Method for modifying mud

Abstract

To provide a modification method capable of surely solidifying highly water-containing soft mud and surely reducing the elution of heavy metals or the like.SOLUTION: In the method for modifying mud, a first chemical is added to and mixed with target mud having a water content of 10 to 70%, and then a second chemical is added thereto. The first chemical is a liquid material in which an alkali silicate composed of an alkali oxide and silicon dioxide is mixed with water, and a molar ratio of the silicon dioxide to the alkali oxide is 2.4 to 4.1. The amount of the alkali silicate added per 1m3 of the target mud is 150 to 1200mol in terms of silica dioxide and 40 to 350mol in terms of alkali oxide. The second agent contains a substance that generates trivalent iron ions. The amount of the ferric ion-generating material added per 1m3 of the target mud is 20 to 300mol in terms of the amount of ferric ions generated.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for modifying mud. [Background technology]

[0002] High-moisture soft mud is generated during shield tunneling, river channel excavation, dredging, and other construction work. High-moisture soft mud has a high water content, making it difficult to handle, for example, during transportation. Furthermore, if the high-moisture soft mud contains heavy metals, it is necessary to reduce their elution. To address these issues, a treatment method has been known in the past for mud generated by slurry shield tunneling, in which a solidified body with a high cone index is formed and the elution of heavy metals from this solidified body is reduced (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6084745 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional treatment methods have sometimes failed to achieve their full effect due to various reasons. Therefore, the present invention aims to provide a modification method for high-moisture soft mud that can reliably solidify the mud and reliably reduce the elution of heavy metals, etc. [Means for solving the problem]

[0005] The present invention is a method for modifying mud, in which a first agent is added to and mixed with target mud having a water content of 10 to 70%, and then a second agent is added. The first agent is a liquid mixture of water and an alkali silicate composed of an alkali oxide and silicon dioxide, and the molar ratio of silicon dioxide to alkali oxide is 2.4 to 4.1. 3The amount of alkali silicate added per 1 m of target mud is 150 to 1200 mol in terms of silicon dioxide and 40 to 350 mol in terms of alkali oxide, and the second agent contains a substance that generates trivalent iron ions, 3 The method for improving mud soil is provided, in which the amount of the substance that generates trivalent iron ions added per unit of soil is 20 to 300 mol in terms of the amount of trivalent iron ions generated.

[0006] The solidification of the target mud proceeds through polymerization, gelation, and chemical bonding of the silica in the first agent to the soil particles. The reaction is accelerated by the metal ions provided by the second agent and the change in pH from alkaline to neutral. The pH of the target mud is adjusted to the appropriate range by the alkaline first agent and the acidic second agent. The addition of the second agent promotes the insolubilization of heavy metals, primarily due to the action of trivalent iron ions generated by the second agent.

[0007] The present invention may further have at least one of the following characteristics. ·Alkali silicate is sodium silicate, and alkali oxide is sodium oxide. The molar ratio of the amount of trivalent iron ions to the total amount of silicon dioxide and alkali oxide is 0.05 to 0.30. The second agent further contains a substance that generates magnesium ions, and is applied to 1 m of target mud. 3 The amount of the substance that generates magnesium ions added per unit time is 5 to 80 mol in terms of the amount of magnesium ions generated. The molar ratio of the amount of magnesium ions to the total amount of silicon dioxide and alkali oxide is 0.01 to 0.07. The second agent is an aqueous solution or suspension in water. The target mud is mud generated by excavation using the shield method. [Effects of the Invention]

[0008] According to the present invention, a modification method can be provided that targets soft mud with high water content, can reliably solidify the mud, and can reliably reduce the elution of heavy metals and the like. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention relates to a method for modifying high-moisture soft mud (hereinafter sometimes simply referred to as "mud") generated during shield tunneling, river channel excavation, dredging, and other construction projects. Specifically, two types of chemicals are added to the target mud at intervals to granulate and solidify the mud, thereby increasing the cone index and reducing the leaching of heavy metals and other substances. In this specification, "heavy metals, etc." refers to cadmium, hexavalent chromium, cyanide, mercury, selenium, lead, arsenic, fluorine, boron, and their compounds, which are classified as Type 2 specified hazardous substances under the Soil Contamination Countermeasures Act. Therefore, "heavy metals, etc." is a concept that also includes cyanide, arsenic, fluorine, and boron. Preferred embodiments of the present invention are described in detail below.

