JP3848627B2 - Method for producing soil repair agent - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention produces a contaminated soil repairing agent composed of particles containing fine metallic iron and ferrous oxide, which is used to detoxify and repair soil contaminated with organic halides, hexavalent chromium and the like. Regarding the method.
[0002]
[Prior art]
In the past, organic halogen compounds such as trichlorethylene have been used for cleaning machinery and semiconductors. Since these organic halogen compounds are carcinogenic, they are recognized as harmful substances. In recent years, their use has been suppressed and emission management has become strict. However, contaminated soil due to past use of organohalogen compounds remains, which is an environmental problem. Moreover, it may be contaminated with hexavalent chromium due to the drainage of the plating factory.
[0003]
Known methods for purifying soil contaminated with volatile organic compounds such as organic halides include a soil gas suction method, a groundwater pumping method, and a soil excavation method. The soil gas suction method forcibly sucks the target substances present in the unsaturated zone. A suction well is installed in the ground by boring, and the inside of the suction well is depressurized by a vacuum pump, and the vaporized organic The compounds are collected in a suction well, guided to the underground, and treated by a method such as adsorption of organic compounds in soil gas onto activated carbon. When the contamination by the organic compound extends to the aquifer, a method is adopted in which a submersible pump is installed in the suction well and the water is pumped up simultaneously with the soil gas. The underground pumping method is a method of setting up a pumping well in soil and pumping up contaminated groundwater. Furthermore, the soil excavation method is a method in which contaminated soil is excavated, and the excavated soil is subjected to wind drying and heat treatment to remove and collect organic compounds.
[0004]
As a method of purifying contaminated water such as collected water or ground water as described above, for example, in Japanese Patent No. 2636171, after removing dissolved oxygen in contaminated water, the contaminated water is applied to a metal surface such as iron. A method for reducing and removing organic halide contained in contaminated water by contacting is disclosed. Such a method for purifying contaminated water using the reducing action of iron is also described in JP-A-3-106496, JP-A-10-263522, and the like. In any of these methods, the contaminated water is treated by passing it through a certain portion such as a layer containing iron or a filter.
However, these methods are not methods for directly purifying soil, but methods for purifying contaminated water collected by the soil gas suction method, groundwater pumping method, etc., or contaminated water such as rivers and groundwater. The amount of processed material is extremely large, and the processing often takes a long time. It is also a drawback that the processing steps are often complicated. For this reason, a method for directly and simply purifying soil that is a source of contamination is required. In addition, for soil contaminated with hexavalent chromium, a method of purifying with a reducing agent such as ferrous sulfate is known, but when it exists in the form of trivalent and hexavalent chromium as in the case of chromium ore, Since ferrous sulfate has a short time to exhibit a reducing action, it cannot be sufficiently reduced.
[0005]
Therefore, a purifying agent that exhibits a reducing action over a long period of time has been invented, and a method that utilizes a reaction between metallic iron and ferrous oxide has been invented. For example, in the technique described in Japanese Patent Application Laid-Open No. 2001-198567, a technique using a soil restoration agent obtained by slurrying fine iron powder is shown. This method is an excellent method capable of repairing the soil by directly injecting a fine iron powder slurry into the ground. In addition, a method has been proposed in which fine dust containing a large amount of metallic iron generated from a steelmaking converter (hereinafter referred to as converter dust) is used as the fine iron powder. This method is highly economical because it uses fine converter dust generated during stagnation.
[0006]
[Problems to be solved by the invention]
As described above, in the method of using converter dust as a soil restoration agent, not only when used as a slurry in the method disclosed in 2001-198567, but also mixed with soil in a low moisture state. There is also a demand for dried converter dust. However, because converter dust is easily oxidized, there is a problem that it cannot be a good soil remedial agent unless proper recovery and drying methods are implemented.
