SODIUM FERRITE PARTICLE POWDER AND PRODUCTION METHOD THEREOF

Abstract

The sodium ferrite particle powder according to the present invention is characterized in that at least one metal or more selected from the metal group consisting of silicon, aluminum, titanium, manganese, cobalt, nickel, magnesium, copper and zinc is contained in an amount of 0.05 to 20% by weight in terms of the oxide, and the molar ratio of Na/Fe is 0.75 to 1.25.

Claims

1. A sodium ferrite particle powder, characterized in that at least one metal or more selected from the metal group consisting of silicon, aluminum, titanium, manganese, cobalt, nickel, magnesium, copper and zinc is contained in an amount of 0.05 to 20% by weight in terms of the oxide, and the molar ratio of Na/Fe is 0.75 to 1.25.

2. The sodium ferrite particle powder according to claim 1, characterized in that at least one metal or more selected from the metal group consisting of silicon, aluminum, titanium, manganese, cobalt, nickel, copper and zinc is contained in an amount of 0.05 to 1% by weight in terms of the oxide.

3. The sodium ferrite particle powder according to claim 1, characterized in that at least one metal or more selected from the metal group consisting of aluminum, magnesium, silicon, titanium and zinc is contained in an amount of more than 1% by weight and 20% by weight or less in terms of the oxide.

4. The sodium ferrite particle powder according to any one of claims 1 to 3, wherein the axial ratio of the average major axis diameter to the average minor axis diameter of the primary particles is 1 to 2.

5. The sodium ferrite particle powder according to any one of claims 1 to 4, wherein the powder pH value is 8 to 14.

6. A method for producing the sodium ferrite particle powder as described in any one of claims 1 to 5, comprising a step of mixing an iron oxide fine particle powder, a particle powder made of the sodium raw material, and at least one metal or more compound selected from the metal group consisting of silicon, aluminum, titanium, manganese, cobalt, nickel, magnesium, copper and zinc, and reacting them at a temperature of 150 to 500° C. in the solid phase.

7. A method for producing the sodium ferrite particle powder as described in any one of claims 1 to 5, comprising a step of mixing a particle powder made of the sodium raw material with an iron oxide particle powder containing at least one metal or more selected from the metal group consisting of silicon, aluminum, titanium, manganese, cobalt, nickel, magnesium, copper and zinc in the form of an oxide, and reacting them at a temperature of 150 to 500° C. in the solid phase.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0040] FIG. 1 is a result of thermogravimetric analysis after fixing carbon dioxide with the sodium ferrite particle powder obtained in Example 1.

[0041] FIG. 2 is a result of thermogravimetric analysis after fixing carbon dioxide with the sodium ferrite particle powder obtained in Example 10.

DESCRIPTION OF EMBODIMENTS

[0042] The configuration of the present invention will be described in more detail as follows.

[0043] The carbon dioxide fixing recovery material according to an embodiment of the present invention will be described.

[0044] In the sodium ferrite particle according to the present embodiment, the amount of at least one metal selected from the metal group consisting of silicon, aluminum, titanium, manganese, cobalt, nickel, magnesium, copper and zinc is 0.05 to 20% by weight in terms of the oxide. In the case of the above-described range of % by weight, the carbon dioxide fixing recovery performance may be enhanced in some cases. Preferably, the above-described range of % by weight is 0.1 to 18% by weight.

[0045] The sodium ferrite particle powder according to the embodiment of the present invention has a molar ratio of Na/Fe of 0.75 to 1.25. If the molar ratio of Na/Fe is less than 0.75, the powder will have a low content of sodium ferrite particles to be produced, and the carbon dioxide fixing recovery performance will be inferior. Further, when the molar ratio of Na/Fe exceeds 1.25, a large amount of alkaline components such as NaOH and Na.sub.2CO.sub.3 which are by-products remain. The alkaline component is also a cause of gelation of the paint, and it is hard to say that a highly dispersible paint can be formed, and it is hard to say that it is a particle powder having excellent moldability and processability. More preferably, the molar ratio of Na/Fe is 0.80 to 1.20, and further preferably 0.90 to 1.10.

[0046] In the sodium ferrite particle powder according to the present embodiment, the amount of at least one metal or more selected from the metal group consisting of silicon, aluminum, titanium, manganese, cobalt, nickel, copper and zinc is preferably 0.05 to 1% by weight in terms of the oxide. In the case of the above-described range of % by weight, the carbon dioxide fixing recovery performance may be enhanced in some cases. More preferably, the above-described range of % by weight is 0.1 to 0.8% by weight.

[0047] When the sodium ferrite particle powder according to the present embodiment contains 0.05 to 1% by weight of the metal, it preferably contains 70% by weight or more of the crystal phase of α-sodium ferrite. The compound having the α-sodium ferrite crystal is a layered compound in which iron, oxygen, and sodium are arranged in layers, and oxygen hexagonal lattices parallel to the layers are arranged in a pattern of . . . ABCABC . . . . Sodium ions between the oxygen hexagonal lattices move to the surface of α-sodium ferrite particles and react with carbon dioxide. Therefore, this reaction is said to be a topochemical reaction while maintaining the shape of α-sodium ferrite particles. It is preferable to contain a large amount of α-sodium ferrite crystal phase because it is excellent in the repeatability of fixing recovery of carbon dioxide. More preferably, the content of the crystal phase of α-sodium ferrite is 75% by weight or more, and further preferably 80% by weight or more.

[0048] When the sodium ferrite particle powder according to the present embodiment contains 0.05 to 1% by weight of the metal, it preferably contains 2 to 25% by weight of the crystal phase of β-sodium ferrite. In the crystal phase of β-sodium ferrite, oxygen hexagonal lattices are arranged in a pattern of . . . ABABAB . . . . In addition, the volume of β-sodium ferrite per mole is expected to be 1.3 times higher than that of α-sodium ferrite. Therefore, it is preferable that the ratio of α-sodium ferrite to β-sodium ferrite is appropriately adjusted according to the purpose. More preferably, the amount of the crystal phase of β-sodium ferrite is 3 to 22% by weight, and further preferably 5 to 20% by weight.

