Method and device for measuring ion concentration

Abstract

To provide a method for measuring ion concentration, capable of simply and correctly determining or calculating the concentration of specific metal ions in sample water including coexistence ions.SOLUTION: A method for measuring the concentration of specific metal ions in sample water comprises: a step S11 of measuring the potential value P of the sample water; a step S12 of contacting the sample water to a specific metal adsorbent 20 to obtain specific metal removal sample water; a step S13 of adding a specific metal compound to the specific metal removal sample water to prepare a standard solution having a specific metal concentration C1; a step S14 of measuring the potential value P1 of the standard solution; and a step S16 of comparing the potential value P with the potential value P1 to determine or calculate the size of the specific metal concentration in the sample water to the specific metal concentration C1. The used specific metal adsorbent 20 has a free base formation rate of less than 50%.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an ion concentration measurement method and an ion concentration measurement device.

Background Art

[0002] Conventionally, a method of simply measuring a specific ion concentration in sample water using an ion-selective electrode (hereinafter referred to as the ion electrode method) is known. The ion electrode method measures the ion concentration of a solution by using two electrodes, an ion-selective electrode corresponding to the ion to be measured and a reference electrode, and obtaining the electromotive force (hereinafter referred to as the potential value) between the two electrodes.

[0003] Here, in the case of sample water in which coexisting ions are present in addition to the ions to be measured, the ion electrode method may make accurate measurement difficult because the potential value is affected by the coexisting ions, or the pretreatment therefor may be complicated.

[0004] On the other hand, a measurement method (hereinafter referred to as the fluorine concentration measurement method) that can simply and accurately measure the concentration of fluoride ions in sample water by the ion electrode method even when coexisting ions are present in the sample, as in the measurement method described in Patent Document 1, has been proposed.

[0005] The fluorine concentration measurement method first uses a fluorine adsorbent that adsorbs fluoride ions, and brings the sample water into contact with the fluorine adsorbent to obtain a fluorine-removed sample water from which fluoride ions have been removed.

[0006] A reference solution having a predetermined fluoride ion concentration (hereinafter simply referred to as "fluorine concentration") is prepared by adding a fluorine compound having a known concentration to the obtained fluorine-removed sample water again. Here, a plurality of types (a plurality of levels) of reference solutions having different fluoride ion concentrations are prepared. The potentials of the reference solutions at a plurality of levels are measured, and the relationship between the fluorine concentration and the potential value is created as a calibration curve.

[0007] At this time, since the sample water and the reference solution have substantially the same composition except for the fluoride ion component, the calibration curve created is basically a function of only the fluoride concentration. As a result, the fluoride concentration can be calculated from the measured potential value even in the presence of coexisting ions.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] When applying the fluoride concentration measurement method of Patent Document 1 to the measurement of the concentration of specific metal ions such as heavy metals (hereinafter referred to as specific metal ions), in the creation of the calibration curve, in the same manner as above, a step of removing specific metal ions from the sample water to obtain a specific metal-removed sample water is required. At this time, the removal of specific metal ions is performed using a specific metal adsorbent instead of a fluoride adsorbent. Then, a predetermined amount of a specific metal compound with a known concentration of specific metal ions (hereinafter simply referred to as "specific metal concentration") is added to the specific metal-removed sample water to prepare reference solutions at a plurality of levels of a predetermined specific metal concentration. Thereafter, the potentials of the reference solutions at a plurality of levels are measured to create a calibration curve.

[0010] However, in this case, as shown in FIG. 10, the variation of the calibration curve becomes large. FIG. 10 is a diagram showing the calibration curve obtained when applying the fluoride concentration measurement method to the measurement of the specific metal concentration. The specific metal ion targeted for measurement in FIG. 10 is specifically copper ion (Cu 2+ ).

[0011] In FIG. 10, the "potential value" on the horizontal axis is the result of measuring the potential values of each reference solution, and the "specific metal concentration" on the vertical axis is the specific metal concentration in each reference solution. In FIG. 10, the potential values of three reference solutions derived from the same sample water, which are adjusted to approximately the same specific metal concentration, are measured respectively. From FIG. 10, the measurement results of the potential values of the three reference solutions have large variations. As a result, although the three reference solutions are adjusted to approximately the same specific metal concentration, the slopes of the calibration curves created vary. That is, simply replacing the fluorine adsorbent with a specific metal adsorbent results in large variations in the calibration curve.

[0012] As a result of the investigation and analysis by the applicants regarding this, it was found that when preparing a reference solution by adding a specific metal compound to a sample water for specific metal removal, impurities derived from the added specific metal compound are generated in the reference solution. Thereby, a part of the specific metal ions of the specific metal compound added to the sample water for specific metal removal is consumed for the generation of impurities, and the true content of the specific metal ions dissolved in the sample water for specific metal removal becomes smaller than the added amount. At this time, the measured potential values vary due to variations in the amount of impurities generated. From the above, since it is difficult to directly apply the conventional fluorine concentration measurement method, there is a problem that it is difficult to simply and accurately determine or calculate the specific metal concentration in a sample water containing coexisting ions.

[0013] The present invention has been made in view of the above problems, and an object thereof is to provide an ion concentration measurement method, an ion concentration measurement device, a water treatment method, and a water treatment device capable of simply and accurately determining or calculating the specific metal concentration in a sample water containing coexisting ions.

Means for Solving the Problems

[0014] According to one aspect of the present invention, an ion concentration measurement method is a method for measuring the concentration of specific metal ions, which are specific metal ions in a sample water, and a step of measuring the potential value P of the sample water; a step of bringing the sample water into contact with a specific metal adsorbent to obtain a sample water for specific metal removal; A step of adding a specific metal compound to the specific metal-removed sample water to prepare a reference solution with a specific metal concentration C1; A step of measuring the potential value P1 of the reference solution; A step of comparing the potential value P and the potential value P1 to determine whether the specific metal concentration in the sample water is greater than or less than the specific metal concentration C1; It has; As the specific metal adsorbent, one with a free base form conversion rate of less than 50% is used.