In the prior art such as the method disclosed in Japanese Patent Application Laid-Open No. 2001-198567, the converter dust is simply collected by a general converter dust collector and used as a slurry. In this method, since the oxidation rate of the converter dust is low due to the presence of water, the problem of the oxidation of the converter dust is small. However, in the treatment and storage of dried converter dust, soil remediators for converter dust are generally used because of the lack of appropriate methods despite the importance of oxidation prevention. There wasn't.
[0007]
In other words, in the prior art, when the converter dust is recovered, dried, and stored, if an inappropriate treatment is performed, metallic iron and ferrous oxide in the converter dust are oxidized to ferric oxide. The problem was not solved. Thus, when metallic iron or the like of converter dust has been oxidized, it loses the function of reacting with organic halides and hexavalent chromium, and is suitable for adding converter dust to the soil. Even when no measures were taken, there was a problem that the converter dust under construction was oxidized.
As described above, the converter dust has a problem that the performance is deteriorated by oxidation, and it is difficult to use the low-moisture converter dust as a soil repair agent. The method according to the prior art has the above-mentioned various problems when producing and storing a low moisture soil remediation agent produced from converter dust. Therefore, a new technique for solving these problems has been demanded.
[0008]
[Means for Solving the Problems]
The present invention has been made in order to solve the problems of the prior art as described above, and the gist thereof is as shown in the following (1) to (4).
(1) When the converter gas generated from the steelmaking converter 1 is processed by the non-combustion converter gas recovery device 2, the converter dust obtained by collecting the converter gas with the wet dust collector 3 and water having a dissolved oxygen concentration of 4 ppm or less The dehydrated product is dehydrated with a dehydrator 14 to produce a dehydrated product, and the dehydrated product is heated to a temperature of 350 ° C. or lower in the fine dust dryer 16 and oxygen in an atmosphere that is an index for evaluating the progress of iron oxidation A method for producing a soil repairing agent, comprising drying the dehydrated product under the condition that the product of the concentration and the drying time is 200 minutes / volume% or less.
(2) A mixture of converter dust and water obtained by applying a mixture of converter dust and water having a dissolved oxygen concentration of 4 ppm or less to the wet classifier 5 and having an average particle diameter of about 0.3 to 5 microns and water. (1), characterized in that dehydration is performed by dehydrating to produce a dehydrated product having a water content of approximately 30% by mass or less, and drying the dehydrated product in an atmosphere of fine dust dryer 16 at 10% by volume or less The manufacturing method of the soil restoration agent of description.
(3) Soil characterized in that the converter dust dried by any of the methods described in (1) or (2) above is filled in a container having an oxygen concentration of 10% by volume or less and blocked from outside air. A method for producing a restoration agent.
(4) Dehydration of a mixture of converter dust and water of coarse particles having an average particle size of about 50 to 200 microns obtained by applying a mixture of converter dust and water having a dissolved oxygen concentration of 4 ppm or less to the wet classifier 5 The dehydrated product thus obtained is dried inside the coarse dust dryer 15 at a temperature of 350 ° C. or less and under the condition that the product of the oxygen concentration in the atmosphere and the drying time is 800 minutes / volume% or less. A method for producing a soil repairing agent.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
An example of the configuration of an apparatus for collecting and drying converter dust is shown in FIG. 1 includes a steelmaking converter 1, a non-combustion gas recovery device 2, a wet dust collector 3, a slurry recovery trough 4, a wet classification device 5, a precipitation tank 6, an over water circulation pipe 7, a concentrated slurry pump 8, Concentrated slurry pipe 9, concentrated slurry tank 10, stirring device 11, concentrated slurry recovery pump 12, concentrated slurry recovery pipe 13, dehydrator 14, coarse dust dryer 15, and fine dust dryer 16 .
