Groundwater purification methods and purification materials

Abstract

To provide a method of purifying underground water, capable of neutralizing acidic water and preventing metal components from leaking outside while preventing clogging from occurring in the ground including excavation muck and slag accumulated in the past or expected to be generated, and a purifying agent.SOLUTION: The method of purifying underground water according to the present invention, comprises a first-liquid supplying step of supplying the ground containing underground water with a first liquid, a second-liquid supplying step of supplying the ground with a second liquid, a mixing step of mixing the first liquid and the second liquid in the ground to form a salt, with the first liquid containing a calcium compound, the second liquid containing a carbonate compound, and the concentration of the calcium compound in the first liquid and the concentration of the carbonate compound in the second liquid each being below a saturated concentration at a temperature in the supply environment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for purifying groundwater and a purification material. [Background technology]

[0002] In mountain tunnel construction and other projects, excavated spoil is repurposed for embankments and storage areas, or in slag heaps, for example, the sulfide minerals contained in the excavated spoil and slag oxidize over time, leading to problems caused by acidification. Specifically, when rainwater seeps through acidified excavated spoil and slag, acidic water with a low pH is generated, containing high levels of dissolved substances such as harmful metals (e.g., lead, cadmium), zinc (highly toxic to aquatic organisms), and iron (which causes discoloration). If this acidic water intermittently seeps into the aquifer in the ground, it can exceed the buffering capacity of the soil and groundwater, raising concerns that the acidic water containing high levels of the aforementioned metals will spread into the surrounding environment. Therefore, various technologies have been proposed to address these concerns.

[0003] For example, Patent Document 1 discloses a ground improvement method for neutralizing acidic soil, which uses at least one alkaline material selected from the group consisting of blast furnace slag, converter slag, coal ash, limestone, and lime, having a predetermined particle size. Furthermore, Patent Document 2 discloses a method for impregnating acidic soil with a suspension of lime powder, which is powdered limestone, using a borehole. Furthermore, Patent Document 3 discloses a method for forming calcium carbonate in soil containing acidic water by supplying a calcium salt solution as a first liquid and a carbonate solution as a second liquid. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2000-282034

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] Since the method described in Patent Document 1 is a method of mixing gravel-like alkaline materials with contaminated soil, when attempting to modify the ground infiltrated with acidic water (ground containing acidic water generated from excavated waste or mine tailings stockpiled in the past), the ground must be excavated and the alkaline materials must be mixed, resulting in a significant increase in working costs and working time. In addition, the gravel-like alkaline material used in the method described in Patent Document 1 has a large particle size and a small specific surface area, so the effect of neutralizing acidic water is low, and the adsorption ability of metals cannot be said to be sufficient.

[0006] Since the method described in Patent Document 2 is a method of infiltrating a suspension of lime powder into the target ground, unlike the method described in Patent Document 1, it is possible to target the ground infiltrated with acidic water (ground containing acidic water generated from excavated waste or mine tailings stockpiled in the past) for modification. However, the method described in Patent Document 2 is effective as long as the permeability of the excavated waste or mine tailings is high. However, when the excavated waste or mine tailings are weathered and become finer, resulting in a significant decrease in permeability, the injection range of the lime powder suspension becomes narrower, and the injection efficiency also significantly decreases.

[0007] Since the method described in Patent Document 3 is a method of supplying two solutions, a calcium salt solution and a carbonate solution, to the ground, unlike Patent Document 2, it is not greatly affected by the permeability of the excavated waste or mine tailings, and concerns based on acidic water can be eliminated. However, in Patent Document 3, the concentrations of the respective compounds contained in the two solutions were not sufficiently examined. Therefore, the inventors conducted a detailed examination of the concentrations of each compound in the two solutions and found that, depending on the concentration of each compound, the compounds may precipitate and clog in the ground, which could lead to problems such as the inability to properly supply the two solutions.

[0008] From this perspective, the present invention aims to provide a method for purifying groundwater and a purification material that neutralizes acidic water and suppresses the leakage of metals, while preventing clogging in ground containing excavated spoil, slag, etc., that have been stockpiled in the past or will be generated in the future. [Means for solving the problem]

[0009] A groundwater purification method according to the present invention for solving the aforementioned problems comprises a first liquid supply step of supplying a first liquid to ground containing groundwater, a second liquid supply step of supplying a second liquid to the ground, and a mixing step of mixing the first liquid and the second liquid in the ground to form a salt, wherein the first liquid contains a calcium compound, the second liquid contains a carbonate compound, the concentration of the calcium compound in the first liquid and the concentration of the carbonate compound in the second liquid are below the saturation solubility at the temperature of the supply environment, and the results obtained by sampling groundwater upstream of the ground to which the first and second liquids are supplied and measuring the concentration of metal cations before and after adding the first and second liquids to the groundwater. Based on, The aforementioned metal cation reacts with carbonate ions. Taking into account the amount of carbonate ions consumed, The supply amount of the second liquid and the concentration of the carbonate compound in the second liquid are adjusted. Furthermore, the groundwater purification method according to the present invention includes a first liquid supply step of supplying a first liquid to ground containing groundwater, a second liquid supply step of supplying a second liquid to the ground, and a mixing step of mixing the first liquid and the second liquid in the ground to form a salt, wherein the first liquid contains a calcium compound, the second liquid contains a carbonate compound, the concentration of the calcium compound in the first liquid and the concentration of the carbonate compound in the second liquid are less than the saturation solubility at the temperature of the supply environment, and immediately before the first liquid and the second liquid come into contact in the mixing step, the concentration of the calcium compound in the first liquid is 1.0 to 2.5 mol / L, and the concentration of the carbonate compound in the second liquid is 0.2 to 0.5 mol / L. According to the present invention, by mixing a first liquid containing a calcium compound with a second liquid containing a carbonate compound to form a salt (calcium carbonate), both solutions can be properly penetrated even in soil with low permeability, and salt can be formed at a depth effective for purifying groundwater in the soil. As a result, according to the present invention, the formed salt (calcium carbonate) can properly neutralize acidified groundwater and also adsorb metals to suppress leakage. Furthermore, according to the present invention, since the concentration of the calcium compound in the first solution and the concentration of the carbonate compound in the second solution are below their saturation solubility at the temperature of the supply environment, the two solutions can be mixed without the calcium compound and carbonate compound precipitation, thereby preventing clogging caused by the precipitation of the two compounds.

