Detection method for rapidly determining main content of magnesium hydroxide and calcium oxide in process of preparing high-purity magnesium hydroxide from salt lake bischofite

Abstract

The invention discloses a detection method for rapidly determining the main content of magnesium hydroxide and calcium oxide in the process of preparing high-purity magnesium hydroxide from salt lake bischofite, which comprises the following steps: determining the main content of magnesium hydroxide: weighing a proper amount of sample, dissolving with hydrochloric acid and fixing the volume to obtain a test solution; taking a proper amount of the test solution, adding triethanolamine to mask interfering ions, adjusting the pH value with an ammonia-ammonium chloride buffer solution, taking chrome black T as an indicator, and titrating the main content of magnesium hydroxide with an EDTA standard solution; and measuring the content of calcium in magnesium hydroxide: taking a proper amount of the test solution, adding triethanolamine to mask interfering ions, adjusting the pH value by using a sodium hydroxide solution, adding a proper amount of a calcium indicator, and titrating the content of magnesium calcium hydroxide by using an EDTA standard solution. The method is simple and easy to implement, can quickly and accurately analyze and detect the main content and the calcium oxide content in the magnesium hydroxide, can realize complete dissolution of the magnesium hydroxide, and does not artificially introduce a large number of impurity elements, so that the system error is reduced, and the detection quality is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of substance content detection, and particularly relates to a detection method for rapidly determining the main content of magnesium hydroxide and calcium oxide during the preparation of high-purity magnesium hydroxide from bischofite in salt lake brine. Background Art

[0002] Using bischofite, a by-product of potassium salt production in salt lakes, as raw material, and adopting the ammonia-lime combined process, the raw material bischofite is dissolved and refined into brine. Ammonia gas and brine are simultaneously added to the reaction kettle, and the reaction is completed under specific conditions. A belt filter is used for dehydration, washing, and drying to obtain high-purity magnesium hydroxide with a purity greater than 99%. With the acceleration of the industrialization process of salt lake resource utilization, in the existing chemical analysis methods for the main content of magnesium hydroxide, the sample weighing amount is large, the dissolution time is long, the dilution times are many, the detection process is relatively cumbersome, the detection error is large, and the detection time is long, and the product quality in the production process cannot be timely feedback. Therefore, researching a detection method that can not only completely dissolve magnesium hydroxide but also not artificially introduce a large number of impurity elements to reduce systematic errors, improve detection quality, and timely guide production has become an urgent technical problem in the industry. Summary of the Invention

[0003] Aiming at the defects existing in the prior art, the present invention provides a method that is simple and easy to implement and can quickly and accurately analyze and detect the main content and calcium oxide content in magnesium hydroxide.

[0004] To solve the above technical problems, the present invention adopts the following technical solution: A detection method for rapidly determining the main content of magnesium hydroxide and calcium oxide during the preparation of high-purity magnesium hydroxide from bischofite in salt lake brine is carried out according to the following steps:

[0005] Including the following steps:

[0006] I. Determining the main content of magnesium hydroxide: Weigh an appropriate amount of the sample, dissolve it with hydrochloric acid, transfer it to a volumetric flask and make it up to volume to obtain a test solution; Take an appropriate amount of the test solution, add triethanolamine to mask interfering ions, adjust the pH value with an ammonia-ammonium chloride buffer solution, use eriochrome black T as an indicator, and titrate the main content of magnesium hydroxide with an EDTA standard solution;

[0007] II. Determining the calcium oxide content in magnesium hydroxide: Take an appropriate amount of the test solution, add triethanolamine to mask interfering ions, adjust the pH value with sodium hydroxide solution, add an appropriate amount of calconcarboxylic acid indicator, and titrate the calcium oxide content in magnesium hydroxide with an EDTA standard solution.

[0008] The specific process of step I is as follows:

[0009] (1) Weigh 1 g of the sample, accurate to 0.0002 g, and place it in a 250 mL beaker. Moisten it with a small amount of water, cover it with a watch glass, add hydrochloric acid solution to dissolve the sample to obtain a solution. Transfer the solution to a 250 mL volumetric flask, dilute it to the mark with water, and shake well. This solution is the test solution A for the determination of the content of magnesium ions and calcium oxide content.

