Iron ion supply device and iron ion supply method

Abstract

To provide means capable of efficiently and stably supplying a large amount of iron ions into water regardless of a presence or absence of dissolved oxygen at an installation site.SOLUTION: An iron ion supply device 100 includes: an iron ion elution part 1; a cathode part 50 electrically connected to the iron ion elution part 1; and a conductor wire 80 electrically connecting the iron ion elution part 1 and the cathode part 50. The iron ion elution part 1 includes: one or more carbon-iron composites 10; and a current collector 20 disposed in contact with the carbon-iron composites 10. The cathode part 50 has: a cathode body 51 made of a conductive material; and a current collector 60 as a second current collector disposed in contact with the cathode body 51. The cathode part 50 has a function of consuming electrons generated by the iron ion supply device 100.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an iron ion supply device and an iron ion supply method for stably supplying a high concentration of iron ions over a long period of time by being installed in water to purify an aquatic environment, for example, a bottom sediment environment.

Background Art

[0002] Enclosed sea areas such as harbors are in an environment where excessive organic matter flowing in from coastal cities accumulates and eutrophication tends to progress. The progress of eutrophication not only causes the occurrence of red tides, etc., but also deteriorates the bottom sediment environment due to the accumulation and decay of excessive organic matter and nutrients on the bottom. Therefore, problems have often occurred in the past where hydrogen sulfide is generated from the bottom sediment that has turned into a strongly reducing dark-colored sludge generally widely called mud, greatly damaging the fishing industry and the living environment.

[0003] As a method for suppressing the generation of hydrogen sulfide, there are reports (Non-Patent Document 1, Non-Patent Document 2) of spraying iron powder, iron oxide, or iron hydroxide on the bottom sediment, but there is a problem that spraying must be repeated regularly in order to obtain a continuous effect. For this reason, in order to continuously supply iron ions or iron hydroxide into water, an iron ion supply device (Patent Document 1) has been proposed in which an iron ion elution part holding an iron supply material with a conductivity holding member is electrically connected to a conductive cathode. However, although this device can supply iron ions into water, the electrical resistance between the iron ion elution part and the cathode tends to increase, and improvement is required to continuously elute iron ions efficiently.

[0004] In addition, since dissolved oxygen in water is required for iron ions to elute from the iron supply material, the installation location of the iron supply material is limited to the vicinity of the water surface where there is a lot of dissolved oxygen, and it has been necessary to supply iron ions at a location away from the bottom layer where hydrogen sulfide is generated.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Document

[0006]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] The prior art had room for further improvement in order to continuously supply iron ions efficiently. Therefore, an object of the present invention is to provide a means capable of stably supplying a large amount of iron ions efficiently into water regardless of the presence or absence of dissolved oxygen at the installation location.

Means for Solving the Problems

[0008] As a result of intensive studies, the present inventors have found that the problems of the prior art can be solved by the following configuration, and have completed the present invention. That is, the iron ion supply device of the present invention is an iron ion supply device that supplies iron ions into water, and includes an iron ion elution part that releases iron ions, and a cathode part that is electrically connected to the iron ion elution part. In the iron ion supply device of the present invention, the iron ion elution part has a carbon-iron composite that is a sintered body of iron particles and a carbon material, and a first current collector disposed in contact with the carbon-iron composite, and the cathode part has a cathode body made of a conductive material and a second current collector disposed in contact with the cathode body. It is characterized in that the electrical resistance between the iron ion elution part and the cathode part is 10 Ω or less.

[0009] In the iron ion supply device of the present invention, the electrical resistance measured between the cathode part and the end part on the opposite side of the conducting wire connected to the cathode part may be 7 Ω or less.

[0010] In the iron ion supply device of the present invention, the cathode part may further include a holding member for holding the cathode body, and the material of the holding member may be a synthetic resin.

[0011] In the iron ion supply device of the present invention, the cathode body may be a linear, net-shaped or granular member formed of a conductive material having a higher redox potential than iron.

[0012] In the iron ion supply device of the present invention, the cathode part may be installed at the water surface or at a depth within 1 m from the water surface.

[0013] The iron ion supply method of the present invention is characterized by installing the above iron ion supply device in water to elute iron ions.

Effect of the Invention

[0014] The iron ion supply device of the present invention can efficiently and continuously elute iron ions and supply them into water regardless of the presence or absence of dissolved oxygen at the installation location, and can be widely used for environmental purification, wastewater treatment, etc.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0016] Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings as appropriate. The sizes, ratios of members, etc. in each figure are different from the actual sizes, ratios, etc. for the convenience of illustration, and the present invention is not limited by the drawings.

[0017] [Iron Ion Supply Device] FIG. 1 is a schematic diagram showing a schematic configuration of an iron ion supply device according to an embodiment of the present invention. The iron ion supply device 100 includes an iron ion elution unit 1, a cathode unit 50 electrically connected to the iron ion elution unit 1, and a conducting wire 80 electrically connecting the iron ion elution unit 1 and the cathode unit 50. Note that for the actual device, it only needs to satisfy the concept of this figure, and the positions, sizes, etc. of the iron ion elution unit 1 and the cathode unit 50 are not restricted by the description in the figure.

[0018] The iron ion elution unit 1 includes a carbon iron composite 10 that is a sintered body of iron particles and a carbon material, and a current collector 20 as a first current collector disposed in contact with the carbon iron composite 10. The cathode unit 50 includes a cathode body 51 made of a conductive material and a current collector 60 as a second current collector disposed in contact with the cathode body 51.

[0019] The iron ion supply device 100 according to the present embodiment collects electrons (e 2+ ) generated when iron ions (Fe - ) elute from the carbon-iron composite 10 of the iron ion elution part 1 immersed in water such as seawater 110, etc., with the current collector 20, and guides them to the cathode part 50 installed on the water surface 110a through the conducting wire 80, and consumes them outside the carbon-iron composite 10. The carbon-iron composite 10 generates electrons when iron elutes into water as divalent ions as shown in the following formula (1) by a local battery formed between carbon and iron. However, the generated electrons are considered to inhibit the elution 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 of the carbon-iron composite 10. Therefore, by separately providing the cathode part 50 on the water surface 110a where dissolved oxygen is abundant or in the vicinity thereof, electrons can be consumed and the elution of iron ions from the carbon-iron composite 10 can be promoted (= increase in the amount of iron ion elution). Fe→Fe 2+ +2e - (1) H 2 O+1 / 2O 2 +2e - →2OH - (2)

[0020] [Iron ion elution part] The iron ion elution part 1 includes one or a plurality of carbon-iron composites 10 and a current collector 20 arranged in contact with the carbon-iron composite 10. In the embodiment illustrated in FIG. 1, the current collector 20 also serves as a holding member that holds the carbon-iron composite 10 in a state where it can contact water. A holding member may be provided separately from the current collector 20. The current collector 20 is formed of a conductive material, and it is sufficient that the current collector 20 and the carbon-iron composite 10 are held in a contacting state. In the present embodiment, in the iron ion elution part 1, one or a plurality of granular carbon-iron composites 10 are accommodated inside a cage-shaped current collector 20 (also a holding member) whose outer shape is, for example, cylindrical. Hereinafter, the carbon-iron composite 10 and the current collector 20 constituting the iron ion elution part 1 will be described in this order.

[0021] [Carbon-iron composite] The carbon-iron composite 10 used in the iron ion elution part 1 of this embodiment is a composite of a carbon material and metallic iron directly or by using a binder (binding agent). The carbon-iron composite 10 is a material that can supply iron ions by immersing it in water due to the local battery effect utilizing the potential difference between carbon and iron. The shape of the carbon-iron composite 10 is preferably granular or lumpy, since the larger the surface area, the greater the amount of iron ions that can be generated. The carbon-iron composite 10 preferably has a breaking hardness of 50N or more, more preferably 80N or more. If the breaking hardness is less than 50N, the particles come into contact with each other due to shaking caused by the water flow, and the carbon-iron composite 10 is easily broken. If the carbon-iron composite 10 is broken by the water flow, the effect of the local battery will disappear due to the separation of iron and carbon, and there is a risk that the elution of divalent iron ions will be reduced.