[0010] In the groundwater purification method according to the present invention, it is preferable that at least one of the concentration of the calcium compound in the first liquid and the concentration of the carbonate compound in the second liquid is less than 0.6 mol / L immediately before the first liquid and the second liquid come into contact in the mixing step. According to the present invention, since at least one of the concentrations of the calcium compound in the first solution and the carbonate compound in the second solution immediately before contact between the first and second solutions is less than 0.6 mol / L, it is possible to avoid the formation of a strong gel that does not easily break down after mixing the two solutions, and to prevent clogging caused by the gel.

[0011] Also, According to the present invention, since the concentration of the calcium compound in the first solution and the concentration of the carbonate compound in the second solution immediately before contact between the first and second solutions are within predetermined ranges, the metal (zinc ion) adsorption capacity of the salt (calcium carbonate) formed by mixing the two solutions can be made very high.

[0012] In the groundwater purification method according to the present invention, it is preferable to adjust the supply amount of the first liquid and the concentration of the calcium compound in the first liquid, and the supply amount of the second liquid and the concentration of the carbonate compound in the second liquid, in the mixing step, so that the calcium ions and carbonate ions supplied to the ground are equimolar. According to the present invention, the first and second liquids are adjusted so that the calcium ions and carbonate ions supplied to the ground are equimolar, so that both ions react without excess or deficiency (Ca 2+ +CO3 2- →CaCO3) and salt (calcium carbonate) can be formed appropriately.

[0013] Also, According to the present invention, since the first and second liquids are adjusted taking into account the amount of metal cations in the groundwater, it is possible to address situations where the supplied carbonate ions decrease due to binding with metal cations in the groundwater, thereby enabling the formation of salt (calcium carbonate) more appropriately.

[0014] The purifying material according to the present invention for solving the aforementioned problems is , earthA purifying material for purifying groundwater by supplying it to ground containing sewage, wherein a first liquid and a second liquid are supplied to the ground and mixed together, the first liquid contains a calcium compound, and the second liquid contains a carbonate compound, the concentration of the calcium compound in the first liquid and the concentration of the carbonate compound in the second liquid are below the saturation solubility at the temperature of the supply environment, and immediately before the first liquid and the second liquid come into contact, the concentration of the calcium compound in the first liquid is 1.0 to 2.5 mol / L, and the concentration of the carbonate compound in the second liquid is 0.2 to 0.5 mol / L. 。 Ma Furthermore, in the purifying material according to the present invention, it is preferable that the supply amount of the first liquid and the concentration of the calcium compound in the first liquid are adjusted so that the calcium ions and carbonate ions supplied to the ground are equimolar, and that the supply amount of the second liquid and the concentration of the carbonate compound in the second liquid are adjusted. According to the present invention, by mixing a first liquid containing a calcium compound with a second liquid containing a carbonate compound to form a salt (calcium carbonate) which is a purifying material, both solutions can be properly penetrated even in soil with low permeability, and salt can be formed at a depth that is effective for purifying groundwater in the soil. As a result, according to the present invention, the formed salt (calcium carbonate) can properly neutralize acidified groundwater and also adsorb metals to suppress leakage. Furthermore, according to the present invention, since the concentration of the calcium compound in the first solution and the concentration of the carbonate compound in the second solution are below their saturation solubility at the temperature of the supply environment, the two solutions can be mixed without the calcium compound and carbonate compound precipitation, thereby preventing clogging caused by the precipitation of the two compounds. [Effects of the Invention]

[0015] According to the groundwater purification method and purification material of the present invention, it is possible to neutralize acidic water and suppress the leakage of metals while preventing clogging in ground containing excavated spoil, slag, etc. that have been stored in the past or will be generated in the future. [Brief explanation of the drawing]

