Soil cleaning method

Abstract

To provide a soil cleaning method that demonstrates superior effectiveness in decontaminating polluted soil.SOLUTION: A soil cleaning method performs the following soil cleaning process at least two times, wherein the soil is brought into contact with a soil cleaner composition that contains the following components (a), (b), and (c) as well as water, followed by removing all or part of the soil cleaner composition from the mixture of the soil and the soil cleaner composition. Components (a): at least one selected from compounds capable of producing hydroxyl radicals, (b): a bivalent iron compound, and (c): at least one selected from hydroxycarboxylic acid, polycarboxylic acid and salts thereof.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for washing soil and a kit for producing a soil washing composition. [Background technology]

[0002] In recent years, there have been many cases of serious soil contamination in a variety of situations, including illegal dumping of industrial waste, waste disposal in factories, and accidental leakage of hazardous substances from final disposal sites, as well as accidental or long-term leakage of various oils at the sites or former sites of petroleum refineries, gas stations, chemical plants, etc.

[0003] Conventional methods for remediating such contaminated soil include incineration after excavation, solidification / fixation, containment, bioremediation, and decomposition / removal methods. In addition, in-situ oxidation decomposition technology using the Fenton reaction is known as a purification technology that uses chemicals to decompose and remove organic compounds in soil contaminated with organic compounds. The Fenton reaction is a method in which hydrogen peroxide reacts catalytically with an iron (II) compound, causing a complex chain reaction and generating the highly oxidizing hydroxyl radical (·OH), as shown in the following reaction formula. Fe 2+ + H 2 O 2 → Fe 2+ + OH - + OH There are various methods for generating hydroxyl radicals other than the Fenton reaction, but this reaction is the most basic method. In this reaction, hydroxyl radicals are generated from hydrogen peroxide by the action of divalent iron, and the generated hydroxyl radicals have the strongest oxidizing power of all radicals. Taking advantage of this strong oxidizing power, it is applied in various fields, such as the decomposition of harmful substances and persistent pollutants.

[0004] Patent Document 1 discloses an organic compound decomposition material that is composed of a reducing agent, a metal oxide, and an oxidizing agent. Patent Document 2 discloses a method for purifying organic pollutants, in which hydrogen peroxide and an iron-based catalyst are added to the pollutants, and then a persulfate is added to the pollutants. Patent Document 3 discloses a method for cleaning up contaminated ground for cleaning up ground contaminated with organic matter, the method comprising the steps of supplying hydrogen peroxide and ferrous chloride to the contaminated ground and agitating the contaminated ground with an agitator. Patent Document 4 discloses a method for in-situ cleaning of soil contaminated with organic compounds, in which hydrogen peroxide is supplied to the soil and water is passed through the soil to perform cleaning. Patent Document 5 discloses a method for purifying contaminated soil, which includes an oxidative decomposition step of oxidatively decomposing hydrocarbon compounds in the contaminated soil, in which a Fenton's reagent containing hydrogen peroxide and divalent iron is added to the contaminated soil in the oxidative decomposition step. Patent Document 6 discloses a method for removing a biofilm by contacting a metal-containing biofilm formed in an aqueous system with (a) a compound capable of generating hydroxyl radicals and (b) a reducing agent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2004-249237 A [Patent Document 2] JP 2006-341195 A [Patent Document 3] JP 2001-79534 A [Patent Document 4] JP 2007-237132 A [Patent Document 5] JP 2020-195970 A [Patent Document 6] International Publication No. 2020 / 230626 Summary of the Invention [Problem to be solved by the invention]

[0006] In the treatment by the Fenton method, the reaction may end instantly or the ferrous iron may be oxidized and precipitated immediately, which may make it difficult to expand the treatment area or maintain the treatment capacity for a long time. For example, when purifying highly contaminated soil, the reaction may end instantly, so the amount of oxidizing agent and ferrous iron may be increased more than necessary. However, if an excessive amount of ferrous iron is used, the amount of oxidized iron sludge increases, and the cost of treatment may worsen the economic efficiency. Furthermore, if it flows into groundwater, it may cause a phenomenon called "red water", in which the groundwater turns red. Also, if an excessive amount of oxidizing agent is used, if the ferrous iron is oxidized, the strong decomposition ability of the Fenton reagent is lost, and the oxidizing agent remains in the water, which decomposes and releases oxygen gas. It is expected that the oxygen gas generated by this will lift and move soil particles, affecting the ground in another place. The present invention provides a soil washing method and kit that are excellent in cleaning contaminated soil. [Means for solving the problem]

