JP2006043628A - Heavy metal or the like immobilizing body, and method for cleaning contaminated water and soil using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an efficiently cleaning method capable of removing an environmental risk by cleaning water and soil contaminated with a heavy metal or the like in a contaminated site. <P>SOLUTION: (1) A heavy metal or the like immobilizing body includes a cleaning agent containing iron oxide, metal iron and a calcium compound filled into a tower or a tank. (2) When used, this heavy metal or the like immobilizing body is brought into contact with water into which a contaminant (ground water, exuded water in a final disposal place or the like) is dissolved. When the soil is cleaned, the excavated soil is introduced into a soil tank, water is supplied to elute the contaminant from the soil, the water is brought into contact with the heavy metal or the like immobilizing body, and the operation is repeated until the concentration of the contaminant arrives at a value not exceeding an emission control standard. When excavation is difficult, the ground water around the contaminated soil is pumped up, then the water is brought into contact with the heavy metal or the like immobilizing body to be cleaned, water is repeatedly poured into the contaminated soil, and the operation is repeated. Viscous soil hardly water permeable can also be cleaned. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to an immobilized body such as heavy metal and a method for using the same, and more specifically, an immobilized body such as heavy metal that can selectively remove heavy metal from water contaminated with heavy metal and the like, and contaminated with heavy metal using the same. The present invention relates to a method for purifying water and / or soil.

  Soil contamination is a serious social problem, and land made of soil contaminated with heavy metals and the like is managed by administrative agencies and the like as land with environmental risks that may cause the contaminants to leach out. To remove this environmental risk, technology is needed to remove the pollutants from the contaminated soil.

  As a method for treating contaminated soil (contaminated soil) at the site of contamination, a method of insolubilizing heavy metals and the like by injecting a chemical such as cement is known. Although this method can prevent elution of heavy metals and the like, the environmental risk cannot be removed because the content of heavy metals and the like does not decrease.

  Soil that cannot insolubilize heavy metals, etc. is transported to the final disposal site of the interception type and the management type and disposed of in landfill. In this way, clean soil is backfilled at the contaminated site, thus eliminating the environmental risks at the contaminated site. However, since it is expected that the final disposal site will be short, it will be difficult to implement in the future.

  Generally, soil is classified as follows according to particle size. That is, a gravel component having a particle size of 2 mm or more, a coarse sand component of 0.425 to 2 mm, a fine sand component of 0.075 to 0.425 mm, a fine sand (silt) component of 0.005 to 0.075 m, It is a clay component of 005 mm or less.

  Of these, pollutants are likely to accumulate in silt and clay with a large specific surface area. The silt and clay accumulated with these contaminants have a small particle size, and can be separated and removed from gravel, coarse sand and fine sand with little contamination by washing the soil with water. This method is called a “soil cleaning method” and is an effective means for reducing the amount of soil finally disposed of. However, it cannot cope with the shortage of final disposal sites.

  In addition, a purification method is known in which contaminated groundwater is pumped and treated.

  Volatile organic compounds (VOC) in the pumped ground water can be separated by oil-water separation, aeration, activated carbon adsorption, or the like. Further, it can be decomposed by oxidation with ultraviolet rays (UV) or the like, and environmental standards can be easily observed.

  On the other hand, heavy metals and the like in groundwater can be separated by coagulation sedimentation, filtration, ion exchange, or the like after treatment with alkali to produce insoluble compounds. However, processing techniques for heavy metals and the like are limited. In particular, the method of separating by flocculation precipitation after forming an insoluble compound is a treatment method for satisfying the wastewater standard, and establishment of a treatment technique that satisfies the environmental standard of 1/10 is desired. In addition, a wide space and a long residence time are required for the production of insoluble compounds and coagulation precipitation. Furthermore, in order to finally dispose of the insoluble compound separated by the coagulation sedimentation, a stabilization treatment for preventing re-elution is necessary.

  Regarding the treatment of heavy metals and the like, the US Environmental Agency compares the treatment technology with the cost before the standard value of arsenic in tap water is revised to the level of Japanese environmental standards (Non-patent Document 1).

  The treatment technique (method) taken up here is each of an adsorption treatment using activated alumina, an ion exchange treatment using an ion exchange membrane, and a treatment combining production of a hardly water-soluble compound and membrane separation.

  Among them, the adsorption method using activated alumina and the ion exchange method using an ion exchange membrane have a problem in the regeneration or disposal of the treated activated alumina or ion exchange membrane. On the other hand, the treatment method combining the generation of a poorly water-soluble compound and membrane separation is an improvement of the conventional coagulation precipitation method, and the time required for separation can be omitted by using membrane separation. However, since a long residence time is still required for the production of the poorly water-soluble compound, the enlargement of the apparatus is inevitable. Therefore, when compared in terms of processing costs, adsorption processing with activated alumina, which performs processing in a neutral range, is the cheapest processing method. Next, the ion exchange method and the treatment method combining the generation of a hardly water-soluble compound and membrane separation are performed in this order.

  When processing arsenic (trivalent arsenic) contained in water in a reduced state such as groundwater, it cannot be processed as it is, and it is necessary to oxidize arsenic to pentavalent by performing chlorine treatment or the like.

