JP2012024750A - Method for treating leachate of final disposal site - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating the leachate of a final disposal site by which the expense of chemicals and an operation cost can be reduced.SOLUTION: The leachate W of a final disposal site is divided using an amphoteric ion-exchange resin 4, into a first solution having low Caconcentration and high Naand SOconcentrations and a second solution having concentrations opposite thereof, and the first and second solutions are separately treated. Thus, the occurrence of scale by CaSOcan be suppressed to the minimum without needing addition of sodium carbonate or the like to remove the calcium ion, and an operation cost can be reduced. Besides, the amount of lead or the like collected in the solution having high calcium ion concentration can be controlled by controlling the switch timing of the first and second solutions discharged from the amphoteric ion-exchange resin on the basis of the calcium ion concentration and/or electrical conductivity of their solutions.

Description

  The present invention relates to a method for preventing calcium scale, and more particularly, to a method for preventing generation of scale due to calcium in a final disposal site, a cement manufacturing process, or the like.

  Waste disposal sites and other final disposal sites are facilities for disposing of wastes that are difficult to recycle. However, in view of the danger of exhaustion, effective use of wastes that have been treated at the final disposal site so far Is promoted.

  Incineration ash generated when municipal waste is incinerated has recently been recycled as a raw material for cement in view of the danger of depleting the final disposal site. Of municipal incineration ash, fly ash that is carried with gas and collected by the dust collector contains 10 to 20% of chlorine, so water-soluble chlorine contained in fly ash using water washing and desalination equipment After removing the compound with water, it is used as a cement raw material (see, for example, Patent Document 1).

  On the other hand, a chlorine bypass facility that removes chlorine that causes problems such as blockage of a preheater is used in a cement manufacturing facility. In recent years, recycling of waste containing incinerated ash as cement raw material or fuel has been promoted, and as the amount of waste processed increases, the amount of volatile components such as chlorine brought into the cement kiln also increases. The amount of dust generated is also increasing. Therefore, all the chlorine bypass dust cannot be used in the cement pulverization process, and the chlorine bypass dust is also washed with water (for example, see Patent Document 2).

Japanese Patent Laid-Open No. 11-100343 JP 2001-129513 A

However, in the final disposal site, calcium ions (Ca ²⁺ ) contained in the leachate and calcium sulfate (CaSO ₄ ) are generated from SO ₄ ^2- and adhere to the equipment as a scale in the filtration device and the wastewater treatment process at the later stage. However, there is a problem that stable operation is hindered. In addition, the incineration ash and chlorine bypass dust washing filtrate in the cement manufacturing process have the same problems as the leachate in the final disposal site.

  Therefore, for example, as shown in FIG. 10, in the final disposal site 50, a chemical reaction tank is used to remove calcium that causes scale generation and harmful heavy metals from the leachate W stored in the sedimentation / regulation pond 51. The chemicals are added at 52, and these are precipitated and removed by the filtration device 53, and then discharged after disinfection through COD treatment and removal of suspended solids (SS).

  However, in order to remove the calcium, it is necessary to add a large amount of sodium carbonate or potassium carbonate, which increases the cost of the drug and raises the operating cost.

  Therefore, the present invention has been made in view of the problems in the above-described conventional technology, and minimizes adverse effects on operation due to scale adhesion at a final disposal site or the like, and reduces operation costs including drug costs. The purpose is to suppress.

  In order to achieve the above object, the present invention provides a method for preventing calcium scale, which comprises converting a solution containing calcium ions into a solution having a low calcium ion concentration and a solution having a high calcium ion concentration using an amphoteric ion exchange resin. Separating and treating each solution separately.

According to the present invention, the amphoteric ion exchange resin is used to separate a solution with a low calcium ion concentration and a solution with a high calcium ion concentration and treat each solution separately. Even if sodium carbonate or the like is not added to remove calcium ions, scale generation due to CaSO ₄ or the like can be minimized, and the operating cost can be greatly reduced.

  In addition, when a general ion exchange resin such as a strong acid cation exchange resin is used, it is necessary to regenerate the resin using a strong acid or the like, whereas an amphoteric ion exchange resin regenerates the resin only with water. Therefore, complicated reproduction processing is not required.