[0010] (2) Pipette 5 mL of test solution A and place it in a 250 mL conical flask. Add 50 mL of water, 5 mL of triethanolamine solution, 10 mL of ammonia-ammonium chloride buffer solution, and ten drops of eriochrome black T indicator. Titrate with the standard titration solution of disodium ethylenediaminetetraacetate until the solution changes from purplish red to pure blue as the end point.

[0011] (3) First, calculate the total content of calcium and magnesium in the sample ω1, expressed as a percentage, and calculate according to formula (1):

[0012] ω1 = C×(V1 - V2)×M1×250 / (5×m) / 100×100%

[0013] In the formula:

[0014] C—the accurate value of the concentration of the standard titration solution of disodium ethylenediaminetetraacetate, unit: mol / L;

[0015] V1—the value of the volume of the standard titration solution of disodium ethylenediaminetetraacetate consumed during titration, unit: mL;

[0016] V2—the volume consumed by the blank solution, unit: mL;

[0017] M1—the value of the molar mass of magnesium hydroxide, unit: g / mol, M1 = 58.32;

[0018] m—the value of the mass of the test sample, unit: g;

[0019] 250 / 5—dilution volume ml;

[0020] Subtract the measured calcium ion content ω2 from the total content of calcium and magnesium ω1 to obtain the main content ω4 of magnesium hydroxide.

[0021] The specific process of step two is as follows:

[0022] Pipette 50 mL of test solution A and place it in a 250 mL conical flask. Add 30 ml of primary water and 5 mL of triethanolamine solution. While shaking, add sodium hydroxide solution drop by drop. When the solution just starts to precipitate, pH = 13, and add a little calcium indicator. Then titrate with the standard titration solution of disodium ethylenediaminetetraacetate until the solution changes from wine red to pure blue as the end point.

[0023] First, calculate the calcium ion content ω2 in the sample, expressed as a percentage, and calculate according to the following formula:

[0024] ω2 = C × V × M2 × 250 / 50 / m / 100 × 100%

[0025] In the formula:

[0026] C — The accurate value of the concentration of the standard titration solution of disodium ethylenediaminetetraacetate, unit: mol / L;

[0027] V — The value of the volume of the standard titration solution of disodium ethylenediaminetetraacetate consumed during titration, unit: mL;

[0028] M2 — The value of the molar mass of calcium ion [Ca 2+ , unit: g / mol, M2 = 40.08;

[0029] m — The value of the mass of the test sample, unit: g;

[0030] 250 / 50 - Dilution volume ml

[0031] The calcium oxide content is calculated as the mass fraction ω3 of calcium oxide, and the value is expressed in %, according to the following formula:

[0032] ω3 = ω2 × 1.399

[0033] In the steps for determining the main content of magnesium hydroxide, the purity of triethanolamine is analytical pure, the mass concentration is 1 + 1; the pH value of the ammonia - ammonium chloride buffer solution is 10, the mass concentration of eriochrome black T indicator is 0.2%, the dosage is 10 drops, and the concentration of the standard solution of disodium ethylenediaminetetraacetate is 0.025M.

[0034] In the steps for determining the calcium oxide content in magnesium hydroxide, the purity of triethanolamine is analytical pure, the mass concentration is 1 + 1, the concentration of sodium hydroxide is 10M, the mass concentration of calcium indicator is 2%, the dosage is 0.1g; the concentration of the standard solution of disodium ethylenediaminetetraacetate is 0.025M.