  In particular, it is difficult to reduce the concentration of arsenic below the environmental standard by the method of generating poorly water-soluble compounds. After reducing it below the standard for wastewater, treatment with activated alumina or reverse osmosis membrane, ion exchange method is used in combination with the environmental standard. It is necessary to:

  In addition, all of the methods reported here are arsenic treatment methods, and can be applied to many heavy metals etc. in order to apply to the restoration of the environment such as general soil and groundwater contaminated with heavy metals etc. Therefore, establishment of an inexpensive processing method is desired.

  The purification method that pumps and treats contaminated groundwater is used to contain the diffusion of contaminated groundwater, but if a large amount of groundwater is pumped and treated in a short period of time, the groundwater level changes, and the groundwater This will adversely affect the flow and ground environment. Therefore, the method of pumping up and treating groundwater must be performed over time and requires a long time for purification. Also, the contaminated soil remains intact and cannot be purified.

  Therefore, a method for purifying contaminated soil by pumping contaminated groundwater, purifying it, and pouring it into contaminated soil has been studied.

  This method is said to be able to purify unsaturated layer sand having a relatively large particle size. In ordinary strata, there is a gravel layer composed of sand and gravel above the impervious layer composed of silt and clay, and in this gravel layer, there is an aquifer where groundwater is present and above it. There is a layer where there is no groundwater, but an unsaturated layer is a layer where there is no groundwater.

  The method of pouring groundwater that has been pumped and purified into the contaminated soil is a containment measure that prevents the diffusion of contaminated groundwater to the periphery, as is the case with the method of pumping and purifying groundwater. Such measures must be taken because the technology for efficiently separating heavy metals and the like has not been established, and purification of soil and groundwater requires a long period of time.

  Attempts have been made to pour purified water by surrounding the contaminated soil with sheets or soil cement.

  This method is used to strengthen measures to prevent the diffusion of contaminated groundwater, and in order to purify groundwater and soil in a short period of time, at least a large amount of groundwater is required compared to the groundwater flowing into the contaminated area. It needs to be pumped and purified. However, since a processing method for purifying heavy metals or the like quickly and inexpensively to environmental standards or less has not been established, a method that combines the generation of insoluble compounds and agglomeration and precipitation must be used. Residence time is required, and it is difficult to secure a large amount of clean washing water, and it takes a long time to purify soil and groundwater. This prevented the reuse of contaminated land.

  On the other hand, as a “purification method using iron powder”, a purification wall composed of a metal iron powder layer for decomposing volatile organic compounds (VOC) is formed perpendicular to the groundwater flow, or metal iron powder is applied to the soil. An insolubilization method of mixing or spraying is known.

  Although such a method using a purification wall is attracting attention as a maintenance-free method, it takes a long time to purify because the flow rate of groundwater is slow. Moreover, although the insolubilization method can be easily implemented on site, the environmental risk cannot be reduced because the contaminants are not removed and remain on site. Attempts have been made to magnetically separate the contaminants adsorbed on the used iron powder together with the iron powder, but the iron powder is oxidized to produce red rust and is difficult to separate easily.

  As one of the detoxification methods for pollutants, a mixture of iron sulfate and sodium hydroxide is added to wastewater containing heavy metals, heated to 60 ° C or higher, and dissolved heavy metal ions are dissolved in solid form. “Ferrite treatment” that is recovered as ferrite is known. However, if this method is used to purify pumped-up groundwater, it is necessary to investigate the properties of groundwater, especially the content of heavy metal ions, and to add iron sulfate and sodium hydroxide corresponding to the amount. Since the type and concentration of heavy metal to be produced are not determined, the recovered ferrite must be disposed of, and this method is not always easy to apply.

  As described in Patent Document 1, the present inventors have developed an environmental purification material mainly composed of particles of an iron-based compound having a passive film formed on the surface, and the passive film is an elution of iron ions. It was clarified that it was effective in suppressing the occurrence of red rust caused by This passive film is considered to have an action of adsorbing eluted iron ions and heavy metal ions contained in contaminated water.

  Further, in Patent Document 2, after the particle size of an environmental purification material (purification material) having an oxide film on its surface is set to 1 mm or more, the fine soil contaminated with heavy metals is purified (treated). The present inventors have proposed a method for separating the purification material, on which heavy metals are fixed on the surface, from the soil after the treatment from the soil by magnetism or further by sieving using the difference in particle size. This makes it possible to reduce the content of heavy metals at the contaminated site or the content of other pollutants without transporting and discarding contaminated soil to the final disposal site. However, since the cost for mixing the purification material and soil and subsequent separation increases, establishment of an inexpensive treatment technique using iron powder or an iron-based compound is desired.

JP 2003-126871 A

JP 2004-76027 A United States Environmental Protection Agency (2000), “Technologies and Costs for Removal of Arsenic from Drinking Water”, EPA 815R00028, Prepared by Malcolm Pirnie, Inc. under contract 68C60039 for EPA ORD, December 2000

  As mentioned above, in order to purify water and soil contaminated with heavy metals, etc., insolubilization treatment of heavy metals with chemicals such as cement, methods to pump up and purify contaminated groundwater, purification methods using iron powder, heavy metals Various methods, such as ferritization treatment for wastewater containing sewage, etc. have been implemented.Further, after pumping up and purifying contaminated groundwater, it can be poured into contaminated soil to purify the soil, A method of surrounding the area with sheets, soil cement, etc. and pouring purified water is also being studied and tested.