[0010] The mud targeted by the modification method of this embodiment has a moisture content of 10 to 70%. This moisture content may be 15 to 65%, or 20 to 60%. First, the first chemical is added to the target mud and mixed, and then the second chemical is added and mixed.

[0011] If the pH of the target soil is not within the range of 5.0 to 9.0, an appropriate pH adjuster may be added to adjust the pH to 5.0 to 9.0 prior to the addition of the first chemical agent.

[0012] The first agent is a liquid mixture of water and an alkali silicate composed of an alkali oxide and silicon dioxide. Alkaline silicates are generally expressed by the formula X2O·nSiO2 (where X represents an alkali metal, and n is a positive number representing the molar ratio (SiO2 / X2O)). The alkali silicate used in this embodiment has a molar ratio of silicon dioxide to alkali oxide (i.e., "n") of 2.4 to 4.1. n may be 2.7 to 4.0, 3.1 to 3.9, or 3.1 to 3.2.

[0013] In the first chemical, the alkali metal (X) is preferably sodium or potassium, and more preferably sodium. When the alkali metal (X) is sodium, the first chemical is a mixture of sodium silicate and water (so-called "water glass"). That is, the first chemical is a viscous alkaline liquid containing a mixture of sodium oxide, silicon dioxide, and the acidic components of water. If the composition formula of sodium silicate is Na2O·nSiO2 and the coexisting water is expressed in mH2O, the ratio (m / n) is preferably 4 to 10, more preferably 5 to 10, and even more preferably 7 to 10. The specific gravity of the mixture of sodium silicate and water at 20°C is preferably 1.20 to 1.60, more preferably 1.25 to 1.50, and even more preferably 1.28 to 1.45.

[0014] Furthermore, in a mixture of sodium silicate and water, the content calculated as silicon dioxide is preferably 20 to 40 wt%, more preferably 22 to 35 wt%, and even more preferably 24 to 30 wt%. In a mixture of sodium silicate and water, the content calculated as sodium oxide is preferably 4 to 20 wt%, more preferably 5 to 15 wt%, and even more preferably 6 to 10 wt%. In a mixture of sodium silicate and water, the content of water is preferably 40 to 80 wt%, more preferably 50 to 75 wt%, and even more preferably 55 to 70 wt%.

[0015] Target mud 1m 3 The amount of alkali silicate added per unit is 150 to 1200 mol in terms of silicon dioxide and 40 to 350 mol in terms of alkali oxide. The amount added may be 200 to 1100 mol, 300 to 1000 mol, 400 to 900 mol, or 500 to 800 mol in terms of silicon dioxide. The amount added may also be 50 to 300 mol, 60 to 280 mol, 70 to 250 mol, or 80 to 220 mol in terms of alkali oxide.

[0016] The second agent contains a substance that dissolves in water to produce trivalent iron ions. Examples of such substances include iron(III) sulfate (ferric sulfate), ferric polysulfate, and ferric chloride. These substances may also be hydrated.

[0017] Target mud 1m 3 The amount of the substance that generates trivalent iron ions added per unit of time is an amount that generates 20 to 300 mol of trivalent iron ions per unit of time. The amount added may be 30 to 250 mol, 40 to 200 mol, 50 to 180 mol, or 60 to 160 mol of trivalent iron ions per unit of time.

[0018] Furthermore, the molar ratio of the amount of trivalent iron ions generated to the total amount of silicon dioxide and alkali oxide may be 0.05 to 0.30, 0.06 to 0.25, 0.07 to 0.20, or 0.10 to 0.15.