[0015] According to this, in the step of obtaining the specific metal-removed sample water, by using a specific metal adsorbent whose free base form conversion rate is adjusted to less than 50%, the ion concentration measurement method can suppress the generation of impurities in the step of preparing the reference solution. As a result, in the step of adding a specific metal compound to the specific metal-removed sample water to prepare a reference solution, the ion concentration measurement method can make the amount of specific metal ions added to the specific metal-removed water equal to the amount of specific metal ions dissolved in the specific metal-removed water. Thereby, the specific metal concentration C1 and the potential value P1 can be accurately associated. Therefore, the ion concentration measurement method can simply and accurately determine whether the specific metal concentration in the sample water is greater than or less than the specific metal concentration C1 even when there are coexisting ions.

[0016] The ion concentration measurement method according to the second invention is a method for measuring the concentration of specific metal ions, which are specific metal ions in the sample water, A step of measuring the potential value P of the sample water; A step of bringing the sample water into contact with a specific metal adsorbent to obtain a specific metal-removed sample water; A step of adding a specific metal compound to the specific metal-removed sample water to prepare a first reference solution with a specific metal concentration C1; A step of preparing a second reference solution with a specific metal concentration C2 by adding or not adding a specific metal compound to the specific metal-removed sample water; A step of obtaining the potential value P1 of the first reference solution; A step of obtaining the potential value P2 of the second reference solution; A step of creating a calibration curve representing the correlation between the specific metal concentration and the potential value using the specific metal concentrations C1 and C2 and the potential values P1 and P2; A step of calculating the specific metal concentration of the sample water corresponding to the potential value P based on the calibration curve; It has, As the specific metal adsorbent, one with a free base form conversion rate of less than 50% is used.

[0017] According to this, in the step of obtaining the specific metal removal sample water, by using a specific metal adsorbent whose free base form conversion rate is adjusted to less than 50%, the ion concentration measurement method can suppress the generation of impurities in the step of preparing the reference solution. As a result, the ion concentration measurement method can equalize the added amount of specific metal ions added to the specific metal removal water and the amount of specific metal ions dissolved in the specific metal removal water in the step of preparing the reference solution, so that an accurate calibration curve can be obtained in the calibration curve creation step. Therefore, the ion concentration measurement method can simply and accurately measure the specific metal concentration in the sample water even when there are coexisting ions.

[0018] In the ion concentration measurement method according to the third invention, the free base form conversion rate is adjusted to less than 50% by alkali-washing the specific metal adsorbent during the regeneration of the specific metal adsorbent performed after using the specific metal adsorbent.

[0019] According to this, the ion concentration measurement method can easily adjust the free base form conversion rate during the regeneration of the specific metal adsorbent. Therefore, the ion concentration measurement method can simply measure the specific metal concentration in the sample water even when there are coexisting ions.

[0020] The ion concentration measurement device according to the fourth invention includes a measurement unit equipped with an ion electrode meter for measuring the potential value of the sample water, A first supply means for supplying the sample water to the measurement unit, A specific metal removal unit in which a specific metal adsorbent is disposed, A second supply means for supplying the sample water to the specific metal removal unit, A third supply means for supplying the specific metal-removed sample water discharged from the specific metal removal section to the measurement section; A specific metal compound supply means for adding a specific metal compound to the specific metal-removed sample water supplied to the measurement section to prepare a reference solution; An arithmetic unit that calculates the value or magnitude relationship of the specific metal concentration in the sample water from the potential value of the sample water measured by the measurement section and the potential value of the reference solution and having The specific metal adsorbent has a free base form conversion rate of less than 50%.

[0021] According to this, the ion concentration measuring device can suitably carry out the ion concentration measuring method of the present invention. That is, the ion concentration measuring device can simply and accurately measure the specific metal concentration in the sample water even when coexisting ions are present.

[0022] The ion concentration measuring device according to the fifth invention includes a measurement section provided with an ion electrode meter for measuring the potential value of sample water, A first supply means for supplying the sample water to the measurement section, A specific metal removal section in which a specific metal adsorbent is disposed, A second supply means for supplying the sample water to the specific metal removal section, A specific metal compound supply means for supplying a specific metal compound to the specific metal-removed sample water discharged from the specific metal removal section, A mixing section for mixing the specific metal-removed sample water discharged from the specific metal removal section and the specific metal compound supplied from the specific metal compound supply means to prepare a reference solution, A third supply means for supplying the reference solution to the measurement section, An arithmetic unit that calculates the value or magnitude relationship of the specific metal concentration in the sample water from the potential value of the sample water measured by the measurement section and the potential value of the reference solution and having The specific metal adsorbent has a free base form conversion rate of less than 50%.

[0023] According to this, by supplying the reference solution to the measurement unit in a pre-mixed state, it is possible to prevent measurement errors due to insufficient mixing of the reference solution. Therefore, the ion concentration measuring device can accurately measure the concentration of a specific metal in the sample water even when there are coexisting ions.

[0024] In the ion concentration measuring device according to the sixth invention, the free base form conversion rate is adjusted to less than 50% by alkali-washing the specific metal adsorbent during the regeneration of the specific metal adsorbent that is performed after using the specific metal adsorbent.

[0025] According to this, the ion concentration measuring device can easily adjust the free base form conversion rate during the regeneration of the specific metal adsorbent. Therefore, the ion concentration measuring device can easily measure the concentration of a specific metal in the sample water even when there are coexisting ions.

Effect of the Invention

[0026] According to the ion concentration measuring method and the ion concentration measuring device of the present invention, even when there are coexisting ions in the sample water, the concentration of a specific metal in the sample water can be easily and accurately determined or calculated.

