A method for detecting manganese elements in carbon-coated lithium manganese iron phosphate

Abstract

The invention discloses a method for detecting manganese element in carbon-coated lithium iron manganese phosphate, and relates to the technical field of manganese element detection. The specific detection method is as follows: S1, ammonium ferrous sulfate calibration; S1-1, using an electric oven to dry a working reagent potassium dichromate to a constant weight, and the temperature of the electric oven is set to 120°C±2°C; S1-2, weighing 0.1000±0.0004g of the working reagent potassium dichromate in the above steps, and dissolving it in 25ml of ultrapure water; S1-3, adding 10ml of sulfur-phosphorus mixed acid solution, and adding 70ml of ultrapure water; S1-4, titrating with the prepared ammonium ferrous sulfate solution until the orange-yellow color disappears; S1-5, adding 2 drops of N-phenylated anthranilic acid indicator, and continuing to titrate until the solution changes from purple-red to bright green as the end point. The method for detecting manganese element in carbon-coated lithium manganese iron phosphate mainly avoids the influence of incomplete digestion of samples on data accuracy. The method of manual titration is used for detection, which can completely digest the lithium manganese iron phosphate, improve the detection stability, and control the extreme difference within 0.2%.

Description

Technical Field

[0001] The invention relates to the technical field of manganese element detection, and in particular to a method for detecting manganese element in carbon-coated lithium manganese iron phosphate. Background Art

[0002] The electronic conductivity of lithium manganese iron phosphate is extremely poor. Through the calculation of electron energy and by first principles, it is found that the energy gap for electron transition in lithium iron phosphate is 0.3eV, which has semiconductor characteristics, while the energy gap for electron transition in lithium manganese iron phosphate is 2eV, which is an insulator. In order to improve the poor conductivity of lithium manganese iron phosphate, bulk doping can be used to reduce the band gap width of Mn3+, thereby improving the conductivity of the material.

[0003] Chemical element analysis, also known as component analysis, is required during the production and testing of lithium manganese iron phosphate. Generally, spectroscopy (ultraviolet, infrared, nuclear magnetic resonance); chromatography (gas chromatography, liquid chromatography, ion chromatography); mass spectrometry (mass spectrometer, gas chromatography-mass spectrometry, liquid-mass spectrometry); energy spectrum (fluorescence spectrum, diffraction spectrum); and thermal spectrum (thermogravimetric analyzer, differential scanning calorimeter) are used to comprehensively analyze the samples. Through the combined use of multiple separation and analysis methods, qualitative and quantitative analysis of each component in the sample is carried out to determine the structure of the components, have a comprehensive understanding of the samples, and conduct product testing in various links such as raw material acceptance, furnace analysis, and finished product inspection.

[0004] However, the existing detection method is to heat and digest lithium manganese iron phosphate with aqua regia, filter out impurities (mainly carbon) with qualitative filter paper, and use inductively coupled plasma spectrometer (ICP-OES) for determination, select appropriate spectral lines, configure standard solution concentration, and eliminate spectral line background interference. After the sample is heated and digested, the sample liquid is not clear and transparent and needs to be filtered. Due to the high manganese content and the small amount of sample contained in the filter residue, the ICP detection range of the same sample exceeds 0.6%, which cannot meet people's usage needs well. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for detecting manganese elements in carbon-coated lithium manganese iron phosphate, which solves the problem that the current detection method proposed in the above background technology will affect the accuracy of the detection data due to incomplete sample digestion.

[0006] To achieve the above objectives, the present invention is implemented by the following technical solutions: a method for detecting manganese elements in carbon-coated lithium manganese iron phosphate, the specific detection method is as follows:

[0007] S1, ammonium ferrous sulfate calibration;

[0008] S1-1. Dry the working reagent potassium dichromate to constant weight in an electric oven;

[0009] S1-2, weigh 0.1000±0.0004g of potassium dichromate, the working reagent in the above step, and dissolve it in 25ml of ultrapure water;

[0010] S1-3, add 10 ml of sulfuric acid and phosphoric acid mixed solution and 70 ml of ultrapure water;

[0011] S1-4, titrate with the prepared ammonium ferrous sulfate solution until the orange-yellow color disappears;

[0012] S1-5, add 2 drops of N-phenylanthranilic acid indicator, and continue titrating until the solution changes from purple-red to bright green;

[0013] S2, weighing;

[0014] S2-1, take 0.3±0.0005g sample;

[0015] S2-2, adding a small amount of ultrapure water to the above sample;

[0016] S2-3, after adding the digestion reagent, shake it to mix evenly;

[0017] S3, digestion;

[0018] S3-1. First, place a graphite furnace and use the graphite furnace to heat the sample until the sample is completely dissolved;

[0019] S3-2. After the sample is completely dissolved, remove the test tube and cool it down. Then add 20 ml of concentrated phosphoric acid and shake it to make it uniform and moderate.