  In the method for preventing calcium scale, the timing of switching the solution discharged from the amphoteric ion exchange resin between the low calcium ion concentration solution and the high calcium ion concentration solution is discharged from the amphoteric ion exchange resin. Can be controlled based on the calcium ion concentration and / or electrical conductivity of the solution. This makes it possible to control the amount of lead and the like recovered in a solution having a low calcium ion concentration.

  Further, in the method for preventing calcium scale, switching of the solution discharged from the amphoteric ion exchange resin between the solution having a low calcium ion concentration and the solution having a high calcium ion concentration is discharged from the amphoteric ion exchange resin. When the calcium ion concentration of the solution to be applied becomes 1/300 or more of the calcium ion concentration of the solution supplied to the amphoteric ion exchange resin. Thereby, the calcium scale can be accurately prevented. Alternatively, when the chlorine ion concentration of the solution discharged from the amphoteric ion exchange resin is 2/3 or less of the chlorine ion concentration of the solution supplied to the amphoteric ion exchange resin, the calcium scale is also accurately adjusted. Can prevent well.

  Furthermore, in the calcium scale prevention method, the supply amount of the solution containing the calcium ions to the amphoteric ion exchange resin can be made equal to the supply amount of reclaimed water to the amphoteric ion exchange resin. As a result, the amount of reclaimed water used can be reduced, and the waste water treatment facility at the subsequent stage can be downsized.

In the method for preventing calcium scale, the solution containing calcium ions further contains Na ⁺ , K ⁺ , Cl ⁻ , SO ₄ ²⁻ , and Cl ⁻ can be recovered in the solution having a high calcium ion concentration. Calcium ions and Cl ⁻ can be removed by utilizing the phenomenon that calcium chloride passes through the amphoteric ion exchange resin at a low rate, and the final solution contains Ca ²⁺ , Na ⁺ , K ⁺ , Cl ⁻ , SO ₄ ^2−. The leachate from the disposal site can be treated appropriately.

  In the calcium scale prevention method, harmful substances contained in the separated solution having a high calcium ion concentration can be removed.

  Moreover, in the said calcium scale prevention method, the solution containing the said calcium ion can be used as the leachate of a final disposal site, and can suppress the operating cost including the chemical | medical agent cost of a final disposal site low.

  Furthermore, the separated solution having a high calcium ion concentration can also be used for promoting stabilization of the final disposal site, and the amphoteric ion exchange resin can regenerate the resin only with water, but a large amount of calcium is contained. Although there is a disadvantage that water is generated, the above disadvantage is compensated by using the generated water containing a large amount of calcium to promote stabilization of the final disposal site, and the treatment and stabilization promotion of leachate at the final disposal site are reduced. This can be done at a low cost.

  Further, the solution containing calcium ions can be used as a filtrate obtained by washing incineration ash or / and chlorine bypass dust with water, or as a waste water of a salt recovery facility for recovering salt from seawater. Operating costs including chemical costs for wastewater treatment can be kept low.

  As described above, according to the present invention, it is possible to minimize the adverse effect on the operation due to the adhesion of the scale in the final disposal site or the like, and to keep the operation cost including the drug cost low.

It is a flowchart which shows an example of the leachate treatment system of the final disposal site using the prevention method of the calcium scale concerning this invention. It is the schematic for demonstrating operation | movement of the ion exchange resin used for the processing system shown in FIG. It is a graph which shows the operation example of the ion exchange resin shown in FIG. It is a flowchart which shows 1st Example of the processing system shown in FIG. It is a flowchart which shows 2nd Example of the processing system shown in FIG. It is a flowchart which shows 3rd Example of the processing system shown in FIG. It is a flowchart which shows 4th Example of the processing system shown in FIG. It is a flowchart which shows 5th Example of the processing system shown in FIG. It is a flowchart which shows 6th Example of the processing system shown in FIG. It is a flowchart which shows an example of the processing system of the conventional final disposal site.

  Next, modes for carrying out the present invention will be described with reference to the drawings. In the following description, a case where the present invention is used for preventing calcium scale in a final disposal site will be described as an example.

