Soil cleaning method

Abstract

To provide a soil cleaning method that demonstrates superior effectiveness in decontaminating polluted soil.SOLUTION: A soil cleaning method involves bringing the soil into contact with a soil cleaner composition that contains the following components (a), (b), and (c) as well as water. Components (a): at least one selected from hydrogen peroxide, persulfate and percarbonate, (b): polyferric sulfate, 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. It is a reaction in which divalent iron acts to generate hydroxyl radicals from hydrogen peroxide, 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 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. Patent Document 2 discloses a method for treating colored wastewater, in which the wastewater is first treated with a reducing agent, and then a peroxide and a metal salt are added thereto for treatment. Patent Document 3 discloses a method for deodorizing water to be treated, which comprises adding (1) polyferric sulfate, (2) an iron (II) compound, (3) a magnesium salt, and (4) hydrogen peroxide to the water to be treated, which contains methyl sulfide or methyl disulfide. Patent Document 4 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 2020-195970 A [Patent Document 2] Japanese Patent Application Publication No. 9-85266 [Patent Document 3] Japanese Patent Application Publication No. 11-104660 [Patent Document 4] International Publication No. 2020 / 230626 Summary of the Invention [Problem to be solved by the invention]

[0006] In the past, ferrous sulfate (II) was generally used as a Fenton reaction catalyst. However, ferrous iron is quickly oxidized and precipitated, losing its catalytic activity. Therefore, it is known that the oxidized ferrous iron is reduced in the Fenton reaction system by using a reducing agent in combination, and the oxidized ferrous iron is present as ferrous iron in the system. However, the use of a reducing agent in combination poses a problem in the treatment of the washing wastewater after purification. In general, washing wastewater containing iron ions can be easily insolubilized as ferric hydroxide by adding an alkaline agent to the washing wastewater to remove the iron ions, and the iron can be removed by filtration, etc. However, in washing wastewater containing a reducing agent, it is difficult to insolubilize the iron ions even if an alkaline agent is added, and special treatment, such as adding a strong oxidizing agent, is required. The present invention provides a soil washing method and kit that are excellent in cleaning properties for contaminated soil. [Means for solving the problem]

[0007] The present invention relates to a method for washing soil, which comprises contacting soil with a soil washing agent composition containing the following components (a), (b), and (c) and water: (a) Component: one or more selected from hydrogen peroxide, persulfates, and percarbonates (b) Ingredient: Ferric polysulfate (c) Component: one or more selected from hydroxycarboxylic acids, polycarboxylic acids, and their salts

[0008] The present invention also relates to a soil washing method, which comprises contacting soil with a soil washing agent composition containing the above-mentioned components (a), (b), (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.

[0009] 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 component (a) and the above-mentioned component (b) are contained in different agents. Effect of the Invention

[0010] 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

[0011] The reason why the soil washing method of the present invention has excellent washing properties for contaminated soil is not entirely clear, but is presumed to be as follows. Hydroxyl radicals (also called OH radicals) generated by the Fenton reaction are immediately deactivated, whereas in a system containing one or more selected from hydrogen peroxide, persulfates, and percarbonates as component (a), and ferric polysulfate as component (b), some kind of radical is generated, although the mechanism of generation is unknown. Although the amount of these radicals generated is less than the amount of OH radicals generated in the Fenton reaction, the generated radicals persist for a long time, and therefore it is presumed that the amount of radicals contributing to soil washing increases, thereby improving the soil washability. It is presumed that component (c) forms a complex with trivalent iron ions, thereby increasing the amount of radicals generated, thereby improving the soil cleaning power. It is also believed that when soil is washed multiple times with a soil washing composition containing components (a), (b) and (c), the amount of radicals in the composition decreases more slowly in the second and subsequent soil washings. This is believed to be because the oxidation-reduction potential of the soil washing composition becomes higher than that of the first soil washing due to the addition of the compound capable of generating hydroxyl radicals in the first washing in the second and subsequent soil washings, slowing down the deactivation of radicals. It should be noted that the soil washing method of the present invention is not limited to the above-mentioned mechanism of action.

