Ph evaluation method for steelmaking slag for marine use

Abstract

To provide a method for evaluating the pH of steelmaking slag for marine use, which allows for simpler, more inexpensive, and more accurate evaluation of the pH of steelmaking slag even in brackish water areas where the pH buffering effect is weak.SOLUTION: The pH of seawater in which steelmaking slag for marine use is immersed is estimated using the following regression equation (1) based on the pH measured by immersing the steelmaking slag in purified water and an index indicating the pH buffering capacity of seawater. Regression equation (1): Y=(α1*E+α2)*X+(β1*E+β2). In equation (1), Y is the pH of seawater, X is the pH measured by immersing steelmaking slag in purified water, E is an index indicating the pH buffering capacity of seawater, and α1, α2, β1, and β2 are constants determined by regression analysis.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the pH of steelmaking slag intended for marine use. [Background technology]

[0002] Steelmaking slags, such as pre-processed slag, converter slag, electric furnace slag, and cast slag, generated at steelworks are used for roadbeds and other civil engineering and construction materials. These steelmaking slags are also used in marine areas as base materials for seaweed bed development and as fertilizers. Because steelmaking slag contains water-soluble free CaO (free lime) and Ca(OH)2, their use as base materials for seaweed bed development and as fertilizers can cause problems when they come into contact with environmental waters such as river water and seawater, or rainwater, resulting in the elution of calcium ions and alkali (hydroxide ions), causing the water to become cloudy. To address this issue, one method for insolubilizing the water-soluble calcium components in steelmaking slag is to react steelmaking slag with carbonation, which involves reacting steelmaking slag with carbon dioxide.

[0003] Steelmaking slag, the amount of alkali elution of which has been reduced by various methods, undergoes pH evaluation to determine whether it can be dumped into the sea. pH evaluation of steelmaking slag is mainly carried out at the steelmaking slag production site or near the slag yard, and a simple method is used. Specifically, a commonly used method involves dumping a slag sample into artificial seawater, stirring it, and measuring the pH after a certain period of time has passed.

[0004] Here, the "pH evaluation of steelmaking slag" refers to the process of obtaining quantitative indicators related to the alkaline elution of steelmaking slag and the increase in seawater pH. Therefore, in the following, the criteria for determining whether steelmaking slag can be dumped into the sea and the process of making that determination are not included in the pH evaluation method.

[0005] One specific example of a pH evaluation method is the "pH, cloudiness test method" described in Non-Patent Document 1. In this test method, a slag sample is filled to a height of 40 mm in a container with a diameter of φ80 mm and a height of 50 mm, and the container and the slag sample are immersed in artificial seawater with a volume five times the weight of the sample. After 30 minutes or more have passed, an elution operation is performed in which the outer periphery of the container is stirred 10 times at a cycle of once per second, and the pH of the seawater is measured.

[0006] Another pH evaluation method similar to the above-mentioned "pH, White Cloudiness Test Method" is the Geotechnical Society standard JGS T 211, "pH Test Method for Soil Suspensions." In this test method, a sample is directly placed in a beaker containing distilled water, suspended with a stirring rod, and the pH of the distilled water is measured after 30 minutes or more have passed. When evaluating the pH of steelmaking slag before it is dumped into the sea, the same test method is used, except that the distilled water is replaced with artificial seawater and the soil is replaced with steelmaking slag. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Guide to Marine Use of Converter Steelmaking Slag, Japan Iron and Steel Federation, 2008, 50 pages Summary of the Invention [Problem to be solved by the invention]

[0008] If the sea area where steelmaking slag is dumped is brackish, the ion concentrations of all elements present in seawater tend to be low when freshwater mixes with seawater. This reduces the pH buffering effect of seawater (the ability to make the pH less susceptible to change), which may make the seawater's pH more likely to increase when steelmaking slag is dumped.

[0009] Although all of the above pH evaluation methods are simple to operate, they use artificial seawater and have not been used to evaluate the seawater in the area where steelmaking slag is actually dumped. Therefore, it is not possible to properly evaluate the pH of steelmaking slag in brackish water areas where the pH buffering effect is weak.

[0010] One method that may seem to solve this problem is to use seawater (actual seawater) collected from the target sea area where steelmaking slag is actually dumped as the solvent for pH evaluation, rather than artificial seawater. However, when using actual seawater, the pH of steelmaking slag is evaluated using actual seawater for each production lot, which requires large amounts of actual seawater to be delivered to the steelmaking slag inspection site.

[0011] To do this, first, large amounts of actual seawater must be collected from the target sea area using an electric pump or similar. Next, the seawater must be transported to the slag testing site, but since the target sea area and the steelmaking slag testing site are often far apart, significant transportation costs are required. Furthermore, a space is required to store large amounts of actual seawater at the testing site after transportation. From these perspectives, evaluating the pH of steelmaking slag using actual seawater inherently requires a lot of effort and expense.

[0012] In light of the above issues, there is currently a need for a simple, inexpensive, and more accurate method for evaluating the pH of steelmaking slag in each target sea area, even in brackish waters where the pH buffering effect is weak.

[0013] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a method for evaluating the pH of steelmaking slag for marine use, which enables the pH evaluation of steelmaking slag to be carried out more simply, inexpensively, and with greater accuracy, even in marine areas that are brackish waters with little pH buffering effect. [Means for solving the problem]

[0014] In order to solve the above problems, the present inventors conducted extensive research and came up with the idea of ​​performing a regression analysis that takes into account an index indicating the pH buffering capacity of seawater, and discovered that the number of samples of pH measured using actual seawater should be limited to a level that allows regression analysis of the causal relationship with the index indicating the pH buffering capacity of seawater. Based on this discovery, the present inventors conducted further research and have completed the present invention as described below. The gist of the present invention, which was completed based on these findings, is as follows.

