Method for treating rocks containing heavy metals

Abstract

To provide a processing method for rock including heavy metals or the like capable of restraining dispersion of heavy metals or the like into atmosphere without needing re-blending coarse and fine grain rocks once separated.SOLUTION: A processing method for rocks including heavy metals or the like comprises classifying the rock into coarse grain rock and fine grain one, blending the fine grain rock with an insolubilization material and filling that material-including fine grain rock and the coarse grain rock so as to alternately layer. Since the material does not predetermine that the rock or the above material is totally uniform, the filling work, for example, and new generation of the heavy metals-including rock can be performed in parallel and further, the rock derived from other places can be received.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for treating rocks containing heavy metals and the like. [Background technology]

[0002] Various treatment methods have been proposed to prevent heavy metals and other substances contained in rock debris generated during rock excavation work and other such work from dispersing into the environment. Mixing an insolubilizing agent is a common method for preventing the elution of heavy metals and other substances. However, crushing the rock debris to facilitate mixing with the insolubilizing agent increases the elution of heavy metals and other substances, resulting in the need for a large amount of insolubilizing agent. Therefore, an insolubilization system is known that makes it possible to easily and uniformly insolubilize heavy metals and other substances without crushing the rock debris (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6663296 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the insolubilization system of Patent Document 1, the coarse and fine rocks are separated, and then remixed after an insolubilizing agent is added to the fine rocks. Furthermore, striving for uniformity through remixing makes it difficult to adjust the amounts of coarse and fine rocks. Therefore, the present invention aims to provide a method for treating rocks containing heavy metals and other substances, which does not require remixing the separated coarse and fine rocks and can suppress the diffusion of heavy metals and other substances into the environment. [Means for solving the problem]

[0005] The present invention provides a method for treating rocks containing heavy metals, etc., by classifying the rocks containing heavy metals, etc. into coarse-grained rocks and fine-grained rocks, mixing the fine-grained rocks with an insolubilizing agent, and piling up the fine-grained rocks mixed with the insolubilizing agent and the coarse-grained rocks in alternating layers.

[0006] In this treatment method, fine-grained rocks that are prone to heavy metal leaching are subjected to insolubilization treatment, and then the fine-grained rocks and coarse-grained rocks are piled up in alternating layers. This allows the insolubilized fine-grained rocks to be treated without being mixed with the coarse-grained rocks. In some cases, the amount of coarse-grained and fine-grained rocks piled up can be adjusted by varying the thickness of the pile. In other words, since the present invention does not require the rocks and insolubilizing material to be uniform throughout the entire pile, it is possible to, for example, pile up the rocks in parallel with the new generation or insolubilization treatment of heavy metal-containing rocks, or to accept rocks from other sources.

[0007] In this treatment method, it is preferable to first pile up fine-grained rock mixed with an insolubilizing agent. In this case, even if heavy metals or the like are eluted from the layer of coarse-grained rock piled on top of that, the heavy metals or the like will be adsorbed by the layer containing the insolubilizing agent underneath.

[0008] In this treatment method, it is preferable to set the classification point to a value within the range of 2 mm to 40 mm for classification. Coarse-grained rock obtained when classified within this range is unlikely to have concentrations exceeding environmental standards even if heavy metals are eluted, so there is little need to mix it with an insolubilizing agent.

[0009] In this treatment method, it is preferable to pile up the soil in at least four layers. Also, in this treatment method, the insolubilizing agent may contain a trivalent iron compound and a substance that generates divalent iron ions upon contact with water.

[0010] In this treatment method, it is preferable to crush some of the coarse-grained rock in advance, measure the amount of heavy metals, etc. eluted from the crushed material, and determine the amount of insolubilizing agent to be mixed with the fine-grained rock so that it can adsorb the heavy metals, etc. contained in the coarse-grained rock even if they are eluted. By determining the amount of insolubilizing agent in this way, it is possible to more reliably prevent heavy metals, etc. from being dispersed into the environment.

