Method for monitoring total hardness of water on line

Abstract

The invention provides a method for monitoring the total hardness of water on line. The method comprises the following steps: S1, adjusting the pH value of a water sample to 10 + / -0.1; s2, taking chrome black T as an indicator, titrating the water sample by adopting an EDTA disodium standard solution, and measuring the absorbance A of the water sample at a specific wavelength in the titration process; s3, determining a titration end point based on the change of the absorbance A, and obtaining the titration volume VEDTA of the EDTA disodium standard solution at the titration end point; and S4, obtaining the total hardness of the water sample based on the titration volume VEDTA. According to the method, the total hardness of water is monitored based on an EDTA titration method, the absorbance of a water sample under different developing conditions is measured by adopting double light sources and double wavelengths in the titration process, and the titration speed is adjusted and the titration end point is judged by utilizing the absorbance, so that the purpose of monitoring the total hardness of water is achieved, and online monitoring of the total hardness of water is realized; and operation is more convenient, cost is lower, and popularization and application 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 total water hardness. Background Art

[0002] As we all know, calcium (Ca) is widely present in various types of natural water, with a concentration ranging from a few milligrams to hundreds of milligrams per liter of natural water. Calcium (Ca) mainly comes from the weathering and dissolution of calcium-containing rocks and is the main component of water hardness. Magnesium (Mg) is also a common component in natural water. It mainly comes from the weathering and dissolution of dolomite containing magnesium carbonate and other rocks. At the same time, magnesium salts are also the main factor in water hardening.

[0003] Generally, water with too high hardness is not suitable for direct use in life and industry. For example, water with too high hardness is not suitable for boiler operation. Long-term heating of water with high hardness will cause scale to form on the inner wall of the boiler, which will not only increase energy consumption but also pose an explosion risk. Therefore, it is very necessary to test the water hardness.

[0004] At present, the main methods for detecting water hardness are flame atomic absorption spectrometry, ICP-AES method, and EDTA titration method. However, flame atomic absorption spectrometry and ICP-AES methods are expensive and can only be used for laboratory testing, and cannot be applied to online monitoring; and although the EDTA titration method is relatively low in cost, the operation steps are cumbersome, and manual titration and observation of the titration end point are required. It can only be used in the laboratory and cannot achieve the task of online water quality monitoring. Therefore, it is urgent to invent a method for online monitoring of total water hardness. Summary of the invention

[0005] The purpose of the present invention is to provide a method for online monitoring of total water hardness. The method monitors the total water hardness based on the EDTA titration method, and adopts dual light sources and dual wavelengths to measure the absorbance of water samples under different color development conditions during the titration process, and then uses the absorbance to adjust the titration speed and determine the titration end point, thereby achieving the purpose of monitoring the total water hardness. Not only does the method realize online monitoring of the total water hardness, but it is also more convenient to operate and more cost-effective, which is conducive to popularization and application.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for online monitoring of total water hardness, comprising:

[0008] S1, adjust the pH of the water sample to pH = 10 ± 0.1;

[0009] S2, using chrome black T as an indicator, using EDTA disodium standard solution to titrate the water sample, and determining the absorbance A of the water sample at a first specific wavelength during the titration process, and then adjusting the titration speed based on the absorbance A of the water sample at the first specific wavelength and converting the absorbance A of the water sample at a second specific wavelength;

[0010] S3, determining the titration endpoint based on the change in the absorbance A of the water sample at the second specific wavelength, and obtaining the titration volume V of the disodium EDTA standard solution at the titration endpoint EDTA ;

[0011] S4, based on the titration volume V of the disodium EDTA standard solution at the titration endpoint EDTA The total hardness of the water sample is obtained.

[0012] Optionally, the step S1 of adjusting the pH of the water sample to pH=10±0.1 comprises:

[0013] S11, adding a buffer solution with a pH value of 10 into the water sample and monitoring the pH value of the water sample;

[0014] S12, determine whether the pH value of the water sample is greater than 10.1. If so, add hydrochloric acid solution to adjust the pH value of the water sample until the pH value of the water sample is equal to 10±0.1; and determine whether the pH value of the water sample is less than 9.9. If so, add ammonia solution to adjust the pH value of the water sample until the pH value of the water sample is equal to 10±0.1.