[0049] In the sodium ferrite particle powder according to the present embodiment, the amount of at least one metal or more selected from the metal group consisting of aluminum, magnesium, silicon, titanium and zinc is preferably more than 1% by weight and 20% by weight or less in terms of the oxide. In the case of the above-described range of % by weight, the carbon dioxide absorption performance may be enhanced in some cases. More preferably, the above-described range of % by weight is 1.2% by weight or more and 18% by weight or less.

[0050] When the sodium ferrite particle powder according to the present embodiment contains the metal in an amount of more than 1% by weight and 20% by weight or less, it is preferable that the sodium ferrite particle powder contains 50% by weight or more of the crystal phase of β-sodium ferrite. As described above, the volume of β-sodium ferrite per mole is preferably 1.3 times higher than that of α-sodium ferrite. More preferably, the amount of the crystal phase of β-sodium ferrite is 55% by weight or more, and further preferably 60% by weight or more. The upper limit is about 98% by weight.

[0051] When the sodium ferrite particle powder according to the present embodiment contains the metal in an amount of more than 1% by weight and 20% by weight or less, it is preferable that the sodium ferrite particle powder contains 2 to 50% by weight of the crystal phase of α-sodium ferrite. As described above, it is preferable to contain a large amount of α-sodium ferrite crystal phase because it is excellent in the repeatability of carbon dioxide absorption. More preferably, the amount of the crystal phase of α-sodium ferrite is 5 to 48% by weight, and further preferably 10 to 45% by weight.

[0052] The sodium ferrite particle powder according to this embodiment preferably has a powder pH of 8 to 14. Since the powder pH is 8 or more basic, it is easy to catch carbon dioxide which is weakly acidic. On the other hand, when the powder pH exceeds 14, gelation of the paint occurs, and it is difficult to achieve high dispersibility. The powder pH is preferably 8.2 to 13.5, more preferably 8.4 to 13, and further preferably 9 to 13.

[0053] The sodium ferrite particle powder according to this embodiment preferably has a BET specific surface area of 2 to 7 m.sup.2/g. When the BET specific surface area is less than 2 m.sup.2/g, it becomes difficult to come into contact with carbon dioxide contained in the gas, and the carbon dioxide absorption performance becomes low. Further, when the BET specific surface area exceeds 7 m.sup.2/g, industrial production thereof becomes difficult. More preferably, the BET specific surface area is 2.1 to 6.5 m.sup.2/g, more preferably 2.6 to 6.0 m.sup.2/g, and further preferably 3.0 to 6.0 m.sup.2/g.

[0054] The sodium ferrite particle powder according to this embodiment preferably has an average primary particle diameter of 50 to 1000 nm. If it is less than 50 nm, industrial production becomes difficult. Further, if it exceeds 1000 nm, the carbon dioxide absorption performance becomes low. The average primary particle size is preferably 100 to 700 nm, more preferably 100 to 500 nm.

[0055] The sodium ferrite particle powder according to this embodiment has an axial ratio (average major axis diameter/average minor axis diameter) of primary particles of 1.0 to 2.0. When the axial ratio of the primary particles exceeds 1, the primary particles tend to aggregate with each other, and it becomes difficult to maintain a highly dispersible state after coating. As a result, it cannot be said that the particle powder has excellent moldability and process ability. Further, the axial ratio cannot be less than 1. More preferably, the axial ratio of the primary particles is 1.05 to 1.9, and further preferably 1.1 to 1.8.

[0056] When the sodium ferrite particle powder according to the present embodiment is applied as a carbon dioxide fixing recovery material, carbon dioxide can be selectively adsorbed from a gas containing carbon dioxide and fixed. The adsorption temperature is about 0° C. to 100° C., which is the room temperature to the exhaust gas outlet temperature. More preferably, it is about 0° C. to 50° C. Since no additional heating from the outside is required, the energy cost for adsorption can be kept low (the above is the carbon dioxide fixing step).

[0057] In the sodium ferrite particle powder according to the present embodiment, it is preferable that carbon dioxide incorporated in the above-mentioned carbon dioxide fixing step is desorbed at a temperature of 200° C. or lower in a gas atmosphere containing no carbon dioxide, to recover carbon dioxide. Since the desorption temperature is as low as 200° C. or lower, the energy cost for desorption can be kept low (the above is the carbon dioxide recovery step).

[0058] The sodium ferrite particle powder according to the present embodiment can be used as it is, but when it is brought into contact with a large amount of carbon dioxide, the superficial velocity of the adsorption tower can be controlled. That is, the sodium ferrite particle powder may be granulated or supported on a carrier to form a spherical molded body having a diameter of about 100 μm to 10 mm More preferably, it is a spherical molded product having a diameter of 200 μm to 7 mm. At this time, it is preferable that the molded body containing the sodium ferrite particle powder has a specific surface area of 1 to 1000 m.sup.2/g so that the contact with carbon dioxide is not hindered even if the diameter of the molded body is increased. Further, the shape of the molded body is not particularly limited, but is preferably spindle shape, rectangular parallelepiped shape, dice-shape, or cylindrical shape, in addition to the spherical shape. In addition, a sodium ferrite particle powder can be processed into a paint and applied onto mesh, non-woven fabric, and honeycomb so that carbon dioxide can be fixedly recovered, or a sodium ferrite particle powder can be filled in a column to give a filter so that carbon dioxide can be fixedly recovered.

[0059] Next, a method for producing the sodium ferrite particle powder according to an embodiment of the present invention will be described.

[0060] The sodium ferrite particle powder according to the present embodiment can be obtained by mixing an iron oxide particle powder, a particle powder made of the sodium raw material, and at least one metal or more compound selected from the metal group consisting of silicon, aluminum, titanium, manganese, cobalt, nickel, magnesium, copper and zinc, and reacting them at a temperature of 150 to 500° C. in the solid phase.