[0011] In this treatment method, the site of the embankment is preferably a storage facility formed in the natural ground, which allows rocks containing heavy metals and the like to be contained. [Effects of the Invention]

[0012] According to the present invention, a method for treating rocks containing heavy metals and the like can be provided, which does not require remixing of the coarse-grained rocks and fine-grained rocks that have been separated, and can suppress the diffusion of heavy metals and the like into the environment. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view of a storage facility to which a treatment method according to one embodiment of the present invention is applied. DETAILED DESCRIPTION OF THE INVENTION

[0014] A preferred embodiment of the present invention will be described in detail below with reference to the drawings. The treatment method of this embodiment is a treatment method for preventing heavy metals and the like from being dispersed into the environment from rocks containing heavy metals and the like (hereinafter referred to as "heavy metal-containing rocks"). Here, the heavy metal-containing rocks may be, for example, rock rubble generated during rock excavation work. Rock rubble contains rocks of various particle sizes, and the largest may be rocks with particle sizes of approximately 300 mm. In the treatment method of this embodiment, the heavy metal-containing rocks are preferably those with particle sizes of 300 mm or less. In the treatment method of this embodiment, insolubilization of heavy metals and the like is performed without crushing the heavy metal-containing rocks.

[0015] In this embodiment, "heavy metals, etc." refers to cadmium and its compounds, hexavalent chromium compounds, cyanide compounds, mercury and its compounds, selenium and its compounds, lead and its compounds, arsenic and its compounds, fluorine and its compounds, and boron and its compounds, which are designated as Type 2 specified hazardous substances among the specified hazardous substances in the Soil Contamination Countermeasures Act. Therefore, "heavy metals, etc." is a concept that also includes cyanide compounds, arsenic, fluorine, and boron, which are not normally called heavy metals. Rocks may contain at least one type of heavy metal.

[0016] First, the target rock containing heavy metals and the like is classified using an arbitrary classifier. For example, a vibrating screen is used as the classifier. Here, it is preferable to set the classification point to a value within a range of 2 mm to 40 mm and perform classification. Furthermore, the classification point may be a value within a range of 30 mm to 40 mm, a value within a range of 20 mm to 30 mm, a value within a range of 10 mm to 20 mm, or a value within a range of 2 mm to 10 mm. Furthermore, these lower and upper limits may be combined as appropriate. In this embodiment, the coarse particle fraction obtained by this classification is called "coarse particle rock" and the fine particle fraction is called "fine particle rock."

[0017] Next, the fine-grained rock obtained by classification is mixed with an insolubilizing agent. The insolubilizing agent used in this embodiment is a composition containing a trivalent iron compound and a substance that generates divalent iron ions upon contact with water. As will be described later, the insolubilizing agent of this embodiment may further contain a substance that generates calcium ions upon contact with water.

[0018] A trivalent iron compound is a compound containing iron with an oxidation number of 3. Examples of trivalent iron compounds include iron(III) oxide, iron(III) hydroxide, iron(III) oxide hydroxide, iron(III) chloride, and iron(III) sulfate. From the viewpoint of capturing and insolubilizing heavy metals, etc., compounds with low water solubility are preferred. From the viewpoint of mixability with fine-grained rock, it is preferable that the trivalent iron compound be in powder form.

[0019] The substance that generates divalent iron ions upon contact with water may be any substance that dissociates or ionizes to generate divalent iron ions upon contact with water, regardless of its water solubility. Examples of such substances include iron(II) chloride, iron(II) sulfate, iron(II) hydroxide, iron(II) sulfate, and metallic iron. Iron(II) chloride and metallic iron are preferred. The substance is preferably in powder form to facilitate mixing with fine-grained rock. In particular, metallic iron is preferably reduced iron powder (sponge iron powder) with a high specific surface area and high reactivity. Furthermore, special iron powder, which is surface-treated reduced iron powder, is even more preferred.

