JP2002020806A - Method for producing iron powder for removing contamination - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the optimum method in terms of production cost and contamination removing performance in a method in which a halogen-containing organic contaminant is brought into reaction with iron to reductively dehalogenate and detoxicate the same. SOLUTION: In ferrous powder metallurgy, ferrous waste such as iron powder obtainable by pulverizing a green compact below standards produced in compacting and iron powder leaked-out to the circumference of a die at the time of compacting which contain, by mass, 0.01 to 1.5% graphite and/or 0.01 to 4.0% nickel is subjected to heating treatment to produce the iron powder for removing contamination.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing iron powder for purifying pollution used for purifying groundwater and soil by halogen-containing organic pollutants.

[0002]

2. Description of the Related Art In recent years, groundwater and soil have been contaminated by organochlorine compounds such as trichloroethylene which have been used in large quantities as a degreasing solvent in semiconductor factories, metal processing factories, etc., and have been discharged and dumped after use. However, it has become a major social problem. Conventionally, as a method of solving these pollutions, there are a vacuum extraction method, a pumping aeration method, and the like, in which contaminated groundwater is extracted outside the soil and detoxified and treated, and the soil is contaminated. Thermal desorption and pyrolysis methods that excavate soil and make it harmless by heat treatment are known. Furthermore, microorganisms are used as a method to decompose and detoxify contaminants in groundwater or soil. A purification method using a bioremediation method is known.

[0003] However, methods such as a vacuum extraction method and a pumping aeration method use activated carbon or decomposition to remove or decompose pollutants after pumping and extracting groundwater or soil gas containing pollutants from the ground. In order to use the agent, high-cost separate treatment is required, such as installing equipment on the ground and detoxifying and embedding generated contaminants. In addition, the method of pyrolyzing excavated soil at a high temperature requires a large-scale facility for heat-treating the soil, and the soil particles themselves are deteriorated by heat, and for example, the function of the soil to inhabit living organisms is significantly impaired. Therefore, it is difficult to reuse the soil after treatment. Furthermore, the bioremediation method cannot be applied to all soils due to differences in soil characteristics, and even when applicable, the reaction is slow due to the action of microorganisms and requires a long treatment period.

In order to overcome the above-mentioned problems of the conventional countermeasures against pollution of groundwater and soil, various methods have been proposed in which halogen-containing organic contaminants are reacted with iron to reductively dehalogenate and detoxify them. And is gaining attention. For example, Japanese Unexamined Patent Publication No. Hei 5-501520 discloses that a groove is formed in a flow path of groundwater, and iron having a granular shape, a piece shape, a fibrous shape, or the like is filled and brought into contact with a halogen-containing organic pollutant. It describes a method of dehalogenating and detoxifying it. The iron used here does not need to be specially adjusted, and wastes generated in a metal cutting process and metal powders generated in an iron casting process are used. In addition, Tokuhyo Heihei 6-50
No. 6631, in principle, JP-A-5-50152
The method is similar to the method of Japanese Patent Publication No. 0, but uses a method in which activated carbon is mixed with metallic iron. These are all methods of purifying pollutants in groundwater flowing in a saturated zone.

On the other hand, Japanese Patent Application Laid-Open No. 11-235577 discloses a method of detoxifying an organic chlorine-based compound contained in an unsaturated zone soil having a groundwater level or higher or a soil after excavation by a reducing action with iron powder. Have been. The iron powder used in this method contains 0.1% or more of C and 0.05 m ² / g.
Having a specific surface area of at least 50%
It must have a particle size that passes through a sieve of μm, and sponge-like reduced iron ore powder is considered to be good.

[0006]

The above-mentioned methods of reacting a halogen-containing organic contaminant with iron to reductively dehalogenate and detoxify them are all particularly excellent in cost performance. And groundwater / soil pollution countermeasures. However, there is a problem that the iron material used in these methods is not necessarily optimized for the intended use. That is, iron used in the method disclosed in Japanese Patent Publication No. 5-501520 is waste generated in the metal cutting process and metal powder generated in the iron casting process. However, the reaction rate with halogen-containing organic contaminants is insufficient. In addition, the method disclosed in Japanese Patent Publication No. 6-506631 loses the merit that the cost of the iron material is low by mixing the iron material with expensive activated carbon. Furthermore, the iron powder used in the method of JP-A-11-235577 is sponge iron powder obtained by a usual ore reduction method, and is not optimized for dehalogenation of halogen-containing organic pollutants. From the point of view of the production cost of iron powder,
It is clearly inferior to the method using waste.
Therefore, in the method of reacting a halogen-containing organic contaminant with iron to reductively dehalogenate and render it harmless,
There is a need for an optimal method in terms of manufacturing cost and pollution remediation ability.