[0016] [Figure 1] This is a plan view of the purification equipment used in the groundwater purification method according to this embodiment. [Figure 2] This graph shows the amount of zinc adsorbed onto calcium carbonate per unit weight in each test case in Example 1 (adsorption amount when the zinc ion concentration in the liquid phase is the water quality environmental standard value of 0.03 mg / L). [Figure 3] This graph shows the change in pH over time when using calcium carbonate synthesized using the first and second solutions in Example 2, and when using limestone powder. [Figure 4] This is a photograph of the solutions used in Example 3; the right side shows Solution 1, which contains calcium chloride, and the left side shows Solution 2, which contains sodium carbonate. [Figure 5] This is a photograph of the calcium carbonate immediately after synthesis, obtained by mixing the first solution (a 0.6 mol / L calcium chloride solution) and the second solution (a 0.6 mol / L sodium carbonate solution) in Example 3. [Figure 6] This is a photograph of calcium carbonate after mixing the first solution (0.6 mol / L calcium chloride solution) and the second solution (0.6 mol / L sodium carbonate solution) in Example 3 and letting it stand for 1 hour. [Figure 7] This is a photograph of calcium carbonate immediately after mixing the first solution (7 mol / L calcium chloride solution) and the second solution (0.5 mol / L sodium carbonate solution) in Example 3. [Figure 8] This is a photograph of calcium carbonate immediately after synthesis by mixing the first solution (0.5 mol / L calcium chloride solution) and the second solution (2 mol / L sodium carbonate solution) in Example 3. [Figure 9A] This is an electron microscope image of calcium carbonate (purification material A) at a magnification of 2,000x in Example 5. [Figure 9B] This is an electron microscope image of calcium carbonate (purification material B) at a magnification of 2,000x in Example 5. [Figure 9C] This is an electron microscope image of limestone powder in Example 5 at a magnification of 2,000x. [Figure 10A] This is an electron microscope image of calcium carbonate (purification material A) at a magnification of 20,000x in Example 5. [Figure 10B] This is an electron microscope image of calcium carbonate (purification material B) at a magnification of 20,000x in Example 5. [Figure 10C] This is an electron microscope image of limestone powder in Example 5 at a magnification of 20,000x. [Modes for carrying out the invention]

[0017] First, the purification equipment used in the groundwater purification method according to this embodiment will be explained using Figure 1, which is a plan view of the purification equipment S1. [Purification equipment] The purification facility S1 is a facility that forms a chemical barrier against acidic water generated by the oxidation of excavated spoil and slag. The purification facility S1 comprises a plurality of upstream observation holes 1B (four in Figure 1) located upstream in the direction of groundwater flow (direction indicated by the arrows in Figure 1), a plurality of downstream observation holes 2B (four in Figure 1) located downstream in the direction of flow, and a plurality of solution supply wells 1 (16 in Figure 1) located between the upstream observation holes 1B and the downstream observation holes 2B in the direction of flow. The solution supply wells 1 are arranged in rows that intersect with respect to the direction of flow (direction indicated by the arrows in Figure 1). The solution supply well 1 is a pipe for supplying the first and second liquids (described later) to the ground (and the groundwater in the ground). While it is possible to distinguish between the well for the first liquid and the well for the second liquid, if the first and second liquids are supplied to the ground alternately, the distinction may not be made (a configuration in which both the first and second liquids are supplied from the same well). Furthermore, the upstream observation well 1B and the downstream observation well 2B are wells for observing the composition of the groundwater before and after the supply of the first and second liquids.

[0018] The circle surrounding the solution supply well 1 shown in Figure 1 represents a hypothetical cylindrical region where, if the solutions (first liquid and second liquid) supplied from the solution supply well 1 do not flow, the voids between soil particles are assumed to be replaced by each solution. In reality, each solution does not remain in this cylindrical region but diffuses downstream with the flow of groundwater, forming salts. However, by designing the purification equipment S1 so that these hypothetical cylindrical regions overlap, a chemical barrier of salts that purifies groundwater can be formed without leakage. Therefore, it is preferable to set the spacing of the solution supply wells 1 and the amount of each solution supplied from the solution supply well 1 so that the above-mentioned hypothetical cylindrical regions overlap. The row of solution supply wells 1 may be a single row, but from the viewpoint of overlapping the cylindrical areas described above to suppress groundwater leakage, it is preferable to have two or more rows arranged in a staggered pattern. The purification equipment S1 is not particularly limited as long as it is configured to supply the solution to the ground. For example, it may be equipment equipped with injection holes into which the solution can be injected into the ground using a packer, equipment equipped with inclined wells or horizontal wells to supply the solution to the ground, or a device that installs a trench in the shallow part of the ground and supplies the solution in a curtain-like manner.

[0019] Next, a method for purifying groundwater according to this embodiment will be described. [Methods for purifying groundwater] The groundwater purification method according to this embodiment includes a first liquid supply step, a second liquid supply step, and a mixing step. Furthermore, the groundwater purification method according to this embodiment may include a supply condition setting step before the first liquid supply step.

[0020] (Supply condition setting process) In the supply condition setting process, various parameters of the supply environment are measured and analyzed in advance, and supply conditions such as the concentration of each compound in the first and second liquids to be supplied to the ground are set. Here, the various parameters of the supply environment include, for example, the temperature of the supply environment, the concentration of metal cations in the groundwater, the concentration of carbonate ions, and the pH.

[0021] (Supply condition setting process: Below the saturation solubility of the supply environment temperature) In the supply condition setting step, the temperature of the supply environment is measured, and based on the obtained temperature, the saturation solubility of the calcium compound (C1 S mol / L) and the saturation solubility of the carbonate compound (C2 S mol / L) are determined. Then, the concentration of the calcium compound in the first liquid (C1 mol / L) is set to be less than the saturation solubility (C1 < C1 S ), and the concentration of the carbonate compound in the second liquid (C2 mol / L) is set to be less than the saturation solubility (C2 < C2 S ). By setting the concentration of the calcium compound in the first liquid to be less than the saturation solubility (C1 < C1 S ) and the concentration of the carbonate compound in the second liquid to be less than the saturation solubility (C2 < C2 S ), precipitation of the calcium compound and the carbonate compound can be avoided before the working fluid is supplied to the ground, so that clogging caused by precipitation of the two compounds can be prevented. Here, the "saturation solubility at the temperature of the supply environment" is the saturation solubility of each compound at the lowest temperature exhibited by each solution from when the first liquid and the second liquid are prepared as the working fluid until the time of mixing in the ground. More specifically, it is the saturation solubility of each compound at the lowest temperature among the temperature of the supply location (solution supply well or ground to be supplied), the temperature of the groundwater, and the liquid temperature of each prepared solution. Note that the concentration of the calcium compound in the first liquid (C1 mol / L) and the concentration of the carbonate compound in the second liquid (C2 mol / L) are the concentrations of each compound in the first liquid and the second liquid immediately after preparation of the working fluid. A part of the first liquid and the second liquid immediately after preparation of the working fluid can be sampled and measured using a known measuring device (for example, an inductively coupled plasma mass spectrometer, an ion chromatograph, or a total organic carbon meter). Simply, the electrical conductivity of the first liquid and the second liquid immediately after preparation of the working fluid can be measured and compared with the electrical conductivity at a known concentration for measurement.