  However, since a treatment method for purifying heavy metals or the like quickly and inexpensively below the environmental standard has not been established, at present, it is necessary to use a method that combines the generation of insoluble compounds and coagulation sedimentation. A large area and long residence time are required to clean up the land, preventing the reuse of contaminated land. The environmental purification material proposed by the present inventors, for example, having a particle diameter of 1 mm or more is also effective in reducing the content of heavy metals and other pollutants at the contaminated site, but has the disadvantage of increasing costs.

  The present invention has been made in view of such a situation, and it is an object of the present invention to provide an efficient purification method capable of purifying water or soil contaminated with heavy metals or the like at a contaminated site and removing environmental risks. .

  In general, soil contamination proceeds by adsorption of contaminants dissolved in water (for example, groundwater) to the soil. Adsorption is different from groundwater at the interface (in this case, the surface of the soil) with other phases where substances in the gas phase or liquid phase (in this case, pollutants in groundwater) come into contact with it It is a phenomenon that reaches equilibrium in concentration, and according to this adsorption equilibrium, the content of contaminants on the soil surface increases and soil contamination proceeds.

  The adsorption capacity of pollutants to the soil is easily affected by the particle size and composition of the soil. For example, clay having a small particle size has a larger specific surface area than sand, and thus can adsorb more pollutants. Alumina and iron oxide are known to adsorb contaminants more easily than nonpolar silica.

  When groundwater is contaminated, an adsorption equilibrium exists between sand and clay that coexist with the groundwater. Therefore, even if contaminated groundwater is taken out of the system, contaminants adsorbed on sand and clay are eluted in the newly supplied groundwater. Therefore, when the pollutants contained in groundwater (for example, heavy metals) are to be less than the environmental standards, the elution of the pollutants from the sand and clay (that is, the adsorption equilibrium with the sand and clay) is considered at the same time. It is necessary to elute pollutants from sand and clay with purified water below environmental standards. This is because the groundwater cannot be purified beyond the adsorption equilibrium.

Furthermore, in order to promote the elution of pollutants from soil, not only the target pollutants, but also clean wash water from which components that hinder the elution of pollutants dissolved in groundwater are removed is necessary. is there. In the ground water, for example, Na ⁺ , K ⁺ , Ca ²⁺ , Mg ²⁺ , HCO ₃ ⁻ , Cl ⁻ , SO ₄ ²⁻ , CO ₃ ²⁻ , NO ₃ ⁻ , NO ₂ ⁻ , PO ₄ ³⁻ , F ⁻ , SiO ₂ , NH ₄ ⁺ , Fe, Mn, Al, As, etc. are dissolved, and the presence of these substances prevents the target pollutant from elution from the soil. It is.

  For example, in a reduced state such as groundwater, iron ions are divalent and arsenic ions are trivalent. Divalent iron ions dissolved in groundwater are oxidized to trivalent on the ground, and insoluble precipitates are produced. Therefore, piping such as water injection wells used when pumping groundwater into the contaminated soil after purification by pumping it up Is prone to blockage. Therefore, it is necessary to remove Fe. In addition, trivalent arsenic ions are difficult to remove as they are, and pretreatment such as oxidation is necessary.

  In order to solve the above-mentioned problems, the present inventors washed a large amount of clean water with contaminants adsorbed on the contaminated soil, and eluted the contaminants from the soil according to the adsorption equilibrium. The method of purifying was examined.

  As a result, hexavalent chromium was added to a “purifier filling body” configured to fill a tank-shaped container with a sintered body of metallic iron, iron oxide and calcium oxide, and to introduce and discharge contaminated water thereto. By passing the contaminated water contained, it was confirmed that hexavalent chromium was reduced and immobilized on the surface of the cleaning agent, and clean water was obtained. Furthermore, the soil was washed with this water, and it was found that pollutants adsorbed on the soil surface could be eluted to clean the contaminated soil.

  The present invention has been made on the basis of such findings, and the gist of the present invention is that of the following (1) immobilized body such as heavy metal, and the contaminated water and soil of (2) to (4) below using the same. There is a purification method.

  (1) An immobilization body such as a heavy metal in which a purification agent containing iron oxide, metallic iron and a calcium compound is packed in a tower or a tank.

  The "immobilized body such as heavy metal" here will be described in detail later, but is not limited to a tower shape or a tank shape filled with the purifier, but is not limited to a conventional tower shape or a tank shape. It also has the function of immobilizing, reducing, or detoxifying other contaminants, such as heavy metals, etc., on the cleaning agent.

  In addition, “heavy metal, etc.” means the same as “heavy metal, etc.” defined in “Summary of Survey Results on Soil Contamination Survey / Target Cases and Response Status in 2000” published by the Ministry of the Environment It is a generic term that includes not only metals that are relatively large in density and generally called heavy metals, such as lead, chromium, and zinc, but also harmful elements such as arsenic, fluorine, boron, and cyan.

