Method for evaluating carbon dioxide fixation ability of calcium-containing waste

Abstract

To provide a method capable of evaluating quantitatively in a short time, when evaluating carbon dioxide fixing capacity of calcium-containing waste.SOLUTION: For at least two or more kinds of samples, the pH of a mixture to which a certain amount of water is added is held in the range of 5 or more and 9 or less with an acid, and then the calcium element concentration and the sulfur element concentration of a supernatant (1) obtained by solid-liquid separation are measured. Next, the pH of a mixture obtained by adding a certain amount of water to the residue (1) obtained by the solid-liquid separation is maintained in a range of 3 or more and less than 5 with an acid, and then the calcium element concentration and the sulfur element concentration of the supernatant (2) obtained by the solid-liquid separation are measured. Finally, a carbon dioxide fixation coefficient obtained by subtracting the total sulfur element concentration from the total calcium element concentration of the supernatant (1) and the supernatant (2) is calculated and compared to quantitatively evaluate the carbon dioxide fixation capacity of the calcium-containing waste in a short time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the carbon dioxide fixation capacity of calcium-containing waste when immobilizing carbon dioxide with calcium-containing waste. [Background technology]

[0002] Carbon dioxide accounts for approximately 90% of greenhouse gas emissions, and various methods for separating and capturing carbon dioxide are being considered. One of these methods is to fix carbon dioxide using calcium-containing substances. This method involves reacting calcium with carbon dioxide to form calcium carbonate, which is difficult to dissolve in water, and then fixing the carbon dioxide.

[0003] The ability of a material to fix carbon dioxide is evaluated by the amount and rate of fixation of carbon dioxide. Hereinafter, carbon dioxide fixation capacity is defined as the rate of fixation of carbon dioxide when carbon dioxide is absorbed using the same method. The amount of carbon dioxide fixation can usually be calculated by multiplying the rate of fixation of carbon dioxide by the reaction time.

[0004] Calcium compounds are used in various processes, such as steel manufacturing, power generation, and combustion. Most of these materials are discarded as "calcium-containing waste," such as steel slag, cinders, and soot. This "calcium-containing waste" is difficult to dispose of as is, so it is reacted with carbon dioxide in the air through aging and carbonation treatment processes to prevent heavy metal leaching and stabilize its properties. Furthermore, "calcium-containing waste" is processed and sold as concrete, cement, and soil conditioners with carbon dioxide absorption and fixation properties. Products designed to fix carbon dioxide are generally adjusted and controlled so that each product has the same carbon dioxide fixation capacity.

[0005] On the other hand, because the properties of waste are not controlled, there is a large variation in the carbon dioxide fixation rate even for waste discharged from the same process. Therefore, in order to accurately evaluate the carbon dioxide fixation rate of waste, carbon dioxide fixation tests are conducted in a simulated environment. Because pretreatment to homogenize the composition and the construction of an experimental environment are required to conduct fixation tests, it is difficult to analyze multiple samples simultaneously in parallel, and the inability to measure multiple samples in a short period of time is an issue. Furthermore, because various adjustments are made to the samples when investigating the carbon dioxide fixation rate, the carbon dioxide fixation rate calculated based on the test results often differs from the actual carbon dioxide fixation rate, which is also an issue.

[0006] Given this background, methods for quantitatively evaluating the amount and rate of carbon dioxide fixation in a sample in a short period of time have been investigated. For example, Non-Patent Documents 1, 2, and 3 propose methods for calculating the amount of carbon dioxide fixation by releasing carbon dioxide fixed in a sample through pressure, heat, or a chemical reaction and then measuring the amount. These methods are widely used to investigate the amount of carbon dioxide fixation, but because they involve evaluation after the sample has absorbed carbon dioxide, they have the drawback of being able to measure the amount of fixation but not the fixation rate.