[0012] The soil washing method of the present invention is a method for washing soil, which comprises contacting soil with a soil washing agent composition containing the following components (a), (b), and (c) and water: (a) Component: one or more selected from hydrogen peroxide, persulfates, and percarbonates (b) Ingredient: Ferric polysulfate (c) Component: one or more selected from hydroxycarboxylic acids, polycarboxylic acids, and their salts The soil washing method of the present invention may be a soil washing method in which soil is contacted with a soil washing agent composition containing the components (a), (b), and (c) and water, and then a part or all of the soil washing agent composition is removed from the mixture of the soil and the soil washing agent composition, the soil washing method being performed two or more times.

[0013] <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 soil washing agent composition for washing soil contaminated with one or more selected from petroleum-based compounds, volatile organic compounds, and heavy metals, a soil washing agent composition for washing soil contaminated with petroleum-based compounds and / or volatile organic compounds, or a soil washing agent composition for washing soil contaminated with petroleum-based compounds.

[0014] <Component (a)> Component (a) is one or more compounds selected from hydrogen peroxide, persulfates, and percarbonates. Examples of the persulfate salt of the component (a) include alkali metal persulfates such as sodium persulfate and potassium persulfate, and examples of the percarbonate salt include alkali metal percarbonates such as sodium percarbonate and potassium percarbonate. From the viewpoints of availability, economy, and radical generation ability, one or more selected from sodium persulfate and sodium percarbonate are preferred, and from the viewpoint of heavy metal elution due to alkalinity, sodium persulfate is more preferred. From the viewpoint of the amount of radicals generated, the component (a) is preferably hydrogen peroxide.

[0015] <(b) Component> Component (b) is polyferric sulfate. Component (b) polyferric sulfate can be prepared, for example, by oxidizing sulfuric acid in an aqueous solution of ferrous sulfate to less than 0.5 moles per mole of ferrous sulfate, according to the method described in JP-B-51-17516. The component (b) is a compound represented by the following general formula (1). [Fe 2 (OH) n (SO 4 ) 3-n / 2 ] m (1) [However, 0 <n≦2、m=f(n)である。〕

[0016] <(c) component> Component (c) is at least one selected from hydroxycarboxylic acids, polycarboxylic acids, and salts thereof. The 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 forming a complex with trivalent 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 forming a complex with trivalent iron ions. From the viewpoint of forming a complex with trivalent iron ions, the number of carbon atoms of 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 forming a complex with trivalent 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. (c) From the viewpoint of forming a complex with trivalent iron ions, the components 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.

[0017] Examples of salts of component (c) include alkali metal salts such as sodium and potassium, and alkaline earth metal salts such as calcium.

[0018] 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), and (c) and the optional components described below, and for example, the content of water in the composition is 90% by mass or more and 99.9% by mass or less.

[0019] <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 radical generation, 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 preventing excess component (a) remaining in water.

[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 of preferably 0.01 mass % or more, more preferably 0.02 mass % or more, and even more preferably 0.05 mass % or more from the viewpoint of radical generation, 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 the amount of iron sludge generated during wastewater treatment.

[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 0.01 mass % or more, more preferably 0.02 mass % or more, and even more preferably 0.05 mass % or more from the viewpoint of iron ion complex formation, 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 agent composition of the present invention, the mass ratio (a) / (b) of the content of component (a) to the content of component (b) is, from the viewpoint of efficient radical generation, preferably 0.05 or more, more preferably 0.1 or more, even more preferably 0.2 or more, still more preferably 0.5 or more, and still more preferably 0.7 or more, and from the viewpoint of excess component (a) remaining, is preferably 20 or less, more preferably 10 or less, even more preferably 5 or less, still more preferably 4 or less, still more preferably 3 or less, and still more preferably 2 or less.

[0023] In the soil washing agent composition of the present invention, the mass ratio (b) / (c) of the content of the component (b) to the content of the component (c) is, from the viewpoint of continuous generation of hydroxyl radicals through complex formation, preferably 0.05 or more, more preferably 0.1 or more, even more preferably 0.5 or more, still more preferably 0.7 or more, still more preferably 1 or more, and from the viewpoint of treatment of washing wastewater after washing, is preferably 80 or less, more preferably 40 or less, even more preferably 20 or less, still more preferably 10 or less, still more preferably 5 or less.