[0015] Optionally, the first specific wavelength is 540 nm, and the second specific wavelength is 700 nm; the step S2 of determining the absorbance A of the water sample at the first specific wavelength during the titration process, and then adjusting the titration speed based on the absorbance A of the water sample at the first specific wavelength and converting the determination of the absorbance A of the water sample at the second specific wavelength includes:

[0016] S21, when the titration starts, the absorbance A of the water sample at a wavelength of 540 nm is measured. 540 ;

[0017] S22, judging the absorbance A 540 Is it greater than or equal to the first absorbance threshold value A1? If so, use rapid titration and record the number of titration drops N1 of the disodium EDTA standard solution during the rapid titration; if not, go to step S23;

[0018] S23, judging the absorbance A 540Is it greater than the second absorbance threshold value A2? If so, use slow titration and record the number of titration drops N2 of the disodium EDTA standard solution during the slow titration. If not, go to step S24;

[0019] S24, switching the wavelength of the emitting light source from 540 nm to 700 nm and adopting slow titration, while recording the number of titration drops N3 of the disodium EDTA standard solution during the slow titration process and measuring the absorbance A of the water sample at a wavelength of 700 nm 700 .

[0020] Optionally, the step S3 of determining the titration endpoint based on the change in absorbance A of the water sample at the second specific wavelength includes:

[0021] Determine the absorbance A 700 Is it greater than or equal to the third absorbance threshold value A3? If so, the absorbance A 700 The moment when the third threshold value A3 is reached is regarded as the titration endpoint.

[0022] Optionally, the first absorbance threshold A1 is 0.2A, the second absorbance threshold A2 is 0.1A±0.02A, and the third absorbance threshold A3 is 0.35A.

[0023] Optionally, the titration volume V of the disodium EDTA standard solution at the titration endpoint in step S4 is EDTA =V EDTA1 +V EDTA2 +V EDTA3 ,in,

[0024] V EDTA1 is the total titration volume of the disodium EDTA standard solution in the rapid titration process of step S22, V EDTA2 is the total titration volume of the disodium EDTA standard solution in the slow titration process of step S23, V EDTA3 It is the total titration volume of the disodium EDTA standard solution during the slow titration process described in step S24.

[0025] Optionally, the titration volume of each drop of disodium EDTA standard solution in the rapid titration process is 0.1 mL, and the titration volume of each drop of disodium EDTA standard solution in the slow titration process is 0.05 mL;

[0026] V EDTA1 =N1*0.1, V EDTA2 =N2*0.05, V EDTA3 =N3*0.05.

[0027] Optionally, the total hardness of the water sample in step S4 is obtained by the following formula:

[0028] Total hardness of water sample 以CaCO3计 =(C EDTA *(N1*0.1+N2*0.05+N3*0.05)*100.1) / V 水样 in,

[0029] The total hardness of the water sample is expressed as CaCO3, and 1mmol / L of the total amount of calcium and magnesium is equivalent to 100.1mg / L of hardness expressed as CaCO3.

[0030] C EDTA is the concentration of disodium EDTA standard solution, in mmol / L,

[0031] V 水样 is the volume of the water sample in mL.

[0032] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0033] For example, the method for online monitoring of total water hardness provided by the present invention is based on the EDTA titration method to monitor the total water hardness, and uses dual light sources and dual wavelengths to measure the absorbance of water samples under different color development conditions during the titration process, and then uses the absorbance to adjust the titration speed and determine the titration end point, thereby achieving the purpose of monitoring the total water hardness. It not only realizes the online monitoring of the total water hardness, but also makes the operation more convenient and the cost more economical, which is conducive to popularization and application.

