Iron ion eluent and iron ion supply device

Abstract

To provide means for stably, in a long term, high concentration of iron ions by a simple structure.SOLUTION: An iron ion elution body 1 comprises: a plurality of carbon ferrous composite bodies 10; and a holding member 20 comprising therein, the carbon ferrous composite bodies 10, and supplies the iron ions into water. The holding member 20 is configured so that fluid can transmit between an inside and an outside thereof. A material of the holding member 20 may be for example, a natural fiber, a synthetic fiber, metal, and an inorganic fiber, and is preferably a conductive material. When the iron ion elution body 1 is installed in water, on the carbon ferrous composite bodies 10, on a contact interface between the carbon, the iron and water, a local battery is formed by a potential difference between the carbon and iron, thereby eluting divalent iron ion (Fe2+). When potentials stay on the carbon ferrous composite bodies 10, elution of the iron ion is disturbed, therefore electrons are preferably transferred to an outside of a system by a conductive assist material 30.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an iron ion eluting body and an iron ion supplying device that are placed in water to stably supply high concentrations of iron ions for a long period of time and purify aquatic environments, such as bottom sediment environments. [Background technology]

[0002] Enclosed sea areas such as ports and harbors are prone to eutrophication due to the accumulation of excess organic matter flowing in from coastal cities. Eutrophication not only causes red tides, but also worsens the bottom sediment environment as excess organic matter and nutrients accumulate and decay on the bottom. As a result, hydrogen sulfide is generated from the bottom sediment, which has become a highly reducing, dark, sludge commonly known as sludge, and this has frequently caused serious damage to the fishing industry and living environment.

[0003] To address this issue, it has been reported that the generation of hydrogen sulfide can be suppressed by spraying iron powder, iron oxide, or iron hydroxide on the bottom sediment (Non-Patent Documents 1 and 2). However, because the mechanism by which iron or iron compounds suppress hydrogen sulfide generation is primarily due to a chemical reaction between the two, there is a problem in that spraying must be repeated periodically to achieve a continuous effect.

[0004] However, because iron hydroxide and iron oxide can easily be generated by oxidizing iron ions eluted in the environment, there is a demand for methods and devices that can continuously supply iron ions to the environment. For example, proposed methods include the introduction of a sintered body of carbon and metallic iron particles (Patent Document 1), a method in which a bonded body of carbon material and metallic iron is immersed in water as an iron ion eluent (Patent Document 2), and a device that obtains iron ion-containing water by passing water through a container containing plate-shaped metallic iron and granular carbon material (Patent Document 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-053304 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-183676 [Patent Document 3] Patent No. 5539579 [Non-patent literature]

[0006] [Non-Patent Document 1] Inoue, T., Fujiwara, Y., Nakamura, Y., 2017. Suppression of sulfide elution from sediments by iron application. Journal of the Society of Marine Science and Technology, 23, 25-30. [Non-patent document 2] Kanaya Gen, Kikuchi Eisuke, 2009. Experimental study on the removal of free hydrogen sulfide from brackish water sediments by adding iron. Northeast Asian Studies, 13, 17-28. Summary of the Invention [Problem to be solved by the invention]

[0007] It is difficult to continuously supply high concentrations of iron ions stably for a long period of time using conventional technologies. For example, the method of Patent Document 2 and the device of Patent Document 3 have issues such as problems with the contact area and durability of the contact between the carbon material and metallic iron, and the need for a separate aeration device to increase the amount of iron ion elution.

[0008] Therefore, an object of the present invention is to provide a means that has a simple structure yet is capable of eluting high concentrations of iron ions stably for a long period of time. [Means for solving the problem]

[0009] As a result of extensive research, the present inventors have found that the problems of the prior art can be solved by the following configuration, and have thus completed the present invention. That is, the iron ion eluent of the present invention is an iron ion eluent for supplying iron ions into water, At least one carbon-iron composite; a holding member that holds the carbon-iron composite in a state where it can come into contact with water; Equipped with Furthermore, a conductive auxiliary material is provided that is placed in contact with the carbon-iron composite, or the holding member is formed of a conductive material.

[0010] In the iron ion eluting material of the present invention, the carbon-iron composite may be a sintered body of iron particles and a carbon material.

[0011] In the iron ion eluting body of the present invention, the holding member may be a mesh-like or cage-like structure that allows liquid to pass through, and the conductive additive may be housed inside the structure.

[0012] In the iron ion eluent of the present invention, the holding member may be formed of a conductive material, and the carbon-iron composite and the holding member may be in contact with each other.

[0013] The iron ion supply device of the present invention comprises any one of the iron ion eluting bodies described above and a conductive cathode electrically connected to the iron ion eluent; It is equipped with:

[0014] In the iron ion supply device of the present invention, the cathode may be placed on or near the water surface.

[0015] The iron ion supplying device of the present invention may have an iron ion elution capacity of 2000 mg / kg or more when immersed in a saline solution with a concentration of 3% by weight for 5 days. [Effects of the Invention]

[0016] The iron ion eluent and iron ion supply device of the present invention have a simple structure yet can elute high concentrations of iron ions into water stably for a long period of time, and can be widely used in environmental purification, wastewater treatment, etc. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram of an iron ion eluting material of the present invention. [Figure 2]FIG. 1 is a schematic diagram of a carbon-iron composite used in the iron ion eluent of the present invention. [Figure 3] 1 is a schematic diagram of an iron ion supply device of the present invention. [Figure 4] FIG. 2 is another schematic diagram of the iron ion supply device of the present invention. [Figure 5] FIG. 1 is a schematic diagram of a test device in Example 1. [Figure 6] FIG. 1 is a schematic diagram of a test device in Example 2. [Figure 7] FIG. 10 is a schematic diagram of a test device in Example 3. [Figure 8] FIG. 10 is a schematic diagram of a test device in Example 4. [Figure 9] FIG. 10 is a schematic diagram of a test device in Example 7. [Figure 10] FIG. 10 is a schematic diagram of a test device in Example 8. [Figure 11] FIG. 10 is a schematic diagram of a test device in Example 9. [Figure 12] FIG. 1 is a schematic diagram of a test device in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings as appropriate. The size and proportions of components in each drawing are different from the actual size and proportions for the sake of convenience, and the present invention is not limited by the drawings.

[0019] [Iron ion eluate] FIG. 1 is a schematic diagram illustrating an iron ion eluter according to one embodiment of the present invention. The iron ion eluter 1 includes one or more carbon-iron composites 10 and a holding member 20 that holds the carbon-iron composites 10 in a state where they can come into contact with water, and supplies iron ions to the water. The iron ion eluter 1 may include a conductive additive 30 that is placed in contact with the carbon-iron composites 10, or the holding member 20 may be made of a conductive material and hold the carbon-iron composites 10 in contact with the holding member 20. In this embodiment, the iron ion eluter 1 includes one or more granular carbon-iron composites 10, together with the conductive additive 30, housed inside a cage-like holding member 20 that has an outer shape such as a cylindrical shape. The iron-carbon composite 10, the holding member 20, and the optional conductive additive 30 that constitute the iron ion eluting body 1 will be described below in this order.

