WO2022264797A1 - Method for estimating carbonation rate of steelmaking slag and method for carbonation treatment of steelmaking slag - Google Patents

Abstract

A method for estimating the carbonation rate of a steelmaking slag that comprises supplying a carbon dioxide-containing gas to the steelmaking slag and estimating the the carbonation rate of the steelmaking slag having been subjected to the carbonation treatment to carbonate the steelmaking slag. This method for estimating the carbonation rate of a steelmaking slag comprises: determining a function representing the estimated carbonation rate (W_%) of the steelmaking slag after the carbonation treatment, said function containing, as variables, the volume fraction (V_e) of components other than metallic iron contained in the steelmaking slag before the carbonation treatment, the particle diameter (particle size distribution) (D_s) of the particles constituting the steelmaking slag before the carbonation treatment, the apparent density (ρ_s) of the steelmaking slag before the carbonation treatment, the carbon dioxide concentration (V_CO2) in the carbon dioxide-containing gas supplied to the steelmaking slag in the carbonation treatment, and the treatment time (t) of the carbonation treatment; determining the values of the individual variables; and calculating the estimated carbonation rate (W_%) by applying the thus determined values of the variables to the function.

Description

Method for estimating carbonation rate of steelmaking slag and carbonation treatment method for steelmaking slag

The present invention relates to a method for estimating the carbonation rate of steelmaking slag and a carbonation treatment method for steelmaking slag.

Steelmaking slag is an industrial by-product generated in steel mills and is used, for example, in roadbeds and hot asphalt mixes. Steelmaking slags used for these applications must meet hydration expansion criteria to prevent road bumps and the like. JIS A 5015 "Iron and steel slag for roads" can be mentioned as such a hydration expansion standard. Hydration expansion of steelmaking slag results from hydration of free CaO (f—CaO) contained in the steelmaking slag. Therefore, in order to suppress hydration expansion of steelmaking slag, an aging treatment is performed to hydrate f-CaO in steelmaking slag in advance. However, since Ca(OH) ₂ generated by this aging treatment is water-soluble, a highly alkaline aqueous solution or cloudy water is produced when it comes into contact with water. Therefore, in order to reduce the content of water-soluble Ca components such as f-CaO and Ca(OH) ₂ in steelmaking slag, Ca components and _CO2 are reacted to form water-insoluble _CaCO3 . processing is being done. The reaction in this carbonation treatment is that Ca components (CaO and Ca(OH) ₂ ) are dissolved in water to form Ca ²⁺ and CO ₂ is dissolved in water to form CO ₃ ²⁻ , which is mainly used in steelmaking. CaCO ₃ is produced on the surface of the steelmaking slag by reacting through the adhering water on the slag surface.

Carbonation treatment of steelmaking slag is expected not only as a technique for reducing such water-soluble Ca components, but also as a technique for reducing the amount of CO ₂ emitted from steelworks. Against this background, techniques have been proposed for improving the efficiency of the carbonation treatment of steelmaking slag.

For example, Patent Literatures 1 and 2 respectively disclose techniques for suppressing granulation of steelmaking slag particles when steelmaking slag is stirred and subjected to carbonation treatment. Patent Document 1 discloses that the water content is adjusted to 0.5 to 4% by mass by drying steelmaking slag before carbonation treatment. Patent Document 2 discloses that the steelmaking slag is stirred from before carbonation to after carbonation so that the reduction rate of slag particles having a particle size of 2.36 mm or less contained in the steelmaking slag is less than 30%. .

Further, in Patent Document 3, iron and steel slag after aging treatment is stored in a pressure vessel and sealed, and a pressurized CO ₂ -containing gas is supplied to increase the pressure in the pressure vessel to 0.1 MPaG or more and 2.0 MPaG. It is disclosed to contact steel slag with a CO2 _- containing gas while maintaining the following:

Furthermore, in Patent Document 4, regarding the conditions of carbonation treatment in which a CO ₂ -containing gas having a CO ₂ concentration of 1 vol% or more and less than 100 vol% is supplied and brought into contact with steelmaking slag, the pH of water eluted from the treated slag is controlled as a multivariable function of the treatment time of carbonation treatment, the content of water-soluble Ca component contained in steelmaking slag, and the _CO2 concentration of CO2 _- containing gas.

