METHOD FOR PRODUCING SUSPENSION CONTAINING CaCO3 AND METHOD FOR PRODUCING POWDER CONTAINING CaCO3

Abstract

To provide a method for producing calcium carbonate from sludge water more efficiently than conventional methods.SOLUTION: A method for producing a slurry containing CaCO3, comprising a CO2 gas injection step in which CO2 gas is injected into slurry water containing cementitious materials to obtain a slurry containing CaCO3. It is characterized by controlling the pH of the sludge water into which the CO2 gas is injected during the CO2 gas injection step to be 7 or higher. This is made possible to obtain a slurry containing CaCO3 at a higher concentration than conventional methods and provide a method for generating calcium carbonate from sludge water more efficiently than conventional methods.SELECTED DRAWING: Figure 13

Description

[Technical Field]

[0001] The present invention relates to a method for producing a CaCO3-containing suspension and a method for producing a CaCO3-containing powder, and in particular to a method for producing a CaCO3-containing suspension by injecting CO2 gas into sludge water containing a cement-based material to obtain a CaCO3-containing suspension, and a method for producing a CaCO3-containing powder by obtaining a CaCO3-containing powder from the suspension. [Background technology]

[0002] Sludge water is water collected from washing vehicles and concrete mixers at ready-mix concrete plants, with aggregate removed, and if the concentration is below a certain level, this sludge water can be reused as concrete mixing water. However, this recycling does not mean that all sludge water can be treated, and the solids in the sludge water remaining after recycling are separated and treated as industrial waste.

[0003] Furthermore, in addition to reusing sludge water as it is as mixing water for concrete, there are also known techniques for recovering components from the sludge water.

[0004] Patent Documents 1 and 2 disclose techniques for separating and recovering calcium carbonate, a useful resource, from sludge water.

[0005] Specifically, Patent Documents 1 and 2 disclose a concrete sludge treatment device that includes an elution reaction device that elutes calcium into a liquid from concrete sludge water or dewatered concrete sludge discharged during the production of concrete or concrete products and the cleaning of equipment used in the production, a precipitation reaction device that precipitates calcium carbonate from the liquid into which the calcium has been eluted, and carbon dioxide supply means that supplies carbon dioxide to the precipitation reaction device main body.

[0006] According to this concrete sludge treatment device, calcium eluted from concrete sludge such as sludge water reacts with carbonate ions derived from carbon dioxide supplied from a carbon dioxide supply means in the precipitation reaction device body to produce calcium carbonate. The obtained calcium carbonate can then be recycled as a resource, and the recycled calcium carbonate can be used, for example, as a cement material or a desulfurization agent.

[0007] Furthermore, Patent Document 3 discloses a method for treating concrete waste, which comprises contacting concrete waste with carbon dioxide gas, then immersing the concrete waste in water containing carbon dioxide gas, followed by solid-liquid separation, and boiling the filtrate to obtain carbonates.

[0008] According to this method for treating waste concrete, it is possible to obtain recycled aggregate and cement extender with low water absorption from waste concrete, and at the same time, it is possible to recover highly pure calcium carbonate from waste concrete. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-136770 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-279552 [Patent Document 3] Japanese Patent Application Publication No. 11-319765 Summary of the Invention [Problem to be solved by the invention]

[0010] As mentioned above, the techniques disclosed in Patent Documents 1 and 2 can obtain calcium carbonate from concrete sludge such as sludge water, but the pH of the sludge water decreases due to the continuous supply of carbon dioxide. CO2 is in equilibrium with bicarbonate ions and carbonate ions in water, but under low pH conditions, the equilibrium shifts to the CO2 side, so the carbonate ions decrease, and the carbonate ions and Ca 2+The reaction with CaCO3 is inhibited.

[0011] According to the concrete waste treatment method described in Patent Document 3, calcium carbonate is obtained from concrete waste, but no method for obtaining calcium carbonate from sludge water is disclosed. In addition, the produced calcium carbonate is first dissolved in water as calcium hydrogen carbonate, and then boiled to decompose it, thereby obtaining calcium carbonate, which involves many steps and requires energy and labor.

[0012] Therefore, there has been a demand for a method for producing calcium carbonate from sludge water more efficiently than before.

[0013] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing calcium carbonate from sludge water more efficiently than conventional methods. [Means for solving the problem]

[0014] The present inventors have conducted extensive research to achieve the above object, and as a result have found that a suspension containing CaCO3 at a higher concentration than conventional suspensions can be obtained by controlling the pH at 7 or higher when CO2 gas is blown into the sludge water, which led to the completion of the present invention.