[0035] In the present invention, magnesium hydroxide is dissolved with hydrochloric acid for reaction to generate magnesium ions, and a small amount of trivalent iron, trivalent aluminum, divalent manganese and other ions are masked with triethanolamine. At a pH value of 10, with eriochrome black T as the indicator, the total amount of calcium and magnesium is titrated with the standard titration solution of disodium ethylenediaminetetraacetate (EDTA), and the calcium content is subtracted from it to calculate the content of magnesium hydroxide. The whole method is simple and easy to operate, can quickly and accurately analyze and detect the main content and calcium oxide content in magnesium hydroxide, and at the same time can achieve complete dissolution of magnesium hydroxide and no artificially introduced large amounts of impurity elements.

[0036] When using the complexometric titration method to determine the main content of magnesium hydroxide and calcium oxide, the selection of the sample weight has a significant impact on the accuracy of the determination result and the introduction of impurities. This method introduces fewer impurities in rapid determination, which is mainly attributed to the following aspects:

[0037] ①Differences in impurity introduction during the dissolution process: When the sample weighing amount is relatively large, the time required for complete dissolution of magnesium hydroxide is longer. During the longer dissolution process, the solution has a longer contact time with the surrounding environment and is more likely to absorb impurities in the air, such as carbon dioxide, dust, etc. Carbon dioxide may react with the components in the solution, changing the properties of the solution. In contrast, with a sample weighing amount of 1 g in this method, the dissolution rate is relatively fast, greatly shortening the contact time between the solution and potential impurities in the environment and reducing the possibility of impurity introduction. ②Residual impurities and contamination degree of the dissolution equipment: During the sample dissolution process, impurities may remain on the surfaces of the containers (such as beakers) and stirring utensils used. When the sample weighing amount is relatively large, due to the larger solution volume, the contact area with the containers and stirring utensils is larger, and the contact time may also be longer, making it easier to elute the residual impurities on the equipment surface into the solution. In comparison, with a sample weighing amount of 1 g in this method, the solution volume is small, the contact area with the equipment surface is relatively small, and the amount of impurities eluted from the equipment is correspondingly reduced, reducing the possibility of impurity introduction. ③Differences in impurity interference in the reaction system: In complexometric titration, impurities in the sample may interfere with the reaction between magnesium hydroxide and the complexing agent (such as EDTA). When the sample weighing amount is relatively large, if the sample itself contains a certain amount of impurities, the relative content of these impurities in the solution will increase with the increase in the sample weighing amount, thus having a more significant interference on the complexometric reaction. For example, if the sample contains trace amounts of calcium ion impurities, in a solution with a relatively large sample weighing amount, the calcium ion concentration is relatively high, which may react with EDTA and interfere with the accurate determination of magnesium hydroxide. In this method, when the sample weighing amount is 1 g, the concentration of the same amount of calcium ion impurities in the solution is lower, and the degree of interference on the complexometric reaction is relatively small. ④Dosage and effect of the masking agent: To eliminate the interference of impurities on complexometric titration, a masking agent is usually used. When the sample weighing amount is relatively large, due to the relatively high content of impurities, more masking agent may be required to mask the impurity ions. However, too much masking agent itself may contain impurities or introduce new chemical equilibria in the solution, having a potential impact on the determination. In this method, when the sample weighing amount is 1 g, the relative content of impurities is low, the dosage of the masking agent required is small, reducing the risk of introducing impurities or causing other complex effects due to the masking agent, and enabling better control of impurity introduction during the entire determination process. ⑤Human operation errors and impurity introduction: When the sample weighing amount is relatively large, due to the large sample quantity and more dilution times, it is relatively difficult to precisely control during operations such as dissolution, transfer, dilution, and volume fixation, and it is more likely to have operation errors, such as sample spillage, incomplete solution transfer, etc. These errors not only affect the accuracy of the determination results but may also introduce impurities during re-operation or remedial processes. In this method, with a sample weighing amount of 1 g, the operation is more convenient, and operations such as dissolution, transfer, and volume fixation can be carried out more precisely, reducing the possibility of mixing impurities due to improper operation.

