Method for monitoring acidity of water quality on line

Abstract

The invention provides a method for monitoring the acidity of water on line, which comprises the following steps: adding a water sample and a titration indicator into a titration cell, uniformly mixing, measuring the absorbance A background of the water sample mixed with the titration indicator at the wavelength lambda, and taking the absorbance A background as an absorbance background value; titrating the water sample by using a NaOH standard solution as a titrant, and measuring the absorbance A of the water sample at the wavelength lambda in the titration process; taking the moment when the absorbance A is greater than or equal to the absorbance threshold A in the titration process as a titration end point, and obtaining the titration volume of the NaOH standard solution at the titration end point; obtaining the acidity of the water sample based on the titration volume. The method adopts an acid-base indicator titration method to monitor the water acidity and determines the titration end point in combination with the absorbance change of the indicator in the titration process, not only realizes online monitoring of the water acidity, but also is simple and convenient to operate, does not need high-frequency maintenance, can effectively reduce the use cost, improves the water acidity monitoring precision, and is suitable for popularization and application. And application and popularization are facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of water quality monitoring, and in particular relates to a method for online monitoring of water acidity. Background Art

[0002] In surface water, the pH of water will be reduced due to the dissolution of CO2 or the entry of acidic wastewater discharged by machinery, mineral processing, electroplating, pesticides, printing and dyeing, chemical industry and other industries, forming an acid corrosion environment. Due to the corrosiveness of acid, it will destroy the normal living conditions of fish and other aquatic organisms and crops, thus causing the death of fish and crops. In addition, acidic wastewater will also corrode pipes and damage buildings. Acidity is an important indicator to measure changes in water bodies. Therefore, it is very necessary to monitor the acidity of water quality.

[0003] At present, the main methods for detecting water acidity are acid-base indicator titration and potentiometric titration. Among them, the acid-base indicator titration is a laboratory method that requires manual operation and cannot be used online; and although the potentiometric titration is convenient to measure and can be monitored online, the electrodes are immersed in different solutions for a long time, which will lead to a short life span and require frequent replacement, resulting in high maintenance costs, which is not conducive to widespread application. Therefore, there is an urgent need for an online monitoring method for water acidity with low maintenance costs, which can be conducive to promotion and application. Summary of the invention

[0004] The purpose of the present invention is to provide a method for online monitoring of water acidity. The method adopts an acid-base indicator titration method to monitor the water acidity and determines the titration end point in combination with the absorbance change of the indicator during the titration process. Not only does the method realize online monitoring of water acidity, but it is also simple and convenient to operate and does not require high-frequency maintenance. It can effectively reduce the cost of use, improve the accuracy of water acidity monitoring, and is conducive to popularization of applications.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for online monitoring of water acidity, comprising:

[0007] S1, add the water sample and titration indicator into the titration cell and mix them evenly, and measure the absorbance A of the water sample mixed with the titration indicator at wavelength λ 本底 And used as the absorbance background value;

[0008] S2, using a NaOH standard solution as a titrant to titrate the water sample mixed with a titration indicator, and measuring the absorbance A of the water sample mixed with the titration indicator at a wavelength λ during the titration process;

[0009] S3, the absorbance A during the titration process is greater than or equal to the absorbance threshold A 阈值The moment of titration is taken as the titration endpoint, and the titration volume V of the NaOH standard solution at the titration endpoint is obtained. NaOH ;

[0010] S4, based on the titration volume V NaOH Get the acidity of the water sample.

[0011] Optionally, before step S1, the method further includes:

[0012] It is pre-determined whether the pH of the water sample is less than or equal to 3.7. If so, methyl orange is used as the titration indicator and the acidity obtained is methyl orange acidity. If not, phenolphthalein is used as the titration indicator and the acidity obtained is phenolphthalein acidity.

[0013] Optionally, before step S1, the method further includes:

[0014] Pre-determine whether the titration number n of the NaOH standard solution at the titration end point is greater than or equal to the drop number threshold D 阈值 If yes, methyl orange is used as the titration indicator and the acidity obtained is methyl orange acidity; if no, phenolphthalein is used as the titration indicator and the acidity obtained is phenolphthalein acidity.

