Metal salt separation system for separating metal salt from solution containing metal salt, system for recovering carbon dioxide from seawater by separating carbonate from seawater, and carbon dioxide recovery method

Abstract

To adjust the alkalinity of a solution reduced in alkalinity.SOLUTION: A metal salt separation system 1 for separating a metal salt from a solution containing the metal salt includes an electrical treatment machine 30 for electrically treating the solution containing the metal salt to produce acidic water and basic water, a metal salt separation device 60 for separating the metal salt from the basic water produced by the electrical treatment machine 30, and an alkalinity adjustment device 80 for adjusting alkalinity of the solution treated by the electrical treatment machine.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a metal salt separation system that separates metal salts from a solution containing the metal salts, a system that recovers carbon dioxide from seawater by separating carbonates from the seawater, and a carbon dioxide recovery method. [Background technology]

[0002] Conventionally, metal resources have been separated from solutions containing metal ions by electrical treatment. Typically, seawater is subjected to electrical processing to separate metal resources. Seawater contains sodium (1.1 wt%), magnesium (0.13 wt%), calcium (0.04 wt%), potassium (0.04 wt%), strontium (7.8 ppm), lithium (0.17 ppm), and other metal resources, and electrodialysis is used to concentrate and separate these metal resources.

[0003] In particular, magnesium is used in applications such as fireproofing and adsorbents, compounding agents for rubber and plastics, heavy metal treatment agents, and water quality improvement agents, and technologies for recovering it from seawater have been developed. For example, methods proposed for obtaining magnesium hydroxide include adding basic minerals to seawater, concentrating concentrated seawater by electrodialysis and adding a basic solution, and producing a basic solution by electrolyzing concentrated seawater.

[0004] Examples of solutions containing metal ions include seawater, groundwater typically found in hot springs, and solutions containing calcium and the like formed when concrete dissolves in water. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2024-37212 [Patent Document 2] Japanese Patent Application Laid-Open No. 2024-62549 [Patent Document 3] Japanese Patent Application Publication No. 2024-70482 Summary of the Invention [Problem to be solved by the invention]

[0006] Acidic water and basic water can be produced by subjecting a solution containing metal ions to electrical treatment, and the metal ions can be separated. However, the solution from which the metal ions have been separated may have a reduced alkalinity. Furthermore, releasing a solution with reduced alkalinity directly into the natural environment can have a negative impact on the environment. However, prior art has not taken into consideration the impact of a solution with reduced alkalinity on the natural environment. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the present invention provides a metal salt separation system for separating metal salts from a solution containing the metal salts, the system comprising: an electric treatment machine that produces acidic water and basic water by electrically treating the solution containing the metal salts; a metal salt separation device that separates the metal salts from the basic water produced by the electric treatment machine; and an alkalinity adjustment device that adjusts the alkalinity of the solution treated by the electric treatment machine. The electric treatment machine may be a bipolar membrane electrodialysis device. The pH of the solution may also be adjusted by a water electrolysis device. [Effects of the Invention]

[0008] According to one embodiment of the present invention, the metal salt separation system can reduce the impact on the natural environment by adjusting the alkalinity of the solution obtained by separating metals from a solution containing metal ions using an alkalinity adjustment device before releasing the solution into the natural environment. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a graph showing the relationship between the amount of calcium carbonate produced and the carbon dioxide released from seawater. [Figure 2]FIG. 1 is a diagram showing the relationship between calcium carbonate production amount and alkalinity of seawater. [Figure 3] This figure shows that the pH of seawater decreases due to the production of calcium carbonate in seawater. [Figure 4] FIG. 1 is a diagram showing an example of a metal salt separation apparatus equipped with an alkalinity adjusting device for separating metal salts from seawater. [Figure 5] In this example, an alkalinity adjusting device is configured by placing an additive in the seawater flow path. [Figure 6] In this embodiment, an alkalinity adjusting device 80 is configured by placing an additive in a water tank and storing seawater in the water tank. [Figure 7] In this example, multiple additives are arranged in parallel, with valves placed before and after each additive. [Figure 8] In this example, an alkalinity adjusting device 80 is disposed in the path of acidified seawater produced by a bipolar membrane electrodialysis device. [Figure 9] In this example, an alkalinity adjusting device 80 is disposed in the path of basic seawater produced by a bipolar membrane electrodialysis device. [Figure 10] In this example, an alkalinity adjusting device is arranged downstream of the path for acidified seawater produced by a bipolar membrane electrodialysis device, the path for basic seawater produced by a bipolar membrane electrodialysis device, and the mixing tank. [Figure 11] This is an example in which multiple sensors are installed in the solution flow path. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an example of separating metal salts from seawater according to one embodiment of the present invention will be described with reference to the accompanying drawings.