Japanese Patent No. 6260115 Japanese Patent No. 6413451 Japanese Patent No. 6626342 Japanese Patent No. 6299375

All of Patent Documents 1 to 3 are aimed at ensuring or efficient carbonation of steelmaking slag, and do not estimate the carbonation rate of steelmaking slag after carbonation treatment. Further, in Patent Document 4, the pH of water eluted from steelmaking slag after carbonation treatment is controlled as a function including variables of f-CaO content of steelmaking slag and _CO2 concentration of _CO2 -containing gas. is shown. However, Patent Document 4 does not show estimating the carbonation rate of steelmaking slag. Therefore, in order to confirm the carbonation rate of the steelmaking slag after the carbonation treatment, there was no choice but to analyze the steelmaking slag after the carbonation treatment.

Further, referring to these documents for the description of the carbonation treatment method, Patent Documents 1 and 2 describe that the carbonation treatment conditions are set in consideration of the adjustment of the water content and the diameter of the steelmaking slag. there is However, just by setting such conditions, the variation in the carbonation rate still cannot be reduced, and the target carbonation rate is sometimes not achieved. In addition, as in Patent Document 3, the carbonation treatment time can be shortened compared to the carbonation treatment under atmospheric pressure by controlling the pressure in the pressurized container by performing the carbonation treatment under pressurized conditions. can. However, even if the condition setting of Patent Document 3 is adopted, the variation in the carbonation rate cannot be eliminated. Furthermore, the technique of Patent Document 4 performs carbonation treatment considering only f—CaO and Ca(OH) ₂ as phases in steelmaking slag that contribute to carbonation. As will be described later, only by considering these conditions, the variation in the carbonation rate still cannot be reduced, and the target carbonation rate is sometimes not achieved. In the conventional carbonation treatment method, since the variation in the carbonation rate is large, it is necessary to frequently confirm that the steelmaking slag after the carbonation treatment is sufficiently carbonized, which requires a lot of time and effort. .

An object of the present invention is to solve the above problems and to provide a method for estimating the carbonation rate of steelmaking slag and a method for carbonation treatment of steelmaking slag that can accurately estimate the carbonation rate of steelmaking slag after carbonation treatment. .

　ただし、式（１）において、Ｗ_％は、質量％で表した推定炭酸化率である。Ｖ_ｅは、体積％で表した、炭酸化処理前の製鋼スラグに含まれる金属鉄以外の成分の体積分率である。Ｄは、ｍｍで表した炭酸化処理前の製鋼スラグの比表面積径である。ρ_ｒ，ｉは、炭酸化処理前の製鋼スラグの見かけ密度（ρ_ｓ）の、炭酸カルシウムの密度に対する比である。ｋは、ｍｍ^２を単位とする定数である。Ｖ_ＣＯ２は、標準状態（１ａｔｍ、０℃）換算の体積％／時間（ｈ）で表した、二酸化炭素含有ガス中の二酸化炭素濃度の時間平均値である。ｔは、時間（ｈ）で表した炭酸化処理の処理時間である。Ｃは、ｍｍ^２を単位とする定数である。
［３］　製鋼スラグに二酸化炭素含有ガスを供給し、前記製鋼スラグを炭酸化させる製鋼スラグの炭酸化処理方法であって、［１］または［２］に記載の製鋼スラグの炭酸化率の推定方法において、前記推定炭酸化率（Ｗ_％）を目標とする炭酸化率として設定し、当該目標とする炭酸化率に対応した処理条件を決定し、前記処理条件にて炭酸化処理を行う、製鋼スラグの炭酸化処理方法。
［４］　前記二酸化炭素含有ガスが、炭素含有物質を反応させて発生した排ガスである、［３］に記載の製鋼スラグの炭酸化処理方法。
［５］　前記二酸化炭素含有ガスが、製鉄所内で発生する副生ガスである、［３］に記載の製鋼スラグの炭酸化処理方法。
［６］　前記二酸化炭素含有ガスが、製鉄所内で発生する副生ガスである、［４］に記載の製鋼スラグの炭酸化処理方法。 The present invention is intended to solve the above problems, and the means thereof are as follows.
[1] A method for estimating the carbonation rate of steelmaking slag, in which a carbon dioxide-containing gas is supplied to steelmaking slag to carbonize the steelmaking slag, and the carbonation rate of the steelmaking slag is estimated. There is
Volume fraction (V _e ) of components other than metallic iron contained in the steelmaking slag before the carbonation treatment, particle size (particle size distribution) (D _s ) of particles constituting the steelmaking slag before the carbonation treatment , the apparent density (ρ _s ) of the steelmaking slag before the carbonation treatment, the carbon dioxide concentration (V _CO2 ) in the carbon dioxide-containing gas supplied to the steelmaking slag in the carbonation treatment, and the carbonation treatment Determining a function representing the estimated carbonation rate (W _% ) of the steelmaking slag after the carbonation treatment, including as variables a treatment time (t) of
Determining the values of the volume fraction (V _e ), the particle size (particle size distribution) (D _s ) and the apparent density (ρ _s ), respectively;
Determining the value of the carbon dioxide concentration (V _CO2 ) and the value of the treatment time (t), respectively;
The determined volume fraction (V _e ), the particle size (particle size distribution) (D _s ), the apparent density (ρ _s ), the carbon dioxide concentration (V _CO2 ) and the treatment time (t) calculating the estimated carbonation rate (W _% ) using the function;
A method for estimating the carbonation rate of steelmaking slag, including.
[2] Using the specific surface area diameter (D) of the steelmaking slag before the carbonation treatment as the particle size (particle size distribution) (D _s ) of the particles,
said function comprises, as said variable of said apparent density (ρ _s ), the ratio (ρ _r,i ) of said apparent density (ρ _s ) to the density of calcium carbonate;
The method for estimating the carbonation rate of steelmaking slag according to [1], wherein the function is represented by the following formula (1).