[0007] The present invention relates to a soil washing method, which comprises contacting soil with a soil washing agent composition containing the following components (a), (b), and (c) and water, and then performing soil washing two or more times, and removing a part or all of the soil washing agent composition from a mixture of the soil and the soil washing agent composition: Component (a): one or more compounds selected from compounds capable of generating hydroxyl radicals (b) Ingredient: Divalent iron compound (c) Component: one or more selected from hydroxycarboxylic acids, polycarboxylic acids, and their salts

[0008] The present invention also relates to a kit for producing a soil cleaning agent composition comprising multiple agents containing components selected from the above-mentioned components (a), (b), and (c), wherein the above-mentioned components (a) and (b) are contained in different agents. Effect of the Invention

[0009] According to the present invention, there are provided a soil washing method having excellent cleaning properties for contaminated soil and a kit for producing a soil washing composition. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The reason why the soil washing method of the present invention has excellent washing power for contaminated soil is not entirely clear, but is presumed to be as follows. In the Fenton reaction, component (a), a compound capable of generating hydroxyl radicals, catalytically reacts with component (b), a compound containing divalent iron, causing a complex chain reaction that generates highly oxidizing hydroxyl radicals (hereinafter referred to as OH radicals). It is believed that component (c) forms a complex with iron ions and inhibits the insolubilization of compounds containing trivalent iron that are generated in the chain reaction, making the reaction easier to occur, which is believed to allow the Fenton reaction to continue for a long period of time. In addition, it is presumed that the inclusion of component (c) and further component (d), which reduces trivalent iron ions to divalent iron ions, increases the amount of OH radicals produced by the Fenton reaction, thereby improving the soil cleaning power. Furthermore, it is presumed that when soil is washed multiple times with a soil washing composition containing components (a), (b) and (c), the amount of OH radicals in the composition gradually decreases in the second and subsequent washings of the soil. This is presumed to be due to the fact that the addition of a compound capable of generating hydroxyl radicals in the first washing makes the redox potential of the soil washing composition for the second washing higher than that of the soil washing composition for the first washing, slowing the deactivation of OH radicals. The soil washing method and the kit for producing the soil washing composition of the present invention are not limited to the above-mentioned mechanism of action.

[0011] The soil washing method of the present invention involves washing the soil two or more times by contacting the soil with a soil washing agent composition containing the following components (a), (b), and (c) and water, and then removing a part or all of the soil washing agent composition from the mixture of the soil and the soil washing agent composition. Component (a): one or more compounds selected from compounds capable of generating hydroxyl radicals (b) Ingredient: Divalent iron compound (c) Component: one or more selected from hydroxycarboxylic acids, polycarboxylic acids, and their salts

[0012] <Soil Cleaning Agent Composition> First, the soil washing agent composition used in the soil washing method of the present invention will be described in detail. The soil washing agent composition of the present invention contains component (a), component (b), component (c) and water. The soil washing agent composition of the present invention may be a washing agent composition for soil contaminated with one or more selected from petroleum-based compounds, volatile organic compounds and heavy metals, which washes soil contaminated with one or more selected from petroleum-based compounds, volatile organic compounds and heavy metals, or may be a washing agent composition for soil contaminated with petroleum-based compounds, which washes soil contaminated with petroleum-based compounds.

[0013] <Component (a)> Component (a) is a compound capable of generating hydroxyl radicals. The component (a) may be a compound that generates hydroxyl radicals through the Fenton reaction. Examples of the component (a) include one or more compounds selected from hydrogen peroxide, percarbonates, and organic peracids, and from the viewpoints of availability, economy, and hydroxyl radical generating ability, one or more compounds selected from hydrogen peroxide and percarbonates are preferred. Examples of the percarbonates include alkali metal percarbonates such as sodium percarbonate and potassium percarbonate, and from the viewpoints of availability, economy, and hydroxyl radical generating ability, sodium percarbonate is preferred.

[0014] <(b) Component> Component (b) is a divalent iron compound. Component (b) may be one or more selected from sulfates, nitrates, halides, perchlorates, hydroxides, and oxides of iron(II). From the viewpoints of solubility in water, availability, and economy, component (b) is preferably one or more selected from sulfates, nitrates, and hydrochlorides of iron(II). These salts may be hydrates. Component (b) is preferably ferrous sulfate. Examples of ferrous sulfate include ferrous sulfate anhydride and ferrous sulfate heptahydrate. Component (b) may be a compound capable of generating divalent iron ions in the soil washing agent composition, i.e., component (b) may be a mixture of a trivalent iron compound and a reducing agent capable of reducing the trivalent iron ions of the iron compound to divalent iron ions. The trivalent iron compound may be one or more selected from sulfates, nitrates, halides, perchlorates, hydroxides, and oxides of iron (III). As the trivalent iron compound, ferric polysulfate, ferric chloride, and the like may also be used. As a reducing agent capable of reducing trivalent iron ions to divalent iron ions, component (d) which will be described in detail later may be used.