In the steelmaking converter 1, oxygen is blown to the molten iron to remove carbon and the like in the molten iron. The converter gas mainly composed of carbon monoxide generated at this time is recovered by the non-combustion gas recovery device 2 without being burned. This converter gas contains converter dust containing metallic iron. This converter dust is a coarse particle formed when oxygen is blown to the molten iron, the iron evaporates at the fire point, and becomes fine particles when it is cooled and blown off by the oxygen jet There is dust. The fine dust has an average particle diameter of 0.3 to 5 microns and contains a large amount of metallic iron at the time of generation. The coarse dust has an average particle size of 50 to 250 microns and contains a large amount of metallic iron at the time of generation.
[0010]
The converter dust is separated from the converter gas by the wet dust collector 3. In the wet dust collector 3, the dust is separated from the gas by sprinkling water at the throat portion. The dust collected from the sprayed water contains converter dust at a concentration of several mass% and is recovered as a slurry.
The slurry containing the converter dust thus obtained is sent to the coarse particle separator 5 via the slurry collection trough 4, where coarse dust having an average particle size of about 50 to 250 microns and an average particle size of 0.3. Separating fine dust of about -5 microns into a slurry with a lot of coarse dust and a slurry with a lot of fine dust. However, depending on the application of soil restoration, it is not necessary to separate the coarse and fine particles. In that case, the coarse-grain separator 5 is bypassed.
Thereafter, a slurry containing fine dust is precipitated in the settling tank 6 to produce a slurry in which fine dust is concentrated. Here, the sedimentation tank 6 has a structure for sedimenting particles, and generally a circular thickener is used. The supernatant water generated when the fine dust is precipitated in the settling tank 6 is reused as dust collecting water in the over water circulation pipe 7.
When the coarse particle dust is separated by the wet classifier coarse 5 and the soil restoration agent is produced using this as a raw material, when the coarse particle slurry needs to be concentrated, Allow the grain dust to settle.
[0011]
The converter dust slurry concentrated in the settling tank 6 is transferred to the concentrated slurry tank 10 via the concentrated slurry pipe 9 by the power of the concentrated slurry pump 8. The concentrated slurry tank 10 is preferably a cylindrical tank, and since iron powder particles hit the inner surface, the one made of steel, stainless steel, or concrete is preferable. In the concentrated slurry tank 10, the concentrated slurry is stirred by the stirring device 11 so that the fine dust does not settle and solidify at the bottom. The concentrated slurry having a predetermined powder concentration is recovered via the concentrated slurry recovery pipe 13 using the power of the concentrated slurry recovery pump 12. The concentrated slurry recovery pipe 13 is preferably a steel circular pipe.
The recovered slurry is dehydrated by the dehydrator 14 so that the water content is about 30% by mass or less. The dehydrated product produced here is transferred to the fine dust dryer 16 where the moisture is dried to about 5% by mass or less. The type of the fine dust dryer 16 has a feed blade inside, and the type such as a rotary type drying device that dries the converter dust while stirring it is the best, but other types may also be used. It is necessary to have a mechanism that can control the oxygen concentration in the apparatus during drying. Place the dried fine dust in a closed container.
[0012]
The coarse dust separated by the wet classifier 5 is drained and then sent to the coarse dust dryer 15 where it is dried. The type of the coarse dust dryer 15 may be a type such as a rotary dryer, but may be another type. It is desirable to have a mechanism that can control the oxygen concentration in the apparatus during drying. The dried coarse dust is also placed in a closed container.
In the above process, converter dust is collected and dried to produce a soil restoration agent. To produce a high-performance soil restoration agent, it is necessary to suppress oxidation of the converter dust. is important. In order for converter dust to function as a soil restoration agent, it is important that metal iron and ferrous oxide react effectively on the surface of the soil restoration agent particles in the earth and sand. In our experiments, although there is a slight difference depending on the soil repair conditions, it is roughly that the total ratio of metallic iron and ferrous oxide (including ferrous hydroxide) is 40% by mass or more. It was clarified that the conditions of the soil repairing agent were good in the present invention, and in the present invention, the conditions for producing a soil repairing agent satisfying this condition were clarified.
