JP4499139B2 - Conductive diamond granules for fluidized bed and fluidized bed for fluidized bed electrolytic treatment equipment - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a conductive bed granular material for fluidized bed containing nitrogen and boron and a fluidized bed for a fluidized bed electrolytic treatment apparatus.

  Environmental regulations for industrial wastewater, domestic wastewater, etc. are becoming more stringent not only for national and local governments but also for the whole world. Industrial wastewater that was once drainable can be regulated by manufacturers. And the processing method has become a problem in processing companies. In recent years, research on carbon dioxide electrolytic reduction from various angles has been conducted in relation to environmental problems.

  Industrial and household wastewater treatment methods include, for example, chemical treatment, physical treatment, electrolytic treatment using strong oxidizing agents and reducing agents, but safety, ease of operation, and compact equipment. Electrolytic treatment that is easy to use is widely adopted.

  When electrolytic treatment such as wastewater is performed, it is difficult to cause an electrolytic reaction when the concentration of reactants in the wastewater is low or the electrode reaction rate is slow. Therefore, there is an electrolysis method using a fluidized bed electrolytic treatment apparatus using a granular electrode in order to increase the electrolysis area of the electrode and the solution.

  This method is characterized by the fact that the contact area between the electrode area and the electrolyte solution can be increased, and the reaction amount can be increased.

  However, there are many problems in the electrolysis method using the fluidized bed electrolytic treatment apparatus. For example, when metals such as lead and tin are used as conductive fluid particles in fluidized beds in fluidized bed electrolytic treatment equipment, lead and tin as electrode components are eluted into the electrolyte and harmful metals are discharged into the environment. Will do. In addition, although electrodes using platinum, gold, and the like do not have the above-described drawbacks, they have the disadvantage that the current density during the electrolytic reaction is low and the potential window is narrow.

  On the other hand, the diamond thin film produced by chemical vapor deposition is insoluble in the electrolyte, can increase the current density, and has a wide potential window, so it can be oxidized to a potential region that cannot be used with other metal electrodes. In recent years, a substance having a potential and a reduction potential can be detected electrochemically, can be electrolyzed, and can be synthesized electrochemically. However, the diamond thin film has a problem that it is difficult to establish synthesis conditions by chemical vapor deposition, and the conductivity is low.

  Accordingly, an object of the present invention is to obtain diamond particles for a fluidized bed having conductivity. Another object of the present invention is to provide a fluidized bed using the conductive diamond granular material as one component.

  Therefore, as a result of intensive studies to obtain conductive diamond particles, the present inventors have found that conductivity can be imparted by incorporating nitrogen and boron into the diamond, thereby completing the present invention. It has come.

(1) That is, the conductive diamond granular material for fluidized beds used for the electrolytic treatment of the electrolytic solution of the present invention contains boron and nitrogen, and has an average particle diameter of 1 μm to 1 mm.

(2) It is preferable that the conductive diamond granular material for fluidized bed used for the electrolytic treatment of the electrolytic solution of the present invention contains 10 ppm or more of boron and 1 ppm or more of nitrogen.

(3) In the conductive bed granular material for fluidized bed used for the electrolytic treatment of the electrolytic solution of the present invention, boron is uniformly dispersed with a bulk density of 1.6 g / cm ³ or more in a nitrogen-containing atmosphere. It is preferable to be obtained by converting a graphite material by a high pressure synthesis method.

(4) In the conductive diamond granular material for fluidized bed used for the electrolytic treatment of the electrolytic solution of (3) above, the hydrogen content of the graphite material is preferably 1000 ppm or less.

(5) In the conductive diamond granular material for fluidized bed used for the electrolytic treatment of the electrolytic solution of the present invention, a boron-containing graphite material is obtained from a mixed raw material powder of a boron-containing compound powder and a carbonaceous powder in an inert gas atmosphere. After being obtained, the boron-containing graphite material is preferably obtained by conversion by a high-pressure synthesis method.

(6) In the conductive diamond granular material for fluidized beds used for the electrolytic treatment of the electrolytic solution of the present invention, the average particle diameter of the boron-containing compound powder is preferably 1 μm to 100 μm.

(7) In the conductive bed granular material for fluidized bed used in the electrolytic treatment of the electrolytic solution of (5) above, it is preferable that the average particle diameters of the boron-containing compound powder and the carbonaceous powder are the same.

(8) The fluidized bed for the fluidized bed electrolytic treatment apparatus used for the electrolytic treatment of the electrolytic solution of the present invention is based on the conductive diamond granular material for fluidized bed according to any one of (1) to (7) above. It consists of an electrolytic solution containing a plurality of conductive fluid particles.