[0015] <(c) component> Component (c) is at least one member selected from the group consisting of hydroxycarboxylic acids, polycarboxylic acids, and salts thereof. From the viewpoint of complex formation with divalent iron ions, component (c) is preferably one or more selected from monovalent organic acids, divalent organic acids, and salts thereof, each having a first dissociation constant (hereinafter referred to as pKa1) of 1.2 or more and 4.6 or less. From the viewpoint of complex formation with divalent iron ions, the pKa1 of the component (c) is preferably 1.8 or more, more preferably 2.5 or more, and is preferably 3.9 or less, more preferably 3.3 or less. The molecular weight (Mw) of the organic acid of component (c) may be, for example, 70 or more, further 75 or more, further 95 or more, and 200 or less, further 180 or less, further 165 or less, further 160 or less, from the viewpoint of complex formation with divalent iron ions. The number of carbon atoms in the organic acid of component (c) is preferably 2 or more and preferably 8 or less, more preferably 6 or less, and even more preferably 4 or less, from the viewpoint of complex formation with divalent iron ions. From the viewpoint of complex formation with divalent iron ions, the organic acid of component (c) is preferably a carboxylic acid, and more preferably a monocarboxylic acid or dicarboxylic acid. Examples of component (c) include one or more organic acids or salts thereof selected from hydroxymonocarboxylic acids having 2 or 3 carbon atoms and a molecular weight of 70 to 200, and further 180 to 180; dicarboxylic acids having 3 or 4 carbon atoms and a molecular weight of 70 to 200, and further 180 to 180; hydroxycarboxylic acids having 5 to 8 carbon atoms and a molecular weight of 70 to 200, and further 180 to 180; and salts thereof. From the viewpoint of complex formation with divalent iron ions, the components (c) are tartaric acid (pKa1: 2.98, Mw: 150.1), succinic acid (pKa1: 4.19, Mw: 118.1), malic acid (pKa1: 3.4, Mw: 134.1), malonic acid (pKa1: 2.9, Mw: 104.1), 3-hydroxypropionic acid (pKa1: 4.5, Mw: 90.1), and lactic acid (pKa1: 3.86, Mw: 90.1). ), glycolic acid (pKa1: 3.83, Mw: 76.1), maleic acid (pKa1: 1.92, Mw: 116.1), fumaric acid (pKa1: 3.02, Mw: 116.1), gluconic acid (pKa1: 3.86, Mw: 196), and salts thereof, or one or more organic acids or salts thereof are preferred, and one or more selected from tartaric acid, malic acid, succinic acid, and salts thereof are more preferred.

[0016] Examples of salts of component (c) include alkali metal salts such as sodium and potassium, and alkaline earth metal salts such as calcium.

[0017] The soil washing agent composition of the present invention contains water. The water may be tap water, groundwater, river water, lake water, well water, etc. The water may be the remainder of the composition excluding the components (a), (b), (c) and other components, and for example, the content of water in the composition is 90% by mass or more and 99.9% by mass or less.

[0018] <Composition, optional ingredients, etc.> The soil washing composition of the present invention, i.e., the soil washing composition to be contacted with soil during soil washing, contains component (a) in an amount of preferably 0.01 mass % or more, more preferably 0.03 mass % or more, and even more preferably 0.07 mass % or more from the viewpoint of generating hydroxyl radicals, and preferably 3.0 mass % or less, more preferably 1.0 mass % or less, and even more preferably 0.5 mass % or less, from the viewpoint of component (a) remaining in water due to an instantaneous reaction.

[0019] The amount of component (a) used in the soil washing agent composition of the present invention is, in terms of hydrogen peroxide, preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and even more preferably 0.07% by mass or more from the viewpoint of generating hydroxyl radicals, and is preferably 3.0% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less, from the viewpoint of component (a) remaining in water due to an instantaneous reaction.

[0020] The soil washing composition of the present invention, i.e., the soil washing composition to be contacted with soil during soil washing, contains component (b) in an amount, calculated as iron ion, of preferably 0.005% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.02% by mass or more from the viewpoint of hydroxyl radical production, and preferably 0.2% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.06% by mass or less from the viewpoint of the amount of iron sludge produced.

[0021] The soil washing composition of the present invention, i.e., the soil washing composition to be contacted with soil during soil washing, contains component (c) in an amount of preferably 0.001 mass % or more, more preferably 0.005 mass % or more, and even more preferably 0.01 mass % or more from the viewpoint of complex formation of divalent iron ions, and preferably 1.0 mass % or less, more preferably 0.5 mass % or less, even more preferably 0.3 mass % or less, and even more preferably 0.2 mass % or less from the viewpoint of treatment of washing wastewater after washing.

