JP2007209827A - Purifying method of polluted soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detoxify excavated soil polluted with organic chlorine compounds using a little amount of a treatment agent. <P>SOLUTION: This purifying method of polluted soil comprises steps for: kneading by supplying water to excavated polluted soil and agitating and mixing to form slurry to lower pollution concentration of the polluted soil; separating polluted water from the slurry-like polluted soil; purifying the polluted water separated in the separation step; and mixing and agitating the polluted water separated in the separation step with residual soil and a metal reducing agent containing iron powder of zero valent. The mixture is stored in a vessel and aged for a given period to decompose the organic chlorine compounds. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a purification technique for soil contaminated with harmful substances, and more particularly to a purification process for soil contaminated with an organic chlorine compound such as PCB (polychlorinated biphenyl).

  Soil contaminated with organochlorine compounds represented by PCBs and the like is present in the ground such as a factory site without being decomposed so much.

  Further, this PCB or the like is excavated from the ground for soil purification and stored in a container such as a drum can.

  In particular, the excavated contaminated soil is stored in large quantities without being subjected to purification treatment, and the purification treatment is urgently needed.

  Conventionally known methods include, for example, a thermal decomposition method, an iron powder method, an alkali catalyst chemical decomposition method, a melt solidification method, and an iron powder method.

  However, it is desired to develop a method in which contaminated soil is purified so as to satisfy environmental standard values and the number of treatment steps is small.

  Among the various processing methods, the following are known as typical solutions.

  There are electrical parts such as transformers and capacitors that contain difficult-to-decompose harmful substances such as PCB, waste liquid, and waste oil as constituent members or parts thereof.

  This harmful substance is stored in various containers such as drums and boxes, charged into a melting furnace as fuel, and melted at a high temperature to thermally decompose the harmful substance (see, for example, Patent Document 1). ).

  Further, there is a method in which after excavating soil contaminated with an organic halogen compound, iron powder is mixed into the excavated soil and piled up on the ground in a pile shape and left for several days to several months.

  There is also a method of decomposing pollutants and mixing them with hydrocarbons such as ethane and ethylene by mixing iron powder into excavated soil and backfilling it underground.

There is also a treatment method for preventing recurrence of contamination due to contaminants remaining in the surrounding soil (see, for example, Patent Document 2).
Also, dioxin-contaminated solids are pulverized with a pulverizer, the atmosphere of the pulverized material is replaced with an inert gas, and a reducing metal is introduced into the pulverized material and mixed.

The pulverized dioxin-contaminated mixture obtained from the pulverized material and the reducing metal is transferred to the dehalogenation reactor while maintaining the inert gas atmosphere, and the pulverized material is reduced with the reducing metal. Thus, a dehalogenation reaction of dioxins is performed (for example, see Patent Document 3).
JP 2004-154666 A JP 2001-577 A JP 2003-190932 A

  However, what is described in Patent Document 1 is a thermal decomposition process, which requires a high-temperature incinerator, which complicates equipment and becomes large-scale.

  Hazardous substances in this thermal decomposition treatment include devices such as PCBs, waste liquids, waste oils, etc. that are difficult to decompose (hereinafter referred to as PCBs) or contaminated with PCBs, articles such as parts, PCBs, etc. Contaminated soil, contaminated water, etc. mixed with or a container such as a drum can.

  Further, since combustion is performed while maintaining a high temperature in a high-temperature incinerator, continuous operation is required, and the amount of fuel consumed increases.

  There is also a problem of undecomposed by combustion and dioxins in the middle of decomposition.

  Next, the thing of patent document 2 mixes iron powder with excavated soil, piles up the obtained mixture in the shape of a pile (pile), hangs a sheet, and is left still for several days to several months. is there.

  When excavating this contaminated soil, the soil excavated from the contaminated site contains large contaminants such as stones and glass, and components having greatly different particle sizes.

  For this reason, when mixing iron powder with excavated soil, it is difficult to disperse | distribute iron powder uniformly in excavated soil.

  In addition, a mixture of iron powder in the vicinity of the excavation site is piled up on a pile in the shape of a pile and hung on a sheet, and left still, but the bottom of the pile is in contact with the ground. May leak the mixture.

  Moreover, it is difficult for the hills formed of the mixture to break down due to weathering or the like and maintain the initial shape, and the mixture is easily exposed from the sheet.

  Furthermore, the required amount of water in the mixture necessary for preventing oxidation by contact of iron powder with air and promoting reductive decomposition of the organic halogen compound cannot be maintained.