[0034] For another example, the method provided by the present invention does not require manual titration, which saves human resources to a certain extent, and can perform continuous 24-hour uninterrupted online monitoring, fully meeting the current needs of online monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A flowchart of an implementation method for online monitoring of total water hardness provided by an embodiment of the present invention;

[0036] Figure 2 is the absorbance A of the water sample in the embodiment of the present invention and the titration volume V of the titrant disodium EDTA standard solution EDTA The relationship curve between them. DETAILED DESCRIPTION

[0037] 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.

[0038] 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.

[0039] An embodiment of the present invention provides a method for online monitoring of total water hardness.

[0040] Reference Figure 1 The method for online monitoring of total water hardness may include the following steps:

[0041] S1, adjust the pH of the water sample to pH = 10 ± 0.1;

[0042] S2, using chrome black T as an indicator, using EDTA disodium standard solution to titrate the water sample, and measuring the absorbance A of the water sample at a first specific wavelength during the titration process, and then adjusting the titration speed based on the absorbance A of the water sample at the first specific wavelength and converting the absorbance A of the water sample at a second specific wavelength;

[0043] S3, determining the titration endpoint based on the change in the absorbance A of the water sample at the second specific wavelength, and obtaining the titration volume V of the disodium EDTA standard solution at the titration endpoint EDTA ;

[0044] S4, based on the titration volume V of disodium EDTA standard solution at the titration endpoint EDTA Get the total hardness of the water sample.

[0045] One of the difficulties in online monitoring of total water hardness based on EDTA titration is the control of the pH value of the water sample.

[0046] In some embodiments, the step S1 of adjusting the pH of the water sample to pH=10±0.1 may include the following steps:

[0047] S11, adding a buffer solution with a pH value of 10 into the water sample and monitoring the pH value of the water sample;

[0048] S12, determine whether the pH value of the water sample is greater than 10.1. If so, add hydrochloric acid solution to adjust the pH value of the water sample until the pH value of the water sample is equal to 10±0.1; and determine whether the pH value of the water sample is less than 9.9. If so, add ammonia solution to adjust the pH value of the water sample until the pH value of the water sample is equal to 10±0.1.

[0049] Since the online water quality changes dynamically, in the embodiments of the present invention, the above-mentioned technical means are used to solve the problem of controlling the pH value of the water sample, which can not only meet the working conditions of a wider range of online monitoring, but also is easy to operate and can also make the control of the pH value of the water sample more accurate.

[0050] In some embodiments, the buffer solution with a pH value of 10 can be prepared by the configuration method in the national standard GB / T 7477-1987 "Determination of the total amount of calcium and magnesium in water - EDTA titration method".

[0051] In some embodiments, a water sample and a buffer solution with a pH value of 10 can be added to a titration cell first, and the pH value of the water sample can be detected using a pH meter in the titration cell. In this way, the detection of the pH value of the water sample can be easily implemented and the operation is simple.

[0052] In some embodiments, a hydrochloric acid solution with a concentration of 5 mol / L is used to adjust the pH of the water sample.

[0053] In some embodiments, the pH of the water sample is adjusted using an aqueous ammonia solution with a concentration of 3 mol / L.

[0054] The second difficulty in online monitoring of total water hardness based on EDTA titration is the online determination of the titration endpoint.

[0055] In the embodiment of the present invention, the titration endpoint is determined online based on the change trend of the absorbance of the water sample at a specific wavelength during the titration process.

[0056] In a specific implementation, the embodiment of the present invention will adopt dual light sources and dual wavelengths, that is, a light source with two wavelengths, to measure the absorbance of water samples of different colors during the titration process, and adjust the titration speed according to the absorbance A of the water sample at the first specific wavelength, and switch the light source to convert the absorbance A of the water sample at the second specific wavelength, and then determine the titration end point according to the change in the absorbance A of the water sample at the second specific wavelength, thereby achieving the purpose of online monitoring of the total hardness of water quality.