  (2) A method for purifying contaminated water, wherein the immobilized body such as the heavy metal according to (1) is contacted with water in which the contaminant is dissolved.

  Here, “pollutants” refers to heavy metals, organic chlorine compounds, and other organic compounds that are difficult and harmful to treat.

  If the water in which the pollutant in (2) is dissolved includes groundwater, leachate from a final disposal site, or wastewater from a factory, the effect of purification is great.

  (3) Put the excavated soil into a soil tank, supply water, and the supplied water and heavy metal as described in (1) above until the concentration of contaminants eluted from the soil is below the environmental standard A method for remediating contaminated soil that repeats contact with immobilized bodies.

  In the soil purification method of (3), the viscous soil separated from the excavated soil is placed in a soil tank, water is supplied, and the concentration of the contaminants eluted from the viscous soil is below the environmental standard. By repeating the contact between the supplied water and the immobilization body such as heavy metal as described in (1) above, the contaminated viscous soil can be purified.

  Here, “viscous soil” generally refers to clay soil containing the silt component having a particle size of 0.075 mm or less.

  (4) After pumping up groundwater around the contaminated soil, purify it by bringing it into contact with an immobilized body such as heavy metal as described in (1) above, and then pouring water into the contaminated soil again. A method for purifying groundwater, the method for purifying contaminated soil and / or groundwater in which the pumping and water injection are repeated until the concentration of pollutants contained in the pumped groundwater reaches an environmental standard or lower.

  In the purification method (4), it is possible to purify the hardly permeable viscous soil by repeating pumping and water injection.

  In the purification method (4), if the contaminated area is surrounded by a water-impervious wall and purified, it is effective for preventing diffusion to the surrounding area of the contaminated groundwater, and further flows into the area surrounded by the impermeable wall. If the amount of groundwater is higher than the amount of groundwater to be pumped and injected, the period required for purification can be shortened.

  The immobilized body such as heavy metal of the present invention immobilizes, reduces, or renders harmless heavy metal or the like, organic chlorine compounds, and other organic compounds that are difficult to treat and harmful to the purification agent filled in the immobilized body. It has a function. In addition, according to the method for purifying contaminated water and soil of the present invention using this immobilization body such as heavy metals, water and soil contaminated with heavy metals and the like can be efficiently purified at the contaminated site to reduce environmental risks. Can do.

  Hereinafter, the present invention, that is, the immobilized body of heavy metal or the like of (1), the method of purifying contaminated water of (2), the method of purifying contaminated soil of (3), and the contaminated soil of (4) and A method for purifying groundwater will be described in detail.

  The immobilized body such as heavy metal (1) is “an immobilized body in which a purification agent containing iron oxide, metallic iron and a calcium compound is packed in a tower or a tank”.

  Since this cleaning agent contains iron oxide, metallic iron, and calcium compound, when in contact with contaminated water, (a) insolubilization reaction of heavy metal or the like by the calcium compound between the cleaning agent and heavy metal, (b ) Ferrite reaction of ferrous hydroxide and alkali with ferrous hydroxide and (c) Oxidation / reduction reaction between ions of metal iron and heavy metal, etc. occur. Depending on the type and amount of contaminants and other conditions, either of these reactions may proceed, or one or two of these reactions may proceed.

  The insolubilization reaction of heavy metals and the like by the calcium compound in (a) above, the calcium compound in the purifying agent dissolves and the pH of the contaminated water rises, and the heavy metal ions in the contaminated water produce poorly soluble hydroxides and calcium salts. It is a reaction to. For example, cadmium, copper, mercury, zinc, iron, manganese, nickel, fluorine, arsenic acid, etc. are insoluble because the generated hydroxides and calcium salts are poorly soluble. However, lead, manganese, antimony, boric acid, cyan, hexavalent chromium, selenium, nitrate nitrogen, etc. cannot be insolubilized.

In the ferritization reaction of heavy metal or the like by ferrous hydroxide and alkali in (b), heavy metal dissolved in contaminated water is taken in as ferrite and immobilized on the purifier. As described above, the “ferritization treatment” is used for wastewater treatment containing heavy metals and the like, and iron sulfate and sodium hydroxide are added to the wastewater so that 2NaOH / FeSO ₄ (molar ratio) = 1. When added and maintained at 60 ° C. or higher, the ferritization reaction represented by the following formulas (1) and (2) (wherein M represents a heavy metal other than iron) proceeds.

(3-x) Fe ²⁺ + xM ²⁺ + 6OH ⁻ → Fe _3-x M _x (OH) ₆ ... (1)
Fe _3-x M _x (OH) ₆ + O ₂ → M _x Fe _3-x O ₄ (2)
In the cleaning agent used in the immobilized body of heavy metals and the like of the present invention, iron ions involved in the reaction of the above formula (1) are supplied by dissolution of metallic iron in the cleaning agent, and hydroxide ions are present in water. Supplied by a calcium compound that elutes hydroxide ions in small increments below. Therefore, even without adding iron sulfate or sodium hydroxide, iron ions and hydroxide ions are supplied little by little, and the ferritization reaction can proceed.