[0007]

Means for Solving the Problems The present inventor has conducted intensive studies to solve the above-mentioned problems, and completed the present invention. That is,
The present invention provides a method for producing iron powder for contamination purification, which comprises producing iron powder for contamination purification by heating iron-based waste generated in iron-based powder metallurgy.

[0008] The iron-based waste comprises non-standard green compacts generated in press molding, iron powder obtained by pulverizing the green compacts, and iron powder leaking around the mold during press molding. The present invention provides a method for producing any of the above-mentioned iron powder for purification of contamination, comprising at least one selected from the group consisting of:

The iron-based waste is graphite: 0.01-1.
5% by mass and / or nickel: 0.01 to 4.
The present invention provides a method for producing any of the above-mentioned iron powder for purification of contamination, which contains 0% by mass.

The heat treatment is performed in an inert gas atmosphere,
The present invention provides a method for producing the iron powder for purification of any of the above, which is performed at 00 to 900 ° C.

[0011] The present invention provides a method for producing any of the above-mentioned iron powders for purification, wherein the particle diameters of the iron powders for contamination purification are adjusted to 10 to 3000 µm by a sieve classification method.

Further, the present invention provides an iron powder for purification produced by any one of the above-mentioned methods for producing iron powder for purification.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, iron-based waste generated in iron-based powder metallurgy will be described. Iron-based powder metallurgy
This is a technique in which iron powder is mixed, the mixture is filled in a mold, and a green compact obtained by press molding is heated and sintered to produce a product. Here, many metal products manufactured by iron-based powder metallurgy generally require strict dimensional accuracy, and in the stage of press forming, non-standard products of about several percent in terms of dimensional accuracy are generated. Is inevitable at present.

Since such nonstandard products have not been heat-sintered yet, it is not so difficult to pulverize them back into iron powder having the same particle size as the original iron powder, but they are treated as industrial waste. It is usually done. The reason is that in iron-based powder metallurgy, iron powder of a single standard shipped from an iron powder manufacturer is not used as it is, but iron powder of various standards is mixed and used according to the application. Is to be. Iron powder production methods include an oxide reduction method, a water atomization method, a carbonyl method, and the like, and various properties such as shape, structure, apparent density, and compressibility of the same pure iron powder vary depending on the production method. In addition, in iron-based powder metallurgy, various components such as pure iron powder with graphite added, nickel, copper, molybdenum and the like diffused and adhered to the iron powder surface are mixed and used. There are various ways of mixing. Further, as the iron powder, not only pure iron powder but also alloy powder is used. Therefore, non-standard products generated in the press molding of iron-based powder metallurgy, even if iron powder is recovered therefrom, such as by separating various iron powder, again,
It is practically impossible to use it for iron-based powder metallurgy applications. Therefore, it is treated as industrial waste.

[0015] Further, iron powder that has leaked out around the mold during press molding of iron-based powder metallurgy is also treated as industrial waste for the same reason as described above.

In view of the above-mentioned situation, the present inventor has found that iron-based waste generated in iron-based powder metallurgy has no useful use and can be obtained at low cost, and contains graphite and nickel. Focus on the fact that various types of iron-based waste are contained, and that non-standard green compacts generated during press molding can be easily returned to iron powder by grinding. As a result of diligent research on the use of iron, even if the iron-based waste is used for purification as it is, the pollution-purifying effect is hardly exhibited, but the heat-treated iron-based waste exhibits an excellent effect. The present inventors have found that iron powder for pollution purification can be obtained, and have completed the present invention.