However, in formula (1), W _% is the estimated carbonation rate expressed in mass %. V _e is the volume fraction of components other than metallic iron contained in the steelmaking slag before carbonation, expressed in volume %. D is the specific surface area diameter of the steelmaking slag before carbonation in mm. ρ _r,i is the ratio of the apparent density (ρ _s ) of steelmaking slag before carbonation to the density of calcium carbonate. k is a constant in units of ^mm2 . V _CO2 is the time-averaged concentration of carbon dioxide in a carbon dioxide-containing gas expressed in volume % per hour (h) under standard conditions (1 atm, 0° C.). t is the treatment time of the carbonation treatment expressed in hours (h). C is a constant in mm ² .
[3] A method for carbonating steelmaking slag by supplying carbon dioxide-containing gas to steelmaking slag to carbonize the steelmaking slag, wherein the carbonation rate of steelmaking slag is estimated according to [1] or [2]. In the method, the estimated carbonation rate (W _% ) is set as the target carbonation rate, the treatment conditions corresponding to the target carbonation rate are determined, and the carbonation treatment is performed under the treatment conditions. A carbonation treatment method for steelmaking slag.
[4] The carbonation treatment method for steelmaking slag according to [3], wherein the carbon dioxide-containing gas is an exhaust gas generated by reacting a carbon-containing substance.
[5] The carbonation treatment method for steelmaking slag according to [3], wherein the carbon dioxide-containing gas is a by-product gas generated in a steelworks.
[6] The carbonation treatment method for steelmaking slag according to [4], wherein the carbon dioxide-containing gas is a by-product gas generated in a steelworks.

According to the present invention, the carbonation rate of steelmaking slag after carbonation treatment can be accurately estimated. In addition, it becomes possible to obtain steelmaking slag processed to a target carbonation rate.

4 is a graph showing the relationship between the target carbonation rate and the actual carbonation rate in the carbonation treatment methods for steelmaking slag according to the examples and comparative examples of the present invention. 4 is a graph plotting pass/fail of actual carbonation rates with respect to recommended processing times and actual processing times in methods of carbonating steelmaking slag according to examples and comparative examples of the present invention.

[Method for estimating carbonation rate of steelmaking slag]
A method for estimating the rate of carbonation of steelmaking slag according to one embodiment of the present invention (hereinafter sometimes simply referred to as “first embodiment”) is a carbonation treatment that supplies carbon dioxide-containing gas to steelmaking slag. This is to estimate the carbonation rate of the steelmaking slag produced. The method for estimating the carbonation rate of steelmaking slag is based on the volume fraction (V _e ) of components other than metallic iron contained in steelmaking slag before carbonation treatment, the particle size of particles that make up steelmaking slag before carbonation treatment ( particle size distribution) (D _s ), apparent density of steelmaking slag before carbonation (ρ _s ), carbon dioxide concentration in carbon dioxide-containing gas supplied to steelmaking slag in carbonation (V _CO2 ), and carbonation Determining a function representing the estimated carbonation rate (W _% ) of steelmaking slag after carbonation, including as variables treatment time (t), volume fraction (V _e ), particle size (particle size distribution) (D _s ) and apparent density (ρ _s ) values, respectively, carbon dioxide concentration (V _CO2 ) values and treatment time (t) values respectively, the determined volume fraction rate (V _e ), particle size (particle size distribution) (D _s ), apparent density (ρ _s ), carbon dioxide concentration (V _CO2 ) and the treatment time (t) are used in the function to estimate the carbonation rate (W _% ).