  In the ferritization reaction, many heavy metals are taken into the ferrite structure instead of iron ions and become insoluble. Arsenic, cadmium, chromium, copper, lead, and the like are known as heavy metals that become ferrite instead of iron ions. From the viewpoint of the ionic radius, molybdenum, manganese, nickel, selenium, antimony, zinc, and the like can be ferritized. It can cope with iron ions and arsenic ions contained in groundwater and can be converted to ferrite.

  As the calcium compound, calcium hydroxide, calcium oxide, calcium carbonate and the like are used, and calcium oxide is particularly preferable.

  It is important to mix iron oxide with the purifier in order to advance the ferritization reaction. As iron oxide, magnetite is desirable, and this enables the ferrite formation reaction to proceed remarkably even at room temperature. Furthermore, by mixing iron oxide in the purifier, generation of red water due to oxidation of dissolved divalent iron ions is suppressed.

  The oxidation / reduction reaction between metal iron and heavy metal ions in (c) (that is, oxidation reaction of metal iron and reduction reaction of heavy metal, etc.) proceeds in most heavy metals and nitrate nitrogen. Furthermore, compared with the dissolution reaction of metallic iron, the oxidation reaction with a more basic hydroxide ion proceeds, so that a reduction reaction of boric acid that is less basic than the dissolution reaction of metallic iron can be performed.

  Moreover, the oxidation (dissolution) reaction of metallic iron and the electron produced | generated by the effect | action of metallic iron and an alkali are used for reduction (decomposition | disassembly) reactions, such as an organochlorine compound and other volatile organic compounds (VOC). Taking an organochlorine compound as an example, when represented by RCl (R represents an alkyl group), the organochlorine compound is reduced and decomposed according to the following formula (3). Other pollutants that are easily reduced are also decomposed and rendered harmless.

RCl + H ⁺ + 2e ⁻ → RH + Cl ⁻ (3)
As described above, the purification agent containing iron oxide, metallic iron, and calcium compound used in the immobilized body such as heavy metal of the present invention is effective for purification of many pollutants. This is a suitable treatment method in place of heavy metal treatment such as activated alumina treatment.

  As the cleaning agent, a mixture of iron oxide, metallic iron and calcium oxide is desirable. Among them, a sintered body of iron oxide, metallic iron, and calcium oxide is particularly desirable because it can control the particle size and has excellent water permeability.

  The mixing ratio of iron oxide is desirably less than 40% by mass with respect to the total amount of the purifying agent. This is because, when the content of iron oxide is 40% by mass or more, it is difficult to immobilize heavy metals or the like on the surface of the cleaning agent but as ferrite can be fixed to the cleaning agent. Moreover, in this purifier, the total mass of iron (that is, the total amount of metallic iron and iron oxide converted to the amount of iron) is 60% by mass so that supply of iron ions necessary for the ferritization reaction can be ensured. The above is desirable.

  Moreover, it is desirable that the particle size of the purifier is in the range of 0.1 to 5.0 mm that can ensure water permeability. If the particle size is smaller than 0.1 mm, the contact area with the contaminated water is large and the purification ability is excellent, but the resistance when circulating the water is large and the treatment efficiency is lowered. On the other hand, when the particle diameter exceeds 5.0 mm, the packing density of the purifying agent decreases, and the amount of the heavy metal immobilized body decreases, so that the processing ability tends to be lowered. The cleaning agent can be used with the particle size adjusted, but it is economically advantageous to use a mixture of various particle sizes.

  The immobilized body such as heavy metal of the present invention is a product in which the above-mentioned purification agent is packed in a tower or a tank, and has a function of purifying water in which contaminants are dissolved. The size of the immobilization body such as heavy metal is preferably such that the empty residence time is 5 minutes or more with respect to the flow rate of the contaminated water to be supplied. This is because if the empty residence time is less than 5 minutes, the contaminant cannot be sufficiently fixed, reduced or decomposed, and it is difficult to obtain clean washing water.

  The method (2) for cleaning contaminated water is “a cleaning method for contacting the immobilized body such as heavy metal and water in which the contaminant is dissolved”.

  Here, the “contaminant” means a heavy metal or the like, an organic chlorine compound, or an organic compound that is difficult to be treated and harmful as described above.

  The “water in which the pollutant is dissolved”, that is, the water to be treated is not particularly limited. For example, surface water, ground water, tap water, industrial water, industrial wastewater, leachate and the like can be mentioned. If the water to be treated contains groundwater, leachate from the final disposal site, or wastewater from factories, etc., these often contain relatively high concentrations of heavy metals, etc. Is particularly big.

  In the cleaning method (2), an immobilized body such as heavy metal is brought into contact with water in which contaminants are dissolved. The above-mentioned “contact with an immobilized body such as heavy metal” means contact with a purifying agent filled in the immobilized body such as heavy metal.

