Method for detecting sulfate content in bitter brine

Abstract

This invention provides a method for detecting sulfate content in bittern, belonging to the field of chemical detection technology. This invention uses potentiometric titration to detect sulfate content in bittern, resulting in a short determination cycle and a relatively simple method that requires minimal auxiliary equipment. The detection endpoint is determined by an ion-selective electrode, reducing errors caused by human operation. Furthermore, it exhibits a wide linear range and is well-suited for optimizing and improving detection technology in the bittern chemical industry.

Description

Technical Field

[0001] This invention belongs to the field of chemical detection technology, specifically relating to a method for detecting sulfate content in bittern. Background Technology

[0002] Sea salt bittern is the liquid produced after seawater salt production. Its main components include calcium, magnesium, sodium, chloride, potassium, and sulfate ions. Potassium chloride, magnesium chloride, and magnesium sulfate, produced from bittern, are basic raw materials in agriculture, chemical industry, and pharmaceutical industry. The production principle of sea salt bittern industry mainly relies on phase diagrams, with stepwise crystallization based on different saturation levels. The sulfate concentration in bittern plays a crucial role in the production process; excessively high sulfate concentrations will produce double salts, affecting the quality of the main product. Therefore, accurate detection of sulfate concentration in bittern is essential for the quality of bittern products.

[0003] In the traditional bittern chemical industry, the main method for sulfate detection is based on GB / T 13025.8-2012 "General Test Methods for Determination of Sulfate in Salt Industry", which uses gravimetric or volumetric methods. However, with the development of technology, ion chromatography and potentiometric titration have gradually been adopted by the bittern chemical industry. However, potentiometric titration is used for the detection of finished products such as sodium chloride and potassium chloride in bittern chemicals.

[0004] Volumetric methods have lower precision and accuracy than the other three methods, making them suitable for testing scenarios with low accuracy requirements and large testing workloads. Gravimetric methods are low-cost but time-consuming, making them suitable for testing scenarios with high accuracy requirements and low timeliness requirements. Ion chromatography has the highest precision and accuracy, but requires more auxiliary equipment and higher investment, and the standard curve preparation process requires a high level of expertise from the testing personnel.

[0005] To address the industry pain points of existing technologies, such as large human error in endpoint determination using visual volumetric methods, long detection cycles using gravimetric methods, and high costs of ion chromatography equipment, there is an urgent need to further optimize the detection technology for the bittern chemical industry. Summary of the Invention

[0006] The purpose of this invention is to provide a method for detecting sulfate content in bittern. This invention uses potentiometric titration to detect sulfate content in bittern, and the detection endpoint is determined by an ion-selective electrode, which reduces errors caused by human operation and has a wide linear range, making it more suitable for optimizing and improving detection technology in the bittern chemical industry.

[0007] To achieve the objectives of this invention, the following technical solutions are provided: A method for detecting sulfate content in bittern includes the following steps: S1. Adjust the pH value of the bittern sample to be tested to 3~4 to obtain acidified bittern; S2. The acidified bittern and excess barium chloride solution are mixed to carry out a precipitation reaction to obtain a reaction solution containing barium sulfate precipitate; a barium chloride solution with the same amount and concentration as the excess barium chloride solution is used as a blank sample. S3. Perform potentiometric titration on the reaction solution and blank sample, and calculate the sulfate content in the bittern sample to be tested by the volume of EDTA standard solution consumed at the titration endpoint and Equation 1. Formula 1; In Equation 1, w 硫酸根 The concentration of sulfate ions is in g / L; M 硫酸根 c is the molar mass of sulfate, 96.06 g / mol; EDTA V1 represents the concentration of the EDTA standard solution, in mol / L; V2 represents the Mg content in the bittern sample to be tested. 2+ The volume of EDTA standard solution consumed, in mL; V2 is the Mg content in the bittern to be tested. 2+ and Ba 2+ V3 is the total volume of EDTA standard solution consumed (mL); V3 is the volume of EDTA standard solution consumed by the blank sample (mL); V is the volume of the bittern to be tested (mL).

[0008] Preferably, the average concentration of magnesium sulfate in the bittern sample to be tested is 51-65 g / L, the average concentration of magnesium chloride is 110-130 g / L, the average concentration of potassium chloride is 21-35 g / L, and the average concentration of sodium chloride is 120-140 g / L; Mg 2+ The total concentration is 40~45g / L.