In the first embodiment, first, based on the relationship between the properties of steelmaking slag to be subjected to carbonation treatment, the conditions of carbonation treatment, and the carbonation rate of steelmaking slag obtained, the carbonation rate of steelmaking slag after carbonation treatment A function is determined that estimates the carbonation rate. This function is the volume fraction of components other than metallic iron contained in the steelmaking slag before carbonation (V _e ), the particle size (particle size distribution) of the particles that make up the steelmaking slag before carbonation (D _s ), , the apparent density of the steelmaking slag before carbonation (ρ _s ), the carbon dioxide concentration in the carbon dioxide-containing gas supplied to the steelmaking slag (V _CO2 ), and the carbonation time (t) as variables. The function may be determined by regression analysis of the relationship between each of the variables obtained from the actually performed carbonation treatment and the carbonation rate of steelmaking slag after carbonation treatment, and may be determined by thermodynamic calculation. may decide.

In the present embodiment, the estimated or actually measured carbonation rate (W _% ) of steelmaking slag is defined by the following formula (2).

By including the volume fraction (V _e ) as a variable in the function for estimating the carbonation rate, among the phases (components) contained in the steelmaking slag to be carbonated, It is possible to remove the influence of the phases that do not exist, and the accuracy of estimating the carbonation rate is improved. In addition to f-CaO and Ca(OH) ₂ , steelmaking slag generally contains C ₃ S (3CaO.SiO ₂ ), C ₂ S (2CaO.SiO ₂ ), C ₄ AF (2CaO.(2-x) Al ₂ O ₃ .xFe ₂ O ₃ ), C ₂ F (2CaO.Fe ₂ O ₃ ), f-MgO, Mg(OH) ₂ , and metallic iron (granular iron). Of these phases, except metallic iron, reacts with carbon dioxide to form CaCO ₃ or MgCO ₃ by carbonation treatment, but metallic iron does not react with carbon dioxide. For this reason, in estimating the carbonation rate after carbonation treatment, it is considered that the estimation accuracy is improved by excluding metallic iron from consideration rather than considering all phases in the steelmaking slag. If the amounts of all the phases that contribute to carbonation are considered and evaluated, the carbonation rate of steelmaking slag after carbonation treatment can be estimated with extremely high accuracy. However, considering variations in sampling samples and errors in analysis and measurement, it is sufficient to approximate and evaluate that all phases other than metallic iron in the steelmaking slag to be treated contribute to carbonation.

The volume fraction (V _e ) is the mass of the steelmaking slag to be treated before treatment (m _s (kg)), the apparent density of the steelmaking slag to be treated before treatment (ρ _s (kg/m ³ ) ) and the content of metallic iron ( _MM-Fe (% by mass)) in the steelmaking slag to be treated, it can be calculated from the following formula (3). Here, _MM-Fe is determined by chemically analyzing the slag to be treated. As a chemical analysis method, a volumetric method (titration method) or the like can be used.

In addition, the function includes the particle size (particle size distribution) (D _s ) and apparent density (ρ _s ) of the particles that make up the steelmaking slag as variables, so that the reaction rate of the carbonation reaction is estimated. can be reflected in That is, the carbonation reaction proceeds from the surface of the particles that make up the steelmaking slag. Therefore, the reaction rate is affected by the surface area of the particles that make up the steelmaking slag. Therefore, the surface area can be estimated from the grain size and apparent density of the particles that make up the steelmaking slag. As the particle diameter (particle size distribution) (D _s ) of the particles, the specific surface area diameter (D) can be used. The specific surface area diameter (D) can be calculated from the following formula (4) using the particle size (particle size distribution) D _i of the particles constituting the steelmaking slag and the number n _i of particles having the particle size. can. Regarding the apparent density (ρ _s ), since the operation control of the carbonation treatment is usually performed by the mass of the steelmaking slag, the particles constituting the steelmaking _slag having the particle size (particle size distribution) By making it possible to convert the mass of , to the number _ni of particles having the relevant particle size, it also contributes to the derivation of the specific surface area diameter (D). Further, the particle size (particle size distribution) D _i of the particles constituting the steelmaking slag can be measured by, for example, a sieving (mesh) method. The number n _i of particles having the particle size can be calculated, for example, by dividing the weight of each sieve mesh after sieving by the weight per particle of the size of the sieve mesh.