  The method of contacting is not particularly limited, but, for example, a method in which water in which contaminants are dissolved is continuously sent from the bottom of the tower or tank filled with the above-described purifier and discharged from above is used in the tower or tank. This is desirable because it is easy to bring the entire cleaning agent packed in the container into contact with contaminated water. In addition, it is necessary to consider that the processing amount does not exceed the amount commensurate with the size of the immobilization body such as heavy metal (an amount capable of securing an empty residence time of 5 minutes or more).

  By this method, clean water from which heavy metals and other contaminants are removed is obtained.

  The method for purifying contaminated soil in (3) described above is as follows: “Put the excavated soil into a soil tank, supply water, and supply the water until the concentration of contaminants eluted from the soil falls below the environmental standard. It is a “purification method that repeats contact between water and an immobilized body such as heavy metal (1)”.

  This method is particularly applicable when the pollutant (contaminated soil) is in a shallow place and the soil and groundwater in the deeper part are not contaminated.

  Specifically, first, the contaminated soil is excavated and placed in a soil tank. Although it is not necessary to use a special soil tank, it is desirable to select a suitable shape in consideration of the situation at the site because water is introduced to elute the pollutants from the soil.

  Subsequently, water is supplied to the soil tank to elute the pollutants from the soil, and the pump installed between the soil tank and the fixed body such as heavy metal is operated so that the water in the soil tank is fixed to the heavy metal fixed body. Water is circulated through a pipe arranged to circulate between soil tanks. Usually, it is desirable to take a system in which water (supernatant water) in the soil tank is extracted, introduced below the immobilized body such as heavy metal, extracted from above, and returned to the upper side of the soil tank. Depending on the soil quality, it is possible to extract from the bottom of the soil tank, but the fine particles in the soil are mixed with the immobilized body such as heavy metals together with water, and the time for the contaminated water to come into contact with the purifier is reduced. , Purification efficiency decreases. In addition, when recovering a cleaning agent from an immobilized body such as heavy metal whose purification performance has deteriorated, separation from the cleaning agent tends to be difficult.

  The water is circulated until the concentration of contaminants eluted from the soil falls below the environmental standard (water quality environmental standard). This is because environmental risks are not eliminated unless they are below the environmental standards.

  The circulation rate of water is not particularly limited. However, when the circulation speed is increased, the period required for purification is shortened, but the soil rises in the water and becomes turbid, so that it is difficult to separate the soil from the circulating water. On the other hand, when the circulation rate is slow, the separability of soil and circulating water is improved, but it takes a long time for purification. Therefore, it is desirable to adjust the circulation speed as appropriate according to soil quality, soil contamination, and the like.

  The number of water cycles depends on the soil quality and soil contamination, but if clean wash water circulates more than 20 times in the soil tank, most of the pollutants in the soil are directed to fixed bodies such as heavy metals. Moving. If it is less than 20 times, the movement of pollutants from the soil may be insufficient. The amount of water to be used is not particularly limited as long as these elution and circulation operations can be performed without hindrance.

  The soil from which contaminants have been removed in this way can be backfilled if the amount of elution of heavy metals and other pollutants is below the water quality standard, and after backfilling there is no environmental risk. Available as

  In the soil purification method of (3), the viscous soil separated from the excavated soil is put into a treatment tank, water is supplied, and the concentration of the contaminants eluted from the viscous soil is below the environmental standard. By repeating the contact between the supplied water and the immobilization body such as heavy metal as described in (1) above, the contaminated viscous soil can be purified.

  Separation of the viscous soil from the excavated soil may be performed by sieving, but the above-described “soil cleaning method” may be applied depending on the soil condition and other conditions.

  As the method of bringing the supplied water into contact with the immobilization body such as heavy metal, a method of arranging a pipe between the soil tank and the immobilization body such as heavy metal and circulating the water with a pump may be applied. Usually, most of the pollutants are adsorbed on the cohesive soil, and thus by adopting such a method, the pollutants can be efficiently removed from the soil.

  The method for purifying contaminated soil and / or groundwater according to (4) described above is as follows: “After pumping up the groundwater around the contaminated soil, it is purified by bringing it into contact with an immobilized body such as heavy metal as described in (1) above and contaminated again. In this method, the contaminated soil and / or groundwater is purified by repeating the pumping and water injection until the concentration of pollutants contained in the pumped groundwater reaches the environmental standard or lower. is there.

  This method is applicable when the pollutant (contaminated soil) is deep and it is difficult to excavate, or when groundwater in a deep part is contaminated.

  In implementing this method, first, a pumping well for pumping up groundwater around the contaminated soil and a water injection well for purifying the pumped water and pouring it into the contaminated soil are set up in the contaminated area. .

  Next, the pumped ground water is brought into contact with a fixed body such as heavy metal to be cleaned. Specifically, the pumped-up groundwater is sent to a fixed body such as heavy metal. At that time, as described above, attention is paid to the empty residence time (preferably 5 minutes or more). In addition, it is desirable to adopt a method in which the pumped-up groundwater is continuously sent from below the fixed body such as heavy metal and discharged from above.

  Subsequently, the purified groundwater is supplied to the water injection well. As the water injection well, it is simple and effective to use a sand column or the like.