[0007] Furthermore, Non-Patent Document 4 proposes a method for estimating the maximum amount of carbon dioxide that can be fixed from the amount of calcium element eluted. According to this method, the cation concentration (Na + , K. + , Mg 2+ , Ca 2+ ) it is possible to calculate the maximum amount of carbon dioxide that can be fixed as carbonate. However, it has been found that when the amount of carbon dioxide fixed in waste is calculated using this method, depending on the components contained, the result may differ significantly from the results of carbon dioxide fixation tests.

[0008] Meanwhile, a method has been proposed for analyzing the reaction rate of a sample by simulation, as described in Patent Document 1, for example. However, in this method, the sample to be analyzed must be divided into a plurality of cells, and many items must be measured for each cell, such as the diffusion coefficient, reaction rate constant, and the amount of carbon dioxide accumulated at a certain time, the amount of calcium hydroxide accumulated, and the amount of calcium carbonate accumulated. Although this method can perform accurate analysis, it requires a large amount of work to measure the sample, making it unsuitable for measuring a large number of samples.

[0009] Patent Document 2 proposes a method in which carbon dioxide is sprayed onto a reaction solution and the end of carbonation is determined by measuring the pH of the reaction solution. According to this method, the end of carbonation can be determined by measuring calcium ions, carbonate ions, and bicarbonate ions, and the optimal pH range for carbonation is between 8.5 and 11.8. While the progress of carbonation had previously been monitored using methods such as those described in Non-Patent Documents 1, 2, and 3, using pH as an indicator makes it easier to determine the carbonation status of a sample. However, determining the optimal pH range for carbonation of wastes other than slag requires measuring calcium ions, carbonate ions, and bicarbonate ions each time, which increases the workload when dealing with a wide variety of wastes with different properties. Furthermore, while this method requires measuring the amount of carbon dioxide fixation at two points, at the start and end of the reaction, the workload required for measuring carbon dioxide fixation remains a challenge, as measurements of carbon dioxide fixation are still performed using methods such as those described in Non-Patent Documents 1, 2, and 3. [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] Hiroaki Sato and five others, "Experimental study on the creation of a calibration curve for measuring calcium carbonate content using the gas pressure quantitative method," Geotechnical Journal, 2021, Vol. 16, No. 2, pp. 143-157 [Non-patent document 2] Hiroaki Sato and five others, "Method for measuring calcium carbonate content in steelmaking slag using ignition method," Journal of the Japan Society of Civil Engineers, Vol. 71, No. 1, pp. 14-19, 2015 [Non-patent document 3] Tomotaka Morishita and four others, "Application of Carbonate Content Measurement Method Using Carbon Dioxide Detector Tube to Steelmaking Slag," Environmental Resources Engineering, Vol. 60, No. 4, 2013, pp. 167-173 [Non-patent document 4] Umino, Madoka, and three others, "Quantitative evaluation of carbon dioxide fixation amount in steel slag and speculation of carbon dioxide fixation mechanism for the creation of a low-carbon society," Geotechnical Journal, Vol. 9, No. 4, 2014, pp. 469-478 [Patent documents]

[0011] [Patent Document 1] Patent No. 4160836 [Patent Document 2] Patent No. 5783057 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been made in view of the above circumstances, and provides a method for quantitatively evaluating the carbon dioxide fixation capacity of calcium-containing waste in a short period of time. [Means for solving the problem]

[0013] As a result of intensive research to solve the above problems, the inventors of the present invention discovered that by immersing calcium-containing waste in two stages in an aqueous solution of a specific pH range and subtracting the elemental sulfur concentration from the elemental calcium concentration in the supernatant, the carbon dioxide fixation coefficient obtained is proportional to the carbon dioxide fixation rate. By comparing these values, they have completed a method for quantitatively evaluating the carbon dioxide fixation capacity of calcium waste in a short period of time.