[0022] In the soil washing composition of the present invention, the mass ratio (a) / (b) of the content of component (a) in terms of hydrogen peroxide to the content of component (b) in terms of iron ions is preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 1.0 or more, from the viewpoint of efficient production of hydroxyl radicals, and is preferably 100 or less, more preferably 50 or less, and even more preferably 10 or less, from the viewpoint of remaining excess component (a).

[0023] In the soil washing agent composition of the present invention, the mass ratio (b) / (c) of the content of component (b) calculated as iron ions to the content of component (c) is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.1 or more, from the viewpoint of continuous generation of hydroxyl radicals due to complex formation, and is preferably 10 or less, more preferably 5 or less, and even more preferably 3 or less, from the viewpoint of treatment of washing wastewater after washing.

[0024] <(d) component> The soil washing agent composition of the present invention may optionally contain (d) a compound having a reducing effect capable of reducing trivalent iron ions to divalent iron ions (excluding component (c)) (hereinafter referred to as component (d)). The component (d) is preferably one or more selected from ascorbic acid and its salts, tannic acid, erythorbic acid and its salts, ascorbic acid derivatives and its salts, hydrosulfite, hydroxymethanesulfonate, pyrosulfite, sulfite, hydrogensulfite, thiosulfate, thiourea dioxide, and gallic acid, and from the viewpoints of availability and reducibility, it is preferably one or more selected from ascorbic acid and its salts, hydrosulfite, and hydroxymethanesulfonate, and from the viewpoint of the amount of hydroxyl radical generated, it is preferably one or more selected from ascorbic acid and its salts. Examples of salts of the component (d) include alkali metal salts such as sodium and potassium, and alkaline earth metal salts such as calcium.

[0025] When the soil washing agent composition of the present invention contains component (d), the soil washing agent composition of the present invention, i.e., the soil washing agent composition to be contacted with soil during soil washing, contains component (d) in an amount of preferably 0.005 mass % or more, more preferably 0.01 mass % or more, and even more preferably 0.05 mass % or more from the viewpoint of the amount of hydroxyl radicals generated, and preferably 0.3 mass % or less, more preferably 0.2 mass % or less, and even more preferably 0.1 mass % or less from the viewpoint of treatment of washing wastewater after washing.

[0026] When the soil washing composition of the present invention contains component (d), the mass ratio (b) / (d) of the content of component (b) calculated as iron ions to the content of component (d) in the soil washing composition of the present invention is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.1 or more, from the viewpoint of efficient production of hydroxyl radicals by reduction action, and is preferably 20 or less, more preferably 10 or less, and even more preferably 3 or less, from the viewpoint of treatment of washing wastewater after washing.

[0027] <(e) component> The soil washing agent composition of the present invention may optionally contain (e) one or more selected from polyferric sulfate and ferric chloride [hereinafter referred to as component (e)]. Polyferric sulfate can be prepared, for example, by the method described in JP-B-51-17516, by oxidizing sulfuric acid in an aqueous solution of ferrous sulfate to less than 0.5 mol per mol of ferrous sulfate.

[0028] When the soil washing agent composition of the present invention contains component (e), the soil washing agent composition of the present invention, i.e., the soil washing agent composition to be contacted with soil during soil washing, contains component (e) in an amount of preferably 0.01 mass % or more, more preferably 0.05 mass % or more, and even more preferably 0.1 mass % or more from the viewpoint of improving the washing properties of aromatic compounds and unsaturated hydrocarbon components, and preferably 2.0 mass % or less, more preferably 1.0 mass % or less, and even more preferably 0.5 mass % or less from the viewpoint of reducing the amount of iron sludge generated.

[0029] <Other ingredients> The soil washing composition of the present invention may contain other optional components as appropriate depending on the purpose, within the range that does not impair the effects of the present invention. For example, the soil washing composition of the present invention may contain components such as gelling inhibitors, thickeners, fragrances, dyes, pigments, bactericides, preservatives, pH adjusters, and pH buffers.

[0030] The soil washing agent composition of the present invention can wash soil contaminated with one or more selected from petroleum compounds, volatile organic compounds, and heavy metals. That is, the present invention can remove oily dirt such as petroleum compounds, volatile organic compounds, and heavy metals from soil. Examples of petroleum compounds include petroleum hydrocarbons. Examples of petroleum compounds may be gasoline, kerosene, light oil, heavy oil, and machine oil. Examples of volatile organic compounds may be benzene, toluene, xylene, and volatile organic chlorine compounds such as trichloroethylene, dichloromethane, tetrachloroethylene, and carbon tetrachloride. Examples of heavy metals may be lead, hexavalent chromium, cadmium, arsenic, mercury, and compounds thereof.