[0015] Optionally, when methyl orange is used as the titration indicator, the wavelength λ is the wavelength λ of methyl orange. 甲基橙 , and the methyl orange wavelength λ 甲基橙 It is 460nm.

[0016] Optionally, the absorbance threshold A 阈值 A is the absorbance threshold of methyl orange 甲基橙阈值 , and the methyl orange absorbance threshold A 甲基橙阈值 Located in the range of [0.5A, 0.7A].

[0017] Optionally, the methyl orange absorbance threshold A 甲基橙阈值 is 0.5A.

[0018] Optionally, when phenolphthalein is used as the titration indicator, the wavelength λ is the phenolphthalein wavelength λ 酚酞 , and the phenolphthalein wavelength λ 酚酞 It is 515nm.

[0019] Optionally, the absorbance threshold A 阈值 A is the absorbance threshold of phenolphthalein 酚酞阈值 , and the phenolphthalein absorbance threshold A 酚酞阈值 Located in the range of [0.4A, 0.6A].

[0020] Optionally, the phenolphthalein absorbance threshold A 酚酞阈值It is 0.4A.

[0021] Optionally, the acidity in step S4 is obtained by the following formula:

[0022]

[0023] Among them, the acidity is measured in CaCO3, and the unit is mg / L;

[0024] C NaOH is the concentration of the NaOH standard solution at the titration endpoint, in mol / L;

[0025] V NaOH is the titration volume of the NaOH standard solution at the titration endpoint, in L;

[0026] 50.05 is the molar mass of 1 / 2CaCO3, in g / mol;

[0027] V 水样 is the volume of the water sample, in L.

[0028] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0029] For example, the method provided by the present invention adopts the acid-base indicator titration method to monitor the acidity of water quality and determines the titration end point in combination with the absorbance change of the indicator during the titration process. It not only realizes the online monitoring of the acidity of water quality, but also is simple and convenient to operate, does not require high-frequency maintenance, can effectively reduce the cost of use, improve the accuracy of water quality acidity monitoring, and is conducive to popularization of applications.

[0030] For another example, the pH value of a water sample may be pre-detected, and the methyl orange acidity or phenolphthalein acidity of the water sample may be selected to be monitored based on the pre-detected pH value of the water sample, so as to save reagents and improve efficiency and monitoring accuracy.

[0031] For another example, the methyl orange acidity or phenolphthalein acidity of the water sample can be selected to be monitored based on the number of titration drops of the NaOH standard solution at the titration endpoint, so as to ensure that the acidity of the water sample can be measured in each time period using the method provided by the present invention, thereby facilitating continuous monitoring of the corresponding water area.

[0032] For another example, the method provided by the present invention can be operated online for 24 hours continuously to conduct continuous monitoring of water bodies, reflect real-time monitoring results, and provide uninterrupted feedback on the parameters of the factory production process, which can effectively improve production quality and production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention is a flowchart of an implementation method of online monitoring of water acidity in an embodiment of the present invention. Specific implementation plan

[0034] In order to make the purpose, features and beneficial effects of the present invention more clearly understood, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described below are only used to explain the present invention, rather than to limit the present invention.

[0035] In addition, for the convenience of description, only the parts related to the present invention are shown in the drawings instead of all structures. In addition, the same or similar reference numerals may be used in the drawings to refer to the same or similar components in different embodiments.

[0036] An embodiment of the present invention provides a method for online monitoring of water acidity.

[0037] Reference Figure 1 The method for online monitoring of water acidity may include the following steps:

[0038] S1, add the water sample and titration indicator into the titration cell and mix them evenly, and measure the absorbance A of the water sample mixed with the titration indicator at wavelength λ 本底 And used as the absorbance background value;

[0039] S2, using a NaOH standard solution as a titrant to titrate the water sample mixed with a titration indicator, and measuring the absorbance A of the water sample mixed with the titration indicator at a wavelength λ during the titration process;

[0040] S3, the absorbance A during the titration process is greater than or equal to the absorbance threshold A 阈值 The moment of titration is taken as the titration endpoint, and the titration volume V of the NaOH standard solution at the titration endpoint is obtained. NaOH ;

[0041] S4, based on the titration volume V NaOH Get the acidity of the water sample.