Brief Description of the Drawings

[0027]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 3C

Figure 3D

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

[0028] Hereinafter, an ion concentration measurement method according to an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description will not be repeated.

[0029] [Regarding the Ion Concentration Measurement Method] With reference to FIG. 1, the flow of the ion concentration measurement method according to an embodiment of the present invention will be described. FIG. 1 is a flowchart of the ion concentration measurement method according to an embodiment of the present invention.

[0030] As shown in FIG. 1, the ion concentration measurement method includes a sample water measurement step S11 of measuring the potential value of sample water, a specific metal removal step S12 of removing ions of a specific metal (specific metal ions) to be measured for ion concentration from the sample water, a reference solution preparation step S13 of adding a specific metal compound to prepare a reference solution with a predetermined concentration, a reference solution measurement step S14 of measuring the potential value of the obtained reference solution, a calibration curve creation step S15 of creating a calibration curve from the predetermined concentration and potential value of the reference solution, and a specific metal concentration determination / calculation step S16 of determining or calculating the concentration of specific metal ions from the obtained calibration curve and the potential value of the sample water. Incidentally, although it is repetitive, in this specification, "specific metal concentration" means "specific metal ion concentration" which is the concentration of metal ions of the specific metal to be measured.

[0031] The sample water to be used for measurement may or may not contain specific metal ions. Specific metal ions are, for example, ions of heavy metals such as copper, zinc, cadmium, nickel, etc. Sample water containing these is, for example, various industrial wastewaters, process wastewaters, domestic wastewaters, etc. from industries such as industry, agriculture, and fishery. The sample water may contain any amount of any coexisting ions other than specific metal ions.

[0032] The sample water may be adjusted in pH as necessary prior to the sample water measurement step S11. At that time, the pH of the sample water is preferably 2.0 or more, more preferably 2.5 or more, even more preferably 2.8 or more, and preferably 7.0 or less, more preferably 6.0 or less, even more preferably 5.0 or less. The sample water may be diluted with water as necessary.

[0033] In the sample water measurement step S11, the potential value of the sample water is measured with an ion electrode meter by the ion electrode method to obtain the potential value P of the specific metal ion. As the ion electrode meter, a known electrode meter is used, and one equipped with a specific metal ion electrode that generates a potential value corresponding to the specific metal concentration (activity) in the solution is used. By combining the specific metal ion electrode and the reference electrode to form a battery and measuring the electromotive force thereof, a potential value corresponding to the specific metal concentration (activity) in the solution can be obtained. The measured potential value P may be configured to be displayed and stored in, for example, an ion concentration meter connected to the ion electrode meter. The potential value P obtained in the sample water measurement step S11 is a value affected by the coexisting ions in the sample water. Therefore, the specific metal concentration cannot be directly determined from this potential value P.

[0034] In the specific metal removal step S12, the sample water having the same origin as that used in the sample water measurement step S11 is brought into contact with the specific metal adsorbent 20 to obtain the specific metal-removed sample water. As the specific metal adsorbent 20, a known adsorbent capable of adsorbing specific metal ions is used, and for example, a resin capable of ion exchange such as a chelate resin is used.

[0035] A chelate resin is a resin into which a chelate-forming group that forms a chelate (complex) with a metal ion is introduced. In the chelate-forming group, a ligand, which is a molecule that binds to the metal ion, binds to a metal ion capable of binding to the ligand to form a chelate. As a result, the chelate resin adsorbs specific metal ions. There are various chelate resins, for example, those into which an iminodiacetic acid group, a polyamine group, or a methylglucamine group is introduced as the chelate-forming group, and an appropriate one is selected according to the type of ion to be adsorbed, the pH of the sample water, etc. Note that the chelate resin tends to change the strength of attracting metal ions when the pH of the solution changes. Generally, the adsorption rate of metal ions by the chelate resin decreases when the pH of the solution decreases.

[0036] When sample water containing specific metal ions is continuously passed through the specific metal adsorbent 20, most of the chelating groups are exchanged, and further ion exchange becomes impossible, that is, the specific metal ions cannot be adsorbed. Therefore, generally, an acid or an alkali is passed through the specific metal adsorbent 20 that has been used multiple times to release the adsorbed specific metal ions from the chelating groups again, thereby restoring the specific metal adsorbent 20 to the state before ion exchange, and regeneration is performed.

[0037] The specific metal adsorbent 20 used in the specific metal removal step S12, although will be described in detail later, in the regeneration step of the specific metal adsorbent 20, one with a free base formation rate adjusted to less than 50% is used. However, from the perspective of obtaining a more accurate calibration curve, it is preferable to use the specific metal adsorbent 20 with a free base formation rate adjusted to less than 40%.

[0038] Note that the specific metal concentration in the specific metal removal sample water does not have to be completely 0 mg / L, but it may be reduced to such an extent that sufficient accuracy (for example, within an error of ±5%) can be obtained when determining the specific metal concentration of the sample water.

[0039] The contact between the sample water and the specific metal adsorbent 20 may be carried out in a tank or may be carried out by passing the liquid through an adsorption column. In the former case, for example, the specific metal adsorbent 20 is added to the sample water stored in the tank. In the latter case, the sample water is passed through an adsorption column filled with the specific metal adsorbent 20.

[0040] In the reference solution preparation step S13, a reference solution is prepared by adding a specific metal compound to the specific metal removal sample water obtained in the previous step. The type of the specific metal compound is not particularly limited, but it is preferably added as a solution (specific metal compound solution) from the perspective of easily preparing a reference solution with a predetermined concentration. It is simple and preferable to use a solution (specific metal ion standard solution) in which the specific metal concentration is adjusted in advance to a known standard value as the specific metal compound solution.