[0022] (Supply condition setting step: at least one is less than 0.6 mol / L) In the supply condition setting step, immediately before the first liquid and the second liquid come into contact in the mixing step, the concentration of the calcium compound in the first liquid (C1 B(mol / L), and the concentration of the carbonate compound in the second solution (C2 B At least one of the values ​​(mol / L) is less than 0.6 mol / L (C1 B <0.6, C2 B It is preferable to set the concentration such that at least one of the following conditions is met: <0.6. If the concentration of the calcium compound in the first solution and the concentration of the carbonate compound in the second solution are both 0.6 mol / L or higher when the two solutions come into contact, a gel-like substance (a strong gel that does not easily break down) will be generated during the process of forming calcium carbonate. This can cause clogging in the ground due to the gel, potentially leading to malfunctions in the purification equipment. Note that the concentration of each compound in each solution (C1) is measured "immediately before the first and second solutions come into contact during the mixing process." B mol / L, C2 B mol / L) means, for example, if the first liquid is supplied to the ground and diluted with groundwater, and then the second liquid is supplied directly, then the C1 of the first liquid B The mol / L value was lower than the C1 mol / L immediately after the solution was prepared, and the C2 of the second solution B The mol / L value will be approximately the same as the C2 mol / L value immediately after the solution is prepared. Also, if the first and second solutions come into contact after being diluted by the groundwater in the soil, the C1 of the first solution will be... B The mol / L value was lower than the C1 mol / L immediately after the solution was prepared, and the C2 of the second solution B The mol / L value will also be lower than the C2mol / L value immediately after the solution was prepared. Furthermore, if the first liquid is supplied to the ground and diluted with groundwater, and then the second liquid is supplied directly, the concentration of calcium compounds in the first liquid (C1 B The concentration of the carbonate compound (C2) in the second liquid can be measured, for example, by sampling the first liquid from the supply pipe that supplies the second liquid after the first liquid has been supplied to the ground, and using a known measurement method. B Since the concentration of the carbonate compound in the second solution (C2mol / L) immediately after preparation is the same value (because the second solution does not become diluted between preparation and contact with the first solution), it can be measured using the same method as described above for measuring the concentration of the carbonate compound in the second solution (C2mol / L). Also, the concentration of the calcium compound in the first solution (C1 B (mol / L) and the concentration of the carbonate compound in the second solution (C2 B The concentration (mol / L) can also be determined by calculating the concentration at the point just before the two solutions come into contact using numerical simulation.

[0023] (Supply condition setting process: 1.0~2.5mol / L, 0.2~0.5mol / L) In the supply condition setting process, immediately before the first liquid and the second liquid come into contact in the mixing process, the concentration of the calcium compound in the first liquid (C1 B The concentration (mol / L) becomes 1.0 to 2.5 mol / L (C1 B =1.0~2.5), concentration of the carbonate compound in the second solution (C2 B (C2) The concentration (mol / L) will be 0.2 to 0.5 mol / L. B It is preferable to set the concentration to such a range as 0.2 to 0.5. This is because when the two solutions come into contact while the concentrations of the calcium compound in the first solution and the carbonate compound in the second solution are both within the predetermined ranges described above, calcium carbonate with excellent adsorption capacity for metals (zinc ions) is formed.

[0024] (Supply condition setting process: equimolar) In the supply condition setting process, it is preferable to set the supply amount of the first liquid and the concentration of the calcium compound in the first liquid, and the supply amount of the second liquid and the concentration of the carbonate compound in the second liquid, so that the calcium ions and carbonate ions supplied to the ground are equimolar. For example, if the concentration of the calcium compound in the first solution (C1 mol / L) is set higher than the concentration of the carbonate compound in the second solution (C2 mol / L), the supply amount of the second solution should be set to be greater than the supply amount of the first solution so that the calcium ions supplied by the first solution and the carbonate ions supplied by the second solution are equimolar. When the calcium ions and carbonate ions supplied to the ground are equimolar, both ions will react without excess or deficiency (Ca 2+ +CO3 2- →CaCO3) and salt (calcium carbonate) can be formed appropriately.