[0042] The method provided in the embodiment of the present invention adopts the acid-base indicator titration method to monitor the acidity of water quality and determines the titration end point in combination with the absorbance change of the indicator during the titration process. It not only realizes the online monitoring of the acidity of water quality, but also is simple and convenient to operate, does not require high-frequency maintenance, can effectively reduce the cost of use, improve the accuracy of water quality acidity monitoring, and is conducive to popularization of applications.

[0043] In some embodiments, the acidity of the water sample may include methyl orange acidity or phenolphthalein acidity. Accordingly, in a specific implementation, methyl orange or phenolphthalein may be used as a titration indicator.

[0044] In some embodiments, the choice of monitoring the methyl orange acidity or the phenolphthalein acidity of the water sample can be based on the pH value of the water sample.

[0045] In some embodiments, the following steps may be included before step S1:

[0046] It is pre-determined whether the pH value of the water sample is less than or equal to 3.7. If so, methyl orange is used as a titration indicator and the acidity obtained is the methyl orange acidity. If not, phenolphthalein is used as a titration indicator and the acidity obtained is the phenolphthalein acidity. This is because when the pH value is greater than 3.7, methyl orange will not change color, and then there will be no absorbance change, and the titration end point cannot be determined.

[0047] In a specific implementation, a pH electrode can be used to pre-detect the pH value of a water sample. When the pH of the water sample is ≤3.7 pH, the methyl orange acidity of the water sample is monitored; when the pH of the water sample is >3.7 pH, the phenolphthalein acidity of the water sample is monitored. In this way, reagents can be saved and efficiency can be improved.

[0048] In some embodiments, it is also possible to select whether to monitor the methyl orange acidity or the phenolphthalein acidity of the water sample based on the number of titration drops of the NaOH standard solution at the titration endpoint, especially when the volume of the titration cell is limited.

[0049] In some embodiments, the following steps may be included before step S1:

[0050] Pre-determine whether the number of drops n of the NaOH standard solution at the titration endpoint is greater than or equal to the drop threshold n 阈值 If yes, methyl orange is used as the titration indicator and the acidity obtained is the methyl orange acidity. If no, phenolphthalein is used as the titration indicator and the acidity obtained is the phenolphthalein acidity.

[0051] In some embodiments, the number of drops of the NaOH standard solution at the titration endpoint, i.e., the drop threshold n, can be calculated according to the pH value of the water sample. 阈值 The specific implementation process adopts conventional technical means in this field, which will not be repeated here.

[0052] In some embodiments, the drop count threshold n 阈值 For 200 drops.

[0053] For example, if the number of titration drops n of the NaOH standard solution at the titration endpoint is less than 200 drops, then choose to monitor the phenolphthalein acidity of the water sample; if the number of titration drops n of the NaOH standard solution at the titration endpoint is greater than or equal to 200 drops, then choose to monitor the methyl orange acidity of the water sample and appropriately reduce the volume of the water sample added.

[0054] In this way, it can be ensured that the acidity of the water sample can be measured at each time period by using this method, so as to facilitate continuous monitoring of the corresponding water area. For example, the acidity of the water quality can be automatically monitored every hour.

[0055] When methyl orange is used as a titration indicator, a light source with a wavelength of 460 nm is selected during the titration process. That is, the wavelength λ is the wavelength λ of methyl orange. 甲基橙 And the wavelength of methyl orange is 甲基橙 This is because the orange methyl orange indicator solution has maximum absorption at a wavelength of 460nm.

[0056] Accordingly, the absorbance threshold A 阈值 A is the absorbance threshold of methyl orange 甲基橙阈值 .

[0057] In some embodiments, the methyl orange absorbance threshold A 甲基橙阈值 Specifically, a comparison experiment can be conducted between manual titration and instrument titration combined with absorbance monitoring, with the manual titration result as the judgment standard, and the instrument titration result is compared with the manual titration result to correct the judgment threshold of the absorbance A of the titration endpoint of the instrument titration.

[0058] In some embodiments, the indication error of the instrument titration result relative to the manual titration result can be determined as ±5%, and the determination threshold of the absorbance A of the titration endpoint of the titration using the methyl orange indicator can be determined based on this.

[0059] In some embodiments, the methyl orange absorbance threshold A 甲基橙阈值 In other words, the absorbance A at the titration endpoint is determined to be within the range of [0.5A, 0.7A], where A = lg (ADC 发射 / ADC 接收 ).