[0022] The carbon-iron composite 10 may be, for example, a conventionally known one in which carbon fibers are fastened to an iron material, a carbonaceous material such as iron powder and charcoal is granulated with cement or clay, or iron powder is baked and solidified with shochu dregs, organic sludge, starch, or blackstrap molasses. Among these, a carbon-iron composite 10 made by granulating iron and carbon with a carbon precursor and baking and sintering is preferred. Such carbon-iron composite 10 is most preferred because it can continuously release iron ions stably for a long period of time, the carbon precursor used for granulation becomes hard carbon after sintering, the strength of the granulated material is high, and there is no elution of substances such as heavy metals and organic compounds that impose a burden on the environment.

[0023] FIG. 2 is a diagram schematically showing the external configuration of a preferred example of the 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 immobilized by the carbonaceous material 13. The carbonaceous material 13 is an amorphous solidified product containing 95% by weight or more of conductive carbon, functions as a structure for supporting the iron particles 11, and forms a local battery by contact with the iron particles 11. The carbon-iron composite 10 is a porous body having a predetermined bulk density and open porosity, and a plurality of pores 15 are formed. The carbonaceous material 13 may exist in a state where a portion derived from a carbonaceous raw material such as coke and an adhesive portion derived from an organic substance such as an organic binder can be distinguished, or alternatively, the two may be substantially integrated in a state where they cannot be distinguished from each other to form the carbonaceous material 13.

[0024] The weight ratio of the iron particles 11 to the carbonaceous material 13 in the carbon-iron composite 10 (iron particles 11: carbonaceous material 13) can be adjusted according to the persistence of divalent iron ion elution in water. For example, it is in the range of 5:95 to 95:5, preferably 20:80 to 80:20, more preferably 30:70 to 70:30. When the weight ratio of the iron particles 11 to the carbonaceous material 13 is less than 5% by weight, there is too much carbonaceous material 13, the contact area with water is small, the supply ability of divalent iron ions is low, and the persistence deteriorates. On the other hand, when the weight ratio of the iron particles 11 to the carbonaceous material 13 exceeds 95% by weight, a local battery is formed and sufficient iron ion supply ability is provided, but due to the low carbon content, the integrated product becomes brittle, and the iron particles 11 are likely to fall off from the surface or the carbon-iron composite 10 is likely to collapse. In addition, the carbon-iron composite 10 contains metal oxides such as silica (10% by weight or less) and other trace elements (such as Ni and Mn) in addition to iron and carbon, but the above weight ratio simply refers to the ratio of iron element to carbon element. Further, the carbonaceous material 13 contains carbonized carbon obtained by firing an organic substance such as an organic binder in addition to the carbonaceous raw material such as coke pre-mixed.

[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. Also, the open porosity is more preferably 30 to 60%. If the open porosity is less than 20%, the elution amount of divalent iron ions decreases, and if it exceeds 70%, the strength of the material decreases and it is likely to collapse, which is not preferable.

[0026] The carbon-iron composite 10 elutes divalent iron ions into water due to the formation of a local battery by the contact of zero-valent metallic iron with carbon. Therefore, as the iron particles 11, even if it is iron oxide at the stage of the iron raw material for obtaining the carbon-iron composite material, it may be metallic iron in the final product after firing. Preferably, a steel material mainly composed of iron (Fe) and containing at least one of carbon (C), manganese (Mn), and nickel (Ni) in an amount of 0.5% by weight or more is used as the raw material. In addition, examples of such iron particles 11 include cast iron, carbon steel, stainless steel, etc., but are not limited thereto.

[0027] The iron particles 11 constituting the carbon-iron composite 10 gradually become smaller because they release divalent iron ions into water due to the local battery effect with the sintered carbon in seawater. Therefore, the particle size of the iron particles 11 to be used is preferably 200 to 5 mesh according to the JIS standard. In the JIS standard, the smaller the mesh number, the larger the particle size. Therefore, when it is said "5 mesh or less", for example, "4 mesh" is not included. If the particle size is smaller than that of 200 mesh, it is too small, so the contact period with water becomes short, and there is a risk of ignition and dust explosion during manufacturing. Also, if the particle size is larger than that of 5 mesh, it is too large, so mixing, kneading, and granulation become difficult. The shape of the iron particles 11 may be, for example, granular such as spherical, or may be an irregular lump. In FIG. 2, for convenience of explanation, the iron particles 11 are drawn in a polyhedral shape with a regular hexagon in plan view, but it is not limited thereto.

[0028] The carbonaceous material 13 constituting the carbon-iron composite 10 is necessary to form a local battery with iron, and contact with the iron particles 11 is very important. As the raw material (carbonaceous raw material) of the carbonaceous material 13 for forming the local battery, for example, coke, charcoal, coal powder, graphite, coal tar pitch, carbides of organic compounds and polymeric materials, etc. can be used. These can be used alone or in combination of two or more. The shape of the carbonaceous raw material is not limited, but a powdery or lumpy shape that increases the number of contact points with the iron particles 11 after sintering and easily exhibits the local battery function is preferable, and an amorphous external shape is also acceptable. It is preferable that 50% by weight or more of the carbonaceous raw material to be mixed 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, and in particular, pitch coke powder that has a temperature history of 450°C or more and is conductive is more preferable.

[0029] Pitch coke powder with a temperature history of 450°C or more does not melt and flow at high temperatures like coal tar pitch or polymer materials, so 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 represented by coke powder is preferably, for example, 300 to 5 mesh according to the JIS standard in order to increase the number of contact points with the iron particles 11 after sintering to make the local battery function more efficient and to improve granulation properties. 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, and the elution efficiency decreases. On the other hand, if the particle size is smaller than 300 mesh, the bulk density becomes too small, which not only deteriorates the mixability and granulation properties, but also may cause fire and dust explosion.

[0030] The coke powder may be any of those obtained from petroleum or coal-based heavy oil. Among these, coke obtained from coal-based heavy oil is preferred because it is mesophase-rich and easily becomes needle coke, and therefore has high electrical conductivity, resulting in easy flow of current as a local battery and easy generation of iron ions.

[0031] The carbon-iron composite 10 illustrated in Fig. 2 is a sintered body of carbon having conductivity that is not an organic substance and iron. However, it is preferable to use an organic binder that carbonizes at a high temperature in the manufacturing process. By using an organic binder, aggregation of powdery raw materials can be promoted, the granulation rate can be increased, and the yield can be improved. Further, when the organic binder carbonizes during sintering, the physical properties (strength, surface state, disintegration resistance, etc.) of the carbon-iron composite 10 can be improved, and the adhesion between the iron particles 11 and the carbonaceous material 13 can be made strong. From such a viewpoint, as the organic binder, it is preferable to use pitch, phenol resin, lignin, or lignin sulfonate mainly composed of a phenol component, which has a fixed carbon content of 20% by weight or more and contains many aromatic rings. Among these, coal tar pitch, which is excellent in fixed carbon and binding strength, is most preferable.

[0032] Coal tar pitch is decomposed and volatilized by firing at 500 °C or higher in an inert or reducing atmosphere, and hydrogen, oxygen, nitrogen, sulfur components, etc. other than fixed carbon are volatilized, and substantially 95% or more of the fired product becomes carbon. Further, since hydrogen, oxygen, nitrogen, sulfur, etc. are released during firing, coal tar pitch forms voids, increases the contact area between water and iron, and contributes to efficient iron ion generation. Furthermore, since coal tar pitch becomes a strong carbide having conductivity, it is a good binder for fixing the iron particles 11 and the carbonaceous material 13. Among coal tar pitches, those having a fixed carbon content of 50% by weight or more are preferable also from the viewpoint of maintaining the shape during firing. Examples of such coal tar pitches include BP and IP (both product names) manufactured by Chem Co., Ltd.

[0033] The organic binder is preferably blended in an amount in the range of, for example, 5 to 20 parts by weight with respect to 100 parts by weight of the mixture of the iron raw material and the carbonaceous raw material. If the amount of the organic binder is less than 5 parts by weight, it has no effect as a binder. If it exceeds 20 parts by weight, the organic binder melts during firing, and thus a desired shape, a suitable bulk density, and an open porosity cannot be obtained. In addition, when a composite is formed only from the iron raw material and an organic binder such as coal tar pitch, the organic binder melts during firing, and the shape of the composite cannot be maintained.