[0015] That is, it has been found that the above-mentioned object can be achieved by a method for producing a suspension containing CaCO3, which includes a CO2 gas injection step of injecting CO2 gas into sludge water containing cement-based materials to obtain a suspension containing CaCO3, and which is characterized in that in the CO2 gas injection step, the pH of the sludge water into which CO2 gas has been injected is controlled to 7 or higher.

[0016] It is also preferable that the pH is controlled by stopping the injection of CO2 gas when the pH value decreases as a result of the injection of CO2 gas, and restarting the injection of CO2 gas when the pH value increases as a result of the elution of alkaline components from the cementitious material.

[0017] Furthermore, it is preferable that the pH is controlled by dissolving an alkaline component from the cementitious material and supplying an alkaline component from the outside.

[0018] The above-mentioned object can also be achieved by a method for producing powder containing CaCO3, which includes a CO2 gas injection step of injecting CO2 gas into sludge water containing cementitious materials to obtain a suspension containing CaCO3, and a solid-liquid separation step of performing solid-liquid separation of the CaCO3-containing suspension to obtain powder containing CaCO3, wherein the pH of the sludge water into which CO2 gas has been injected is controlled to 7 or higher in the CO2 gas injection step. [Effects of the Invention]

[0019] According to the method for producing a suspension containing CaCO3 and the method for producing a powder containing CaCO3 of the present invention, the pH of the sludge water into which CO2 gas has been injected is controlled at 7 or more in the CO2 gas injection step, so that the equilibrium between CO2, bicarbonate ions, and carbonate ions in the sludge water shifts to the carbonate ion side, and the carbonate ions and Ca 2+ This promotes the reaction with CaCO3 to form CaCO3.

[0020] Therefore, a suspension containing CaCO3 at a higher concentration than conventionally can be obtained, and a method for producing calcium carbonate from sludge water more efficiently than conventionally can be provided. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a flow diagram showing a method for producing a CaCO3-containing suspension of the present invention. [Figure 2] FIG. 1 is a flow chart showing a method for producing a powder containing CaCO3 according to the present invention. [Figure 3] This is an equilibrium diagram of carbonate species in seawater at a practical salinity of S=35 and a temperature of t=25°C. [Figure 4]1 is a graph showing the changes over time in the pH and dissolved CO 2 concentration (mg / L) of simulated sludge water under the CO 2 gas injection conditions of Test Examples 1-1 to 1-2 and Test Example 2. [Figure 5] 1 is a graph showing the change over time in pH of simulated sludge water under CO 2 gas injection conditions in Test Examples 3-1 to 3-9. [Figure 6] 1 is a graph showing the change over time in pH of simulated sludge water under CO 2 gas injection conditions in Test Examples 4-1 to 4-6. [Figure 7] 1 is a graph showing the change over time in pH of simulated sludge water under CO 2 gas injection conditions in Test Examples 5-1 to 5-6. [Figure 8] 1 is a graph showing the change over time in the dissolved CO 2 concentration (mg / L) of simulated sludge water under the CO 2 gas injection conditions of Test Examples 3-1 to 3-9. [Figure 9] 1 is a graph showing the change over time in the dissolved CO 2 concentration (mg / L) of simulated sludge water under the CO 2 gas injection conditions of Test Examples 4-1 to 4-6. [Figure 10] 1 is a graph showing the change over time in the dissolved CO 2 concentration (mg / L) of simulated sludge water under the CO 2 gas injection conditions of Test Examples 5-1 to 5-6. [Figure 11] 10 is a graph showing the changes over time in the pH and dissolved CO 2 concentration (mg / L) of simulated sludge water under the CO 2 gas injection conditions of Test Examples 6-1 to 6-2 and Test Example 7, which are in the intermittent supply section. [Figure 12] 1 is a graph showing the change in CH(Ca(OH)2) concentration (wt%) in simulated sludge water due to differences in the cumulative amount of CO2 gas supplied after carbonation treatment in each test example. [Figure 13] 1 is a graph showing the change in CC (CaCO3) concentration (wt%) in simulated sludge water due to differences in the cumulative amount of CO2 gas supplied after carbonation treatment in each test example. [Figure 14] 1 is a graph showing the amount of fixed CO2 (wt%) depending on the difference in the cumulative amount of CO2 gas supplied after carbonation treatment in each test example. DETAILED DESCRIPTION OF THE INVENTION

[0022] <Method for producing a suspension containing CaCO3> The method for producing a suspension containing CaCO3 according to the present invention has a CO2 gas injection step (S110) as shown in FIG. 1.