[0013]
First, oxidation in converter dust is prevented by operation which collects converter dust. In the experiments by the present inventors, it was found that the oxidation rate is low in slurry water having a low oxygen concentration of 4 ppm or less. In order to minimize the oxidation of converter dust, a dissolved oxygen concentration of 3 ppm or less is desirable. As a method for reducing the dissolved oxygen concentration, there are a method using an oxygen removing agent such as hydrazine and a method of heating water to 50 ° C. or more to drive out dissolved oxygen.
Next, in the dehydration process, the converter dust is secured to some extent to prevent the converter dust from directly contacting the air. This is because if the moisture is reduced too much, the converter dust comes into direct contact with air and the converter dust is oxidized. Therefore, in the case of converter dust or fine dust from which coarse particles are not separated, the water content is set to about 17 to 30% by mass. In the case of moisture of about 30% by mass or more, it is better to avoid converter dust because it becomes sludge and it takes time to process after dehydration. In the case of coarse dust, the water content is preferably about 5 to 15% by mass.
[0014]
In the drying process after dehydration, the drying temperature, drying time, and oxygen concentration of the atmosphere in the drying apparatus are set to an appropriate range. When the temperature during drying is 350 ° C. or higher, the oxidation rate becomes excessive, so the drying temperature is preferably 350 ° C. or lower. Further, the present inventors have found that the oxidation rate of iron is proportional to the oxygen concentration of the atmosphere and the drying time. For this reason, in the fine dust dryer 16 and the coarse dust dryer 15, the product of the drying time and the oxygen concentration of the atmosphere is made smaller than a predetermined value.
Since there are many fine dust particles with a particle size of around 1 micron, the product of the oxygen concentration in the drying device atmosphere in the fine dust dryer 16 and the drying time is 200 minutes / volume% or less. However, the fine dust is oxidized Therefore, it is necessary to finish the drying within 10 minutes at an oxygen concentration of air, and it may be difficult to make this condition. Therefore, it is desirable that the oxygen concentration is 10% by volume or less. Dry in the atmosphere. In the case of coarse dust having a particle size of around 100 microns and a relatively slow oxidation reaction, the product of the oxygen concentration in the drying apparatus atmosphere and the drying time in the coarse dust dryer 15 is 800 minutes / volume% or less. And Under the above conditions, the converter dust dried after being recovered is in a state of little oxidation.
The dried converter dust produced by the above method is packed in a container. Dry converter dust is easily oxidized. In particular, in order to store fine dust, the oxygen concentration in the container is preferably 10% by volume or less. This converter dust in the container is transported to the soil repair site where it is mixed with earth and sand. After construction, the soil repairing agent of the present invention reacts with harmful substances in the soil and renders them harmless.
[0015]
【Example】
The manufacture result of the soil restoration agent performed using the method of this invention is shown. The converter dust generated from the 230-ton converter was collected, dehydrated and dried by the apparatus shown in FIG. The dehydrator 14 was a filter press type device, and the coarse particle dust drying device 15 and the fine particle dust drying device 16 were rotary type drying devices having feed blades.
Example 1
In this embodiment, coarse dust and fine dust are an example of treatment using mixed converter dust as a soil repair agent. Since the coarse dust and fine dust were not separated, the coarse separator 5 was bypassed and the slurry was concentrated in the settling tank 6. The oxygen concentration of the slurry water was 3.4 ppm. From the concentrated slurry tank 10, a slurry having a converter dust concentration of 25 mass% was sent to the dehydrator 14. In the dehydrator 14, a dehydrated cake having a moisture content of 23% by mass was produced and sent to the fine dust drying device 16. The drying conditions of the fine dust drying device 16 were an atmospheric temperature of 310 ° C., an internal oxygen concentration of 8% by volume, and a drying time of 22 minutes. The product of drying time and oxygen concentration in this treatment was 176 minutes and volume%, and was within the scope of the present invention. This converter dust was stored in an airtight container having an oxygen concentration of 5% by volume.