Hereinafter, the method for producing the iron powder for purification of contamination of the present invention will be described in detail. In the method for producing iron powder for purification of contamination of the present invention, iron-based waste generated in iron-based powder metallurgy is used as a raw material. As iron-based waste,
At least one selected from the group consisting of non-standard green compacts generated in press molding as described above, iron powder obtained by pulverizing the green compact, and iron powder leaked around the mold during press molding. Preferably, it contains a species. These usually contain about 0.5 to 1.5% by mass of graphite and also partially contain nickel, so that the content of graphite and nickel in the iron-based waste described later is easily adjusted to a preferable range, and thus it is preferable. The green compact used in the present invention can be a non-standard green compact after press molding as it is,
It is preferable to use iron powder obtained by grinding. This is because by pulverization, as described later, it is easy to mix and use with other types of iron powder and the like. The pulverization of the green compact can be easily performed by a normal iron powder manufacturer without investing in new equipment. For this reason, waste generated in the metal cutting process and low-cost iron powder almost equivalent to a method using metal powder that appears in the iron casting process can be obtained. Iron powder is suitably used in the present invention.

The particle size (particle size before heat treatment) of the iron powder obtained by pulverizing the green compact and the iron powder leaking around the mold at the time of press molding has a particle size of 10 to 1000 by a sieve classification method.
μm, more preferably 100 to 300 μm. If the particle size of the iron powder is less than 10 μm, it may be difficult to handle in the subsequent steps.
If it exceeds 00 μm, the uniformity with graphite and alloy components in the subsequent mixing step may be impaired. Particle size adjustment
The classification can be performed by sieving or the like.

The iron-based waste used in the present invention preferably contains graphite and / or nickel, and more preferably has these on the surface. When graphite is present on the surface of iron-based waste, it absorbs halogen-containing organic pollutants and acts as a cathode reaction site,
A reductive dehalogenation reaction can be promoted. Further, when nickel is present on the surface of the iron-based waste, nickel functions as a hydrogen generation catalyst, and the reduction reaction by hydrogen generated on the nickel surface is promoted. Due to the combined effect of these actions, the reaction rate of the dehalogenation reaction of iron-based waste having graphite and nickel on the surface is improved as compared with pure iron-based waste.

The graphite content in the iron-based waste is 0.1%.
It is preferably from 0.1 to 1.5% by mass, and from 0.1 to 1.
More preferably, it is 0% by mass. Graphite content is 0.0
If it is less than 1% by mass, the reaction rate constant may not be the same as that of an iron-based waste without graphite, and if it exceeds 1.5% by mass, the effect may be saturated. The content of nickel in the iron-based waste is preferably 0.01 to 4.0% by mass, and more preferably 0.1 to 1.0% by mass. If the nickel content is less than 0.01% by mass, the reaction rate constant may not be the same as that of an iron-based waste without nickel, and if it exceeds 4.0% by mass, the effect may be saturated. . In addition, since the nickel content of the current ordinary partially alloyed iron powder for powder metallurgy is a maximum of 4 to 5% by mass, there is no need to separately add nickel, so that the cost performance is excellent.

In order to set the content of graphite and nickel in the iron-based waste within the above-mentioned preferred range, an iron-based waste satisfying the above-mentioned preferred range may be used alone, or various iron-based wastes may be mixed. You may use it. As described above, non-standard green compacts generated in press molding, iron powder obtained by pulverizing the green compact, and iron powder leaking around the mold during press molding are usually 0.5 to 0.5. Since it contains about 1.5% by mass of graphite and partly contains nickel, these single types may be used alone as iron-based waste in the above range, or a mixture of two or more types may be used. The above range may be adopted, or the above range may be mixed with iron-based waste generated other than iron-based powder metallurgy, for example, leakage powder or dust collection powder in an iron powder production process of an iron powder factory.

The iron-based waste may contain components (eg, Cu) other than graphite and nickel, but has a remarkable effect on the purpose of reductively dehalogenating organic chlorine compounds and the like. Is not recognized, so its content is not particularly limited.

As described above, the method of the present invention for producing iron powder for purifying contamination uses iron-based waste generated in iron-based powder metallurgy as a raw material. There is a feature of the present invention in producing the iron powder for purification. The surface of iron powder used in iron-based powder metallurgy is coated with various organic binders to prevent segregation. Therefore, iron-based waste generated in iron-based powder metallurgy contains various organic binders. For this reason, even if the iron-based waste generated in iron-based powder metallurgy is used as it is for purification of pollution,
Since it contains an organic binder, it has low reactivity and cannot be used. Therefore, in the present invention, the iron-based waste is subjected to heat treatment to thermally decompose or volatilize and remove the organic binder component, thereby obtaining highly reactive iron powder for contamination purification.