[0014] That is, the present invention provides the following for at least two or more types of samples: First step: A step of measuring the concentrations of calcium and sulfur elements in the supernatant (1) obtained by immersing the sample in an aqueous solution having a pH of 5 or more and 9 or less and then separating the solid from the liquid. Step 2: A step of immersing the residue (1) obtained in Step 1 in an aqueous solution having a pH of 3 or more and less than 5, and then measuring the concentrations of calcium and sulfur elements in the supernatant (2) obtained by solid-liquid separation. The third step is to calculate the carbon dioxide fixation coefficient as follows and compare the values. Carbon dioxide fixation coefficient = [(calcium concentration in supernatant (1) + calcium concentration in supernatant (2)) - (sulfur concentration in supernatant (1) + sulfur concentration in supernatant (2)] This is a method for evaluating the carbon dioxide fixation capacity of calcium-containing waste, which comprises:

[0015] (1st step) According to this configuration, in the first step, a certain amount of water is added to the sample, and the mixture is then soaked for a certain period of time while constantly adjusting the pH of the mixture to within the range of 5 to 9 using an acid such as sulfuric acid, nitric acid, or hydrochloric acid. The soaked liquid is then subjected to solid-liquid separation, and the calcium concentration (1) and sulfur concentration (1) contained in the supernatant (1) are measured. When sulfuric acid is used to adjust the pH, the sulfur concentration calculated from the amount of sulfuric acid added is subtracted from the measured value to determine the sulfur concentration eluted from the calcium-containing waste. The residue (1) obtained by solid-liquid separation of the soaked liquid is then subjected to the second step.

[0016] The ratio of calcium-containing waste to water can be set as desired, but it is necessary to immerse at least the entire calcium-containing waste in water. In this case, it is preferable to add water in an amount 1 to 100 times the weight of the calcium-containing waste, more preferably in the range of 10 to 50 times, and most preferably in the range of 10 to 50 times the weight of the sample, and the amount of water added relative to the weight of the sample should be consistent between the samples being compared.

[0017] If the amount of water is less than 1:1 relative to the calcium-containing waste, it will be difficult to extract the soluble calcium or soluble sulfur components sufficiently, which will cause variations in the analytical values. Also, if the amount of water is 100:1 or more, the calcium or sulfur element concentrations in the supernatant will be low, and may fall below the lower analytical limit.

[0018] The concentrations of calcium and sulfur elements can be measured using commonly used methods such as atomic absorption spectrometry, ICP atomic emission spectrometry, ion chromatography, and titration. However, it is preferable to use instrumental analysis such as atomic absorption spectrometry or ICP atomic emission spectrometry, which can simultaneously analyze calcium and sulfur elements.

[0019] The pH of the immersion solution can be set anywhere between 5 and 9, but it is preferable to limit the pH fluctuation of the immersion solution to within ±0.5. Because the amount of soluble calcium extracted increases with a lower pH, pH fluctuations of greater than ±0.5 can result in variations in the amount of soluble calcium extracted. If the pH of the immersion solution is greater than 9, the concentration of calcium carbonate exceeds the concentration of calcium ions at atmospheric carbon dioxide partial pressure, potentially resulting in the precipitation of some of the calcium components in the supernatant as calcium carbonate, resulting in a decrease in the calcium element concentration in the supernatant. If the pH of the immersion solution is less than 5, the amount of calcium eluted under neutral and alkaline conditions, which are highly reactive with carbon dioxide but produce low extraction amounts, cannot be evaluated, potentially resulting in poor accuracy in the carbon dioxide fixation coefficient calculated in the third step.

[0020] The soaking time can be set arbitrarily, but it is preferably 20 minutes or more. In this case, it is more preferable to make the soaking time the same for all samples being compared. If the soaking time is less than 20 minutes, the extraction of soluble calcium components will be insufficient, which will cause variations in the analytical values.