[0060] Furthermore, the methyl orange absorbance threshold A 甲基橙阈值 The absorbance threshold value of methyl orange is determined to be 0.5A. That is, 0.5A is determined as the endpoint of the titration process. 甲基橙阈值 The titration volume V of the NaOH standard solution is obtained based on the number of titration drops n. NaOH甲基橙 .

[0061] In some embodiments, the titration volume is 0.1 ml, then the titration volume V NaOH甲基橙 =n*0.1.

[0062] When methyl orange is used as a titration indicator, the methyl orange acidity of the water sample is obtained by the following formula:

[0063]

[0064] Among them, the acidity of methyl orange is measured in CaCO3, and the unit is mg / L;

[0065] C NaOH is the concentration of NaOH standard solution, in mol / L;

[0066] V NaOH甲基橙 It is the titration volume of NaOH standard solution at the titration endpoint using methyl orange as titration indicator, in L;

[0067] 50.05 is the molar mass of 1 / 2CaCO3, in g / mol;

[0068] V 水样 is the volume of the water sample, in L.

[0069] When phenolphthalein is used as a titration indicator, a light source with a wavelength of 515 nm is selected during the titration process. That is, the wavelength λ is the wavelength λ of phenolphthalein. 酚酞 And the wavelength of phenolphthalein 酚酞 The pink phenolphthalein indicator solution has a maximum absorption at a wavelength of 515 nm.

[0070] Accordingly, the absorbance threshold A 阈值 A is the absorbance threshold of phenolphthalein 酚酞阈值 .

[0071] In some embodiments, the phenolphthalein absorbance threshold A 酚酞阈值 Specifically, a comparison experiment can be conducted between manual titration and instrument titration combined with absorbance monitoring, with the manual titration result as the judgment standard, and the instrument titration result is compared with the manual titration result to correct the judgment threshold of the absorbance A of the titration endpoint of the instrument titration.

[0072] In some embodiments, the indication error of the instrument titration result relative to the manual titration result can be determined as ±5%, and the determination threshold of the absorbance A of the titration endpoint of the titration using the phenolphthalein indicator can be determined based on this.

[0073] In some embodiments, the phenolphthalein absorbance threshold A 酚酞阈值 In other words, the absorbance A at the titration endpoint is determined to be within the range of [0.4A, 0.6A], where A = lg (ADC 发射 / ADC 接收 ).

[0074] Furthermore, the phenolphthalein absorbance threshold A 酚酞阈值 The phenolphthalein absorbance threshold A is determined to be 0.4A. That is, 0.4A is determined as the judgment end point of the titration process. 酚酞阈值The titration volume V of the NaOH standard solution is obtained based on the number of titration drops n. NaOH酚酞 .

[0075] In some embodiments, the titration volume is 0.1 ml, then the titration volume V NaOH酚酞 =n*0.1.

[0076] When phenolphthalein is used as a titration indicator, the phenolphthalein acidity of the water sample is obtained by the following formula:

[0077]

[0078] Among them, phenolphthalein acidity is measured in terms of CaCO3, and the unit is mg / L;

[0079] C NaOH is the concentration of NaOH standard solution, in mol / L;

[0080] V NaOH酚酞 It is the titration volume of NaOH standard solution at the titration endpoint using phenolphthalein as titration indicator, in L;

[0081] 50.05 is the molar mass of 1 / 2CaCO3, in g / mol;

[0082] V 水样 is the volume of the water sample, in L.

[0083] To facilitate understanding of the technical solutions provided by the embodiments of the present invention, specific embodiments are given below.

[0084] Example 1

[0085] The method provided in the embodiment of the present invention is used to monitor the acidity of a water sample in the intermediate production link of a process workshop of a chemical plant. The pH value of the water sample is about 2. In this embodiment, methyl orange solution is used as an indicator to monitor the methyl orange acidity of the water sample.