[0061] When the above-mentioned iron oxide particle powder and the particle powder of the sodium raw material were mixed, and then the metal group was further mixed and subjected to a solid phase reaction, the metal group component tended to suppress the growth of the primary particles of sodium ferrite. Therefore, it becomes a particle powder having a large BET specific surface area, which is preferable as a carbon dioxide absorbent. Further, as a characteristic of the solid phase reaction, the crystal growth of sodium ferrite tends to be isotropic, so that the axial ratio of the primary particles tends to be suppressed.

[0062] The amount of the metal such as silicon, aluminum, titanium, manganese, cobalt, nickel, magnesium, copper and zinc to be added and calcinated is preferably more than 1% by weight and 20% by weight or less in terms of the oxide with respect to iron oxide. This is because, as described above, the carbon dioxide absorption performance may be enhanced. The content of the metal is more preferably 1.1% by weight to 19% by weight, and further preferably 1.2% by weight to 18% by weight. As the metal, oxides, hydroxides, chlorides and carbonates of various metals may be used as raw materials. Moreover, a composite of the above mentioned metals may be used.

[0063] For the iron oxide particle powder, hematite, magnetite, maghemite, and goethite can be used. When iron oxide particle powder and sodium raw material particle powder are mixed and calcinated, α-sodium ferrite is usually produced at 600° C. and β-sodium ferrite is produced at 800° C. (Non-Patent Literature 1). When a group of metals is mixed with this system and subjected to a solid phase reaction, sodium ferrite is formed at a low temperature of 150 to 500° C., and further, there is formed a composition with more β-sodium ferrite crystal phase than α-sodium ferrite crystal phase. By addition of this metal group, fine sodium ferrite is formed. Further, it is more preferable that the carbon dioxide absorption performance is also improved by forming a large amount of β-sodium ferrite. Further, since it is calcinated at a temperature lower than usual, sintering is less likely to occur, and it becomes a particle powder having a large BET specific surface area, which is preferable as a carbon dioxide absorbent.

[0064] The shape of the iron oxide particle powder can be selected from needle shape, spindle shape, spherical shape, tetrahedron, hexahedron, and octahedron.

[0065] As the particle size of the iron oxide particle powder, any size from 10 nm to 1 μm can be selected.

[0066] As the particle powder of the sodium raw material, sodium nitrite, sodium sulfate, sodium carbonate, sodium hydrogen carbonate, and sodium hydroxide can be used. However, considering industrial use, sodium nitrite and sodium sulfate, which may generate toxic nitrite gas or sulfurous acid gas during production should be avoided.

[0067] In general, the solid phase reaction is a synthetic method in which a solid and a solid are mixed and the elements are moved and reacted without a solvent. Since no solvent is used as a reaction mother liquor, wastes such as a solvent when used for the liquid phase reaction can be suppressed. Further, in the case of the solid phase reaction at a low temperature, which is also a feature of the present invention, the reaction can be extremely concentrated, so that the energy cost can be suppressed to a low level. Moreover, since the high reaction concentration and washing are not required, a high yield of the product can be expected.

[0068] <Function>

[0069] In the present embodiment, the sodium ferrite particle powder containing at least one metal or more selected from silicon, aluminum, titanium, manganese, cobalt, nickel, magnesium, copper and zinc in an amount of more than 1% by weight and 20% by weight or less in terms of the oxide had an excellent performance of adsorbing carbon dioxide in a gas, confining it in a solid, and removing it. It is presumed that this is because silicon, aluminum, titanium, manganese, cobalt, nickel, magnesium, copper, and zinc contained in the sodium ferrite particle powder were solid-solved in the generated sodium ferrite particles or were present on the surface of the particles, while inhibited the crystal growth of the sodium ferrite particles and helped to make the sodium ferrite particles uniform and finer. Furthermore, it is presumed that the metal has a catalytic action, which significantly improves the carbon dioxide absorption ability originally possessed by sodium ferrite, and it has achieved an excellent performance capable of absorbing carbon dioxide at room temperature and discharging it to the outside of the system at 200° C. or lower. Further, it is presumed that the sodium ferrite particle powder having a high BET specific surface area and being closer to a spherical shape has become a material having excellent moldability and processability while maintaining the original carbon dioxide absorption performance.

[0070] Next, a method for producing a sodium ferrite particle powder according to another embodiment of the present invention will be described.

[0071] The sodium ferrite particle powder according to the present embodiment can also be obtained by mixing a particle powder made of the sodium raw material with an iron oxide particle powder containing at least one metal or more selected from the metal group consisting of silicon, aluminum, titanium, manganese, cobalt, nickel, magnesium, copper and zinc in the form of an oxide, and reacting them at a temperature of 150 to 500° C. in the solid phase.

[0072] When the iron oxide particle powder metal-treated with the above-mentioned metal oxide and the particle powder made of the sodium raw material were subjected to a solid-phase reaction, the contained metal component tended to suppress the growth of the primary particles of sodium ferrite. Therefore, it becomes a particle powder having a large BET specific surface area, which is preferable as a fixing recovery material for carbon dioxide. Further, as a characteristic of the solid phase reaction, the crystal growth of sodium ferrite tends to be isotropic, so that the axial ratio of the primary particles tends to be suppressed.

[0073] The amount of the metal such as silicon, aluminum, titanium, manganese, cobalt, nickel, magnesium, copper and zinc that are metal-treated with iron oxide is preferably 0.05 to 5% by weight in terms of the oxide with respect to the iron oxide. This is because, as described above, the carbon dioxide fixing recovery performance may be improved in some cases. The content of the metal is preferably 0.1 to 4% by weight, and further preferably 0.15 to 3% by weight.