[0057] In an embodiment of the present invention, chrome black T is used as an indicator, and after the chrome black T indicator is added to the titration cell, it will be complexed with the calcium and magnesium ions in the titration cell water sample, so that the water sample color becomes purple (i.e., the color after chrome black T is complexed with calcium and magnesium ions), and then the water sample is titrated using a disodium EDTA standard solution, at which time the calcium and magnesium ions in the water sample will leave chrome black T and preferentially complex with EDTA, and the calcium and magnesium ions complexed by chrome black T are reduced, causing the purple-red color produced by the complexation of chrome black T and calcium and magnesium ions to gradually become lighter. In a specific implementation, this process can be embodied by the change in the absorbance A of the water sample at the first specific wavelength, which is specifically embodied as the titration process continues, and the absorbance A of the water sample at the first specific wavelength gradually decreases.

[0058] In the embodiment of the present invention, the titration speed can also be adjusted by the change of the absorbance A of the water sample at the first specific wavelength, so that the titration speed of the titrant is changed from fast to slow, so as to monitor the titration end point.

[0059] In an embodiment of the present invention, the light source can also be switched by the change of the absorbance A of the water sample at the first specific wavelength to measure the absorbance A of the water sample at the second specific wavelength, and then the titration end point can be determined by the absorbance A of the water sample at the second specific wavelength.

[0060] When the absorbance A of the water sample at the first specific wavelength gradually decreases to a certain threshold, most of the calcium and magnesium ions in the water sample are complexed by EDTA, and the color of the water sample changes from purple-red to light red. At this time, the light source with the first specific wavelength is turned off, and the light source with the second specific wavelength is turned on, and the titration end point is then determined online by the absorbance A of the water sample at the second specific wavelength.

[0061] When the absorbance A of the water sample at the first specific wavelength gradually decreases to a certain threshold value and most of the calcium and magnesium ions in the water sample are complexed by EDTA, a large amount of replaced chrome black T will exist in the water sample. Since chrome black T appears sky blue in a solution with a pH value of 10±0.1, a large amount of replaced chrome black T will gradually change the color of the water sample to sky blue. At this time, turn on the light source with the second specific wavelength, and the titration endpoint can be determined online by the absorbance A of the water sample at the second specific wavelength.

[0062] In the embodiment of the present invention, the light source with the first specific wavelength is switched to the light source with the second specific wavelength because the purple-red to light red water sample and the sky blue water sample have maximum absorption at different wavelengths, respectively. The purple-red to light red water sample has maximum absorption at the first specific wavelength, and the sky blue water sample has maximum absorption at the second specific wavelength.

[0063] In some embodiments, the first specific wavelength is 540nm, and the second specific wavelength is 700nm. The first specific wavelength is used at the beginning of titration, when the water sample is purple-red and the absorbance at the wavelength of 540nm is the largest, the absorbance signal is stable, and the error is small; the second specific wavelength is used when determining the titration end point, when the water sample is sky blue and the absorbance at the wavelength of 700nm is the largest, the absorbance signal is stable, the error is small, and the titration end point can be accurately determined.

[0064] In some embodiments, the step S2 of determining the absorbance A of the water sample at the first specific wavelength during the titration process, and then adjusting the titration speed based on the absorbance A of the water sample at the first specific wavelength and switching to determine the absorbance A of the water sample at the second specific wavelength comprises the following steps:

[0065] S21, at the beginning of titration, measure the absorbance A of the water sample at a wavelength of 540nm 540 ;

[0066] S22, determine the absorbance A 540Is it greater than or equal to the first absorbance threshold value A1? If so, use rapid titration and record the number of titration drops N1 of the disodium EDTA standard solution during the rapid titration; if not, go to step S23;

[0067] S23, determine the absorbance A 540 Is it greater than the second absorbance threshold value A2? If so, use slow titration and record the number of titration drops N2 of the disodium EDTA standard solution during the slow titration. If not, go to step S24;

[0068] S24, switch the wavelength of the emission light source from 540nm to 700nm and use slow titration, while recording the number of titration drops N3 of the EDTA disodium standard solution during the slow titration process and measuring the absorbance A of the water sample at a wavelength of 700nm 700 .