[0019] The second agent may further contain a substance that dissolves in water to produce magnesium ions. Examples of such substances include magnesium sulfate, magnesium chloride, magnesium oxide, and magnesium carbonate. From the viewpoint of not increasing the pH of the mud, magnesium sulfate, magnesium chloride, magnesium oxide, and magnesium carbonate are preferred, and from the viewpoint of water solubility, magnesium sulfate and magnesium chloride are preferred. These substances may also be hydrates.

[0020] Target mud 1m 3 The amount of the substance that generates magnesium ions added per unit of time is preferably an amount that generates 5 to 80 mol of magnesium ions per unit of time, and may be 10 to 70 mol, 15 to 65 mol, 20 to 60 mol, or 25 to 55 mol of magnesium ions per unit of time.

[0021] Furthermore, the molar ratio of the amount of magnesium ions generated to the total amount of silicon dioxide and alkali oxide may be 0.01 to 0.07, 0.02 to 0.06, 0.025 to 0.055, or 0.03 to 0.05.

[0022] The second agent may further contain at least one substance such as iron sulfate (I), polyiron sulfate (III), iron chloride (III), etc. Note that the addition of phosphoric acid tends to increase the elution of heavy metals, etc. (especially arsenic and hexavalent chromium).

[0023] The second agent may be in an aqueous solution or suspension in water.

[0024] After adding the first agent to the target mud, the time interval before adding the second agent is preferably at least 5 seconds, more preferably 8 seconds, and even more preferably 10 seconds. The upper limit of this time interval may be 20 seconds, 30 seconds, or even 60 seconds. The effects of both agents can be fully exerted by adding the second agent once the first agent has been thoroughly mixed with the target mud and the buffering effect of the target mud has settled. Furthermore, it is preferable to mix for at least the above-mentioned time after adding the second agent.

[0025] The pH of the mud after the second chemical has been added and mixed is preferably 5.0 to 9.0, more preferably 5.5 to 8.8, and even more preferably 5.8 to 8.6.

[0026] The cone index of the mud after adding the second agent and mixing is set at 200kN / m, in order to be recognized as construction waste soil and to make it easier to transport. 2 Preferably, it is 300 kN / m or more. 2 More preferably, it is 400 kN / m or more. 2 More preferably, it is equal to or greater than this.

[0027] The target mud may be mud generated by excavation using a shield tunneling method. In this case, it is preferable to add the first chemical to the mud as early as possible. For example, the first chemical can be added while the mud discharged from the cutting blade is being transported upward by a screw conveyor.

[0028] <Effects> In the modification method of this embodiment, the first chemical is added to the target mud and mixed thoroughly, and then the second chemical is added and mixed. This causes the target mud to solidify (or granulate and solidify), reducing the fluidity of the mud. The pH of the mud is adjusted to an appropriate range by selecting an appropriate blend ratio of the first and second chemicals. At the same time, the insolubilization of heavy metals is promoted by the action of trivalent iron ions generated by the second chemical.

[0029] As a result, the cone index of the target mud before adding the first agent was 200kN / m 2 Even if the strength is less than 200kN / m, it can be increased by granulation and solidification. 2 or more, and even 400 kN / m 2 Once granulation and solidification are complete, the improved soil can be transported and used without requiring a curing period.

[0030] In addition, the elution of heavy metals, etc., is particularly suppressed, especially arsenic and hexavalent chromium.

[0031] The pH of the improved soil is usually 5.0 to 9.0, making it easy to handle afterwards.

[0032] In this embodiment, the first chemical is a liquid, so it is easy to mix with the target mud, and the device for mixing can be small.

[0033] In this embodiment, the effect of this embodiment is particularly advantageous when the second agent contains a substance that generates magnesium ions. Trivalent iron ions have the role of insolubilizing heavy metals, etc., and if free silicic acid species remain in the mud, the trivalent iron ions will bind to them, inhibiting their function. When magnesium ions are added, the magnesium ions preferentially bind to the silicic acid species, reducing the degree to which the function of the trivalent iron ions is inhibited, allowing the trivalent iron ions to fully perform their intended function.