(9) The present invention is used for the electrolytic treatment of the electrolytic solution according to any one of the above (1) to (7) used in a fluidized bed electrolytic treatment apparatus used for treatment of industrial or household wastewater. It is a conductive diamond granule for fluidized beds. Moreover, this invention is for fluidized beds used for the electrolytic treatment of the electrolyte solution of any one of said (1)-(7) used for the fluidized bed electrolytic treatment apparatus used for the process of the solution containing copper. This is a conductive diamond granular material.

  In the present invention, a conductive diamond granular material can be obtained by adding nitrogen and boron by a high-pressure synthesis method, and this granular material is used as one configuration of a fluidized bed electrolytic treatment apparatus. In addition, there are obtained effects that the potential window is wide, the current density is large, and the durability is excellent. Moreover, the conductive diamond granular material for fluidized beds used for the electrolytic treatment of the electrolytic solution of the present invention can be used for treatment of industrial or household wastewater or treatment of a solution containing a metal (for example, copper). it can.

  Embodiments of the present invention will be described below. The conductive diamond granule according to the present invention preferably contains boron and nitrogen, contains 10 ppm or more of boron, and contains 1 ppm or more of nitrogen. It is because sufficient electrical conductivity cannot be provided when the boron and nitrogen contents are less than the above-described values.

  In order to produce the above conductive diamond for fluidized bed, it is preferable to synthesize exclusively by a high temperature and high pressure method. That is, for example, since it is converted to diamond particles in an atmosphere containing nitrogen such as in the air, it contains nitrogen and also contains boron, so that conductivity can be imparted and improved. The conductive diamond granular material containing nitrogen and boron according to the present invention has an electric specific resistance of 20 mΩ · cm or less.

  In addition, the conductive diamond granular material of the present invention has an average particle size (adjusted by appropriately adjusting the pressure, temperature, and pressurization time at the time of synthesis so that the contact area between the later-described electrolytic treatment liquid and the electrode can be increased. The average particle diameter is preferably 1 μm to 1 mm. If the average particle diameter is larger than 1 mm, the contact area with the electrolytic solution is reduced, which is not preferable. The average particle size of the conductive diamond particles is more preferably 1 μm to 700 μm. Furthermore, it is preferable to appropriately adjust the average particle size of the raw material powder for synthesis so that the particle size of each conductive diamond granular material is as uniform as possible.

  The conductive diamond granular material according to the present invention is obtained by, for example, a method of synthesizing a graphite molded body containing boron at a high temperature and a high pressure, or a mixed raw material powder of a boron-containing compound powder and a carbonaceous powder by a high pressure synthesis method. A method of converting to

  More specifically, the raw materials for producing diamond use artificial graphite powder, graphitizable carbon powder and boron compound powder as raw materials, and these powders are mixed, molded, fired, graphitized, and highly purified by any method. Can be illustrated.

  Examples of the artificial graphite powder include powder obtained by adding a binder to fillers such as pyrolytic graphite, quiche graphite, coke and the like, powder obtained by pulverizing a graphitized article that has been molded, fired, graphitized, and graphite powder obtained by pulverizing expanded graphite. . The average particle size of the artificial graphite powder is preferably equal to the particle size of other components, that is, boron compound and graphitizable carbon powder. To prevent uneven distribution of each component of the raw material for producing diamond, a powder of 1 to 100 μm is used. It is preferable to use it.

  As the graphitizable carbon powder, petroleum coke, coal coke, pitch coke and the like can be used. Among these, mesophase microspheres produced by heat-treating pitches are preferable because they have self-sintering properties and can be fired without using a binder. Further, it is preferable to use those graphitizable carbon powders having an average particle size of 50 μm or less. The artificial graphite powder preferably has an average particle size of 50 μm or less, like the graphitizable carbon powder. By aligning the particle diameters of the raw material powders to the same level, they are uniformly mixed without being unevenly distributed.

  Examples of the boron compound include boron alone, boron oxide, boric acid, borosilicate, boron carbide, boron nitride and the like. Among these, boron carbide and boron nitride are preferably used. Moreover, the yield of the diamond excellent in the electroconductivity aiming at using the average particle diameter of a boron compound 1-100 micrometers can be improved. Among these, it is more preferable to use a 2-50 μm powder in order to improve the yield of conductive diamond.