[0074] For the iron oxide particle powder, hematite, magnetite, maghemite, and goethite can be used. In order to contain a large amount of the crystal phase of α-sodium ferrite, magnetite and maghemite having a spinel structure in which oxygen hexagonal lattices have a pattern of . . . ABCABC . . . which is the same as the crystal phase of α-sodium ferrite are preferable (Reference: Shoichi Okamoto, “Crystal Formation and Phase Transition of Sodium Orthoferrite”, Nagaoka University of Technology, Research Report No. 8 (1986), pp. 37-42).

[0075] The shape of the iron oxide particle powder can be selected from needle shape, spindle shape, spherical shape, tetrahedron, hexahedron, and octahedron.

[0076] As the particle size of the iron oxide particle powder, any size from 10 nm to 1 μm can be selected.

[0077] As the particle powder of the sodium raw material, sodium nitrite, sodium sulfate, sodium carbonate, sodium hydrogen carbonate, and sodium hydroxide can be used. However, considering industrial use, sodium nitrite and sodium sulfate, which may generate toxic nitrite gas or sulfurous acid gas during production should be avoided.

[0078] In general, the solid phase reaction is a synthetic method in which a solid and a solid are mixed and the elements are moved and reacted without a solvent. Since no solvent is used as a reaction mother liquor, wastes such as a solvent when used for the liquid phase reaction can be suppressed. Further, in the case of the solid phase reaction at a low temperature, which is also a feature of the present invention, the reaction can be extremely concentrated, so that the energy cost can be suppressed to a low level. Moreover, since the high reaction concentration and washing are not required, a high yield of the product can be expected.

[0079] <Function>

[0080] In the present embodiment, the sodium ferrite particle powder containing at least one metal or more selected from silicon, aluminum, titanium, manganese, cobalt, nickel, magnesium, copper and zinc in an amount of 0.05 to 1% by weight in terms of the oxide further had an excellent property of adsorbing carbon dioxide in a gas, confining it in a solid, and releasing carbon dioxide by heating. It is presumed that this was because silicon, aluminum, titanium, manganese, cobalt, nickel, magnesium, copper, and zinc contained in the iron oxide particle powder as a raw material were solid-solved in the generated sodium ferrite particles or were present on the surface of the particles, while inhibited the crystal growth of the sodium ferrite particles and helped to make the sodium ferrite particles uniform and finer. Furthermore, it is presumed that the metal has a catalytic action, which significantly improves the carbon dioxide fixing recovery ability originally possessed by sodium ferrite, and it has achieved an excellent performance capable of fixing carbon dioxide in a temperature range from room temperature to 100° C. and recovering it at 200° C. or lower. Further, it is presumed that by using a sodium ferrite particle powder closer to sphere having a high BET specific surface area in addition to the above features, a material having excellent moldability and processability while maintaining the original carbon dioxide fixing recovery performance can be obtained.

EXAMPLES

[0081] Typical embodiments of the present invention are as follows.

[0082] Analysis of elements (excluding oxygen) in the sodium ferrite particle powder according to the present invention and their raw materials was carried out by a scanning fluorescent X-ray analyzer ZSX Primus II manufactured by Rigaku.

[0083] The % by weight of the crystal phase of the sodium ferrite particle powder according to the present invention was identified and quantified by a fully automatic multipurpose X-ray diffractometer D8 ADVANCE manufactured by BRUKER.

[0084] The BET specific surface area of the sodium ferrite particle powder according to the present invention was measured by the BET method using nitrogen using Multisorb-16 manufactured by QUANTA CHROME.

[0085] The major axis diameters and minor axis diameters of primary particles of the sodium ferrite particle powder according to the present invention were measured for 350 primary particles that shown in the micrograph by a scanning electron microscope S-4800 manufactured by Hitachi High-Tech Corporation, and the values of the average major axis diameter and the average minor axis diameter of the primary particles are shown.

[0086] The axial ratio of the sodium ferrite particle powder according to the present invention is shown as the ratio of the average major axis diameter to the average minor axis diameter (average major axis diameter/average minor axis diameter).

[0087] The average primary particle diameter of the sodium ferrite particle powder according to the present invention is shown as the average value of the average major axis diameter and the average minor axis diameter.

[0088] For the powder pH value of the sodium ferrite particle powder according to the present invention, 5 g of a sample was weighed in a 300 ml Erlenmeyer flask, 100 ml of boiled pure water was added to this, it was heated to maintain the boiling state for about 5 minutes, then, the flask was plugged and allowed to cool to room temperature, water corresponding to weight loss was added and the flask was plugged again, and the content was shaken for 1 minute, and allowed to stand still for 5 minutes, then, the pH of the resultant supernatant was measured according to JIS Z8802-7, and the obtained value was taken as the powder pH value.

[0089] For the carbon dioxide fixing recovery ability of the sodium ferrite particle powder according to the present invention, 100 mg of a sample was placed on a combustion boat and placed in an acrylic pipe equipped with an inlet/outlet pipe, and a (carbon dioxide+nitrogen) mixed gas adjusted to a humidity range of 20 to 100% and a carbon dioxide concentration range of 1 to 100 vol % was introduced at 500 mL/min from the inlet, and for obtaining the adsorption amount of carbon dioxide after 2 hours, the sample was heated from room temperature to 200° C. by a differential heat thermogravimetric simultaneous measuring device STA7000 manufactured by Hitachi High-Tech Corporation, and the carbon dioxide absorption and discharge amount was determined from the heat loss.

[0090] To evaluate the dispersibility of the sodium ferrite particle powder according to the present invention, 10 parts by weight of the sodium ferrite powder was weighed, and 1 part by weight of alkylamine, 89 parts by weight of propylene glycol monomethyl ether acetate, and 100 parts by weight of 1.5 mm glass beads were added. Then, the mixture was shaken with a paint conditioner for 2 hours, and the glass beads were separated and removed from the slurry. The dispersed particle size of the obtained slurry was measured by a concentrated particle size analyzer FPAR1000 manufactured by Otsuka Electronics. When the cumulative 50% value (D50) of the scattering intensity distribution was 2 times or less of the average primary particle size, it was judged as a sample with good dispersibility and was evaluated as “∘”, and when it was more than 2 times, it was evaluated as “x”.

