WO2023010803A1 - Water sample hardness measurement method based on water sample turbidity change - Google Patents

Abstract

A water sample hardness measurement method based on a water sample turbidity change, comprising the following steps: S1, constructing a mathematical model related to water hardness and water turbidity; S2, enabling a water sample to be in contact with a calcium/magnesium ion precipitant to convert calcium ions and magnesium ions in the water sample into insoluble salts, and measuring the water sample turbidity of the water sample; and S3. substituting the water sample turbidity for the water turbidity in the mathematical model to calculate the hardness of the water sample. According to the method, the characteristic that the calcium ions and the magnesium ions can be converted into the insoluble salts that are insoluble in water is used, the calcium/magnesium ion precipitant is introduced to convert the calcium ions and magnesium ions into the insoluble salts, such that the turbidity of the water sample changes significantly, and the reaction phenomenon in the process is obvious, the test accuracy is high, and a hardness value of the water sample can be quickly and accurately obtained without tedious pre-calibration or expensive instruments.

Description

A water sample hardness detection method based on the change of water sample turbidity technical field

The invention belongs to the technical field of water quality detection, and in particular relates to a water sample hardness detection method based on water sample turbidity changes.

Background technique

Water is the source of life. Human beings cannot do without water in life and production activities. The quality of drinking water is closely related to human health. With the development of social economy, scientific progress and the improvement of people's living standards, people's drinking The water quality requirements are constantly improving, and the drinking water quality standards are also continuously developed and improved accordingly. Water hardness refers to the total amount of calcium and magnesium ions in the water body. If the hardness of the water body is too high, it will have an impact on human health. Drinking water with high hardness for a long time will cause diseases in the cardiovascular, nervous, urinary and hematopoietic systems. It will also be harmful to production and life. Water hardness detection and analysis is an important task of water quality analysis, which affects public production and life safety.

The existing water hardness testing methods mainly include the following: EDTA titration, ICP spectroscopic analysis, calcium ion selective electrode potential analysis, etc. These methods are cumbersome and complicated to operate, and generally require the use of chemical titrants for auxiliary detection , before the calibration step of the formal detection, in addition, the above method also relies on the expensive instrument detection carrier, which not only increases the cost of water hardness detection, but also requires continuous maintenance of the instrument, however, the accuracy of the above test method There are also problems that are difficult to control. Individual operating differences of testers, pollution or aging of equipment, etc. may cause deviations in test results that cannot be ignored. Based on various problems existing in existing water hardness detection methods, the popularization and application of water hardness detection technology in life and production is promoted.

Contents of the invention

The purpose of the present invention is to provide a water sample hardness detection method based on the change of water sample turbidity, so as to realize accurate detection of water quality hardness through simple and convenient operation steps.

According to one aspect of the present invention, there is provided a water sample hardness detection method based on water sample turbidity changes, comprising the following steps: S1. constructing a mathematical model related to water body hardness and water body turbidity; S2. making the water sample and calcium and magnesium ions Contact with the precipitant to convert the calcium ions and magnesium ions in the water sample into insoluble salts, and test the turbidity of the water sample; S3. Substitute the turbidity of the water sample into the turbidity of the water body in the mathematical model to calculate the hardness of the water sample . The present invention utilizes the characteristic that calcium and magnesium ions can be converted into insoluble salts that are insoluble in water, and converts calcium and magnesium ions into insoluble salts by introducing a calcium and magnesium ion precipitant, so that the turbidity of the water sample changes significantly, The reaction phenomenon of the above process is obvious, the test accuracy is high, and the hardness value of the water sample can be obtained quickly and accurately without cumbersome pre-calibration or expensive instruments. The above method does not need to involve the use of titrants and pre-calibration operations, and has low requirements on hardware equipment, so it can save cumbersome and complicated daily maintenance of instruments, and has the advantages of simple operation, high reliability, and environmental protection.