[0009] Preferably, the bittern is marine salt-producing bittern.

[0010] Preferably, the concentration of the barium chloride solution is 0.2~1.0 mol / L.

[0011] Preferably, the molar concentration of the EDTA standard solution is 0.1~0.3 mol / L.

[0012] Preferably, the reagent used to adjust the pH value is a hydrochloric acid solution; the concentration of the hydrochloric acid solution is 1.0~3.0 mol / L.

[0013] Preferably, the potentiometric titration uses a mercury electrode as the indicator electrode and a calomel electrode as the reference electrode.

[0014] Preferably, the titration parameters for the potentiometric titration include: burette accuracy ±0.01mL, signal resolution ≥0.1mL, temperature compensation range of 0~100℃, endpoint determination threshold of 4mV / min, pre-titration volume of 10% of the total titration volume, and stirring speed of 400±50rpm.

[0015] This invention provides a method for detecting sulfate content in bittern, comprising the following steps: S1, adjusting the pH of the bittern sample to be tested to 3-4 to obtain acidified bittern; S2, mixing the acidified bittern with excess barium chloride solution to perform a precipitation reaction, obtaining a reaction solution containing barium sulfate precipitate; using a barium chloride solution of equal volume and concentration as a blank sample; S3, performing potentiometric titration on the reaction solution and the blank sample, and calculating the sulfate content in the bittern sample by the volume of EDTA standard solution consumed at the titration endpoint and Equation 1. This invention detects the sulfate content in bittern by potentiometric titration. During the titration process, two potential abrupt changes occur. The first potential abrupt change, V1, represents the Mg content in the bittern. 2+ The volume of titrant consumed, the second potential jump value V2 is the Ba in the bittern. 2+ and Mg 2+ The total amount of titrant consumed, and the excess Ba in the sample. 2 + The volume of titrant consumed is V2-V1. A barium chloride solution for preparing a blank sample is prepared and titrated using potentiometric titration to determine the titration volume V3. The sulfate concentration in the sample is calculated according to Equation 1. This invention features a short measurement cycle and a relatively simple method, requiring minimal auxiliary equipment. The detection endpoint is determined by an ion-selective electrode, reducing errors caused by human operation. Furthermore, it has a wide linear range, making it suitable for optimizing and improving detection technology in the bittern chemical industry. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is the potentiometric titration curve for detecting sulfate content in bittern by potentiometric titration in Example 1 of the present invention. Detailed Implementation

[0018] This invention provides a method for detecting the sulfate content in bittern, comprising the following steps: S1. Adjust the pH value of the bittern sample to be tested to 3~4 to obtain acidified bittern; S2. The acidified bittern and excess barium chloride solution are mixed to carry out a precipitation reaction to obtain a reaction solution containing barium sulfate precipitate; a barium chloride solution with the same amount and concentration as the excess barium chloride solution is used as a blank sample. S3. Perform potentiometric titration on the reaction solution and blank sample, and calculate the sulfate content in the bittern sample to be tested by the volume of EDTA standard solution consumed at the titration endpoint and Equation 1. Formula 1; In Equation 1, w 硫酸根 The concentration of sulfate ions is in g / L; M 硫酸根 c is the molar mass of sulfate, 96.06 g / mol; EDTA V1 represents the concentration of the EDTA standard solution, in mol / L; V2 represents the Mg content in the bittern sample to be tested. 2+ The volume of EDTA standard solution consumed, in mL; V2 is the Mg content in the bittern to be tested. 2+ and Ba 2+ V3 is the total volume of EDTA standard solution consumed (mL); V3 is the volume of EDTA standard solution consumed by the blank sample (mL); V is the volume of the bittern to be tested (mL).

[0019] In this invention, unless otherwise specified, all raw materials and reagents are commercially available products well known to those skilled in the art.

[0020] In this invention, the average concentration of magnesium sulfate in the bittern sample to be tested is 51-65 g / L, preferably 55-60 g / L; the average concentration of magnesium chloride is 110-130 g / L, preferably 110-120 g / L; the average concentration of potassium chloride is 21-35 g / L, preferably 25-29 g / L; the average concentration of sodium chloride is 120-140 g / L, 128-135 g / L; Mg 2+ The total concentration was 40-45 g / L. In a specific embodiment of the present invention, the average concentration of magnesium sulfate in the bittern sample to be tested was 59.7 g / L, the average concentration of magnesium chloride was 120.77 g / L, the average concentration of potassium chloride was 29.75 g / L, and the average concentration of sodium chloride was 135.69 g / L; Mg 2+ The total concentration was 43.08 g / L.