[0031] The soil washing composition of the present invention may be a soil washing composition comprising component (a), component (b), component (c), and water, for washing soil contaminated with one or more selected from petroleum compounds, volatile organic compounds, and heavy metals. The above-mentioned preferred embodiments can be appropriately applied to this soil washing composition. In addition, the contents of each of the above-mentioned components can be applied to this soil washing composition by replacing them with the blending amounts.

[0032] <Kit for producing soil cleaning agent composition> The present invention provides a kit for producing a soil washing agent composition comprising multiple agents including components selected from component (a), component (b), and component (c), wherein component (a) and component (b) are contained in separate agents.

[0033] Examples of kits of the present invention include: (1) A kit consisting of a preparation containing component (a) but not containing component (b) and a preparation containing components (b) and (c) but not containing component (a). (2) A kit consisting of a preparation containing the components (a) and (c) but not the component (b), and a preparation containing the component (b) but not the component (a). (3) A kit consisting of a preparation containing component (a) but not containing component (b), a preparation containing component (b) but not containing component (a), and a preparation containing component (c) (which preparation may optionally contain component (a) or component (b)). Examples include:

[0034] In the kit of the present invention, it is preferable to store and supply the oxidizing component (a) and the divalent iron compound (b) separately from the viewpoint of compound stability, and it is preferable to supply the kit of an agent containing the components (a) and (c) and an agent containing the component (b) from the viewpoint of workability during production of the soil washing agent composition. When the components (b) and (c) are solid or liquid, and the reactivity of the components (b) and (c) is low, it is possible to supply the kit of an agent containing the components (a) and an agent containing the components (b) and (c). From the viewpoint of the stability and workability of the agent, it is more preferable to use a kit consisting of an agent containing the components (a) and (c) but not the component (b), and an agent containing the component (b) but not the component (a). Specific examples and preferred examples of the components (a), (b), and (c) are the same as those of the soil washing agent composition of the present invention. The matters described in the soil washing agent composition of the present invention can be appropriately applied to the kit of the present invention.

[0035] In each of the agents constituting the kit of the present invention, the contents of the components (a), (b) and (c) may be, for example, amounts such that a soil washing agent composition of the present invention containing these components in the contents or mass ratios within the above-mentioned ranges can be produced.

[0036] Each of the agents constituting the kit of the present invention may optionally contain component (d), component (e) and other optional components. The preferred embodiments are the same as those of the soil washing agent composition of the present invention. It is preferable that components (d) and (e) are contained in an agent that contains component (b) but does not contain component (a).

[0037] A plurality of agents including components selected from component (a), component (b), component (c), optionally component (d), and optionally component (e) are mixed at the time of washing soil, and either undiluted or diluted with water to prepare a specified soil washing agent composition. The kit for producing the soil washing composition of the present invention is suitably used for preparing the soil washing composition of the present invention.

[0038] The agent containing component (a) preferably contains component (a) in an amount of 3% by mass or more, further 5% by mass or more, further 25% by mass or more, and 100% by mass or less, further 90% by mass or less, and may contain 100% by mass. Furthermore, the agent containing the component (b) preferably contains 5% by mass or more of the component (b), further 10% by mass or more, further 20% by mass or more, and preferably 100% by mass or less, further preferably 90% by mass or less, and may contain 100% by mass of the component (b). Furthermore, the agent containing the component (c) preferably contains 5% by mass or more, further 10% by mass or more, further 20% by mass or more, and 100% by mass or less, further 90% by mass or less of the component (c), and may contain 100% by mass. Furthermore, the agent containing the component (d) preferably contains 5% by mass or more, further 10% by mass or more, further 20% by mass or more, and 100% by mass or less, further 90% by mass or less of the component (d), and may contain 100% by mass. Furthermore, the agent containing the component (e) preferably contains 5% by mass or more, further 10% by mass or more, further 20% by mass or more, and 100% by mass or less, further 90% by mass or less of the component (e), and may contain 100% by mass.