FIG. 1 shows a leachate treatment system (hereinafter referred to as “treatment system”) at a final disposal site to which the calcium scale prevention method according to the present invention is applied. The adjustment tank 3 for storing the leachate W, the leachate W from the adjustment tank 3 as a solution with high calcium ion concentration (hereinafter referred to as “calcium-containing water”) L3, and the calcium ion concentration is low and the SO ₄ ²⁻ concentration is high. The amphoteric ion exchange resin 4 separated into a solution (hereinafter referred to as “SO ₄ -containing water”) L4, the reclaimed water tank 5 for storing the reclaimed water L5 supplied to the amphoteric ion exchange resin 4, and the amphoteric ion exchange resin 4 were discharged. comprising a calcium-containing water tank 6, SO ₄ containing water tank 7 for storing each of calcium-containing water L3 and SO ₄ containing water L4, a heavy metal removing device 8, and a COD processor 9 .

  The adjustment tank 3 collects leachate W such as rainwater that has permeated through the waste layer of the final disposal site 2 and is prepared to equalize the change of water quality and quantity of the leachate W. A sand settling tank for sedimentation and separation of earth and sand is provided.

  The amphoteric ion exchange resin 4 is provided to remove calcium contained in the leachate W discharged from the adjustment tank 3. The amphoteric ion exchange resin has a function of allowing ion exchange with both cation and anion by making the base material cross-linked polystyrene or the like and having a quaternary ammonium group and a carboxylic acid group in the same functional group chain. Resin. For example, amphoteric ion exchange resin, Diaion (registered trademark), AMP03 manufactured by Mitsubishi Chemical Corporation can be used. The amphoteric ion exchange resin 4 can separate the electrolyte and the non-electrolyte in the aqueous solution, and can also separate the electrolytes from each other.

The heavy metal removing device 8 is provided for removing heavy metals such as lead contained in the SO ₄ -containing water L4, and a commonly used device such as a chemical reaction tank or a filter press can be used.

The COD treatment device 9 is provided to reduce the COD of the SO ₄ -containing water L4 from which heavy metals have been removed by the heavy metal removal device 8, and a general septic tank or the like can be used.

  Next, the operation of the processing system 1 having the above configuration will be described with reference to FIG.

Collect leachate W of the final disposal site 2 to the adjusting tank 3 water, after suppressing the change of the amount of water is supplied to amphoteric ion-exchange resin 4, on the leachate W calcium-containing water L3 and SO ₄ containing water L4 To separate. As shown in FIG. 2, this amphoteric ion exchange resin 4 performs batch processing continuously, and is previously filled with water (FIG. 2A), and then the amphoteric ion exchange resin from the adjustment tank 3. Leached water W is introduced into 4 and then reclaimed water L5 for regenerating the amphoteric ion exchange resin 4 is introduced (FIG. 2 (b)). Then, as shown in FIG. 2 (c), it is first discharged SO ₄ containing water L4, then, calcium-containing water L3 is discharged in this order over time.

Here, the switching timing of the SO ₄ -containing water L4 and calcium-containing water L3 is determined by measuring the concentrations of Ca ²⁺ , SO ₄ ²⁻ , chloride and Pb ^{2+ in} the treatment liquid discharged from the amphoteric ion exchange resin 4. As a result, it can be controlled based on one or more measurement results selected from the group consisting of electrical conductivity and pH. The SO ₄ -containing water L4 and the calcium-containing water L3 discharged from the amphoteric ion exchange resin 4 are temporarily stored in the SO ₄ -containing water tank 7 and the calcium-containing water tank 6, respectively.

Next, the calcium-containing water L3 stored in the calcium-containing water tank 6 is discharged. On the other hand, the SO ₄ -containing water L ₄ stored in the SO ₄ -containing water tank 7 removes heavy metals using the heavy metal removing device 8, further reduces COD by the COD processing device 9, and then discharges it.

As described above, according to this embodiment, the leachate W with calcium-containing water L3 via the amphoteric ion exchange resin 4 after separation in the SO ₄ containing water L4, for processing each separately, The generation of scale due to CaSO ₄ can be minimized without adding sodium carbonate or the like for removing calcium as in the prior art, and the operating cost can be greatly reduced.