[0086] In the specific implementation, three sampling points are selected to take 500ml water samples, 500ml water samples, and 500ml water samples respectively, and water samples 1, water sample 2 and water sample 3 are obtained in sequence. When monitoring the acidity of water samples, a certain volume of V is first 水样 The water sample (water sample 1 or water sample 2 or water sample 3) is added to the quartz titration cell. One side of the quartz titration cell is provided with an emitting light source with a wavelength of 460nm, and the other side of the quartz titration cell is provided with a receiving photocell for receiving the signal emitted by the light source. Before the titration begins, a certain amount of methyl orange solution is added and the methyl orange solution and the water sample are mixed evenly by the rotor at the bottom of the quartz titration cell, and then the absorbance signal of the water sample is recorded and used as the background signal A. 本底; Then use a titration pump to drip C with a concentration of 0.02 mol / L NaOH The sodium hydroxide standard solution is titrated until the absorbance A of the water sample increases sharply. The titration is stopped and the titration volume V of the NaOH standard solution at the titration end point using methyl orange as the titration indicator is obtained by the titration number n of the titration pump. NaOH甲基橙 , thus based on the titration volume V NaOH甲基橙 Calculate the methyl orange acidity of the water sample.

[0087] The above method was used to monitor the acidity of methyl orange in water sample 1, water sample 2 and water sample 3, and the results were as follows:

[0088] Sample name Test results (mg / L) Indication error (%) Water sample 1 475.3 1.13 Water sample 2 462.1 0.72 Water sample 3 432.5 -0.64

[0089] Furthermore, the indication error of the measurement results obtained in this embodiment is calculated using the measurement results in the comparative example below, that is, the corresponding water sample measurement results of the comparative example are used as the true value of the actual water sample, and the indication error of the measurement results of this embodiment is obtained to be ≤±5%, which meets industry requirements.

[0090] Example 2

[0091] The method provided in the embodiment of the present invention is used to monitor a general water sample in the intermediate production link of a process workshop of a water treatment plant. In this embodiment, phenolphthalein solution is used as an indicator to monitor the phenolphthalein acidity of the water sample.

[0092] In the specific implementation, three process water samples are taken respectively, and 500ml of water sample 4, 500ml of water sample 5 and 500ml of water sample 6 are obtained in turn. When monitoring the acidity of the water sample, a certain volume V 水样 The water sample (water sample 4 or water sample 5 or water sample 6) is added to the quartz titration cell. One side of the quartz titration cell is provided with an emitting light source with a wavelength of 515nm, and the other side of the quartz titration cell is provided with a receiving photocell for receiving the signal emitted by the light source. Before the titration begins, a certain amount of phenolphthalein solution is added and the phenolphthalein solution and the water sample are mixed evenly by the rotor at the bottom of the quartz titration cell, and then the absorbance signal of the water sample is recorded and used as the background signal A. 本底 ; Then use a titration pump to drip C with a concentration of 0.02 mol / L NaOH The sodium hydroxide standard solution is titrated until the absorbance A of the water sample increases sharply. The titration is stopped and the titration volume V of the NaOH standard solution at the titration end point using phenolphthalein as the titration indicator is obtained by the titration number n of the titration pump. NaOH酚酞 , thus based on the titration volume V NaOH酚酞 Calculate the phenolphthalein acidity of the water sample.

[0093] The above method was used to monitor the phenolphthalein acidity of water sample 4, water sample 5 and water sample 6, and the results were as follows:

[0094] Sample name Test results (mg / L) Indication error (%) Water sample 4 108.1 -2.17 Water sample 5 95.7 -2.45 Water sample 6 113.2 0.62

[0095] Furthermore, the indication error of the measurement results obtained in this embodiment is calculated using the measurement results in the comparative example below, that is, the corresponding water sample measurement results of the comparative example are used as the true value of the actual water sample, and the indication error of the measurement results of this embodiment is obtained to be ≤±5%, which meets industry requirements.

[0096] Comparative Example

[0097] The actual water samples taken from Example 1 and Example 2 were manually titrated using the acid-base indicator titration method in the "Water and Wastewater Monitoring and Analysis Methods" (Fourth Edition) compiled by the State Environmental Protection Administration, and the manual titration results of water sample 1, water sample 2, water sample 3, water sample 4, water sample 5, and water sample 6 in Example 1 and Example 2 were obtained as follows:

[0098] Sample name Test results (mg / L) Water sample 1 470.2 Water sample 2 458.7 Water sample 3 435.3 Water sample 4 110.5 Water sample 5 98.1 Water sample 6 112.5

[0099] By comparing the results of the proportional detection with those of Example 1 and Example 2, the indicated error is calculated to be within ±5%. Therefore, the detection data obtained by the method provided in the embodiment of the present invention is valid, and the data accuracy is basically equivalent to the national standard method. The detection result can be used as a standard for judging the acidity in the water body. Compared with the national standard method, the method provided in the embodiment of the present invention has the advantage of being able to operate online for 24 hours continuously, continuously monitor the water body, reflect the real-time monitoring results, and provide uninterrupted feedback on the parameters of the factory production process, which can effectively improve the production quality and production efficiency.