[0039] <How to wash soil> The soil washing method of the present invention is a soil washing method which involves contacting soil with a soil washing agent composition containing the following components (a), (b), and (c) and water, and then performing a soil washing process two or more times to remove a part or all of the soil washing agent composition from the mixture of the soil and the soil washing agent composition: Component (a): one or more compounds selected from compounds capable of generating hydroxyl radicals (b) Ingredient: Divalent iron compound (c) Component: one or more selected from hydroxycarboxylic acids, polycarboxylic acids, and their salts

[0040] In addition, the soil washing method of the present invention may be a method for washing excavated soil, which comprises contacting excavated soil contaminated with one or more selected from petroleum-based compounds, volatile organic compounds, and heavy metals with a soil washing agent composition containing the components (a), (b), and (c) and water, and then performing two or more soil washings of the soil, which include removing a part or all of the soil washing agent composition from a mixture of the soil and the soil washing agent composition. The matters described in the soil washing composition of the present invention can be appropriately applied to the soil washing method of the present invention. For example, specific examples and preferred aspects of the (a) component, the (b) component, the (c) component, and optional components in the soil washing method of the present invention are the same as those in the soil washing composition of the present invention. The soil washing method of the present invention can use the soil washing composition of the present invention and / or a kit for producing the soil washing composition of the present invention.

[0041] In the soil washing method of the present invention, soil and water can be mixed, and then components (a), (b) and (c) can be mixed therewith. Also, in the soil washing method of the present invention, soil can be mixed with an agent containing components (a) and (c), an agent containing (b) and water.

[0042] In the soil washing method of the present invention, in the mixture of soil and soil washing agent composition, the ratio of the soil washing agent composition (liquid) to soil (solid) (liquid / solid mass ratio: liquid-solid ratio) is preferably 0.6 or more, more preferably 0.7 or more, and even more preferably 0.8 or more from the viewpoint of efficient washing, and is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.2 or less, from the viewpoint of reducing washing wastewater.

[0043] In the soil washing method of the present invention, the time for contacting the soil with the soil washing agent composition is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 15 minutes or more, from the viewpoint of washing performance, and is preferably 24 hours or less, more preferably 16 hours or less, and even more preferably 10 hours or less, from the viewpoint of work efficiency. In the soil washing method of the present invention, the mixture obtained by mixing the soil and the soil washing agent composition may be stirred and mixed. The time for stirring and mixing the mixture is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 15 minutes or more from the viewpoint of mixing uniformity, and is preferably 2 hours or less, more preferably 1 hour or less, and even more preferably 30 minutes or less from the viewpoint of energy consumption of the stirrer.

[0044] In the cleaning method of the present invention, from the viewpoint of cleaning performance, component (a) can be used in an amount of preferably 0.005 mass % or more, more preferably 0.01 mass % or more, even more preferably 0.04 mass % or more, and preferably 1.5 mass % or less, more preferably 0.5 mass % or less, even more preferably 0.3 mass % or less, relative to the mixture of soil and water.

[0045] In the soil washing method of the present invention, component (b) can be used in an amount of preferably 0.002 mass% or more, more preferably 0.005 mass% or more, even more preferably 0.01 mass% or more, and preferably 0.1 mass% or less, more preferably 0.05 mass% or less, even more preferably 0.03 mass% or less, based on the mixture of soil and water.

[0046] In the soil washing method of the present invention, the total amount of components (a) and (b) can be preferably 0.007 mass% or more, more preferably 0.015 mass% or more, and preferably 1.6 mass% or less, more preferably 0.5 mass% or less, based on the mixture of soil and water.

[0047] In the soil washing method of the present invention, component (c) can be used in an amount of preferably 0.005 mass % or more, more preferably 0.01 mass % or more, and preferably 0.5 mass % or less, based on the mixture of soil and water.

[0048] In the soil washing method of the present invention, the total amount of components (a), (b) and (c) can be preferably 0.012 mass% or more, more preferably 0.025 mass% or more, and preferably 2.1 mass% or less, more preferably 0.8 mass% or less, based on the mixture of soil and water.

[0049] In the soil washing method of the present invention, the soil can be washed two or more times, preferably three or more times, from the viewpoint of efficient washing, and preferably five or less times from the viewpoint of treatment of recovered water.

[0050] When soil washing is performed multiple times, the soil is mixed with the soil washing composition of the present invention to wash the soil, and then a part or all of the soil washing composition is removed from the mixture of the soil and the soil washing composition. In the soil washing method of the present invention, a mixing step of mixing the soil with the soil washing composition and a step of removing the soil washing composition from the mixture of the soil and the soil washing composition are performed as one soil washing step, and this step is repeated two or more times. In the soil washing method of the present invention, a procedure for separating the soil from the soil washing composition can be carried out in order to remove a part or all of the soil washing composition from a mixture of the soil and the soil washing composition. Examples of the separation procedure include a procedure for precipitating the soil by standing to remove the supernatant liquid which is the soil washing composition, and a procedure for separating the soil from the soil washing composition by filtration using a mesh or the like. The amount of the soil washing agent composition removed from the mixture of soil and the soil washing agent composition is, from the viewpoint of recontamination, preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more of the soil washing agent composition mixed with the soil, and, from the viewpoint of dehydration, is 100% by mass or less, preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0051] In the method for washing soil of the present invention, rinsing of the washed soil may or may not be performed. From the viewpoint of simplifying the process, etc., the rinsing step may not be performed in the present invention.