[0021] In this invention, the concentration of the barium chloride solution is 0.2~1.0 mol / L, and in specific embodiments it can be 0.5 or 0.8 mol / L.

[0022] In this invention, the molar concentration of the EDTA standard solution is 0.1~0.3 mol / L, and in a specific embodiment it can be 0.2 mol / L; the preparation method of the EDTA standard solution includes the following steps: Weigh 37.3 g of disodium ethylenediaminetetraacetate dihydrate, dissolve it in 5 L of water, shake well, and store in a reagent bottle for later use. Standardization: Pipette 20.00 mL of zinc oxide standard solution into a 150 mL beaker, add 5 mL of ammonia-ammonium chloride buffer solution and 4 drops of Eriochrome Black T indicator, and titrate with disodium ethylenediaminetetraacetate standard titration solution until the solution changes from wine red to bright blue.

[0023] In this invention, the reagent used to adjust the pH value is hydrochloric acid solution with a concentration of 1.0~3.0 mol / L, which can be 1.5 or 2.0 mol / L in specific embodiments. Since bittern samples are obtained from the natural environment, some samples may contain trace amounts of carbonate and bicarbonate ions due to changes in the natural environment. Carbonate and bicarbonate ions easily react with barium chloride solution to form precipitates, thus causing the detection results to be too high. Because carbonate and bicarbonate ions cannot exist stably in an acidic environment, they decompose into carbon dioxide with stirring and volatilize naturally. Therefore, adding hydrochloric acid to the sample to adjust the pH value to 3~4 has the effect of shielding carbonate, bicarbonate ions, and other interfering ions in the sample, which can improve the accuracy of the detection results.

[0024] In this invention, the potentiometric titration uses a mercury electrode as the indicator electrode and a calomel electrode as the reference electrode.

[0025] In this invention, the titration parameters for potentiometric titration include: burette accuracy ±0.01mL, signal resolution ≥0.1mL, temperature compensation range of 0~100℃, endpoint determination threshold of 4mV / min, pre-titration volume of 10% of the total titration volume, and stirring speed of 400±50rpm.

[0026] To further illustrate the present invention, the method for detecting sulfate content in bittern provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0027] The sources and parameters of the instruments and reagents used in the following embodiments of the present invention are as follows: Automatic potentiometric titrator: Leici ZDJ-4B; EDTA (ethylenediaminetetraacetic acid): analytical grade, Tianjin Kemeo Chemical Reagent Co., Ltd. Barium chloride: analytical grade, Tianjin Kemeo Chemical Reagent Co., Ltd.; Hydrochloric acid: analytical grade, Tianjin Kemeo Chemical Reagent Co., Ltd.

[0028] Example 1 Preparation of EDTA standard solution: Weigh 37.3 g of disodium ethylenediaminetetraacetate dihydrate, dissolve in 5 L of water, shake well, and store in a reagent bottle for later use. Standardization: Pipette 20.00 mL of zinc oxide standard solution into a 150 mL beaker, add 5 mL of ammonia-ammonium chloride buffer solution and 4 drops of Eriochrome Black T indicator, and titrate with disodium ethylenediaminetetraacetate standard titration solution until the solution changes from wine red to bright blue. EDTA =0.1988 mol / L.

[0029] The bittern from salt production in the Bohai Sea during spring was used as the test sample. The average concentrations of magnesium sulfate, magnesium chloride, potassium chloride, and sodium chloride in the bittern were 59.7 g / L, 120.77 g / L, 29.75 g / L, 135.69 g / L, and Mg... 2+ The total concentration was 43.08 g / L; 1 mol / L hydrochloric acid was added to adjust the sample to a slightly acidic state (pH 3-4) to obtain the pretreated sample. Take 10 mL of the pretreated sample and add 50 mL of 0.2 mol / L barium chloride solution. Let it stand at room temperature for 1-2 min to allow precipitation, obtaining the reaction solution. Using a mercury indicator electrode and a saturated calomel reference electrode, perform complexometric titration of the reaction solution with EDTA standard solution. During the titration, two potential abrupt changes occur. The first potential abrupt change, V1, represents the concentration of Mg in the sample. 2+ The volume of EDTA consumed, and the second potential jump value V2 is the Ba in the sample. 2+ and Mg 2+ The total amount of EDTA consumed, barium chloride solution in excess Ba 2+ The volume of EDTA consumed is V2-V1 (e.g.) Figure 1 As shown, the first jump position is approximately between 4.31 and 6.46 on the horizontal axis, which is Mg. 2+ The endpoint of the complexometric titration with EDTA; the second jump position is close to the horizontal axis at 10.8: corresponding to Mg in the system. 2+ with Ba 2+ (Endpoint of complexometric titration with EDTA).