[0025] (Supply condition setting process: concentration of metal cations and carbonate ions, pH) In the supply condition setting process, it is preferable to set the supply amount of the first liquid and the concentration of the calcium compound in the first liquid, and the supply amount of the second liquid and the concentration of the carbonate compound in the second liquid, taking into consideration the concentration of metal cations, carbonate ions, and pH in the groundwater. Specifically, the following steps (1) to (4) are performed: (1) After sampling groundwater from the upstream observation well 1B shown in Figure 1, (2) an indoor test is conducted on the sampled groundwater to measure the composition (concentration of metal cations and carbonate ions, pH) before and after adding the first and second liquids. Based on the results of the indoor test, the amount of calcium ions remaining in the groundwater and the pH that should be increased are calculated. (3) Based on the calculated values, the supply amount of the first liquid and the concentration of the calcium compound in the first liquid are set, and the supply amount of the second liquid and the concentration of the carbonate compound in the second liquid are set. (4) Each set concentration meets the aforementioned concentration condition (C1 <C1 S , C2 <C2 S , C1 B <0.6, C2 B <0.6, C1 B =1.0~2.5, C2 B Check if the condition (e.g., 0.2 to 0.5) is met. Metal cations (Mn and Zn) in groundwater react with carbonate ions to produce carbonates. Furthermore, carbonate ions in groundwater not only react with calcium to form calcium carbonate, but also react with hydrogen ions to form bicarbonate ions (CO3). 2- +H + →HCO3 - ), or it returns to carbonic acid (HCO3 - +H + The phenomenon of →H2CO3 occurs. Therefore, by taking into account the concentrations of metal cations and carbonate ions in the groundwater and setting the supply conditions for the first and second liquids (by performing the operations (1) to (4) described above), salt (calcium carbonate) can be formed more appropriately. Furthermore, the concentrations of metal cations and carbonate ions in groundwater can be measured using known measuring devices (for example, inductively coupled plasma mass spectrometers, ion chromatographs, and total organic carbon analyzers).

[0026] A more detailed example of the calculation methods described in (1) to (3) above is shown below. [1] The required service life for the purifying material (calcium carbonate) is set as A (years). [2] The pH of the groundwater is B, the groundwater flow velocity is C (m / year), and the cross-sectional area through which the groundwater passes in the aquifer is D (m 2 If this is the case, the cumulative amount of hydrogen ions E (mol) over A years is given by the following equation. E = A × 10 -B ×C×D×1000 [3] Assuming that 1 mole of calcium carbonate consumes 1 mole of hydrogen ions, the amount of calcium carbonate required is E(mol), therefore, at least E(mol) of calcium ions and carbonate ions are needed for the synthesis of the purifying agent. [4] In the laboratory test in (2), if the concentration of the calcium compound in the first solution added to the groundwater is F (mol / L), then for example, if it is calcium chloride, the concentration of calcium ions is also F (mol / L), and the amount of the first solution added G (L) is given by the following equation. G = E ÷ F Similarly, if the concentration of the carbonate compound in the second liquid added to the groundwater is H (mol / L), then, for example, if it is sodium carbonate, the concentration of carbonate ions is also H (mol / L), and the amount of the second liquid added, I (L), is given by the following equation. I = E ÷ H [5](2) In the results of the laboratory test, for example, if the amount of calcium ions remaining in the groundwater is J (mol), an equivalent amount of carbonate ions is required in addition. However, since carbonate ions may also react with metal ions other than calcium contained in the groundwater, the amount of metal ions other than calcium may be included in J (mol). If the amount of the second solution added remains at I (L), the concentration of the carbonate compound in the second solution increases from H (mol / L) to K (mol / L) as shown by the following equation. K = (E + J) ÷ I [6] Based on the above considerations, the concentrations and amounts of calcium and carbonate compounds added are as follows. Concentration of calcium compound in solution 1: F (mol / L), Amount of solution 1 added: G (L) Concentration of the carbonate compound in the second solution: K (mol / L), Amount of the second solution added: I (L)

[0027] Regarding the supply condition setting process, we have explained how to set supply conditions based on various items of different supply environments, but it is not necessary to implement all of them. For example, in the supply condition setting process, supply conditions may be set based only on saturated solubility, or they may be set based on both saturated solubility and a concentration of less than 0.6 mol / L.

[0028] (1st liquid supply process) In the first liquid supply process, the first liquid is supplied to the ground containing groundwater. The first liquid is a solution containing a calcium compound, and the concentration of the calcium compound in the first liquid should be the value set in the supply condition setting step described above. Calcium compounds are calcium ions (Ca 2+ The compound contains ), and examples include calcium chloride (CaCl2), calcium bromide (CaBr2), calcium iodide (CaI2), and calcium nitrate (Ca(NO3)2). Among these, calcium chloride is preferred because it does not pose a risk of causing nitrogen contamination of groundwater and is inexpensive.

[0029] (Second liquid supply process) In the second liquid supply process, the second liquid is supplied to the ground containing groundwater. The second liquid is a solution containing a carbonate compound, and the concentration of the carbonate compound in the second liquid should be the value set in the supply condition setting step described above. Carbonate compounds are carbonate ions (CO3 2-The compound contains ), and examples include sodium carbonate (Na2CO3), potassium carbonate (K2CO3), and ammonium carbonate ((NH4)2CO3). Among these, sodium carbonate is preferred because it does not pose a risk of causing nitrogen contamination of groundwater and is inexpensive.

[0030] (The order of the first liquid supply process and the second liquid supply process) The order of the first liquid supply process and the second liquid supply process is not particularly limited. For example, they may be repeated alternately as follows: first liquid supply process → second liquid supply process → first liquid supply process →… or second liquid supply process → first liquid supply process → second liquid supply process →… Furthermore, if separate solution supply wells are provided for supplying the first liquid and the second liquid, the first liquid supply process and the second liquid supply process may be performed simultaneously.

[0031] (Mixing process) In the mixing process, the first liquid and the second liquid mix together to form a salt. In detail, during the mixing process, calcium ions (Ca) of the calcium compound of the first liquid are released. 2+ ) and the carbonate ions (CO3) of the carbonate compound in the second solution. 2- ) reacts with to form calcium carbonate (CaCO3). This calcium carbonate can neutralize acidified groundwater (raise the pH) and also adsorb metals (such as zinc ions).