[0069] In some embodiments, determining the titration endpoint based on the change in absorbance A of the water sample at the second specific wavelength described in step S3 includes:

[0070] Determine absorbance A 700 Is it greater than or equal to the third absorbance threshold value A3? If so, then the absorbance A 700 The moment when the third threshold value A3 is reached is regarded as the titration endpoint.

[0071] In the embodiment of the present invention, the first absorbance threshold A1 is the determination condition for switching the titration speed; the second absorbance threshold A2 is the determination condition for switching light sources of different wavelengths; and the third absorbance threshold A3 is the determination condition for determining the titration endpoint.

[0072] Specifically, the purpose of setting the first absorbance threshold A1 is to avoid rapid titration resulting in the absorbance A of the water sample at the first specific wavelength suddenly being less than or equal to the second absorbance threshold A2 and thus missing the opportunity to switch the light source.

[0073] In order to accurately determine when the absorbance A of the water sample at the first specific wavelength reaches the second absorbance threshold A2, the embodiment of the present invention chooses to pre-set the first absorbance threshold A1 before the second absorbance threshold A2 to adjust the rapid titration to slow titration to prevent missing the opportunity to switch the light source.

[0074] In some preferred embodiments, the relationship between the first absorbance threshold value A1 and the second absorbance threshold value A2 may be A1≥2A2. In this way, the titration speed of the water sample before the absorbance A at the first specific wavelength reaches the second absorbance threshold value A2 can be slowed down to increase the titration time, so that the absorbance A of the water sample at the first specific wavelength can be accurately determined when it reaches the second absorbance threshold value A2.

[0075] When the absorbance A of the water sample at the first specific wavelength is less than or equal to the second absorbance threshold value A2, the signal sensitivity of the absorbance A of the water sample at the first specific wavelength decreases and can no longer reflect the color change of the water sample.

[0076] Specifically, when the absorbance A of the water sample at the first specific wavelength no longer changes with the increase of the titration volume, it means that the second absorbance threshold value A2 has been reached. Therefore, a threshold determination test can be performed based on this to determine the second absorbance threshold value A2.

[0077] In the threshold determination test, the pH of the water sample is first adjusted to pH = 10 ± 0.1, and then chrome black T is used as an indicator and disodium EDTA standard solution is used to titrate the water sample. During the titration process, the absorbance A of the water sample at the first specific wavelength is measured. When the absorbance A of the water sample at the first specific wavelength no longer changes with the increase of the titration volume, the value is the second absorbance threshold value A2.

[0078] After the second absorbance threshold value A2 is determined, the first absorbance threshold value A1 can be further determined based on the second absorbance threshold value A2.

[0079] The third absorbance threshold value A3 can be obtained according to the absorbance measurement result of the titration endpoint of the water sample at the second specific wavelength. Specifically, the total hardness of the water sample can be manually titrated using the national standard method, and the sky blue titration solution of the manual titration endpoint of the national standard method can be added to the titration cell of the analyzer, and then the light source of the second specific wavelength is turned on and the absorbance of the sky blue titration solution at the second specific wavelength is measured multiple times, and then the average value of the multiple measurement results is used as the third absorbance threshold value A3.

[0080] In some embodiments, the first absorbance threshold A1 is 0.2A, the second absorbance threshold A2 is 0.1A±0.02A, and the third absorbance threshold A3 is 0.35A.

[0081] Furthermore, a titration curve may be drawn using the first absorbance threshold value A1, the second absorbance threshold value A2 and the third absorbance threshold value A3, that is, a relationship curve between the absorbance A of the water sample and the titration volume VEDTA of the titrant disodium EDTA standard solution.

[0082] Figure 2 It is a relationship curve between the absorbance A of the water sample in the embodiment of the present invention and the titration volume VEDTA of the titrant disodium EDTA standard solution.