[0034] The organic binder typified by coal tar pitch is preferably a powder or granule that is solid at room temperature in order to be uniformly mixed with the iron raw material and the carbonaceous raw material. The particle size of this powder or granule is preferably, for example, 200 to 32 mesh. If the particle size of the organic binder is too small, the bulk density becomes too small, and the mixing and kneading properties deteriorate. If it is too large, there is a possibility that the inside of the mixture, heat-melted product, and granulated product becomes non-uniform. In addition, the coal tar pitch preferably has a softening point in a temperature range of, for example, 30 to 150°C. The use of such a coal tar pitch with a softening point is very convenient for briquetting machines that mold (granulate) the mixture while heating, granulation methods using intermolecular forces such as melt granulation and dry granulation. After granulation by these methods, it can be directly fired, so that the carbon-iron composite 10 can be efficiently produced.

[0035] In addition to coal tar pitch, phenolic resin, etc., a granulation aid for improving granulation properties may be added to the organic binder. The granulation aid is not particularly limited as long as it becomes a carbonaceous material 13 during sintering. Examples of the granulation aid include, for example, gelatin, starch paste, molasses, lignin sulfonate, konjac powder, sodium alginate, polyvinyl alcohol, dextrin, ethyl cellulose, carboxymethyl cellulose, polyacrylamide, etc., which are suitable. When using a granulation aid, the weight mixing ratio of the organic binder to the granulation aid (organic binder: granulation aid) is preferably, for example, 100:0 to 30:70. By adjusting the mixing ratio of the granulation aid so as to be within such a range, the carbon-iron composite 10 having a desired shape can be easily manufactured without adversely affecting the bulk density, open porosity, fracture hardness, etc. during sintering.

[0036] The carbon-iron composite 10 may further contain, in addition to iron and carbon, mineral-based inorganic substances containing elements such as silicon, aluminum, magnesium, calcium, phosphorus, sodium, potassium, etc., within a range that does not prevent the elution of divalent iron ions due to physical property values such as fracture hardness, bulk density, open porosity, etc. and the local battery effect.

[0037] The carbon-iron composite 10 can be manufactured by blending an organic binder with a mixture of an iron raw material and a carbonaceous raw material, granulating into a desired shape if necessary, and then firing and sintering at a temperature of 500 °C or higher in an inert or reducing atmosphere.

[0038] The mixing order of the iron raw material, carbonaceous raw material, and organic binder is not particularly limited. The organic binder may be blended after first preparing a mixture of the iron raw material and the carbonaceous raw material, or all the raw materials may be blended at once. The same applies when blending other additives. For the blending method, general mixing and kneading machines such as various blenders, mixers, kneaders, etc. can be used.

[0039] The mixture containing various raw materials is granulated into any desired shape as needed. The granulation shape is not particularly limited and can be, for example, spherical, ellipsoidal, cylindrical, irregular, etc. Among these, spherical or ellipsoidal shapes are preferred because the contact area with seawater or the like becomes large. Also, the size of the granulated product is not particularly limited, but in the case of a sphere, a diameter of 5 mm or more, preferably about 5 to 100 mm, is preferred. When the shape of the granulated product is other than spherical, it is preferably sized to have a volume comparable to that of a sphere with a diameter of 5 to 100 mm. Although granulation can be carried out manually, from the viewpoints of workability, safety, shape control, etc., it is preferable to use a granulator such as a pelletizer or a briquetting machine.

[0040] When 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, a top charge furnace, a shuttle furnace, a tunnel furnace, a rotary kiln, a roller hearth kiln, a microwave, etc. can be used, but it is not limited thereto. Also, the pre-firing treatment may be either continuous or batch type. The firing temperature is more preferably 700°C or higher, even 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 can be surely carbonized and the reduction of iron oxide contained in the iron raw material can also be carried out. The carbon-iron composite 10 obtained by firing can be used as an iron ion source that exhibits rapid elution of divalent iron ions and high fracture hardness without environmental load. Note that the firing may be carried out multiple times, and after immersing a once-sintered sintered body in an aqueous solution of a compound such as iron or manganese, firing can be carried out again.

[0041] After undergoing the sintering process, the carbon-iron composite 10 is then slowly cooled while remaining in an inert or reducing atmosphere, or after slow cooling, it is allowed to cool to a temperature at which it can be handled in an air atmosphere, and then it is stored in the internal space of the holding member and used as the iron ion elution part 1.

[0042] [First current collector] The current collector 20 as the first current collector has a function of reducing the electrical resistance between the iron ion elution part 1 and the cathode part 50 by widely contacting and pressing and fixing on the surface of the carbon-iron composite 10, and promoting the external movement of electrons generated in the carbon-iron composite 10. At the same time, it can also hold the carbon-iron composite 10. When the iron ion elution part 1 is installed in water, a local battery is formed at the contact interface of carbon, iron, and water in the carbon-iron composite 10 due to the potential difference between carbon and iron, and divalent iron ions (Fe 2+ ) are eluted. At this time, the electrons generated along with the elution (ionization) of iron need to be finally consumed at another location. Since the retention of electrons in the carbon-iron composite 10 hinders the elution of iron ions, it is preferable to collect the electrons by the current collector 20 and efficiently move them to the cathode part 50. By using the current collector 20, the elution amount of iron from the carbon-iron composite 10 can be increased. Moreover, with only the carbon-iron composite 10, iron hydroxide due to the bonding of the hydroxyl groups generated on the carbon on its surface and iron ions is likely to deposit on the surface of the carbon-iron composite 10, leading to a decrease in the iron ion generation ability. Therefore, it is also possible to appropriately mix the carbon-iron composite 10 with a conductive auxiliary material (for example, coke particles of a conductive material) to avoid the deposition of iron hydroxide on the surface of the carbon-iron composite 10. Note that the conductive auxiliary material is a granular conductive material such as coke that has a function of promoting the external movement of electrons generated in the carbon-iron composite 10. By using it in combination with the current collector 20, electrons can be transferred to the cathode part 50 more efficiently, so the elution amount of iron from the carbon-iron composite 10 can be increased, and thus it is preferably used.

[0043] The material of the current collector 20 is not particularly limited as long as it is electrically conductive and does not corrode or dissolve in water, and for example, stainless steel, metals more noble than iron, carbon materials, etc. Among these, metals such as stainless steel are preferred because they have a high degree of freedom in shape, are highly corrosion resistant, are inexpensive, and can be used as a holding container.

[0044] The shape of the current collector 20 is not limited, and may be arbitrarily selected from spheres, ellipsoids, cubes, prisms, cylinders, polyhedrons, irregular granular or lumpy bodies, woven fabrics made of short fibers, long fibers, or continuous fibers, felts, meshes, etc., but a shape such as wire or mesh is preferable so that iron ions are eluted without being blocked from the carbon-iron composite 10. One or more current collectors 20 may be provided depending on the shape and size of the cathode 50.

[0045] [Holding material] The iron ion elution unit 1 may have a holding member for holding the carbon-iron composite 10 as an optional configuration. In FIG. 1, the current collector 20 also serves as the holding member, but if the carbon-iron composite 10 is heavy, the current collector 20 alone cannot withstand the load of the carbon-iron composite 10, and there is a risk that the carbon-iron composite 10 will be washed away due to corrosion deterioration caused by long-term use. Therefore, a holding member may be provided separately from the current collector 20. The holding member has a space capable of storing at least one carbon-iron composite 10 therein, and is configured to allow liquid to pass between the inside and outside of the holding member. The outer shape of the holding member may be, for example, a rectangular parallelepiped, a cube, a cylinder, or the like. The holding member may also be a basket, a bag, a net, a dish, or the like.