[0011] As mentioned above, seawater is rich in metal resources such as sodium (1.1 wt%), magnesium (0.13 wt%), calcium (0.04 wt%), potassium (0.04 wt%), strontium (7.8 ppm), and lithium (0.17 ppm). The amount of seawater on Earth is approximately 1.37 billion km². 3 It is said that there are almost infinite metal resources in seawater, and efforts are being made to extract the metal resources present in seawater.

[0012] On the other hand, to prevent global warming, there is a global demand for reducing carbon dioxide (CO2) emissions and for carbon dioxide capture and storage (CCS) technology. While previous CCS efforts have focused on industrial exhaust gases and atmospheric carbon dioxide, in recent years attention has been focused on capturing carbon dioxide in seawater (DOC; Direct Ocean Capture or Ocean-based Carbon Dioxide Removal).

[0013] Approximately 30% of anthropogenic carbon dioxide is dissolved in the ocean, and the concentration of carbon dioxide in seawater per volume is said to be approximately 120 times that of the air. When carbon dioxide is captured from seawater, the seawater absorbs carbon dioxide from the atmosphere to maintain equilibrium between seawater and the atmosphere, resulting in a reduction in the amount of carbon dioxide in the atmosphere.

[0014] A method has been proposed for efficiently capturing carbon dioxide from seawater by acidifying seawater using bipolar membrane electrodialysis, and research is currently underway.

[0015] In addition, bipolar membrane electrodialysis produces acidified seawater and basified seawater. Technologies have been proposed to recover carbon dioxide gas from acidified seawater and to recover carbon dioxide from basified seawater as calcium carbonate for use in building materials.

[0016] As a method for separating metal salts from seawater, dissolved carbonate ions (CO3 2- A method has been proposed in which uranium dioxide (CO₂) is combined with metal ions (e.g., calcium ions and magnesium ions) in seawater to precipitate carbonate minerals (e.g., calcium carbonate and magnesium carbonate). This method not only has the effect of separating the metal salts for industrial use and recycling resources, but also has the effect of removing CO₂ from seawater.

[0017] The present invention makes it possible to return seawater, after removing metal salts and carbon dioxide, to the sea in a state that does not adversely affect the natural environment.

[0018] More specifically, it is known that, for example, a liquid obtained by removing metal salts (e.g., calcium carbonate) and carbon dioxide from seawater has a lower alkalinity than seawater. In this embodiment, the alkalinity of seawater from which metal salts have been separated is adjusted using an alkalinity adjusting device, and the seawater is returned to the sea with an alkalinity close to that before the metal salts were separated.

[0019] Hereinafter, this embodiment will be described in detail, starting with the seawater. The formation of calcium carbonate (CaCO3) and its relationship to carbon dioxide and calcium carbonate released from seawater FIG. 1 shows the relationship between the amount of calcium carbonate produced and the amount of carbon dioxide released from seawater. FIG. 2 is a graph showing the relationship between calcium carbonate production and alkalinity of seawater.

[0020] The relationship between calcium carbonate production and carbon dioxide released from seawater Figure 1 shows that when calcium carbonate is produced in seawater, the amount of carbon dioxide released from seawater into the atmosphere increases. For example, the simulation results showed that when 1.0 mmol of calcium carbonate is produced in seawater, approximately 0.83 mmol of carbon dioxide is released into the atmosphere.

[0021] Furthermore, as shown in Figure 2, the simulation results showed that the alkalinity of seawater decreases as calcium carbonate is produced.

[0022] The above simulation is the result of a chemical equilibrium calculation in seawater using the geochemical software PHREEQC, which takes into account the complexity of seawater composition. The simulation was carried out by adding a specified amount of calcium carbonate (CaCO 3) This was obtained by generating a precipitate and then performing a chemical equilibrium calculation under atmospheric carbon dioxide concentration conditions (420 ppm).