[0020] When a substance that generates ferrous ions upon contact with water is added to and mixed with fine-grained rock to be insolubilized, it dissolves in the water contained in the fine-grained rock and generates iron (II) ions. It is not necessary for all of the added substance to become iron (II) ions; the amount to be added must be determined in advance, taking into account solubility, so that enough iron (II) ions are generated to be effective as an insolubilizer. For example, a substance with high solubility in water, such as iron (II) chloride, can be considered to be almost entirely ionized. On the other hand, a substance with low solubility, such as metallic iron, must be used after the degree of ionization has been determined in advance.

[0021] The content ratio of the trivalent iron compound and the substance that generates divalent iron ions in the insolubilizing material of this embodiment is such that when the insolubilizing material of this embodiment is mixed with fine-grained rock, 1 mol of trivalent iron in the trivalent iron compound is 1 mol of divalent iron ions. 1.00×10 -4 ~3.00×10 -2 is the content ratio in mol 1.30×10 -4 ~2.50×10 -2 Preferably, the content ratio is such that mol 3.00×10 -4 ~1.50×10 -2 It is more preferable that the content ratio is such that the amount of 7.00×10 -4 ~8.00×10 -3 It is more preferable that the content ratio is such that the amount of the hydroxyl group is 1 / mol. 1.00×10 -3 ~3.00×10 -3 It is particularly preferable that the content ratio is such that the amount of the hydroxyl group is 1 / 2 mol. Here, "when the insolubilizing agent is mixed with the fine-grained rock" refers to the period from immediately after mixing the insolubilizing agent to one hour.

[0022] When the substance that generates divalent iron ions is metallic iron, the content ratio of metallic iron is 1 mol of trivalent iron in the trivalent iron compound. 1.00×10 -4 ~1.50×10 -0 mol, 5.00×10 -4 ~1.00×10 -0 mol is more preferred, 1.00×10 -3 ~7.00×10 -1 mol, more preferably 1.00×10 -2 ~3.00×10 -1 It is particularly preferred that the molar ratio is 1:1. When metallic iron is used, the above-mentioned "when the insolubilizing agent is mixed with the fine-grained rock" refers to the period from immediately after mixing the insolubilizing agent to 6 hours later.

[0023] When the material that produces divalent iron ions is metallic iron, the reduction of metallic iron can also reduce hexavalent chromium and hexavalent selenium, thereby producing an insolubilizing effect. Therefore, if it is known in advance that the fine-grained rock contains a large amount of hexavalent chromium and hexavalent selenium, it is preferable to set the iron powder content high.

[0024] The insolubilizing agent may further contain a substance that generates calcium ions upon contact with water. Examples of such substances include calcium oxide, calcium hydroxide, calcium sulfate, calcium carbonate, calcium bicarbonate, and calcium silicate. The substance is preferably in powder form to facilitate mixing with fine-grained rock.

[0025] The content ratio of calcium ions is 1 mole of trivalent iron in the trivalent iron compound when mixed with fine-grained rock. 1.0×10 -2 ~1.5×10 -0 Preferably, the content ratio is such that mol 5.0×10 -2 ~1.2×10 -0 It is more preferable that the content ratio is such that the amount of 1.0×10 -1 ~1.0×10 -0 It is more preferable that the content ratio is such that the mol 1.5×10 -1 ~8.0×10 -1 It is particularly preferable that the content ratio is such that the amount of the hydroxyl group is 1 / 2 mol. The numerical range is 2.0 x 10 -1 ~7.0×10 -1 It may also be mol.

[0026] Since the insolubilizing agent of this embodiment is a composition containing at least two or three of the above components, it is preferably stored in a dry state to prevent mutual reaction before adding and mixing with the fine-grained rock. Alternatively, these components may be stored separately and added to the fine-grained rock simultaneously or separately when used. When adding them simultaneously, a premixed composition, like the insolubilizing agent described above, may be prepared and then added.

[0027] The total amount of insolubilizing agent added (mixed amount) may be 0.5 to 30% (i.e., 5 to 300 kg is added per ton of fine-grained rock), 1 to 20%, or 5 to 10%, when the mass of the fine-grained rock is taken as 100%. In terms of the number of moles of divalent iron ions generated, it is 6.9 x 10 -3 mol ~ 1.6 × 10 2 The preferred range is 8.3 x 10 -2 mol ~ 1.5 × 10 1 mol, 8.3 x 10 -1 mol ~ 1.2 × 10 1It may also be mol.