[0038] In summary, in the rapid determination of the main content of magnesium hydroxide and calcium oxide, this method is more conducive to reducing the introduction of impurities in multiple aspects such as sample dissolution, reaction system, separation and masking, and operation process, thereby improving the accuracy and reliability of the determination results. Detailed implementation manners

[0039] To make the objectives, technical solutions and advantages of the present invention clearer, the following describes the technical solutions of the present invention clearly and completely through specific embodiments. The following specific embodiments are used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0040] It should be noted that the "titration" mentioned in the present invention refers to determining the content of a certain solute through the quantitative reaction of two solutions, and specific methods existing in the prior art can be used for implementation.

[0041] The method of the present invention is carried out according to the following steps:

[0042] I. Drug preparation

[0043] 1. Preparation of 0.025M disodium ethylenediaminetetraacetate (EDTA) standard solution: Weigh 9.31 g of disodium ethylenediaminetetraacetate (EDTA), dissolve it with water free of carbon dioxide, transfer it to a 1000 ml volumetric flask, dilute it to the mark, and let it stand for one week before standardizing with zinc oxide reference reagent.

[0044] 2. Preparation of 0.025M zinc oxide reference reagent: Prepare the zinc oxide reference reagent by the direct method. Weigh 2.0345 g of zinc oxide reagent calcined to constant weight at 850 - 900 °C and put it into a 150 ml beaker, moisten it with a little water, add hydrochloric acid with a volume concentration of (1 + 1) for dissolution. After complete dissolution, transfer it to a 1000 ml volumetric flask, dilute it to the mark and shake well.

[0045] 3. Standardization of 0.025M EDTA standard solution: Pipette 5 ml of the prepared zinc oxide reference (6 parallels), add 10 ml of water free of carbon dioxide, add 10 ml of ammonia-ammonium chloride buffer solution, add 10 drops of eriochrome black T indicator, and titrate with the prepared EDTA standard solution until the solution changes from wine red to pure blue as the end point. Record the consumed volume. At the same time, do a blank test, adding the same reagents as in the standard without adding the sample.

[0046] Calculate the concentration C of the EDTA standard solution, expressed in mol / l, according to the following formula:

[0047] C EDTA =C zno *V 1- V2 / V

[0048] In the formula: C zno Concentration of zinc oxide reference reagent, mol / l

[0049] Volume of zinc oxide reference reagent taken by V1

[0050] Volume consumed by the blank V2

[0051] V Volume of the EDTA standard solution consumed.

[0052] 4. Preparation of (1+1) triethanolamine: Measure 500 ml of primary pure water into a 1000 ml reagent bottle, add 500 ml of triethanolamine and shake well.

[0053] 5. Preparation of 0.2% Eriochrome Black T indicator: Weigh 0.2 g of Eriochrome Black T into a 250 ml beaker, dissolve it in 100 ml of absolute ethanol, and then add 10 ml of ammonia-ammonium chloride buffer solution.

[0054] 6. Preparation of 2% calcium indicator: Weigh 2 g of calcium indicator and 100 g of sodium chloride, mix and grind them, and after grinding finely, transfer them to a 100 ml reagent bottle.

[0055] II. Sample determination

[0056] 1. Select a representative magnesium hydroxide sample (about 500 g) from the production site, mix the sample well, weigh 1 g of the sample on an electronic balance accurate to 0.0002 g into a 250 ml beaker, moisten it with less water, add 10 ml of (1+1) hydrochloric acid for dissolution. After the sample is completely dissolved, transfer it to a 250 ml volumetric flask, dilute it to the mark and shake well. This solution is test solution A and is used for the determination of the total calcium and magnesium.

[0057] 2. Pipette 5 mL of test solution A and place it in a 250 mL conical flask. Add 20 mL of primary water, 5 mL of triethanolamine solution, 10 mL of ammonia-ammonium chloride buffer solution and 10 drops of Eriochrome Black T indicator. Titrate with a 0.025 M disodium ethylenediaminetetraacetate (EDTA) standard titration solution until the solution changes from purple-red to pure blue as the end point, record the consumed volume, and at the same time do a blank test.