[0024] <(d) component> From the viewpoint of treating washing wastewater, the soil washing agent composition of the present invention preferably does not contain a water-soluble reducing agent (d). Regarding the water-soluble reducing agent of component (d), the term "water-soluble" may mean, for example, that 1.0 g or more of the reducing agent dissolves in 100 g of water at 20° C. Component (d) is a compound such that the redox potential of a 1% by mass aqueous solution of the water-soluble reducing agent, obtained by dissolving the water-soluble reducing agent of component (d) in ion-exchanged water at 20°C, is lower than the redox potential of ion-exchanged water at 20°C. The oxidation-reduction potentials in ion-exchanged water and in a 1% by mass aqueous solution of component (d) are oxidation-reduction potentials measured by the following method. Component (d) may be, for example, a compound having a reducing action capable of reducing trivalent iron ions to divalent iron ions. Specific examples of component (d) include ascorbic acid and its salts, tannic acid, erythorbic acid and its salts, hydrosulfite, hydroxymethanesulfonate, pyrosulfite, sulfite, hydrogensulfite, thiosulfate, thiourea dioxide, gallic acid, etc. Examples of salts of component (d) include alkali metal salts such as sodium and potassium, and alkaline earth metal salts such as calcium.

[0025] <Method for measuring the oxidation-reduction potential of ion-exchanged water and a 1 mass % aqueous solution of component (d)> The oxidation-reduction potentials of ion-exchanged water and a 1% by mass aqueous solution of component (d) at 20° C. were measured by the following method. 99 g of 20°C ion-exchanged water is weighed into a 100 ml beaker, and the electrodes of an oxidation-reduction potentiometer (Mother Tools Digital ORP Meter YK-23RP) are immersed in it. The value measured after 3 minutes is regarded as the "oxidation-reduction potential of ion-exchanged water at 20°C." 1 g of component (d) is added to 99 g of this ion-exchanged water, mixed with a magnetic stirrer, and after confirming that it is completely dissolved, the electrodes of an oxidation-reduction potentiometer (Mother Tools Digital ORP Meter YK-23RP) are similarly immersed, and the value measured after 3 minutes is the "oxidation-reduction potential of a 1% by mass aqueous solution (20°C) of the water-soluble reducing agent, component (d)." Component (d) is a compound for which the value obtained by subtracting the "oxidation-reduction potential of a 1% by mass aqueous solution (20°C) of the water-soluble reducing agent, component (d)" from the "oxidation-reduction potential of ion-exchanged water at 20°C" is negative.

[0026] From the viewpoint of washing wastewater treatment, the content of the component (d) in the soil washing composition of the present invention is preferably 0.01 mass% or less, more preferably 0.008 mass% or less, even more preferably 0.005 mass% or less, and 0 mass% or more. It is preferable that the soil washing composition of the present invention does not contain the component (d), that is, the content of the component (d) in the soil washing composition is 0 mass%. In the soil washing agent composition of the present invention, by setting the content of the component (d) in the composition within the above range, the treatment of washing wastewater after soil washing becomes easy.

[0027] <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.

[0028] 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, heavy metals, and the like from soil. Examples of petroleum compounds include petroleum hydrocarbons such as gasoline, kerosene, light oil, heavy oil, and machine oil. Examples of volatile organic compounds include benzene, toluene, xylene, and volatile organic chlorine compounds such as trichloroethylene, dichloromethane, tetrachloroethylene, and carbon tetrachloride. Examples of heavy metals include lead, hexavalent chromium, cadmium, arsenic, mercury, and compounds thereof.

[0029] 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.

[0030] <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 the following component (a) and component (b) are contained in separate agents:

[0031] 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:

[0032] In the kit of the present invention, it is preferable to store and supply the oxidizing component (a) and the polyferric sulfate component (b) separately from the viewpoint of compound stability, and it is preferable to supply them as a 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 them as a 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.

[0033] 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.

[0034] A plurality of agents containing components selected from component (a), component (b) and component (c) are mixed at the time of washing soil, and then 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.

[0035] 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.

[0036] <How to wash soil> The method for washing soil of the present invention is a method for washing soil, which comprises contacting soil with a soil washing agent composition containing the following components (a), (b), and (c) and water: (a) Component: one or more selected from hydrogen peroxide, persulfates, and percarbonates (b) Ingredient: Ferric polysulfate (c) Component: one or more selected from hydroxycarboxylic acids, polycarboxylic acids, and their salts The soil washing method of the present invention may be a soil washing method in which soil is contacted with a soil washing agent composition containing the components (a), (b), and (c) and water, and then a part or all of the soil washing agent composition is removed from the mixture of the soil and the soil washing agent composition, the soil washing agent composition being performed two or more times.