[0032] (Other processes) In this embodiment, the groundwater purification method may include a feedback step after the mixing step in which the supply conditions are readjusted based on the results of analyzing the liquid (first liquid + second liquid + groundwater) sampled at the downstream observation well 2B in Figure 1. Furthermore, the groundwater purification method according to this embodiment may include a check step in which the effectiveness of calcium carbonate (purification material) is checked based on the results of analyzing the liquid sampled at the downstream observation well 2B in Figure 1.

[0033] [Purification material] The purifying material according to this embodiment is a salt (calcium carbonate) formed by mixing the first liquid and the second liquid described above. The purifying material according to this embodiment is formed by first and second liquids based on predetermined supply conditions, and therefore differs from limestone powder in properties (particle size, specific surface area, etc.). As a result, it exhibits excellent adsorption capacity for metal cations (such as zinc ions) and pH neutralization capacity. [Examples]

[0034] [Example 1: Zinc adsorption capacity test] (Example 1: Preparation of test cases 1-10) Two solutions, Solution 1 and Solution 2, were prepared with the concentrations of sodium chloride and sodium carbonate shown in Table 1 (concentrations before mixing). Then, the amounts of Solution 1 and Solution 2 shown in Table 1 were poured into a 50 ml resealable polypropylene container, mixed by inverting, and allowed to stand for a while. In test cases 1 to 10, the volumes of the first and second solutions were determined so that the amount of calcium carbonate produced was calculated to be 0.2 g, and the amounts of calcium ions and carbonate ions were equimolar across each test case. Then, to the containers after standing, zinc chloride (ZnCl2) solution of the same concentration and volume for each test case was added, and distilled water was added to unify the liquid volume in the containers to 40 ml, thus preparing the samples for test cases 1 to 10.

[0035] (Example 1: Preparation of Test Case 11) 0.2 g of limestone powder was added to a centrifuge tube, and zinc chloride solution of the same concentration and volume as in the other test cases was added. Distilled water was then added to bring the total volume to 40 ml, thus preparing the sample for test case 11. For the limestone powder used, we used Softon 1,200 (manufactured by Shiraishi Calcium Co., Ltd.), a commercially available product.

[0036] (Example 1: Test Contents) The prepared samples were continuously shaken for 24 hours at a rotation speed of 10 revolutions per minute using a rotary shaker. The supernatant was then filtered through a resin filter (pore size 0.45 μm), and the zinc ion concentration in the supernatant was measured using an ICP-MS instrument. Then, the measurement results obtained for each test case (amount of adsorption per unit weight to the adsorbent at adsorption equilibrium, and ion concentration of the liquid phase at adsorption equilibrium) were approximated by power estimation using the following Freundlich-type adsorption isotherm to obtain an approximate curve. Since multiple measurement results are required for each test case in the power estimation of the measurement results, the test was performed multiple times for each test case by changing the amount of zinc chloride solution added, and an approximate curve was obtained from the measurement results obtained. Based on the obtained approximate curve, the amount of zinc adsorbed onto calcium carbonate when the zinc ion concentration in the liquid phase is the water quality environmental standard value of 0.03 mg / L was calculated for each test case. Note that the Freundlich type adsorption isotherm is C S =kC w 1 / n It is represented as C S : Amount of adsorption per unit weight to the adsorbent at the time of adsorption equilibrium, C w : Ion concentration of the liquid phase at adsorption equilibrium, k, n: Coefficients specific to the adsorbent. Then, from the above measurements, C S , C w The values ​​obtained are then used for power approximation to obtain k and n specific to the calcium carbonate synthesized in each test case.

[0037] [Table 1]

[0038] (Example 1: Examination of Results) Figure 2 shows the amount of zinc adsorbed onto calcium carbonate per unit weight in each test case (adsorption amount when the zinc ion concentration in the liquid phase is 0.03 mg / L, which is the water quality environmental standard). The calcium carbonate synthesized from the first solution (calcium chloride solution) and the second solution (sodium carbonate solution) in Test Cases 1-10 all showed higher zinc adsorption capacity compared to the case using Softon 1,200, a limestone powder (Test Case 11). Among these, the calcium carbonate synthesized in Test Cases 2, 3, 4, 6, 7, and 8, where the concentration of calcium chloride in the first solution was in the range of 1.0-2.5 mol / L and the concentration of sodium carbonate in the second solution was in the range of 0.2-0.5 mol / L, showed extremely high zinc adsorption capacity.

[0039] [Example 2: Neutralization ability test] (Example 2: Test details) In a 250 ml glass beaker, a first solution (25 ml) containing calcium chloride at a concentration of 0.2 mol / L and a second solution (5 ml) containing sodium carbonate at a concentration of 1 mol / L were added to synthesize 0.5 g of calcium carbonate in the beaker. In addition, 0.5g of Softon 1,200 (manufactured by Shiraishi Calcium Co., Ltd.) was added as limestone powder to a 250ml glass beaker. Distilled water was added to each beaker to adjust the volume to 50 ml, and the mixture was continuously stirred with a magnetic stirrer. During this stirring, 4.5 ml of acidic water, adjusted to pH 2.2 using dilute sulfuric acid, was added to each beaker, and the pH change was measured at 1-second intervals for 60 seconds. The pH was measured using a pH meter in the liquid phase (liquid portion) of each beaker.