[0023] [CO2 gas injection step (S110)] In this step, CO2 gas is injected into the sludge water containing the cementitious material to obtain a suspension containing CaCO3.

[0024] Here, the cementitious material is a material for forming a cement hardened body including cement. Cement is an inorganic binder that exhibits curability when kneaded with water, and examples thereof include hydraulic cement. As the hydraulic cement, simple cements such as Portland cement (JIS R5210), hydraulic lime, Roman cement, and natural cement may be used, or mixed cements (JIS R5211, R5212, R5213) such as lime mixed cement and mixed Portland cement may be used.

[0025] The cementitious material may contain aggregates. Aggregates are generally used in the production of concrete and are added to suppress heat generation due to the hydration reaction of the cement composition, suppress shrinkage, and reduce the amount of cement used to reduce costs. Aggregates are classified into coarse aggregates and fine aggregates. Coarse aggregates are those that remain by mass at least 85% on a 5 mm sieve, and fine aggregates are those that pass through a 5 mm sieve and pass through a 10 mm sieve by mass 100%. Examples of the aggregate material include river sand, mountain sand, sea sand, blast furnace slag, and copper slag. However, the cementitious material may contain aggregates, but the sludge water does not contain aggregates.

[0026] The cementitious material may optionally contain admixtures such as AE agents (air entraining agents), water reducing agents (AE water reducing agents, water reducing agents, high performance AE water reducing agents, etc.), fluidizing agents, setting and hardening regulators, flash setting agents, rust preventives, and waterproof agents.

[0027] As mentioned above, sludge water is the suspension (the suspension before separation of supernatant water and sludge water) that is collected from the washing water of concrete mixers in ready-mixed concrete plants and ready-mixed concrete transport vehicles and from which aggregate has been removed.

[0028] The CO2 gas may be any gas containing CO2, and preferably a gas containing CO2 at a high concentration. Examples of gases containing CO2 at a high concentration include, but are not limited to, exhaust gas from waste incineration facilities such as combustible waste incineration facilities, exhaust gas from power plants such as thermal power plants and biomass power plants, and gases generated in cement manufacturing processes such as cement kiln exhaust gas. The CO2 gas has a concentration of, for example, 5 v / v% or more, preferably 7 v / v% or more. Considering high efficiency over time, a gas containing CO2 at a higher concentration is preferable, and a gas containing CO2 at 20 v / v% or more is particularly preferable.

[0029] The CO2 gas may be supplied to the sludge water in any form, but from the viewpoint of allowing the CO2 gas to remain in the sludge water for a long period of time, promoting its conversion to bicarbonate ions and carbonate ions, and increasing the contact area with calcium ions in the sludge water, it is preferable that the CO2 gas be injected into the sludge water in the form of bubbles with a diameter of 250 μm or less, and more preferably in the form of bubbles with a diameter of less than 100 μm.

[0030] When CO2 gas is injected into sludge water, the pH of the sludge water drops, but this process is characterized by controlling the pH of the sludge water into which CO2 gas has been injected at 7 or higher.

[0031] Figure 3 is an equilibrium diagram of carbonate species in seawater at a practical salinity value of S = 35 and a temperature of t = 25°C, and is taken from Figure 1.2.1 on page 6 of Meteorological Research Institute Technical Report No. 41 (March 2000), entitled "High-precision analysis of total carbon dioxide concentration in seawater by coulometric titration method and measurement of radiocarbon isotope ratios of atmospheric carbon dioxide and total carbon dioxide in seawater."

[0032] As shown in the figure, when the pH drops from 11 to 7, the proportion of carbonate ions decreases and the proportion of CO2 begins to increase. Therefore, if the pH of the sludge water into which CO2 gas has been injected falls below 7, the equilibrium between CO2, bicarbonate ions, and carbonate ions in the sludge water shifts toward CO2, reducing the efficiency of calcium carbonate production. Therefore, as mentioned above, it is important to maintain the pH of the sludge water into which CO2 gas has been injected at 7 or higher.