[0020] [Carbon-iron composite] The carbon-iron composite 10 used in the iron ion eluter 1 of this embodiment is a composite of a carbon material and metallic iron, either directly or using a binder. The carbon-iron composite 10 is a material that can supply iron ions by immersing it in water, due to the local cell effect that utilizes the potential difference between carbon and iron.

[0021] The carbon-iron composite 10 is preferably granular or lumpy, since a larger surface area can generate more iron ions. The breaking hardness of the carbon-iron composite 10 is preferably 50 N or more, and more preferably 80 N or more. If the breaking hardness is less than 50 N, the particles will come into contact with each other due to shaking caused by the water flow, making the carbon-iron composite 10 more likely to be broken. If the carbon-iron composite 10 is broken by the water flow, the iron and carbon will separate, eliminating the effect of the local battery and potentially reducing the amount of ferrous ions eluted. Furthermore, it is preferable that the carbon-iron composite 10 does not self-disintegrate even when immersed in the sea for more than one year. This is because the carbon-iron composite 10 can be prevented from disintegrating and falling to the seabed due to the rocking motions caused by tides, ocean currents, waves, etc. in the sea. From this perspective, it is even more preferable that the carbon-iron composite 10 has a breaking hardness of 50 N or more after 10 days of immersion in 5 wt% salt water, and maintains at least half of the breaking hardness before immersion in salt water. By maintaining a breaking hardness after 10 days of immersion in 5 wt% salt water at least half of the breaking hardness before immersion in salt water, the effect of the local battery can be maintained for a long period of time. The breaking hardness is preferably 50N or more, more preferably 80N or more, and most preferably 100N or more, even after immersion in seawater or freshwater for one month.

[0022] Examples of conventionally known carbon-iron composites 10 that can be used include those in which carbon fibers are fastened to iron material, those in which iron powder and a carbonaceous material such as charcoal are granulated with cement or clay, and those in which iron powder is baked and solidified with shochu dregs, organic sludge, starch, or blackstrap molasses. Among these, preferred is a carbon-iron composite 10 made by granulating iron and carbon with a carbon precursor and then baking and sintering the granulated material (see Patent Document 1). Such carbon-iron composites 10 are most preferred because they can continuously release iron ions stably over a long period of time, the carbon precursor used for granulation becomes hard carbon after sintering, resulting in high granular strength, and they do not leach out substances such as heavy metals and organic compounds that place a burden on the environment.

[0023] FIG. 2 is a diagram schematically illustrating the external configuration of a preferred example of a carbon-iron composite 10. As shown in FIG. 2, the carbon-iron composite 10 is a porous sintered body containing a plurality of iron particles 11 and a carbonaceous material 13. In the carbon-iron composite 10, the plurality of iron particles 11 are fixed by the carbonaceous material 13. The carbonaceous material 13 is an amorphous solidified material containing 95% by weight or more of conductive carbon. It functions as a structure supporting the iron particles 11 and forms a local battery through contact with the iron particles 11. The carbonaceous material 10 is a porous body having a predetermined bulk density and open porosity, and has a plurality of pores 15 formed therein. The carbonaceous material 13 may be present in a state in which a portion derived from the carbonaceous raw material, such as coke, and an adhesive portion derived from an organic material, such as an organic binder, are distinguishable from each other, or the two may be substantially integrated to form the carbonaceous material 13 in a state in which they are indistinguishable from each other.

[0024] The weight ratio of iron particles 11 to carbonaceous material 13 in the carbon-iron composite 10 (iron particles 11:carbonaceous material 13) can be adjusted depending on the sustainability of ferrous ion elution in water, but is, for example, in the range of 5:95 to 95:5, preferably 20:80 to 80:20, and more preferably 30:70 to 70:30. If the weight ratio of iron particles 11 to carbonaceous material 13 is less than 5 wt%, the amount of carbonaceous material 13 is too high, resulting in a small contact area with water, a low ability to supply ferrous ions, and poor sustainability. On the other hand, if the weight ratio of iron particles 11 to carbonaceous material 13 exceeds 95 wt%, a local battery is formed and sufficient iron ion supply capacity is provided, but the low carbon content makes the integrated composite brittle, leading to the iron particles 11 falling off from the surface and the collapse of the carbon-iron composite 10. The carbon-iron composite 10 contains oxygen (10% by weight or less) and trace amounts of other elements (Ni, Mn, etc.) in addition to iron and carbon, but the weight ratio above simply refers to the ratio of iron element to carbon element. The carbonaceous material 13 also contains carbonaceous raw materials such as coke that are blended in advance, as well as carbonized organic materials such as organic binders.

[0025] The carbon-iron composite 10 is preferably a porous sintered body having a bulk density of 1.1 to 4.0 and an open porosity of 20 to 70%. Here, the bulk density is more preferably 1.3 to 3.5. The open porosity is more preferably 30 to 60%. If the open porosity is less than 20%, the amount of ferrous ions eluted will be small, and if it exceeds 70%, the strength of the material will decrease and it will be prone to collapse, which is undesirable.

[0026] Furthermore, the carbon-iron composite 10 preferably has an amount of ferrous ions eluted after 10 days in salt water with a concentration of 3 wt % or more, preferably 3 to 5 wt %, of 2 ppm or more, more preferably 5 ppm or more, and even more preferably 10 ppm or more.

[0027] Furthermore, the carbon-iron composite 10 preferably exhibits a weight loss rate of 3% or less at temperatures between room temperature and 500°C in thermogravimetric analysis in an inert atmosphere. A weight loss rate of 3% or less at temperatures between room temperature and 500°C indicates that the organic binder and coke powder are completely carbonized. Therefore, the carbon-iron composite 10 is less likely to disintegrate when placed in water, and organic compounds harmful to the environment are not eluted from the carbon-iron composite 10, so no additional environmental burden is created.

[0028] In the carbon-iron composite 10, zero-valent metallic iron forms a local battery when it comes into contact with carbon, and divalent iron ions are eluted into water. Therefore, even if the iron particles 11 are in the form of iron oxide in the raw iron material stage, they are sufficient as long as they become metallic iron in the final product after firing. However, it is preferable to use a steel material containing iron (Fe) as the main component and at least one of carbon (C), manganese (Mn), and nickel (Ni) in an amount of 0.5% by weight or more. Examples of such iron particles 11 include, but are not limited to, cast iron, carbon steel, and stainless steel.

[0029] The iron particles 11 constituting the carbon-iron composite 10 gradually become smaller in size as they release divalent iron ions into the seawater due to a local battery effect with the sintered carbon. Therefore, the particle size of the iron particles 11 used is preferably 200 to 5 mesh according to the JIS standard. Note that, since the smaller the mesh number in the JIS standard, the larger the particle size, the term "5 mesh or less" does not include, for example, "4 mesh." Particle sizes smaller than 200 mesh are too small, resulting in a short contact period with water and the risk of fire, dust explosion, and the like during production. Furthermore, particle sizes larger than 5 mesh are too large, making mixing, kneading, and granulation difficult. The shape of the iron particles 11 may be, for example, spherical or granular, or may be an irregular block. For ease of explanation, the iron particles 11 are depicted in FIG. 2 as a regular hexagonal polyhedron in plan view, but this is not limiting.