[0046] The material of the holding member is not particularly limited as long as it can support the weight of the carbon iron composite 10 and is not easily corroded or decomposed in water. For example, natural fibers, synthetic fibers, metals, inorganic fibers, etc. may be used. When the holding member also serves as the current collecting member 20, it is necessary to be composed of a conductive material, and a material that is a good electrical conductor is preferred. If the material constituting the holding member that also serves as the current collecting member 20 is a good electrical conductor, by bringing the plurality of carbon iron composites 10 housed inside into contact with the holding member, the electrons generated by the local battery effect in the carbon iron composite 10 can be efficiently flowed to the cathode portion 50 through the holding member, and the elution amount of iron ions can be increased. In this case, a metal such as stainless steel, which has a high degree of freedom in shape and can also be used as a holding container, is preferred.

[0047] It is preferable that the holding member can take out the carbon iron composite 10 housed therein. Due to long-term use, flocs such as iron hydroxide generated from the carbon iron composite 10 may accumulate and cause clogging, or biofilms may form on the surface due to the attachment and growth of microorganisms, resulting in a decrease in the elution amount of iron ions. By making the holding member have a structure in which the carbon iron composite 10 can be taken out, it is possible to facilitate the reuse of the holding member, the replacement, cleaning, and recycling of the carbon iron composite 10, and reduce the operation cost.

[0048] From the viewpoint of increasing the elution amount of iron ions, it is preferable that a plurality of carbon iron composites 10 are housed in the internal space of the holding member.

[0049] The iron ion elution part 1 having the above configuration can supply iron ions to the surroundings by being installed in water as it is. There is no particular limitation on the installation position in water, and it may be at the bottom 120, in the water, or on the water surface 110a. The iron ion elution part 1 can also be installed in an oxygen-deficient region with less dissolved oxygen. In addition, iron ions can be contained in the outflow water by directly pouring seawater or the like into the iron ion elution part 1, or by storing it in a container such as a tank and passing water through the inside.

[0050] As a method of installing the iron ion elution part 1, for example, a method of suspending it from a floating body such as a quay wall or a buoy, a pile fixed to the seabed 120, etc., a method of fixing it to a net cage used for aquaculture such as the bottom of a ship, fish, shellfish, seaweed, etc. is preferable. In these installation methods, for example, it can be moored using a long member such as a rope or a chain, or fixed using a detachable adapter. When fixing the iron ion elution part 1, it may be in a state where it can swing due to the water flow. Also, one end may be fixed to the seabed 120 and the other end fixed to a float, and the iron ion elution part 1 may be moored so as to be in a floating state in the water using a rope or the like.

[0051] [Cathode part] The cathode part 50 has a cathode body 51 made of a conductive material and a current collector 60 as a second current collector arranged in contact with the cathode body 51. The cathode part 50 has a function of consuming the electrons generated by the iron ion supply device 100. That is, when the iron ion elution part 1 is installed in water, the electrons generated accompanying the elution (ionization) of iron are sent to the cathode part 50 via the conducting wire 80 and consumed by reacting with oxygen in the water (see formula (2)).

[0052] [Cathode body] The material of the cathode body 51 is not particularly limited as long as it is conductive, and examples thereof include conductive materials such as metal materials and carbon materials. However, a material having high electrical conductivity and a higher redox potential than iron is preferable. Examples of such metal materials include stainless steel, nickel, copper, platinum, etc., and examples of carbon materials include coke, graphite, porous carbon, carbon fiber, carbon cloth, carbon mat, carbon felt, carbon paper, etc. It is more preferable to use a carbon material having a high specific surface area and being difficult to corrode even in seawater 110 as the cathode part 50, and a porous body of a carbon material is most preferable.

[0053] The shape of the cathode body 51 is not particularly limited, and examples thereof include a linear shape, a net shape, a granular shape, a sheet shape, a plate shape, a rod shape, a string shape, a lattice shape, a bellows shape, a block shape, a porous shape, etc. Further, shapes with unevenness on these shapes, those subjected to hole processing, shapes obtained by bending or curving these shapes, etc. can be mentioned. Among these, from the viewpoints such as good water permeability and large surface area can be secured when stored in the holding member, it is preferable that the member is formed into a linear shape, a net shape, a woven fabric shape, a felt shape, a granular shape, etc. In particular, when the cathode body 51 is formed by integrating granular materials, not only can the surface area of the cathode body be increased, but also the contact points between the current collector 60 and the cathode body 51 can be increased, so that the electrons transmitted from the anode can be efficiently consumed by the dissolved oxygen in the vicinity of the cathode, which is more preferable. Further, a catalyst part for promoting the electrode reaction may be disposed on the surface of the cathode body 51.

[0054] [Second current collector] The current collector 60 as the second current collector has a function of reducing the electrical resistance between the iron ion elution part 1 and the cathode part 50 by being press-fixed on the surface of the cathode body 51 and efficiently transmitting the electrons generated in the carbon-iron composite 10 to the cathode body 51. When the contact pressure between the current collector 60 and the cathode body 51 is weak, the contact resistance increases, and it becomes difficult to reduce the electrical resistance between the iron ion elution part 1 and the cathode part 50 to 10 Ω or less. When the iron ion elution part 1 is installed in water, the electrons generated with the elution (ionization) of iron are sent to the cathode part 50 via the conducting wire 80 and consumed by reacting with oxygen. In this process, if the movement of electrons from the carbon-iron composite 10 to the cathode body 51 is delayed, the elution of iron ions is hindered. Therefore, it is preferable to once collect the electrons received at the cathode part 50 by the current collector 60 and transmit them to the cathode body 51 while eliminating the influence of the contact resistance. By using the current collector 60, the elution amount of iron from the carbon-iron composite 10 can be increased.

[0055] The material of the current collector 60 is not particularly limited as long as it is a conductive material that does not corrode or dissolve in water. For example, stainless steel, titanium, which is likely to form a passive state, or platinum, a carbon material, etc., which are less likely to corrode, can be used. Among these, from the viewpoint of high degree of freedom in shape and economic advantage, metals such as stainless steel are preferred.

[0056] The shape of the current collector 60 is not limited, and it can be arbitrarily selected and used from shapes such as spheres, ellipsoids, cubes, prisms, cylinders, polyhedrons, irregular granular or massive bodies, woven fabrics, felts, meshes, etc. made of short fibers, long fibers, continuous fibers, etc. However, from the viewpoint of continuously reducing the electrical resistance between the iron ion elution part 1 and the cathode part 50, for example, it is preferably a three-dimensional solid shape such as a sphere, ellipsoid, cube, prism, cylinder, etc. or a combination thereof, or a member formed into a sheet shape, net shape, rod shape, plate shape, etc. using a plurality of linear and linear bodies. In addition, as long as the current collector 60 can make the electrical resistance between the iron ion elution part 1 and the cathode part 50 10 Ω or less, one or a plurality of them may be arranged.

[0057] [Holding member] The cathode part 50 may optionally have a holding member 70 that holds the cathode body 51 and the current collector 60. The holding member 70 has a space capable of accommodating the cathode body 51 and the current collector 60 inside, and is configured such that liquid can pass through its inside and outside. As the outer shape of the holding member 70, for example, a rectangular parallelepiped, cube shape, cylindrical shape, etc. may be used. Also, the holding member 70 may be cage-shaped, bag-shaped, net-shaped, dish-shaped, etc.

[0058] The material of the holding member 70 is not particularly limited as long as it is not easily corroded or decomposed in water. For example, it may be a synthetic resin such as natural fiber or synthetic fiber, metal, inorganic fiber, etc. However, since there is a risk of damage due to corrosion deterioration during long-term use and the cathode body 51 may be washed away, a synthetic resin, which is a material that is difficult to corrode and has excellent durability, is preferred. Since the iron ion supply device 100 is provided with the current collector 60 in the cathode part 50, the holding member 70 itself does not need to be conductive, and the durability can be improved by providing the holding member 70 made of synthetic resin.

[0059] There is no particular limitation on the installation position of the cathode 50 having the above configuration, and it may be at the bottom 120, in the water, or at the water surface 110a. The cathode part 50 is preferably provided outside the iron ion elution part 1, and may be arranged separately from or adjacent to the iron ion elution part 1. In FIG. 1, in the iron ion supply device 100, the iron ion elution part 1 is below the cathode part 50 and the whole is completely buried in water. On the other hand, the cathode part 50 is located near the water surface at a depth within 1 m from the water surface 110a or the water surface rich in dissolved oxygen. It is preferable to install the cathode part 50 so that at least a part thereof is exposed to the atmosphere, or to install it at the water surface 110a or near the water surface where the oxygen concentration is high, because the consumption of electrons proceeds efficiently. Incidentally, the iron ion elution part 1 may be arranged at the water surface 110a and near the water surface in the same manner as the cathode part 50.