[0100] Although specific embodiments have been described above, these embodiments are not intended to limit the scope of the present disclosure, even when only a single embodiment is described with respect to specific features. The feature examples provided in the present disclosure are intended to be illustrative rather than limiting, unless otherwise stated. In specific implementations, the technical features of one or more dependent claims may be combined with the technical features of the independent claims, based on actual needs and where technically feasible, and the technical features from the corresponding independent claims may be combined in any appropriate manner rather than just by the specific combinations listed in the claims.

[0101] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A method for online monitoring of water acidity, characterized in that: include: S1, add the water sample and titration indicator into the titration cell and mix them evenly, and measure the absorbance A of the water sample mixed with the titration indicator at wavelength λ 本底 And used as the absorbance background value; S2, using a NaOH standard solution as a titrant to titrate the water sample mixed with a titration indicator, and measuring the absorbance A of the water sample mixed with the titration indicator at a wavelength λ during the titration process; S3, the absorbance A during the titration process is greater than or equal to the absorbance threshold A 阈值 The moment of titration is taken as the titration endpoint, and the titration volume V of the NaOH standard solution at the titration endpoint is obtained. NaOH ; S4, based on the titration volume V NaOH Get the acidity of the water sample.

2. The method according to claim 1, characterized in that Before step S1, the method further includes: It is pre-determined whether the pH of the water sample is less than or equal to 3.

7. If so, methyl orange is used as the titration indicator and the acidity obtained is methyl orange acidity. If not, phenolphthalein is used as the titration indicator and the acidity obtained is phenolphthalein acidity.

3. The method according to claim 1, characterized in that Before step S1, the method further includes: Pre-determine whether the titration number n of the NaOH standard solution at the titration end point is greater than or equal to the drop number threshold D 阈值 If yes, methyl orange is used as the titration indicator and the acidity obtained is methyl orange acidity; if no, phenolphthalein is used as the titration indicator and the acidity obtained is phenolphthalein acidity.

4. The method according to claims 1 to 3, characterized in that When methyl orange is used as the titration indicator, the wavelength λ is the wavelength λ of methyl orange. 甲基橙 , and the methyl orange wavelength λ 甲基橙 It is 460nm.

5. The method according to claim 4, characterized in that The absorbance threshold A 阈值 A is the absorbance threshold of methyl orange 甲基橙阈值 , and the methyl orange absorbance threshold A 甲基橙阈值 Located in the range of [0.5A, 0.7A].

6. The method according to claim 3, characterized in that The methyl orange absorbance threshold A 甲基橙阈值 is 0.5A.

7. The method according to claims 1 to 3, characterized in that When phenolphthalein is used as the titration indicator, the wavelength λ is the phenolphthalein wavelength λ 酚酞 , and the phenolphthalein wavelength λ 酚酞 It is 515nm.

8. The method according to claim 7, characterized in that The absorbance threshold A 阈值 A is the absorbance threshold of phenolphthalein 酚酞阈值 , and the phenolphthalein absorbance threshold A 酚酞阈值 Located in the range of [0.4A, 0.6A].

9. The method according to claim 8, characterized in that The phenolphthalein absorbance threshold A 酚酞阈值 It is 0.4A.

10. The method according to claim 1, characterized in that The acidity in step S4 is obtained by the following formula: Among them, the acidity is measured in CaCO3, and the unit is mg / L; C NaOH is the concentration of the NaOH standard solution at the titration endpoint, in mol / L; V NaOH is the titration volume of the NaOH standard solution at the titration endpoint, in L; 50.05 is the molar mass of 1 / 2CaCO3, in g / mol; V 水样 is the volume of the water sample, in L.

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