[0083] Reference Figure 2 , when the absorbance of the water sample is A 540 When the absorbance of the water sample is greater than or equal to 0.2A, use rapid titration and record the number of drops N1 of the EDTA disodium standard solution during the rapid titration process; when the absorbance of the water sample is A 540When the absorbance of the water sample is less than 0.2A and greater than 0.1A±0.02A, use slow titration and record the number of drops N2 of the EDTA disodium standard solution during the slow titration process; 540 When it is less than or equal to 0.1A±0.02A, the wavelength of the emitting light source is switched from 540nm to 700nm and slow titration is adopted, and the number of titration drops N3 of the disodium EDTA standard solution during the slow titration is recorded.

[0084] In a specific implementation, the titration volume V of the disodium EDTA standard solution at the titration endpoint described in step S4 is EDTA =V EDTA1 +V EDTA2 +V EDTA3 Among them, V EDTA1 V is the total titration volume of the disodium EDTA standard solution in the rapid titration process of step S22; EDTA2 V is the total titration volume of the disodium EDTA standard solution during the slow titration process of step S23; EDTA3 is the total titration volume of the disodium EDTA standard solution during the slow titration process in step S24, and V EDTA3 It is the total titration volume of the disodium EDTA standard solution from the start of the slow titration process to the titration endpoint in step S24.

[0085] In some embodiments, the titration volume of each drop of EDTA disodium standard solution during the rapid titration process is 0.1 mL, and the titration volume of each drop of EDTA disodium standard solution during the slow titration process is 0.05 mL. In this case,

[0086] V EDTA1 =N1*0.1,

[0087] V EDTA2 =N2*0.05,

[0088] V EDTA3 =N3*0.05.

[0089] Then the total hardness of the water sample described in step S4 can be obtained by the following formula:

[0090] Total hardness of water sample 以CaCO3计 =(C EDTA *(N1*0.1+N2*0.05+N3*0.05)*100.1) / V 水样 in,

[0091] The total hardness of the water sample is expressed as CaCO3, and 1mmol / L of the total amount of calcium and magnesium is equivalent to 100.1mg / L of hardness expressed as CaCO3.

[0092] C EDTAis the concentration of disodium EDTA standard solution, in mmol / L,

[0093] V 水样 is the volume of the water sample in mL.

[0094] To facilitate understanding of the technical solutions provided by the embodiments of the present invention, specific embodiments are given below.

[0095] Example

[0096] First, 500 ml of tap water was collected from Yunsong Cuiting Community in Shanghai and recorded as water sample 1, 500 ml of tap water was collected from Lanse Chengbang Community in Shanghai and recorded as water sample 2, and 500 ml of tap water was collected from Lido Huating Community in Shanghai and recorded as water sample 3. Then, the total hardness of water sample 1, water sample 2 and water sample 3 was monitored using the method provided in an embodiment of the present invention.

[0097] Reagent preparation:

[0098] The reagent preparation volume is sufficient for use for more than one month, including:

[0099] 1.0L of pH 10 buffer solution,

[0100] 1.0L 5mmol / L EDTA disodium standard solution,

[0101] 0.1L of chrome black T indicator,

[0102] 1.0L of 5mol / L hydrochloric acid solution,

[0103] 1.0L of 3mol / L ammonia solution.

[0104] Implementation process of online monitoring of total water hardness:

[0105] (1) First, place the reagents in the reagent position of the monitoring system and connect the pipelines; use the metering device to measure a certain volume V 水样 The water sample (can be water sample 1, water sample 2, or water sample 3) is added to the titration cell, V 水样 The volume can be determined according to the size of the titration cell; after the water sample is added to the titration cell, the magnetic stirrer rotor of the titration cell keeps rotating at a low speed, and the rotor speed should be able to mix the water sample evenly without generating bubbles; then a certain volume of buffer solution is added, and the buffer solution and the water sample are stirred evenly by the rotor; then a pH electrode is used to detect the pH value of the mixture of the water sample and the buffer solution. If the pH is greater than 10.1, a 5 mol / L hydrochloric acid solution is dripped in. If the pH is less than 9.9, a 3 mol / L ammonia solution is dripped in until the pH is 10±0.1, and the titration of the acid-base regulating solution is stopped.