[0023] The alkalinity of seawater can be defined as the number of moles of hydrogen ions equivalent to the excess of proton acceptors relative to the proton donors contained in 1 kg of sample, but other definitions may also be used.

[0024] Considering the example of calcium ions in seawater, calcium ions and bicarbonate ions exist in seawater with their electric charges balanced. When calcium carbonate precipitates, water and carbon dioxide are produced, and there is concern that carbon dioxide will be released into the atmosphere. This is true not only for calcium ions, but also for other metal ions.

[0025] In this embodiment, by adjusting the alkalinity of the solution after separating metal salts from seawater, the alkalinity of the solution after separating metal salts from seawater with reduced alkalinity can be made to be the same as that of seawater before the metal ions were separated, and the solution can be released into the sea, thereby reducing the impact on the environment, including the sea and the atmosphere.

[0026] Figure 3 shows that the pH of seawater decreases due to the formation of calcium carbonate. It can be seen that the formation of calcium carbonate in seawater reduces the alkalinity of the seawater and also reduces the pH.

[0027] Metal salt separation equipment that separates metal salts from seawater 4 is a diagram showing an example of a metal salt separation apparatus equipped with an alkalinity adjusting device for separating metal salts from seawater. Each component will be described below, but the description does not limit the present invention to the examples.

[0028] seawater 10 The seawater 10 may be collected directly from the sea or transported from the sea by vehicle or the like. By installing the metal salt separation system 1 on the seashore, seawater can be easily collected and the treated seawater can be easily returned to the sea. The seawater 10 may be seawater present in the sea or water with components similar to seawater.

[0029] Pre-processing machine 20 When seawater is electrically treated, it is preferable to perform pretreatment in advance to remove impurities. For pretreatment, UF membranes (ultrafiltration membranes), MF membranes (microfiltration membranes), and NF membranes (nanofiltration membranes) can be used, which can produce high-quality treated water. In addition, additives may be added to the pretreatment to increase the efficiency of removing fine particles.

[0030] Bipolar membrane electrodialysis device 30 The electrical treatment of seawater by an electrical treatment machine can be carried out by a bipolar membrane electrodialysis device 30.

[0031] The seawater treated by the pretreatment device 20 is then converted into acidified seawater and basic seawater by the bipolar membrane electrodialysis device 30. The pH of the basic seawater is preferably in the range of 9.3 to 9.7, and more preferably 9.5. The electrical treatment is not limited to the bipolar membrane electrodialysis device 30, and any other electrical treatment may be used as long as it produces acidified seawater and basic seawater.

[0032] The acidified seawater produced by the bipolar membrane electrodialysis device 30 is sent to a carbon dioxide desorption unit 50. The basic seawater produced by the bipolar membrane electrodialysis device 30 is sent to a carbonate mineral precipitation tank 60.

[0033] Electrode solution tank 40 The bipolar membrane electrodialysis device 30 may be connected to an electrode solution tank 40. The electrode solution tank 40 can supply the electrode solution to the bipolar membrane electrodialysis device 30 when the electrode solution is insufficient in the bipolar membrane electrodialysis device 30, and can recover the electrode solution when the electrode solution is in excess in the bipolar membrane electrodialysis device 30.

[0034] Carbon dioxide desorption unit 50 The carbon dioxide desorption unit 50 is a device that recovers carbon dioxide from the acidified seawater produced by the bipolar membrane electrodialysis device 30. By adsorbing carbon dioxide using the carbon dioxide desorption unit 50, it is possible to prevent carbon dioxide from leaking from seawater into the atmosphere, or to cause carbon dioxide in the atmosphere to be absorbed by seawater. As the carbon dioxide desorption unit 50, a well-known device that can recover carbon dioxide dissolved in a liquid can be used.

[0035] The carbon dioxide recovered by the carbon dioxide desorption unit 50 may be stored so as not to dissolve again in seawater, or may be supplied to a carbonate mineral precipitation tank. By supplying the recovered carbon dioxide to the carbonate mineral precipitation tank, it can be fixed as carbonate minerals.

[0036] Carbonate mineral settling tank 60 A carbonate mineral settling tank can be used as the metal salt separation device. The carbonate mineral precipitation tank 60 is a device for recovering metal salts from the basic seawater produced by the bipolar membrane electrodialysis device 30. A known device can be used for the carbonate mineral precipitation tank 60. Instead of precipitating minerals, metal salts may be separated and recovered from the liquid by other means, such as filtration separation using a filter.