[0040] (Example 2: Examination of Results) Figure 3 shows the results of the time-dependent change in pH in the liquid phase of each beaker. Calcium carbonate synthesized from a first solution containing calcium chloride and a second solution containing sodium carbonate (solid line in Figure 3) consistently maintained a higher pH than limestone powder (dotted line in Figure 3) after the addition of acidic water. This is thought to be because limestone powder is made by crushing natural limestone, and since natural limestone undergoes long-term crystal growth, the bonds between calcium carbonate molecules are strong, and only the surface of the calcium carbonate particles reacted with acidic water. From these results, it can be inferred that calcium carbonate synthesized from the first solution containing calcium chloride and the second solution containing sodium carbonate can neutralize acidic water in a smaller amount than limestone powder.

[0041] [Example 3: Gelation Confirmation Test] (Example 3: Test Details) Calcium carbonate was synthesized by mixing a first solution containing calcium chloride at a concentration of 0.6 mol / L, as shown on the right side of Figure 4, with a second solution containing sodium carbonate at a concentration of 0.6 mol / L, as shown on the left side of Figure 4. Figure 5 shows the calcium carbonate immediately after synthesis using the two solutions in Figure 4. The calcium carbonate was in a gel-like state (it did not dissolve easily with just a light shake of the beaker), and it gradually dissolved over time. Figure 6 shows the calcium carbonate after 1 hour of synthesis using the two solutions in Figure 4. It had become a slurry, and the calcium carbonate particles had settled. These results confirm that when using a first solution containing calcium chloride at a concentration of 0.6 mol / L and a second solution containing sodium carbonate at a concentration of 0.6 mol / L, the synthesis of calcium carbonate in the ground can result in a gel-like state, raising concerns about clogging of the ground and malfunctions in the purification equipment.

[0042] Figure 7 shows the calcium carbonate immediately after synthesis from the first solution containing calcium chloride at a concentration of 7 mol / L and the second solution containing sodium carbonate at a concentration of 0.5 mol / L. Figure 8 also shows the calcium carbonate immediately after synthesis from the first solution containing calcium chloride at a concentration of 0.5 mol / L and the second solution containing sodium carbonate at a concentration of 2 mol / L. Here, the 7 mol / L calcium chloride solution and the 2 mol / L sodium carbonate solution are at concentrations approximately equal to their saturation solubility at 20°C, indicating that they are set to very high concentrations. Furthermore, the appearance of the calcium carbonate immediately after synthesis in Figures 7 and 8 both appears to be a gel-like substance, but when a gentle force is applied (by lightly shaking the beaker), it dissolves easily and changes into a slurry.

[0043] (Example 3: Examination of Results) Based on the results in Figures 4-8, if at least one of the concentrations of calcium chloride in the first solution and sodium carbonate in the second solution is less than 0.6 mol / L, even if it initially forms a gel, the gel state will easily be released by vibration, etc., and it will easily penetrate into the ground by groundwater or the flow of the solution, so it is thought that it will not hinder construction.

[0044] [Example 4: Test to confirm the effect of metal ions] (Example 4: Test Contents) To 1 L of acidic water with the composition shown in Table 2, 15 ml of Solution 1, containing 1 mol / L calcium chloride, and 15 ml of Solution 2, containing 1 mol / L sodium carbonate, were added, and the pH and metal ion concentration in the liquid phase were measured. pH was measured using a pH meter, calcium ion concentration was measured using an ion chromatograph, and other metal ion concentrations were measured using an inductively coupled plasma emission spectrometer. The results are shown in Table 2.

[0045] [Table 2]

[0046] (Example 4: Review of Results) First, as shown in Table 2, the pH increased to 9.0 upon the addition of the first and second solutions, confirming the neutralizing effect on acidic water. Next, comparing the concentrations of each metal ion in acidic water with the concentrations of each metal ion in the liquid phase after the addition of the first and second solutions (after the addition of the second solution), the calcium ion concentration was higher in the liquid phase after the addition of the second solution, while the concentrations of other metal ions were lower in the liquid phase after the addition of the second solution. In addition, IC (inorganic carbon concentration: indicating the concentration of carbon derived from inorganic substances in the liquid phase. Here, it is thought to mainly indicate the amount of carbonate ions and bicarbonate ions) was higher in the liquid phase after the addition of the second solution. If we assume that the carbonate ions in the sodium carbonate solution and the calcium ions in the calcium chloride solution reacted without excess or deficiency during the addition of the two solutions, then all the added carbonate and calcium ions should precipitate as calcium carbonate, and the calcium ion concentration and IC in the liquid phase should remain unchanged after the addition of the two solutions. However, in reality, the added carbonate ions are consumed by reacting with various ions in the acidic water, which is thought to have caused differences in calcium ion concentration and IC. Furthermore, while it is possible that the concentration of metal ions in the liquid phase decreased due to adsorption to the generated calcium carbonate and the formation of hydroxide precipitates due to pH changes, it is also thought that some reacted with carbonate ions to form carbonates and precipitate. From these results, if we ignore the calcium ions originally present in the groundwater, the amount of remaining calcium ions can be calculated to be 350 mg / L. Assuming a calcium ion mass number of 40,000 mg / mol, the amount of remaining calcium ions is 8.75 × 10⁻⁶. -3 The concentration is mol / L. Considering that an equivalent amount of carbonate ions is needed in addition to the calcium ions, if 15 ml of sodium carbonate solution (second solution) is added, it is preferable to set the concentration of sodium carbonate in the second solution to 1.58 mol / L. Furthermore, taking into account the amount of calcium ions originally contained in the groundwater, it is also possible to set the concentration of the sodium carbonate solution higher or the concentration of the calcium chloride solution lower. From these results, it was confirmed that it is preferable to set the supply amount of the first solution and the concentration of the calcium compound in the first solution, and the supply amount of the second solution and the concentration of the carbonate compound in the second solution, taking into consideration the concentration of metal cations in the groundwater.