  In other words, the evaporation of water due to the drying of the mixture changes the balance between the oxidation rate of iron powder and the desalination reaction rate of PCB and the like, and it is difficult to perform reductive decomposition of a stable organochlorine compound over a certain period.

  Moreover, the thing of patent document 3 requires the grinder which grind | pulverizes a contaminated solid substance, and also mixes the reducing metal of metallic sodium with the grind | pulverized substance grind | pulverized with the grinder, and makes a dehalogenation process reaction. .

  At this time, an apparatus for maintaining an inert gas or a reducing atmosphere is necessary, which complicates the entire system, resulting in a problem that the operating cost increases.

  The present invention solves the above-mentioned conventional problems, and excavated soil contaminated with PCB or the like is reliably (here, the certainty is below a reference value that conforms to environmental standards), and further has a zero value. By effectively using the amount of treatment agent, which is a metal reducing agent containing iron powder, the running cost can be reduced as a result, and a method for purifying contaminated soil that meets environmental standards (detoxification) is provided. The purpose is to do.

  The present invention provides a kneading step in which water is supplied to excavated soil contaminated with an organic chlorine compound and then mixed to obtain slurry-like soil, and the slurry-like soil is divided into at least coarse-grained soil and fine-grained soil. A separation step of separating into a particle size group, a mixing step of stirring and mixing the separated fine-grained soil, a metal reducing agent containing zero-valent iron powder, and water, and mixing the mixture into a container The organochlorine compound is detoxified by storing and curing in the container for a certain period of time.

  According to the method for purifying contaminated soil of the present invention, excavated soil contaminated with an organic chlorine compound such as PCB can be subjected to purification treatment of contaminated soil that meets environmental standards with an appropriate amount of treatment agent used. it can.

  1st invention supplies water to the excavated contaminated soil, agitates and mixes, and reduces the contamination concentration of the contaminated soil as a slurry, and separation for separating contaminated water from the contaminated soil in the slurry A step of purifying the contaminated water separated in the separation step, and after the contaminated water is separated in the separation step, the water is agitated and mixed with residual metal, a metal reducing agent containing zero-valent iron powder, and the water. And a mixing step for preparing a mixture. The mixture is stored in a container, and is cured in the container for a certain period of time to decompose the organic chlorine compound.

  As a result, the concentration of organochlorine compounds adhering to the contaminated soil can be reduced, the amount of metal reducing agent containing the necessary zero-valent iron powder is minimized, and the contaminated soil and zero-valent iron are further reduced. It is possible to uniformly agitate and mix a metal reducing agent containing powder and water to promote contact between the organochlorine compound adhering to the soil surface and the metal reducing agent.

  Further, by curing in a sealed container, a stable decomposition reaction can be caused, and the contaminated soil can be purified. Furthermore, the contaminated water containing the organochlorine compounds that have separated and eluted from the contaminated soil can be purified in the purification treatment step.

  Moreover, it is not necessary to completely detach and elute the organic chlorine compound adhering to the surface of the contaminated soil, and it is sufficient to reduce the contamination concentration on the surface of the contaminated soil. This eliminates the need to use a large and complex treatment device that cleans the contaminated soil surface completely. Therefore, the excavated soil contaminated with an organic chlorine compound typified by PCB or the like can be detoxified with a small amount of treatment agent used.

  According to a second aspect of the present invention, there is provided a method for purifying contaminated soil according to the first aspect, wherein the treated water purified in the purification step is used as the supply water in the kneading step. As a result, water can be reused, and the amount of water such as tap water can be reduced.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the contaminated soil purification method is characterized in that the treated water purified in the purification step is used as supply water in the mixing step. As a result, the supply amount of water such as tap water can be reduced and the economy can be improved.

  Hereinafter, a purification method for contaminated soil according to an embodiment of the present invention will be described with reference to the flowchart of FIG.

  First, the contaminated soil which is the purification processing object excavated from the contaminated area is selected (S101).

  This sorting process is performed by a sorting device such as a sieve, and various sorts of contaminants, particularly large-sized contaminants such as stone and glass, are removed by the sorting device depending on the situation of the contaminated area.

  As the sorting device, a vibration sieve device, a rotary sieve device (Trommel) or the like that has already been put into practical use can be used.