[0037] Mixing Tank 70 The mixing tank 70 is a device that mixes the acidified seawater from which carbon dioxide has been removed in the carbon dioxide desorption unit 50 and the basic seawater from which metal salts have been removed in the carbonate mineral precipitation tank 60. The mixing tank 70 can neutralize the acidified seawater and the basic seawater.

[0038] Alkalinity Adjuster 80 The alkalinity adjuster 80 is a device for adjusting the alkalinity of seawater whose alkalinity has decreased due to the separation of metal salts. The alkalinity adjuster 80 can adjust the alkalinity of seawater by mixing additives with seawater in an aquarium.

[0039] As an additive for adjusting alkalinity, calcium hydroxide, magnesium hydroxide, calcium oxide, magnesium oxide, etc. can be used.

[0040] Alternatively, natural ores containing calcium and magnesium, such as olivine, forsterite, quicklime, and basalt, can be used. Compared to the former additives, the use of natural ores is cheaper and produces less carbon dioxide, resulting in the ability to adjust alkalinity with less environmental impact.

[0041] Furthermore, industrial waste materials containing calcium and magnesium, such as concrete and scallop shells, can be used as additives. When using industrial waste as an additive, it is desirable to constantly monitor the waste using a sensor or the like to prevent harmful substances from leaking outside. When harmful substances are detected, it is preferable to stop operation or issue an alarm. By adopting this configuration, it is possible to stop the discharge of harmful substances to the outside. Furthermore, if a device for adsorbing harmful substances is provided, it can have the function of purifying seawater.

[0042] ocean release 90 The seawater whose alkalinity has been adjusted by the alkalinity adjusting device 80 may be returned to the sea as is, or may be transported by vehicle or the like and stored in another location.

[0043] According to the above embodiment, the impact on the environment can be reduced by adjusting the alkalinity of seawater from which metal salts have been separated using the alkalinity adjustment device 80. In particular, by preventing the alkalinity of seawater from decreasing, it is possible to prevent carbon dioxide dissolved in the seawater from leaking into the atmosphere, and also to make it easier for carbon dioxide in the atmosphere to be absorbed into the sea, thereby preventing global warming caused by carbon dioxide on a global scale and allowing the device to function as a device for recovering carbon dioxide from seawater.

[0044] Other embodiments Figure 5 shows an example of an alkalinity adjustment device configured by placing an additive in a flow path in the seawater treatment process. The arrows in Figure 5 indicate the flow of seawater. The flow path may be configured as a pipe or the like. By configuring the flow path as a pipe, it is possible to prevent carbon dioxide generated in the seawater treatment process from being released into the atmosphere.

[0045] Additives 81 and 82 are placed inside a pipe-shaped alkalinity adjusting device 80. Seawater 85, whose alkalinity has not been adjusted, becomes alkalinity-adjusted seawater 86 by passing through the additives 81 and 82, and is then released into the sea.

[0046] The alkalinity adjustment device 80 may be provided with an alkalinity sensor 105 that measures alkalinity. The alkalinity of seawater can be measured using the output of the alkalinity sensor 105, and the device can be configured to release the seawater into the sea when it reaches a predetermined alkalinity. If the seawater does not reach the predetermined alkalinity, the seawater can be made to reach the predetermined alkalinity by stopping the flow of seawater or slowing down the flow rate of the seawater. Although alkalinity can be easily measured using an alkalinity sensor, a pH sensor, which is less expensive than an alkalinity sensor, may be used instead to measure alkalinity or obtain an approximate value.

[0047] If the specified alkalinity is not achieved even after stopping the flow of seawater, additives can be added or replaced to achieve the specified alkalinity.

[0048] In this embodiment, an example in which additives are arranged in two stages in the flow path is shown, but the additives may be arranged in one stage or in two or more stages. When additives are arranged in multiple stages, additives of the same material and the same size may be used in the multiple stages, or additives of different materials may be arranged, or additives of the same material but different sizes may be arranged. Furthermore, additives of different materials may be arranged in one stage.

[0049] Alternatively, the alkalinity adjusting device 80 may be formed by arranging a plurality of flow paths provided with additives in parallel.