[0030] The carbonaceous material 13 constituting the carbon-iron composite 10 is necessary for forming a local battery with iron, and contact with iron is extremely important. Examples of the carbonaceous material 13 (carbonaceous raw material) for forming the local battery include coke, charcoal, coal powder, graphite, coal tar pitch, and carbides of organic compounds and polymeric materials. These can be used alone or in combination. The carbonaceous raw material may be in any shape, but powdery or lumpy forms are preferred, as they increase the number of contact points with the iron particles 11 after sintering and facilitate local battery function. An irregular shape is also acceptable. Preferably, 50% by weight or more of the carbonaceous raw material blended with the iron raw material is a solid carbonaceous material that melts at high temperatures and does not exhibit fluidity. Examples of such solid carbonaceous materials include graphite and coke powder. Pitch coke powder, which has a temperature history of 450°C or higher and is electrically conductive, is particularly preferred.

[0031] Pitch coke powder with a temperature history of 450°C or higher does not melt and flow at high temperatures like coal tar pitch or polymeric materials. Therefore, it is easy to maintain the granulated shape and to obtain a porous carbon-iron composite 10. The particle size of the carbonaceous raw material, typified by coke powder, is preferably 300 to 5 mesh according to the JIS standard, for example, to increase the number of contact points with the iron particles 11 after sintering, thereby improving the efficiency of the local battery function and granulation. If the particle size is larger than 5 mesh, the number of contact points for forming the local battery with the iron particles 11 decreases, resulting in a decrease in elution efficiency. On the other hand, if the particle size is smaller than 300 mesh, the bulk density becomes too small, which not only deteriorates mixing and granulation properties but also poses the risk of fire, dust explosion, etc.

[0032] The coke powder can be either petroleum-based or coal-based heavy oil-derived coke. Among these, coke derived from coal-based heavy oil is preferred because it is mesophase-rich and easily becomes needle coke, which results in high electrical conductivity, which in turn facilitates the flow of current as a local battery, and facilitates the generation of iron ions.

[0033] The carbon-iron composite 10 shown in FIG. 2 is a sintered body of iron and non-organic, electrically conductive carbon. It is preferable to use an organic binder that carbonizes at high temperatures during the manufacturing process. The use of an organic binder promotes the aggregation of powdery raw materials, increasing the granulation rate and improving yield. Furthermore, the carbonization of the organic binder during sintering improves the physical properties (strength, surface condition, disintegration resistance, etc.) of the carbon-iron composite 10 and strengthens the adhesion between the iron particles 11 and the carbonaceous material 13. From this perspective, preferred organic binders include pitch, phenolic resin, lignin, or lignin sulfonate, which contains 20% or more by weight of fixed carbon and a large amount of aromatic rings. Among these, coal tar pitch, which has excellent fixed carbon and binding strength, is the most preferred.

[0034] When coal tar pitch is fired at 500°C or higher in an inert or reducing atmosphere, hydrogen, oxygen, nitrogen, sulfur, and other components other than fixed carbon are decomposed and volatilized, resulting in a firing product that is essentially 95% or more carbon. Furthermore, coal tar pitch releases hydrogen, oxygen, nitrogen, sulfur, and other components during firing, forming voids that increase the contact area between water and iron, contributing to efficient iron ion generation. Furthermore, coal tar pitch becomes a strong, electrically conductive carbide, making it an effective binder for fixing iron particles 11 and carbonaceous material 13. Among coal tar pitches, those with a fixed carbon content of 50% by weight or more are preferred in terms of maintaining their shape during firing. Examples of such coal tar pitches include BP and IP (both product names) manufactured by C-Chem Co., Ltd.

[0035] The organic binder is preferably blended in an amount of, for example, 5 to 20 parts by weight per 100 parts by weight of the mixture of iron raw material and carbonaceous raw material. If the organic binder is less than 5 parts by weight, it will not function as a binder, and if it exceeds 20 parts by weight, the organic binder will melt during firing, making it impossible to obtain the desired shape, suitable bulk density, or open porosity. Furthermore, if a composite is formed using only an iron raw material and an organic binder such as coal tar pitch, the organic binder will melt during firing, making it impossible to maintain the shape of the composite.

[0036] The organic binder, typically coal tar pitch, is preferably in powder form so that it can be uniformly mixed with the iron raw material and the carbonaceous raw material. The particle size of this powder is preferably 200 to 32 mesh, for example. If the particle size of the organic binder is too small, the bulk density will be too low, which will deteriorate the mixing and kneading properties. If the particle size is too large, the mixing, heat melting, and the interior of the granulated product may become non-uniform. Furthermore, it is preferable that the coal tar pitch has a softening point within a temperature range of, for example, 30 to 150°C. The use of coal tar pitch with such a softening point is very convenient for granulation methods that utilize intermolecular forces, such as briquetting machines that mold (granulate) a mixture while heating, melt granulation, and dry granulation. After granulation by these methods, the mixture can be fired as is, allowing for efficient production of the carbon-iron composite 10.

[0037] In addition to coal tar pitch or phenolic resin, a granulation aid may be added to the organic binder to improve granulation properties. The granulation aid is not particularly limited as long as it becomes carbonaceous material 13 during sintering. Suitable examples of the granulation aid include gelatin, starch paste, blackstrap molasses, lignin sulfonate, konjac flour, sodium alginate, polyvinyl alcohol, dextrin, ethyl cellulose, carboxymethyl cellulose, and polyacrylamide. When a granulation aid is used, the weight ratio of the organic binder to the granulation aid (organic binder:granulation aid) is preferably 100:0 to 30:70, for example. By adjusting the granulation aid ratio within this range, a carbon-iron composite 10 having a desired shape can be easily produced without adversely affecting the bulk density, open porosity, fracture hardness, and other properties during sintering.

[0038] The carbon-iron composite 10 may further contain, in addition to iron and carbon, inorganic minerals containing elements such as silicon, aluminum, magnesium, calcium, phosphorus, sodium, and potassium, as long as the physical properties such as fracture hardness, bulk density, and open porosity and the elution of divalent iron ions due to the local battery effect are not hindered.

[0039] The carbon-iron composite 10 can be produced by blending an organic binder with a mixture of an iron raw material and a carbonaceous raw material, granulating the mixture into a desired shape as needed, and then firing and sintering the mixture at a temperature of 500°C or higher in an inert or reducing atmosphere.

[0040] The order in which the iron raw material, carbonaceous raw material, and organic binder are mixed is not particularly limited; a mixture of the iron raw material and carbonaceous raw material may be prepared first, and then the organic binder may be mixed, or all the raw materials may be mixed at once. The same applies when other additives are mixed. For the mixing method, general mixing and kneading devices such as various blenders, mixers, and kneaders can be used.