Preferably, the calcium and magnesium ion precipitant includes a phosphate supply material, which is selected from at least one of phosphate and phosphoric acid; the insoluble substance is hydroxyapatite. Phosphates include orthophosphate, monohydrogen orthophosphate, and dihydrogen phosphate. According to the expression habit in this field, the above-mentioned hydroxyapatite is often written in the form of (Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ ) to highlight that it is composed of two parts: hydroxyl and apatite; among them, calcium Ions can be replaced by a variety of metal ions through ion exchange reactions to form M apatite corresponding to metal ions (M represents metal ions replacing calcium ions). In this scheme, (Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ ) Apatite formed by replacing at least a part of calcium ions with magnesium ions also belongs to the scope included in the above-mentioned hydroxyapatite. In the present invention, the calcium and magnesium ion precipitating agent adopted aims at providing phosphate ions, so that calcium and magnesium ions and phosphate ions are converted into hydroxyapatite which is insoluble in water, and the involved precipitation reaction has very high sensitivity , the turbidity changes rapidly and obviously, which is conducive to improving the accuracy of estimating the hardness of water samples based on turbidity. In addition, the above reaction does not involve highly toxic or expensive reagents, which is in line with the pursuit of environmental protection and cost saving, and is conducive to the popularization and application of water sample hardness detection methods based on water sample turbidity changes.

Preferably, in S2, it includes adjusting the pH value of the water sample to be alkaline, so that the calcium and magnesium ions in the water sample react with the calcium and magnesium ion precipitant to convert into hydroxyapatite under alkaline conditions. Under alkaline reaction conditions, calcium and magnesium ions can quickly react with phosphate and transform into insoluble substances. Taking calcium ions as an example, the precipitation reaction involved is 5Ca ²⁺ +OH ^－ +3PO ₄ ^3－ ＝ Ca ₅ (PO ₄ ) ₃ OH.

Preferably, in S2, the calcium and magnesium ions in the water sample are converted into hydroxyapatite by reacting with the calcium and magnesium ion precipitating agent at a pH greater than 10.

Preferably, in S2, the calcium and magnesium ions in the water sample are converted into hydroxyapatite by reacting with the calcium and magnesium ion precipitant at a pH greater than 12.

The pH of the water sample affects the reaction degree of the precipitation reaction, so that the precipitation reaction of the water sample to form hydroxyapatite occurs when the pH is greater than 10, which is conducive to the complete precipitation of calcium and magnesium ions in the water sample and improves the turbidity of the water sample. Correlation with hardness. When the pH of the water sample is further increased to pH > 12, the calcium and magnesium ions are completely precipitated under the action of the calcium and magnesium ion precipitant, and there is a strong correlation between the turbidity and hardness of the water sample at this time, that is, using the present invention The provided method can accurately estimate the hardness of water samples.

Preferably, the phosphate feed material is selected from at least one of potassium phosphate, potassium dihydrogen phosphate, and phosphoric acid. .

Preferably, the water sample suitable for the water sample hardness detection method is a water body whose hardness does not exceed 1000ppm.

Preferably, the water sample suitable for the water sample hardness detection method is a water body whose hardness does not exceed 500ppm.

If the hardness of the water body is too high, large particles of insoluble salts are likely to be generated in the precipitation reaction, and these insoluble salts are easy to settle down in the water body, causing deviations in the detection of turbidity, thereby reducing the accuracy of hardness estimation.

The turbidity test involved in the water sample hardness detection method provided by the present invention is based on the following turbidity principle: compare the test object with the turbidity standard solution prepared with kaolin, and the turbidity is not high, and it is stipulated that one liter of distilled water contains 1 Milligrams of silica is a unit of turbidity. The methods that can be selected as turbidity test include scattering method and transmission method. The type of measurement method and the corresponding parameter settings will have different degrees of influence on the accuracy of turbidity detection. Applicable methods for turbidity testing are the scattering method and the transmission method.