[0050] Other embodiments FIG. 6 shows an embodiment in which an alkalinity adjusting device 80 is configured by placing additives 81 and 82 in water tanks 87 and 88 and storing seawater in the water tanks 87 and 88.

[0051] When alkalinity adjustment device 80 is configured using water tanks 87 and 88, industrial waste such as concrete blocks and scallop shells can be easily reused as additives 81 and 82. For example, industrial waste that can be used as additives can be placed in a large water tank such as a swimming pool using industrial machinery such as a shovel, and the industrial waste used as additives can be collected.

[0052] When seawater is to be moved from the water tanks 87 and 88 for further treatment, this can be easily achieved by installing a pump 100 in the water tanks 87 and 88 .

[0053] The water tanks 87, 88 may be provided with an alkalinity sensor 105. It is preferable to change the rotation speed of the pump 100 in the water tanks 87, 88 according to the output of the alkalinity sensor 105. When the alkalinity in the water tanks 87, 88 is low, the flow rate of the pump 100 can be reduced, and when the alkalinity in the water tanks 87, 88 is high, the flow rate of the pump 100 can be increased, thereby keeping the alkalinity of the seawater within a predetermined range.

[0054] Other embodiments FIG. 7 shows an example in which additives 81 and 82 are arranged in parallel, with valves 110, 111, 112, and 113 arranged before and after each additive.

[0055] As the alkalinity adjusting device 80 adjusts the alkalinity of the seawater, the additives 81, 82 may become worn out, contaminated, or chemically changed, making it impossible to increase the alkalinity of the seawater. When the additives 81, 82 can no longer exert the desired effect, they must be replaced.

[0056] In this embodiment, the additives 81, 82 can be removed and new additives 81, 82 can be placed by closing the valves 110, 111, 112, 113 before and after the additives 81, 82 to be replaced.

[0057] In this embodiment, additives 81 and 82 are arranged in parallel, and valves 110, 111, 112, and 113 are arranged before and after each additive. Therefore, for example, when replacing additive 81, valves 110 and 111 are closed and valves 112 and 113 are opened. Therefore, when replacing additive 81, seawater can be treated by additive 82, and there is no need to stop operation.

[0058] Furthermore, by controlling the opening and closing of the valves 110, 111, 112, and 113 depending on the amount of seawater to be treated, rather than for the purpose of replacing the additives 81 and 82, it becomes possible to select whether to perform treatment using one additive 81 or two additives 81 and 82. Although this embodiment shows an example in which two additives 81 and 82 are arranged in parallel, it is also possible to configure the system so that three or more additives are arranged in parallel.

[0059] Other embodiments FIG. 8 shows an example in which an alkalinity regulator 80 is disposed in the path of acidified seawater produced by a bipolar membrane electrodialysis device 30.

[0060] By placing the alkalinity regulator 80 in the path of the acidified seawater, the additives 81 and 82 become more soluble, and the alkalinity of the seawater can be stably increased. Other embodiments

[0061] FIG. 9 shows an example in which an alkalinity adjusting device 80 is disposed in the path of the basic seawater produced by the bipolar membrane electrodialysis device 30. By disposing the alkalinity regulator 80 in the path of the basic seawater produced by the bipolar membrane electrodialysis device 30, it is possible to prevent the generation of gas due to the reaction between acid and alkali.

[0062] Other embodiments FIG. 10 shows an example in which an alkalinity adjuster 80 is disposed downstream of the path for acidified seawater produced by the bipolar membrane electrodialysis apparatus 30, the path for basified seawater produced by the bipolar membrane electrodialysis apparatus 30, and the mixing tank 70.

[0063] By disposing the alkalinity adjuster 80 in the path of the acidified seawater produced by the bipolar membrane electrodialysis device 30, the path of the basified seawater produced by the bipolar membrane electrodialysis device 30, and downstream of the mixing tank 70, it is possible to appropriately respond to changes in the state of seawater and the operation of the bipolar membrane electrodialysis device 30, etc.

[0064] In addition, alkalinity adjusting devices 80 may be provided at any two locations: in the path of the acidified seawater produced by the bipolar membrane electrodialysis device 30, in the path of the basified seawater produced by the bipolar membrane electrodialysis device 30, and downstream of the mixing tank 70.