[0034] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. [Example]

[0035] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0036] <Materials used> [mud] Raw mud 1: Mud collected from shield construction. Water content: 58.0% Raw mud 2: Mud collected from a construction site excavation site. Moisture content: 41.7% Raw mud 3: Mud collected from shield construction. Water content: 33.0% Raw mud 4: Mud extracted from Kasaoka clay powder with water added to adjust the moisture content. Moisture content: 60.0% Raw mud 5: Mud collected from a construction site excavation site. Water content: 43.9% The moisture content was measured using a microwave oven-based soil moisture content test method (draft) (recommended by the NPO Housing Ground Quality Association (draft)).

[0037] [First drug] Solution A: The following three types of sodium silicate manufactured by Toso Sangyo Co., Ltd. These are aqueous solutions with three different ratios of silicon dioxide, sodium oxide, and water. "No. 2": The molar ratio of silicon dioxide to sodium oxide is 2.4 to 2.6. "No. 3": The molar ratio is 3.1 to 3.2. "No. 4": The molar ratio is 3.9 to 4.1.

[0038] [Second drug] Solution B: The following three types were used. All of them are aqueous solutions. Solution B1: 300g of magnesium sulfate dissolved in 1 liter of iron(III) sulfate solution (45% concentration; manufactured by Furukawa Chemicals Co., Ltd.). Solution B2: Iron (III) sulfate aqueous solution (45% concentration; manufactured by Furukawa Chemicals Co., Ltd.) Solution B3: 300g of magnesium sulfate dissolved in 1 liter of water.

[0039] <Procedure> The raw mud used, the amount of liquid A added, the amount of liquid B (liquid B1, liquid B2, or liquid B3) added, the order in which liquid A and liquid B were added, and the mixing time after the addition of the previously added liquid are shown in Table 1. As a representative example, the procedure for Example 1-1 is shown below.

[0040] [Example 1-1] The target mud, raw mud 1 (volume 100 mL, weight approximately 170 g), was placed in a container, and liquid A was added and mixed for 10 seconds using a hand mixer. Immediately after that, liquid B1 was added and mixed for 10 seconds using a hand mixer. The following measurements were performed on the resulting improved soil. pH…JGS0211:2020 pH test of soil suspension Cone index…JIS A1228:2020 Cone index test method for compacted soil Arsenic elution: elution test according to Ministry of the Environment Notification No. 46 Hexavalent chromium elution: elution test according to Ministry of the Environment Notification No. 46

[0041] Using the same procedures, experiments were conducted using the materials shown in Table 1 (Examples 1-2 to 1-11, Comparative Examples 1-1 to 1-3, Examples 2-1 to 2-6, Comparative Examples 2-1 to 2-3, Example 3-1 to 3-3, Example 4-1, Comparative Example 4-1, Example 5-1, Comparative Example 5-1). In addition, the pH, Cone Index, arsenic elution, and hexavalent chromium elution were measured for raw mud 1, raw mud 2, raw mud 3, raw mud 4, and raw mud 5 themselves.

[0042] <Result> [Evaluation criteria] The pH of the improved soil should be 5.8 to 8.6. The cone index should be 200 kN / m 2 Those with a score of 200 kN / m or more are marked as "○" 2 Those with less than this level were marked "X." The standard value for arsenic leaching is 0.01 mg / kg. The standard value for hexavalent chromium leaching is 0.05 mg / kg.

[0043] [Example using raw mud 1] In the examples (Examples 1-1 to 1-11) in which the amount of Liquid A added, the amount of Liquid B1 added, the order in which Liquid A and Liquid B1 were added, and the mixing time after the addition of Liquid A were appropriate, the pH of the improved soil was within the appropriate range, the Cone Index was high, and the amounts of arsenic and hexavalent chromium leaching were below the standard values.