[0047] [Example 5: Particle Shape Confirmation Test] (Example 5: Test Contents) The particle shapes of the following were confirmed using an electron microscope: calcium carbonate (purification material A) synthesized by mixing a first solution containing 1 mol / L calcium chloride and a second solution containing 1 mol / L sodium carbonate; calcium carbonate (purification material B) synthesized by mixing a first solution containing 0.2 mol / L calcium chloride and a second solution containing 1 mol / L sodium carbonate; and Softon 1,200 (manufactured by Shiraishi Calcium Co., Ltd.), which is limestone powder.

[0048] (Example 5: Examination of Results) Figures 9A to 9C are electron microscope images taken at a magnification of 2,000x. Figure 9A is a photograph of calcium carbonate (purification material A), Figure 9B is a photograph of calcium carbonate (purification material B), and Figure 9C is a photograph of limestone powder. Furthermore, Figures 10A to 10C are electron microscope images taken at a magnification of 20,000x. Figure 10A is a photograph of calcium carbonate (purification material A), Figure 10B is a photograph of calcium carbonate (purification material B), and Figure 10C is a photograph of limestone powder. The calcium carbonate synthesized by varying the concentration of calcium chloride in the first solution differed in particle shape and the way primary particles aggregated (Figures 9A, 9B, 10A, 10B). This difference in the properties of the calcium carbonate is thought to be the reason for the difference in zinc adsorption, as shown in Example 1. Furthermore, while irregularities were observed on the particle surface of the synthesized calcium carbonate, the particle surface of the limestone powder was smooth (Figures 9A-9C, 10A-10C). Therefore, it is considered that the specific surface area of ​​the synthesized calcium carbonate is larger than that of the limestone powder. Generally, the larger the specific surface area of ​​a substance, the larger the contact area with the liquid phase and the higher the reactivity. Thus, as shown in Example 1, it is considered that the synthesized calcium carbonate had a higher zinc adsorption capacity than the limestone powder. Similarly, regarding pH neutralization ability, in addition to the strength of the bonds between molecules mentioned above, the specific surface area is also thought to influence the pH neutralization ability in terms of reactivity with acidic water. As shown in Example 2, it is thought that the synthesized calcium carbonate had a higher pH neutralization ability than limestone powder. [Explanation of Symbols]

[0049] 1 Solution supply well 1B Upstream observation well 2B Downstream observation well

Claims

1. A first liquid supply process that supplies the first liquid to ground containing groundwater, A second liquid supply step for supplying the second liquid to the ground, The process includes a mixing step in which the first liquid and the second liquid mix in the ground to form a salt, The first solution contains a calcium compound, and the second solution contains a carbonate compound. The concentration of the calcium compound in the first solution and the concentration of the carbonate compound in the second solution are below their saturation solubility at the temperature of the supply environment. A method for purifying groundwater, characterized by sampling groundwater upstream of the ground to which the first liquid and the second liquid are supplied, measuring the concentration of metal cations before and after adding the first liquid and the second liquid to the groundwater, and adjusting the supply amount of the second liquid and the concentration of the carbonate compound in the second liquid based on the results of this measurement and taking into account the amount of carbonate ions consumed by the reaction of the metal cations with carbonate ions.

2. A first liquid supply process that supplies the first liquid to ground containing groundwater, A second liquid supply step for supplying the second liquid to the ground, The process includes a mixing step in which the first liquid and the second liquid mix in the ground to form a salt, The first solution contains a calcium compound, and the second solution contains a carbonate compound. The concentration of the calcium compound in the first solution and the concentration of the carbonate compound in the second solution are below their saturation solubility at the temperature of the supply environment. A method for purifying groundwater, characterized in that, immediately before the first liquid and the second liquid come into contact in the mixing step, the concentration of the calcium compound in the first liquid is 1.0 to 2.5 mol / L, and the concentration of the carbonate compound in the second liquid is 0.2 to 0.5 mol / L.

3. The method for purifying groundwater according to claim 1, characterized in that, immediately before the first liquid and the second liquid come into contact in the mixing step, at least one of the concentrations of the calcium compound in the first liquid and the carbonate compound in the second liquid is less than 0.6 mol / L.

4. The method for purifying groundwater according to claim 1 or 2, characterized in that, in the mixing step, the amount supplied of the first liquid and the concentration of the calcium compound in the first liquid are adjusted so that the calcium ions and carbonate ions supplied to the ground are equimolar, and the amount supplied of the second liquid and the concentration of the carbonate compound in the second liquid are adjusted.

5. A purification material that purifies groundwater by being supplied to ground containing groundwater, It is formed by supplying the first liquid and the second liquid to the ground and mixing them together. The first solution contains a calcium compound, and the second solution contains a carbonate compound. The concentration of the calcium compound in the first solution and the concentration of the carbonate compound in the second solution are below their saturation solubility at the temperature of the supply environment. A purifying material characterized in that, immediately before the first liquid and the second liquid come into contact, the concentration of the calcium compound in the first liquid is 1.0 to 2.5 mol / L, and the concentration of the carbonate compound in the second liquid is 0.2 to 0.5 mol / L.

6. The purification material according to claim 5, characterized in that the supply amount of the first liquid and the concentration of the calcium compound in the first liquid are adjusted so that the calcium ions and carbonate ions supplied to the ground are equimolar, and the supply amount of the second liquid and the concentration of the carbonate compound in the second liquid are adjusted.

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