[0015] [1] A method for evaluating the pH of steelmaking slag intended for marine use, in which the pH of seawater in which steelmaking slag intended for marine use has been immersed is estimated using the following regression equation (1) based on the pH measured by immersing the steelmaking slag in purified water and an index indicating the pH buffering capacity of the seawater. Y = (α1·E + α2)·X + (β1·E + β2) regression equation (1) Here, in the above regression equation (1), Y: pH of seawater X: pH measured after immersing the steelmaking slag in the purified water E: An index showing the pH buffering capacity of seawater α1, α2, β1, β2: Constants determined by regression analysis is. [2] A method for evaluating the pH of steelmaking slag intended for marine use, in which the pH of seawater in which steelmaking slag intended for marine use has been immersed is estimated using the following regression equation (2) based on the pH measured by immersing the steelmaking slag in purified water and an index indicating the pH buffering capacity of the seawater. Y = α3·X + (β3·E + β4) Regression equation (2) Here, in the above regression equation (2), Y: pH of seawater X: pH measured after immersing the steelmaking slag in the purified water E: An index showing the pH buffering capacity of seawater α3, β3, β4: Constants determined by regression analysis is. [3] A method for evaluating the pH of steelmaking slag intended for marine use according to [1], in which the solute concentration of seawater is used as an index showing the pH buffering capacity of the seawater. [4] A method for evaluating the pH of steelmaking slag intended for marine areas according to [1], in which a physical quantity correlated with the solute concentration of seawater is used as an index showing the pH buffering capacity of the seawater. [5] A method for evaluating the pH of steelmaking slag intended for marine use, as described in [1], in which the pH of seawater after adding a predetermined amount of alkaline substance is used as an indicator of the pH buffering capacity of the seawater. [6] A method for evaluating the pH of steelmaking slag intended for marine use described in [1], in which α1 = 0 in the regression equation (1) is set to estimate the pH of seawater in which the steelmaking slag intended for marine use is immersed. [7] A method for evaluating the pH of steelmaking slag intended for marine use, as described in [2], in which the solute concentration of seawater is used as an index showing the pH buffering capacity of the seawater. [8] A method for evaluating the pH of steelmaking slag intended for marine use, as described in [2], in which a physical quantity correlated with the solute concentration of seawater is used as an index showing the pH buffering capacity of the seawater. [9] A method for evaluating the pH of steelmaking slag intended for marine use, as described in [2], in which the pH of seawater after adding a predetermined amount of alkaline substance is used as an indicator of the pH buffering capacity of the seawater.

[10] The method for evaluating the pH of steelmaking slag intended for marine use according to any one of [1] to [9], wherein the steelmaking slag is slag that has been subjected to a carbonation treatment. [Effects of the Invention]

[0016] As described above, according to the present invention, it is possible to evaluate the pH of steelmaking slag more simply, inexpensively, and with greater accuracy, even if the target sea area is a brackish water area with little pH buffering effect. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram showing an example of the flow of regression analysis for obtaining a regression equation used in a method for evaluating the pH of steelmaking slag intended for marine use in an embodiment of the present invention. [Figure 2] 1 is a graph showing the relationship between the electrical conductivity of seawater and the pH of seawater after addition of NaOH. [Figure 3]FIG. 1 is a graph showing the relationship between the pH when an alkaline material is added to artificial seawater and the pH when an alkaline material is added to purified water. [Figure 4] 1 is a flow chart showing the flow of the method for evaluating the pH of steelmaking slag intended for marine use according to the embodiment. [Figure 5] FIG. 1 is a graph showing the relationship between the measured pH value of slag when immersed in seawater and the estimated pH value using a regression equation for each example of the present invention. [Figure 6] FIG. 1 is a graph showing the relationship between the measured pH value of slag when immersed in seawater and the estimated pH value using a regression equation for each comparative example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0019] (Focus on steelmaking slag) The steelmaking slag intended for marine use, which is a by-product generated in the steelmaking process of the iron and steel industry, is in the form of powder or granules. Examples of such steelmaking slag include converter slag, electric furnace slag, pre-treated slag, decarburization slag, desulfurization slag, dephosphorization slag, desiliconization slag, electric furnace oxidizing slag, electric furnace reducing slag, secondary refining slag, and ingot casting slag. Furthermore, such steelmaking slag may be in the form of a powder or granule mixture of the above-mentioned various slags.

[0020] Furthermore, the steelmaking slag intended for marine use that is the focus of the present invention may be obtained by carbonating the various steelmaking slags described above (so-called carbonated slag). The carbonation conditions for obtaining the carbonated slag are not particularly limited. For example, the carbonated slag may be obtained by stirring steelmaking slag in a carbon dioxide gas atmosphere, by bringing steelmaking slag into contact with water containing carbon dioxide to carbonate it, or by aging steelmaking slag outdoors for a long period of time to carbonate it.

[0021] In this embodiment, the particle size of the steelmaking slag is not particularly specified. The particle size of the steelmaking slag may be adjusted to the particle size when actually dumped into the sea, or may be sampled by dividing it into smaller pieces so that the sample to be evaluated is representative.