  The size of the mesh of the vibration sieve device and the rotary sieve device may be set to an optimum condition as appropriate according to the type and characteristics of the excavated contaminated soil, the size of contaminants, and the like. Further, depending on the state of the excavated contaminated soil, visual selection may be performed. Further, large contaminants may be removed and the particle size of the contaminated soil may be selected.

  As a result, large contaminants are removed, and the working efficiency of the subsequent purification treatment step and the decomposition efficiency of the organic chlorine compound can be improved. In addition, what is necessary is just to employ | adopt the sorting process of this contaminated soil by the condition of the excavated contaminated soil.

  Next, water is supplied to the contaminated soil from which large contaminants such as stone and glass are removed, and the mixture is stirred and mixed to form slurry soil (S102).

  In this kneading step, for example, a kneading device (mixer) provided with rotating blades driven by a motor and rotating the rotating blades is used. By supplying water to the contaminated soil and stirring and mixing, the soil lump enveloping the lump of soil, gravel, etc. is released and unraveled.

  Further, the organic chlorine compound adhering to the surface of the contaminated soil is separated into the supplied water by the cleaning action by the supplied water and the rubbing action between the contaminated soils to reduce the concentration of contamination.

  Therefore, it is not necessary to use a large and complicated treatment apparatus that completely cleans the contaminated soil surface.

  If the amount of water supplied to the soil is too small, it will not be possible to make it finer, and there will be a situation where the soil mass that has wrapped gravel etc. will not be unraveled, and if it is too much, the total amount will be increased. Is more undesirable.

  The amount of water supplied to the soil may be adjusted according to the moisture content of the excavated soil.

  As a result of obtaining the optimum mixing ratio of soil and water, it varies depending on the moisture content of the soil. For example, for soil having a moisture content of 60%, by supplying 1.5 times the weight ratio of water, Soil can be obtained.

  Moreover, with respect to the soil whose water content exceeds 85%, slurry-like soil can be obtained by supplying water at a weight ratio of 1 times.

  Furthermore, for soil having a water content of 15% or less, slurry-like soil can be obtained by supplying three times the water by weight.

  Moreover, what is necessary is just to use general waters, such as tap water, river water, and groundwater, for the water used for supply water.

  In addition, by supplying surfactant and organic solvent with water to the contaminated soil and mixing with stirring, the removal and elution of organochlorine compounds adhering to the surface of the contaminated soil are promoted to reduce the contamination concentration more quickly. Can do.

  In addition, the level at which the contamination concentration on the contaminated soil surface is reduced can be adjusted based on the contamination concentration of the excavated contaminated soil according to the mixing and mixing time, water supply amount, surfactant and organic solvent supply amount in the kneading step. it can.

  Next, the slurry soil is separated into contaminated soil and contaminated water (S103).

  In this separation step, for example, a coagulation sedimentation apparatus is used.

  First, in the slurry-like soil stored in a certain amount in the coagulating sedimentation apparatus, the contaminated soil having the contamination concentration reduced due to the difference in specific gravity settles in the lower part and is separated into this contaminated soil and the contaminated water which is the supernatant water.

  The coagulating sedimentation apparatus is preferable in that it can separate and capture fine particle soil contained in water.

  In the separation step, a dehydrator (filter press), a centrifugal separator or the like can be used in addition to the coagulation sedimentation apparatus.

  The dehydrator feeds slurry-like soil into a filter and applies pressure to the filter to dehydrate the water content to about 30%.

  Moreover, you may dehydrate the contaminated soil settled in the lower part with the coagulation sedimentation apparatus with the dehydration apparatus.

  Next, the contaminated water purified in the separation step is purified (S104).

  In the contaminated water purification treatment step, for example, a filtration device having activated carbon, a device for irradiating ultraviolet rays to the contaminated water, a reduction treatment device for mixing and detoxifying a metal reducing agent containing zero-valent iron powder in the contaminated water, etc. Can be used.

  In addition, reuse of water, such as a tap water, becomes possible by using the treated water refine | purified at the purification process step for the supply water in a kneading | mixing step.

  Next, the contaminated soil separated in the separation step, a metal reducing agent containing zero-valent iron powder, and water are stirred and mixed to obtain a mixture (S105, mixing step). In this mixing step, a metal reducing agent and water are supplied to the reducing agent mixing tank based on the contaminated soil and zero-valent fine-particle iron powder separated in the separating step, and the mixture is stirred and mixed by the stirring means. It is.

  Moreover, what is necessary is just to use general waters, such as a tap water, river water, groundwater, as the water used for supply water in this mixing step.