[0033] The pH of the sludge water into which CO2 gas has been injected may be controlled in any manner so long as the pH of the sludge water is controlled to be at least 7. However, for example, the pH is preferably controlled by stopping the injection of CO2 gas when the pH value decreases as a result of the injection of CO2 gas, and resuming the injection of CO2 gas when the pH value increases as a result of the elution of alkaline components from the cementitious material. Hereinafter, this type of pH control of the sludge water is referred to as the intermittent supply method.

[0034] The intermittent supply method allows carbonate ions and bicarbonate ions to be maintained in the sludge water for a longer period of time, even if the pH falls below 7, compared to when CO2 gas is continuously injected, thereby increasing the efficiency of calcium bicarbonate production. Furthermore, the intermittent supply method allows the pH of the sludge water to be maintained at 7 or higher simply by stopping and restarting the CO2 gas injection, further simplifying the method for producing a CaCO3-containing suspension of the present invention. Note that changes in pH can be measured and monitored using a well-known pH meter.

[0035] In the intermittent supply method, the pH of the sludge water into which CO2 gas has been injected is preferably controlled at 7 or higher, more preferably at 8 or higher, particularly preferably at 9 or higher, and most preferably at 10 or higher.

[0036] The higher the lower limit of the pH to be controlled, the faster the pH of the sludge water will recover (rise) after CO2 gas injection is stopped, and the sooner CO2 gas injection can be resumed.

[0037] In the intermittent supply method, the timing for restarting CO2 gas injection after stopping it is when the pH has risen to a certain level and the equilibrium between CO2, carbonate ions, and bicarbonate ions in the sludge water has shifted toward carbonate ions; for example, this can be when the pH exceeds 11. However, as mentioned above, it is sufficient that the equilibrium has shifted toward carbonate ions; strictly speaking, exceeding pH 11 is not a required condition.

[0038] It is also preferable that the pH of the sludge water into which CO2 gas has been injected is controlled by dissolving alkaline components from the cementitious material and supplying alkaline components from the outside.

[0039] The cement in the cement-based material contains alkaline components (mainly CaO). Examples of externally supplied alkaline components include NaOH, KOH, and Ca(OH)2. Among these, it is preferable that the externally supplied alkaline component is Ca(OH)2, since it can be a source of alkaline components and also a source of Ca.

[0040] The external supply of an alkaline component is carried out, for example, when the pH of the sludge water is lowered by the injection of CO2 gas and approaches 7.

[0041] From the viewpoint of maintaining the equilibrium of CO2, carbonate ions, and bicarbonate ions in the sludge water in favor of carbonate ions, it is preferable to control the pH at 8 or higher by supplying alkaline components from the outside in addition to dissolving alkaline components from the cementitious material, more preferably at 9 or higher, and most preferably at 10 or higher.

[0042] The injection of CO2 gas into sludge water containing a cementitious material is carried out, for example, until the cumulative supply amount of the CO2 gas reaches 0.6 L per 1 g of cement in the sludge water when using CO2 gas with a purity of 99.5 v / v% in a suspension of ordinary Portland cement. Therefore, when the CO2 concentration in the CO2 gas is 10 v / v%, the cumulative supply amount of the CO2 gas can be appropriately adjusted so that the cumulative supply amount is 0.6 × 99.5 v / v% / 10 v / v% = 5.97 L ≒ 6 L (above, CO2 gas injection step (S110)).

[0043] <Method for producing powder containing CaCO3> The method for producing the powder containing CaCO3 according to the present invention has a CO2 gas injection step (S210) and a solid-liquid separation step (S220), as shown in FIG. 2.

[0044] [CO2 gas injection step (S210)] In this step, CO2 gas is injected into sludge water containing a cementitious material to obtain a suspension containing CaCO3. Since this step is the same as the CO2 gas injection step (S110) of the method for producing the suspension containing CaCO3 described above, the description thereof is omitted here (above, CO2 gas injection step (S210)).

[0045] [Solid-liquid separation step (S220)] In this step, the suspension containing CaCO3 is subjected to solid-liquid separation to obtain a powder containing CaCO3.

[0046] For solid-liquid separation, well-known solid-liquid separation equipment such as a centrifuge and a filter press can be used.

[0047] The powder containing CaCO3 obtained after solid-liquid separation may optionally be further subjected to a drying treatment to reduce its weight. For the drying treatment, well-known dryers such as a hot air dryer and a steam-heated drum dryer can be used (above, solid-liquid separation step (S220)).