[0022] (Regarding regression analysis taking into account the pH buffering capacity of seawater) Next, before explaining the pH evaluation method for steelmaking slag intended for marine use (hereinafter abbreviated as "pH evaluation method") according to an embodiment of the present invention, we will first explain the regression analysis that takes into account the pH buffering capacity of seawater, as discovered by the present inventors.

[0023] As mentioned above, the present inventors came up with the idea of ​​performing a regression analysis that takes into account the pH buffering capacity of seawater in order to realize a pH evaluation method that takes into account the pH buffering capacity of seawater. Figure 1 is a schematic diagram showing an example of the flow of regression analysis for obtaining a regression equation used in a pH evaluation method for steelmaking slag intended for marine use in an embodiment of the present invention. In such regression analysis, as shown schematically in Figure 1 and described in detail below, (a) an investigation of the pH buffering capacity of seawater, (b) an investigation of pH changes when steelmaking slag is immersed in seawater and purified water, and (c) a regression analysis using the obtained investigation results are carried out.

[0024] Here, the order in which the above (a) investigation of the pH buffering capacity of seawater and (b) investigation of the pH change when steelmaking slag is immersed in seawater and purified water, respectively, is carried out is not particularly specified, and investigation (b) may be carried out after investigation (a), investigation (b) may be carried out after investigation (a), or investigation (a) and investigation (b) may be carried out in parallel. The contents of these (a) to (c) will be explained in detail below.

[0025] <(a) Investigation of the pH buffering capacity of seawater> In this embodiment, the pH buffering capacity of seawater refers to its ability to suppress an increase in pH in the phenomenon in which alkali elutes from steelmaking slag immersed in seawater, causing the seawater's pH to rise. In other words, the higher the pH buffering capacity of seawater, the lower the pH of the seawater after immersion in steelmaking slag. To investigate the pH buffering capacity of seawater, various characteristics of seawater that are related to the pH buffering capacity of seawater are measured using different actual seawater samples collected from various locations. More specifically, physical quantities that serve as indicators of the pH buffering capacity of seawater are measured using different actual seawater samples collected from various locations. Below, examples of physical quantities that serve as indicators of the pH buffering capacity of seawater are described.

[0026] [Solute concentration in seawater] An example of a physical quantity that serves as an index of the pH buffering capacity of seawater is the solute concentration of seawater. The solute concentration is also expressed as salt content, salt concentration, or solid content, and is measured as a physical quantity such as the solute mass per unit volume, mass concentration, or volume concentration. The solute concentration may be measured by a so-called heat drying method or by using various known measuring devices. The solute concentration may also be determined indirectly from a physical quantity that has a correlation with the solute concentration, as described below.

[0027] [Physical quantities correlated with solute concentrations in seawater] Alternatively, a physical quantity correlated with the solute concentration of seawater may be used as an index of the pH buffering capacity of seawater, such as the concentration of a specific component contained in seawater or a physical quantity other than concentration that can be obtained by analyzing seawater using various methods.

[0028] For example, the "concentration of a specific component contained in seawater" includes the calcium concentration, potassium concentration, magnesium concentration, sodium concentration, chlorine concentration, silicon and silicic acid concentration, sulfur concentration, sulfate ion concentration, etc. These various component concentrations are physical quantities that have a positive correlation with the solute concentration in seawater.

[0029] Furthermore, examples of "physical quantities other than concentration that can be obtained by analyzing seawater using various methods" include the refractive index, electrical resistivity, electrical conductivity (EC), specific gravity, density, freezing point, melting point, and specific heat of seawater. Of these physical quantities, the refractive index, electrical conductivity, specific gravity, and density are physical quantities that have a positive correlation with the solute concentration of seawater. Furthermore, the electrical resistivity, freezing point, melting point, and specific heat are physical quantities that have a negative correlation with the solute concentration of seawater.

[0030] The above physical quantities can be measured using various known measurement methods, and the measurement method is not particularly limited in this embodiment. For example, among the above physical quantities, electrical conductivity (EC) is a physical quantity that can be measured accurately with simple operations, and therefore, attention may be paid to electrical conductivity (EC) as an indicator of the pH buffering capacity of seawater. Electrical conductivity can be measured by the method specified in JIS K0130:2008 "General Rules for Measuring Electrical Conductivity," and compact, portable meters equipped with electrode cells for electrical conductivity are also commercially available. Therefore, accurate measurements can be made with simple operations.

[0031] [Seawater pH after adding alkaline substances] Furthermore, as an index showing the pH buffering capacity of seawater, attention may be paid to the pH of seawater itself after adding a predetermined amount of alkaline substance (for example, a strong alkaline substance).

[0032] The alkaline substance to be added to the collected seawater is not particularly limited, but it is preferable to use a substance that is highly soluble in seawater and is readily available and safe. Furthermore, such an alkaline substance may be solid or liquid at room temperature. Examples of such alkaline substances include sodium hydroxide (NaOH) and potassium hydroxide (KOH).

[0033] The amount of alkaline substance to be added is not particularly limited, and may be, for example, within the range of 1.0 to 5.0 mmol / L in terms of hydroxide ion concentration.

[0034] A specific example is a method in which sodium hydroxide (NaOH) reagent is added to seawater so that the concentration of NaOH increases by 1.0 mmol / L, the mixture is stirred, and the pH is measured after the pH has stabilized. The pH measured by this method is almost independent of the pH of the seawater before addition, and is related to the pH buffer capacity. In other words, the higher the pH buffer capacity, the lower the pH.