[0041] The mixture of various raw materials is granulated into any shape as needed. The granule shape is not particularly limited, and can be, for example, spherical, spheroidal, cylindrical, irregular, etc. Among these, spherical or spheroidal shapes are preferred because they increase the contact area with seawater, etc. The size of the granules is not particularly limited, but in the case of a spherical shape, a diameter of 5 mm or more is preferred, and preferably a diameter of about 5 to 100 mm. In addition, if the shape of the granules is other than spherical, it is preferable to size them so that they have a volume similar to that of a sphere with a diameter of 5 to 100 mm. Although granulation can be carried out manually, it is preferable to use a granulator such as a pelletizer or briquette machine in terms of workability, safety, shape control, etc.

[0042] If water or an organic solvent is used during granulation, the granulated raw material mixture is dried at 60°C or higher and then fired and sintered in an inert or reducing atmosphere at 500°C or higher. For firing, equipment such as a lead hammer furnace, top charge furnace, shuttle furnace, tunnel furnace, rotary kiln, roller hearth kiln, or microwave oven can be used, but is not limited to these. Furthermore, the calcination process can be performed either continuously or batchwise. The firing temperature is preferably 700°C or higher, more preferably 900°C or higher, and most preferably 1000°C or higher. By firing in an inert or reducing atmosphere at 500°C or higher, the organic binder is reliably carbonized and iron oxide contained in the iron raw material can be reduced. The carbon-iron composite 10 obtained by firing can be used as an environmentally friendly iron ion source that exhibits rapid leaching of divalent iron ions and high fracture hardness. The firing may be carried out multiple times, and the sintered body may be immersed in an aqueous solution of a compound of iron, manganese, or the like, and then fired again.

[0043] The carbon-iron composite 10 that has undergone the sintering process is then slowly cooled in an inert or reducing atmosphere, or slowly cooled and then allowed to cool to a temperature that allows it to be handled in the air, after which it is stored in the internal space of the holding member 20 and used as the iron ion eluting body 1.

[0044] [Holding member] The holding member 20 has a space therein that can accommodate at least one carbon-iron composite 10, and is configured to allow liquid to pass between its interior and exterior. The outer shape of the holding member 20 may be, for example, a rectangular parallelepiped, a cube, a cylinder, or the like. The holding member 20 may also be basket-shaped, bag-shaped, net-shaped, dish-shaped, or the like.

[0045] The material of the holding member 20 is not particularly limited as long as it is not easily corroded or decomposed in water. Examples include natural fibers, synthetic fibers, metals, and inorganic fibers. However, it is preferably made of a conductive material, and a material that is a good conductor is more preferable. If the material constituting the holding member 20 is an electrically good conductor, contacting the multiple carbon-iron composites 10 housed inside with the holding member 20 allows electrons generated by the local battery effect in the carbon-iron composites 10 to be efficiently exchanged through the holding member 20, thereby increasing the amount of iron ion elution. Therefore, the material constituting the holding member 20 is preferably metal or carbon, and more preferably carbon fiber, stainless steel, or titanium. The conductive material constituting the holding member 20 may be used alone or in combination of two or more types.

[0046] It is preferable that the carbon-iron composite 10 stored inside the holding member 20 be removable. Over long-term use, flocs such as iron hydroxide generated from the carbon-iron composite 10 may accumulate, causing clogging, or microorganisms may attach and grow, forming a biofilm on the surface, reducing the amount of iron ion elution. By designing the holding member 20 so that the carbon-iron composite 10 can be removed, it becomes easier to reuse the holding member 20 and replace, clean, and recycle the carbon-iron composite 10, thereby reducing operating costs.

[0047] It is preferable that a plurality of carbon-iron composites 10 are stored in the internal space of the holding member 20 in order to increase the amount of iron ions eluted, and it is desirable that a conductive additive 30 made of a conductive material is further stored in addition to the carbon-iron composites 10.

[0048] [Conductive additive] The conductive additive 30 has the function of promoting the external movement of electrons generated in the carbon-iron composite 10. When the iron ion eluting material 1 is placed in water, a local battery is formed at the contact interface between the carbon and iron in the carbon-iron composite 10 and the water due to the potential difference between the carbon and iron, and divalent iron ions (Fe 2+) is eluted. At this time, electrons generated with the elution (ionization) of iron are ultimately consumed at another location in the carbon-iron composite 10. However, if electrons remain in the carbon-iron composite 10, they will hinder the elution of iron ions. Therefore, it is preferable to transfer the electrons outside the system using the conductive additive 30. By using the conductive additive 30, the amount of iron eluted from the carbon-iron composite 10 can be increased. Furthermore, when the carbon-iron composite 10 is used alone, iron hydroxide formed by bonding between hydroxyl groups generated on the carbon on its surface and iron ions tends to accumulate on the surface of the carbon-iron composite 10, leading to a decrease in the iron ion generation capacity. Therefore, it is possible to prevent the accumulation of iron hydroxide on the surface of the carbon-iron composite 10 by mixing the carbon-iron composite 10 with an appropriate amount of conductive additive 30.

[0049] The material of the conductive additive 30 is not particularly limited as long as it is electrically conductive and does not corrode or dissolve in water, and for example, metals more noble than stainless steel or iron, carbon materials, etc. Since the iron ion eluate 1 is held in water, carbon materials such as charcoal, bamboo charcoal, natural graphite, artificial graphite, steel coke, needle coke, and compacts thereof are more preferred for the purpose of having a low specific gravity and quickly transferring electrons out of the system, and natural graphite, artificial graphite, steel coke, needle coke, and compacts thereof are even more preferred, and the material should have a volume resistivity of 1×10 measured by a four-terminal method. -2 Needle coke, a carbon material with high electrical conductivity of Ω·cm or less, and compacts made from needle coke are most preferred.

[0050] The shape of the conductive additive 30 is not particularly limited, and any of a sphere, ellipsoid, cube, prism, cylinder, polyhedron, irregular granular or lumpy body, a plate or sheet such as woven fabric, felt, or mesh, or a cotton-like material made of short fibers, long fibers, or continuous fibers can be selected and used, but it is preferable to select and use one that has a large contact area with the carbon-iron composite 10 and the conductive holding member 20.

[0051] The iron ion eluting body 1 having the above-described configuration can supply iron ions to the surrounding area by simply placing it in water. There are no particular restrictions on the location in water; it can be on the bottom, underwater, or on the surface of the water. However, it is preferable to place the iron ion eluting body 1 so that at least a portion of it is exposed to the atmosphere, or to place it on or near the surface of the water, where the oxygen concentration is high, because this increases the amount of iron ions generated. Furthermore, seawater or the like can be poured directly onto the iron ion eluting body 1, or the iron ion can be contained in the outflow water by placing it in a container such as a tank and passing water through it.