Measuring turbidity by scattering method: The light source of the turbidity testing equipment emits light, makes it pass through a section of sample, and detects how much light is scattered by the particles in the water from a direction 90° to the incident light.

Turbidity by transmission: Turbidity can also be estimated by using a colorimeter or spectrophotometer to measure the degree of attenuation of transmitted light intensity caused by the obstruction of particulate matter in the sample.

Preferably, in the step involving testing the turbidity of the water sample, the water sample turbidity of the water sample is tested by a scattering method. Within the scope of application of the water sample hardness detection method provided by the present invention, compared with the transmission method, the use of the scattering method to obtain the water sample turbidity value can improve the accuracy of water sample turbidity detection. Preferably, the mathematical model is a linear function. The turbidity of the water body has a strong linear relationship with its hardness, and the linear correlation number between the two can be as high as 0.99 or more. Using the linear relationship obtained by fitting the turbidity of the water body and the hardness of the water body can accurately calculate the hardness of the water body.

Preferably, in S2, a calibration operation is also included: before the water sample is in contact with the calcium and magnesium ion precipitant, the turbidity detection is performed on the water sample, and the obtained turbidity value is N1; After the reaction, the water sample is tested for turbidity, and the obtained turbidity value is N2; the correction function relationship is constructed using N1 and N2, and the correction function relationship is used to obtain the corrected turbidity value; the corrected turbidity value obtained through the calibration operation is replaced in S3 The turbidity of the water sample is substituted into the mathematical model to calculate the hardness of the water sample. For example, perform a difference calculation (correction function relationship) on N1 and N0 to correct N1, use the resulting difference as the corrected turbidity value, and use the corrected turbidity value as the water sample turbidity in the mathematical model to substitute into the mathematics Model calculation to estimate the hardness of the water sample.

Description of drawings

Fig. 1 is the linear relationship constructed in the standard solution utilizing the corresponding concentration gradient between 20ppm and 400ppm in Example 1;

Fig. 2 is the linear relationship constructed in the standard solution utilizing the corresponding concentration gradient between 20ppm and 500ppm in Example 1;

FIG. 3 is the linear relationship constructed in Example 2.

Figure 4 is the relationship between hardness and turbidity based on calcium carbonate precipitation in Comparative Examples.

Detailed ways

In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the present invention, rather than Full examples.

Example 1

A mathematical model for water sample detection hardness is constructed as follows:

S1. Prepare 500mL calcium chloride solution (20-400mg/L) with different concentration gradients, 500mL 0.2M potassium dihydrogen phosphate solution, and 500mL 0.5M sodium hydroxide solution.

S2. The amount of calcium chloride solution required for each test is 100mL, and the turbidity and hardness of calcium chloride solutions with different concentration gradients are measured respectively, and the recorded turbidity is N1, and the calcium chloride solution of each concentration gradient The standard hardness of the solution is determined by conventional titration.

S3. In order to completely convert the calcium ions in the calcium chloride solution into Ca ₅ (PO ₄ ) ₃ OH insoluble salts, the concentration gradient of the calcium oxide solution is used as the conversion basis to make calcium chloride, sodium hydroxide, and dihydrogen phosphate The molar ratio of potassium satisfies 1:8.4:3.6, and the corresponding dosage of sodium hydroxide and potassium dihydrogen phosphate is calculated; taking 100mL 200mg/L calcium chloride solution as an example, according to n=CV, calculate the content of calcium chloride Quality, according to the experimental plan, the molar ratio of calcium chloride to sodium hydroxide to potassium dihydrogen phosphate is 1:8.4:3.6, and the volume of 0.5M sodium hydroxide solution required is calculated to be 3.027mL, and the required volume of 0.2M The volume of potassium dihydrogen phosphate solution is 3.243 mL.