[0060] [Conducting wire] The iron ion elution part 1 is electrically connected to the cathode part 50 by the conducting wire 80. The conducting wire 80 is for transferring electrons generated when iron ions elute from the carbon-iron composite 10 to the cathode part 50. The material of the conducting wire 80 is not particularly limited as long as it is a conductive material. For example, copper, stainless steel, titanium, carbon fiber, etc. are preferable, and copper is more preferable from the viewpoint of reducing electrical resistance. Also, the conducting wire 80 can be either a single wire or a stranded wire, but preferably its periphery is coated with an insulating material such as a synthetic resin from the viewpoints of corrosion resistance and durability. The connection part of the conducting wire 80 with the current collectors 20 and 60 is preferably coated with a water-resistant and waterproof adhesive or the like from the viewpoint of corrosion resistance. The conducting wire 80 can be used with a necessary length and thickness, but as will be described later, it is preferably used with a length and thickness such that the electrical resistance between the iron ion elution part 1 and the cathode part 50 is 10 Ω or less.

[0061] The connection between the iron ion elution part 1 and the cathode part 50 by the conducting wire 80 may be such that the carbon-iron composite 10 and the cathode body 51 are directly connected, or the carbon-iron composite 10 and the cathode part 50 may be connected via the current collector 20 and / or the current collector 60, but it is preferable to connect via the current collector 20 and the current collector 60. In addition, when the holding member of the iron ion elution part 1 is formed of a good electrical conductor that also serves as the function of the current collector 20, the holding member and the cathode part 50 may be connected by the conducting wire 80.

[0062] In the iron ion supply device 100, the electrical resistance between the iron ion elution part 1 and the cathode part 50 is 10 Ω or less, preferably 9 Ω or less, and more preferably 5 Ω or less. When the electrical resistance exceeds 10 Ω, the elution of iron ions becomes insufficient, and the effects of the invention cannot be fully exerted. In the iron ion supply device 100, current collectors (current collector 20 and current collector 60) are provided on both the iron ion elution part 1 and the cathode part 50, and by reducing the contact resistance, an electrical resistance of 10 Ω or less is realized, promoting the flow of electrons from the iron ion elution part 1 to the cathode part 50. In addition, in order to make the electrical resistance between the iron ion elution part 1 and the cathode part 50 10 Ω or less, it is important to sufficiently suppress the electrical resistance on the cathode part 50 side. Therefore, the electrical resistance measured between the cathode part 50 and the end part on the opposite side of the conducting wire 80 connected to the cathode part 50 is preferably 7 Ω or less, and more preferably 4 Ω or less. The electrical resistance is measured by the method shown in the examples described later.

[0063] As an optional configuration, the iron ion supply device 100 can include an ammeter 90 disposed between the iron ion elution part 1 and the cathode part 50 and connected to the conducting wire 80. It is preferable to install the ammeter 90 and periodically or continuously measure the current value flowing between the iron ion elution part 1 and the cathode part 50. By the ammeter 90, in addition to being able to confirm an increase in the resistance value due to the occurrence of corrosion or the like as a decrease in the current value, it is possible to detect the consumption of the iron-carbon composite 10 in the iron ion elution part 1 and sudden troubles.

[0064] As described in detail above, the iron ion supply device 100 can be widely used in the field of environmental improvement such as suppressing the generation of hydrogen sulfide from the bottom sediment in closed waters such as harbors and lakes and purifying sludge by activating microorganisms by being installed in water such as seawater 110 or fresh water. In addition, since the configuration of the iron ion supply device 100 can be flexibly adjusted, it can also be applied to small-scale waters such as park ponds and moats.

Examples

[0065] Examples are shown below to more specifically explain the features of the present invention. However, the scope of the present invention is not limited to the examples. In the following examples, unless otherwise specified, various measurements and evaluations are as follows.

[0066] [Open porosity] After measuring the dry weight (A) of the sample, the sample was submerged in water, the pressure was reduced to vacuum in a desiccator, and it was held for 60 minutes to be saturated with water. The sample taken out of the water was transferred to a wire basket to drain the water, the saturated sample was filled into a graduated cylinder and weighed, and the weight (B) of the saturated sample was obtained by subtracting the empty weight of the graduated cylinder. At this time, the volume of the open pores of the sample is calculated by the following formula. Volume of open pores (cm 3 ) = [Weight of saturated sample (B) - Dry weight of sample (A)] ÷ 1 (Specific gravity of water) Water was added to the graduated cylinder filled with the saturated sample up to the upper end of the sample, and the volume of the sample was obtained by calculating the difference between the volume C (filled volume) up to the water surface and the weight D (void volume) of the injected water. Volume of sample (cm 3 ) = Filled volume (C) - Void volume (D) The porosity was calculated as follows using the volume of the open pores and the volume of the sample. Porosity (%) = [Volume of open pores (cm 3 ) / Volume of sample (cm 3 )] × 100

[0067] [Water absorption rate] After measuring the dry weight (A) of the sample, the sample was submerged in water to absorb water, taken out of the water after 24 hours, transferred to a wire basket to drain the water, and the weight (B) of the water-absorbed sample was obtained. The sample gradually absorbs water and its weight increases with the passage of time after being submerged in water. At this time, the volume of water absorbed by the sample is calculated by the following formula. Volume of absorbed water (cm 3 ) = [Weight of water-absorbed sample (B) - Dry weight of sample (A)] ÷ Specific gravity of water (1) Using the volume of the sample obtained in the process of measuring the above porosity, the water absorption rate was calculated as follows. Water absorption rate (%) = [Volume of absorbed water (cm 3 ) / Volume of sample (cm 3 )] × 100

[0068] [Bulk density] Using the dry weight (A) of the sample and the volume of the sample obtained in the process of measuring the above porosity, it was calculated as follows. Bulk density (g / cm 3 ) = Dry weight of sample (g) ÷ Volume of sample (cm 3 )

[0069] [Bulk density] It was calculated as follows using the dry weight (A) of the sample and the filled volume (C) of the sample obtained in the process of measuring the above-mentioned open porosity. Bulk density (g / cm 3 ) = Dry weight of sample (g) ÷ Filled volume of sample (cm 3 )

[0070] [Crushing hardness] The load at which the particles of the sample are crushed was defined as the crushing hardness. For the measurement of the crushing hardness, a wooden hardness tester 1600-C (maximum 200 N) manufactured by Fujiwara Seisakusho was used. A load was applied to the sample particles, and the load at which the particles were crushed was measured for 10 samples, and the average value was taken as the crushing hardness.

[0071] [Electrical resistance] The electrical resistance of the iron ion elution part or the cathode part equipped with a current collector was measured using a multi-tester (Model 1110 manufactured by Kyoritsu Electric Instrument Co., Ltd.). The measurement terminals were pressed against the opposite end of the conductor connected to the current collector and multiple locations of the carbon iron composite or the cathode material. The locations on the measurement surface of the carbon iron composite or the cathode material were arbitrarily set to 10 locations, and the average value was taken as the electrical resistance (A) of the iron ion elution part or the electrical resistance (B) of the cathode part. The electrical resistance between the iron ion elution part and the cathode part (iron ion supply device) through the current collector was taken as the total value (A + B) of the respective electrical resistances.