Among the variables in the function, carbon dioxide concentration (V _CO2 ) and treatment time (t) are operating conditions that affect the carbonation reaction. There is a correlation between the two. If the carbon dioxide concentration (V _CO2 ) is high, the carbonation process proceeds quickly, so the treatment time (t) for obtaining the same carbonation rate is shortened. On the other hand, if the carbon dioxide concentration (V _CO2 ) is low, the carbonation treatment will be difficult to proceed, and the treatment time (t) for obtaining the same carbonation rate will be long. The carbon dioxide concentration (V _CO2 ) may be set to a constant value when the carbonation treatment is performed while supplying a gas having a constant carbon dioxide concentration. On the other hand, when the carbon dioxide concentration in the gas fluctuates as the reaction conditions fluctuate, such as when using an exhaust gas generated by reacting a carbon-containing substance as the carbon dioxide-containing gas, the carbon dioxide concentration (V _CO2 ) should preferably reflect the change.

As the function, it is preferable to use the one represented by the following formula (1). By using this function, the carbonation rate of steelmaking slag can be estimated with higher accuracy.

In equation (1), W _% is the estimated carbonation rate expressed in mass %. V _e is the volume fraction of components other than metallic iron contained in the steelmaking slag before carbonation, expressed in volume %. D is the specific surface area diameter of the steelmaking slag particles before carbonation in mm. ρ _r,i is the ratio of the apparent density (ρ _s ) of steelmaking slag before carbonation to the density of calcium carbonate. k is a constant in units of ^mm2 . V _CO2 is the time-averaged concentration of carbon dioxide in a carbon dioxide-containing gas expressed in volume % per hour (h) under standard conditions (1 atm, 0° C.). t is the carbonation time in hours (h). C is a constant in mm ² . Thus, the function of Equation (1) includes the ratio (ρ _r,i ) of apparent density (ρ _s ) to calcium carbonate density as a variable of apparent density (ρ _s ).

The constant C is calculated from the following formulas (5) and (6).

Here, W _%,0 in the formula indicates the carbonation rate (% by mass) actually measured for the steelmaking slag (before carbonation treatment) used for the carbonation treatment. W _d indicates the weight loss rate at 500-850° C. obtained by thermogravimetric analysis (TG). MM _CaCO3 denotes the molar mass of _CaCO3 (=100.1 g/mol). MM _CO2 denotes the molar mass of _CO2 (=44.0 g/mol). The value of _Wd corresponds to the weight reduction rate due to decarboxylation of _CaCO3 .

In addition, the constant k is the volume fraction (V _e ), the particle size (particle size distribution) of the steelmaking slag (D _s ) (the specific surface area of the steelmaking slag: D), and the apparent density ratio (ρ _r,i ). , the carbon dioxide concentration (V _CO2 ), the treatment time (t), and the residual difference between the estimated carbonation rate (W _% ) calculated by the above formula (1) from the value of the constant C and the measured carbonation rate The value that minimizes the sum of squares is determined by the following equation (7). According to the inventor's research, if the slag is steelmaking slag, the constant k is 1.0×10 −5 to 1.0×10 ⁻³ .

In the first embodiment, by analyzing and measuring the steelmaking slag used for the carbonation treatment, the volume fraction (V _e ), the particle size (particle size distribution) of the steelmaking slag (D _s ), and ρ _s are calculated. Determine each. When the above formula (1) is used as the function for estimating the carbonation rate, the actually measured carbonation rate (mass %) (W _%,0 ) is also measured. In addition, when estimating the carbonation rate in the carbonation treatment to be performed, based on the carbonation treatment conditions to be applied, and when estimating the carbonation rate in the actually performed carbonation treatment, , the above carbon dioxide concentration (V _CO2 ) and treatment time (t) are determined based on the applied carbonation treatment conditions. Then, the determined volume fraction (V _e ), particle size (particle size distribution) (D _s ) of steelmaking slag particles, apparent density (ρ _s ), carbon dioxide concentration (V _CO2 ), and treatment time (t) Estimated percent carbonation (W _% ) is calculated using the function described above.