[0037] In the soil washing method of the present invention, the soil washing agent composition preferably contains the following component (d) in an amount of 0.01 mass % or less, from the viewpoint of improving the ability to remove iron ions contained in the washing waste liquid: Component (d): a water-soluble reducing agent, the redox potential of a 1% by mass aqueous solution of the water-soluble reducing agent dissolved in ion-exchanged water at 20°C being lower than the redox potential of ion-exchanged water at 20°C.

[0038] In the soil washing method of the present invention, by setting the content of component (d) in the soil washing agent composition within the content range of component (d) described above for the soil washing agent composition, treatment of washing wastewater after soil washing becomes easy. The component (d) is the same as the component (d) mentioned in the soil washing agent composition of the present invention. In the presence of the water-soluble reducing agent (component (d)), trivalent iron ions become divalent iron ions. In addition, while trivalent iron ions are likely to precipitate in the washing wastewater, divalent iron ions are unlikely to precipitate, and the removability of iron from the washing wastewater tends to decrease. Examples of component (d) include ascorbic acid and its salts, tannic acid, erythorbic acid and its salts, ascorbic acid derivatives and their salts, hydrosulfite, hydroxymethanesulfonate, pyrosulfite, sulfite, hydrogensulfite, thiosulfate, thiourea dioxide, and gallic acid.

[0039] 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 components (a), (b) and (c) 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.

[0040] 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.

[0041] In the soil washing method of the present invention, in a mixture of soil and soil washing composition, the ratio of the amount of the soil washing composition (liquid) to the amount of the 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.

[0042] 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.

[0043] In the soil washing method of the present invention, from the viewpoint of washing properties, 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] In the soil washing method of the present invention, the soil is washed at least once, preferably at least twice, more preferably at least three times from the viewpoint of improving washability, and preferably not more than five times from the viewpoint of treating washing wastewater.

[0049] 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 can be repeated two or more times.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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 soil in situ, 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.

[0054] 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 soil can be allowed to settle naturally and only the supernatant liquid can be removed. The time for allowing the soil to settle naturally is preferably 10 minutes or more, more preferably 15 minutes or more, and even more preferably 30 minutes or more.

[0055] After washing, the soil can be reused by backfilling it in the area where it was taken or in another location. EXAMPLES

[0056] The soil washing agent compositions shown in Tables 1 and 2 were prepared using the following components. <Component (a)> Hydrogen peroxide: 30% by weight aqueous solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Sodium persulfate: (Fujifilm Wako Pure Chemical Industries, Ltd.) <(b) 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%. <(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 (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.)

[0057] [How to evaluate cleaning performance] (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.

[0058] (2) Evaluation of cleaning ability A soil washing composition of 50 g was prepared so as to have the composition shown in the table. However, the soil washing composition was prepared by using 40 g of washing solution A.1 and 10g of cleaning solution B 1 A kit consisting of the above was prepared, and cleaning solution A was used during cleaning. 1 and cleaning solution B 1 The cleaning solution A was mixed and used. 1 is component (a), and if component (c) is included, component (c), and the balance is water, and cleaning solution B is 1 is component (b), and if component (d) is contained, it is component (d), and the remainder is water. Put 50 g of the simulated contaminated sand prepared in (1) into a 100 ml screw tube, and add cleaning solution A to the screw tube. 1 After adding 40g of cleaning solution B, 1 10 g of the above was added, and the mixture was stirred and washed for 10 minutes at 20 rpm using an end-over-end rotating mixer (Rotor 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. 1 and cleaning solution B 1 The mixture was stirred, allowed to stand, and the supernatant was removed in the same manner to obtain samples that had been washed twice and samples that had been washed 3 times. After removing the supernatant, the 100 ml screw tube containing the simulated 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, 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.