[0091] <Production Method of Iron Oxide Particle Powder Used as Raw Material for Sodium Ferrite Particle Powder>

[0092] Iron oxide 1 (100ED manufactured by Toda Kogyo Corp., hematite, specific surface area 11 m.sup.2/g)(1000 parts by weight) was added to and mixed with 10,000 parts by weight of pure water, and sodium hydroxide was added to the obtained suspension to adjust pH to 11. After that, No. 3 water glass (manufactured by Tokuyama Corporation, the amount of Si in the water glass which is a high-concentration sodium silicate aqueous solution corresponds to 29% by weight in terms of SiO.sub.2)(17.2 parts by weight)(corresponding to 0.5% by weight in terms of SiO.sub.2, with respect to the iron oxide 1) was added, and then the mixture was stirred and mixed. Then, sulfuric acid was added to the suspension to adjust the pH to 9, and a SiO.sub.2 film was deposited on the surface of the iron oxide 1 particles in the suspension. Then, the obtained suspension was filtered, and Na.sup.+ ion and SO.sub.4.sup.2− ion which could be impurities were washed with water and dried to obtain treated iron oxide 1. As a result of fluorescent X-ray analysis, the amount of SiO.sub.2 present on the surface of the obtained treated iron oxide 1 was 0.25% by weight in terms of SiO.sub.2.

[0093] A treatment was carried out in the same manner as in the above-described metal treatment except that the type, the shape and the BET specific surface area of the iron oxide particles used, and the type and the addition amount of the metal treatment agent were changed, to obtain treated iron oxides 2 to 9 treated with metals.

[0094] Table 1 shows various characteristics of the obtained treated iron oxides 1 to 9. Here, the addition amounts and coating amounts of the metal treatment agents: sodium silicate, aluminum sulfate, titanium chloride, cobalt sulfate, nickel sulfate, copper sulfate and zinc sulfate are listed in Table 1, as SiO.sub.2, Al.sub.2O.sub.3, TiO.sub.2, CoO, NiO, CuO and ZnO, respectively. Subsequently, sodium ferrite particle powders were produced from the obtained treated iron oxides 1 to 9 as a raw material.

TABLE-US-00001 TABLE 1 metal treatment of iron oxide particle metal treatment agent addition amount metal-coated product name of iron oxide particle (in termes coated metal-treated name of BET of oxide) amount iron oxide iron oxide type shape (m.sup.2/g) type (% by weight) type (% by weight) treated iron oxide 1 hematite granular 11 sodium silicate 0.5 SiO.sub.2 0.25 iron oxide 1 treated iron oxide 2 hematite granular 7 aluminum sulfate 1.5 Al.sub.2O.sub.3 1.20 iron oxide 2 treated iron oxide 3 magnetite sphere 4 titanium chloride 1.0 TiO.sub.2 0.82 iron oxide 3 treated iron oxide 4 magnetite sphere 10 manganese sulfate 0.5 MnO 0.28 iron oxide 4 treated iron oxide 4 magnetite sphere 10 cobalt sulfate 0.2 CoO 0.12 iron oxide 5 treated iron oxide 4 magnetite sphere 10 nickel sulfate 0.2 NiO 0.15 iron oxide 6 treated iron oxide 4 magnetite sphere 10 copper sulfate 0.1 CuO 0.07 iron oxide 7 treated iron oxide 4 magnetite sphere 10 zinc sulfate 0.1 ZnO 0.07 iron oxide 8 treated iron oxide 5 goethite needle 20 sodium silicate + 0.5 + 0.5 SiO.sub.2 + Al.sub.2O.sub.3 0.25 + 0.15 iron oxide 9 aluminum sulfate

[0095] <Production Method of Sodium Ferrite Particle Powder>

Example 1

[0096] The particles of the treated iron oxide 1 obtained above were weighed (10 parts by weight), whereas a sodium hydroxide particle powder as a sodium raw material was weighed so as to have Na/Fe=1.0 (molar ratio). After mixing the raw materials, they were pulverized with mixing in a sample mill. This mixed pulverized product was placed in a crucible and subjected to a solid phase reaction at 400° C. for 16 hours. Then, it cooled to room temperature and pulverized with a sample mill to obtain a sodium ferrite particle powder. The BET specific surface area of the obtained particle powder was 3.0 m.sup.2/g. According to quantification of the primary particles by a scanning electron microscope, the average major axis diameter was 0.7 μm, the average minor axis diameter was 0.4 μm, the average particle diameter was 0.5 μm, and the axial ratio was 1.6. The powder pH was relatively high at 13.8.

[0097] Analysis of elements contained in the resultant sodium ferrite particle powder was performed by fluorescent X-ray, as a result, the molar ratio of Na/Fe was 1.0, which was almost the same as the charging ratio of the raw materials, and the silicon component was contained in an amount of 0.18% by weight as a heterogeneous oxide SiO.sub.2. Further, the obtained powder was found to be composed of 95% by weight of α-sodium ferrite crystal phase, 4% by weight of β-sodium ferrite crystal phase and 1% by weight of γ-Fe.sub.2O.sub.3 crystal phase, according to quantification of the powder X-ray diffraction pattern. Therefore, it is presumed that the heterogeneous oxide SiO.sub.2 is amorphous or is solid-solved in each crystal phase as Si.

[0098] In order to investigate the carbon dioxide fixing recovery performance of the obtained sodium ferrite particle powder, 1.00 parts by weight of a sample was placed on a No. 2 combustion boat (12×60×9 mm) and aerated through 500 mL/min of model combustion exhaust gas for 3 hours. Generally, the exhaust gas when fuel is burned in the atmosphere is composed of a maximum of 80 vol % nitrogen, 20 vol % carbon dioxide, and 80 to 100% humidity. Therefore, at room temperature of 25° C., 400 mL/min of nitrogen and 100 mL/min of carbon dioxide were mixed and bubbled into water to obtain a model combustion exhaust gas having 20 vol % carbon dioxide and 80% relative humidity.