[0072] [Iron ion elution amount] The iron ion elution part (or iron ion elution device) was installed in seawater. After eluting iron ions for a certain period, the supernatant of the seawater and the iron hydroxide slurry sedimented at the bottom were sampled. Nitric acid was added to each sample to completely dissolve the iron hydroxide particles, and then the iron ion concentration was measured by ICP-MS analysis to determine the total amount of iron contained in the seawater. This total amount of iron was divided by the number of days of iron ion elution to obtain the iron ion elution amount. Iron ion elution amount (g / day) = Total amount of iron contained in seawater (g) ÷ Iron ion elution period (days)

[0073] [Carbon-Iron Composite] Table 1 shows the mixing ratios of the raw materials of the carbon-iron composite. That is, cast iron powder (Takeuchi Industry Co., Ltd., 28 mesh and 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 coal coke powder (3 mm and under) were granulated using binder pitch (Nippon Steel Chemical & Material Co., Ltd., softening point: 85 °C, fixed carbon content 58%) and starch (Asada Flour Milling Co., Ltd., α - modified wheat flour, residual carbon rate 10%) in a briquette machine (pocket size: 28×25×depth 6.5 mm), and fired and sintered at a temperature of 900 °C in a non - oxidizing atmosphere to produce the carbon - iron composite. Table 2 shows the characteristic values of the carbon - iron composite. When approximating the carbon - iron composite to an ellipsoid based on the pocket size of the briquette machine, the apparent surface area per particle was 15 cm 2 and the average weight was 16 g.

[0074]

Table 1

[0075]

Table 2

[0076] [Cathode Material A (Granular Needle Coke)] Needle coke (manufactured by Nippon Steel Chemical & Material Co., Ltd.) produced from coal - based heavy oil was prepared. By screening this needle coke using sieves with an aperture of 11.2 mm and 19 mm, cathode material A with a particle size of 11.2 - 19 mm was obtained.

[0077] [Cathode Material B (Granular Graphite)] Needle coke (manufactured by Nippon Steel Chemical & Material Co., Ltd.) produced from carboniferous heavy oil was pulverized and adjusted to a particle size distribution of 25% in the range of 0.250 - 0.500 mm, 45% in the range of 0.075 - 0.249 mm, and 30% 0.074 mm or less. To 100 parts by weight of these needle coke particles, 40 parts by weight of binder pitch (manufactured by Nippon Steel Chemical & Material Co., Ltd., softening point: 97°C) produced from carboniferous heavy oil was added, and the mixture was heated and kneaded at 200°C for 20 minutes. This kneaded material was extruded and molded into a rod shape with a diameter of 20 mm. This molded body was fired in a non-oxidizing atmosphere at 900°C, and further graphitized at 2650°C in a nitrogen atmosphere. After crushing the obtained graphite rod, it was sieved using sieves with mesh sizes of 11.2 mm and 19 mm to obtain cathode material B with a particle size of 11.2 - 19 mm.

[0078] [Cathode Material C (Granular Coal Coke)] Coal coke (volatile content less than 1%) for ironmaking obtained by carbonizing coal powder in a coke oven was prepared. This coal coke was sieved using sieves with mesh sizes of 11.2 mm and 19 mm to obtain cathode material C with a particle size of 11.2 - 19 mm.

[0079] Table 3 shows the characteristic values such as the bulk density of the cathode materials used in the examples.

[0080]

Table 3

[0081] [Example 1] For 0.5 kg of the carbon-iron composite, a stainless steel expanded metal (SUS304, wire diameter 0.4 mm, mesh size 10 mm, size 100×200 mm) was prepared as a holding member and current collector, and a coated copper wire (stranded conductor diameter 1.8 mm) with a length of 1 m was connected to the end of the stainless steel expanded metal. The connection part was coated with a waterproof adhesive. The carbon-iron composite was wound with the stainless steel expanded metal serving as the holding member and current collector, and the joints of the expanded metal were tightened with a resin tie band to hold the carbon-iron composite with the stainless steel expanded metal to form an iron ion elution part. At this time, the electrical resistance between the coated copper wire and the carbon-iron composite through the current collector was 1.6 Ω.

[0082] Next, for 1 kg of the cathode material A (granular needle coke), a polypropylene container (Inomata Chemical Co., Ltd. model Wide 4571, with 8 mm diameter holes, width 166×depth 293×height 115 mm) was prepared as a holding member, and a stainless steel bar (SUS304, with M10 thread) with a length of 252 mm was prepared as a current collector. One end of a coated copper wire with a length of 1 m was connected to the end of the stainless steel bar of the current collector with a stainless steel nut, and the connection part between the stainless steel bar and the coated copper wire was coated with a waterproof adhesive. The cathode material A was put into the container, and the stainless steel bar of the current collector was placed on its upper surface, and the stainless steel bar and the bottom surface of the container were tightened with a resin tie band to compress and fix the stainless steel bar to the cathode material A to form a cathode part. At this time, the electrical resistance between the coated copper wire and the cathode material A through the current collector was 1.7 Ω.

[0083] The iron ion elution part and the cathode part were separated so as not to come into contact with each other in a plastic bucket with an inner diameter of 700 mm filled with 80 L of seawater, and the iron ion supply device was immersed in the seawater and installed for 10 days. During the iron ion elution period, the seawater was air bubbled (2 L / min) to keep the dissolved oxygen concentration of the seawater at 5 - 6 ppm. The current was measured by connecting the ends of both coated copper wires taken out from the seawater to the measurement terminals of a digital multimeter (VOAC7502 manufactured by Iwasaki Communication Co., Ltd.) with alligator clips, and the current between the iron ion elution part and the cathode part was measured twice a day, and the average value during the iron ion elution period was calculated. After the iron ion elution, seawater was collected and the iron ion elution amount was measured by ICP-MS analysis. The schematic configuration of the iron ion supply device of Example 1 is shown in Figure 3, and the evaluation results are shown in Table 4.

[0084] [Example 2] Iron ions were eluted into seawater under the same conditions as in Example 1, except that the cathode material A was 2 kg. At this time, the electrical resistance between the coated copper wire and the cathode material A through the current collector was 1.6 Ω. The evaluation results of Example 2 are shown in Table 4.

[0085] [Example 3] Iron ions were eluted into seawater under the same conditions as in Example 1, except that 2.8 kg of cathode material B was used as the cathode material. At this time, the electrical resistance between the coated copper wire and the cathode material B through the current collector was 1.3 Ω. The evaluation results of Example 3 are shown in Table 4.

[0086] [Example 4] Iron ions were eluted into seawater under the same conditions as in Example 1, except that 1.7 kg of cathode material C was used as the cathode material. At this time, the electrical resistance between the coated copper wire and the cathode material C through the current collector was 2.4 Ω. The evaluation results of Example 4 are shown in Table 4.

[0087] [Example 5] For 1 kg of the carbon iron composite, a polyethylene mesh bag was prepared as the holding member, and a stainless steel turtle shell mesh (wire diameter 0.4 mm, mesh size 10 mm, size 100×100 mm) was prepared as the current collector. A coated copper wire with a length of 1 m was connected to the end of the stainless steel turtle shell mesh of the current collector, and the connection part was coated with a waterproof adhesive. The stainless steel turtle shell mesh of the current collector was laid on the inner bottom of the polyethylene mesh bag, and the carbon iron composite was packed into the mesh bag so that it contacted the upper surface of the stainless steel turtle shell mesh. Then, the mouth of the mesh bag was tightened so that the carbon iron composite and the stainless steel turtle shell mesh were in close contact, and it was tied with a resin binding band to form an iron ion elution part. At this time, the electrical resistance between the coated copper wire and the carbon iron composite through the current collector was 2.4 Ω.

[0088] Next, for 4 kg of the cathode material A, two polypropylene containers (Inomata Chemical's Wide 4571 type, connected in series, with an 8-mm diameter hole, width 166 × depth 550 × height 115 mm) as the holding members and a 400-mm long stainless steel bar (SUS304, with an M10 screw) as the current collector were prepared, and a cathode was made in the same manner as in Example 1. At this time, the electrical resistance between the coated copper wire and the cathode material A through the current collector was 1.6 Ω. Iron ions were eluted in the same manner as in Example 1, and the amount of eluted iron ions was measured. The evaluation results of Example 5 are shown in Table 4.

[0089] [Example 6] Iron ions were eluted into seawater under the same conditions as in Example 5, except that the length of the stainless steel bar of the current collector was changed to 30 mm. At this time, the electrical resistance between the coated copper wire and the cathode material A through the current collector was 2.3 Ω. The evaluation results of Example 6 are shown in Table 4.