[0052] Preferred methods for installing the iron ion eluting body 1 on or near the water surface, such as the ocean surface, include suspending it from a floating body such as a quay or a buoy, or a stake fixed to the water bottom, or fixing it to the bottom of a ship or a fish pond used for cultivating fish, shellfish, seaweed, etc. These installation methods can include mooring it with a long member such as a rope or chain, or fixing it with a detachable adapter. When fixing the iron ion eluting body 1, it may be in a state where it can sway with the water current. Alternatively, it may be moored so that one end is fixed to the water bottom and the other end is fixed to a float using a rope or the like, so that the iron ion eluting body 1 floats in the water.

[0053] [Iron ion supply device] 3 is a schematic diagram of an iron ion supplying device according to one embodiment of the present invention, which uses an iron ion eluter 1. The iron ion supplying device 100 includes the iron ion eluter 1, a cathode 101 electrically connected to the iron ion eluter 1, and a conductor 102 electrically connecting the iron ion eluter 1 and the cathode 101. Note that an actual device only needs to satisfy the concept of this diagram, and the positions and sizes of the cathode 101 and the iron ion eluter 1 are not limited to those shown in the diagram.

[0054] The iron ion supply device 100 according to the present embodiment extracts iron ions (Fe ions) from the carbon-iron composite 10 of the iron ion eluting body 1 immersed in water such as seawater 110. 2+ ) is dissolved, the electrons (e -) is collected by the conductive additive 30 and the holding member 20 and conducted via a conductor 102 to a cathode 101 placed on the water surface 110a, where it is consumed outside the carbon-iron composite 10. The carbon-iron composite 10 generates electrons when iron dissolves into the water as divalent ions, as shown in the following formula (1), due to a local battery formed between the carbon and iron. However, the generated electrons are thought to inhibit the dissolution of iron ions from the carbon-iron composite 10 unless they are consumed by the reaction shown in the following formula (2) at another location in the carbon-iron composite 10. Therefore, by separately providing a cathode 101 on the water surface 110a, which is rich in dissolved oxygen, the electrons can be consumed, promoting the dissolution of iron ions from the carbon-iron composite 10 (i.e., increasing the amount of iron ions dissolved). Fe → Fe 2+ +2e - (1) H2O+1 / 2O2+2e - →4OH - (2)

[0055] The iron ion elution ability of the iron ion supplying device 100 is preferably evaluated not by the eluted iron ion concentration but by the amount of eluted iron per unit weight (1 kg) of the carbon-iron composite 10 used in the iron ion supplying device 100 when immersed in a 3 wt % saline solution for 5 days. This is because the amount of eluted iron ions is significantly affected by the iron / carbon ratio of the carbon-iron composite 10, the number of carbon-iron composites 10, and the size (= surface area) of the carbon-iron composites 10. If the amount of eluted iron ions per unit weight of the carbon-iron composite 10 is large, the amount of carbon-iron composite 10 required to elute a desired concentration of iron ions into the environment is reduced, allowing for a lightweight and compact device, which is particularly advantageous in the case of a floating iron ion supplying device (see, for example, Figure 4). The iron ion elution ability when immersed in a 3 wt % saline solution for 5 days is such that the amount of iron ions generated per unit weight of the carbon-iron composite 10 is preferably 2000 mg / kg or more, more preferably 2500 mg / kg or more, and even more preferably 3000 mg / kg or more.

[0056] The material of the cathode 101 is not particularly limited, and examples thereof include conductive materials such as metal materials and carbon materials. However, materials with high electrical conductivity and a higher standard electrode potential than iron are preferred. Examples of such metal materials include stainless steel, titanium, copper, and platinum. Examples of carbon materials include coke, graphite, porous carbon, carbon fiber, carbon cloth, carbon mat, carbon felt, and carbon paper. It is more preferable to use a carbon material with a high specific surface area and that is resistant to corrosion even in seawater 110 as the cathode 101, and a porous carbon material is most preferred.

[0057] The shape of the cathode 101 is not particularly limited, and examples thereof include a sheet, plate, rod, string, mesh, lattice, bellows, block, porous, etc., and further includes shapes with irregularities or holes, bent or curved shapes, etc. Also, granular aggregates may be aggregated to form the cathode 101, and a catalyst portion for promoting the electrode reaction may be disposed on the surface of the cathode 101.

[0058] The cathode 101 is preferably provided outside the iron ion eluter 1, and may be disposed either separately from or adjacent to the iron ion eluter 1. In Fig. 3, the iron ion supply device 100 is completely submerged in water, with the iron ion eluter 1 located below the cathode 101. On the other hand, the cathode 101 is located at or near the water surface 110a, but the iron ion eluter 1 may also be located at or near the water surface 110a, like the cathode 101.

[0059] The iron ion eluter 1 is electrically connected to the cathode 101 via a conductor 102. The conductor 102 transports electrons generated when iron ions are eluted from the carbon-iron composite 10 to the cathode 101. The conductor 102 is preferably made of stainless steel, titanium wire, or carbon fiber, which have excellent corrosion resistance, and more preferably titanium wire from the viewpoint of corrosion resistance and durability against vibration. The conductor 102 is preferably coated with an insulating material such as synthetic resin. The connection between the iron ion eluter 1 and the cathode 101 by the conductor 102 may be such that the carbon-iron composite 10 is directly connected to the cathode 101, or such that a current collector (not shown) is provided and the cathode 101 is connected via the current collector. The conductive additive 30 may be connected to the cathode 101 by the conductor 102, and when the holding member 20 of the iron ion eluter 1 is made of a good electrical conductor, the holding member 20 may be connected to the cathode 101 by the conductor 102.

[0060] 4 is a conceptual diagram of another example of an iron ion supply device using the iron ion eluter 1. Note that an actual device only needs to satisfy the concept of this diagram, and the positions and sizes of the cathode 101 and the iron ion eluter 1 are not limited to those shown in the diagram.

[0061] The iron ion supplying device 200 shown in Fig. 4 includes an iron ion eluting body 1, a cathode 101 electrically connected to the iron ion eluting body 1, and a float 103 that provides buoyancy to these. The material and shape of the cathode 101 are the same as those of the embodiment shown in Fig. 3. The float 103 is not particularly limited as long as it is made of a material and has a structure that provides buoyancy in water, and a buoy, float, or the like can be used. The iron ion supplying device 200 is configured to float on the water surface 110a by the buoyancy of the float 103.

[0062] In the iron ion supply device 200, an iron ion eluter 1 having an electrically conductive retaining member 20 is located directly below a cathode 101, and the entire iron ion eluter 1 is completely submerged in water, such as seawater 110. Meanwhile, the cathode 101 is located directly above the iron ion eluter 1, with a portion of the iron ion eluter exposed to the atmosphere. The iron ion eluter 1 and the cathode 101 are electrically connected to each other. In the iron ion supply device 200 shown in FIG. 4, electrons generated when iron ions are eluted from the carbon-iron composite 10 are transferred to the cathode 101 through the retaining member 20 or the conductive additive 30. Although not shown, the iron ion eluter 1 and the cathode 101 may be electrically connected using a conductor. Other configurations and effects of the iron ion supply device 200 shown in FIG. 4 are similar to those of the iron ion supply device 100 shown in FIG. 3.