[0058] (3) First, calculate the calcium and magnesium ion content ω1 in the test sample, expressed as a percentage, and calculate according to formula (1):

[0059] ω1 = C * (V1 - V2) × M × 250 / 5 / m / 1000 × 100%

[0060] ω 1(％) = 0.025 mol / l × (13.65 ml - 0.05 ml) × 58.3 g / mol × 5 / 1.0002 g = 99.47%

[0061] ω4 = ω1 - ω2 = 99.45 - 0.02 = 99.43%

[0062] In the formula:

[0063] C—the exact numerical value of the concentration of the standard titration solution of disodium ethylenediaminetetraacetate (EDTA), unit is mole per liter (mol / L);

[0064] V1—the numerical value of the volume of the standard titration solution of disodium ethylenediaminetetraacetate (EDTA) consumed during titration, unit is milliliter (mL);

[0065] V2—the volume consumed by the blank solution

[0066] M—the numerical value of the molar mass of magnesium hydroxide [Mg(OH)2], unit is gram per mole (g / mol) (M = 58.3);

[0067] m—the numerical value of the mass of the test sample, unit is gram (g)

[0068] 250 / 5—dilution volume ml

[0069] ω1—the result of the total determination of calcium and magnesium

[0070] ω2—the determination of calcium content

[0071] ω4—the main content of magnesium hydroxide.

[0072] 4. Use a pipette to transfer 50 mL of test solution A into a 250 mL conical flask, add 20 ml of primary water and 5 mL of triethanolamine solution. While shaking, add sodium hydroxide solution drop by drop. When the solution just starts to precipitate, the pH = 13. Add a little calcium indicator. Then titrate with a 0.025 M standard titration solution of disodium ethylenediaminetetraacetate (EDTA) until the solution changes from wine red to pure blue as the end point.

[0073] First, calculate the calcium ion content ω2 in the test sample, with the numerical value expressed in %, and calculate according to the following formula:

[0074] ω2 = C×(V1 - V2)×M2×250 / 50 / m / 100×100%

[0075] ω2 = 0.025 mol / L×(0.10 ml - 0.05 ml)×40.08 g / mol / 2 / 1.0002

[0076] ω2(%) = 0.02

[0077] In the formula:

[0078] C—the exact numerical value of the concentration of the standard titration solution of disodium ethylenediaminetetraacetate (EDTA), unit is mole per liter (mol / L);

[0079] V1—the numerical value of the volume of the standard titration solution of disodium ethylenediaminetetraacetate (EDTA) consumed during titration, unit: milliliter (mL);

[0080] V2—the volume of the blank solution consumed

[0081] M2—the numerical value of the molar mass of calcium ion [Ca 2+ , unit: gram per mole (g / mol) (M = 40.08);

[0082] m—the numerical value of the mass of the test sample, unit: gram (g);

[0083] 250 / 50 - dilution volume ml

[0084] The calcium oxide content is calculated as the mass fraction ω3 of calcium oxide, and the numerical value is expressed in %, calculated according to the following formula:

[0085] ω3 = ω2 × 1.399 = 0.02 × 1.399 = 0.027%

[0086] The data comparison between the method of the present invention and the national standard is shown in Table 1

[0087] Table 1 Data comparison between the method of the present invention and the national standard

[0088]

[0089] The above data shows that: the method of this invention can meet the requirements of analysis and testing.

[0090] The present invention has been described in detail above. The above description is only the preferred embodiments of the present invention, and the scope of implementation of the present invention cannot be limited. That is, all equivalent changes and modifications made according to the scope of this application should still fall within the scope covered by the present invention.

Claims

1. A method for rapidly determining the main content of magnesium hydroxide and calcium oxide in the process of preparing high-purity magnesium hydroxide from salt lake bischofite, characterized in that: The following steps are involved:

1. Determine the main content of magnesium hydroxide: weigh an appropriate amount of sample, dissolve it with hydrochloric acid, transfer it to a volumetric flask to obtain a test solution; take an appropriate amount of test solution, add triethanolamine to mask interfering ions, adjust the pH value with ammonia-ammonium chloride buffer solution, use chrome black T as an indicator, and use EDTA standard solution to titrate the main content of magnesium hydroxide; 2. Determination of calcium oxide content in magnesium hydroxide: Take an appropriate amount of test solution, add triethanolamine to mask interfering ions, adjust the pH value with sodium hydroxide solution, add an appropriate amount of calcium indicator, and use EDTA standard solution to titrate the calcium oxide content in magnesium hydroxide.