As a result of the treatment of Example 1, a soil restoration agent for converter dust having an average particle size of 12 microns, metallic iron of 24% by mass and ferrous oxide of 37% by mass and moisture of 2% by mass can be produced. It was. The soil remediation agent was examined by a trichlorethylene removal reaction test. 73% of trichlorethylene was able to be decomposed | disassembled by reaction for 5 days on the conditions of the mixing | blending of 15 gram with respect to 1 liter of soil. In this test, a removal rate of 60% or more is acceptable.
[0016]
(Example 2)
This example is an example of treatment using fine dust as a soil repair agent. The oxygen concentration of the slurry water was 2.3 ppm. From the concentrated slurry tank 10, a slurry having a converter dust concentration of 22 mass% was sent to the dehydrator 14. In the dehydrator 14, a dehydrated cake having a water content of 26% by mass was produced and sent to the fine dust drying device 16. The drying conditions of the fine dust drying device 16 were an atmospheric temperature of 200 ° C., an internal oxygen concentration of 5% by volume, and a drying time of 20 minutes. The product of drying time and oxygen concentration in this treatment was 100 minutes and volume%, and was within the scope of the present invention. The converter dust was stored in an airtight container having an oxygen concentration of 3% by volume.
As a result of the treatment of Example 2, a soil restoration agent for converter dust having an average particle size of 2.2 microns, 19% by mass of metallic iron and 39% by mass of ferrous oxide and 5% by mass of water is produced. I was able to. The soil remediation agent was examined by a trichlorethylene removal reaction test. Under the condition of blending 15 grams per liter of soil, 81% of trichlorethylene could be decomposed by reaction for 5 days.
[0017]
Example 3
This example is an example of treatment using coarse dust as a soil repair agent. Coarse-grain dust was separated and recovered from the coarse-grain separator 5 and drained to obtain coarse-grain dust having a moisture content of 11% by mass. This was sent to the coarse dust drying device 15. The oxygen concentration of the slurry water was 2.5 ppm. The drying conditions of the coarse dust dryer 15 were an atmospheric temperature of 300 ° C., an internal oxygen concentration of 16% by volume, and a drying time of 30 minutes. The product of drying time and oxygen concentration in this treatment was 480 minutes and volume%, and was within the scope of the present invention. This converter dust was stored in an airtight container having an oxygen concentration of 8% by volume.
As a result of the treatment of Example 3, a soil restoration agent for converter dust having an average particle size of 81 microns, 45% by mass of metallic iron and 22% by mass of ferrous oxide and 1% by mass of water can be produced. It was. The soil remediation agent was examined by a trichlorethylene removal reaction test. Under the condition of blending 15 grams per liter of soil, 66% of trichlorethylene could be decomposed after 100 days of reaction. In this test, the long-term reactant performance of coarse dust was measured.
[0018]
(Comparative Example 1)
In this comparative example, the processing is performed using fine dust as a soil repairing agent, but this is an example outside the conditions of the present invention. The oxygen concentration of the slurry water was 3.5 ppm as in Example 2. From the concentrated slurry tank 10, a slurry having a converter dust concentration of 23 mass% was sent to the dehydrator 14. In the dehydrator 14, a dehydrated cake having a water content of 24% by mass was produced and sent to the fine dust drying device 16. The drying conditions of the fine dust drying device 16 were an atmospheric temperature of 230 ° C., an internal oxygen concentration of 12% by volume, and a drying time of 20 minutes. The product of drying time and oxygen concentration in this treatment was 240 minutes and volume%, which was outside the scope of the present invention.
As a result of the treatment of Comparative Example 1, a soil repair agent for converter dust having an average particle size of 1.7 microns, 10% by mass of metallic iron and 28% by mass of ferrous oxide and 3% by mass of water is manufactured. I was able to. This soil restoration agent was subjected to a trichlorethylene removal reaction test under the condition of 15 grams per liter of soil. Only 41% of trichlorethylene was decomposed in the reaction for 5 days. Thus, the activity of the converter dust treated outside the conditions of the present invention was low.