[0099] The sample after aeration was weighed (10 mg), and heated to 200° C. at 10° C./min while being aerated with dry air at 300 mL/min using a thermogravimetric measuring device, and the desorption temperature and desorption amount of carbon dioxide adsorbed on the sample were measured. FIG. 1 shows a measurement chart with the horizontal axis as the sample temperature. The TG curve showed the % by weight of the residual sample at each temperature when the initial value was 100% by weight, and the decrease in the sample was considered to be due to the release of carbon dioxide. The DTG curve is a differential curve of the TG curve, and the temperature at which the maximum value of the DTG curve is taken is regarded as the carbon dioxide desorption temperature. The DTA curve showed a downwardly convex curve, and it was found that the endothermic reaction was carried out at around 114° C. When this was regarded as a thermal decomposition reaction of NaHCO.sub.3 and quantified, the desorption temperature of carbon dioxide was 114° C., and the desorption amount of carbon dioxide was 18% by weight with respect to the sample solid content, thus, excellent carbon dioxide fixing recovery performance became clear.

[0100] Further, when the sample after aeration was reprepared and the weight was measured, it was 1.30 parts by weight, and an increase in mass of 30% by weight was confirmed. When the X-ray diffraction of this sample was measured, 70% by weight of Na.sub.1-x FeO.sub.2 and 30% by weight of NaHCO.sub.3 were confirmed, and it was found that carbon dioxide was fixed on the sodium ferrite particle powder. Further, this sample was heated in an electric furnace at 120° C. for 1 hour, and the weight was measured to be 1.12 parts by weight, thus, it was found that 0.18 parts by weight (18% by weight with respect to NaFeO.sub.2 solid content) of carbon dioxide could be adsorbed and desorbed in this cycle. When the X-ray diffraction of this sample was measured, 90% by weight of NaFeO.sub.2 and 10% by weight of Na.sub.2CO.sub.3 were confirmed. Further, when carbon dioxide was brought into contact with this sample in the same manner as described above, the amount was increased to 1.30 parts by weight, and when heated, the amount was reduced to 1.12 parts by weight, and 0.18 parts by weight of carbon dioxide could be absorbed and desorbed. This operation was repeated 10 times, and it was confirmed that there was no change in the mass increase and decrease. From this, it was clarified that the obtained sodium ferrite particle powder was excellent in the fixing recovery performance of carbon dioxide, particularly in repeatability.

[0101] When the dispersibility of the obtained sodium ferrite particle powder was evaluated, the dispersed particle size was within twice the average primary particle size, which was good.

Examples 2-9

[0102] The sodium ferrite particle powder according to the present invention was obtained in the same manner as in Example 1 except that the type of the metal-treated iron oxide fine particles and the type of the sodium source were variously changed.

[0103] Table 2 shows the production conditions in Examples 1 to 9, Table 3 shows various characteristics of the obtained sodium ferrite particle powder, and Table 4 shows the carbon dioxide fixing recovery performance and dispersibility thereof. For samples with good dispersibility, those with a dispersed particle size within twice the average primary particle size were marked with ∘, and those with a dispersed particle size exceeding 2 times were marked with x.

Comparative Example 1

[0104] The iron oxide 1 was weighed (10 parts by weight), whereas a sodium hydroxide particle powder was weighed so that Fe:Na=1:1 (molar ratio), and 100 parts by weight of pure water was added to dissolve the sodium hydroxide particle powder, and they were kneaded for 2 hours in an automatic mortar. This was dried at 80° C. for 2 hours, and pulverized with mixing in a sample mill. This mixed pulverized product was placed in a crucible and heat-treated at 400° C. for 2 hours. The product was found by powder X-ray diffraction to be 25% by weight of the α-sodium ferrite crystal phase and the remaining 75% by weight of the γ-Fe.sub.2O.sub.3 crystal phase. The BET specific surface area was 1.0 m.sup.2/g. The axial ratio was 3.8. Further, when the carbon dioxide fixing recovery performance was examined in the same manner as in Example 1, the temperature was raised to 200° C., but the desorption of carbon dioxide could not be confirmed.

[0105] The production conditions of Comparative Example 1 are shown in Table 2, the properties of the obtained sodium ferrite particle powder are shown in Table 3, and the carbon dioxide fixing recovery performance and dispersibility thereof are shown in Table 4.

TABLE-US-00002 TABLE 2 iron oxide raw raw material charging calcination material Na/Fe Temperature Time type sodium raw material (molar ratio) (° C.) (hr) Example 1 treated iron oxide 1 sodium hydroxide 1.0 400 16 Example 2 treated iron oxide 2 sodium hydroxide 1.1 400 16 Example 3 treated iron oxide 3 sodium hydroxide 1.2 300 16 Example 4 treated iron oxide 4 sodium hydroxide 0.9 300 16 Example 5 treated iron oxide 5 sodium oxide 0.8 200 16 Example 6 treated iron oxide 6 sodium carbonate 1.0 400 16 Example 7 treated iron oxide 7 sodium carbonate 1.0 400 16 Example 8 treated iron oxide 8 sodium oxide 1.0 400 16 Example 9 treated iron oxide 9 sodium hydroxide 1.0 400 16 Comparative iron oxide 1 sodium hydroxide 1.0 400 16 Example 1