In each of the above-mentioned powders, boron compound powder is 0.5 to 15% by mass, preferably 0.5 to 10% by mass, and graphitizable carbon powder is 76 to 98.9% by mass, preferably 81 to 98.8% by mass. %,
Artificial graphite powder is mixed at a mixing ratio of 1 to 9% by mass.

  This mixture is mixed for 1 minute to 2 hours with a mixer such as a V-type mixer or a ball mill. The mixture is molded by means of extrusion molding, cold isostatic pressing, hot molding or the like so as to have an arbitrary shape and size, and is fired at 600 ° C. to 1300 ° C. in a non-oxidizing atmosphere (primary firing) ) After the primary firing, firing (secondary firing) is performed at 1800 ° C. to 2200 ° C., preferably 1900 ° C. to 2100 ° C. in an inert gas atmosphere. Next, heat treatment is performed at 2400 ° C. to 2600 ° C. in a non-oxidizing atmosphere to further increase the degree of graphitization and to sublimate impurities to obtain a graphite material with increased purity. Thereby, hydrogen content can be 1000 ppm or less, and the conversion efficiency to a conductive diamond can further be improved.

  As described above, by firing at about 2000 ° C., boron, which is a component for imparting conductivity, is dispersed evenly while suppressing the volatilization wear of the boron component, and it is possible to perform machining and heat treatment. A boron-containing graphite material having improved important physical properties such as conductivity and thermal expansion coefficient can be obtained. The reason why the above important physical properties are improved is not clear, but by heating beyond the temperature limit for the stable presence of the boron component, liberation of the boron component, transition to the carbon moiety, diffusion, recombination, etc. This is considered to be because there is almost no loss of the boron component, it is very uniformly dispersed, and graphitization of the carbon portion has progressed due to high-temperature firing. In addition, due to such high-temperature firing, a boron-containing graphite material as if it was a pure graphite material is a solid body in which boron is uniformly dispersed throughout, or an aggregate of graphite crystals partially substituted by ceramic. It seems to have changed.

By processing in this way, the bulk density is 1.6 g / cm ³ or more, preferably 1.7 g / cm ³ or more, and a graphite material in which the boron component is uniformly dispersed is obtained. If the bulk density is less than 1.6 g / cm ³ , the conversion efficiency to diamond is deteriorated, which is not preferable. When the content of elements such as boron that contribute to conductivity is less than 0.1% by mass, sufficient conductivity cannot be imparted to diamond converted from graphite. Moreover, when it contains more than 15 mass%, boron carbide etc. will precipitate and it may be unpreferable on application.

  It is also possible to perform a purification treatment for the purpose of reducing the content of impurities such as hydrogen in the graphite material. Thereby, the yield of conductive diamond can be further improved. If impurities such as moisture, hydrogen, oxygen, etc., especially hydrogen, are contained even in a small amount in the graphite material, the conversion efficiency of the graphite material into diamond is extremely lowered. Therefore, the graphite material subjected to the graphitization treatment at the above-described high temperature is heat-treated at a pressure of 0.1 Pa or less, preferably 0.01 Pa or less, at a temperature of 1800 ° C. or more for 2 hours or more. By this treatment, impurities such as moisture, hydrogen and oxygen in the graphite material, particularly hydrogen, are further reduced, and the hydrogen content can be 1000 ppm or less, preferably 500 ppm or less, more preferably 50 ppm or less. The hydrogen content was measured with a carbon / hydrogen / water analyzer (RH-IE type (manufactured by LECO)).

  The boron-containing graphite material that has undergone the above treatment is converted to conductive diamond. The method for synthesizing diamond is preferably a high-pressure synthesis method. As for the conditions of high-pressure synthesis, the heating temperature is preferably 1300 to 1500 ° C, more preferably 1350 to 1450 ° C. The pressure is preferably in the range of 1-10 GPa, more preferably 3-7 GPa. The pressing time is preferably 1 minute to 1 hour. By this operation, conductive diamond containing 10 ppm or more of boron and 1 ppm or more of nitrogen, having an average particle diameter of 10 to 500 μm and a uniform particle diameter can be produced.

  Among these, conductive diamond particles having a particle diameter of 10 to 300 μm are used as the conductive fluid particles of the fluidized bed in the fluidized bed electrolytic treatment apparatus.