[0028] The amount of insolubilizer added is preferably determined taking into account the amount of heavy metals and other substances that may be eluted from the coarse-grained rock. Specifically, it is preferable to collect a small amount of coarse-grained rock as a test sample in advance, crush it, and measure the amount of heavy metals and other substances eluted from the crushed material (elution amount). This determines an amount that will adsorb the heavy metals and other substances even if all of the heavy metals and other substances contained in the coarse-grained rock are eluted. This makes it possible to prevent not only the heavy metals and other substances that are easily eluted in fine-grained rock, but also the heavy metals and other substances that are difficult to elute in coarse-grained rock from dispersing into the environment. It is preferable to perform this measurement each time the rock is classified, and to determine the amount of insolubilizer to be added each time.

[0029] The method of mixing with fine rocks can be selected appropriately depending on the volume and properties of the fine rocks and the construction conditions. For example, a backhoe, a backhoe with a mixing bucket, a soil improver, a road stabilizer, etc. can be used.

[0030] When fine-grained rock is mixed with a trivalent iron compound and a substance that generates divalent iron ions upon contact with water, the water in the fine-grained rock generates divalent iron ions. The resulting iron hydroxide adsorbs onto the surface of the trivalent iron compound, forming an insoluble material. This process simultaneously insolubilizes heavy metals and other substances in the fine-grained rock, potentially reducing their leaching from the fine-grained rock. This method, which combines a trivalent iron compound that exhibits an insolubilizing effect in an oxidizing atmosphere with a substance that generates divalent iron ions in a reducing atmosphere, can be applied to a variety of fine-grained rocks, regardless of pH or redox potential. Furthermore, calcium ions insolubilize heavy metals and other substances in alkaline environments. Therefore, when the pH of fine-grained rock is alkaline or when the pH of fine-grained rock shifts to the alkaline side, the presence of calcium ions in the fine-grained rock can further insolubilize heavy metals and other substances.

[0031] After mixing the fine-grained rock with the insolubilizing agent, the fine-grained rock and the coarse-grained rock are piled up in a storage facility. As shown in Figure 1, the fine-grained rock mixed with the insolubilizing agent is piled up in a storage facility 1 consisting of a water-impermeable sheet (water-impermeable structure) 3 installed on natural ground 2, forming a fine-grained rock layer 4. Next, coarse-grained rock is piled up on top of the fine-grained rock layer 4, forming a coarse-grained rock layer 5. After that, the pile is repeated so that the fine-grained rock layers 4 and the coarse-grained rock layers 5 are alternately layered. Note that "to pile up" here means to pour in rock and spread it evenly, and also implies filling up the target space.

[0032] The number of layers is preferably two or more for each of the fine-grained rock layer 4 and the coarse-grained rock layer 5 (four or more layers in total). It is preferable that the uppermost layer be the coarse-grained rock layer 5, i.e., the total number of layers is an even number. The thickness ratio of the fine-grained rock layer 4 to the coarse-grained rock layer 5 may be 1:0.5 to 1:10, 1:1 to 1:8, 1:1.3 to 1:5, or 1:1.5 to 1:3.5.

[0033] Once the fill reaches the upper limit of the storage facility, the fill is finished. A waterproof structure may be installed on top of the top layer to cover the top layer. This completes the containment structure for rocks containing heavy metals, etc.

[0034] In the past, a common method for preventing heavy metals and other substances contained in rock rubble from dispersing into the environment was to mix them with an insolubilizing agent to suppress the elution of heavy metals and other substances. However, crushing the rubble to facilitate mixing with the insolubilizing agent required time-consuming crushing and increased the elution of heavy metals and other substances, necessitating the use of a large amount of insolubilizing agent. In contrast, the treatment method of this embodiment does not require crushing of heavy metal-containing rocks and other substances. After classifying the heavy metal-containing rocks, the fine-grained rocks from which heavy metals are easily eluted are subjected to insolubilization treatment. The fine-grained rocks and coarse-grained rocks are then piled up in alternating layers. This method allows treatment without the need for a process of mixing the insolubilized fine-grained rocks with coarse-grained rocks.