TABLE-US-00003 TABLE 3 primary particle axis ratio (average heterogeneous oxide major axis average contained average average diameter/ primary crystal phase content Na/Fe major axis minor axis average particle α-NaFeO2 β-NaFeO2 γ-Fe2O3 (% by powder BET (molar diameter diameter minor axis diameter (% by (% by (% by type weight) pH (m.sup.2/g) ratio) (μm) (μm) diameter) (μm) weight) weight) weight) Example 1 SiO.sub.2 0.18 13.8 3.0 1.0 0.7 0.4 1.6 0.57 95 4 1 Example 2 Al.sub.2O.sub.3 0.84 12.8 2.7 1.1 0.6 0.5 1.2 0.55 80 19 1 Example 3 TiO.sub.2 0.59 13.4 2.2 1.2 0.8 0.5 1.8 0.63 75 24 1 Example 4 MnO 0.20 11.8 5.3 0.9 0.4 0.2 1.8 0.28 92 6 2 Example 5 CoO 0.08 13.3 4.2 0.8 0.4 0.3 1.3 0.35 94 2 4 Example 6 NiO 0.10 12.8 5.2 1.0 0.4 0.3 1.3 0.36 90 3 7 Example 7 CuO 0.05 13.4 4.8 1.0 0.4 0.3 1.3 0.36 93 4 3 Example 8 ZnO 0.06 13.3 4.4 1.0 0.4 0.3 1.4 0.34 89 3 8 Example 9 SiO.sub.2 + 0.20 + 0.12 12.9 2.5 1.0 0.7 0.5 1.4 0.60 92 5 3 Al.sub.2O.sub.3 Comparative — — 12.1 1.0 1.0 2.3 0.6 3.8 1.45 25 nd 75 Example 1

TABLE-US-00004 TABLE 4 CO2 dispersed particle recovery CO2 diameter/average temperature recovery amount dispersed particle primary particle (° C.) (% by weight) diameter (μm) diameter dispersibility Example 1 114 18 0.6 1.2 ◯ Example 2 113 15 0.8 1.3 ◯ Example 3 110 10 0.9 1.5 ◯ Example 4 112 18 0.5 1.2 ◯ Example 5 110 18 0.4 1.1 ◯ Example 6 113 18 0.5 1.4 ◯ Example 7 114 18 0.4 1.1 ◯ Example 8 114 18 0.4 1.2 ◯ Example 9 118 12 0.9 1.5 ◯ Comparative — nd precipitated × × Example 1 unmeasurable

Example 10

[0106] Iron oxide fine particles 10 (100ED manufactured by Toda Kogyo Corp., hematite, specific surface area 11 m.sup.2/g) were weighed (10 parts by weight), whereas a sodium hydroxide particle powder as a sodium raw material was weighed so that Na/Fe=1.0 (molar ratio), and hydrotalcite (manufactured by Toda Kogyo Corp., specific surface area 10 m.sup.2/g) was weighed (1 part by weight) and added. The raw materials were mixed, then, pulverized with mixing in a sample mill. This mixed pulverized product was placed in a crucible and subjected to a solid phase reaction at 400° C. for 16 hours. Then, it cooled to room temperature and pulverized with a sample mill to obtain a sodium ferrite particle powder. The BET specific surface area of the obtained particle powder was 4.0 m.sup.2/g. According to quantification of the primary particles by a scanning electron microscope, the average major axis diameter was 0.7 μm, the average minor axis diameter was 0.4 μm, the average particle diameter was 0.55 μm, and the axial ratio was 1.8. The powder pH was relatively high at 13.8.

[0107] When the analysis of elements contained in the obtained sodium ferrite particle powder was performed by fluorescent X-ray, the Na/Fe molar ratio was 1.0, which was almost the same as the raw material charging ratio, and the amount of MgO was 6.0% by weight and Al.sub.2O.sub.3 was 3.5% by weight, that is, the amount of the heterogeneous metal oxides was 9.5% by weight. Furthermore, according to quantification of the obtained powder X-ray diffraction pattern, it was found that 76% by weight was composed of β-sodium ferrite crystal phase, 11% by weight was composed of α-sodium ferrite crystal phase and 8% by weight was composed of γ-Fe.sub.2O.sub.3 crystal phase. Therefore, it is presumed that the heterogeneous oxides MgO and Al.sub.2O.sub.3 are in an amorphous state or are solid-solved in each crystal phase as Mg and Al.

[0108] The carbon dioxide absorption evaluation of the obtained sodium ferrite particle powder was performed as follows. First, carbon dioxide was introduced into a desiccator (13 L) to create a model unpleasant indoor environment with a carbon dioxide concentration of 4000 ppm and a humidity of 80% at room temperature of 25° C. and sealed. Next, 10 g of the sodium ferrite particle powder was quickly put into a desiccator (13 L), and the carbon dioxide concentration after 30 minutes was measured with a carbon dioxide densitometer. The carbon dioxide concentration after 30 minutes was 1 ppm or less, which is the detection limit of the carbon dioxide concentration, indicating excellent carbon dioxide absorption performance.

[0109] In order to examine the amount of carbon dioxide desorbed from the obtained sodium ferrite particle powder, 100 mg of a sample was placed on a No. 2 combustion boat (12×60×9 mm) and aerated through 500 mL/min of model combustion exhaust gas for 3 hours. Generally, the exhaust gas when fuel is burned in the atmosphere is composed of a maximum of 80 vol % nitrogen, 20 vol % carbon dioxide, and 80 to 100% humidity. Therefore, at room temperature of 25° C., 400 mL/min of nitrogen and 100 mL/min of carbon dioxide were mixed and bubbled into water to obtain a model combustion exhaust gas having 20 vol % carbon dioxide and 80% relative humidity.

[0110] The sample after aeration was weighed (10 mg), and heated to 200° C. at 10° C./min while being aerated with dry air at 300 mL/min using a thermogravimetric measuring device, and the desorption temperature and desorption amount of carbon dioxide adsorbed on the sample were measured. FIG. 2 shows a measurement chart with the horizontal axis as the sample temperature. The TG curve showed the % by weight of the residual sample at each temperature when the initial value was 100% by weight, and the decrease in the sample was considered to be due to the release of carbon dioxide. The DTG curve is a differential curve of the TG curve, and the temperature at which the maximum value of the DTG curve is taken is regarded as the carbon dioxide desorption temperature. The DTA curve showed a downwardly convex curve, and it was found that the endothermic reaction was carried out at around 114° C. When this was regarded as a thermal decomposition reaction of NaHCO.sub.3 and quantified, the desorption temperature of carbon dioxide was 114° C., and the desorption amount of carbon dioxide was 18% by weight with respect to the sample solid content, thus, excellent carbon dioxide discharge performance became clear.