[0044] In the example where liquid B was not added (Comparative Example 1-1), the pH of the improved soil exceeded the appropriate range, and the amount of arsenic eluted exceeded the standard value.

[0045] In the cases where solution B was added first (Comparative Examples 1-2 and 1-3), the pH of the improved soil exceeded the appropriate range.

[0046] [Example using raw mud 2] In the cases where the amount of Liquid A added, the amount of Liquid B1 or Liquid B2 added, the order of adding Liquid A and Liquid B1 or Liquid B2, and the mixing time after adding Liquid A were appropriate (Examples 2-1 to 2-6), the pH of the improved soil was within the appropriate range, the Cone Index was high, and the amount of arsenic leaching was below the standard value.

[0047] In the example where no solution B was added (Comparative Example 2-1), the example where a small amount of trivalent iron ions was added (Comparative Example 2-2), and the example where no trivalent iron ions were added (Comparative Example 2-3), the pH of the improved soil exceeded the appropriate range, the Cone index was small, and the amount of arsenic leaching exceeded the standard value.

[0048] [Example using raw mud 3] In the cases where the amount of Liquid A added, the amount of Liquid B1 added, the order in which Liquid A and Liquid B1 were added, and the mixing time after the addition of Liquid A were appropriate (Examples 3-1 to 3-3), the pH of the improved soil was within the appropriate range, the Cone index was high, and the amount of arsenic leaching was below the standard value.

[0049] [Example using raw mud 4 and raw mud 5] ·Mud 1m 3 When the amount of the substance that generates trivalent iron ions per unit volume was within the range of 20 to 300 mol, the pH of the modified soil was within the appropriate range and the Cone Index was high (Examples 4-1 and 5-1). However, when the amount added was outside the range of 20 to 300 mol, the pH of the modified soil was not within the appropriate range (Comparative Examples 4-1 and 5-1). When the amount added exceeded 300 mol, the Cone Index of the modified soil was particularly low (Comparative Example 4-1).

[0050] [Table 1] [Industrial Applicability]

[0051] The present invention can be used for on-site treatment of high-moisture soft mud generated during civil engineering work.

Claims

1. A method for improving mud, comprising adding and mixing a first agent to a target mud having a water content of 10 to 70%, and then adding a second agent; The first agent is a liquid mixture of an alkali silicate composed of an alkali oxide and silicon dioxide, and water, the molar ratio of the silicon dioxide to the alkali oxide is 2.4 to 4.1; 1 m of the target mud ３ the amount of the alkali silicate added is 150 to 1200 mol in terms of silicon dioxide and 40 to 350 mol in terms of alkali oxide, the second agent comprises a substance that generates trivalent iron ions, 1 m of the target mud ３ The method for improving mud, wherein the amount of the substance that generates trivalent iron ions added per unit area is 20 to 300 mol in terms of the amount of trivalent iron ions generated.

2. The alkali silicate is sodium silicate, 2. The method for modifying mud according to claim 1, wherein the alkali oxide is sodium oxide.

3. The method for modifying mud according to claim 1, wherein the molar ratio of the amount of the trivalent iron ions to the total amount of the silicon dioxide and the alkali oxide is 0.05 to 0.

30.

4. the second agent further comprises a substance that generates magnesium ions; 1 m of the target mud ３ 2. The method for modifying mud according to claim 1, wherein the amount of the substance that generates magnesium ions added per unit time is 5 to 80 mol in terms of the amount of magnesium ions generated.

5. The method for modifying mud according to claim 4, wherein the molar ratio of the amount of magnesium ions to the total amount of silicon dioxide and alkali oxide is 0.01 to 0.

07.

6. The method for modifying mud according to claim 1, wherein the second chemical is an aqueous solution or a suspension in water.

7. 2. The method for modifying mud according to claim 1, wherein the target mud is mud generated by excavation using a shield tunneling method.

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