[0063] Another example of an iron ion supply device using the iron ion eluter 1 is a wire-free device configuration in which the iron ion eluter 1 and the cathode 101 are not connected by a conductor 102 but are placed close to each other (within approximately 0.5 m, preferably within 0.1 m) and spaced apart from each other. In this case, electrons generated when iron ions are eluted from the carbon-iron composite 10 reach the cathode 101 through the water, so the transmission of electrons generated from the iron ion eluting material 1 to the cathode 101 is slower than in a wired type (e.g., the device shown in Fig. 3). Therefore, it is preferable to use a cathode 101 with a large surface area, such as a granular porous carbon electrode housed in a housing made of a conductive material, and to place it above the iron ion eluting material 1 or to the side in consideration of the water flow. The housing used here can have a structure similar to that of the holding member 20. In the case of a wired iron ion supply device, the iron ion eluting body 1 and the cathode 101 are arranged at a distance from each other, so that they are "electrically unconnected" when not immersed in water. However, in actual use when they are immersed in seawater or other water, they are "electrically connected" using water as a medium, so that even the wired iron ion supply device has an "electrically connected cathode 101."

[0064] As described above in detail, the iron ion eluting body 1 and the iron ion supplying devices 100, 200 can be installed in seawater 110, freshwater, or other water and used widely in environmental improvement fields, such as suppressing the generation of hydrogen sulfide from bottom sediments in closed bodies of water such as harbors and lakes, and purifying sludge by activating microorganisms. Furthermore, the iron ion eluting body 1 and the iron ion supplying devices 100, 200 can be applied to small bodies of water such as park ponds and moats because the device configuration can be flexibly adjusted. [Example]

[0065] The results of experiments carried out to demonstrate the present invention will be described below as examples, but the present invention is not limited to these examples.

[0066] [Bulk density] Measurement was performed by the Archimedes method.

[0067] [Open porosity] The dry weight of the sample, the weight in water when immersed in pure water, and the weight saturated with water when evacuated and saturated with water were measured, and the open porosity was calculated using the obtained weights according to the following formula. Open porosity (%) = [(saturated weight - dry weight) / (saturated weight - submerged weight)] x 100

[0068] [Fracture hardness] The load at which the granules collapse (buckle) was taken as the crushing load (breaking hardness). A Fujiwara Seisakusho Kiya-type hardness tester 1600-C (maximum 200N) was used to measure the load, applying a compressive load to the sample. The maximum load was taken as the crushing load, and the average value of five granules was used.

[0069] [Ni and Cr elution confirmed] In the examples and comparative examples in which a stainless steel mesh basket (SUS304) was used, the iron-carbon composite 10 was removed after the test, and the seawater 110 containing iron hydroxide was heated and dissolved in 10% nitric acid. The concentrations of nickel and chromium ions were measured simultaneously with the iron ion measurement by ICP atomic emission spectrometry.

[0070] [Iron ion elution amount and elution capacity] The iron ion eluting body 1 (or iron ion supplying device 100) of each of the examples and comparative examples was immersed in seawater 110 (salinity: 3 wt%) and allowed to stand. After immersion for 5 days, iron hydroxide generated in the seawater 110 was completely dissolved by adding 10 wt% nitric acid. The iron ion concentration in the seawater 110 after immersion was measured using a Pack Test (Kyoritsu Chemical Research Total Iron WAK-Fe) and used as the amount of eluted iron. The iron ion elution capacity was calculated by dividing the iron ion concentration by the weight (unit: kg) of the iron ion generating source (iron plate, iron ball, or carbon-iron composite 10) used in the iron ion eluting body 1 (or iron ion supplying device 100). Note that the stainless steel cage was not considered as an iron ion generating source when calculating the iron ion elution capacity. During the measurement, the cathode 101 was positioned near the water surface as shown in Figure 3, and the iron ion eluting body 1, which functions as an anode, was placed so that its entirety was completely immersed in seawater 110.

[0071] [Carbon-iron composite] A carbon-iron composite 10 having a similar configuration to that shown in Figure 2 was used. Specifically, cast iron powder (Takeuchi Industries Co., Ltd., 28 mesh under, carbon: 2-4 wt%, Si: 4 wt% or less, Mn: 0.5-1.5 wt%, P: 0.03 wt% or less, S: 0.03 wt% or less) and needle coke powder (Nippon Steel Chemical & Material Co., Ltd., 9 mesh under) were granulated in a briquette machine (pocket: 18 x 14 x 3.3 mm deep) using binder pitch (Nippon Steel Chemical & Material Co., Ltd., softening point: 85°C, fixed carbon content: 58%) and starch (Asada Flour Milling Co., Ltd., pregelatinized rye flour, residual carbon content: 10%). The granules were then fired and sintered at 800°C in a non-oxidizing atmosphere to produce the carbon-iron composite 10. Table 1 shows the details of the carbon-iron composite 10 used. The apparent surface area per particle of the carbon-iron composite 10 was 5.1 cm based on the pocket size of the briquette machine. 2 The weight was 2.1 g, the bulk density was 2.02, and the open porosity was 30%.

[0072] [Table 1]

[0073] [Porous carbon material A] True density 1.82g / cm 3 The pitch coke was crushed and adjusted to a particle size blend of 25% 0.250-0.500 mm, 45% 0.075-0.249 mm, and 30% 0.074 mm or less. 40 parts by weight of binder pitch (manufactured by C-Chem, softening point: 97°C) obtained from coal-based heavy oil was added to 100 parts by weight of the pitch coke particles, and the mixture was heated and kneaded at 200°C for 20 minutes. This kneaded mixture was extruded and molded into a 20 mm diameter rod. After molding, it was fired in a non-oxidizing atmosphere at 900°C to obtain a sintered product (carbon compact). This carbon compact was processed into a 20 mm diameter x 48 mm diameter sample to obtain porous carbon material A with a bulk density of 1.40 and a water absorption rate of 8.9%. The water absorption rate was measured by immersing a porous carbon material A whose weight had been measured in advance in pure water at room temperature, removing it after 24 hours, and leaving it to stand at room temperature for 3 minutes. When there were no more drops of water and the water had sufficiently drained, the weight M2 was measured, and the water absorption rate was calculated as the ratio of the increased weight (M2-M1) to the weight M1 before immersion using the following formula. Water absorption rate [%]=[(M2-M1) / M1]×100

[0074] [Porous carbon material B] Needle coke powder (manufactured by C-Chem, 9 mesh under) was granulated in a briquette machine (pocket: 18 x 14 x depth 3.3 mm) using binder pitch (manufactured by C-Chem, softening point: 90°C) and starch (pregelatinized rye flour, manufactured by Asada Flour Milling Co., Ltd.), and fired and sintered at 900°C in a non-oxidizing atmosphere to produce porous carbon material B. The apparent surface area per particle of porous carbon material B was 5.0 cm. 2 The weight was 1.8 g, the bulk density was 1.27, and the open porosity was 39%.