[0020] S3-3. Continue heating the test tube after mixing until the solution inside turns dark purple and the small bubbles disappear;

[0021] S3-4. Remove the test tube, cool it to 70°C, add 90 ml of ultrapure water, and shake it thoroughly to completely dissolve the salts.

[0022] S3-5, cooling the test tube solution to room temperature;

[0023] S4, titration;

[0024] S4-1. Titrate the sample with ammonium ferrous sulfate standard solution until it turns light red;

[0025] S4-2, add 3 drops of N-phenylanthranilic acid indicator;

[0026] S4-3, titrate until the solution changes from light purple to bright yellow;

[0027] S4-4. After 15 seconds, read the solution and record the titration result.

[0028] Optionally, the temperature setting position of the electric oven in step 1-1 during the drying process of the working reagent potassium dichromate is 120°C±2°C.

[0029] Optionally, step 1 is a complete ammonium ferrous sulfate calibration. During the detection process, the above-mentioned cycle steps are repeated five times to obtain 5 parallel samples. The maximum and the minimum of the five values ​​are removed, and the average of the three values ​​is the concentration of the ammonium ferrous sulfate standard solution.

[0030] Optionally, in the process of heating the sample in the graphite furnace in step 3-1, the temperature of the graphite furnace is adjusted and set to 320°C.

[0031] Optionally, the phosphoric acid is used as a dissolving agent and a complexing agent, and the perchloric acid oxidizes the divalent manganese into a complex of trivalent manganese in a concentrated hot phosphoric acid medium.

[0032] Optionally, the final titration result in step 4-4 is estimated to two decimal places.

[0033] The present invention provides a method for detecting manganese elements in carbon-coated lithium manganese iron phosphate, which has the following beneficial effects:

[0034] The detection method of manganese element in carbon-coated lithium manganese iron phosphate mainly avoids the influence of incomplete digestion of samples on data accuracy. The detection is carried out by manual titration method, which can completely digest lithium manganese iron phosphate, improve the detection stability, and control the range within 0.2%. In this scheme, hydrochloric acid and hydrofluoric acid, which are easily made into drugs, are not used. 0.3g of sample is added with 10ml of dilute nitric acid (1:1) and 10ml of perchloric acid, placed in a graphite furnace (the temperature is adjusted to 320°C), and heated until the sample is completely dissolved (no black particles). The sample liquid in the conical flask is milky white. First, perchloric acid reacts with carbon to digest the encapsulated carbon. Then perchloric acid oxidizes manganese from divalent to trivalent in the medium of nitric acid. Since simple ions in pure aqueous solution of trivalent manganese ions are unstable, they can be easily disproportionated into divalent manganese ions and tetravalent precipitates, so it appears turbid milky white. After cooling for 2-3 minutes, add 15-20ml of phosphoric acid and continue to heat until it becomes dark purple and small bubbles disappear. Remove and cool to 70℃, then add 90ml of ultrapure water and shake thoroughly to dissolve the salts. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of the EDS component analysis of the black substance of sample No. 1 in the present invention;

[0036] Figure 2 This is a schematic diagram of the EDS component analysis of the black substance in sample No. 4 of the present invention. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Example 1

[0038] See also Figure 1 to Figure 2 The present invention provides a technical solution: a method for detecting manganese elements in carbon-coated lithium manganese iron phosphate, and the specific detection method is as follows:

[0039] S1, ammonium ferrous sulfate calibration;

[0040] S1-1. Dry the working reagent potassium dichromate to constant weight in an electric oven;

[0041] S1-2, weigh 0.1000±0.0004g of potassium dichromate, the working reagent in the above step, and dissolve it in 25ml of ultrapure water;

[0042] S1-3, add 10 ml of sulfuric acid and phosphoric acid mixed solution and 70 ml of ultrapure water;

[0043] S1-4, titrate with the prepared ammonium ferrous sulfate solution until the orange-yellow color disappears;

[0044] S1-5, add 2 drops of N-phenylanthranilic acid indicator, and continue titrating until the solution changes from purple-red to bright green;

[0045] S2, weighing;

[0046] S2-1, take 0.3±0.0005g sample;

[0047] S2-2, adding a small amount of ultrapure water to the above sample;

[0048] S2-3, after adding the digestion reagent, shake it to mix evenly;

[0049] S3, digestion;

[0050] S3-1. First, place a graphite furnace and use the graphite furnace to heat the sample until the sample is completely dissolved;

[0051] S3-2. After the sample is completely dissolved, remove the test tube and cool it down. Then add 20 ml of concentrated phosphoric acid and shake it to make it uniform and moderate.

