle size distribution required for coarse aggregate having a large particle size could not be achieved.

Comparative Example 6 is a case where a large amount of Cr ore smelting reduction furnace slag is used as a by-product, and the content of MgO is large and free-MgO is present, so the aggregate pulverization rate is 1.7. % increased. For this reason, from Comparative Example 6, it was not possible to produce aggregates that can be used as concrete or roadbed materials with excellent durability.

10 Cylindrical container 12 Cylindrical part 14 Bottom part 16 Perforated plate 20 Aggregate 22 Water

Claims (9)

A method for producing aggregate by heating a by-product generated in a steel manufacturing process to separate the by-product into a metal and an oxide, and producing aggregate using the separated oxide,
The by-product is one or more selected from slag, dust, sludge and used refractories,
A raw material containing a reducing agent is added to the by-product, heated to 1300 ° C. or higher using an electric furnace,
The chemical composition of the oxide is CaO: 17% by mass or more and 59% by mass or less, SiO ₂ : 17% by mass or more and 53% by mass or less, Al ₂ O ₃ : 5% by mass or more and 45% by mass or less _, MgO: 2% by mass. 20 mass% or less, basicity (CaO/SiO ₂ ): 0.7 or more and 2.0 or less,
A method for producing an aggregate, comprising cooling an oxide heated to 1300° C. or higher so that 90% by volume or more of the oxide is crystallized, and reducing the grain size of the cooled oxide to 40 mm or less. 2. The method for producing an aggregate according to claim 1, wherein the by-product contains 1% by mass or more in total of one or more selected from metals and free carbon, and the electric furnace is a resistance heating electric furnace. The method for producing an aggregate according to claim 1 or 2, wherein the basicity (CaO/ _SiO2 ) is 0.7 or more and 1.6 or less. The method for producing an aggregate according to any one of claims 1 to 3, wherein the slag and the used refractory contain a reducing material. The method for producing an aggregate according to any one of claims 1 to 4, wherein the raw material containing the reducing material is one or more selected from coal, coke, paper sludge, waste tires and waste plastics. . The method for producing an aggregate according to any one of claims 1 to 5, wherein a raw material that adjusts the chemical composition of the oxide is further added to the by-product and heated. 7. The method for producing an aggregate according to claim 6, wherein the raw material for adjusting the chemical composition of said oxides is one or more selected from fly ash, sand and gravel. A powdering rate of 1.0% or less, an absolute dry density of 2.5 g/cm ³ or more, a water absorption of 3.0% or less, and a loss mass fraction of 12% or less in a stability test. Yes, the abrasion weight loss is 40% or less, the crystallization rate is 90% by volume or more,
The chemical composition is CaO: 17% by mass or more and 59% by mass or less, SiO ₂ : 17% by mass or more and 53% by mass or less, Al ₂ O ₃ : 5% by mass or more and 45% by mass or less _, MgO: 2% by mass or more and 20% by mass or less , Basicity (CaO/SiO ₂ ): 0.7 or more and 2.0 or less , coarse aggregate. A powdering rate of 1.0% or less, an absolute dry density of 2.5 g/cm ³ or more, a water absorption of 3.0% or less, and a loss mass fraction of 10% or less in a stability test. has a water retention amount of 3% by mass or more and 4.5% by mass or less, and a crystallization rate of 90% by volume or more,
The chemical composition is CaO: 17% by mass or more and 59% by mass or less, SiO ₂ : 17% by mass or more and 53% by mass or less, Al ₂ O ₃ : 5% by mass or more and 45% by mass or less _, MgO: 2% by mass or more and 20% by mass or less , Basicity (CaO/SiO ₂ ): 0.7 or more and 2.0 or less , fine aggregate.

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