[0021] During the immersion, it is preferable to make the liquid flow in order to increase the extraction efficiency of calcium and sulfur components and reduce variation. Various methods of flowing can be selected depending on the shape of the calcium-containing waste, the equipment used for immersion, and the amount of liquid, and can be selected from magnetic stirrers, rotating stirring blades, and circulating the liquid with a pump. For samples with large particle sizes, a magnetic stirrer may not be able to stir the sample, so methods such as rotating stirring blades or circulating the liquid with a pump can also be used.

[0022] The supernatant (1) and the residue (1) can be separated by commonly used methods such as centrifugation, settling separation, and filtration separation. However, in the case of samples with small particle sizes, separation by settling separation may not be possible, and therefore it is preferable to use centrifugation, filtration separation, etc.

[0023] (2nd process) In the second step, a certain amount of water is added to the residue (1) obtained in the first step, and the mixture is immersed for a certain period of time while constantly adjusting the pH of the mixture with an acid such as sulfuric acid, nitric acid, or hydrochloric acid so that it falls within the range of 3 or more and less than 5. The calcium and sulfur element concentrations contained in the supernatant (2) obtained by solid-liquid separation of the immersion liquid are then measured. Note that when sulfuric acid is used to adjust the pH, the sulfur element concentration calculated from the amount of sulfuric acid added is subtracted from the measured value to determine the sulfur element concentration eluted from the calcium-containing waste.

[0024] The ratio of calcium-containing waste to water can be set as desired, but it is necessary to immerse at least the entire calcium-containing waste in water. In this case, it is preferable to add water in an amount 1 to 100 times the weight of the calcium-containing waste, more preferably in the range of 10 to 50 times, and most preferably in the range of 10 to 50 times the weight of the sample, and the amount of water added relative to the weight of the sample should be consistent between the samples being compared.

[0025] If the amount of water is less than 1 part relative to the calcium-containing waste, it will be difficult to sufficiently extract the soluble calcium components or soluble sulfur components, which will result in variations in the analytical values.If the amount of water is 100 parts or more, the concentration of calcium or sulfur elements in the supernatant will be low, and may fall below the lower limit of analysis.

[0026] The concentrations of calcium and sulfur elements can be measured using commonly used methods such as atomic absorption spectrometry, ICP atomic emission spectrometry, ion chromatography, and titration. However, it is preferable to use instrumental analysis such as atomic absorption spectrometry or ICP atomic emission spectrometry, which can simultaneously analyze calcium and sulfur elements.

[0027] The pH of the soaking solution can be set anywhere within the range of 3 or higher and less than 5, but it is preferable to limit the pH fluctuation of the soaking solution to within ±0.5. Because the amount of soluble calcium components extracted increases as the pH decreases, pH fluctuations of more than ±0.5 can cause variations in the amount of soluble calcium components extracted. If the pH of the soaking solution is higher than 5, the amount of calcium element eluted under weakly acidic conditions, which have low reactivity with carbon dioxide but high extraction rates, cannot be evaluated, which may result in poor accuracy of the carbon dioxide fixation coefficient calculated in the third step. If the pH of the soaking solution is lower than 3, components with low reactivity with carbon dioxide are more likely to be extracted, which may result in poor accuracy and variation of the carbon dioxide fixation coefficient calculated in the third step.

[0028] The soaking time can be set arbitrarily, but it is preferably 20 minutes or more. In this case, it is more preferable to make the soaking time the same for all samples being compared. If the soaking time is less than 20 minutes, the extraction of soluble calcium components will be insufficient, which will cause variations in the analytical values.

[0029] During the immersion, it is preferable to make the liquid flow in order to increase the extraction efficiency of calcium and sulfur components and reduce variation. Various methods of flowing can be selected depending on the shape of the calcium-containing waste, the equipment used for immersion, and the amount of liquid, and can be selected from magnetic stirrers, rotating stirring blades, and circulating the liquid with a pump. For samples with large particle sizes, a magnetic stirrer may not be able to stir the sample, so methods such as rotating stirring blades or circulating the liquid with a pump can also be used.