S4. add respectively its calcium chloride content to the sodium hydroxide solution and the potassium dihydrogen phosphate solution of the corresponding portion to the calcium chloride solution of concentration gradient, in this case, the calcium ion in the calcium chloride solution can be at pH= Precipitation reaction occurs under the reaction conditions of 12. Shake it up quickly and put it into a turbidimeter to quickly test the turbidity after the reaction, and record it as N2.

S5. arrange the hardness of the calcium chloride solution of gradient concentration and the data (being N2-N1) of the turbidity change value before and after this calcium chloride solution reacts with potassium dihydrogen phosphate and sodium hydroxide, take the turbidity change value as horizontal Coordinates, the hardness value is the vertical coordinate value, and the linear relationship between the turbidity change value and the hardness value is fitted.

This example is based on the reaction principle of 5Ca ²⁺ +OH ^－ +3PO ₄ ^3－ ＝Ca ₅ (PO ₄ ) ₃ OH↓, and the calcium ions in the calcium chloride solution are converted into insoluble salts to cause the turbidity of the solution. Obvious changes, the relevant data measured before and after the reaction are shown in Table 1. Using the linear relationship of the hardness value of the calcium chloride solution of the concentration gradient and the turbidity change value fitting before and after the precipitation reaction of the calcium chloride solution, wherein, the linear relationship constructed by using the standard solution with a corresponding concentration gradient between 20ppm and 400ppm is as follows As shown in FIG. 1 , and the linear relationship constructed using standard solutions with corresponding concentration gradients ranging from 20 ppm to 500 ppm is shown in FIG. 2 . The R ² of the linear relationship shown in Figure 1 is as high as 0.9967. In contrast, the R ² of the linear relationship shown in Figure 2 drops to 0.9167, and if the calcium chloride concentration of the calcium chloride solution used for calibration is further increased As high as 1000ppm, the generated insoluble salt will obviously settle in a short time due to the large particle size, so that the test of turbidity will have obvious deviation. This shows that the hardness range of the water sample will also have a certain impact on the correlation of the constructed linear relationship. The main reason is that if the hardness is too large, the formed sediment has a large particle size and will settle down immediately, thus affecting the test of turbidity in water. In the range where the hardness of the water sample is lower than 400ppm, the calcium and magnesium ions in the water sample are transformed into insoluble matter according to the above-mentioned precipitation reaction, and the resulting turbidity change can be in a strong positive linear correlation with the hardness of the solution. Based on this, the hardness value of the water sample can be calculated according to the turbidity change value of the water sample, which has high accuracy.

Table 1 This embodiment is used to construct the correlation data of the mathematical model that correlates water sample hardness and water sample turbidity change

Apply the linear relationship constructed in this example to the hardness test of water samples, the water sample test volume is 100mL each time, and the test is carried out according to the following steps:

S1. Use a turbidity meter to measure the turbidity of the water sample to be tested, and record the measured turbidity as N1;

S2. Add sodium hydroxide to the water sample to be tested first, so that the pH value of the water sample reaches above 12, and then add the corresponding amount of sodium hydroxide (5Ca ²⁺ +OH ^- +3PO ₄ ^3- =Ca ₅ (PO ₄ ) ₃ OH↓), potassium dihydrogen phosphate, at this time, the turbidity of the solution can be clearly seen to rise, the solution is shaken, and its turbidity is quickly tested on the turbidimeter, and the recorded The resulting turbidity value is labeled N2.

S3. Calculate the turbidity change value (N2-N1) of the water sample before and after the reaction, bring the turbidity change value into the above linear relationship, and calculate the hardness of the water sample.