[0035] In this embodiment, the amount of coarse-grained rock and fine-grained rock to be filled can be adjusted by changing the layer thickness of the fine-grained rock layer 4 and the coarse-grained rock layer 5. In this embodiment, it is not intended that the rocks and insolubilizing material be uniform throughout the fill, so for example, it is possible to carry out the fill in parallel with the new generation or insolubilization treatment of rocks containing heavy metals, etc., or to accept rocks from other sources.

[0036] In addition, in this embodiment, fine-grained rock mixed with an insolubilizing agent is piled up first, so even if heavy metals, etc. are leached from the coarse-grained rock layer 5, the heavy metals, etc. are adsorbed by the fine-grained rock layer 4 containing the insolubilizing agent below, thereby preventing the heavy metals, etc. from diffusing into the environment.

[0037] In this embodiment, the classification point is set to a value within the range of 2 mm to 40 mm, and the coarse-grained rock obtained when classified within this range is unlikely to have eluted heavy metals exceeding environmental standards, so there is little need to mix it with an insolubilizer, and therefore less insolubilizer is required.

[0038] In this embodiment, a portion of the coarse-grained rock is crushed in advance to measure the amount of heavy metals and other substances eluted from the crushed material, and the amount of insolubilizing material to be mixed with the fine-grained rock is determined to be an amount that will be able to adsorb the heavy metals and other substances contained in the coarse-grained rock even if they are eluted. By determining the amount of insolubilizing material in this way, it is possible to more reliably prevent heavy metals and other substances from being dispersed into the environment.

[0039] Furthermore, in this embodiment, the storage facility 1 has the waterproof sheet 3, so that rocks containing heavy metals and the like can be contained.

[0040] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, although the above embodiment shows a configuration in which rocks containing heavy metals and the like are stored and contained in a storage facility formed in the natural ground, the rocks may be stored in an earth mound at a location other than the storage facility. [Example]

[0041] Below, we will show an example of a study on classification points using rock rubble generated during tunnel excavation work, and an example of a study on the amount of insolubilizing agent used. The example shown here is one example of a study on numerical values, and the content of the present invention is not limited to this example.

[0042] <Example of classification point consideration> The rock rubble was classified using a "Sieve Shaker 300-MM" (manufactured by Tsutsui Scientific Instruments Co., Ltd.) with the classification point set to 37.5 mm. An arsenic leaching test was conducted on the coarse-grained rock (coarse particle fraction) in accordance with JIS K 0058-1:2005 "Testing Methods for Chemical Substances of Slags." Similar slag leaching tests were also conducted using the same rock rubble with classification points set to 19 mm, 9.5 mm, and 2 mm. The results are shown in Table 1.

[0043] [Table 1]

[0044] The results shown in Table 1 indicate that there is a classification point where the arsenic concentration eluted from coarse-grained rock is 0.3 mg / L or less. In other words, it is clear that coarse-grained rock does not need to be mixed with an insolubilizing agent depending on its particle size.

[0045] <Example of considering the amount of insolubilizer used> (Arsenic adsorption capacity of immobilized fine-grained rock) The amount of insolubilizer used was investigated for fine-grained rock obtained by classification with a classification point of 2 mm. The insolubilizer used was a mixture of iron (III) oxide and iron powder in a weight ratio of 100:8.

[0046] Fine-grained rock was mixed with 50 kg / t of insolubilizer. A 0.7 mg / L arsenic solution was repeatedly added in small amounts, and the arsenic concentration of the supernatant was measured after each addition. When the arsenic concentration was below 0.3 mg / L, the addition of the arsenic solution was repeated, and when the arsenic concentration exceeded 0.3 mg / L, the addition of the arsenic solution was stopped. In this way, the arsenic adsorption capacity of the coarse-grained rock mixed with the insolubilizer was calculated. Similarly, the arsenic adsorption capacity was calculated when the amount of insolubilizer mixed with fine-grained rock was 10 kg / t, 100 kg / t, and 150 kg / t. The results are shown in Table 2.