Next, a first embodiment of the calcium scale prevention method used in the processing system 1 will be described. As the amphoteric ion exchange resin 4, the amphoteric ion exchange resin, Diaion AMP03 manufactured by Mitsubishi Chemical Corporation, is used, and the leachate W of the final disposal site 2 having the chemical components shown in Table 1 is used as the raw water. No. 4 was passed, and fresh water twice the amount of leachate W was passed as reclaimed water L5. Table 2, FIG. 3 and FIG. 4 show the relationship between the flow rate and the concentration of each component contained in the treatment liquid that has passed through the amphoteric ion exchange resin 4 and the water balance in the treatment system 1 at that time. In FIG. 4, the numbers in the ellipses indicate the weight ratio of each water. Incidentally, Table 1, Table 2 and Figure 3, the measured electric conductivity Cl ^- shows in terms of concentration.

In the graph shown in FIG. 3, the water flow rate / raw water amount 0.14 to 1.43 is SO ₄ -containing water L4, and the water flow rate / raw water amount 1.43 and later is calcium-containing water L3. As is apparent from the table and graph, in the SO ₄ -containing water L4, in addition to SO ₄ ²⁻ , Cl ⁻ and Na ⁺ can be recovered, and Pb ²⁺ , COD and NH ⁴⁺ are also SO ^4. _Since it can isolate | separate toward ₄ containing water L4, about these calcium containing water L3, these removal facilities become unnecessary and can suppress an installation cost and an operating cost low.

As clearly shown in Table 2 and FIG. 3, by using the phenomenon that calcium chloride (Ca ²⁺ and Cl ⁻ ) passes through the amphoteric ion exchange resin, the calcium-containing water L3 and the SO ₄ -containing water L4 The switching timing can be controlled on the basis of the calcium ion concentration of the solution discharged from the amphoteric ion exchange resin 4, and it is possible to avoid mixing of harmful substances such as lead into the calcium-containing water L3. At this time, the solution discharged from the amphoteric ion exchange resin 4 is 1/20 or more of the calcium ion concentration of 3000 mg / l of the leachate W introduced into the amphoteric ion exchange resin 4, that is, 150 mg / l or more, preferably 1 / Calcium scale can be accurately prevented by setting the time to 100 mg or more, 30 mg / l or more, more preferably 1/300 or more to 10 mg / l or more.

  Alternatively, when the solution discharged from the amphoteric ion exchange resin 4 becomes 1/10 or less of the chlorine ion concentration of 7,000 mg / l of the leachate W introduced into the amphoteric ion exchange resin 4, that is, preferably 700 mg / l or less. Is 1/2 or less, that is, 3500 mg / l or less, more preferably 2/3 or less, that is, 4700 mg / l or less. Since the chlorine ion concentration and the electric conductivity are in a proportional relationship, the electric conductivity can be controlled instead of the chlorine ion concentration.

In addition, as shown in FIG. 4, when the leaching water W having a weight of 0.67 and the reclaimed water L5 having a weight of 1.33 are supplied to the amphoteric ion exchange resin 4 as shown in FIG. A SO ₄ -containing water L4 having a weight of 1 is generated and treated separately and discharged.

FIG. 5 shows the water balance in the second embodiment of the calcium scale prevention method used in the treatment system 1, and this embodiment uses the recycled water L5 in order to make the waste water treatment facility of the treatment system 1 small. The case where the amount is suppressed is shown. In FIG. 5, the numbers in the ellipses indicate the weight ratio of each water. In this embodiment, the same amount of reclaimed water L5 as that of the leachate W at the final disposal site 2 is passed, and the weight 1 calcium-containing water L3 and the weight 1 SO ₄ -containing water L4 are separately treated and discharged. .

  FIG. 6 shows a third embodiment of the method for preventing calcium scale used in the treatment system 1, and in this embodiment, in addition to the configuration shown in FIG. A hazardous substance treatment apparatus 10 such as a heavy metal treatment apparatus for treating harmful substances slightly contained in the calcium-containing water L3 discharged from the water tank 6 is provided, and then released after removing harmful substances containing heavy metals such as lead. is doing.

FIG. 7 shows a fourth embodiment of the calcium scale prevention method used in the treatment system 1, and in this embodiment, the calcium-containing water L3 discharged from the calcium-containing water tank 6 in the configuration shown in FIG. And SO ₄ -containing water L4 discharged from the SO ₄ -containing water tank 7 are combined and then discharged. This makes it possible to cover the discharge of the calcium-containing water L3 and SO ₄ containing water L4 at one facility.