According to the method for estimating the carbonation rate of steelmaking slag described above, it is possible to accurately estimate the carbonation rate of steelmaking slag after carbonation treatment from the properties of the steelmaking slag used for the carbonation treatment and the carbonation treatment conditions. can. Therefore, the treatment conditions can be determined so as to obtain the target carbonation rate for the carbonation treatment to be performed. In addition, it is possible to omit the analysis for confirming the carbonation rate of the steelmaking slag after the carbonation treatment, or to reduce the frequency of the analysis even when the analysis is performed.

[Method of carbonating steelmaking slag]
A carbonation treatment method for steelmaking slag according to another embodiment of the present invention (hereinafter sometimes simply referred to as "second embodiment") is a carbonation treatment for supplying carbon dioxide-containing gas to steelmaking slag, By executing the above-described first embodiment, the carbonation treatment is performed under the treatment conditions under which the target carbonation rate is obtained. In other words, the estimated carbonation rate (W _% ) is set as the target carbonation rate, the treatment conditions corresponding to the target carbonation rate are determined, and the carbonation treatment is performed under the treatment conditions.

Steelmaking slag to be treated in the second embodiment is not particularly limited as long as it is steelmaking slag generated in a steelworks and requiring carbonation treatment. Examples of such steelmaking slag include pretreatment slag generated in hot metal pretreatment processes (desiliconization, dephosphorization, and desulfurization), converter slag generated in decarburization processes in converters, and processes in electric furnaces. electric furnace slag generated in the secondary refining process, secondary refining slag generated in the secondary refining process, and ingot-making slag generated in the casting process. Only one type of steelmaking slag may be used alone, or two or more types may be mixed and used. Further, the steelmaking slag may be crushed and classified in advance to adjust the particle size, and then subjected to aging treatment. Steelmaking slag that has not been subjected to aging treatment in advance may be used, and aging and carbonation treatment may be performed simultaneously according to the present embodiment. If the steelmaking slag is pre-aged, the method may be any commonly used method such as atmospheric aging, steam aging, and pressure aging.

In the second embodiment, carbon dioxide-containing gas is supplied to steelmaking slag. As the carbon dioxide-containing gas, it is possible to use carbon dioxide gas, exhaust gas generated by a chemical reaction of carbon-containing substances, such as exhaust gas from automobiles and by-product gases from factories, and the like. In particular, the use of the exhaust gas generated by the reaction of the carbon-containing substance as the carbon dioxide-containing gas leads to a reduction in the amount of carbon dioxide released into the atmosphere, which is preferable in terms of global warming countermeasures. In addition, when the by-product gas generated in the steelworks is used as the carbon dioxide-containing gas, it is possible to perform the water insolubilization treatment of the calcium in the steelmaking slag and the treatment to suppress the emission of carbon dioxide into the atmosphere on the same site. It is efficient because it can

The carbonation treatment equipment used for carbonation treatment in the second embodiment is not particularly limited. For example, steelmaking slag is charged in advance into the carbonation treatment equipment, and carbon dioxide-containing gas is intermittently or continuously supplied to the carbonation treatment equipment for batch processing. Either slag and carbon dioxide-containing gas may be intermittently or continuously supplied to perform continuous treatment. Moreover, for batch type treatment and continuous type treatment, known reactor types such as agitation type, fluidized bed type and fixed bed type can be employed respectively. Furthermore, the pressure inside the reactor may be atmospheric or pressurized. Specific examples of equipment include a rotary kiln, a pro-share mixer, a drum mixer, a tube mill, a roller mill, a ball mill, and a cylindrical pressure vessel (autoclave).

In the second embodiment, before or during the carbonation treatment, the carbonation rate of the steelmaking slag obtained by the carbonation treatment is estimated according to the above-described first embodiment. In this case, the estimated carbonation rate (W _% ) is taken as the target carbonation rate, and the variables in the function used that do not change during the carbonation process are taken as predetermined constants. Then, the values of the variables to be controlled during the carbonation process (control variables) are determined so as to satisfy the above function, while considering the influence of the variables in the function that may fluctuate during the carbonation process. do.

As control variables, the carbon dioxide concentration (V _CO2 ) in the carbon dioxide-containing gas and the carbonation treatment time (t) can be used. When these are used as control variables, the carbon dioxide concentration (V _CO2 ) is determined based on the most recent operational performance of the carbonation facility to be used, and the target carbonation rate is determined based on the V _CO2 value. The value of t can also be determined as obtained. In addition, when using exhaust gas generated by a chemical reaction of a carbon-containing substance as the carbon dioxide-containing gas, the treatment time (t ) may be the only control variable. In this case, by continuously analyzing the carbon dioxide content of the carbon dioxide-containing gas supplied to the steelmaking slag and dividing the total amount of carbon dioxide supplied by the treatment time, the actual average carbon dioxide concentration up to that point Find the value. It is preferable to adjust the processing time (t) by feeding back the actual value of the average carbon dioxide concentration as the carbon dioxide concentration (V _CO2 ) to the above function.