[0035] An example of the relationship between the electrical conductivity of seawater and the pH of seawater after adding NaOH is shown in Figure 2. Figure 2 is a scatter plot showing the relationship between electrical conductivity (EC) and the pH measured by adding NaOH reagent at a concentration equivalent to 1.0 mmol / L for five types of seawater (actual seawater) collected from different locations.

[0036] As is clear from the distribution of plots in Figure 2, when the electrical conductivity of seawater is high, the pH of seawater after the addition of NaOH is low. Conversely, when the electrical conductivity of seawater is low, the pH of seawater after the addition of NaOH is high. These results show that there is a negative correlation between the electrical conductivity of seawater and the pH of seawater after the addition of NaOH. As shown in Figure 2, each plot can be considered to be located near a straight line with a negative slope, and it is clear that the pH of seawater after the addition of NaOH can be used as an indicator of pH buffering capacity.

[0037] In this embodiment, the electrical conductivity may be estimated from the pH of seawater after addition of NaOH, and the estimated value of the electrical conductivity may be used as an index of the pH buffering capacity.

[0038] <(b) Investigation of pH changes when steelmaking slag is immersed in seawater and purified water> To investigate pH changes in steelmaking slag, the steelmaking slag is immersed in seawater and purified water as solvents, and the pH after immersion in seawater and the pH after immersion in purified water are measured.

[0039] [pH measurement range] <Seawater pH measurement range> In this embodiment, the pH range to be evaluated is not particularly specified. However, it is important to be able to determine from the evaluation results whether or not turbidity occurs when steelmaking slag is immersed in seawater. The pH at which seawater can become turbid is generally within the range of 9.0 to 9.5, although this depends on the seawater in question. Therefore, it is important to design an evaluation method that can evaluate a pH within this range.

[0040] Therefore, when investigating the change in pH when steelmaking slag is immersed in seawater, it is preferable to include tests under conditions where the pH of the steelmaking slag after immersion in seawater is less than 9.0, as well as tests under conditions where the pH of the steelmaking slag after immersion in seawater is 9.0 to 9.5, and tests under conditions where the pH of the steelmaking slag after immersion in seawater is greater than 9.5.

[0041] <Purified water pH measurement range> FIG. 3 is a scatter plot showing the relationship between the pH of artificial seawater after the addition of an alkaline material and the pH of purified water in a test in which an alkaline material was added to each of artificial seawater and purified water.

[0042] In this test, the types of alkaline materials added were NaOH solution (titration), Ca(OH)2 reagent, and converter slag powder (particle size 200 μm or less), and the test was conducted by changing the amount added as test conditions.

[0043] When adding the NaOH solution and Ca(OH)2 reagent, the solution was added to the solvent (artificial seawater and purified water), followed by stirring with a stirrer, and the pH was recorded once the pH stabilized. The converter slag powder was added to the solvent (artificial seawater and purified water), followed by stirring with a stirrer for 10 seconds, and the pH was recorded after 30 minutes. The pH measurement results are plotted in Figure 3.

[0044] 3, it can be seen that for all alkaline materials, linearity is obtained for purified water in the pH range of 10.0 or higher and artificial seawater in the pH range of approximately 8.0 to 10.0. As will be described in detail below, the pH evaluation method according to this embodiment uses regression analysis, but it can be seen that if the pH range of the purified water of interest is 10.0 or higher, the pH of seawater can be estimated from the pH of purified water even when a so-called simple regression model is used.

[0045] On the other hand, it can be seen that the slope of the linearity is different in the range of purified water pH below 10.0 compared to the range of purified water pH above 10.0. Therefore, when performing regression analysis using a simple linear model, including the range of purified water pH below 10.0 is thought to result in a large error when estimating the pH during immersion in seawater.

[0046] In light of the above, in this embodiment, it is preferable to prepare the steelmaking slag to be used for the investigation so that the pH of the steelmaking slag when immersed in purified water is in the range of 10.0 or higher.

[0047] [Immersion conditions] In this embodiment, it is important that the conditions for immersing the steelmaking slag in the solvent (seawater or purified water) are not changed for each inspection lot of the steelmaking slag in order to perform an accurate evaluation. Therefore, the relative weighing error for both the steelmaking slag and the solvent is preferably 2% or less, and more preferably 1% or less. For the same reason, the immersion time in the solvent is preferably within 2 minutes, and more preferably within 1 minute, before or after the time set for the investigation method.

[0048] Furthermore, as described above, when immersing steelmaking slag in a solvent (seawater or purified water), taking into consideration the stability of the measurement (variation and reproducibility), it is preferable that the pH of the steelmaking slag when immersed in purified water be 10.0 or higher.

[0049] The volume of each solvent used during the investigation is not particularly specified, and it should be a volume that allows the steelmaking slag used during the investigation to be thoroughly immersed. For example, the volume of the solvent used during the investigation can be 0.1 to 2.0 liters.

[0050] The mass of steelmaking slag to be immersed in each solvent is not particularly limited. However, it is preferable to adjust the mass used depending on the particle size of the steelmaking slag. For example, if the particle size distribution of steelmaking slag is 0 to 5 mm, the mass should be in the range of 30 to 200 g, and if the particle size distribution of steelmaking slag is 0 to 25 mm, the mass should be in the range of 100 to 300 g.

[0051] The immersion time of the steelmaking slag in each solvent is not particularly specified and may be set appropriately, but may be within the range of 20 to 40 minutes, for example.

[0052] The solid-liquid mass ratio (liquid mass / solid mass) is not particularly limited and may be set appropriately, but may be within the range of 5-10, for example.