[0106] (2) Then, a certain volume of chrome black T indicator is added, and the light source of the first specific wavelength, i.e., 540 nm, is turned on to measure the absorbance of the water sample in the titration cell. At the same time, the water sample is titrated using the disodium EDTA standard solution. The titration of the disodium EDTA standard solution can be controlled by a titration pump.

[0107] (3) When the absorbance of the water sample at the first specific wavelength, i.e., 540 nm, is A≥0.2A, rapid titration is performed, and the volume of each drop is 0.1 mL, and the number of drops is recorded as N1;

[0108] When the absorbance of the water sample at the first specific wavelength, i.e., 540 nm, is A<0.2A and A>0.1A±0.02A, slow titration is used, and the volume of each drop is 0.05 mL, and the number of drops is recorded as N2;

[0109] The difference between the fast titration and the slow titration here is that, when the titration frequency is the same, the fast titration is when the titration volume is large each time, and the slow titration is when the titration volume is small each time.

[0110] When the absorbance A of the water sample at the first specific wavelength, i.e., 540nm, is ≤0.1A±0.02A, the light source of the first specific wavelength, i.e., 540nm, is turned off, and the light source of the second specific wavelength, i.e., 700nm, is turned on, and the titration is continued slowly. At this time, the absorbance A of the water sample at the second specific wavelength, i.e., 700nm, will gradually increase;

[0111] When the absorbance A of the water sample at the second specific wavelength, 700 nm, is ≥ 0.35A, the titration is stopped, and the number of drops of the EDTA disodium standard solution slowly titrated during the period when the light source at the second specific wavelength, 700 nm, is turned on is recorded as N3.

[0112] (3) Finally, the total amount of calcium and magnesium and the total hardness are calculated based on the titration drops N1, N2, N3 and the concentration of the disodium EDTA standard solution, and the total hardness of the water is output as CaCO3. That is,

[0113] Total hardness of water sample 以CaCO3计 =(C EDTA *(N1*0.1+N2*0.05+N3*0.05)*100.1) / V 水样 in,

[0114] The total hardness of the water sample is expressed as CaCO3, and 1mmol / L of the total amount of calcium and magnesium is equivalent to 100.1mg / L of hardness expressed as CaCO3.

[0115] C EDTA is the concentration of disodium EDTA standard solution, in mmol / L,

[0116] V水样 is the volume of the water sample in mL.

[0117] The total hardness of water samples 1, 2 and 3 was monitored using the method provided in the embodiment of the present invention, and the test results obtained were as follows:

[0118]

[0119] Among them, the total hardness of the water sample is the hardness expressed in CaCO3.

[0120] Comparative Example

[0121] For water sample 1, water sample 2, and water sample 3 in the above embodiment, the total hardness of the water quality was measured respectively using GB 7477-87 "Determination of the total amount of calcium and magnesium in water - EDTA titration method", and the indication error of the total hardness of the three water samples in the above embodiment was calculated using the national standard measurement results as the true results. The measurement results and indication errors are as follows:

[0122]

[0123]

[0124] From the above results, it can be seen that the indication errors of the three water samples are all ≤±5%, so the test results of the method in the embodiment of the present invention are basically consistent with the national standard method, and the test data is accurate and reliable. In addition, by comparing with the national standard method, the method provided by the embodiment of the present invention does not require manual titration, which saves human resources to a certain extent, and can perform continuous 24h uninterrupted online monitoring, which fully meets the current needs of online monitoring.

[0125] 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.

[0126] 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 total water hardness, characterized in that: include: S1, adjust the pH of the water sample to pH = 10 ± 0.1; S2, using chrome black T as an indicator, using EDTA disodium standard solution to titrate the water sample, and determining the absorbance A of the water sample at a first specific wavelength during the titration process, and then adjusting the titration speed based on the absorbance A of the water sample at the first specific wavelength and converting the absorbance A of the water sample at a second specific wavelength; S3, determining the titration endpoint based on the change in the absorbance A of the water sample at the second specific wavelength, and obtaining the titration volume V of the disodium EDTA standard solution at the titration endpoint EDTA ; S4, based on the titration volume V of the disodium EDTA standard solution at the titration endpoint EDTA The total hardness of the water sample is obtained.