In the second embodiment, the carbonation process is performed under the conditions under which the determined control variables are obtained. As a result, variation in the carbonation rate of steelmaking slag after carbonation treatment is reduced, and steelmaking slag with a small deviation from the target carbonation rate is obtained.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples.

In this example, steelmaking slag generated in the steelmaking process of an ironworks was used. The steelmaking slag was discharged into a pit, solidified and cooled, and repeatedly crushed and classified to have a particle size distribution of more than 0 mm and 40 mm or less. After the steelmaking slag was subjected to steam aging, the steam was stopped and the slag was allowed to cool. A sample sampled from the steelmaking slag after standing to cool was analyzed and measured, and the volume fraction (V _e ), the particle size (particle size distribution) of the steelmaking slag particles (D _s ) (specific surface area diameter D), the apparent density ( ρ _s ) and the actually measured carbonation rate (% by mass) (W _{%, 0} ) were obtained. Based on this result, the above-described formula (1) is determined, and using this, the recommended carbonation treatment time (t) (hereinafter referred to as recommended carbonation treatment time) was calculated. At that time, the density of calcium carbonate used for calculating the apparent density ratio (ρ _{r, i} ) from the apparent density ρ _s (3.0 g/cm ³ ) of the steelmaking slag is 2.71 g/cm ³ , and the constant k was 3.3×10 ⁻⁴ . After that, the steelmaking slag to be treated was charged into an autoclave-type carbonation treatment facility. A by-product gas generated in a steelworks was used as a carbon dioxide-containing gas, which was supplied to steelmaking slag, and the carbonation treatment according to the example was performed for the above-mentioned recommended treatment time (t). Note that the carbon dioxide concentration (V _CO2 ) of the carbon dioxide-containing gas was measured while the carbonation treatment was being performed. Based on this value, the treatment time (t) of the carbonation treatment was finely adjusted.

The carbonation treatment of the comparative example was carried out in the same manner as in the example, except that the carbonation treatment time was determined empirically based on past operational results without relying on formula (1). Note that the carbonation treatment time employed in the carbonation treatment according to the comparative example was different from the recommended treatment time calculated from the formula (1).

Table 1 shows the conditions of the carbonation treatment according to Examples and Comparative Examples. Among the carbonation treatment conditions of the comparative example, the variables and recommended treatment time were not used for the calculation of formula (1), nor were they calculated from formula (1). That is, these values are shown to facilitate comparison between the actual carbonation processing time (actual processing time) and the recommended processing time.

 

 

For steelmaking slag after carbonation treatment according to Examples and Comparative Examples, a thermogravimetric analysis (TG) was performed on a sampled sample to obtain a weight reduction rate (W _d ). In addition, the actual value of the carbonation rate (actual carbonation rate) was calculated in the same manner as the initial carbonation rate (W _%,0 ) described above. The obtained actual carbonation rate is compared with the estimated (target) carbonation rate (W _% ), and the difference between the actual carbonation rate and the estimated (target) carbonation rate (W _% ) is ±3σ (σ: standard deviation ) was judged to be acceptable (○), and that the difference exceeded ±3σ was judged to be unacceptable (×). As a result, all of the steelmaking slags of the examples were determined to be acceptable, whereas all of the steelmaking slags of the comparative examples were determined to be unacceptable. FIG. 1 shows the relationship between the target carbonation rate and the actual carbonation rate of steelmaking slag. Also, FIG. 2 shows a graph in which the pass/fail of the actual carbonation rate is plotted against the recommended processing time and the actual processing time.

From the above results, in the example in which the target carbonation rate is set as the estimated carbonation rate (W _% ) of the formula (1) and the processing time (t) of the carbonation treatment is determined, the processing time is different from that in the example. It can be seen that the actual carbonation rate closely matches the estimated carbonation rate (target carbonation rate) (W _% ) compared to the comparative example in which the carbonation treatment was performed in (t). Also, it can be seen that the actual carbonation rate closely matches the estimated carbonation rate (target carbonation rate) (W _% ) when the actual processing time substantially matches the recommended processing time.