[0041] In the reference solution preparation step S13, a reference solution with a specific metal concentration C1 is prepared. When the specific metal concentration C1 of the reference solution is used to determine the magnitude relationship with the specific metal concentration of the sample water, for example, it is set to the specific metal concentration serving as the reference for the sample water (for example, the emission standard value determined by the Ministry of the Environment, the upper limit value in the specifications of the treatment equipment during the treatment of specific metal ions, or a value obtained by multiplying these values by a safety factor).

[0042] In the reference solution preparation step S13, a first reference solution with a specific metal concentration C1 may be prepared, and a second reference solution with a specific metal concentration C2 may also be prepared. The specific metal concentration C1 of the first reference solution and the specific metal concentration C2 of the second reference solution are appropriately set, for example, to the concentration serving as the reference for the sample water, the concentration appropriate for creating a calibration curve, etc.

[0043] In the reference solution measurement step S14, the potential value of the reference solution prepared in the previous step is measured with an ion electrode meter. In the same manner as in the case of the sample water measurement step S11 described above, the potential value of the reference solution is measured with an ion electrode meter.

[0044] In the reference solution measurement step S14, a potential value P1 is obtained as the potential value of the (first) reference solution with a specific metal concentration C1. When a second reference solution with a specific metal concentration C2 is prepared in the reference solution preparation step S13, a potential value P2 of the second reference solution is obtained in the reference solution measurement step S14. Similarly, when a third reference solution with a specific metal concentration C3, a fourth reference solution with a specific metal concentration C4, etc. are prepared in the reference solution preparation step S13, potential values P3, P4, etc. of the third reference solution, the fourth reference solution, etc. are obtained in the reference solution measurement step S14. Note that the specific metal concentrations C1, C2, C3, C4 are concentrations of different values.

[0045] In the specific metal concentration determination / calculation step S16, the concentration of the sample water is determined or calculated from the measured values of the potential values obtained from the sample water measurement step S11 and the reference solution measurement step S14.

[0046] When determining the concentration of the sample water, the potential value P of the sample water is compared with the potential value P1 of the (first) reference solution with a specific metal concentration C1 to determine whether the specific metal concentration of the sample water is greater than or less than the specific metal concentration C1 of the reference solution. Specifically, if the potential value P of the sample water is greater than the potential value P1 of the reference solution, the specific metal concentration of the sample water is greater than the specific metal concentration C1 of the reference solution; if the potential value P is less than the potential value P1, it is determined that the specific metal concentration of the sample water is less than the specific metal concentration C1. The determination of the specific metal concentration may be performed with respect to the specific metal concentration C2 of the second reference solution, or may be performed with respect to the specific metal concentration C3 of the third reference solution, the specific metal concentration C4 of the fourth reference solution, and so on.

[0047] When calculating the specific concentration of the sample water, prior to the specific metal concentration determination and calculation step S16, a calibration curve creation step S15 is performed to create a calibration curve representing the correlation between the specific metal concentration and the potential value from the specific metal concentrations C1, C2 and the potential values P1, P2.

[0048] In the calibration curve creation step S15, specifically, for example, the potential value is taken on the horizontal axis and the specific metal concentration is taken on the vertical axis, the potential value P1 corresponding to the specific metal concentration C1 of the (first) reference solution and the potential value P2 corresponding to the specific metal concentration C2 of the second reference solution are plotted, and a calibration curve is created by obtaining an approximate line of these plots. From the viewpoint of creating a more accurate calibration curve, it is preferable to further plot the potential value P3 corresponding to the specific metal concentration C3 of the third reference solution, the potential value P4 corresponding to the specific metal concentration C4 of the fourth reference solution, etc., and then obtain an approximate line.

[0049] [Regarding the regeneration method of the specific metal adsorbent] Next, with reference to FIGS. 2 and 3A to 3D, an example of the regeneration method of the specific metal adsorbent used in the specific metal removal step S12 will be described. Although it is repetitive, the specific metal adsorbent that has been used multiple times is regenerated to return the specific metal adsorbent to the state before ion exchange in order to restore its adsorptivity. FIG. 2 is a flowchart of the regeneration process of the specific metal adsorbent. FIGS. 3A to 3D are schematic diagrams showing the state of the specific metal adsorbent in the regeneration process of the specific metal adsorbent.

[0050] As shown in FIG. 2, the regeneration of the specific metal adsorbent includes, for example, an acid desorption step S21, a first water washing step S22, an alkali washing step S23, and a second water washing step S24. However, the regeneration method of the specific metal adsorbent is not limited thereto. As shown in FIG. 3A, the specific metal adsorbent 20 before the regeneration step is in a state of adsorbing specific metal ions. FIG. 3A is a schematic diagram showing a state in which the specific metal adsorbent 20 adsorbs specific metal ions. In FIGS. 3A to 3D, as an example of the specific metal ions, copper ions (Cu 2+ ) are used for explanation. As shown in FIG. 3A, the chelate-forming group 21 of the specific metal adsorbent 20 has a ligand (not shown) that binds 22 to the metal, and the ligand binds 22 to the specific metal ions, that is, adsorbs to form a complex.

[0051] In the acid desorption step S21, by passing an acid solution such as HCl or H2SO4 through the specific metal adsorbent 20, the specific metal ions that formed the complex (chelate) are eluted from the specific metal adsorbent 20. For example, when using an HCl solution, as shown in FIG. 3B, hydrogen ions (H + ) bind 22 to the chelate-forming group 21 instead of the specific metal ions. Chloride ions (Cl - ) accompany as counter ions around the hydrogen ions (hereinafter, this binding 22 state is referred to as "HCl form").