[0111] When the dispersibility of the obtained sodium ferrite particle powder was evaluated, the dispersed particle size was within twice the average primary particle size, which was good.

Examples 11-14

[0112] The sodium ferrite particle powder according to the present invention was obtained in the same manner as in Example 10 except that the type of iron oxide fine particles, the type of sodium source, the type of metal compound and the amount of addition were variously changed.

[0113] Table 5 shows the production conditions in Examples 10 to 14, various characteristics of the obtained sodium ferrite particle powder are shown in Table 6, and the carbon dioxide absorption/discharge performance and dispersibility are shown in Table 7. For the carbon dioxide absorption evaluation, 10 g of carbon dioxide absorbent was put in a desiccator (13 L) having a carbon dioxide concentration of 4000 ppm, and those having a carbon dioxide concentration of 2500 ppm or less after 30 minutes were marked with ∘, and those having a carbon dioxide concentration of more than 2500 ppm were marked with x. For samples with good dispersibility, those with a dispersed particle size within twice the average primary particle size were marked with ∘, and those with a dispersed particle size exceeding 2 times were marked with x.

Comparative Example 2

[0114] The iron oxide 10 was weighed (10 parts by weight), whereas a sodium hydroxide particle powder was weighed so that Fe/Na=1:0 (molar ratio), and 100 parts by weight of pure water was added to dissolve the sodium hydroxide particle powder, and they were kneaded for 2 hours in an automatic mortar. This was dried at 80° C. for 2 hours, and pulverized with mixing in a sample mill. This mixed pulverized product was placed in a crucible and heat-treated at 400° C. for 2 hours. The product was found by powder X-ray diffraction to be 25% by weight of the α-sodium ferrite crystal phase and the remaining 75% by weight of the γ-Fe.sub.2O.sub.3 crystal phase. The BET specific surface area was 1.0 m.sup.2/g. The axial ratio was 3.8. Moreover, when the carbon dioxide absorption/discharge performance was examined in the same manner as in Example 10, the temperature was raised to 200° C., but the desorption of carbon dioxide could not be confirmed.

[0115] Table 5 shows the production conditions of Comparative Example 2, Table 6 shows various characteristics of the obtained sodium ferrite particle powder, and Table 7 shows the carbon dioxide absorption/discharge performance and dispersibility.

TABLE-US-00005 TABLE 5 raw material heterogeneous metal oxide iron oxide particle charging addition amount calcination name of sodium raw Na/Fe (% by weight vs Temperature Time iron oxide type shape BET material (molar ratio) type iron oxide) (° C.) (hr) Example 10 iron oxide 10 hematite granular 11 sodium hydroxide 1.0 hydrotalcite 10 400 16 Example 11 iron oxide 11 hematite granular 7 sodium hydroxide 1.1 alumina 20 400 16 Example 12 iron oxide 12 magnetite sphere 4 sodium carbonate 1.2 silica 10 300 16 Example 13 iron oxide 13 magnetite sphere 10 sodium carbonate 0.9 titanium oxide 5 300 16 Example 14 iron oxide 14 goethite needle 20 sodium oxide 0.8 zinc oxide 5 200 16 Comparative iron oxide 10 hematite granular 11 sodium hydroxide 1.0 — — 400 16 Example 2

TABLE-US-00006 TABLE 6 primary particle axis ratio (average heterogeneous oxide major axis avarage contained average average diameter/ primary crystal phase content Na/Fe major axis minor axis average particle α-NaFeO2 β-NaFeO2 γ-Fe2O3 (% by (molar powder BET diameter diameter minor axis diameter (% by (% by (% by type weight) ratio) pH (m.sup.2/g) (μm) (μm) diameter) (μm) weight) weight) weight) Example 10 MgO, 6.0(MgO) + 1.0 13.8 4.0 0.7 0.4 1.8 0.55 11 76 8 Al2O3 3.0(Al2O3) Example 11 Al2O3 18.0  1.1 12.8 2.7 0.6 0.5 1.2 0.55 33 62 5 Example 12 SiO2 8.2 1.2 13.4 2.2 0.8 0.5 1.8 0.63 27 66 7 Example 13 TiO2 4.3 0.9 11.8 5.3 0.4 0.2 1.8 0.28 42 53 5 Example 14 ZnO 2.1 0.8 12.9 2.5 0.7 0.5 1.4 0.60 37 60 3 Comparative — — 1.0 12.1 1.0 2.3 0.6 3.8 1.45 25 nd 75 Example 2

TABLE-US-00007 TABLE 7 CO2 CO2 dispersed particle CO2 desorbing saturated dispersed particle diameter/avarage absorbing temperature absorption amount diameter primary particle performance (° C.) (% by weight) (μm) diameter dispersibility Example 10 ∘ 114 18 0.6 1.1 ∘ Example 11 ∘ 113 15 0.8 1.5 ∘ Example 12 ∘ 110 10 0.9 1.4 ∘ Example 13 ∘ 112 18 0.5 1.8 ∘ Example 14 ∘ 118 12 0.9 1.5 ∘ Comparative x — nd precipitated x x Example 2 unmeasurable

[0116] As described above, it is clear that the sodium ferrite particle powder according to the present embodiment is a carbon dioxide fixing recovery material excellent in carbon dioxide adsorption and desorption. Further, since the particle powder is excellent in dispersibility, it is clear that the particle powder is excellent in moldability and processability.

INDUSTRIAL APPLICABILITY

[0117] The sodium ferrite particle powder according to the present invention is suitable as a material that can perform fixing recovery of carbon dioxide by adsorption and desorption with non-hazardous inorganic materials without using a dangerous substance such as an aqueous amine solution.