[0090] [Example 7] A stainless steel wire mesh (SUS304, wire diameter 0.4 mm, mesh size 10 mm, size 100 × 100 mm) was prepared as the current collector for the cathode part, and one end of a 1-m long coated copper wire was connected to the end of the stainless steel wire mesh. The connection part between the stainless steel wire mesh and the coated copper wire was coated with a waterproof adhesive. The stainless steel wire mesh of the current collector was laid on the inner bottom of the polypropylene container (Inomata Chemical's Wide 4571 type, connected in series, with an 8-mm diameter hole, width 166 × depth 550 × height 115 mm) of the holding member, and 4 kg of the cathode material A was placed on the upper surface of the stainless steel wire mesh and brought into contact with the stainless steel wire mesh by its own weight to form the cathode part. At this time, the electrical resistance between the coated copper wire and the cathode material A through the current collector was 5.7 Ω. Iron ions were eluted into seawater in the same manner as in Example 5 except for the cathode part. The schematic configuration of the iron ion supply device of Example 7 is shown in Fig. 4, and the evaluation results are shown in Table 5.

[0091] [Example 8] As the current collector material for the cathode part, a stainless steel punching metal plate (material: SUS304, hole diameter: 6 mm, hole pitch: 8 mm, size: 250 × 150 × 1.3 mm) was prepared. One end of a 1 m long coated copper wire was connected to a 6 mm diameter hole in the stainless steel plate by crimping with a stainless steel screw. The connection part between the stainless steel plate and the coated copper wire was coated with a waterproof adhesive. Cathode material A was placed in a container, and the stainless steel plate of the current collector was placed on its upper surface. The stainless steel plate and the bottom surface of the container were tightened with a resin tie band, so that the stainless steel plate was compression-fixed to the cathode material A to form the cathode part. At this time, the electrical resistance between the coated copper wire and the cathode material A through the current collector was 1.3 Ω. Iron ions were eluted into seawater in the same manner as in Example 2 except for the cathode part. The evaluation results of Example 8 are shown in Table 5.

[0092] [Example 9] As the current collector material for the cathode part, a graphite rod (resistivity: 7.6 μΩm, with M20 screw hole, size: diameter 30 × length 260 mm) and an impermeable graphite screw (resistivity: 12.5 μΩm, with 3 mm diameter hole, size: M20 × 60 mm) were prepared. One end of a 1 m long coated copper wire was inserted into a 3 mm diameter hole in the impermeable graphite screw, sealed with a waterproof adhesive and connected, and then screwed and fixed into the M20 screw hole machined on the end face of the graphite rod. Cathode material A was placed in a container, and the graphite rod with a graphite screw of the current collector was placed on its upper surface. The graphite rod and the bottom surface of the container were tightened with a resin tie band, so that the graphite rod was compression-fixed to the cathode material to form the cathode part. At this time, the electrical resistance between the coated copper wire and the cathode material A through the current collector was 2.5 Ω. Iron ions were eluted into seawater in the same manner as in Example 2 except for the cathode part. The evaluation results of Example 9 are shown in Table 5.

[0093] [Comparative Example 1] Iron ions were eluted into seawater in the same manner as in Example 7 except that the stainless steel turtle shell net of the current collector was placed statically on the upper surface of the cathode material A. At this time, the electrical resistance between the coated copper wire and the cathode material A through the current collector was 12.3 Ω. The schematic configuration of the iron ion supply device of Comparative Example 1 is shown in Fig. 5, and the evaluation results are shown in Table 5.

[0094] [Comparative Example 2] 1.5 kg of the carbon-iron composite was placed in a polyethylene mesh bag to form an iron ion elution part. This iron ion elution part was submerged in seawater in a plastic bucket with an inner diameter of 700 mm containing 80 L of seawater and installed for 10 days. During the period of iron ion elution, the seawater was subjected to air bubbling (2 L / min). After iron ion elution, seawater was collected and the iron ion elution amount was measured by ICP-MS analysis. The schematic configuration of the iron ion supply device of Comparative Example 2 is shown in FIG. 6, and the evaluation results are shown in Table 5.

[0095]

Table 4

[0096]

Table 5

[0097] The iron ion supply devices of Examples 1 to 9 have a total resistance between the carbon-iron composite and the cathode material of 10 Ω or less. Therefore, the iron ion elution amount is larger than that of Comparative Example 1 with a total resistance of 14.7 Ω and Comparative Example 2 without a cathode connection, and iron ions can be efficiently supplied into water.

[0098] (Elution of iron ions into oxygen-deficient seawater) [Example 10] A stainless steel wire with a wire diameter of 0.4 mm was wound around one carbon-iron composite particle (16 g) as a current collector, and a coated copper wire (stranded conductor diameter 1.8 mm) with a length of 6 m was connected to the end of the stainless steel wire. The connection part was coated with a waterproof adhesive to form an iron ion elution part. At this time, the electrical resistance between the coated copper wire and the iron ion elution part was 1.2 Ω.

[0099] For 56 g of cathode material A, a stainless steel expanded metal (SUS304 wire diameter 0.4 mm, mesh 10 mm, size 100×200 mm) was prepared as a current collector. A coated copper wire (stranded conductor diameter 1.8 mm) with a length of 3 m was connected to the end of the stainless steel expanded metal. The connection part was coated with a waterproof adhesive. The cathode material A was wound with the stainless steel expanded metal, and the joint of the expanded metal was tightened with a resin tie band to form a cathode part. At this time, the electrical resistance between the coated copper wire and the cathode material A through the current collector was 1.6 Ω.

[0100] A cylindrical acrylic water tank (inner diameter 120 mm, anode tank) with a total length of 2.4 m was filled with seawater, and the whole seawater was bubbled with nitrogen gas from the bottom of the water tank to adjust the dissolved oxygen to less than 0.1 ppm. The iron ion elution part was installed at the bottom of the acrylic water tank. As a cathode tank, a polypropylene (PP) cup (outer diameter 120 mm, capacity 1 L) with one hole with a diameter of 3 mm on the bottom surface was prepared, and this PP cup was inserted inside the upper end of the acrylic water tank to bring the seawater in the acrylic water tank into contact with the bottom surface of the cup. The bottom hole (diameter 3 mm) of the PP cup ensured the conductivity by ions in the seawater between the anode tank and the cathode tank. At the same time, the supply of dissolved oxygen from the cathode tank was restricted to maintain the anode tank in a hypoxic state.

[0101] After 0.7 L of seawater was put into the PP cup and the cathode part was immersed, the coated copper wires of the iron ion elution part and the cathode part were connected (connected to a digital multimeter) to elute iron ions as an iron ion supply device for 7 days. During the period of iron ion elution, the seawater in the PP cup was air bubbled (2 L / min) to keep the dissolved oxygen concentration of the seawater at 6 - 7 ppm.

[0102] The current was measured by a digital multimeter that connected the coated copper wires of the iron ion elution part and the cathode part. The current between the iron ion elution part and the cathode was measured twice a day, and the average value during the iron ion elution period was calculated. After the iron ion elution, the seawater in the anode tank was collected and the iron ion elution amount was measured by ICP-MS analysis. The schematic configuration of the iron ion supply device of Example 10 is shown in Fig. 7, and the evaluation results are shown in Table 6.

[0103] [Comparative Example 3] One carbon-iron composite particle (16 g) and 56 g of granular needle coke (the same as Cathode Material A) were directly contacted and wound with a stainless steel expanded metal (SUS304 wire diameter 0.4 mm, mesh 10 mm, size 100×200 mm) of the holding member, and the joint of the expanded metal was tightened with a resin binding band to form an iron ion elution part.

[0104] A cylindrical acrylic water tank (inner diameter 120 mm) with a total length of 2.4 m was filled with seawater, and the whole seawater was bubbled with nitrogen gas from the bottom of the water tank to make the dissolved oxygen less than 0.1 ppm, and then the iron ion elution part was installed at the bottom of the acrylic water tank. Except for the absence of the cathode part, a PP cup with a bottom hole (diameter 3 mm) was inserted inside the upper end of the acrylic water tank in the same manner as in Example 10, and iron ions were eluted from the iron ion elution part for 7 days. After the iron ions were eluted, seawater was collected and the iron ion elution amount was measured by ICP-MS analysis. The schematic configuration of the iron ion supply device of Comparative Example 3 is shown in Fig. 8, and the evaluation results are shown in Table 6.