FIG. 8 shows a fifth embodiment of the method for preventing calcium scale used in the treatment system 1. In this embodiment, in addition to the configuration shown in FIG. 7, calcium-containing water discharged from the calcium-containing water tank 6 is used. L3 and the SO ₄ -containing water L4 discharged from the SO ₄ -containing water tank 7 are combined and passed through the sand filter 11 and then discharged. As a result, it is possible to remove CaSO ₄ suspended matter that may be generated by the merging of the calcium-containing water L3 and the SO ₄ -containing water L4.

  FIG. 9 shows a sixth embodiment of the method for preventing calcium scale used in the treatment system 1. In this embodiment, the calcium-containing water L3 discharged from the calcium-containing water tank 6 in the configuration shown in FIG. Is returned to the final disposal site 2 and used to promote stabilization of the final disposal site 2. The stabilization of the final disposal site 2 means that it is in the environment and does not change any more and is no longer affected. More specifically, among landfilled waste, degradable waste Substances are decomposed by the action of microorganisms to reduce and stabilize, and other wastes are physically and chemically compressed, decomposed and deteriorated to stabilize.

In the above embodiment, the case where the calcium scale prevention method according to the present invention is applied to the leachate treatment system at the final disposal site is exemplified. A solution containing calcium ions, SO ₄ ^2- , oxalate ions, etc., such as filtrate obtained by washing the chlorine bypass dust obtained in the process, drainage of salt recovery equipment that recovers salt from seawater, The present invention can be applied to any solution that may cause a scale due to.

1 Final disposal site leachate treatment system 2 Final disposal site 3 Conditioning tank 4 Amphoteric ion exchange resin 5 Reclaimed water tank 6 Calcium-containing water tank 7 SO ₄ -containing water tank 8 Heavy metal removal device 9 COD treatment device 10 Toxic substance treatment device 11 Sand Filter

The present invention relates to a method of treating leachate landfill, in particular, to a method for preventing the occurrence of scale caused by Oite calcium final disposal site.

Japanese Patent Laid-Open No. 11-100343

However, in the final disposal site, calcium ions (Ca ²⁺ ) contained in the leachate and calcium sulfate (CaSO ₄ ) are generated from SO ₄ ^2- and adhere to the equipment as a scale in the filtration device and the wastewater treatment process at the later stage. However, there is a problem that stable operation is hindered .

Accordingly, the present invention, the was made in view of the problems of the prior art, minimizing the adverse effects on the operation by scale deposition of definitive final disposal site, low operating costs, including drug costs The purpose is to suppress.

In order to achieve the above object, the present invention provides a method for treating leachable water in a final disposal site, wherein the leachate in the final disposal site uses an amphoteric ion exchange resin, has a low Ca ²⁺ concentration, Na ⁺ concentration and SO ₄ ^2-high concentration first solution, high Ca ²⁺ concentration, and separated into a low Na ⁺ concentration and SO ₄ ^2- concentration second solution, the first and second solutions separately It is characterized by processing.

The solution in the processing method of the leachate of the final disposal site, and prior Symbol first solution that will be discharged from the amphoteric ion exchange resin, the switching timing of the second solution, which is discharged from the amphoteric ion-exchange resin Can be controlled based on calcium ion concentration and / or electrical conductivity. As a result, the amount of lead or the like recovered in the first solution can be controlled.

Further, in the processing method of the leachate of the final disposal site, the the amphoteric ion exchanger before Symbol first that will be discharged from the resin solution, the switching between the second solution, and is discharged from the amphoteric ion-exchange resin It can be when the calcium ion concentration of the solution becomes 1/300 or more of the calcium ion concentration of the solution supplied to the amphoteric ion exchange resin. Thereby, the calcium scale can be accurately prevented. Alternatively, when the chlorine ion concentration of the solution discharged from the amphoteric ion exchange resin is 2/3 or less of the chlorine ion concentration of the solution supplied to the amphoteric ion exchange resin, the calcium scale is also accurately adjusted. Can prevent well.

Further, in the method for treating leachate at the final disposal site, the supply amount of the leachate from the final disposal site to the amphoteric ion exchange resin and the supply amount of reclaimed water to the amphoteric ion exchange resin are made equal. Can do. As a result, the amount of reclaimed water used can be reduced, and the waste water treatment facility at the subsequent stage can be downsized.

In the method for treating leachate in the final disposal site, heavy metals contained in the separated solution having a high calcium ion concentration can be removed.