[0030] The supernatant (2) and the residue (2) can be separated by commonly used methods such as centrifugation, settling separation, and filtration. However, in the case of samples with small particle sizes, settling separation may not be possible, so it is preferable to use centrifugation, filtration, or the like.

[0031] (3rd step) In the third step, the carbon dioxide fixation coefficient is calculated, and the carbon dioxide fixation capacity is evaluated by comparing these values. The carbon dioxide fixation coefficient is defined as the sum of the calcium element concentrations in the supernatant obtained in steps 1 and 2 minus the sulfur element concentrations in the supernatant obtained in steps 1 and 2, according to the following formula: Carbon dioxide fixation coefficient = [(calcium concentration in supernatant (1) + calcium concentration in supernatant (2)) - (sulfur concentration in supernatant (1) + sulfur concentration in supernatant (2)]

[0032] When comparing carbon dioxide fixation coefficients, one or more samples with known carbon dioxide fixation capacity are prepared among the samples to be compared, and by repeating calculations using this as a standard, it is possible to quantitatively evaluate the carbon dioxide fixation capacity of many unknown samples. Another feature of this method is that it allows evaluation of many samples in a short amount of time compared to measuring the carbon dioxide fixation capacity of each sample individually. [Effects of the Invention]

[0033] According to the method of the present invention, two or more calcium-containing wastes are immersed in an aqueous solution of a specific pH range, and the carbon dioxide fixation coefficients obtained by subtracting the elemental calcium concentration from the elemental sulfur concentration in the resulting supernatant are compared. This makes it possible to quantitatively evaluate the carbon dioxide fixation capacity of the calcium-containing wastes in a short period of time. [Brief explanation of the drawings]

[0034] [Figure 1] FIG. 1 is a flow chart showing a process for evaluating the carbon dioxide fixation capacity of calcium-containing waste according to the present invention. [Figure 2] 1 is a flow chart showing one embodiment of the first step. [Figure 3] 10 is a flow chart showing one embodiment of the second step. [Figure 4] FIG. 10 is a diagram showing a method for calculating and comparing the carbon dioxide fixation coefficient in the third step. DETAILED DESCRIPTION OF THE INVENTION

[0035] An example of an embodiment of the present invention will be described below with reference to the drawings. As shown in Fig. 1, in the first step, a certain amount of water is added to a sample to form a mixture, the pH of which is maintained in the range of 5 or more and 9 or less, and the mixture is subjected to solid-liquid separation, and the calcium and sulfur concentrations of the supernatant (1) are measured. In the subsequent second step, a certain amount of water is added to the residue (1) obtained in the first step to form a mixture, the pH of which is maintained in the range of 3 or more and less than 5, and the calcium and sulfur concentrations of the supernatant (2) are measured by solid-liquid separation. In the third step, the carbon dioxide fixation coefficients are calculated for at least two or more samples and compared to quantitatively evaluate the carbon dioxide fixation capacity in a short period of time.

[0036] (1st step) As shown in Figure 2, first, a mixture is prepared by adding 1 to 100 times the amount of water to the sample. Next, the pH of the mixture is maintained within a range of 5 to 9 by adding acid, with fluctuations within ±0.5, and the sample is left to soak in this state for 20 minutes or more. Finally, the supernatant (1) and residue (1) are separated by solid-liquid separation, and the calcium concentration (1) and sulfur concentration (1) of the supernatant (1) are measured.

[0037] (2nd process) As shown in Figure 3, a mixture is prepared by adding 1 to 100 times the amount of water to the residue (1) obtained in the first step. Next, the pH of the mixture is maintained within a range of 3 or more and less than 5, with fluctuations within ±0.5, by adding acid, and the mixture is immersed in this state for 20 minutes or more. Finally, the supernatant (2) and residue (2) are separated by solid-liquid separation, and the calcium concentration (2) and sulfur concentration (2) of the supernatant (2) are measured.