[0053] The stirring conditions during immersion are not particularly limited, and for example, a stirring rod (manual), a magnetic stirrer, an electric stirrer, etc. may be used. In this case, the stirring speed may be adjusted to, for example, 60 to 100 rpm.

[0054] The conditions for immersing the steelmaking slag in purified water do not need to be the same as the conditions for immersing the steelmaking slag in seawater, but it is preferable that the difference between the conditions for immersing the steelmaking slag in seawater and the conditions for immersing the steelmaking slag in purified water be within 50% for any of the solvent volume, steelmaking slag mass, solid-liquid mass ratio, and stirring speed.

[0055] The purified water in which the steelmaking slag is immersed is not particularly limited, and any of distilled water, ion-exchanged water, pure water, and ultrapure water may be used. In this case, it is preferable to use, for example, A3 or A4 grade water as specified in JIS K0557:1998 "Water for use in testing water and wastewater." Furthermore, from the viewpoint of improving the reproducibility of pH evaluation tests, distilled water or ion-exchanged water whose pH has been adjusted to a range of 6.2 to 6.5 by aeration may be used.

[0056] <(c) Regression analysis> Next, using the data from the survey results obtained in the above (a) and (b), a regression analysis is performed to calculate a regression equation for estimating the pH of steelmaking slag after immersion in seawater. In this regression analysis, a simple regression model is used, assuming that the pH of steelmaking slag immersed in seawater is directly proportional to the pH of steelmaking slag immersed in purified water. Hereinafter, the simple regression line in such a simple regression model will be referred to as the "pH regression line."

[0057] The pH regression line equation as described above can be expressed as the following equation (101). Y=a·X + b···Formula (101) Here, in the above formula (101), Y: Estimated pH value of steelmaking slag after immersion in seawater X: pH value measured after immersing steelmaking slag in purified water a: Slope (coefficient) of the pH regression line b: Intercept of the pH regression line (constant term) is.

[0058] Here, Y may be calculated using the pH regression line of the above equation (101) to evaluate the pH of the steelmaking slag. However, in this embodiment, the constants a and b in the above equation (101) are formulated as shown in the following equations (102) and (103) taking into account the pH buffering capacity of seawater.

[0059] a=α1·E + α2 ···Eq.(102) b=β1·E + β2 ···Eq.(103) Here, in the above formulas (102) and (103), E: Index of seawater pH buffering capacity α1, α2, β1, β2: constant parameters is.

[0060] By substituting the above formulas (102) and (103) into the above formula (101), the regression equation for the pH regression line as shown in formula (104) can be obtained.

[0061] Y=(α1 E+α2) X+(β1 E+β2) Formula (104)

[0062] Here, in the above formula (104), the measured pH value when steelmaking slag is immersed in seawater, obtained in the above "(b) Investigation of pH changes when steelmaking slag is immersed in seawater and purified water", is applied as the variable Y, and the measured pH value when steelmaking slag is immersed in purified water, obtained in the above "(b) Investigation of pH changes when steelmaking slag is immersed in seawater and purified water", is applied as the variable X. Furthermore, in the above formula (104), the measured value of the index of pH buffering capacity of interest, obtained in the above "(a) Investigation of pH buffering capacity of seawater", is applied as the variable E.

[0063] Then, the constant parameters α1, α2, β1, and β2 in (104) above are determined by the least squares method. In this case, the method for evaluating the error between the measured pH value obtained by actually immersing the steelmaking slag in seawater and the estimated pH value Y calculated from the regression equation is not particularly limited, and various known methods can be used. For example, the constants α1, α2, β1, and β2 can be determined by the least squares method so that the sum of squared differences between the measured pH value obtained by actually immersing the steelmaking slag in seawater and the estimated pH value Y calculated from the regression equation is minimized.

[0064] Here, the least squares method as described above may be performed manually by a person, or may be performed using various computers with various numerical calculation applications installed.

[0065] By doing the above, it is possible to obtain the regression equation shown below in regression equation (1), which estimates the "pH of seawater after steelmaking slag is immersed in seawater" from the "measured pH value after steelmaking slag is immersed in purified water" and the "measured index of the pH buffering capacity of seawater."

[0066] Y = (α1·E + α2)·X + (β1·E + β2) regression equation (1) Here, in the above regression equation (1), Y: Seawater pH (estimated value) X: pH measured after immersing steelmaking slag in purified water E: Measured value of an index showing the pH buffering capacity of seawater α1, α2, β1, β2: Constants determined by regression analysis is.

[0067] When the constants α1, α2, β1, and β2 are determined by the least squares method, if the usefulness of the constant α1 is considered low, the estimated pH of seawater may be calculated using the following regression equation (1') in which α1 = 0 in the above regression equation (1).

[0068] Y = α2·X + (β1·E + β2) regression equation (1')

[0069] [Variations] In the above regression analysis, the constants a and b in equation (101) are formulated as in equations (102) and (103). However, in a modified example of the regression analysis according to this embodiment, the constants a and b in equation (101) may be formulated as in the following equations (105) and (106).

[0070] a=α3 Equation (105) b = β3 E + β4 Equation (106) Here, in the above formulas (105) and (106), E: Index of seawater pH buffering capacity α3, β3, β4: constant parameters is.

[0071] By substituting the above formulas (105) and (106) into the above formula (101), the regression equation for the pH regression line as shown in formula (107) can be obtained.