[0052] The first water washing step S22 discharges the eluted specific metal ions and the acid solution. If the HCl-form specific metal adsorbent 20 at this stage is subjected to the specific metal removal step S12, the hydrogen ions bound 22 to the chelate-forming group 21 are exchanged with the specific metal ions, and the hydrogen ions are eluted. When the hydrogen ions are eluted, the pH of the sample water decreases. Although it is repetitive, generally, when the pH of the solution decreases, the chelate resin has a problem that the adsorption rate of metal ions decreases.

[0053] To prevent such problems, an alkali washing step S23 is performed as the next step. In the alkali washing step S23, the specific metal adsorbent 20 is washed with an alkali solution such as NaOH or KOH. For example, when the specific metal adsorbent 20 is washed with an NaOH solution, as shown in FIG. 3C from the state shown in FIG. 3B, the hydrogen ions bonded 22 to a part of the chelate-forming group 21 are replaced with sodium ions (Na + +). Hydroxide ions (OH - −) accompany the sodium ions as their counter ions (hereinafter, the state of this bond 22 is referred to as the "free base form"). By continuing the alkali washing, as shown in FIG. 3D, all the chelate-forming groups 21 become the free base form.

[0054] When the free base form of the specific metal adsorbent 20 is subjected to the specific metal removal step S12, the sodium ions bonded 22 to the chelate-forming group 21 are exchanged with specific metal ions, and the sodium ions elute. That is, since hydrogen ions do not elute, the pH of the sample water does not decrease.

[0055] Finally, a second water washing step S24 is performed. In the second water washing step S24, the hydrogen ions eluted in the alkali washing step S23 are discharged together with the alkali solution.

[0056] The ratio of the bonds 22 in the free base form among all the bonds 22 in the chelate-forming groups 21 in the specific metal adsorbent 20 is referred to as the "free base form ratio". In order to prevent the pH decrease of the solution described above, it is generally recommended to adjust the free base form ratio in the alkali washing step S23 to be 50% to 100%. For example, in the state of FIG. 3D, the free base form ratio is 100% within the range of the chelate-forming group 21 shown in the figure, and in the state of FIG. 3C, the free base form ratio is 50%.

[0057] The number of ligands in the chelating group is known as the equivalent per unit adsorbent amount (eq / L-resin) depending on the type of the specific metal adsorbent 20 used, and the amount of the alkaline solution required to convert the binding of all its ligands into the free base form during the alkaline washing step is also known. Since the amount of the alkaline solution correlates with the free base form conversion rate corresponding to the added amount, by adjusting the amount of the alkaline solution to be added, the specific metal adsorbent 20 is adjusted to the desired free base form conversion rate.

[0058] [Measures against Variation in Calibration Curve] Repeatedly, at the initial stage of the development of the ion concentration measurement method, due to impurities generated in the reference solution preparation step S13, the variation in the calibration curve was large and accurate measurement was difficult. As a result of the investigation by the applicants regarding this, it was found that the impurities confirmed in the reference solution preparation step S13 are generated due to the contribution of the magnitude of the free base form conversion rate.

[0059] Specifically, the applicants found that there is a relationship shown in FIG. 4 between the value of the free base form conversion rate of the specific metal adsorbent 20 and the pH of the solution after each step of the ion concentration measurement method, and there is a relationship shown in FIG. 5 between the value of the free base form conversion rate of the specific metal adsorbent 20 and the specific metal concentration in the solution after each step of the ion concentration measurement method. In FIGS. 4 and 5, the measurement was performed for copper ions as an example of specific metal ions (the same applies to FIGS. 6 and 7 described later).

[0060] From FIG. 4, as the free base form conversion rate increases, the pH of the solution after the specific metal removal step S12 and after the subsequent reference solution preparation step S13 becomes higher than that before the specific metal removal step S12. This is because in the specific metal removal step S12, when the free base form conversion rate is high, the free base in the specific metal adsorbent 20 elutes into the specific metal removal sample water.

[0061] Also, as shown in Fig. 5, as the free base formation rate increases, the concentration of the specific metal in the sample water after the reference solution preparation step S13 becomes lower than the specific metal addition amount (the value intended as the concentration of the specific metal in the prepared reference solution, i.e., the target value of the specific metal concentration). This is because when the free base formation rate is high, a part of the metal ions in the added standard solution reacts with the free base eluted into the specific metal removal sample water, and the hydroxide of the specific metal ion [i.e., Cu(OH)2] is generated as an impurity. That is, a part of the added metal ions is consumed for the formation of the hydroxide (impurity), and a deviation occurs between the true content of the specific metal ions dissolved in the sample water and the addition amount of the specific metal ions added in the reference solution preparation step S13. As a result, a correct calibration curve cannot be obtained.

[0062] To prevent this phenomenon, it is necessary to prevent the specific metal ions added in the reference solution preparation step S13 from precipitating as hydroxides. As shown in Fig. 4, if the free base formation rate of the specific metal adsorbent 20 is generally less than 50%, the increase in the pH of the specific metal removal sample water due to the elution of the free base is generally suppressed. At this time, as shown in Fig. 5, the concentration of the specific metal in the reference solution is generally equal to the specific metal addition amount. That is, the precipitation of the hydroxide of the metal ion is suppressed. Therefore, it is advisable to use the specific metal adsorbent 20 provided for the specific metal removal step S12, which is adjusted to have a free base formation rate of less than 50%.

[0063] It is more preferable to use the specific metal adsorbent 20 provided for the specific metal removal step S12, which has a free base formation rate of less than 40%. If the free base formation rate is less than 40%, as shown in Fig. 4, the increase in the pH of the specific metal removal sample water due to the elution of the free base is sufficiently suppressed, and at this time, as shown in Fig. 5, the concentration of the specific metal in the reference solution is almost equal to the specific metal addition amount.