2. The method according to claim 1, characterized in that The step S1 of adjusting the pH of the water sample to pH=10±0.1 includes: S11, adding a buffer solution with a pH value of 10 into the water sample and monitoring the pH value of the water sample; S12, determine whether the pH value of the water sample is greater than 10.

1. If so, add hydrochloric acid solution to adjust the pH value of the water sample until the pH value of the water sample is equal to 10±0.1; and determine whether the pH value of the water sample is less than 9.

9. If so, add ammonia solution to adjust the pH value of the water sample until the pH value of the water sample is equal to 10±0.

1.

3. The method according to claim 1, characterized in that The first specific wavelength is 540 nm, and the second specific wavelength is 700 nm; the step S2 of determining the absorbance A of the water sample at the first specific wavelength during the titration process, and then adjusting the titration speed based on the absorbance A of the water sample at the first specific wavelength and converting the absorbance A of the water sample at the second specific wavelength includes: S21, when the titration starts, the absorbance A of the water sample at a wavelength of 540 nm is measured. 540 ; S22, judging the absorbance A 540 Is it greater than or equal to the first absorbance threshold value A1? If so, use rapid titration and record the number of titration drops N1 of the disodium EDTA standard solution during the rapid titration; if not, go to step S23; S23, judging the absorbance A 540 Is it greater than the second absorbance threshold value A2? If so, use slow titration and record the number of titration drops N2 of the disodium EDTA standard solution during the slow titration. If not, go to step S24; S24, switching the wavelength of the emitting light source from 540 nm to 700 nm and adopting slow titration, while recording the number of titration drops N3 of the disodium EDTA standard solution during the slow titration process and measuring the absorbance A of the water sample at a wavelength of 700 nm 700 .

4. The method according to claim 3, characterized in that Determining the titration endpoint based on the change in absorbance A of the water sample at the second specific wavelength in step S3 includes: Determine the absorbance A 700 Is it greater than or equal to the third absorbance threshold value A3? If so, the absorbance A 700 The moment when the third threshold value A3 is reached is regarded as the titration endpoint.

5. The method according to claim 4, characterized in that The first absorbance threshold value A1 is 0.2A, the second absorbance threshold value A2 is 0.1A±0.02A, and the third absorbance threshold value A3 is 0.35A.

6. The method according to claim 4, characterized in that The titration volume V of the disodium EDTA standard solution at the titration endpoint described in step S4 EDTA =V EDTA1 +V EDTA2 +V EDTA3 , where V EDTA1 is the total titration volume of the disodium EDTA standard solution in the rapid titration process of step S22, V EDTA2 is the total titration volume of the disodium EDTA standard solution in the slow titration process of step S23, V EDTA3 It is the total titration volume of the disodium EDTA standard solution during the slow titration process described in step S24.

7. The method according to claim 6, characterized in that The titration volume of each drop of disodium EDTA standard solution during the rapid titration process is 0.1 mL, and the titration volume of each drop of disodium EDTA standard solution during the slow titration process is 0.05 mL; In EDTA1 =N1*0.1,V EDTA2 =N2*0.05,V EDTA3 =N3*0.

05.

8. The method according to claim 6, characterized in that The total hardness of the water sample in step S4 is obtained by the following formula: Total hardness of water sample 以CaCO3计 =(C EDTA *(N1*0.1+N2*0.05+N3*0.05)*100.1) / V 水样 in, The total hardness of the water sample is expressed as CaCO3, and 1mmol / L of the total amount of calcium and magnesium is equivalent to 100.1mg / L of hardness expressed as CaCO3. C EDTA is the concentration of disodium EDTA standard solution, in mmol / L, V 水样 is the volume of the water sample in mL.

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