[0072] Y=α3·X+(β3·E+β4)...Equation (107)

[0073] Here, in the above formula (107), the measured pH value when steelmaking slag is immersed in seawater, obtained in the above "(b) Investigation of pH changes when steelmaking slag is immersed in seawater and purified water", is applied as the variable Y, and the measured pH value when steelmaking slag is immersed in purified water, obtained in the above "(b) Investigation of pH changes when steelmaking slag is immersed in seawater and purified water", is applied as the variable X. Furthermore, in the above formula (104), the measured value of the index of pH buffering capacity of interest, obtained in the above "(a) Investigation of pH buffering capacity of seawater", is applied as the variable E.

[0074] Then, the constant parameters α3, β3, and β4 in (107) above are determined in the same manner as above using the least squares method. This makes it possible to obtain the regression equation shown in the following regression equation (2), which estimates the "pH of seawater after steelmaking slag is immersed in seawater" from the "measured pH value after steelmaking slag is immersed in purified water" and the "measured index of the pH buffer capacity of seawater."

[0075] Y = α3·X + (β3·E + β4) Regression equation (2) Here, in the above regression equation (2), Y: Seawater pH (estimated value) X: pH measured after immersing steelmaking slag in purified water E: Measured value of an index showing the pH buffering capacity of seawater α3, β3, β4: Constants determined by regression analysis is.

[0076] The regression equations (1) and (2) described above were obtained by regression analysis that took into account the index of the pH buffering capacity of seawater as a variable. Therefore, by using such regression equations (1) and (2), it is possible to accurately estimate pH even when evaluating seawater from a sea area where the pH buffering capacity of seawater is reduced, such as a brackish water area.

[0077] Furthermore, the regression equations (1) and (2) described above were obtained by performing a regression analysis using the measured pH values ​​of steelmaking slag after immersion, measured using actual seawater, and the measured values ​​of the pH buffering capacity index of seawater. Therefore, these regression equations (1) and (2) can be used without further verification to estimate the pH of seawater after immersion of steelmaking slag for actual seawater different from the actual seawater used in the regression analysis. In other words, once the specific regression equations represented by regression equations (1) and (2) are obtained using the measurement results using actual seawater as described above, the pH of various seawater after immersion of steelmaking slag can be easily calculated.

[0078] Furthermore, while the regression analysis described above utilizes measurement results using actual seawater, the amount of actual seawater used for such measurements is sufficient to enable the surveys described in (a) and (b) above to be conducted. Furthermore, the number of samples of measurements using actual seawater is sufficient as long as a statistically significant number of samples is prepared for conducting the regression analysis. Therefore, the regression analysis described above does not require a large amount of actual seawater, and it is possible to conduct the regression analysis inexpensively while suppressing expenses such as the cost of transporting large amounts of actual seawater.

[0079] The regression analysis that takes into account the pH buffering capacity of seawater, which was discovered by the present inventors, has been described in detail above with reference to FIGS.

[0080] (pH evaluation method for steelmaking slag for marine use) Next, a method for evaluating the pH of steelmaking slag intended for marine use according to this embodiment, using the regression equation determined as described above, will be described in detail with reference to Figure 4. Figure 4 is a flow chart showing the flow of the method for evaluating the pH of steelmaking slag intended for marine use according to this embodiment.

[0081] The pH evaluation method for steelmaking slag intended for marine use in this embodiment is a method for evaluating the pH of seawater in which the steelmaking slag intended for marine use is evaluated, and the pH of the seawater in which the steelmaking slag is immersed is estimated using regression equation (1) or regression equation (2) based on the actual measured pH value obtained by immersing the steelmaking slag in purified water and the actual measured value of an index indicating the pH buffering capacity of the seawater being evaluated.

[0082] In more detail, as shown in Figure 4 as an example of the flow, the pH evaluation method for steelmaking slag intended for marine use in this embodiment includes the steps of immersing the steelmaking slag to be evaluated in purified water and measuring the pH (step S1), measuring the pH buffering capacity index used in the regression equation for the seawater to be evaluated (step S2), estimating the pH when the steelmaking slag is immersed in seawater using the obtained measured values ​​and a regression equation obtained in advance (step S3), and evaluating the steelmaking slag to be evaluated using the obtained estimated pH value (step S4).

[0083] Here, when the steelmaking slag to be evaluated is immersed in purified water and the pH is measured (step S1), purified water is prepared in accordance with the investigation conditions described previously in "(b) Investigation of pH changes when steelmaking slag is immersed in seawater and purified water," and the pH measurement range is set, and measurement conditions such as solvent volume, steelmaking slag mass, solid-liquid mass ratio, and stirring speed are set.

[0084] Similarly, when measuring the index of the pH buffering capacity of seawater to be evaluated (step S2), the index of the pH buffering capacity used in the regression equation can be measured in accordance with the previously explained "(a) Investigation of the pH buffering capacity of seawater."

[0085] The order in which the measurement of step S1 and the measurement of step S2 are performed is not particularly limited; the measurement of step S1 may be performed after the measurement of step S2, or the measurement of step S2 may be performed after the measurement of step S1, or the measurement of step S1 and the measurement of step S2 may be performed in parallel.

[0086] By substituting the measured values ​​obtained as described above into the variables X and E of the previously obtained regression equation (1) or regression equation (2), it is possible to easily calculate the "estimated pH value of seawater when the steelmaking slag to be evaluated is immersed in the seawater to be evaluated." In this way, the steelmaking slag to be evaluated can be evaluated using the obtained estimated pH value.

[0087] In calculating the estimated pH value of seawater, the calculation process may be performed manually by a person, or may be performed using various computers with installed numerical calculation applications.