[0064] Next, with reference to FIGS. 6 and 7, the calibration curve and the specific metal concentration measurement results obtained by the ion concentration measurement method according to the present invention will be described. FIG. 6 is a diagram showing an example of a calibration curve created by the ion concentration measurement method of the present invention, and FIG. 7 is a diagram comparing the relationship between the true value and the measured value of the specific metal concentration by the method according to the present invention and the conventional measurement method (that is, when the fluorine concentration measurement method is directly applied to the measurement of the specific metal concentration). In the measurement in the "present invention" in FIGS. 6 and 7, the specific metal adsorbent 20 with the free base form conversion rate adjusted to 40% was used in the specific metal removal step S12. In the "conventional measurement method" in FIG. 7 and the measurement in FIG. 10 described above, the specific metal adsorbent 20 with the free base form conversion rate adjusted to 100% was used in the specific metal removal step S12. Note that FIG. 6 is an example in which the potential values P1, P2, and P3 for the specific metal concentrations C1, C2, and C3 are plotted in the calibration curve creation step described above.

[0065] Similar to FIG. 10, in FIG. 6, the "potential value" on the horizontal axis is the potential value of the reference solution measured in the reference solution measurement step S14, and the "specific metal concentration" on the vertical axis is the specific metal concentration of the reference solution prepared in the reference solution preparation step S13. In FIG. 6, similar to FIG. 10, the potential values of three reference solutions derived from the same sample water, which were adjusted to approximately the same concentration in the reference solution preparation step S13, are measured respectively. From FIG. 6, the variation in the potential measurement results of the three reference solutions by the ion concentration measurement device according to the present invention is significantly reduced compared to FIG. 10 by the conventional measurement method.

[0066] Figure 7 shows the results of measuring the specific metal concentration using various sample waters with different ionic strengths. Specifically, measurements were made on sample waters with ionic strengths of 0.06 mol / L, 0.09 mol / L, and 0.13 mol / L. In Figure 7, the "specific metal concentration (true value)" on the horizontal axis is the true concentration of the specific metal ions contained in the sample water, and the true content of the specific metal ions in the sample water was measured using an atomic absorption photometer by atomic absorption spectrometry. The "specific metal concentration (calculated value)" on the vertical axis is the value calculated from the "specific metal concentration determination and calculation step S16" in the present invention described above. From Figure 7, compared with the conventional measurement method, the measurement method according to the present invention shows better linearity and can perform highly accurate measurements because the variation in the relationship between the true value and the calculated value is significantly smaller.

[0067] As described above, in the specific metal removal step S12, by using the specific metal adsorbent 20 with the free base formation rate adjusted to less than 50%, the ion concentration measurement method can suppress the formation of the hydroxide of the specific metal ions in the reference solution preparation step S13. As a result, the ion concentration measurement method can make the amount of the specific metal ions dissolved in the specific metal removal sample water in the reference solution equal to the added amount in the reference solution preparation step S13, and thus can obtain an accurate calibration curve in the calibration curve creation step S15. Therefore, the ion concentration measurement method can accurately measure the specific metal concentration in the sample water even when there are coexisting ions. At this time, by using an ion selective electrode meter that can selectively detect specific ions, the ion concentration measurement method can easily measure the specific metal concentration.

[0068] In addition, when the free base form conversion rate is adjusted to less than 50%, this is smaller than the free base form conversion rate of 50% to 100% generally recommended when using the specific metal adsorbent 20. In this case, as described above, a decrease in the adsorptivity of the specific metal ions in the specific metal adsorbent 20 is considered as a trade-off, but it does not pose a problem in the usage mode of the specific metal adsorbent 20 in the ion concentration measurement method of the present invention. The specification mode of the specific metal adsorbent 20 in the ion concentration measurement method of the present invention is not a usage mode that requires adsorption of a large amount of specific metal such as wastewater treatment, and it is sufficient if a small amount of specific metal can be adsorbed for calibration curve creation. Therefore, as long as the adsorption of the specific metal necessary for creating the calibration curve is possible, there is no problem even if the free base form conversion rate is adjusted within a range of less than 50%.

[0069] [Ion Concentration Measuring Device] <First Embodiment> Next, with reference to FIG. 8, the ion concentration measuring device 100 of the present invention will be described. FIG. 8 is a diagram showing a configuration example of the ion concentration measuring device 100 according to the first embodiment of the present invention. In the following, the details of the ion electrode meter, the sample water, the specific metal adsorbent 20, the specific metal compound, and the reference solution are referred to the above description.

[0070] From FIG. 8, the ion concentration measuring device 100 includes a measurement unit 1 equipped with an ion electrode meter 2, a first supply means 4 for supplying sample water to the measurement unit 1, a specific metal removal unit 5 in which the specific metal adsorbent 20 is disposed, a second supply means 6 for supplying sample water to the specific metal removal unit 5, a specific metal compound supply means 7 for adding a specific metal compound to the specific metal removal sample water discharged from the specific metal removal unit 5 and supplying a reference solution to the measurement unit 1, a third supply means 9 for supplying the specific metal removal sample water to the measurement unit 1, and an arithmetic unit 10 for calculating the value or magnitude relationship of the specific metal concentration in the sample water from the potential values of the sample water and the reference solution measured by the measurement unit 1.

[0071] The measurement unit 1 includes a tank 3 in which the liquid to be analyzed is stored, an ion electrode meter 2 provided in the tank 3 for measuring the potential value of the liquid to be analyzed, and a discharge unit 11 for discharging the liquid to be analyzed after the potential value is measured from the tank 3. The ion electrode meter 2 is configured to be able to transmit information via wired, wireless, etc. to the calculation unit 10. The calculation unit 10 has a storage device for storing information (not shown).

[0072] A specific metal adsorbent 20 is disposed in the specific metal removal unit 5. The specific metal removal unit 5 may be disposed in an adsorption tank in which the specific metal adsorbent 20 is disposed, a pipeline in which the specific metal adsorbent 20 is disposed, etc. As described above, in the regeneration process of the specific metal adsorbent 20, the specific metal adsorbent 20 with a free base form conversion rate adjusted to less than 50% is used. However, from the viewpoint of obtaining a more accurate calibration curve, it is preferable to use the specific metal adsorbent 20 with a free base form conversion rate adjusted to less than 40%.