[0038] (3rd step) As shown in Figure 4, the carbon dioxide fixation coefficient is calculated, and the carbon dioxide fixation coefficient of a sample with known carbon dioxide fixation capacity is compared with that of an unknown sample to evaluate the carbon dioxide fixation capacity of the unknown sample.

[0039] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. [Example]

[0040] The samples used in the examples are as follows. The calcium and sulfur element contents of each sample were measured using an energy dispersive X-ray fluorescence spectrometer (NEX-CG, manufactured by Rigaku). In addition, the calcium and sulfur element contents of the supernatants (1) and (2) after immersion in the liquid were measured using an ICP optical emission spectrometer (SPECTRO ARCOS, manufactured by Hitachi High-Tech Science).

[0041] Slag A: Slag discharged during steel production using an electric furnace. After being crushed, the sample was passed through a 30-mesh sieve. (Calcium content in the sample: 190,000 mg / kg, sulfur content: 1,200 mg / kg) Dust B: Dust generated at a waste incineration plant. (Calcium content in the sample: 140,000 mg / kg, sulfur content: 31,000 mg / kg) Slag C: Slag obtained from a different source than Slag A. This was slag discharged during steel production using an electric furnace. After being crushed, the sample was passed through a 30-mesh sieve. (Calcium content in the sample: 370,000 mg / kg, sulfur content: 15,000 mg / kg) Slag D: Slag obtained from a different source than Slag A and Slag C. This slag was discharged during the steelmaking process using an electric furnace. It was crushed and passed through a 30-mesh sieve. (Calcium content in the sample: 390,000 mg / kg, sulfur content: 9,400 mg / kg) Cinder E: Cinder generated at a waste incineration plant, crushed and passed through a 30-mesh sieve. (Calcium element content in the sample: 270,000 mg / kg, sulfur element content: 11,000 mg / kg) Reference Example 1

[0042] (Carbon dioxide fixation test using slag A) 5.00 g of slag A and 2.49 g of distilled water were placed in a 50 mL beaker, and while stirring with a magnetic stirrer, a certain amount of carbon dioxide was sprayed from a carbon dioxide cylinder to fix the carbon dioxide in the sample. The carbon dioxide fixation rate of slag A was 0.0972 [mg-CO2 / min]. Reference Example 2

[0043] (Carbon dioxide fixation test using soot B) 4.98 g of dust B and 2.51 g of distilled water were placed in a 50 mL beaker, and while stirring with a magnetic stirrer, a certain amount of carbon dioxide was sprayed from a carbon dioxide cylinder to fix carbon dioxide into the sample. The carbon dioxide fixation rate of dust B was 1.92 [mg-CO2 / min]. Reference Example 3

[0044] (Carbon dioxide fixation test using slag C) 4.97 g of slag C and 2.50 g of distilled water were placed in a 50 mL beaker, and while stirring with a magnetic stirrer, a certain amount of carbon dioxide was sprayed from a carbon dioxide cylinder to fix carbon dioxide into the sample. The carbon dioxide fixation rate of slag C was 3.41 [mg-CO2 / min]. Reference Example 4

[0045] (Carbon dioxide fixation test using slag D) 5.05 g of slag D and 3.30 g of distilled water were placed in a 50 mL beaker, and while stirring with a magnetic stirrer, a certain amount of carbon dioxide was sprayed from a carbon dioxide cylinder to fix carbon dioxide into the sample. The carbon dioxide fixation rate of slag D was 2.74 [mg-CO2 / min]. Reference Example 5

[0046] (Carbon dioxide fixation test using cinder E) A 50 mL beaker was charged with 5.03 g of cinder E and 4.02 g of distilled water, and while stirring with a magnetic stirrer, a certain amount of carbon dioxide was sprayed from a carbon dioxide cylinder to fix the carbon dioxide into the sample. The carbon dioxide fixation rate of cinder E was 1.65 [mg-CO2 / min].