[0052] In the soil washing method of the present invention, the excavated soil may be washed at the location where the soil exists (on-site), or at a location other than the original location (outside the site). For example, the excavated soil can be washed in a washing facility installed in a location other than the site. In this case, for example, soil collected by excavation from the site can be transferred to a washing facility installed in a location other than the site and washed. The washing facility is preferably installed near the site. For example, soil can be collected at a specified location (on-site) in a certain area, and the washing facility can be installed in a location other than the collection location in the same area. In this way, the excavated soil can be washed by installing the washing facility as a so-called on-site plant. In addition, when washing in situ, for example, the soil washing composition can be added to an excavated area and easily stirred and washed with heavy machinery (such as a backhoe or a power shovel). In this case, groundwater can be used as a part of the water in the soil washing composition.

[0053] In the soil washing method of the present invention, it is preferable to centrifuge the soil after washing. The conditions of centrifugation are, for example, a centrifugal acceleration of 100 G or more and 1200 G or less, and a treatment time of 1 minute or more and 10 minutes or less. Centrifugation promotes separation of the soil and the liquid phase, making it easy to recover and reuse (backfill) the soil. If a centrifuge is not available, the mixture can be allowed to settle naturally and only the supernatant liquid can be removed. The time for allowing the mixture to settle naturally is preferably 10 minutes or more, more preferably 15 minutes or more, and even more preferably 30 minutes or more.

[0054] After washing, the soil can be reused by backfilling it in the area where it was taken or in another location. EXAMPLES

[0055] The soil washing agent compositions shown in Tables 1 to 3 were prepared using the following components. <Component (a)> Hydrogen peroxide: 30% by weight aqueous solution of hydrogen peroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Sodium percarbonate / sodium carbonate = 4 / 1 (mass ratio): (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Sodium percarbonate / sodium carbonate = 2 / 1 (mass ratio): (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) <(b) Component> FeSO 4 7H 2 O: Iron(II) sulfate heptahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) <(c) component> Tartaric acid: DL-tartaric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Malic acid: DL-Malic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Succinic acid (Hayashi Pure Chemical Industries, Ltd.) Gluconic acid: 50% by weight aqueous solution of gluconic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) <(d) component> Ascorbic acid: L(+)-ascorbic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Hydrosulfite: Sodium hydrosulfite (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) <(e) component> Polyferric sulfate: Polysulfate (specific gravity 1.45 or more (20℃), iron (Fe 3+ ) 11% by mass or more, iron (Fe 2+ ) 0.07% by mass or less, sulfate ions (SO 4 2- ) 25 mass% or less, manufactured by Nittetsu Mining Co., Ltd.) and polyferric sulfate was converted to 37 mass%.

[0056] [How to evaluate cleaning performance] (1) Cleaning test (1-1) Preparation of simulated contaminated sand Commercially available river sand (Akagi Engei sand from the Watarase River in Gunma Prefecture, which had been washed, de-bittered, sieved, and selected) was dried at 105°C for more than 24 hours and cooled to room temperature. Light oil was then added to the river sand at 0.5% by mass (5000 mg / kg), mixed with a hand mixer until uniform, and left to cure at room temperature for more than 7 days to prepare simulated contaminated sand. (1-2) Evaluation of cleaning ability 50 g of the soil washing agent composition was prepared to have the composition shown in the table. However, a kit consisting of 40 g of washing solution A and 10 g of washing solution B was prepared as the soil washing agent composition, and washing solution A and washing solution B were mixed and used during washing. Washing solution A is component (a), and if it contains component (c), it is component (c) with the remainder being water, while washing solution B is component (b), and if it contains component (d), it is component (d), and if it contains component (e), it is component (e) with the remainder being water. 50 g of the simulated contaminated sand prepared in (1-1) was placed in a 100 ml screw tube, 40 g of cleaning solution A was added to the screw tube, and then 10 g of cleaning solution B was added. The sand was stirred and washed for 10 minutes at 20 rpm using an end-over-end rotating mixer (Rota Mix (model: RKVSD), manufactured by Tokyo Glass Machinery Co., Ltd.). After stirring, the tube was left to stand for 30 minutes, and the supernatant was removed to obtain a sample that had been washed once. Separately, washing solution A and washing solution B were added to the screw tube from which the supernatant had been removed, and the same process of stirring, leaving the tube to stand, and removing the supernatant was repeated to obtain samples that had been washed twice and three times. After removing the supernatant, the 100 ml screw tube containing the contaminated sand was dried in a 40°C oven for 7 days. Next, 50 ml of dichloromethane was added to the 100 ml screw tube containing the sample, and the mixture was stirred with a pencil mixer for 1 minute and allowed to stand for 60 minutes. After the supernatant was transferred to a 50 ml screw tube, the dichloromethane was evaporated. After the evaporation, 30 ml of n-hexane was added, and the oil in the screw tube was dissolved in n-hexane. The n-hexane was then filtered through a 0.8 μm filter (ADVANTEC DISMIC25CS080AN), and the filtrate was transferred to a precisely weighed 30 ml screw tube. After the n-hexane was evaporated from the filtrate, it was dried in a 40°C dryer for 2 hours, and the 30 ml screw tube with the extracted oil remaining was precisely weighed. The quantitative results were used to calculate the amount of diesel fuel contained in 50 g of simulated contaminated sand, and the amount of diesel fuel remaining in the simulated contaminated sand (Total Petroleum Hydrocarbon: TPH (mg / kg)) was calculated. (1-3) Evaluation of sludge volume (1-2) During the first washing, the mixture was stirred and washed for 10 minutes using an end-over-end rotating mixer, and then left to stand for 30 minutes. The height of the sludge (a combination of fine particles derived from river sand and insoluble matter derived from iron) was measured, and the sludge volume was calculated from the diameter of the 100 ml screw tube.