[0047] These results showed that when 10 kg / t of insolubilizing material was mixed, the insolubilized fine-grained rock no longer had the capacity to adsorb any more arsenic, but when 50 kg / t or more of insolubilizing material was mixed, the rock had the capacity to adsorb even more arsenic. Furthermore, it was found that the "arsenic adsorption capacity [B] of fine-grained rock mixed with insolubilizing material" tended to increase almost linearly with the "amount of insolubilizing material relative to the fine-grained rock [A]."

[0048] [Table 2]

[0049] (Understanding the maximum amount of leaching from coarse-grained rock) Next, the coarse-grained rock was crushed to 2mm or less to make it easier for arsenic to leach out. The Environment Agency Notification No. 46 test was repeated 10 times to examine the relationship between the cumulative liquid-solid ratio (L / kg) and the cumulative amount of arsenic leaching (mg / kg). As a result, it was found that the cumulative amount of arsenic leaching converged to approximately 45mg / kg. The same test was performed a total of three times, and each time the cumulative amount of arsenic leaching converged to approximately 45mg / kg.

[0050] Taking this result into consideration and the arsenic adsorption capacity of fine-grained rock, it is possible to derive the allowable thickness of the coarse-grained rock layer relative to the thickness of the fine-grained rock layer during embankment. In other words, the "Arsenic adsorption capacity of fine-grained rock mixed with insolubilizing material [B]" in Table 2 represents the additional adsorption capacity after suppressing the elution of arsenic contained in the fine-grained rock. Therefore, even if arsenic is eluted from the coarse-grained rock, that amount of arsenic can still be adsorbed. Therefore, the thickness ratio of the coarse-grained rock layer to the fine-grained rock layer can be set to the value shown in the rightmost column of Table 2.

[0051] Furthermore, because the "amount of insolubilizing material relative to fine-grained rock [A]" and the "arsenic adsorption capacity of fine-grained rock mixed with insolubilizing material [B]" in Table 2 tend to increase almost linearly, it is possible to determine the minimum "amount of insolubilizing material relative to fine-grained rock [A]" required to make the layer thickness ratio of the coarse-grained rock layer "1." In other words, if [B] is set to 45 mg / kg, a value of [A] = 40 kg / t can be determined, which is between when [A] is 10 kg / t and when it is 50 kg / t. [Industrial Applicability]

[0052] The present invention can be used to treat rock debris generated during tunnel construction, for example. [Explanation of symbols]

[0053] 1...storage facility, 2...ground rock, 3...waterproof sheet, 4...fine-grained rock layer, 5...coarse-grained rock layer.

Claims

1. Rocks containing heavy metals, etc. are classified into coarse-grained rocks and fine-grained rocks, Mixing the fine rock with an insolubilizing agent; The method for treating rocks containing heavy metals and the like comprises piling up the fine-grained rocks mixed with the insolubilizing agent and the coarse-grained rocks in alternating layers.

2. 2. The method according to claim 1, wherein the fine-grained rock mixed with the insolubilizing agent is first piled up.

3. 3. The method according to claim 1, wherein the classification point is set to a value within the range of 2 mm to 40 mm.

4. 4. The method according to claim 1, wherein the soil is piled up in at least four layers.

5. 5. The treatment method according to claim 1, wherein the insolubilizing agent comprises a trivalent iron compound and a substance that generates divalent iron ions upon contact with water.

6. crushing a portion of the coarse-grained rock in advance and measuring the amount of heavy metals and the like eluted from the crushed material; 6. A treatment method according to claim 1, wherein the amount of the insolubilizing agent mixed with the fine-grained rock is an amount that can adsorb heavy metals, etc. contained in the coarse-grained rock even if the heavy metals, etc. are eluted.

7. 7. The method according to claim 1, wherein the site of the embankment is a storage facility formed in the natural ground.

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