[0075] [Example 1] A cylindrical stainless steel mesh basket (material: SUS304, weight: 7.0 g) was prepared as the holding member 20, and one carbon-iron composite 10 was placed inside to form the iron ion eluting material 1. Next, a round screw-cap bottle 104 with an inner diameter of the bottom of 55 mm and a capacity of 220 ml was prepared, and the iron ion eluting material 1 was suspended by a nylon thread 105 using a hole (diameter: 5 mm) drilled in the lid, and 150 ml of natural seawater 110 (salinity: 3 wt %; collected at Hiramatsu Fishing Port, Fukuoka Prefecture; the same applies below) was poured into the bottle until the holding member 20 was completely submerged. The round screw-cap bottle 104 was placed in a thermostatic water bath (not shown), set to a temperature of 27°C, and left to stand for 5 days, after which the amount of iron ions eluted into the seawater 110 in the bottle was measured. The outline of the test device in Example 1 is shown in FIG. 5, and the evaluation results are shown in Table 2.

[0076] [Example 2] A nylon mesh bag (weight 0.7 g) was prepared as the holding member 20, and one carbon-iron composite 10 and one porous carbon material B as the conductive additive 30 were placed inside to prepare the iron ion eluter 1. The porous carbon material B was placed on top of the carbon-iron composite 10 in contact with it. Next, a round screw-cap bottle 104 with an inner diameter of the bottom of 55 mm and a capacity of 220 ml was prepared, and the iron ion eluting body 1 was suspended by a nylon thread 105 using a hole (diameter 5 mm) opened in the lid, and 150 ml of natural seawater 110 was poured into it until the holding member 20 was completely immersed. The round screw-cap bottle 104 was placed in a thermostatic water bath (not shown), set at a temperature of 27° C., and left to stand for 5 days, after which the amount of iron ions eluted into the seawater 110 in the bottle was measured. The outline of the test device in Example 2 is shown in FIG. 6, and the evaluation results are shown in Table 2.

[0077] [Example 3] The amount of iron ions eluted into the seawater 110 in the bottle was measured in the same manner as in Example 2, except that needle coke blocks (LPC-U manufactured by C-Chem, 4.0 g / piece) were used as the conductive additive 30 housed together with the carbon-iron composite 10 in the iron ion eluting body 1. An outline of the test apparatus is shown in Figure 7, and the evaluation results are shown in Table 2.

[0078] [Example 4] A nylon mesh bag (weight 0.7 g) was prepared as the holding member 20, and one carbon-iron composite 10 and carbon fiber (12K, 0.16 g, manufactured by Nippon Graphite Fiber Co., Ltd.) without sizing as the conductive additive 30 were placed inside to prepare the iron ion eluting material 1. The carbon-iron composite 10 was placed on top of the carbon fiber in contact with it. Next, a round screw-cap bottle 104 with an inner diameter of the bottom of 55 mm and a capacity of 220 ml was prepared, and the iron ion eluting body 1 was suspended by a nylon thread 105 using a hole (diameter 5 mm) opened in the lid, and 150 ml of natural seawater 110 was poured into it until the holding member 20 was completely immersed. The round screw-cap bottle 104 was placed in a thermostatic water bath (not shown), set at a temperature of 27° C., and left to stand for 5 days, and the amount of iron ions eluted into the seawater 110 in the bottle was measured. The outline of the test device in Example 4 is shown in FIG. 8, and the evaluation results are shown in Table 2.

[0079] [Example 5] The amount of iron ions eluted into the seawater 110 in the bottle was measured in the same manner as in Example 2, except that the number of carbon-iron composites 10 housed in the iron ion eluter 1 was three and the number of porous carbon materials B serving as the conductive additives 30 was nine. The evaluation results are shown in Table 2.

[0080] [Example 6] Although not shown in the figure, a nylon mesh bag (weight 0.7 g) was prepared as the holding member 20, and one carbon-iron composite 10 and carbon fiber (12K manufactured by Nippon Graphite Fiber Co., Ltd.) without sizing as the conductive additive 30 were placed inside to prepare the iron ion eluting body 1. The carbon-iron composite 10 was placed on top of the soaked carbon fiber so that it was in contact with the carbon fiber. Next, a round screw-cap bottle 104 with a capacity of 220 ml and an inner diameter of the bottom of 55 mm was prepared, and the iron ion eluent 1 was suspended by a nylon thread 105 using a hole (diameter: 5 mm) drilled in the lid. 150 ml of natural seawater 110 was poured into the bottle until the holding member 20 was completely immersed. At this time, one-third of the total length of the carbon fibers was immersed in the seawater 110, and the remaining two-thirds were bundled together to prevent the fibers from breaking and placed as the cathode 101 near the water surface 110a directly above the holding member 20. The round screw-cap bottle 104 was placed in a thermostatic water bath set at 27° C. and left to stand for 5 days, and the amount of iron ions eluted into the seawater 110 in the bottle was measured. The evaluation results are shown in Table 2.

[0081] [Example 7] A cylindrical stainless steel mesh basket was prepared as the holding member 20, and one carbon-iron composite 10 and one porous carbon material B as the conductive additive 30 were placed inside to form an iron ion eluting body 1. Next, the porous carbon material A was prepared as a cathode 101, and the cathode 101 and the holding member 20 were electrically connected using a titanium wire conductor 102 to form an iron ion supplying device 100. A 2000 ml plastic bottle 106 was filled with 1500 ml of natural seawater 110, and placed in a thermostatic water bath (not shown). The bottle was suspended from a hole (5 mm diameter) in the lid so that the iron ion eluting body 1 was located at the bottom and the porous carbon material A was located on the water surface 110a. The thermostatic water bath was set to a temperature of 27°C and left to stand for 5 days, and the amount of iron ions eluted into the seawater 110 in the bottle was measured. The outline of the test device in Example 7 is shown in FIG. 9, and the evaluation results are shown in Table 2.

[0082] [Example 8] A cylindrical stainless steel mesh basket with an openable lid was prepared as the holding member 20, and one carbon-iron composite 10 and two porous carbon materials B as the conductive additives 30 were placed inside to form the iron ion eluting body 1. Next, the lid of the holding member 20 was closed, and five pieces of porous carbon material B (total of 9 g) were piled on top of it so as to be as flat as possible, and placed as a cathode 101 to prepare an iron ion supplying device 100. A 2000 ml plastic bottle 106 was filled with 1500 ml of natural seawater 110 and placed in a thermostatic water bath (not shown). At this time, the porous carbon material B placed on the lid of the holding member 20 was hung by a nylon thread 105 using a hole (5 mm diameter) drilled in the lid of the plastic bottle 106 so that it was exposed above the water surface 110a at a height of about 1 mm, and the iron ion eluting body 1 was completely immersed in the seawater 110. The thermostatic water bath was set to a temperature of 27°C and left to stand for 5 days, and the amount of iron ions eluted into the seawater 110 in the bottle was measured. The outline of the test device in Example 8 is shown in FIG. 10, and the evaluation results are shown in Table 2.