[0057] [Table 1]

[0058] [Table 2]

[0059] [Table 3]

Claims

1. A soil cleaning method, which comprises contacting soil with a soil cleaning agent composition containing soil, the following component (a), component (b), component (c) and water, and then removing part or all of the soil cleaning agent composition from the mixture of the soil and the soil cleaning agent composition, and performing the cleaning of the soil two or more times. Component (a): One or more selected from compounds having hydroxyl radical generating ability Component (b): Ferrous compound Component (c): One or more selected from hydroxycarboxylic acids, polycarboxylic acids and their salts

2. The method for cleaning soil according to claim 1, wherein the mixture of soil and the soil cleaning agent composition is stirred and mixed, and then part or all of the soil cleaning agent composition is removed from the mixture.

3. The method for cleaning soil according to claim 1 or 2, wherein component (a) is one or more selected from hydrogen peroxide and sodium percarbonate.

4. The method for cleaning soil according to claim 1 or 2, wherein the soil cleaning agent composition contains component (a) in an amount of 0.01% by mass or more and 1.0% by mass or less.

5. The method for cleaning soil according to claim 1 or 2, wherein component (b) is ferrous sulfate.

6. The method for cleaning soil according to claim 1 or 2, wherein the soil cleaning agent composition contains component (b) in an amount of 0.005% by mass or more and 0.2% by mass or less in terms of iron ions.

7. The method for cleaning soil according to claim 1 or 2, wherein component (c) is one or more selected from monovalent organic acids, divalent organic acids and their salts having a first dissociation constant of 1.2 or more and 4.6 or less.

8. The method for cleaning soil according to claim 1 or 2, wherein the soil cleaning agent composition contains component (c) in an amount of 0.01% by mass or more and 0.3% by mass or less.

9. The soil cleaning agent composition further contains at least one selected from (d) ascorbic acid and its salts, tannic acid, erythorbic acid and its salts, ascorbic acid derivatives and their salts, hydrosulfite, hydroxymethanesulfonate, pyrosulfite, sulfite, bisulfite, thiosulfate, thiourea dioxide, and gallic acid. The method for cleaning soil according to claim 1 or 2.

10. The soil cleaning agent composition contains at least one selected from (e) ferric polysulfate and ferric chloride. The method for cleaning soil according to claim 1 or 2.

11. The soil is soil contaminated with at least one selected from petroleum compounds, volatile organic compounds, and heavy metals. The method for cleaning soil according to claim 1 or 2.

12. A kit for manufacturing a soil cleaning agent composition composed of a plurality of agents containing components selected from the following (a) component, the following (b) component, and the following (c) component, wherein the following (a) component and the following (b) component are contained in different agents. Component (a): At least one selected from compounds having the ability to generate hydroxyl radicals Component (b): Ferrous compounds Component (c): At least one selected from hydroxycarboxylic acids, polycarboxylic acids, and their salts

13. The kit according to claim 12, wherein the component (a) and the component (c) are contained in the same agent.

14. The agent containing the component (b) further contains at least one selected from (d) ascorbic acid and its salts, tannic acid, erythorbic acid and its salts, ascorbic acid derivatives and their salts, hydrosulfite, hydroxymethanesulfonate, pyrosulfite, sulfite, bisulfite, thiosulfate, thiourea dioxide, and gallic acid. The kit according to claim 12 or 13.