[0059] [Method for evaluating wastewater treatability (iron sedimentation)] A soil washing composition of 300 g was prepared so as to have the composition shown in the table. However, the soil washing composition was prepared using 200 g of washing solution A. 2 and 100g of cleaning solution B 2 A kit consisting of the above was prepared, and cleaning solution A was used during cleaning. 2 and cleaning solution B 2 The cleaning solution A was mixed and used. 2 is component (a), and if component (c) is included, component (c), and the balance is water, and cleaning solution B is 2 is component (b), and if component (d) is contained, it is component (d), and the remainder is water. In a 300 ml beaker, add cleaning solution A. 2 After adding washing solution B 2 The mixed cleaning solution containing the above was stirred for 90 minutes using a magnetic stirrer without adding the simulated contaminated sand. After stirring, the mixed cleaning solution was immediately neutralized to pH 10.5 with 48% sodium hydroxide, left to stand for 24 hours, and the state of iron precipitation was visually determined from the appearance. ○: Iron precipitation is confirmed and the supernatant is not colored ×: No iron precipitate and the supernatant is brown

[0060] The mixed cleaning solution above is a model of cleaning wastewater, and in Examples 1-1 and 1-2, it is found that by shifting the cleaning wastewater to an alkaline region, it is easy to remove the iron ions contained in the cleaning wastewater. For example, by adding a polymer flocculant to the cleaning wastewater and filtering it, it becomes easy to perform activated carbon adsorption treatment to remove oil contained in the cleaning wastewater.

[0061] [Method for measuring the difference in redox potential of component (d)] 99 g of ion-exchanged water at 20°C was weighed into a 100 ml beaker, and the electrodes of an oxidation-reduction potentiometer (Mother Tools digital ORP meter YK-23RP) were immersed in it. The value measured after 3 minutes was regarded as the "oxidation-reduction potential of ion-exchanged water at 20°C." 1 g of component (d) was added to 99 g of this ion-exchanged water, mixed with a magnetic stirrer, and after confirming that it was completely dissolved, the electrodes of an oxidation-reduction potentiometer (digital ORP meter YK-23RP manufactured by Mother Tools) were similarly immersed in the solution. The value measured after 3 minutes was regarded as the "oxidation-reduction potential of a 1% by mass aqueous solution (20°C) of the water-soluble reducing agent, which is component (d)." The difference in the redox potential of component (d) was calculated by subtracting the "redox potential of a 1 mass % aqueous solution (20°C) of the water-soluble reducing agent, component (d)" from the "redox potential of ion-exchanged water at 20°C."

[0062] [Table 1]

[0063] [Table 2]

Claims

1. A method for cleaning soil, which comprises bringing a soil cleaning agent composition containing the following component (a), component (b), component (c) and water into contact with the soil. Component (a): at least one selected from hydrogen peroxide, persulfate and percarbonate Component (b): ferric polysulfate Component (c): at least one selected from hydroxycarboxylic acid, polycarboxylic acid and their salts

2. A method for cleaning soil, which comprises bringing a soil cleaning agent composition containing the following component (a), component (b), component (c) and water into contact with the soil, 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): at least one selected from hydrogen peroxide, persulfate and percarbonate Component (b): ferric polysulfate Component (c): at least one selected from hydroxycarboxylic acid, polycarboxylic acid and their salts

3. The method for cleaning soil according to claim 1 or 2, wherein the content of the following component (d) in the soil cleaning agent composition is 0.01% by mass or less. Component (d): a water-soluble reducing agent, and a compound in which the redox potential of a 1% by mass aqueous solution of the water-soluble reducing agent dissolved in ion-exchanged water at 20 °C is lower than the redox potential of ion-exchanged water at 20 °C

4. The method for cleaning soil according to claim 1 or 2, wherein the mixture of the soil and the soil cleaning agent composition is stirred and mixed.

5. The method for cleaning soil according to claim 1 or 2, wherein the persulfate of component (a) is sodium persulfate.

6. 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.

7. The soil cleaning agent composition contains the component (b) in an amount of 0.01% by mass or more and 1.5% by mass or less, and the method for cleaning soil according to claim 1 or 2.

8. The component (c) is at least one 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, and the method for cleaning soil according to claim 1 or 2.

9. The component (c) is at least one selected from tartaric acid, succinic acid, malic acid, gluconic acid, and their salts, and the method for cleaning soil according to claim 1 or 2.

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

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

12. A kit for producing a soil cleaning agent composition composed of a plurality of agents containing components selected from the following component (a), component (b), and component (c), wherein the following component (a) and the following component (b) are contained in separate agents. Component (a): At least one selected from hydrogen peroxide, persulfate, and percarbonate Component (b): Ferric polysulfate Component (c): At least one selected from hydroxycarboxylic acids, polycarboxylic acids, and their salts