[0083] [Example 9] A cylindrical stainless steel mesh basket was prepared as the holding member 20, and one carbon-iron composite 10 was placed inside to form the iron ion eluting material 1. Next, five pieces of porous carbon material B (9 g in total) were placed in a cylindrical stainless steel mesh basket to prepare a cathode 101. A 2000 ml plastic bottle 106 was filled with 1500 ml of natural seawater 110 and placed in a thermostatic water bath (not shown). An iron ion eluting body 1 was placed on the bottom of the plastic bottle 106 so that it was completely immersed in the seawater 110. The porous carbon material B of the cathode 101 was positioned 5 cm above the iron ion eluting body 1, and was suspended by a nylon thread 105 using a hole (5 mm diameter) opened in the lid, forming a wire-free iron ion supply device 100. The thermostatic water bath was set to a temperature of 27°C and left to stand for 5 days, after which the amount of iron ions eluted into the seawater 110 in the bottle was measured. The outline of the test device in Example 9 is shown in FIG. 11, and the evaluation results are shown in Table 2.

[0084] [Comparative Example 1] A nylon mesh bag was prepared as the holding member 20, and one carbon-iron composite 10 was placed inside to prepare the iron ion eluting material 1. Next, a round screw-cap bottle 104 with an inner diameter of the bottom of 55 mm and a capacity of 220 ml was prepared, and the iron ion eluting body 1 was suspended by a nylon thread 105 using a hole (diameter 5 mm) opened in the lid, and 150 ml of natural seawater 110 was poured into it until the holding member 20 was completely immersed. The round screw-cap bottle 104 was placed in a thermostatic water bath (not shown), set at a temperature of 27° C., and left to stand for 5 days, after which the amount of iron ions eluted into the seawater 110 in the bottle was measured. The outline of the test device in Comparative Example 1 is shown in FIG.

[0085] Comparative Example 2 Although not shown in the figures, a carbon-iron composite 10 was prepared by stacking a carbon fiber reinforced plastic material (CFRP, matrix resin: phenoxy resin Vf 56%, 40×10×1 mm, weight 0.61 g) on ​​a plate-shaped metal member (material: SS400, 40×10×2 mm, 6.2 g) with their faces facing each other and tying them together with nylon thread 105. The iron ion eluting body 1 was immersed in seawater 110 without using a holding member 20, in the same manner as in Example 1, and the amount of iron ions eluted into the seawater 110 in the bottle was measured. The evaluation results are shown in Table 2.

[0086] Comparative Example 3 The amount of iron ions eluted into the seawater 110 in the bottle was measured in the same manner as in Comparative Example 1, except that one steel ball (material: SUJ2, φ10 mm, 4.1 g) was used instead of the carbon-iron composite 10 contained in the iron ion eluter 1. The evaluation results are shown in Table 2.

[0087] Comparative Example 4 The amount of iron ions eluted into the seawater 110 in the bottle was measured in the same manner as in Comparative Example 1, except that one steel ball (material: SUJ2, φ10 mm, 4.1 g) was used instead of the carbon-iron composite 10 housed in the iron ion eluter 1, and a lump of needle coke (LPC-U, manufactured by Nippon Steel Chemical & Material, weighing 4.0 g, one piece) was used as the conductive additive 30. The evaluation results are shown in Table 2.

[0088] Comparative Example 5 The amount of iron ions eluted into the seawater 110 in the bottle was measured in the same manner as in Comparative Example 1, except that the number of carbon-iron composites 10 housed in the iron ion eluter 1 was changed to three. The evaluation results are shown in Table 2.

[0089] [Table 2]

[0090] The iron ion elutors 1 of Examples 1 to 5 eluted greater amounts of iron ions per unit amount of iron-carbon composite 10 used, and also exhibited greater iron ion elution capacity, than those of Comparative Examples 1 and 5, in which the iron-carbon composite 10 was simply placed in a nylon mesh bag; Comparative Example 2, in which CFRP was used in combination with a steel plate; Comparative Example 3, in which only steel balls were used; and Comparative Example 4, in which needle coke was used in combination with steel balls. Furthermore, in Examples 1, 7, and 8, even when SUS was used for the retaining member 20, Ni and Cr were not detected in the immersion water or sediment. Furthermore, in Examples 6 to 8, the amount of iron ion elution was enhanced compared to conventional methods by using the cathode 101 to release electrons generated during the elution of iron ions from the iron-carbon composite 10. Compared to other Examples, the iron ion elution amount and weight output density were higher, demonstrating that a higher concentration of iron ions could be efficiently supplied to water, and that the device could also be miniaturized. Additionally, by placing a cathode 101 with a large surface area near the iron ion elutor 1, as in Example 9, more iron ions could be eluted than in the Comparative Examples. The iron ion supplying device 100 of Example 9 is a wire-free type, and therefore is suitable for use in stagnant water areas such as ponds. Furthermore, as an application example of the iron ion supplying device 100 of Example 9, a seasonal adjustment type of use is also possible, in which, for example, in summer when the water temperature is high and hydrogen sulfide is generated in large amounts from the bottom sediment, the iron ion eluting body 1 and the cathode 101 are connected using the wire 102 to generate a large amount of iron ions, and in winter when the temperature is low and hydrogen sulfide is not generated from the bottom sediment, the device is in a wire-free type to reduce the generation of iron ions.

[0091] Although the embodiments of the present invention have been described in detail above for the purpose of illustration, the present invention is not limited to the above-described embodiments and various modifications are possible. [Explanation of symbols]

[0092] 1...iron ion eluting body, 10...carbon-iron composite, 11...iron particles, 13...carbonaceous material, 15...pores, 20...holding member, 30...conductive aid, 100...iron ion supply device, 101...cathode, 102...conductor, 103...floating body, 200...iron ion supply device

Claims

1. An iron ion eluent for supplying iron ions into water, at least one carbon-iron composite; a holding member that holds the carbon-iron composite in a state where it can come into contact with water; Equipped with The present invention further comprises a conductive additive placed in contact with the carbon-iron composite, the conductive additive being a carbon material selected from the group consisting of natural graphite, artificial graphite, ironmaking coke, needle coke, and compacts thereof; An iron ion eluting body, characterized in that the holding member is a mesh-like or cage-like structure that allows liquid to pass through, and the conductive additive is stored inside the structure.

2. 2. The iron ion eluting material according to claim 1, wherein the carbon-iron composite is a sintered body of iron particles and a carbon material.

3. 3. The iron ion eluent according to claim 1, wherein the holding member is made of a conductive material, and the carbon-iron composite and the holding member are in contact with each other.

4. The iron ion eluent according to claim 3, a conductive cathode provided outside and electrically connected to the iron ion eluting body; An iron ion supply device comprising:

5. 5. The iron ion supply device according to claim 4, wherein the cathode is installed on or near the water surface.

6. 6. The iron ion supplying device according to claim 4, wherein the iron ion elution capacity when immersed in a saline solution having a concentration of 3% by weight for 5 days is 2000 mg / kg or more.

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