[0073] The specific metal compound is temporarily stored in a storage tank 8 and supplied from the storage tank 8 to the tank 3 of the measurement unit 1 by the specific metal compound supply means 7. The specific metal compound solution supplied to the tank 3 by the specific metal compound supply means 7 is mixed with the specific metal removal sample water in the tank 3.

[0074] The first supply means 4 is a flow path for supplying sample water as the liquid to be analyzed to the measurement unit 1. The second supply means 6 is a flow path for supplying sample water to the specific metal removal unit 5. The third supply means 9 is a flow path for supplying the specific metal removal sample water discharged from the specific metal removal unit 5 to the measurement unit 1. The specific metal compound supply means 7 is a flow path for supplying the specific metal compound to the measurement unit 1. These flow paths may be provided with liquid feed pumps.

[0075] The ion concentration measuring device 100 first supplies the sample water to the tank 3 of the measuring unit 1 by the first supply means 4, measures the potential value of the sample water with the ion electrode meter 2, and obtains the potential value P. The obtained potential value P is temporarily stored in the calculation unit 10. After the potential value of the sample water is measured, the sample water is discharged from the discharge unit 11. Thereby, the tank 3 is emptied once. On the other hand, the sample water is supplied to the specific metal removal unit 5 by the second supply means 6, and the specific metal ions in the sample water are removed to generate specific metal removal sample water. The specific metal removal sample water is discharged from the specific metal removal unit 5 and supplied to the emptied tank 3 of the measuring unit 1 by the third supply means 9. The specific metal removal sample water supplied to the tank 3 has a specific metal compound added thereto by the specific metal compound supply means 7, and a (first) reference solution with a specific metal concentration C1 is prepared in the tank 3. The potential value of the (first) reference solution is measured with the ion electrode meter 2 to obtain the potential value P1. The obtained potential value P1 is stored in the calculation unit 10.

[0076] By comparing the potential value P of the sample water and the potential value P1 of the (first) reference solution obtained above in the calculation unit 10, the magnitude relationship of the specific metal concentration of the sample water with respect to the specific metal concentration C1 of the (first) reference solution is determined.

[0077] After measuring the potential value of the first reference solution, the ion concentration measuring device 100 may further add a specific metal compound to the first reference solution by the specific metal compound supply means 7 to prepare a second reference solution. Alternatively, the ion concentration measuring device 100 may prepare a second reference solution without adding a specific metal compound to the specific metal removal sample water before measuring the potential value of the first reference solution.

[0078] In this case, the potential value of the second reference solution is measured with the ion electrode meter 2 to obtain the potential value P2. The obtained potential value P2 is stored in the calculation unit 10. The calculation unit 10 creates a calibration curve representing the relationship between the specific metal concentration and the potential value from the potential value P1 of the first reference solution and the potential value P2 of the second reference solution thus obtained, and calculates the value of the specific metal concentration corresponding to the potential value P of the sample water.

[0079] As described above, by using the ion concentration measuring apparatus 100, the ion concentration measuring method of the present invention can be preferably implemented. That is, the ion concentration measuring apparatus 100 can simply and accurately measure the concentration of a specific metal in sample water even when there are coexisting ions. <Second Embodiment>

[0080] Next, with reference to FIG. 9, the ion concentration measuring apparatus 200 according to the second embodiment of the present invention will be described. FIG. 9 is a diagram showing a configuration example of the ion concentration measuring apparatus 200 according to the second embodiment of the present invention.

[0081] From FIG. 9, the ion concentration measuring apparatus 200 further includes a mixing unit 13 with respect to the ion concentration measuring apparatus 100 according to the first embodiment. The mixing unit 13 mixes the specific metal-removed sample water discharged from the specific metal removal unit 5 and the specific metal compound supplied from the specific metal compound supply means 7. The mixing unit 13 is provided in a flow path communicating with the discharge side of the specific metal removal unit 5, and it is preferable that, for example, an in-line mixer or the like is provided. In the mixing unit 13, the specific metal-removed sample water and the specific metal compound are mixed to prepare a reference solution. A third supply means 9, which is a flow path communicating the mixing unit 13 and the measuring unit 1, supplies the reference solution to the measuring unit 1. Although not shown, the mixing unit 13 may be provided as a mixing tank. By supplying the reference solution to the measuring unit 1 in a pre-mixed state, the ion concentration measuring apparatus 200 can prevent measurement errors due to insufficient mixing of the reference solution. Therefore, the ion concentration measuring apparatus 200 can accurately measure the concentration of a specific metal in sample water even when there are coexisting ions.

[0082] [Water treatment method combining an ion concentration measuring method or an ion concentration measuring apparatus] The present invention also provides a water treatment method combining the ion concentration measuring method or the ion concentration measuring apparatus described above.

[0083] The water treatment method of the present invention is, for example, a water treatment method for removing at least a part of specific metal ions from specific metal ion-containing water which is water to be treated to obtain treated water, and by the ion concentration measurement method described above, the specific metal concentration in the treated water can be measured using the treated water as sample water. The treated water may be, for example, the treated water of the entire plant or the treated water of a unit operation for removing specific metals. By measuring the specific metal concentration of the treated water by the ion concentration measurement method of the present invention, the specific metal concentration of the treated water can be measured simply and accurately. Thereby, it can be determined whether the water treatment is properly performed and whether the quality of the treated water is appropriate. In addition, the water treatment method of the present invention may measure, in addition to the treated water, the water to be treated, intermediate treated water during the process of obtaining the treated water from the water to be treated, etc. using the ion concentration measurement method of the present invention.