According to the present invention, the carbonation rate of steelmaking slag after carbonation treatment can be accurately estimated. Therefore, the present invention is useful in that analysis for confirming the carbonation rate of steelmaking slag after carbonation treatment can be omitted, or even if analysis is performed, the frequency of analysis can be reduced. Further, according to another aspect of the present invention, steelmaking slag with a small deviation from the target carbonation rate can be obtained. Therefore, the present invention is also useful in that it can efficiently suppress the generation of a highly alkaline aqueous solution or cloudy water from steelmaking slag. Furthermore, when the exhaust gas generated by the reaction of the carbon-containing substance is used as the carbon-dioxide-containing gas for carbonating the steelmaking slag, the present invention provides the amount of carbon dioxide emitted into the atmosphere from the estimated carbonation rate. It is also useful in that it is possible to accurately estimate the degree of reduction in carbon dioxide emissions, and that it is possible to actually reduce carbon dioxide emissions as targeted.

Claims (6)

A method for estimating the carbonation rate of steelmaking slag, comprising supplying carbon dioxide-containing gas to steelmaking slag and estimating the carbonation rate of steelmaking slag subjected to carbonation treatment for carbonating the steelmaking slag,
Volume fraction (V _e ) of components other than metallic iron contained in the steelmaking slag before the carbonation treatment, particle size (particle size distribution) (D _s ) of particles constituting the steelmaking slag before the carbonation treatment , the apparent density (ρ _s ) of the steelmaking slag before the carbonation treatment, the carbon dioxide concentration (V _CO2 ) in the carbon dioxide-containing gas supplied to the steelmaking slag in the carbonation treatment, and the carbonation treatment Determining a function representing the estimated carbonation rate (W _% ) of the steelmaking slag after the carbonation treatment, including as variables a treatment time (t) of
Determining the values of the volume fraction (V _e ), the particle size (particle size distribution) (D _s ) and the apparent density (ρ _s ), respectively;
Determining the value of the carbon dioxide concentration (V _CO2 ) and the value of the treatment time (t), respectively;
The determined volume fraction (V _e ), the particle size (particle size distribution) (D _s ), the apparent density (ρ _s ), the carbon dioxide concentration (V _CO2 ) and the treatment time (t) calculating the estimated carbonation rate (W _% ) using the function;
A method for estimating the carbonation rate of steelmaking slag, including. Using the specific surface area diameter (D) of the steelmaking slag before the carbonation treatment as the particle size (particle size distribution) (D _s ) of the particles,
said function comprises, as said variable of said apparent density (ρ _s ), the ratio (ρ _r,i ) of said apparent density (ρ _s ) to the density of calcium carbonate;
The method for estimating the rate of carbonation of steelmaking slag according to claim 1, wherein the function is represented by the following formula (1).

However, in formula (1), W _% is the estimated carbonation rate expressed in mass %. V _e is the volume fraction of components other than metallic iron contained in the steelmaking slag before carbonation, expressed in volume %. D is the specific surface area diameter of the steelmaking slag before carbonation in mm. ρ _r,i is the ratio of the apparent density (ρ _s ) of steelmaking slag before carbonation to the density of calcium carbonate. k is a constant in units of ^mm2 . V _CO2 is the time-averaged concentration of carbon dioxide in a carbon dioxide-containing gas expressed in volume % per hour (h) under standard conditions (1 atm, 0° C.). t is the treatment time of the carbonation treatment expressed in hours (h). C is a constant in mm ² . A carbonation treatment method for steelmaking slag, wherein a carbon dioxide-containing gas is supplied to steelmaking slag to carbonize the steelmaking slag,
3. The method for estimating the carbonation rate of steelmaking slag according to claim 1 or 2, wherein the estimated carbonation rate (W _% ) is set as a target carbonation rate, and a process corresponding to the target carbonation rate Determining conditions and performing carbonation treatment under the treatment conditions;
A carbonation treatment method for steelmaking slag. The carbonation treatment method for steelmaking slag according to claim 3, wherein the carbon dioxide-containing gas is an exhaust gas generated by a reaction of a carbon-containing substance. The carbonation treatment method for steelmaking slag according to claim 3, wherein the carbon dioxide-containing gas is a by-product gas generated in a steelworks. 5. The carbonation treatment method for steelmaking slag according to claim 4, wherein the carbon dioxide-containing gas is a by-product gas generated in a steelworks.

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