The present invention will be specifically described below based on examples.
(Example)
Each raw material was blended so that the boron carbide powder (average particle size 15 μm) was 15% by mass, the mesophase microspheres (average particle size 10 μm) 80% by mass, and the artificial graphite powder (average particle size 5 μm) 5% by mass. Then, dry mixing was performed for 1 hour, and then molded into 340 × 170 × 50 (mm) at a pressure of 80 MPa by a cold isostatic pressing method to obtain a molded body. This compact was packed in coke powder and heated to 1000 ° C. in a non-oxidizing gas atmosphere to obtain a primary fired product. This primary baked product was buried in coke powder in a resistance heating furnace, heat-treated at 2000 ° C. in a vacuum furnace, and further heat-treated at 2400 ° C. in an Acheson furnace to make the dispersibility of boron uniform. This graphite material has a bulk density of 1.65 g / cm ³ , a shore hardness of 12, a specific resistance of 9 μΩ · m, a bending strength of 60 MPa, an elastic modulus of 3 GPa, a boron content of 10% by mass, and a thermal expansion coefficient of 2 × 10 ⁻⁶ / ° C. The thermal conductivity was 40 W / (m · K), and the hydrogen content was 300 ppm.

  Next, the graphite material of the example was processed to φ9 × 2 (mm), and pressurized to 1400 ° C. and 5 GPa for 30 minutes using a belt-type ultra-high pressure device, and converted to diamond. The boron content in this diamond powder was measured by the Mantonil complexing neutralization titration method and the ICP issuance analysis method, and the nitrogen content was measured by the oxygen nitrogen analysis method. The boron content contained 15 ppm or more and nitrogen 2 ppm or more. Thus, conductive diamond particles having an average particle size of 20 μm and a particle size of 10 to 40 μm distributed in a uniform particle size were obtained. The electrical specific resistance was 19 mΩ · cm.

  The diamond granular material containing nitrogen and boron was used as a granular electrode and subjected to a treatment with a copper sulfate solution. After the treatment, copper was detected when the surface of the conductive diamond was observed with EPMA (X-ray microanalyzer). This shows that copper can be recovered from a copper sulfate solution using conductive diamond.

  The present invention can be changed in design without departing from the scope of the claims, and is not limited to the above-described embodiments and examples.

It is a schematic diagram of the fluidized bed electrolytic processing apparatus using the diamond granular material which concerns on this invention.

DESCRIPTION OF SYMBOLS 1 Direction in which electrolyte flows 2 Current collector 3 Conductive diamond granular material 4 Direction in which current flows 5 Counter electrode 6 Electrolyte

Claims (10)

A conductive diamond granular material for a fluidized bed used for electrolytic treatment of an electrolytic solution containing boron and nitrogen and having an average particle diameter of 1 μm to 1 mm. The conductive diamond granular material for fluidized beds used for the electrolytic treatment of the electrolytic solution according to claim 1, containing 10 ppm or more of boron and 1 ppm or more of nitrogen. 2. A graphite material obtained by converting a graphite material having a bulk density of 1.6 g / cm ³ or more and having boron uniformly dispersed in a nitrogen-containing atmosphere by a high-pressure synthesis method. A conductive diamond granular material for fluidized beds used for electrolytic treatment of the electrolytic solution according to 2. The conductive diamond granular material for fluidized beds used for electrolytic treatment of an electrolytic solution according to claim 3, wherein the graphite material has a hydrogen content of 1000 ppm or less. It is obtained by obtaining a boron-containing graphite material from a mixed raw material powder of boron-containing compound powder and carbonaceous powder in an inert gas atmosphere and then converting the boron-containing graphite material by a high-pressure synthesis method. The conductive diamond granular material for fluidized beds used for the electrolytic treatment of the electrolytic solution according to any one of claims 1 to 4. The average particle diameter of the boron-containing compound powder is 1 μm to 100 μm, and the conductive diamond granular material for fluidized bed used for electrolytic treatment of the electrolytic solution according to claim 5 . The conductive diamond granular material for fluidized beds according to claim 5 , wherein the boron-containing compound powder and the carbonaceous powder have the same average particle diameter. Wherein the electrolyte solution electrolysis the electrolyte or Ranaru the conductive fluid particles comprised of conductive diamond granules for fluidized bed which is contains multiple used as claimed in any one of claims 1-7 Fluidized bed for fluidized bed electrolytic treatment equipment. The electroconductive diamond granular material for fluidized beds used for the electrolytic treatment of the electrolyte solution of any one of Claims 1-7 used for the fluidized bed electrolytic treatment apparatus used for a process of industrial or household wastewater . The electroconductive diamond granular material for fluidized beds used for the electrolytic treatment of the electrolyte solution of any one of Claims 1-7 used for the fluidized bed electrolytic treatment apparatus used for the process of the solution containing copper .

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