The heat treatment is preferably performed in an inert gas atmosphere such as a nitrogen atmosphere. When the heat treatment is performed in the air, the surface of the iron-based waste is oxidized, so that the reactivity in the purification of the pollution is reduced. However, the reactivity is high in an inert gas atmosphere. The temperature of the heat treatment is 300 ~
It is preferably 900 ° C, more preferably 400 to 600 ° C. If the temperature is lower than 300 ° C., it may be difficult to sufficiently remove the binder, and 900
When the temperature exceeds ℃, graphite and nickel are rapidly diffused into the iron powder, and these effects may be reduced. The time of the heat treatment is preferably 30 minutes to 4 hours.

In the present invention, the iron-based waste agglomerated by the heat treatment is pulverized to obtain iron powder for purification of contamination, but it is preferable to further adjust the particle size. By adjusting the particle size to an appropriate value, it is possible to obtain an iron powder for purification that is optimal for dehalogenation of halogen-containing organic contaminants. The particle size can be adjusted by sieving or the like.

Particle size of iron powder for purification (particle size after heat treatment)
Generally has a particle size of 10 to 3000 μm by a sieve classification method.
m is preferred, but a more preferred particle size depends on the application. When used for groundwater purification, the particle size according to the sieve classification method is preferably from 200 to 3000 µm, more preferably from 300 to 1000 µm.
In the case of groundwater purification, since iron powder for pollution purification is arranged in the flow path of groundwater, if the particle size is too small, clogging occurs and there is a risk that the flow of groundwater is obstructed.
When the particle size is large, the specific surface area of the iron powder for purification becomes small, and the effect of reductive dehalogenation is reduced. When used for soil purification, the particle size by the sieve classification method is 10
It is preferably 400 μm, more preferably 50 to 200 μm. If the particle size is small, handling as a powder may be difficult, and if the particle size is large,
In some cases, uniform mixing with soil may be difficult, and the specific surface area of the iron powder for purifying pollution may be reduced, thereby reducing the effect of reductive dehalogenation.

The use of the iron powder for purification of pollution produced according to the present invention is not particularly limited, but is preferably used and useful for purification of groundwater and soil. In particular, it is preferably used for contamination with an organic chlorine compound such as trichloroethylene, and also suitably used for contamination with heavy metals such as hexavalent chromium. Moreover, the present invention is extremely useful also from the viewpoint of effective utilization of iron-based waste generated in iron-based powder metallurgy which is currently only treated as industrial waste.

[0028]

The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. 1. Production of Iron Powder for Pollution Purification (1) Raw Material Raw Material 1: Anti-segregation powder containing 1.5 mass% of graphite (K
IP 310A clean mix powder, manufactured by Kawasaki Steel Corporation, iron powder component: Fe-0.15% by mass Mn-0.005% by mass
S-0.12% by mass O-0.007% by mass Cu) was press-molded at a molding pressure of 5 t / cm ² and then pulverized. Material 2: Partially alloyed powder having Ni on the surface (KIP)
Sigma-alloy powder, manufactured by Kawasaki Steel Corporation, alloy component: Fe-4 mass% Ni-0.5 mass% Mo-1.5 mass% Cu) is press-molded at a molding pressure of 5 t / cm ² and then pulverized.

(2) Production The above raw materials 1 and 2 were mixed at the mass ratio shown in Table 1.
The particle size after mixing (particle size before heat treatment) and the contents of graphite and nickel are as shown in Table 1. Next, it was treated at a heating temperature shown in Table 1 for 1 hour in a nitrogen atmosphere, and then pulverized to obtain a contamination-purifying iron powder. The particle size after the heat treatment is as shown in Table 1.