[0019]
(Comparative Example 2)
This comparative example is an example of treatment in which fine dust was treated with a soil repairing agent, but the oxygen concentration of slurry water was high. The oxygen concentration of the slurry water was 5.4 ppm. From the concentrated slurry tank 10, a slurry having a converter dust concentration of 20 mass% was sent to the dehydrator 14. In the dehydrator 14, a dehydrated cake having a moisture content of 29% by mass was produced and sent to the fine dust drying device 16. The drying conditions of the fine dust drying device 16 were an atmospheric temperature of 250 ° C., an internal oxygen concentration of 8% by volume, and a drying time of 20 minutes. The product of drying time and oxygen concentration in this treatment was 160 minutes and volume%, which was within the scope of the present invention.
As a result of the treatment in Comparative Example 2, it was possible to produce a soil repair agent for converter dust having an average particle diameter of 2.1 microns, metal iron of 9% by mass and ferrous oxide of 27% by mass. The soil remediation agent was examined by a trichlorethylene removal reaction test. Only 38% trichlorethylene could be decomposed in the reaction for 5 days under the condition of blending 15 grams per liter of soil. Even in this treatment, the activity of the converter dust was low.
[0020]
【The invention's effect】
In the method of the present invention, since converter dust is used as a restoration material, an inexpensive soil restoration agent can be produced as compared with an iron particle production method such as an atomization method. In addition, since the degree of oxidation of particles containing iron can be controlled, it is possible to manufacture a high-quality soil restoration agent having a stable reaction activity, so that the construction becomes easy and the overall construction cost is reduced. Furthermore, since a large amount of soil restoration agent can be produced once, supply of the soil restoration agent to a large-scale construction is also possible.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram of an apparatus for producing a dry soil repair agent consisting of powders containing a large amount of iron from converter dust for carrying out the method of the present invention.
[Explanation of symbols]
1 ... Steelmaking converter,
2 ... Non-combustion gas recovery device,
3 ... wet dust collector,
4 ... Slurry recovery trough,
5 ... Coarse grain separator,
6 ... sedimentation tank,
7 ... Over water circulation piping,
8 ... Concentrated slurry pump,
9 ... Concentrated slurry piping,
10 ... Concentrated slurry tank,
11: Stirring device,
12 ... concentrated slurry recovery pump,
13 ... Concentrated slurry recovery piping,
14 ... dehydrator,
15 ... Coarse-grain dust drying device,
16 ... Fine dust drying device

Claims (4)

When the converter gas generated from a steelmaking converter is processed by a non-combustion converter gas recovery device, a mixture of converter dust and water having a dissolved oxygen concentration of 4 ppm or less recovered by a wet dust collector is dehydrated. Soil remediation characterized by producing a dehydrated product and drying the dehydrated product at a temperature of 350 ° C. or lower and a product of the oxygen concentration in the drying apparatus atmosphere and the drying time of 200 minutes / volume% or less. Manufacturing method. A mixture of the converter dust and water having a dissolved oxygen concentration of 4 ppm or less was applied to a wet classifier to dehydrate the finely divided converter dust and water to produce a dehydrated product having a water content of 30% by mass or less. The method for producing a soil repairing agent according to claim 1, wherein the dehydrated product is dried in an atmosphere having an oxygen concentration of 10% by volume or less. A method for producing a soil repairing agent, comprising filling the converter dust dried by the method according to claim 1 or 2 into a container having an oxygen concentration of 10% by volume or less. A dehydration product obtained by dehydrating a mixture of the converter dust and water of coarse particles obtained by applying a mixture of the converter dust and water having a dissolved oxygen concentration of 4 ppm or less to a wet classifier at a temperature of 350 ° C. or less, And the manufacturing method of the soil repair agent characterized by drying on condition that the product of the oxygen concentration of drying apparatus atmosphere and drying time is 800 minutes and volume% or less.

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