[0105]

Table 6

[0106] In the iron ion supply device of Example 10, since the connected cathode part efficiently consumes the electrons generated during iron ion elution near the water surface with high dissolved oxygen, the iron ion elution part can elute iron ions even when installed in oxygen-deficient seawater with low dissolved oxygen. On the other hand, the iron ion elution part of Comparative Example 3 could hardly elute iron ions in oxygen-deficient seawater with low dissolved oxygen.

[0107] (Elution of Iron Ions in the Actual Sea Area) [Example 11] For 1.25 kg of the carbon-iron composite, a polyethylene mesh bag was prepared as the holding member, and a stainless steel turtle shell mesh (wire diameter 0.4 mm, mesh size 10 mm, size 100×100 mm) was prepared as the current collector. A coated copper wire (stranded conductor diameter 1.8 mm) with a length of 9 m was connected to the end of the stainless steel turtle shell mesh, and the connection part was coated with a waterproof adhesive. The stainless steel turtle shell mesh of the current collector was laid on the inner bottom of the polyethylene mesh bag, and the carbon-iron composite was packed into the mesh bag so that it contacted the upper surface of the stainless steel turtle shell mesh. Then, the mouth of the mesh bag was tightened so that the carbon-iron composite and the stainless steel turtle shell mesh were in close contact, and it was tied with a resin binding band to form an iron ion elution part. At this time, the electrical resistance between the coated copper wire via the current collector and the iron ion elution part was 1.8 Ω.

[0108] Next, for 5 kg of the granular needle coke of the cathode material A, a polyethylene mesh bag was prepared as the holding member, and a stainless steel disc (diameter 70×10 mm with a central M5 screw hole) and a stainless steel screw (M5) were prepared as the current collector. The end of a coated copper wire (stranded conductor diameter 1.8 mm) with a length of 4 m was wound around the stainless steel screw (M5) and screwed into the center of the stainless steel disc for connection (fixing). The connection part was coated with a waterproof adhesive. After installing the screw-attached stainless steel disc of the current collector on the inner bottom of the polyethylene mesh bag, the cathode material A was packed into the mesh bag. Then, the mouth of the mesh bag was tightened so that the cathode material A and the screw-attached stainless steel disc were in close contact, and it was tied with a resin binding band to form a cathode part. At this time, the electrical resistance between the coated copper wire via the current collector and the cathode part was 2.1 Ω. From the total electrical resistance between the iron ion elution part and the cathode part, the electrical resistance of the iron ion supply device was 3.9 Ω. The schematic configuration of the iron ion supply device of Example 11 is shown in FIG. 9, and the evaluation results are shown in Table 7.

[0109] In order to elute iron ions in the actual sea area, the iron ion elution part and the cathode part connected by a rope were suspended into the sea from a floating pier moored to a pier so that they would not come into contact. The iron ion elution part was placed in an oxygen-deficient water area at a water depth of 6 m near the bottom layer (dissolved oxygen in seawater: 0.2 ppm), and the cathode part was placed in an oxygen-rich water area at a water depth of 1 m near the water surface (dissolved oxygen in seawater: 5.7 ppm). The ends of the coated copper wires connected to the iron ion elution part and the cathode part were connected to a digital multimeter on land, and the current between the iron ion elution part and the cathode part was measured to be 56 mA.

[0110] [Example 12] An iron ion supply device was installed in the actual sea area in the same manner as in Example 11, except that the current collector of the cathode part was made of a stainless steel turtle shell net (wire diameter: 0.4 mm, mesh size: 10 mm, size: 100×100 mm). At this time, the electrical resistance between the coated copper wire and the cathode part through the current collector was 3.2 Ω. The electrical resistance of the iron ion supply device was 5.0 Ω from the total of the electrical resistances of the iron ion elution part and the cathode part. The ends of the coated copper wires connected to the iron ion elution part and the cathode part were connected to a digital multimeter on land, and the current between the iron ion elution part and the cathode was measured to be 47 mA. The evaluation results are shown in Table 7.

[0111] [Comparative Example 4] For 5 kg of the carbon iron composite, a stainless steel wire cage (stainless steel cage) was prepared as a holding member and used also as a current collector. A stainless steel wire (diameter: 1.5 mm) with a length of 9 m was connected to the end of the stainless steel cage. The carbon iron composite was put into this stainless steel cage to form an iron ion elution part. At this time, the electrical resistance between the stainless steel wire and the iron ion elution part through the current collector (stainless steel cage) was 11.1 Ω.

[0112] Next, for 20 kg of granular needle coke of the cathode material A, a stainless steel wire cage (stainless steel cage) was prepared as a holding member and used also as a current collector. A stainless steel wire (diameter 1.5 mm) with a length of 4 m was connected to the end of the stainless steel cage. The cathode material A was put into this stainless steel cage to form a cathode part. At this time, the electrical resistance between the stainless steel wire and the cathode part through the current collector (stainless steel cage) was 7.2 Ω.

[0113] Using the iron ion elution part and the cathode part by the stainless steel cage, an iron ion supply device was installed in the actual sea area in the same manner as in Example 12. From the total electrical resistance of the iron ion elution part and the cathode part, the electrical resistance of the iron ion supply device was 18.3 Ω. The ends of both stainless steel wires connected to the iron ion elution part and the cathode part were connected to a digital multimeter on land, and when the current between the iron ion elution part and the cathode part was measured, it was 51 mA. One week after the iron ion supply device was installed in the actual sea area, the stainless steel wire on the cathode part side was corroded (electro-erosion) and disconnected, so that the current became zero. The schematic configuration of the iron ion supply device of Comparative Example 4 is shown in FIG. 10, and the evaluation results are shown in Table 7.

[0114]

Table 7

[0115] For the iron ion supply devices of Examples 11 and 12, since the total resistance between the carbon iron composite and the cathode material is 10 Ω or less, electrons generated by iron ion elution can easily flow to the cathode part and iron ions can be supplied well for a long period. In Comparative Example 4, the amount of the carbon iron composite was increased to increase the current (iron ion elution amount), but since the resistance of the iron ion supply device was as large as 18.3 Ω, the stainless steel on the cathode part side was corroded (electro-erosion) and the supply of iron ions could not be continued.

[0116] As described above, the embodiments of the present invention have been described in detail for illustrative purposes, but the present invention is not limited to the above embodiments and various modifications are possible.

Explanation of Reference Numerals

[0117] 1... iron ion elution part, 10... carbon-iron composite, 11... iron particles, 13... carbonaceous material, 15... pores, 20... first current collector, 50... cathode part, 51... cathode body, 60... second current collector, 70... holding member, 80... conducting wire, 90... ammeter, 100... iron ion supply device, 110... seawater, 110a... water surface, 120... seabed

Claims

1. An iron ion supply device for supplying iron ions into water, comprising: an iron ion elution part that releases iron ions; a cathode part electrically connected to the iron ion elution part; and characterized in that the iron ion elution part is a carbon-iron composite which is a sintered body of iron particles and a carbon material; and a first current collector disposed in contact with the carbon-iron composite; and the cathode part comprises a cathode body made of a conductive material; and a second current collector disposed in contact with the cathode body; and the iron ion supply device is characterized in that the electrical resistance between the iron ion elution part and the cathode part is 10 Ω or less.

2. The iron ion supply device according to Claim 1, wherein the electrical resistance measured between the cathode part and the end portion on the opposite side of the wire connected to the cathode part is 7 Ω or less.

3. The iron ion supply device according to Claim 1, wherein the cathode part further comprises a holding member for holding the cathode body, and the material of the holding member is a synthetic resin.

4. The iron ion supply device according to Claim 1, wherein the cathode body is a linear, net-like or granular member formed of a conductive material having a higher oxidation-reduction potential than iron.

5. The iron ion supply device according to Claim 1, wherein the cathode part is installed at the water surface or at a depth within 1 m from the water surface.

6. An iron ion supply method, characterized in that the iron ion supply device according to any one of Claims 1 to 5 is installed in water to elute iron ions.

Images