[0052] S3-3. Continue heating the test tube after mixing until the solution inside turns dark purple and the small bubbles disappear;

[0053] S3-4. Remove the test tube, cool it to 70°C, add 90 ml of ultrapure water, and shake it thoroughly to completely dissolve the salts.

[0054] S3-5, cooling the test tube solution to room temperature;

[0055] S4, titration;

[0056] S4-1. Titrate the sample with ammonium ferrous sulfate standard solution until it turns light red;

[0057] S4-2, add 3 drops of N-phenylanthranilic acid indicator;

[0058] S4-3, titrate until the solution changes from light purple to bright yellow;

[0059] S4-4. After 15 seconds, read the solution and record the titration result.

[0060] In this embodiment, the temperature setting position of the electric oven in step 1-1 during the drying process of the working reagent potassium dichromate is 120°C±2°C.

[0061] In this embodiment, step 1 is a complete ammonium ferrous sulfate calibration. The above cycle steps are repeated five times during the detection process to obtain 5 parallel samples. The maximum and the minimum of the five values ​​are removed, and the average of the three values ​​is the concentration of the ammonium ferrous sulfate standard solution.

[0062] In this embodiment, in step 3-1, when the graphite furnace is heating the sample, the temperature of the graphite furnace is adjusted and set to 320°C.

[0063] In this embodiment, phosphoric acid is used as a dissolving agent and a complexing agent, and perchloric acid oxidizes divalent manganese into a complex of trivalent manganese in a concentrated hot phosphoric acid medium.

[0064] In this embodiment, the final titration result in step 4-4 is estimated to two decimal places. Example 2

[0065] S1, ammonium ferrous sulfate calibration;

[0066] S1-1. Use an electric oven to dry the working reagent potassium dichromate to constant weight. The temperature of the electric oven is set to 120°C ± 2°C.

[0067] S1-2, weigh 0.1000±0.0004g of potassium dichromate, the working reagent in the above step, and dissolve it in 25ml of ultrapure water;

[0068] S1-3, add 10 ml of sulfuric acid and phosphoric acid mixed solution and 70 ml of ultrapure water;

[0069] S1-4, titrate with the prepared ammonium ferrous sulfate solution until the orange-yellow color disappears;

[0070] S1-5, add 2 drops of N-phenylanthranilic acid indicator, and continue titrating until the solution changes from purple-red to bright green;

[0071] The above five steps are a complete ammonium ferrous sulfate calibration. Repeat the above cycle steps five times to make 5 parallel samples. Remove the maximum and the minimum of the five values, and take the average of the three values ​​as the concentration of the ammonium ferrous sulfate standard solution.

[0072] S2, weighing;

[0073] S2-1, take 0.3±0.0005g sample;

[0074] S2-2, adding a small amount of ultrapure water to the above sample;

[0075] S2-3, add 10 ml of HCl and 10 ml of HNO3 and shake to mix evenly;

[0076] S3, digestion;

[0077] S3-1. First, place a graphite furnace and adjust the temperature of the graphite furnace to 320°C to heat the sample until the sample is completely dissolved;

[0078] S3-2. After the sample is completely dissolved, remove the test tube and cool it down. Then add 20 ml of concentrated phosphoric acid and shake it to make it uniform and moderate.

[0079] S3-3. Continue heating the test tube after mixing until the solution inside turns dark purple and the small bubbles disappear;

[0080] S3-4. Remove the test tube, cool it to 70°C, add 90 ml of ultrapure water, and shake it thoroughly to completely dissolve the salts.

[0081] S3-5, cooling the test tube solution to room temperature;

[0082] S4, titration;

[0083] S4-1. Titrate the sample with ammonium ferrous sulfate standard solution until it turns light red;

[0084] S4-2, add 3 drops of N-phenylanthranilic acid indicator;

[0085] S4-3, titrate until the solution changes from light purple to bright yellow;

[0086] S4-4. After 15 seconds, read the solution and record the titration result, with the value estimated to two decimal places. Example 3

[0087] S1, ammonium ferrous sulfate calibration;

[0088] S1-1. Use an electric oven to dry the working reagent potassium dichromate to constant weight. The temperature of the electric oven is set to 120°C ± 2°C.