2. Evaluation of Iron Powder for Pollution Purification In a glass vial having a capacity of 100 mL, an electrolyte solution (CaCO ₃ concentration: 40 mg /
L, Na ₂ SO ₃ concentration: 80 mg / L) 50 mL, 10 g of iron powder for purification of contamination and trichloroethylene (TCE)
A standard solution was enclosed. The amount of the TCE standard solution was adjusted so that the initial concentration of TCE was 5 mg / L. Next, this glass vial was set on a shaker installed in a constant temperature room at 23 ° C. ± 1 ° C., and shaken at 200 rpm.
The TCE concentration was measured every 10, 24, and 48 hours using a detector tube. In addition, ten sample bottles were prepared, and the TEC concentration was measured at n = 2 every time. From this result, TC
The reaction rate constant for the E concentration decrease was calculated. As comparative examples, ordinary sponge iron powder (TKH80, manufactured by Kawasaki Steel Corporation),
Using sea-surface iron powder mixed with activated carbon (manufactured by Takeda Pharmaceutical Co., Ltd.) and cast iron powder (first-class reagent, manufactured by Kanto Kagaku Co., Ltd.), T
The reaction rate constant for the decrease in CE concentration was calculated.

The reaction rate constant for decreasing the TCE concentration was calculated as follows. TCE concentrations decreased exponentially over time. In general, when an organic chlorine compound is reductively dechlorinated and decomposed in a reaction with iron powder,
Since the concentration of organochlorine compounds decreases exponentially,
It is generally believed that the reaction rate follows a pseudo-linear equation for the concentration of the reactants in the aqueous solution as shown in the following equation (1). dC _t / dt = −k (obsd) · C _t (1) where C _t : concentration of the reactant at time t, k (o
bsd): Apparent reaction rate constant.

Therefore, the TCE concentration C _t after a certain time has elapsed
Plotting the logarithm of the ratio to the longitudinal axis of the initial concentration C _i,
From the slope of the straight line, the apparent reaction rate constant k (obsd)
I asked. In general, when discussing the reductive dechlorination reaction rate of an organochlorine compound, an apparent reaction rate constant k (ob
sd) is evaluated by a value k (sa) normalized by dividing by the total surface area per unit volume of the solution of the iron powder used in the experiment (for example, Johnson-TL, Schema)
r-MM, and Trannyek-PG; Kine
tics of Halogenated Organ
ic Compound Degradation b
y Iron Metal, Environ. Sci.
Technol. (1996), 30, 2634-26.
40), k (sa) was determined from k (obssd). k
The larger the value of (sa), the higher the reaction rate of the reductive dechlorination reaction of the organic chlorine compound.

The results are shown in Table 1. It can be seen that the iron powder for purification of pollution produced according to the present invention has a larger reaction rate constant than the comparative example. That is, the iron powder for purification of pollution produced according to the present invention has an excellent ability to reductively dechlorinate organic chlorine compounds.

[0034]

[Table 1]

[0035]

The method for producing iron powder for purification of pollution according to the present invention comprises:
A method of reacting halogen-containing organic contaminants with iron to reductively dehalogenate and detoxify it, which is optimal in terms of production cost and pollution purification ability, and iron-based waste generated in iron-based powder metallurgy This method is extremely useful because it is a method that effectively utilizes Moreover, the iron powder for purification of pollution produced by the present invention is suitably used for the purification of groundwater and soil. In particular, it is excellent in the ability to purify pollutants containing halogen-containing organic contaminants such as trichloroethylene, and thus is extremely useful for purifying groundwater and soil contaminated with halogen-containing organic pollutants.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Akio Sonobe 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba F-term inside the Chiba Works, Chiba Works 4D004 AA50 AB05 AC04 BA10 CA04 CA22 DA03 DA06 4G069 AA02 AA08 AA09 BA08A BA08B BB02A BB02B BB02C BC59B BC59C BC66A BC66B BC66C BC68A BC68B BC68C CA05 CA19 DA05 EA02Y EB18Y FA01 FB30 FC02 4K017 AA04 BA06 BB06 BB18 DA09 EK08

Claims (3)

[Claims] 1. A method for producing iron powder for purification, characterized by producing iron powder for purification by heat treatment of iron-based waste generated in iron-based powder metallurgy. 2. The method according to claim 1, wherein the iron-based waste is a non-standard green compact generated in press molding, an iron powder obtained by pulverizing the green compact, and an iron powder leaking around a mold during press molding. The method for producing iron powder for purification according to claim 1, wherein the method further comprises at least one selected from the group consisting of: 3. The iron-based waste is graphite: 0.01-1.
5% by mass and / or nickel: 0.01 to 4.
3. The composition according to claim 1, which contains 0% by mass.
3. The method for producing iron powder for purification of pollution according to item 1.