  This groundwater circulation operation of “pumping” → “cleaning” → “water injection” is repeated 20 times or more. In this way, by repeating the operations of purifying the groundwater, moving the contaminants from the soil to the cleaned groundwater, and repurifying the groundwater containing the contaminants, Even when cutting is difficult, it is possible to clean the contaminated soil.

  Even when the groundwater is contaminated, it can be purified by the above-described circulation operation. If groundwater is contaminated, it is usually in an adsorption equilibrium with or close to the soil in contact with it, and soil in the vicinity of groundwater is also contaminated. Along with this, the soil is also cleaned.

  If pollutants are present in the unsaturated layer (that is, the gravel layer above the poorly permeable layer, where there is no groundwater above the aquifer where groundwater exists) It is also possible to remove contaminants from the unsaturated layer by repeating the operation of eluting the contaminants into the groundwater by spraying the cleaned groundwater.

  In the purification method (4), it is possible to purify the hardly permeable viscous soil by repeating pumping and water injection.

  Cohesive soil generally has a small particle size, adsorbs more pollutants than sand, etc., and has poor water permeability, so it takes time for the pollutants to elute. It is possible to purify by repeating the groundwater circulation operation of “→ water injection”.

  In carrying out the purification method (4) (including the purification of cohesive soil), it is desirable to surround the contaminated area with a water shielding wall. If a water-impervious wall that reaches the depth of the poorly permeable layer is installed in the contaminated area, the inflow and outflow of groundwater to the area can be greatly suppressed and the diffusion of the contaminated groundwater to the periphery can be contained.

  Although soil cement can be used for the impermeable wall, it is desirable to install the impermeable wall using a steel sheet pile. This is because soil cement cannot be removed after purification and disturbs the flow of groundwater around the contaminated area.

  Moreover, in the above-mentioned “method of surrounding a contaminated area with a water shielding wall”, it is possible to suppress the outflow of contaminated groundwater by surrounding the contaminated area with a water shielding wall. It is possible to shorten the period required for purification by pumping and pouring a larger amount of groundwater than the amount of groundwater that flows in. In addition, in order to make the groundwater level in the impermeable wall the same as the outside of the impermeable wall, for example, surrounding groundwater or surface water can be used as the water retained in the purification facility on the ground.

  In the process of carrying out the purification method of the present invention described above, when purification of contaminated water by an immobilization body such as heavy metal becomes insufficient, iron oxide, metal iron and calcium oxide are obtained from the immobilization body. What is necessary is just to take out cleaning agents, such as the sintered compact which consists of, and replace with a new cleaning agent.

  In addition, in order to facilitate the replacement work of the purifier, a plurality of fixed bodies such as heavy metals may be arranged in parallel, or in order to enhance the purification effect, a plurality of heavy metals or the like are fixed. The bodies can also be arranged in series.

  Furthermore, simple purification means such as oil / water separation, aeration, and ultraviolet (UV) oxidation can be installed before or after the fixed body such as heavy metal, and the purification efficiency of volatile organic compounds (VOC) and oil can be increased. .

  Heavy metals and the like removed from the soil and groundwater are chemically immobilized on the iron oxide by the above-described ferritization action, and will not be re-eluted even if water is added. Therefore, the purification agent such as a sintered body made of iron oxide, metallic iron and calcium oxide taken out from the immobilized body such as heavy metal can be finally disposed of as it is. Moreover, since there are many iron components, it can also be reused as an iron-making raw material or a cement raw material.

  Conventionally, in soil purification using iron powder, it has been difficult to separate iron powder mixed with soil. Moreover, in the environmental purification material which the present inventors proposed, there existed a problem that the expense for mixing with soil and subsequent isolation | separation increased. However, if a fixed body such as heavy metal of the present invention in which a purification agent containing iron oxide, metallic iron and calcium oxide is packed in a tower or a tank is used, since it is not premised on direct mixing with soil, There is an advantage that the mixing and separation steps can be omitted.

  Further, the present invention will be described in detail by way of examples.

  In a beaker having an internal volume of 2 liters, 500 g of activated alumina and 1 liter of 10 mg / l (liter) hexavalent chromium aqueous solution were placed and stirred for one day to prepare a simulated contaminated soil solution. By stirring and mixing for one day and night, the hexavalent chromium concentration reached an adsorption equilibrium between the aqueous solution and the activated alumina, and the hexavalent chromium concentration in the aqueous solution decreased to 0.9 mg / l. On the other hand, the hexavalent chromium content in the activated alumina is 18.2 mg / kg. In addition, the average particle diameter of the used activated alumina is 0.043 mm, and it corresponds to the silt of fine particles from the particle size classification of the soil.

  On the other hand, 500 g of a sintered body of iron oxide, metallic iron, and calcium oxide was put into a 300 ml beaker to obtain a fixed body such as a tank-like heavy metal. The sintered body of iron oxide, metallic iron, and calcium oxide used (that is, a purifier) was obtained by sintering dust generated at a steel mill using a rotary kiln type reduced pellet manufacturing apparatus, and having a particle size of 2.7 mm or more. I used one. The main properties (analytical values) are shown in Table 1.