[0089] S1-2, weigh 0.1000±0.0004g of potassium dichromate, the working reagent in the above step, and dissolve it in 25ml of ultrapure water;

[0090] S1-3, add 10 ml of sulfuric acid and phosphoric acid mixed solution and 70 ml of ultrapure water;

[0091] S1-4, titrate with the prepared ammonium ferrous sulfate solution until the orange-yellow color disappears;

[0092] S1-5, add 2 drops of N-phenylanthranilic acid indicator, and continue titrating until the solution changes from purple-red to bright green;

[0093] The above five steps are a complete ammonium ferrous sulfate calibration. Repeat the above cycle steps five times to make 5 parallel samples. Remove the maximum and the minimum of the five values, and take the average of the three values ​​as the concentration of the ammonium ferrous sulfate standard solution.

[0094] S2, weighing;

[0095] S2-1, take 0.3±0.0005g sample;

[0096] S2-2, adding a small amount of ultrapure water to the above sample;

[0097] S2-3, add 10 ml of HClO4 and shake to mix evenly;

[0098] S3, digestion;

[0099] S3-1. First, place a graphite furnace and adjust the temperature of the graphite furnace to 320°C to heat the sample until the sample is completely dissolved;

[0100] S3-2. After the sample is completely dissolved, remove the test tube and cool it down. Then add 20 ml of concentrated phosphoric acid and shake it to make it uniform and moderate.

[0101] S3-3. Continue heating the test tube after mixing until the solution inside turns dark purple and the small bubbles disappear;

[0102] S3-4. Remove the test tube, cool it to 70°C, add 90 ml of ultrapure water, and shake it thoroughly to completely dissolve the salts.

[0103] S3-5, cooling the test tube solution to room temperature;

[0104] S4, titration;

[0105] S4-1. Titrate the sample with ammonium ferrous sulfate standard solution until it turns light red;

[0106] S4-2, add 3 drops of N-phenylanthranilic acid indicator;

[0107] S4-3, titrate until the solution changes from light purple to bright yellow;

[0108] S4-4. After 15 seconds, read the solution and record the titration result. The value should be estimated to two decimal places. Example 4

[0109] S1, ammonium ferrous sulfate calibration;

[0110] S1-1. Use an electric oven to dry the working reagent potassium dichromate to constant weight. The temperature of the electric oven is set to 120°C ± 2°C.

[0111] S1-2, weigh 0.1000±0.0004g of potassium dichromate, the working reagent in the above step, and dissolve it in 25ml of ultrapure water;

[0112] S1-3, add 10 ml of sulfuric acid and phosphoric acid mixed solution and 70 ml of ultrapure water;

[0113] S1-4, titrate with the prepared ammonium ferrous sulfate solution until the orange-yellow color disappears;

[0114] S1-5, add 2 drops of N-phenylanthranilic acid indicator, and continue titrating until the solution changes from purple-red to bright green;

[0115] The above five steps are a complete ammonium ferrous sulfate calibration. Repeat the above cycle steps five times to make 5 parallel samples. Remove the maximum and the minimum of the five values, and take the average of the three values ​​as the concentration of the ammonium ferrous sulfate standard solution.

[0116] S2, weighing;

[0117] S2-1, take 0.3±0.0005g sample;

[0118] S2-2, adding a small amount of ultrapure water to the above sample;

[0119] S2-3, add 10ml of HClO4 and 10ml of HNO3 and shake to mix evenly;

[0120] S3, digestion;

[0121] S3-1. First, place a graphite furnace and adjust the temperature of the graphite furnace to 320°C to heat the sample until the sample is completely dissolved;

[0122] S3-2. After the sample is completely dissolved, remove the test tube and cool it down. Then add 20 ml of concentrated phosphoric acid and shake it to make it uniform and moderate.

[0123] S3-3. Continue heating the test tube after mixing until the solution inside turns dark purple and the small bubbles disappear;

[0124] S3-4. Remove the test tube, cool it to 70°C, add 90 ml of ultrapure water, and shake it thoroughly to completely dissolve the salts.