[0048] Therefore, according to the method for producing a suspension containing CaCO3 and the method for producing a powder containing CaCO3 of the present invention, the pH of the sludge water into which CO2 gas has been injected is controlled at 7 or more in the CO2 gas injection step, so that the equilibrium between CO2, bicarbonate ions, and carbonate ions in the sludge water shifts to the carbonate ion side, and the carbonate ions and Ca 2+ This promotes the reaction with CaCO3 to form CaCO3.

[0049] Therefore, a suspension containing CaCO3 at a higher concentration than conventionally can be obtained, and a method for producing calcium carbonate from sludge water more efficiently than conventionally can be provided.

[0050] Furthermore, the effect of adopting the intermittent CO2 supply method in the present invention is as follows: Sludge water is an industrial waste, and conventionally, the sludge cake obtained by dehydration has been treated as industrial waste, and high-purity calcium carbonate can be produced by blowing CO2 into the supernatant water, which has been reused.

[0051] In this case, when CO2 is injected into the supernatant water or sludge water, the pH drops, and it takes a long time for this pH to rise due to the elution of alkaline components derived from minerals in the sludge water, so waiting for this pH increase results in a loss of time.In particular, when a ready-mixed concrete plant is operating, sludge water is continuously generated, so it is not realistic to stop the treatment of the supernatant water and sludge water while waiting for the pH to increase, and therefore, in the past, the intermittent CO2 supply method that focuses on pH had not been adopted.

[0052] However, in recent years, in response to the need to curb CO2 emissions in order to curb global warming, the inventors believed that the benefits of efficiently pooling CO2 in the form of CaCO3 by supplying CO2 intermittently would outweigh the disadvantages of processing delays. Subsequent experiments verified this hypothesis, and found that the intermittent CO2 supply method is more effective at fixing the amount of CO2 per cumulative amount of CO2 supplied than the continuous supply method (see Figures 13 and 14). Furthermore, the intermittent CO2 supply method does not require the step of adding an alkaline component from the outside, making it cost-effective, and there is no need to consider the effects of other salts being present in the resulting powder containing CaCO3. [Example]

[0053] EXAMPLES The present invention will be specifically explained below by showing examples, but the present invention is not limited to these examples.

[0054] (1) Explanation of the method for producing simulated sludge water and supplying (injecting) CO2 gas Simulated sludge water was prepared by mixing distilled water and ordinary Portland cement in a 1 L beaker to a mass concentration of 95% distilled water and 5% ordinary Portland cement. The beaker containing 1 L of simulated sludge water was placed on a magnetic stirrer and stirred at 600 rpm for 24 hours.

[0055] After 24 hours of stirring, 99.5 v / v% pure CO2 gas was injected into the simulated sludge water at a specified flow rate and for a specified period of time through a tube attached to the tip of a fine bubble diffuser (stone with a nominal pore size of less than 250 μm) (product name: Aircera S20, manufacturer: Sudo Co., Ltd.), and the calcium compounds in the simulated sludge water were carbonated.

[0056] During this carbonation, the simulated sludge water was continuously stirred with a magnetic stirrer at a speed of 600 rpm.

[0057] Table 1 shows the test categories based on the flow rate and duration of CO2 gas supply to the simulated sludge water.

[0058] As shown in Table 1, CO2 gas was supplied continuously in Test Examples 1-1 to 1-2, 2, 3-0 to 3-9, 4-0 to 4-6, and 5-0 to 5-6 (hereinafter, these sections are also referred to as continuous supply sections), and CO2 gas was supplied intermittently in Test Examples 6-1 to 6-2 and 7 (hereinafter, these sections are also referred to as intermittent supply sections).

[0059] In Test Examples 6-1 and 6-7, which were in the intermittent supply section, the supply of CO2 gas was controlled so that the pH range was between 7 and 12. For example, in Test Examples 6-1 and 6-7, the pH decreased after the start of CO2 gas supply, but the supply of CO2 gas was stopped when the pH approached 7, and then the pH rose and was resumed when it approached 12. In addition, in Test Example 6-2, which was in the intermittent supply section, the supply of CO2 gas was controlled so that the pH range was between 10 and 12.

[0060] In addition, while CO2 gas was being supplied, the changes in the pH value and amount of dissolved CO2 in the simulated sludge water were measured every 30 seconds using a pH meter (pH measurement range 0 to 14) (model: HM-30P, manufactured by DKK Toa Corporation) and a dissolved CO2 sensor (CO2 display range 0.00 to 2020 mg / L) (model: CGP-31, manufactured by DKK Toa Corporation) to manage the control values.