  Next, using a rubber tube with an inner diameter of 5 mm, the supernatant liquid of the simulated contaminated soil solution is supplied to the lower part of the fixed body such as heavy metal with a liquid feed pump, and the liquid that reaches the upper part of the fixed body such as heavy metal is the same. In this way, it was fed to the top of the simulated contaminated soil solution. In other words, the water around the contaminated soil (water simulating pumped ground water) is brought into contact with a fixed body such as heavy metal to purify it, and then poured into the contaminated soil again. The irrigation operation (simulated operation) was repeated. The flow rate of the circulated water is 1 liter / h.

  FIG. 1 shows temporal changes in the hexavalent chromium concentration of the supernatant liquid (that is, circulating water) and the hexavalent chromium content of the activated alumina at this time. The thick line parallel to the horizontal axis in the figure is the water quality environmental standard (0.05 mg / l) of hexavalent chromium.

  As can be seen from FIG. 1, both the hexavalent chromium concentration in the circulating water and the hexavalent chromium content of the activated alumina decrease with the passage of the circulation time. Below the standard, the hexavalent chromium content of the activated alumina was 6 mg / kg.

  An important finding obtained in this purification test is that the lower activated alumina phase can be cleaned by supplying and draining the upper aqueous phase without mixing the simulated contaminated soil solution. As described above, the use of the immobilization body such as heavy metal can not only purify the circulating water but also remove hexavalent chromium contained in the activated alumina because the circulating water is purified. This is probably because the equilibrium was changed and the elution of hexavalent chromium from activated alumina was promoted.

  In this way, the fine silt components that have been conventionally considered difficult to purify can be purified by relatively easy means using circulating water.

  This experimental result shows that the immobilization body such as heavy metal of the present invention is effective for removing pollutants existing deep underground.

  In other words, in general geological formations, a gravel layer composed of sand and gravel exists above the impervious layer composed of silt and clay, and this gravel layer is located between the aquifer where groundwater exists and its upper part. When the groundwater is contaminated, the silt and clay of the poorly permeable layer adsorb pollutants and cause soil pollution deep in the ground. When contaminated groundwater is purified, the adsorption equilibrium changes and the corresponding pollutants are eluted from the silt and clay into the groundwater. Therefore, by purifying the groundwater from which the contaminants are eluted, it is possible to reduce the amount of contaminants adsorbed on the silt and clay, and to reduce the amount of contaminants eluted from the silt and clay. In this way, by purifying the groundwater, the amount of contaminants eluted from silt and clay can be reduced below the environmental standard, and the soil can be purified.

  The immobilized body such as heavy metal of the present invention has a function of immobilizing, reducing, or detoxifying heavy metals and the like, organochlorine compounds, and other organic compounds that are difficult to treat and harmful to purification agents. According to the contaminated water and soil purification method of the present invention to be used, water and soil contaminated with heavy metals can be efficiently purified. In addition, there is also an advantage that the process of mixing and separating the soil and the cleaning agent can be omitted when the soil is purified. Accordingly, the heavy metal fixed body of the present invention and the purification method of the present invention using the same are extremely effective in treating contaminated water and soil at the site of contamination and reducing environmental risks, and are widely used for environmental purification. can do.

  Similarly, the contaminants can be removed from the final disposal site by purifying the water leached from the final disposal site and returning it to the final disposal site again.

It is a figure which shows the purification test result of the simulation contaminated soil using fixed bodies, such as a heavy metal of this invention.

Claims (9)

  An immobilized body such as heavy metal, wherein a purification agent containing iron oxide, metallic iron and a calcium compound is packed in a tower or a tank.   A method for purifying contaminated water, comprising contacting the immobilized body such as heavy metal according to claim 1 with water in which the contaminant is dissolved.   The method for purifying contaminated water according to claim 2, wherein the water in which the pollutant is dissolved includes ground water, leachate from a final disposal site, or waste water from a factory or the like.   2. The excavated soil is put in a soil tank, water is supplied, and the supplied water and an immobilized body such as heavy metal according to claim 1 until the concentration of pollutants eluted from the soil is below environmental standards, A method for remediating contaminated soil, characterized in that contact with the soil is repeated.   The viscous soil separated from the excavated soil is put into a soil tank, water is supplied, and the supplied water and the heavy metal according to claim 1 until the concentration of pollutants eluted from the viscous soil is below the environmental standard. A method for purifying contaminated clay soil, characterized by repeating contact with an isofixed body.   After pumping up the groundwater around the contaminated soil, the contaminated soil and / or groundwater is purified by bringing it into contact with the heavy metal fixed body according to claim 1 and purifying it, and then pouring the contaminated soil again. A method for purifying contaminated soil and / or groundwater, wherein the pumping and water injection are repeated until the concentration of contaminants contained in the pumped groundwater reaches an environmental standard or less.   The method for purifying contaminated soil and / or groundwater according to claim 6, wherein the hardly-permeable viscous soil is purified by repeating pumping and water injection.   The method for purifying contaminated soil and / or groundwater according to claim 6 or 7, wherein the contaminated area is surrounded by a water-impervious wall and purified. The method for purifying contaminated soil and / or groundwater according to claim 8, wherein a larger amount of groundwater than the amount of groundwater flowing into the area surrounded by the impermeable walls is pumped and injected.

Images