[0088] As described above, in the pH evaluation method for steelmaking slag intended for marine use according to this embodiment, the steelmaking slag can be evaluated by a simple process of actually measuring the pH of the steelmaking slag to be evaluated when immersed in purified water and an index of the pH buffer capacity of the seawater to be evaluated, and then substituting the obtained measurements into a regression equation. Here, the seawater to be evaluated only needs to be in a volume sufficient to measure the physical quantity that serves as an index of the pH buffer capacity. Furthermore, for the various measurements described above, existing measuring equipment can be used without using special measuring equipment specialized for the pH evaluation method for steelmaking slag intended for marine use according to this embodiment. Therefore, the pH evaluation method for steelmaking slag intended for marine use according to this embodiment can accurately evaluate the pH of steelmaking slag through a simple process while reducing expenses such as the cost of transporting large amounts of actual seawater and the cost of purchasing special measuring equipment.

[0089] The pH evaluation method for steelmaking slag intended for marine use according to this embodiment has been described above with reference to Figure 4. [Example]

[0090] The pH evaluation method for steelmaking slag intended for marine use according to this embodiment will be specifically described below with reference to examples and comparative examples. Note that the examples shown below are merely examples of the pH evaluation method for steelmaking slag intended for marine use according to this embodiment, and the pH evaluation method for steelmaking slag intended for marine use according to this invention is not limited to the examples below.

[0091] <1. Preparation of steelmaking slag> To prepare steelmaking slags with different alkali elution amounts, the steelmaking slags were treated according to the following procedure. First, six types of steelmaking slag were collected from four different production sites (Production Sites 1 to 4), each with a different production location and generation period. Steelmaking slag 2 was subjected to natural aging outdoors for six months, and steelmaking slag 5 was subjected to natural aging outdoors for five months. Steelmaking slags 1 to 6 were crushed and sieved to adjust particle size. After particle size adjustment, steelmaking slag 3 and steelmaking slag 6 were immersed in tap water at a solid-liquid mass ratio of 10 for one week, with the tap water replaced daily to allow alkali elution. After immersion in tap water, the steelmaking slags were filtered and collected, and then dried in a dryer at 105°C for 12 hours.

[0092] 2. Preparation of Carbonated Slag To prepare carbonated slag with different alkali elution amounts, steelmaking slag was processed using the following procedure. First, seven types of steelmaking slag with different production locations and generation times were collected from four different production sites (Production Sites 1 to 4). Each slag was crushed, sieved to adjust particle size, and then carbonation was performed. For the carbonation process, 7 to 10% water was added in a rotary mixer or mortar mixer, and the slag was stirred in a carbon dioxide gas atmosphere (CO2 concentration 90 to 95%). Carbonated slags 1 to 7 were thus prepared.

[0093] Details of the obtained steelmaking slags 1 to 6 and carbonated slags 1 to 7 are summarized in Table 1 below.

[0094] [Table 1]

[0095] <3. Preparation and investigation of seawater> Six types of seawater were prepared from different locations and at different times. The physical quantities that serve as indicators of pH buffering capacity were measured for the six types of seawater obtained using the following two methods. [Salinity] The salinity (mass%) of each sample of seawater was measured using a portable seawater salinity meter. [pH after adding NaOH] To 100 ml of each of the obtained seawater samples, 1.0 ml of sodium hydroxide solution adjusted to a concentration of 0.1 mol / L was added, and the mixture was stirred with a stirring rod, after which the pH was measured using a portable pH meter.

[0096] The results of the seawater survey obtained as described above are summarized in Table 2 below.

[0097] [Table 2]

[0098] <4. pH measurement of each slag> 100 g of each of the steelmaking slags 1 to 6 and carbonated slags 1 to 7 were placed in a beaker containing 1.0 L of seawater. A stirring rod was immersed in the seawater and the mixture was manually stirred at a rate of once per second. The pH was measured within one minute after the stirring was completed using a portable pH meter. The measured pH was used as the pH of the slags immersed in seawater.

[0099] In addition, distilled water corresponding to JIS K0557:1998-A3 grade was prepared as purified water, and each slag sample was placed in the distilled water and the pH was measured in the same manner as above. The obtained pH value was taken as the pH of the slag when immersed in purified water.

[0100] The pH measurement results for each of the obtained slags are summarized in Table 3 below.

[0101] [Table 3]

[0102] <5. Regression analysis> The pH measurement results of each slag and the seawater survey results obtained as described above were used to perform the least squares method based on the linear regression model expressed by the above equation (104). The constants α1, α2, β1, and β2 were determined to obtain regression equation (1). That is, for the pH of steelmaking slag immersed in seawater, the constants α1, α2, β1, and β2 were determined so as to minimize the sum of squares of the difference between the measured pH value (A) and the estimated pH value (Y) obtained by regression analysis. Eight different regression equations (1) were created by changing the type of slag and whether or not the constants (α1, α2, β1, and β2) were used, as shown in Table 4 below. The calculations were performed using a computer with a numerical calculation application installed.

[0103] [Table 4]

[0104] Here, the constants α1 and β1 in regression equation (1) are coefficients of the variable E related to the pH buffering capacity of seawater. Among the conditions shown in Table 4 above, the condition in which both constants α1 and β1 are set to "none" is a condition in which pH buffering capacity is not taken into consideration.

[0105] <6. Evaluation of each regression equation obtained> The measured pH value (A) of steelmaking slag immersed in seawater was compared with the estimated pH value (Y) obtained by regression analysis, and the uncertainty (an index showing the degree of error) was calculated using the following formula. The validity of the eight regression formulas mentioned above was examined using this uncertainty. The calculated uncertainty is a value calculated in the same way as the standard deviation (σ), which is commonly used as an index of error. When the uncertainty σ was 0.200 or less, the pH evaluation method based on the obtained regression formula was deemed valid.