[0061] [Table 1]

[0062] (2) Measurement of the amount of CaCO3 produced by thermogravimetry-differential thermal analysis (TG-DTA) After the carbonation test of calcium compounds in the simulated sludge water was completed, the simulated sludge water was vacuum filtered through filter paper (JIS P 3801 Type 4, diameter 110 mm) to separate the solid and liquid, and the cement paste deposited on the filter paper was dried in a vacuum chamber for more than three days.The solid matter containing CaCO3 on the filter paper was then crushed into a fine powder, and the CaCO3 content was analyzed using a TG-DTA test.

[0063] The TG-DTA test was carried out with a sample mass of 20±1 mg, at room temperature to 1000°C, at a heating rate of 20°C / min, and with a nitrogen (N2) flow rate of 80 ml / min.

[0064] The masses of dehydration of CH (calcium hydroxide, Ca(OH)2) and decarbonation of CC (calcium carbonate, CaCO3) were calculated from the mass differences between 400 and 500 °C and between 600 and 870 °C on the TG curve, respectively.

[0065] Then, based on the mass loss, the contents of CH and CC in each sample were calculated using the following formulas (1) and (2).

[0066]

number

[0067] (In formulas (1) and (2), CH represents the Ca(OH)2 content (wt%), CC represents the CaCO3 content (wt%), and m CH indicates the mass loss (wt%) due to dehydration of CH(Ca(OH)2) from 400 to 500 °C, and m CC indicates the mass loss (wt%) due to decarbonation of CC(CaCO3) at 600 to 850°C. The molecular weights were calculated based on the following: Ca(OH)2: 74.09, HO: 18.02, CaCO3: 100.09, and CO2: 44.01.

[0068] (3) Test results (3-1) Effect of CO2 gas injection conditions on pH change Figure 4 is a graph showing the changes over time in the pH and dissolved CO2 concentration (mg / L) of simulated sludge water under the CO2 gas injection conditions of Test Examples 1-1 to 1-2 and Test Example 2. As shown in the figure, when CO2 gas was injected into the simulated sludge water at an injection rate of 0.2 L / min (Test Examples 1-1 to 1-2) and 0.25 L / min (Test Example 2), the pH decreased from an initial value of 13.5, and in Test Example 2, the pH decreased to 10 60 minutes after the start of CO2 gas injection. These results show that the pH decreased due to CO2 gas injection, and that the pH decreased more rapidly at higher CO2 gas injection rates.

[0069] Figure 5 is a graph showing the change in pH of simulated sludge water over time under the CO2 gas injection conditions of test examples 3-1 to 3-9, Figure 6 is a graph showing the change in pH of simulated sludge water over time under the CO2 gas injection conditions of test examples 4-1 to 4-6, and Figure 7 is a graph showing the change in pH of simulated sludge water over time under the CO2 gas injection conditions of test examples 5-1 to 5-6.

[0070] When the CO2 gas injection rate was 0.5 L / min, in Test Examples 3-1 to 3-6, except for Test Example 3-3, the pH fell below 8 after about 30 minutes of CO2 gas injection, reached 6.3 after 40 minutes of CO2 gas injection, and then remained stable until 60 minutes of CO2 gas supply, as shown in Figure 5. On the other hand, in Test Examples 3-7 to 3-9, the pH decreased more slowly than in Test Examples 3-1 to 3-6 during the CO2 gas supply period of 10 to 50 minutes, and then the pH leveled off at around pH 6.5.

[0071] When the CO2 gas injection rate was 1 L / min, the change in pH with respect to CO2 gas supply time showed a similar trend to when the CO2 gas injection rate was 0.5 L / min, as shown in Figure 6. Twenty minutes after the start of CO2 gas supply, the pH dropped to 6.4 and then remained constant.

[0072] When the CO2 gas injection condition was 2 L / min, there was no significant difference from when the CO2 gas injection condition was 0.5 L / min or 1 L / min, as shown in Figure 7. The pH reached 6.5 15 minutes after the start of CO2 gas supply, and remained almost flat for 30 minutes.

[0073] In addition, under the CO2 gas injection conditions of 0.5 L / min, 1 L / min, and 2 L / min, the pH reached a minimum when the cumulative CO2 supply reached 30 L, and then remained flat.