2. The detection method according to claim 1, characterized in that: The specific process of step one is as follows: (1) Weigh 1 g of the sample, accurate to 0.0002 g, place it in a 250 mL beaker, add a small amount of water to moisten it, cover it with a watch glass, and add hydrochloric acid solution to dissolve the sample to obtain a solution; transfer the solution to a 250 mL volumetric flask, dilute it to the mark with water, and shake well; This solution is test A solution, used for the determination of magnesium ion content and calcium oxide content; (2) Use a pipette to transfer 5 mL of Test A solution into a 250 mL conical flask; add 50 mL of water, 5 mL of triethanolamine solution, 10 mL of ammonia-ammonium chloride buffer solution, and ten drops of chrome black T indicator; titrate with disodium ethylenediaminetetraacetic acid standard titration solution until the solution changes from purple-red to pure blue, which is the end point; (3) First calculate the total amount of calcium and magnesium in the sample, ω1, expressed in %, according to formula (1): ω1=C×V1-V2×M1×250 / 5 / m / 100×100% Where: C—The exact value of the concentration of disodium ethylenediaminetetraacetic acid standard titration solution, in mol / L; V1—the volume of disodium ethylenediaminetetraacetic acid standard titration solution consumed during titration, in mL; V2—blank solution consumption volume, in mL; M1—the numerical value of the molar mass of magnesium hydroxide, in g / mol, M1=58.32; m—the numerical value of the sample mass, in g. 250 / 5—Dilution volume ml The main magnesium hydroxide content ω4 is obtained by subtracting the measured calcium ion content ω2 from the calcium and magnesium content ω1.

3. The detection method according to claim 2, characterized in that: The specific process of step one is as follows: Use a pipette to transfer 50mL of test A solution into a 250mL conical flask, add 30mL of first-grade water and 5mL of triethanolamine solution, and add sodium hydroxide solution dropwise while shaking. When the solution just starts to precipitate, the pH value is 13, and a small amount of calcium indicator is added; then titrate with disodium ethylenediaminetetraacetic acid standard titration solution until the solution changes from wine red to pure blue, which is the end point; First calculate the calcium ion content ω2 in the sample, the value is expressed in %, and is calculated according to the following formula: ω2=C×V×M2×250 / 50 / m / 100×100% Where: C—The exact value of the concentration of the standard titration solution of disodium ethylenediaminetetraacetate, in mol / L; V—the volume of the standard ethylenediaminetetraacetic acid disodium solution consumed during titration, in mL; M2—Calcium ion [Ca 2+ ] is the numerical value of the molar mass, in g / mol, M2=40.08; m—the numerical value of the mass of the sample, in g; 250 / 50-dilution volume ml The calcium oxide content is measured as the mass fraction of calcium oxide ω3, the value is expressed in %, and is calculated according to the following formula: ω3=ω2×1.

399.

4. The detection method according to claim 2, characterized in that: The purity of triethanolamine is analytically pure and the mass concentration is 1+1; the pH value of the ammonia-ammonium chloride buffer solution is 10, the mass concentration of the chrome black T indicator is 0.2% and the dosage is 10 drops, and the concentration of the disodium ethylenediaminetetraacetic acid standard solution is 0.025M.

5. The detection method according to claim 3, characterized in that: In the step of determining the calcium content in magnesium hydroxide, the purity of triethanolamine is analytically pure and the mass concentration is 1+1, the concentration of sodium hydroxide is 10M, the mass concentration of the calcium indicator is 2%, and the dosage is 0.1g; the concentration of the disodium ethylenediaminetetraacetic acid standard solution is 0.025M.

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