  Further, by using the treated water purified in the purification treatment step as the supply water in the mixing step, water can be recycled and the amount of water such as tap water can be reduced.

  Next, the mixture is stored in a container such as a drum can, and the upper opening of the container is sealed with a lid and cured for a certain period of time (for example, standing for several months) and detoxified by a dechlorination reaction. Yes (S106).

  In the container, the organic chlorine compound receives (reduces) electrons on the surface of the iron powder, and changes to a chlorine-free compound such as acetylene to be rendered harmless.

  As the container, it is preferable to use, for example, a stainless steel material or a drum can whose inner surface is resin-coated, whereby leakage of the stored mixture due to corrosion can be prevented. Further, the mixture may be stored through a resin bag.

  It is desirable to seal the mixture so that it does not come into direct contact with the outside air in order to cut off the oxygen source, which is an impediment to the degradation of pollutants by the metal reducing agent, and the upper space of the container is filled with inert gas or reducing gas. It is preferable to keep it.

  As described above, the mixture is stirred and mixed in the reducing agent mixing tank by the stirring means. However, the contaminated soil, metal reducing agent, and water may be stirred and mixed in the container.

  In this case, a stirring means is provided on a member separate from the lid of the container to perform stirring and mixing, and after stirring and mixing, the upper opening of the container is sealed with the lid. Thereby, the whole apparatus can be simplified.

  As the metal reducing agent, zero-valent fine particle iron powder is used as a main component. The iron powder is made into fine particles having an average particle diameter of about 70 μm, for example, and by increasing the specific surface area, the decomposition reactivity of the organic chlorine compound can be improved.

  Further, nickel alloy, carbon-coated iron powder or the like may be blended and used.

  Moreover, the addition amount of the metal reducing agent to the contaminated soil is about 1 to 10% by weight with respect to the soil, and when the addition amount is less than 1% by weight, the decomposition rate is remarkably reduced. Moreover, water prevents the oxidation of a metal reducing agent, and contains more than the saturated water amount of soil in order to disperse | distribute a metal reducing agent uniformly to the whole soil.

  Moreover, you may supply and mix solvents, such as surfactant and alcohol, with a metal reducing agent and water with contaminated soil.

  In this case, detachment and elution of the organic chlorine compound from the soil surface can be promoted, and the decomposition efficiency can be further improved.

  As described above, according to the purification method for contaminated soil of the present invention, the metal reducing agent containing the necessary zero-valent iron powder is minimized by reducing the contamination concentration of the mechanical chlorine compound adhering to the contaminated soil. In addition, the contaminated soil, a metal reducing agent containing zero-valent iron powder, and water can be uniformly stirred and mixed to promote contact between the organochlorine compound adhering to the soil surface and the metal reducing agent.

  Furthermore, by curing in a sealed container, a stable decomposition reaction can be generated, and the contaminated soil can be reliably purified. Furthermore, the contaminated water containing the organochlorine compounds that have separated and eluted from the contaminated soil can be purified in the purification treatment step.

  Moreover, it is not necessary to completely detach and elute the organic chlorine compound adhering to the surface of the contaminated soil, and it is sufficient to reduce the contamination concentration on the surface of the contaminated soil.

  This eliminates the need to use a large and complex treatment device that thoroughly cleans the contaminated soil surface.

  Therefore, the excavated soil contaminated with an organic chlorine compound typified by PCB or the like can be rendered harmless by minimizing the necessary metal reducing agent containing zero-valent iron powder.

  It can be applied to a wide range of uses that require purification of soil contaminated with harmful substances.

The flowchart of the purification treatment method of the contaminated soil of one Example of this invention

Claims (3)

Kneading step of supplying water to the excavated contaminated soil, stirring and mixing, and reducing the contamination concentration of the contaminated soil as a slurry;
A separation step of separating contaminated water from the slurry-like contaminated soil;
A purification treatment step for purifying the contaminated water separated in the separation step;
After separating the contaminated water in the separation step, comprising a mixing step of stirring and mixing the metal reducing agent containing residual soil and zero-valent iron powder and the water into a mixture,
A method for purifying contaminated soil, comprising storing the mixture in a container and curing the organic chlorine compound in the container for a certain period of time. 2. The method for purifying contaminated soil according to claim 1, wherein the treated water obtained by purifying the contaminated water in the purification treatment step is used as water supplied in the kneading step. The method for purifying contaminated soil according to claim 1 or 2, wherein the treated water purified in the purification treatment step is used as water supplied in the mixing step.

Images