[0030] Blank test: 50 mL of 0.2 mol / L barium chloride solution was measured, and the barium chloride solution was titrated with complexometric potential using a mercury indicator electrode and a saturated calomel reference electrode and EDTA standard solution. The point change value V3 that appeared during the titration was the total amount of EDTA consumed by barium ions in the barium chloride solution.

[0031] Five parallel tests were performed, and the specific parameters are shown in Table 1. The relative standard deviation (RSD) was calculated, and the results are shown in Table 2.

[0032] Table 1. Data from 5 parallel tests in Example 1

[0033] Table 2 Sample Detection Data

[0034] Accuracy analysis of detection methods The detection method was validated by the spiked recovery method. Anhydrous sodium sulfate (analytical grade) was used to prepare a sulfate standard solution with a concentration of 0.5004 g / L. 5 mL of the above bittern sample was taken and diluted to a 500 mL volumetric flask. 2 mL of standard solution + 2 mL of bittern sample, 4 mL of standard solution + 4 mL of bittern sample, 6 mL of standard solution + 6 mL of bittern sample, 8 mL of standard solution + 8 mL of bittern sample, and 10 mL of standard solution + 10 mL of bittern sample were taken for detection, and the spiked recovery rate was calculated. The results are shown in Table 3.

[0035] Table 3 Spiked Recovery Data Table

[0036] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for detecting sulfate content in bittern, characterized in that, Includes the following steps: S1. Adjust the pH value of the bittern sample to be tested to 3~4 to obtain acidified bittern; S2. The acidified bittern and excess barium chloride solution are mixed to carry out a precipitation reaction to obtain a reaction solution containing barium sulfate precipitate; a barium chloride solution with the same amount and concentration as the excess barium chloride solution is used as a blank sample. S3. Perform potentiometric titration on the reaction solution and blank sample, and calculate the sulfate content in the bittern sample to be tested by the volume of EDTA standard solution consumed at the titration endpoint and Equation 1. Formula 1; In Equation 1, w 硫酸根 The concentration of sulfate ions is in g / L; M 硫酸根 c is the molar mass of sulfate, 96.06 g / mol; EDTA V1 represents the concentration of the EDTA standard solution, in mol / L; V2 represents the Mg content in the bittern sample to be tested. 2+ The volume of EDTA standard solution consumed, in mL; V2 is the Mg content in the bittern to be tested. 2 + and Ba 2+ V3 is the total volume of EDTA standard solution consumed (mL); V3 is the volume of EDTA standard solution consumed by the blank sample (mL); V is the volume of the bittern to be tested (mL).

2. The detection method according to claim 1, characterized in that, The average concentrations of magnesium sulfate, magnesium chloride, potassium chloride, and sodium chloride in the bittern samples to be tested were 51–65 g / L, 110–130 g / L, 21–35 g / L, and 120–140 g / L, respectively. 2+ The total concentration is 40~45g / L.

3. The detection method according to claim 1 or 2, characterized in that, The bittern mentioned is salt-producing bittern from the sea.

4. The detection method according to claim 1, characterized in that, The concentration of the barium chloride solution is 0.2~1.0 mol / L.

5. The detection method according to claim 1, characterized in that, The molar concentration of the EDTA standard solution is 0.1~0.3 mol / L.

6. The detection method according to claim 1, characterized in that, The reagent used to adjust the pH value is hydrochloric acid solution; the concentration of the hydrochloric acid solution is 1.0~3.0 mol / L.

7. The detection method according to claim 1, characterized in that, The potentiometric titration uses a mercury electrode as the indicator electrode and a calomel electrode as the reference electrode.

8. The detection method according to claim 1, characterized in that, The titration parameters for potentiometric titration include: burette accuracy ±0.01mL, signal resolution ≥0.1mL, temperature compensation range of 0~100℃, endpoint determination threshold of 4mV / min, pre-titration volume of 10% of the total titration volume, and stirring speed of 400±50rpm.

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