[0125] S3-5, cooling the test tube solution to room temperature;

[0126] S4, titration;

[0127] S4-1. Titrate the sample with ammonium ferrous sulfate standard solution until it turns light red;

[0128] S4-2, add 3 drops of N-phenylanthranilic acid indicator;

[0129] S4-3, titrate until the solution changes from light purple to bright yellow;

[0130] S4-4. After 15 seconds, read the solution and record the titration result, with the value estimated to two decimal places.

[0131] Four different digestion reagents were used in the four examples, namely: 10 ml of aqua regia, 10 ml of lHC l +10ml HNO3, 10ml HC l O4 and 10ml HC l O4+10ml of HNO3;

[0132] The specific conditions of sample digestion after using the four digestion reagents are as follows:

[0133]

[0134] This step mainly involves the reaction of perchloric acid and coated carbon.

[0135] 7C+4HClO4=2Cl2↑+2H2O+7CO2↑

[0136] From the sample digestion situation, only perchloric acid and nitric acid can completely digest the sample and carbon element;

[0137] The results of different digestion samples are as follows:

[0138]

[0139] The theoretical value of manganese in the above samples is 12.0%. Except for perchloric acid and nitric acid, which can digest the samples, the others all have black foreign matter residues. From the final test results, there are still a small amount of manganese-containing samples remaining in the black insoluble matter, which leads to large volatility of the data and low data. Only the last group is closer to the theoretical value.

[0140] The EDS component analysis diagram of black matter is shown in the attached figure of the specification.

[0141] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for detecting manganese elements in carbon-coated lithium manganese iron phosphate, characterized in that: The specific detection methods are as follows: S1, ammonium ferrous sulfate calibration; S1-1. Dry the working reagent potassium dichromate to constant weight in an electric oven; S1-2, weigh 0.1000±0.0004g of potassium dichromate, the working reagent in the above step, and dissolve it in 25ml of ultrapure water; S1-3, add 10 ml of sulfuric acid and phosphoric acid mixed solution and 70 ml of ultrapure water; S1-4, titrate with the prepared ammonium ferrous sulfate solution until the orange-yellow color disappears; S1-5, add 2 drops of N-phenylanthranilic acid indicator, and continue titrating until the solution changes from purple-red to bright green; S2, weighing; S2-1, take 0.3±0.0005g sample; S2-2, adding a small amount of ultrapure water to the above sample; S2-3, after adding the digestion reagent, shake it to mix evenly; the digestion reagent is 10ml of dilute nitric acid and 10ml of perchloric acid; S3, digestion; S3-1. First, place a graphite furnace and use the graphite furnace to heat the sample until the sample is completely dissolved; S3-2. After the sample is completely dissolved, remove the test tube and cool it down. Then add 20 ml of concentrated phosphoric acid and shake it to make it uniform and moderate. S3-3. Continue heating the test tube after mixing until the solution inside turns dark purple and the small bubbles disappear; S3-4. Remove the test tube, cool it to 70°C, add 90 ml of ultrapure water, and shake it thoroughly to completely dissolve the salts. S3-5, cooling the test tube solution to room temperature; S4, titration; S4-1. Titrate the sample with ammonium ferrous sulfate standard solution until it turns light red; S4-2, add 3 drops of N-phenylanthranilic acid indicator; S4-3, titrate until the solution changes from light purple to bright yellow; S4-4. After 15 seconds, read the solution and record the titration result.

2. The method for detecting carbon-coated lithium manganese iron phosphate according to claim 1, characterized in that: The temperature setting position of the electric oven in the step 1-1 during the drying process of the working reagent potassium dichromate is 120°C±2°C.

3. The method for detecting manganese element in carbon-coated lithium iron manganese phosphate according to claim 1, characterized in that: The step 1 is a complete ammonium ferrous sulfate calibration. During the detection process, the above cycle steps are repeated five times to obtain 5 parallel samples. The maximum and the minimum of the five values ​​are removed, and the average of the three values ​​is the concentration of the ammonium ferrous sulfate standard solution.

4. The method for detecting manganese element in carbon-coated lithium iron manganese phosphate according to claim 1, characterized in that: In the process of heating the sample in the graphite furnace in step 3-1, the temperature of the graphite furnace is adjusted and set to 320°C.

5. The method for detecting manganese element in carbon-coated lithium iron manganese phosphate according to claim 1, characterized in that: The phosphoric acid acts as a dissolving agent and a complexing agent, and the perchloric acid oxidizes divalent manganese into a complex of trivalent manganese in a concentrated hot phosphoric acid medium.

6. The method for detecting carbon-coated lithium manganese iron phosphate according to claim 1, characterized in that: The final titration result in step 4-4 is estimated to two decimal places.

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