[0084] The specific metal ion-containing water is not particularly limited as long as it contains specific metal ions in any form (for example, free form, salt form, complex form), and examples include wastewater generated in power plants, wastewater generated in various factories, landfill leachate, organic wastewater, process wastewater of various plants, etc. Also, environmental water such as river water, lake water, groundwater, seawater, etc. may be used.

[0085] The present invention also provides a water treatment apparatus for removing at least a part of specific metal ions from specific metal ion-containing water to obtain treated water, which is a water treatment apparatus equipped with the ion concentration measurement apparatus of the present invention. The water treatment apparatus of the present invention preferably can implement the water treatment method described above. By measuring the specific metal concentration of the treated water by the ion concentration measurement apparatus of the present invention, the specific metal concentration of the treated water can be measured simply and accurately. Thereby, it can be determined whether the water treatment is properly performed and whether the quality of the treated water is appropriate. The water treatment apparatus of the present invention can be used for measuring the specific metal concentration in various wastewaters and environmental waters.

[0086] The embodiments of the present invention have been described above with reference to the drawings. However, the present invention is not limited to the above embodiments, and can be implemented in various forms without departing from the gist thereof. The drawings schematically show each component mainly for easy understanding, and the thickness, length, number, interval, etc. of each illustrated component are different from the actual ones for convenience of drawing creation. In addition, the materials, shapes, dimensions, etc. of each component shown in the above embodiments are examples and are not particularly limited, and various changes can be made without substantially departing from the configuration of the present invention.

Explanation of Reference Numerals

[0087] S11 Sample water measurement step S12 Specific metal removal step S13 Standard solution preparation step S14 Standard solution measurement step S15 Calibration curve creation step S15 Specific metal concentration determination / calculation step S21 Acid desorption step S22 First water washing step S23 Alkali washing step S24 Second water washing step 1 Measuring unit 2 Ion electrode meter 4 First supply means 5 Specific metal removal unit 6 Second supply means 7 Specific metal compound supply means 10 Calculation unit 20 Specific metal remover (chelating resin) 21 Chelating forming group 22 Bond

Claims

1. A method for measuring the concentration of a specific metal ion, which is a specific metal ion in a sample water, comprising: measuring the potential value P of the sample water; contacting the sample water with a specific metal adsorbent to obtain a specific metal-removed sample water; adding a specific metal compound to the specific metal-removed sample water to prepare a reference solution with a specific metal concentration C1; measuring the potential value P1 of the reference solution; comparing the potential value P and the potential value P1 to determine the magnitude of the specific metal concentration in the sample water relative to the specific metal concentration C1; and using, as the specific metal adsorbent, one having a free base form conversion rate of less than 50%, wherein the ion concentration measurement method is characterized by this.

2. A method for measuring the concentration of a specific metal ion, which is a specific metal ion in a sample water, comprising: measuring the potential value P of the sample water; contacting the sample water with a specific metal adsorbent to obtain a specific metal-removed sample water; adding a specific metal compound to the specific metal-removed sample water to prepare a first reference solution with a specific metal concentration C1; preparing a second reference solution with a specific metal concentration C2 by adding or not adding a specific metal compound to the specific metal-removed sample water; obtaining the potential value P1 of the first reference solution; obtaining the potential value P2 of the second reference solution; using the specific metal concentrations C1, C2 and the potential values P1, P2 to create a calibration curve representing the correlation between the specific metal concentration and the potential value; calculating the specific metal concentration of the sample water corresponding to the potential value P based on the calibration curve; and using, as the specific metal adsorbent, one having a free base form conversion rate of less than 50%, wherein the ion concentration measurement method is characterized by this.

3. The free base form conversion rate is adjusted to less than 50% by alkali-washing the specific metal adsorbent during regeneration of the specific metal adsorbent performed after using the specific metal adsorbent. The ion concentration measurement method according to claim 1 or claim 2, characterized in that.

4. A measurement unit equipped with an ion electrode meter for measuring the potential value of the sample water, A first supply means for supplying the sample water to the measurement unit, A specific metal removal unit in which a specific metal adsorbent is arranged, A second supply means for supplying the sample water to the specific metal removal unit, A third supply means for supplying the specific metal removal sample water discharged from the specific metal removal unit to the measurement unit, A specific metal compound supply means for adding a specific metal compound to the specific metal removal sample water supplied to the measurement unit to prepare a reference solution, An arithmetic unit for calculating the value or magnitude relationship of the specific metal concentration in the sample water from the potential value of the sample water measured by the measurement unit and the potential value of the reference solution And having, The specific metal adsorbent is an ion concentration measuring device characterized in that the free base form conversion rate is less than 50%.

5. A measurement unit equipped with an ion electrode meter for measuring the potential value of the sample water, A first supply means for supplying the sample water to the measurement unit, A specific metal removal unit in which a specific metal adsorbent is arranged, A second supply means for supplying the sample water to the specific metal removal unit, A specific metal compound supply means for supplying a specific metal compound to the specific metal removal sample water discharged from the specific metal removal unit, A mixing unit for mixing the specific metal removal sample water discharged from the specific metal removal unit and the specific metal compound supplied from the specific metal compound supply means to prepare a reference solution, A third supply means for supplying the reference solution to the measurement unit, An arithmetic unit that calculates the value or magnitude relationship of the specific metal concentration in the sample water from the potential value of the sample water measured by the measurement unit and the potential value of the reference solution and has The specific metal adsorbent is an ion concentration measuring device characterized in that the free base form conversion rate is less than 50%.

6. The free base form conversion rate is adjusted to less than 50% by alkali-washing the specific metal adsorbent during the regeneration of the specific metal adsorbent performed after using the specific metal adsorbent The ion concentration measuring device according to claim 4 or claim 5, characterized by the above.

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