[0106]

number

[0107] Table 5 below shows the specific values ​​of the constants α1, α2, β1, and β2 in each regression equation, and Table 6 below shows the values ​​of the uncertainty σ obtained as described above.

[0108] [Table 5]

[0109] [Table 6]

[0110] As is clear from Table 6 above, the uncertainty σ values ​​for Examples 1 to 6 were all 0.200 or less. Furthermore, a scatter plot showing the relationship between the measured pH values ​​of the slags when immersed in seawater and the estimated pH values ​​using the regression equation for Examples 1 to 6 is shown in Figure 5. As is clear from Figure 5, the plots for each Example are concentrated near a line with a slope of 1, expressed as (measured pH value) = (estimated pH value), indicating that the regression equations for Examples 1 to 6 are able to accurately estimate the pH of each slag when immersed in seawater.

[0111] On the other hand, as is clear from Table 6 above, the uncertainty σ values ​​for Comparative Examples 1 and 2 all exceeded 0.200. Furthermore, a scatter plot showing the relationship between the measured pH values ​​of the slag when immersed in seawater and the estimated pH values ​​using the regression equation for Comparative Examples 1 and 2 is shown in Figure 6. As is clear from Figure 6, the plots for each Comparative Example are not concentrated near a line with a slope of 1, expressed as (measured pH value) = (estimated pH value), and the estimated pH values ​​obtained from the regression equation for Comparative Examples 1 and 2 had large errors. This is thought to be because the regression analysis for Comparative Examples 1 and 2 was performed without taking into account the pH buffering capacity of seawater, resulting in large errors in the estimated pH.

[0112] As described above, it has become clear that the use of the regression equations corresponding to the examples of the present invention makes it possible to accurately estimate the pH of steelmaking slag when immersed in seawater. Therefore, it is believed that even when using these regression equations to estimate the pH of steelmaking slag after immersion in unknown seawater, it is possible to accurately calculate the estimated pH value.

[0113] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0114] The embodiments disclosed herein are illustrative in all respects and are not limiting. The above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope of the appended claims, the technical scope of the present invention as described below, and the spirit thereof. For example, the components of the above-described embodiments may be arbitrarily combined within the scope that does not impair the effects of the components. Furthermore, such an arbitrary combination naturally provides the functions and effects of each of the components involved in the combination, and also provides other functions and effects that are apparent to those skilled in the art from the description of this specification.

[0115] Furthermore, the effects described in this specification are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present invention may achieve other effects that will be apparent to those skilled in the art from the description of this specification, in addition to or in place of the above-described effects.

Claims

1. A method for evaluating the pH of steelmaking slag intended for marine use, in which the pH of seawater in which steelmaking slag intended for marine use has been immersed is estimated using the following regression equation (1) based on the pH measured by immersing the steelmaking slag in purified water and an index indicating the pH buffering capacity of the seawater. Y = (α1 E + α2) X + (β1 E + β2) ... regression equation (1) Here, in the regression equation (1), Y: pH of seawater X: pH measured when the steelmaking slag was immersed in the purified water E: An index showing the pH buffering capacity of seawater α1, α2, β1, β2: Constants determined by regression analysis is.

2. A method for evaluating the pH of steelmaking slag intended for marine use, in which the pH of seawater in which steelmaking slag intended for marine use has been immersed is estimated using the following regression equation (2) based on the pH measured by immersing the steelmaking slag in purified water and an index indicating the pH buffering capacity of the seawater. Y = α3 · X + (β3 · E + β4) ... regression equation (2) Here, in the regression equation (2), Y: pH of seawater X: pH measured when the steelmaking slag was immersed in the purified water E: An index showing the pH buffering capacity of seawater α3, β3, β4: Constants determined by regression analysis is.

3. The pH evaluation method for steelmaking slag intended for marine use according to claim 1, wherein the solute concentration of seawater is used as an index showing the pH buffering capacity of the seawater.

4. The method for evaluating the pH of steelmaking slag intended for marine use according to claim 1, wherein a physical quantity correlated with the solute concentration of seawater is used as an index indicating the pH buffering capacity of the seawater.

5. 2. A method for evaluating the pH of steelmaking slag intended for marine use according to claim 1, wherein the pH of seawater after adding a predetermined amount of alkaline substance is used as an index showing the pH buffering capacity of the seawater.

6. A method for evaluating the pH of steelmaking slag intended for marine use as described in claim 1, wherein the pH of seawater in which the steelmaking slag intended for marine use is immersed is estimated by setting α1 = 0 in the regression equation (1).

7. The pH evaluation method for steelmaking slag intended for marine use according to claim 2, wherein the solute concentration of seawater is used as an index showing the pH buffering capacity of the seawater.

8. The method for evaluating the pH of steelmaking slag intended for marine use according to claim 2, wherein a physical quantity correlated with the solute concentration of seawater is used as an index indicating the pH buffering capacity of the seawater.

9. 3. A method for evaluating the pH of steelmaking slag intended for marine use according to claim 2, wherein the pH of seawater after adding a predetermined amount of alkaline substance is used as an index showing the pH buffering capacity of the seawater.

10. A method for evaluating the pH of steelmaking slag intended for marine use according to any one of claims 1 to 9, wherein the steelmaking slag is a slag that has been subjected to a carbonation treatment.

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