[0065] When a plurality of alkalinity adjustment devices 80 are installed, all of the alkalinity adjustment devices 80 may be operated, or only one alkalinity adjustment device 80 may be operated.

[0066] Other embodiments FIG. 11 shows an example in which a plurality of sensors 106, 107, and 108 are installed in the flow channel.

[0067] In the example of FIG. 11, a sensor 106 is provided upstream of the bipolar membrane electrodialysis device 30, and sensors 107 and 108 are provided before and after the alkalinity adjustment device 80C. The output of the sensors may be visually observed on-site or transmitted to a central control center via wire or wirelessly.Sensors 106, 107, 108 may be alkalinity or pH sensors. A pH sensor may be used as the sensor 106, and alkalinity sensors may be used as the sensors 107 and 108. The output of the sensor 106 can be used to adjust the output of the bipolar membrane electrodialysis device 30, and the outputs of the sensors 107 and 108 can be used to detect the state of the alkalinity adjustment device 80C. In the example of FIG. 11, sensors 107 and 108 are provided before and after the alkalinity adjuster 80C, but sensors 107 and 108 may also be provided before and after the alkalinity adjusters 80A and 80B. Since alkalinity sensors are expensive, alkalinity may be estimated using an inexpensive pH sensor. Alternatively, the state of one alkalinity adjustment device 80 may be detected by sensors 107 and 108, and the state of another alkalinity adjustment device 80 may be estimated. In the example of FIG. 11, a plurality of alkalinity adjusters 80A, 80B, and 80C are provided, but it is clear that the present invention can also be applied to an arrangement having a single alkalinity adjuster. [Explanation of symbols]

[0068] 1. Metal salt separation system 10...Seawater 20...Pre-treatment machine 30...Bipolar membrane electrodialysis device (electrical treatment machine) 40...Electrode solution tank 50...Carbon dioxide desorption unit 60...Carbonate mineral sedimentation tank (metal salt separation device) 70...Mixing tank 80, 80A, 80B, 80C...Alkalinity adjuster 81, 82...additives 87, 88...Aquarium 90…Discharge into the ocean 100...Pump 105, 106, 107, 108...Sensors 110, 111, 1112, 113... Valves

Claims

1. an electric treatment machine for producing acidic water and basic water by electrically treating a solution containing a metal salt; a metal salt separation device for separating metal salts from the basic water produced by the electric treatment machine; an alkalinity adjusting device for adjusting the alkalinity of the solution treated by the electric treatment device; Equipped with A metal salt separation system that separates metal salts from a solution containing metal salts.

2. the electric treatment machine is a bipolar membrane electrodialysis device, the metal salt separation device separates metal salts from the basic water produced by the bipolar membrane electrodialysis device; The metal salt separation system of claim 1 .

3. The alkalinity adjusting device adjusts the alkalinity of the solution obtained by separating metal salts from the basic water produced by the electric treatment machine. The metal salt separation system of claim 1 .

4. The alkalinity adjusting device adjusts the alkalinity of a solution obtained by mixing a solution in which metal salts are separated from the basic water produced by the electric treatment machine with acidic water produced by the electric treatment machine. The metal salt separation system of claim 1 .

5. The alkalinity adjusting device adjusts the alkalinity of the acidic water produced by the electric treatment machine. The metal salt separation system of claim 1 .

6. an electrical treatment machine for producing acidic water and basic water by electrically treating seawater; a metal salt separation device for separating carbonates from the basic water produced by the electric treatment machine; an alkalinity adjusting device for adjusting the alkalinity of the solution treated by the electric treatment device before discharging it into the sea; Equipped with A system that recovers carbon dioxide from seawater by separating carbonates from the seawater.

7. a bipolar membrane electrodialysis device that produces acidic water and basic water by electrically treating seawater; a metal salt separation device that separates carbonates from the basic water produced by the bipolar membrane electrodialysis device; an alkalinity adjusting device for adjusting the alkalinity of seawater obtained by mixing the acidic seawater produced by the bipolar membrane electrodialysis device and basic seawater obtained by separating carbonates from the basic seawater produced by the bipolar membrane electrodialysis device; Equipped with A system that recovers carbon dioxide from seawater by separating carbonates from the seawater.

8. Carbon dioxide is recovered from seawater using the system for recovering carbon dioxide from seawater according to claim 6 or 7. Carbon dioxide capture methods.

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