Example 2

The mathematical model for correlating water sample turbidity and hardness in this embodiment is constructed by referring to the method provided in Example 1 for constructing a mathematical model for detecting hardness of a water sample. Compared with the way that Example 1 is used to construct the above-mentioned mathematical model, the only difference that the present embodiment is used to construct the mathematical model is that by adjusting the feeding amount of sodium hydroxide, the calcium ions in the calcium chloride solution can be adjusted at pH Precipitation reaction occurs in the reaction environment of =11, according to the feeding amount of sodium hydroxide, the feeding amount of potassium dihydrogen phosphate is adaptively adjusted according to the conversion mode provided by embodiment 1, and all the other operating steps and data processing methods are the same as in embodiment 1 Keep it consistent and won't repeat it here. The relevant data measured thus is as shown in table 2, utilizes the hardness value of the calcium chloride solution of concentration gradient in table 2 and the linear relationship of the turbidity change value fitting before and after the precipitation reaction occurs in calcium chloride solution, as shown in Figure 3 As shown, the ^R2 of this linear relationship is 0.9627. Compared with the linear relationship constructed in Fig. 1, the correlation of the linear relationship constructed in this embodiment has declined, and it can also be found by observing the process of the precipitation reaction that compared with Example 1, the After the precipitation reaction occurs, the turbidity of the water sample is lower, which shows that more hydroxyapatite is formed in the high alkalinity solution, which is beneficial to improve the turbidity change caused by the formation of hydroxyapatite and the water turbidity. Linear dependence of sample hardness.

Table 2 This embodiment is used to construct the correlation data of the mathematical model that correlates water sample hardness and water sample turbidity change

comparative example

In addition to hydroxyapatite, calcium can also form insoluble salts with carbonate and sulfate, causing the solution to be cloudy. In this embodiment, standard solutions of CaCl ₂ with different gradients are mixed with 0.5M sodium carbonate or sodium sulfate, and the turbidity of the solution after the reaction is tested. The amount of each water sample test is 100mL, and the test is carried out according to the following steps:

S1. Use a turbidity meter to measure the turbidity of the water sample to be tested, and record the measured turbidity as N1;

S2. Add sodium carbonate or sodium sulfate equivalent to calcium ions to the water sample to be tested, shake the solution well, wait for the turbidity to stabilize, test its turbidity on a turbidimeter, and record the turbidity value Labeled N2.

S3. Arrange the hardness of the calcium chloride solution of gradient concentration and the data (being N2-N1) of turbidity change value before and after adding precipitation reagent reaction, take turbidity change value as abscissa, hardness value as ordinate value, fitting turbidity The linear relationship between the degree change value and the hardness value.

The results of the precipitation reaction corresponding to the use of sodium sulfate as the precipitating agent are shown in Table 3. The hardness of the tested water samples was in the range of 20-500 ppm, the solution was always clear, and no precipitation caused the turbidity to increase. It shows that the solubility of calcium sulfate is high, and it is not easy to form precipitation in the range of low and medium hardness.

Table 3 The relationship between the turbidity and hardness of calcium sulfate in solution

standard solution	Hardness/mg/L	Turbidity value after adding sodium sulfate/NTU
20ppm CaCl2	16	0
50ppm CaCl2	41	0
100ppm CaCl2	81	0

200ppm CaCl2	162	0
400ppm CaCl2	324	0

The precipitation reaction results corresponding to the use of sodium carbonate precipitant are shown in Table 4. The hardness of the tested water samples is in the range of 20-500ppm, and the pH of the solution is maintained at about 11. Compared with the scheme of converting the calcium and magnesium ions in the water sample into hydroxyapatite in Example 1, using sodium carbonate as the calcium and magnesium ion precipitant, the process of solution generation precipitation is relatively slow, and the turbidity of the solution continues to rise until 30 Stable after ~60min. When the CaCl ₂ concentration increases above 150ppm, the solution turbidity exceeds 150NTU, exceeding the measurement range. It shows that the applicability of this method is low, it is only suitable for solutions with a hardness below 140ppm, and the measurement time is long, each sample needs more than 30 minutes. Utilize the linear relationship of the hardness value of the calcium chloride solution of concentration gradient in table 4 and the turbidity change value fitting before and after the precipitation reaction of calcium chloride solution, as shown in Figure 4, the R of this linear relationship is ^0.7962 , far The ^R2 value is lower than the linear relationship constructed in Example 1 and Example 2.