As described above, according to the present invention, minimizing the adverse effects on the operation by scale deposition of definitive final disposal site, it is possible to reduce the operating cost including the drug cost.

It is a flowchart which shows one Embodiment of the processing method of the leachate of the final disposal site concerning this invention. It is the schematic for demonstrating operation | movement of the ion exchange resin used for the processing method of the leachate of the final disposal site shown in FIG. It is a graph which shows the operation example of the ion exchange resin shown in FIG. It is a flowchart which shows 1st Example of the processing system shown in FIG. It is a flowchart which shows 2nd Example of the processing system shown in FIG. It is a flowchart which shows 3rd Example of the processing system shown in FIG. It is a flowchart which shows 4th Example of the processing system shown in FIG. It is a flowchart which shows 5th Example of the processing system shown in FIG. It is a flowchart which shows 6th Example of the processing system shown in FIG. It is a flowchart which shows an example of the processing system of the conventional final disposal site.

Next, modes for carrying out the present invention will be described with reference to the drawings .

FIG. 1 shows a leachate treatment system (hereinafter simply referred to as “treatment system”) of a final disposal site to which the leachate treatment method of the final disposal site according to the present invention is applied. The adjustment tank 3 for storing the leachate W from the field 2, the solution L3 having a high calcium ion concentration (hereinafter referred to as “calcium-containing water”) L3, and the SO ₄ ² having a low calcium ion concentration. ^- a high concentration solution (hereinafter referred to as "SO ₄ containing water") amphoteric ion-exchange resin 4 for separating and L4, the recycled water tank 5 for storing the regeneration water L5 supplied to amphoteric ion-exchange resin 4, an amphoteric ion exchange resin 4 comprising a calcium-containing water tank 6, SO ₄ containing water tank 7, each storing the calcium-containing water L3 and SO ₄ containing water L4 discharged, a heavy metal removing device 8, and a COD processor 9 .

Claims (11)

  Prevention of calcium scale, characterized in that the solution containing calcium ions is separated into a solution having a low calcium ion concentration and a solution having a high calcium ion concentration using an amphoteric ion exchange resin, and each solution is treated separately. Method.   The timing of switching the solution discharged from the amphoteric ion exchange resin between the solution having a low calcium ion concentration and the solution having a high calcium ion concentration is determined according to the calcium ion concentration and / or the solution discharged from the amphoteric ion exchange resin. Or it controls based on electrical conductivity, The prevention method of the calcium scale of Claim 1 characterized by the above-mentioned.   The solution discharged from the amphoteric ion exchange resin is switched between the solution having a low calcium ion concentration and the solution having a high calcium ion concentration. The method for preventing calcium scale according to claim 1 or 2, characterized in that the time is 1/300 or more of the calcium ion concentration of the solution supplied to the amphoteric ion exchange resin.   The solution discharged from the amphoteric ion exchange resin is switched between the solution having a low calcium ion concentration and the solution having a high calcium ion concentration. The method for preventing calcium scale according to claim 1 or 2, characterized in that it is when the chlorine ion concentration of the solution supplied to the amphoteric ion exchange resin is 2/3 or less.   The method for preventing calcium scale according to claim 1, wherein the supply amount of the solution containing the calcium ions to the amphoteric ion exchange resin is made equal to the supply amount of regenerated water to the amphoteric ion exchange resin. . 6. The solution containing calcium ions further contains Na ⁺ , K ⁺ , Cl ⁻ , SO ₄ ²⁻ , and Cl ⁻ is recovered in the solution having a high calcium ion concentration. A method for preventing calcium scale according to claim 1.   The method for preventing calcium scale according to any one of claims 1 to 6, wherein harmful substances contained in the separated solution having a high calcium ion concentration are removed.   The method for preventing calcium scale according to any one of claims 1 to 7, wherein the solution containing calcium ions is leachate from a final disposal site.   The method for preventing calcium scale according to claim 8, wherein the separated solution having a high calcium ion concentration is used for promoting stabilization of the final disposal site.   The method for preventing calcium scale according to any one of claims 1 to 7, wherein the solution containing calcium ions is a filtrate obtained by washing incineration ash and / or chlorine bypass dust with water.   The method for preventing calcium scale according to any one of claims 1 to 7, wherein the solution containing calcium ions is drainage of a salt recovery facility that recovers salt from seawater.

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