[0074] (3-2) Effect of CO2 gas injection conditions on changes in dissolved CO2 concentration Figure 8 is a graph showing the change over time in the dissolved CO2 concentration (mg / L) of simulated sludge water under the CO2 gas injection conditions of Test Examples 3-1 to 3-9, Figure 9 is a graph showing the change over time in the dissolved CO2 concentration (mg / L) of simulated sludge water under the CO2 gas injection conditions of Test Examples 4-1 to 4-6, and Figure 10 is a graph showing the change over time in the dissolved CO2 concentration (mg / L) of simulated sludge water under the CO2 gas injection conditions of Test Examples 5-1 to 5-6.

[0075] Comparing Figures 8 to 10 with Figures 5 to 7, it was found that the slope of the dissolved CO2 concentration graphs in Figures 8 to 10 tended to rise sharply when the graphs in Figures 5 to 7 fell below pH 7. This is thought to be because the pH of the simulated sludge water decreased as the amount of CO2 injected increased, causing the equilibrium between CO2, bicarbonate ions, and carbonate ions in the simulated sludge water to shift toward CO2, and it was experimentally confirmed that the pH at which this equilibrium shifts significantly toward CO2 is around 7. Therefore, it was thought that by controlling the pH to 7 or higher, the equilibrium between CO2, bicarbonate ions, and carbonate ions in this simulated sludge water could be maintained on the carbonate ion side, and the efficiency of calcium carbonate production could be further improved.

[0076] (3-3) Changes in pH and dissolved CO2 concentration in the intermittent supply section 11 is a graph showing the changes over time in the pH and dissolved CO2 concentration (mg / L) of simulated sludge water under the CO2 gas injection conditions of Test Examples 6-1 and 6-2 and Test Example 7, which are the intermittent supply sections. In the intermittent supply sections of Test Examples 6-1 and 7, CO2 gas was intermittently supplied by stopping the supply when the pH reached 7 after the start of CO2 gas supply and then supplying CO2 gas again when the pH rose to approximately 12. In Test Example 6-2, this intermittent supply was performed within the range of pH 10 to pH 12.

[0077] As shown in the figure, in the intermittent supply sections of Test Example 6-1 and Test Example 7, when the pH dropped to 7, the dissolved CO2 concentration (mg / L) peaked at 450 mg / L (Test Example 6-1) and 400 mg / L (Test Example 7), respectively. When the CO2 gas supply was stopped, the pH rose again, and the dissolved CO2 concentration (mg / L) gradually decreased.

[0078] On the other hand, in the intermittent supply section of Test Example 6-2, even when the pH dropped to 10, the peak in the dissolved CO2 concentration (mg / L) hardly appeared, and the rate of increase in pH after the CO2 gas supply was stopped was also faster than in Test Examples 6-1 and 7. (3-4) Effect of cumulative CO2 gas supply on CH concentration (wt%), CC concentration (wt%), and amount of fixed CO2 Figure 12 is a graph showing the change in CH(Ca(OH)) concentration (wt%) in simulated sludge water after carbonation treatment due to differences in the cumulative CO2 gas supply rate for each test example. As shown in the figure, in the section where CO2 gas was continuously supplied at 1 L / min to 2 L / min (Test Examples 4-0 to 4-6 and Test Examples 5-0 to 5-6), the CH2 concentration (wt%) in the simulated sludge water decreased significantly until the cumulative CO2 supply rate reached 10 L, after which it remained flat. On the other hand, in the section where CO2 gas was continuously supplied at 0.5 L / min (Test Examples 3-0 to 3-9), no decrease in the CH2 concentration (wt%) in the simulated sludge water was observed even when the cumulative CO2 supply rate reached 60 L.

[0079] Figure 13 is a graph showing the change in CC(CaCO3) concentration (wt%) in the simulated sludge water after carbonation treatment due to differences in the cumulative CO2 gas supply amount for each test example. As shown in the figure, in the continuous CO2 gas supply section (Test Examples 3-0 to 3-9, Test Examples 4-0 to 4-6, and Test Examples 5-0 to 5-6), the CC(CaCO3) concentration (wt%) in the simulated sludge water tended to increase as the CO2 gas supply amount increased. Furthermore, with the exception of the CC concentration (wt%) when the CO2 gas supply amount was 30 L, the CC(CaCO3) concentration (wt%) in the simulated sludge water per cumulative CO2 gas supply amount tended to increase as the CO2 gas supply rate decreased from 2 L / min to 0.5 L / min.