Table 4 Relationship between turbidity and hardness of calcium carbonate in alkaline (pH11) solution

standard solution	Hardness/mg/L	Turbidity value after adding sodium carbonate/NTU
50ppm CaCl2	41	76
100ppm CaCl2	81	100
125ppm CaCl2	101	171
167ppm CaCl 2	135	over range
200ppm CaCl2	162	over range

The above embodiments are only used to illustrate the technical solution of the present invention rather than limiting the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solution of the present invention can be carried out Modification or equivalent replacement without departing from the spirit and scope of the technical solution of the present invention.

Claims (11)

1. A water sample hardness detection method based on water sample turbidity change, is characterized in that, comprises the following steps:

   S1. Construct a mathematical model related to water hardness and water turbidity;

   S2. Make the water sample contact with the calcium and magnesium ion precipitant, so that the calcium ion and magnesium ion in the water sample are converted into insoluble salts, and the water sample turbidity of the water sample is tested;

   S3. Substituting the turbidity of the water sample into the turbidity of the water body in the mathematical model to estimate the hardness of the water sample.
2. The water sample hardness detection method based on water sample turbidity change as claimed in claim 1, is characterized in that: described calcium and magnesium ion precipitant comprises phosphate radical supply material, and described phosphate radical supply material is selected from phosphate, phosphoric acid At least one; the insoluble matter is hydroxyapatite.
3. The water sample hardness detection method based on the change of water sample turbidity as claimed in claim 2, is characterized in that: in said S2, comprising adjusting the pH value of the water sample to be alkaline, making the calcium and magnesium ions in the water sample and The calcium and magnesium ion precipitation agent is converted into hydroxyapatite under alkaline conditions.
4. The water sample hardness detection method based on the water sample turbidity change as claimed in claim 3, is characterized in that: in said S2, make the calcium and magnesium ions in the water sample and the described calcium and magnesium ion precipitating agent be greater than 10 Under these conditions, the reaction transforms into hydroxyapatite.
5. The water sample hardness detection method based on the change of water sample turbidity as claimed in claim 4, characterized in that: in said S2, the calcium and magnesium ions in the water sample and the calcium and magnesium ion precipitating agent are made at a pH greater than 12 Under these conditions, the reaction transforms into hydroxyapatite.
6. The water sample hardness detection method based on the change of water sample turbidity according to claim 2, characterized in that: the phosphate supply material is selected from at least one of potassium phosphate, potassium dihydrogen phosphate, and phosphoric acid.
7. The water sample hardness detection method based on the change of water sample turbidity according to any one of claims 1 to 6, characterized in that: the water sample suitable for the water sample hardness detection method is a water body whose hardness does not exceed 1000ppm.
8. The water sample hardness detection method based on the change of water sample turbidity according to claim 7, characterized in that: the water sample suitable for the water sample hardness detection method is a water body whose hardness does not exceed 500ppm.
9. The water sample hardness detection method based on the change of water sample turbidity according to claim 7, characterized in that: in the step involving the water sample turbidity test, the water sample turbidity of the water sample is tested by a scattering method.
10. The water sample hardness detection method based on the change of water sample turbidity according to claim 1, characterized in that: the mathematical model is a linear function.
11. The water sample hardness detection method based on water sample turbidity change as claimed in claim 1, is characterized in that:

    In the S2, a calibration operation is also included: before the water sample is in contact with the calcium and magnesium ion precipitant, the turbidity detection is carried out on the water sample, and the obtained turbidity value is N1; After the precipitation reaction of the ion precipitant, the turbidity of the water sample is detected, and the obtained turbidity value is N2; the correction function relationship is constructed by using the N1 and the N2, and the correction function relationship is used to obtain the corrected turbidity value;

    Substituting the corrected turbidity value obtained through the calibration operation for the turbidity of the water sample in S3 into the mathematical model to estimate the hardness of the water sample.

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