[0047] As a summary of Reference Examples 1 to 5, a list of carbon dioxide fixation rates and the ratio of the carbon dioxide fixation rate based on slag C are shown in Table 1. An example of the experimental apparatus for the Reference Examples is shown in FIG. [Table 1] Example 1

[0048] (1st step) A 1000 mL beaker was charged with 10 g of slag A and 500 g of distilled water and stirred with a magnetic stirrer. While stirring, 1 mol / L of nitric acid was added to adjust the pH of the mixture to between 6.5 and 7.5. After 180 minutes of stirring while adjusting the pH, the pH adjustment was stopped and the supernatant A-(1) and residue A-(1) were separated using a vacuum filtration device. Supernatant A-(1) was analyzed using an ICP atomic emission spectrometer, and the calcium and sulfur concentrations were found to be 35.5 mg / L and 3.23 mg / L, respectively. The calcium and sulfur concentrations of soot B, slag C, slag D, and cinder E were also measured, as with slag A. The results are shown in Table 2. (2nd process) Next, residue A-(1) and 500 g of distilled water were placed in a 1000 mL beaker and stirred with a magnetic stirrer. 1 mol / L of nitric acid was added to adjust the pH of the mixture to between 3.5 and 4.5. After 180 minutes of stirring while adjusting the pH, the pH adjustment was stopped and the supernatant A-(2) was separated into solid and liquid phases using a vacuum filtration device. Supernatant A-(2) was analyzed using an ICP atomic emission spectrometer, revealing a calcium concentration of 95.0 mg / L and a sulfur concentration of 1.35 mg / L. The calcium and sulfur concentrations of soot B, slag C, slag D, and cinder E were measured in the same way as for slag A. The results are shown in Table 2. (3rd step) According to the formula for calculating the carbon dioxide fixation coefficient, the carbon dioxide fixation coefficients of slag A, soot B, slag C, slag D, and cinder E were calculated, and then the ratio of the carbon dioxide fixation coefficient of each sample was calculated, assuming that the carbon dioxide fixation coefficient of slag C was 1. The calculated ratios of the carbon dioxide fixation coefficients are shown in Table 2. [Table 2] The ratios (1) of the carbon dioxide fixation coefficients calculated according to the present invention, when the ratios (2) of the carbon dioxide fixation rates of the samples calculated in the carbon dioxide fixation tests of Reference Examples 1 to 5 were set at 100%, are shown in Table 3. The maximum difference between the two values ​​was 17%. [Table 3] Comparative Example 1

[0049] 10 g of slag A and 500 g of distilled water were placed in a 1000 mL beaker and stirred with a magnetic stirrer. While stirring, 1 mol / L of nitric acid was added to adjust the pH of the mixture to between 3.5 and 4.5. After 180 minutes of stirring while adjusting the pH, the pH adjustment was stopped and comparative supernatant A-(1) and comparative residue A-(1) were separated into solid and liquid forms using a vacuum filtration device. Comparative supernatant A-(1) was analyzed using an ICP atomic emission spectrometer, and the calcium and sulfur concentrations were found to be 105 mg / L and 1.50 mg / L, respectively. The calcium and sulfur concentrations of soot B, slag C, slag D, and cinder E were measured in the same way as for slag A. The results are shown in Table 4. According to the formula for calculating the carbon dioxide fixation coefficient, the carbon dioxide fixation coefficients of slag A, soot B, slag C, slag D, and cinder E were calculated, and then the ratio of the carbon dioxide fixation coefficient of each sample was calculated, assuming that the carbon dioxide fixation coefficient of slag C was 1. The calculated ratios of the carbon dioxide fixation coefficients are shown in Table 4. [Table 4] The ratios (1) of the carbon dioxide fixation coefficients calculated according to the present invention, when the ratios (2) of the carbon dioxide fixation rates of the samples calculated in the carbon dioxide fixation tests of Reference Examples 1 to 5 are set at 100%, are shown in Table 5. The difference between the two values ​​was as large as 40% at the maximum. [Table 5] Comparative Example 2