[0080] Furthermore, the CC concentration (wt%) increased rapidly when the cumulative CO2 gas supply amount was between 0 and 30 L, but the increase in the CC concentration (wt%) was small when the cumulative CO2 gas supply amount was between 40 and 60 L. This is thought to be because the carbonation of CH(Ca(OH)2) in the simulated sludge water progressed when the cumulative CO2 gas supply amount was between 0 and 30 L, but when the cumulative CO2 gas supply amount was between 40 and 60 L, the CH(Ca(OH)2) in the simulated sludge water decreased, and the pH of the simulated sludge water fell below 7, shifting the equilibrium between CO2, bicarbonate ions, and carbonate ions toward CO2 and inhibiting CC production.

[0081] On the other hand, in the intermittent CO2 gas supply sections (Test Examples 6-1 to 6-2, Test Example 7), the CC concentration (wt%) per cumulative CO2 gas supply was greater than that of any of the continuous CO2 gas supply sections. In particular, the CC concentration (wt%) reached a maximum of 69.8 wt% in Test Example 7 (CO2 gas supply rate: 1 L / min, pH range: 7 to 12), and the CC concentration (wt%) per cumulative CO2 gas supply was also greatest in Test Example 6-2 (CO2 gas supply rate: 0.5 L / min, pH range: 10 to 12).

[0082] The reason why the CC concentration (wt%) per cumulative amount of CO2 gas supplied was higher in the intermittent CO2 gas supply section than in any of the continuous supply sections is thought to be because the temporary cessation of CO2 gas supply when the pH dropped allowed the carbonate ions and bicarbonate ions in the simulated sludge water to be maintained at a higher concentration than CO2 compared to the continuous supply section.

[0083] Furthermore, among the CO2 gas intermittent supply sections, Test Example 6-2, in which CO2 gas was intermittently supplied in the pH range of 10 to 12, had a higher CC concentration (wt%) per cumulative amount of CO2 gas supplied than Test Example 6-1 (pH range: 7 to 12). This is thought to be because, by managing the pH range at a higher range than Test Example 6-1, the carbonate ions and bicarbonate ions in the simulated sludge water were able to be maintained at higher concentrations than CO2, as shown in Figure 11. Furthermore, according to Figure 11, the pH rose more quickly in Test Example 6-2 after the CO2 gas supply was stopped than in Test Example 6-1, and CO2 gas could be resupplied earlier than in Test Example 6-1, which is thought to have resulted in the rapid and large production of CC (CaCO3).

[0084] Figure 14 is a graph showing the amount of fixed CO2 (wt%) depending on the cumulative amount of CO2 gas supplied after carbonation treatment for each test example. As shown in the figure, the amount of fixed CO2 (wt%) also showed a similar trend to the change in CC (CaCO3) concentration (wt%) in the simulated sludge water in Figure 13. [Industrial Applicability]

[0085] The CaCO3-containing suspension obtained by the method for producing a CaCO3-containing suspension of the present invention can be used as mixing water for concrete. Also, the CaCO3-containing powder obtained by the method for producing a CaCO3-containing powder of the present invention can be used as a cement material or a desulfurization material.

Claims

【Request Item 1】 CO2 is added to sludge water containing cementitious materials. ２ Gas was blown in, and CaCO ３ Obtaining a suspension containing CO ２ CaCO, including a gas blowing step ３ 1. A method for producing a suspension comprising: CO ２ In the gas blowing step, ２ A CaCO3 gas-injected sludge water is characterized by controlling the pH of the sludge water to 7 or more. ３ A method for producing a suspension comprising: 【Request Item 2】 The pH control is carried out by CO ２ If the pH value decreases with the gas injection, CO ２ The gas injection is stopped, and when the pH value rises due to the elution of alkaline components from the cementitious material, CO ２ 2. The method of claim 1, wherein the gas injection is restarted. ３ A method for producing a suspension comprising: 【Request Item 3】 2. The CaCO3 composition according to claim 1, wherein the pH is controlled by dissolving an alkaline component from the cementitious material and supplying an alkaline component from the outside. ３ A method for producing a suspension comprising: 【Request Item 4】 CO2 is added to sludge water containing cementitious materials. ２ Gas was blown in, and CaCO ３ Obtaining a suspension containing CO ２ A gas blowing step; CaCO ３ The suspension containing CaCO ３ A solid-liquid separation step of obtaining a powder containing the CaCO ３ A method for producing a powder comprising: CO ２ In the gas blowing step, ２ A CaCO3 gas-injected sludge water is characterized by controlling the pH of the sludge water to 7 or more. ３ A method for producing a powder comprising:

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