[0050] A 1000 mL beaker was charged with 10 g of slag A and 500 g of distilled water and stirred with a magnetic stirrer. While stirring, 1 mol / L of nitric acid was added to adjust the pH of the mixture to between 6.5 and 7.5. After 180 minutes of stirring while adjusting the pH, the pH adjustment was stopped and the comparative supernatant A-(2)-1 and comparative residue A-(2)-1 were separated into solid and liquid forms using a vacuum filtration device. Comparative supernatant A-(2)-1 was analyzed using an ICP atomic emission spectrometer, and the alkali metal and alkaline earth metal (sodium, potassium, magnesium, and calcium) concentrations were measured. The results are shown in Table 6. The same method was used to obtain comparative supernatant (2)-1 for dust B, slag C, slag D, and cinder E, and the alkali metal and alkaline earth metal concentrations were measured. Next, residue A-(2)-1 and 500 g of distilled water were placed in a 1000 mL beaker and stirred with a magnetic stirrer. To conform to the method described in Non-Patent Document 4, we attempted to control the pH of the mixture by adding 1 mol / L nitric acid to a range of 3.9 to 4.1. However, the pH fluctuated significantly, making it impossible to achieve a proper pH adjustment. Therefore, the pH range was limited to 3.5 to 4.5. After 180 minutes of stirring while adjusting the pH, the pH adjustment was stopped and comparative supernatant A-(2)-2 was subjected to solid-liquid separation using a vacuum filtration device. Comparative supernatant A-(2)-2 was analyzed using an ICP atomic emission spectrometer, and the alkali metal and alkaline earth metal (sodium, potassium, magnesium, calcium) concentrations were measured. The results are shown in Table 6. Comparative supernatants (2)-2 were obtained using the same method for soot B, slag C, slag D, and cinder E, and the alkali metal and alkaline earth metal concentrations were measured. The total alkali metal and alkaline earth metal concentrations of slag A, soot B, slag C, slag D, and cinder E, as well as the ratio of the total alkali metal and alkaline earth metal concentrations of each sample relative to slag C, were calculated and are shown in Table 6. [Table 6] The carbon dioxide fixation capacity (▲1▼) calculated from the ratio of the total concentration of alkali metals and alkaline earth metals when the ratio (▲2▼) of the carbon dioxide fixation rates of each sample calculated in the carbon dioxide fixation tests of Reference Examples 1 to 5 was set to 100% is shown in Table 7. The difference between the two values ​​was as large as 126% at the maximum. [Table 7]

[0051] As described above, by performing evaluation using the method of the present invention, the ability of calcium-containing waste to fix carbon dioxide can be estimated simply and with high accuracy, making it possible to effectively utilize calcium-containing waste.

Claims

1. For at least two or more types of samples, First step: A step of immersing the sample in an aqueous solution having a pH of 5 or more and 9 or less, and then measuring the concentrations of calcium and sulfur elements in the supernatant (1) obtained by solid-liquid separation. Step 2: A step of immersing the residue (1) obtained in Step 1 in an aqueous solution having a pH of 3 or more and less than 5, and then measuring the concentrations of calcium and sulfur elements in the supernatant (2) obtained by solid-liquid separation. Third step: Calculate the carbon dioxide fixation coefficient as follows and compare the values: Carbon dioxide fixation coefficient = [(calcium element concentration in supernatant (1) + calcium element concentration in supernatant (2)) - (sulfur element concentration in supernatant (1) + sulfur element concentration in supernatant (2))] A method for evaluating the carbon dioxide fixation capacity of calcium-containing waste, comprising:

2. 2. The method for evaluating the carbon dioxide fixation capacity of calcium-containing waste according to claim 1, wherein the carbon dioxide fixation capacity of at least one of the samples used is known.

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