Method for detecting lithium fluoride content in aluminum electrolyte

Abstract

This invention belongs to the field of aluminum electrolysis technology, specifically relating to a method for detecting the lithium fluoride content in aluminum electrolytes. The method includes the following steps: mixing and grinding the aluminum electrolyte sample to be tested with a grinding aid, followed by drying and pressing to obtain a sample tablet; the grinding aid includes ethanol; performing LIBS analysis on the sample tablet, and determining the lithium content in the aluminum electrolyte sample based on the obtained lithium element light intensity value and a predetermined standard curve, and then calculating the lithium fluoride content in the aluminum electrolyte sample. This invention provides a method for detecting the lithium fluoride content in aluminum electrolytes based on LIBS technology. Using LIBS technology, analysis can be performed with only simple sample pretreatment (grinding, drying, and pressing), and the detection can be completed within half an hour, solving the problems of low efficiency, cumbersome sample pretreatment, and high operational difficulty of traditional detection methods.

Description

Technical Field

[0001] This invention belongs to the field of aluminum electrolysis technology, and specifically relates to a method for detecting the lithium fluoride content in aluminum electrolytes. Background Technology

[0002] In the aluminum electrolysis production process, the reaction medium that dissolves alumina and electrolytically reduces it to metallic aluminum is called aluminum electrolyte (mainly composed of cryolite / sodium hexafluoroaluminate). The lithium fluoride content in the aluminum electrolyte has a particularly significant impact on production. An appropriate amount (1~3wt%) of lithium fluoride can significantly reduce the primary crystallization temperature of the aluminum electrolyte and improve its conductivity. However, when the lithium fluoride content in the aluminum electrolyte exceeds 5%, phenomena such as reduced electrolysis production stability, reduced current efficiency, increased energy consumption, and furnace deterioration occur. Therefore, it is essential to detect the lithium fluoride content in the aluminum electrolyte.

[0003] Currently, the detection of lithium fluoride content in aluminum electrolytes typically employs the industry standard YS / T 739.5-2023, "Chemical Analysis Methods for Aluminum Electrolytes Part 5: Determination of Lithium Fluoride Content by Flame Atomic Absorption Spectrometry." This method involves dissolving the sample in perchloric acid, heating to remove fluoride, dissolving the salts in hydrochloric acid, and measuring the absorbance at 670.8 nm using an air-acetylene flame on an atomic absorption spectrometer to obtain the lithium content, which is then converted to calculate the lithium fluoride content. Flame atomic absorption spectrometry (FAAS), however, requires the solid aluminum electrolyte sample to be ground and then dissolved at high temperatures using a strong acid (such as perchloric acid or hydrochloric acid) to convert it into a liquid before detection. This pretreatment process is cumbersome and difficult, demanding a high level of operator skill and is time-consuming (typically several hours). Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for detecting the lithium fluoride content in aluminum electrolytes. The detection method provided by this invention uses LIBS technology and only requires simple pretreatment (grinding, drying, and tableting) for analysis, solving the problems of low efficiency, cumbersome sample pretreatment, and high operational difficulty of traditional detection methods.

[0005] This invention provides a method for detecting the lithium fluoride content in aluminum electrolytes, comprising the following steps: The aluminum electrolyte sample to be tested is mixed with a grinding aid and ground, then dried and pressed into tablets to obtain the sample tablets to be tested; the grinding aid includes ethanol; The sample to be tested is subjected to LIBS detection. Based on the obtained lithium element light intensity value and the predetermined standard curve, the lithium content in the aluminum electrolyte sample to be tested is obtained, and the lithium fluoride content in the aluminum electrolyte sample to be tested is calculated.

[0006] Preferably, the grinding time is 70~110s and the rotation speed is 1300~1500r / min.

[0007] Preferably, the ratio of the aluminum electrolyte sample to the grinding aid is 10g:4~10 drops.

[0008] Preferably, the drying temperature is 105~115℃ and the time is 15~25min.

[0009] Preferably, the tablet is pressed at a pressure of 5-15 MPa and held for 15-25 seconds.

[0010] Preferably, when performing LIBS detection, the probe of the LIBS spectrometer is vertically aligned with the surface of the sample to be tested.

[0011] Preferably, the LIBS detection is performed using a handheld LIBS spectrometer.

[0012] Preferably, the predetermined standard curve is obtained by LIBS detection of a standard sample, wherein the Li mass content in the standard sample is 0.235~1.907%.

[0013] Preferably, the standard sample is obtained by mixing high-purity lithium carbonate and aluminum electrolyte standard sample in a certain proportion, followed by drying and tableting; the purity of the high-purity lithium carbonate is ≥99.99%, and the lithium mass content in the aluminum electrolyte standard sample is 0.235%; the mass ratio of the high-purity lithium carbonate to the aluminum electrolyte standard sample is 0~9:91~100.

[0014] Preferably, the predetermined standard curve has the lithium element light intensity value as the X-axis and the lithium mass content of the standard sample as the Y-axis.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for detecting the lithium fluoride content in aluminum electrolytes, comprising the following steps: mixing and grinding the aluminum electrolyte sample to be tested with a grinding aid, followed by drying and pressing to obtain a sample tablet; the grinding aid includes ethanol; performing LIBS detection on the sample tablet, and obtaining the lithium content in the aluminum electrolyte sample based on the obtained lithium element light intensity value and a predetermined standard curve, and then calculating the lithium fluoride content in the aluminum electrolyte sample.

[0016] This invention provides a method for detecting lithium fluoride content in aluminum electrolytes based on LIBS technology. Using LIBS technology, analysis can be performed with only simple sample pretreatment (grinding, drying, and tableting), and the detection can be completed within half an hour. This solves the problems of low efficiency, cumbersome sample pretreatment, and high operation difficulty of traditional FAAS detection methods (flame atomic absorption spectrometry).

[0017] Furthermore, this invention utilizes a handheld LIBS spectrometer to detect the lithium fluoride content in aluminum electrolytes, offering advantages such as simple operation, inexpensive instrument, small sample volume, fast measurement speed, and good result reproducibility. Operators can obtain results within seconds of excitation on the sample surface using the handheld LIBS spectrometer, significantly improving detection efficiency and simplifying the operation process.

[0018] Furthermore, the amount of grinding aid (ethanol) added, grinding time, drying temperature and time, and pressurization pressure and time described in this invention can improve the precision of the detection results. This invention uses a mixture of high-purity lithium carbonate and aluminum electrolyte standard samples in a specific ratio for grinding. Anhydrous ethanol is added to aid grinding. After drying and tableting, the lithium content of the mixed sample is determined using flame atomic absorption spectrometry (FAAS), forming a series of standard samples with known lithium content. This solves the problem of insufficient lithium fluoride content gradient in traditional standard samples. Attached Figure Description

[0019] 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.

[0020] Figure 1 This is a flowchart of the method for detecting lithium fluoride content in aluminum electrolytes according to the present invention; Figure 2 This is a standard curve of lithium in the examples. Detailed Implementation

[0021] This invention provides a method for detecting the lithium fluoride content in aluminum electrolytes, comprising the following steps: The aluminum electrolyte sample to be tested is mixed with a grinding aid and ground, then dried and pressed into tablets to obtain the sample tablets to be tested; the grinding aid includes ethanol; The sample to be tested is subjected to LIBS detection. Based on the obtained lithium element light intensity value and the predetermined standard curve, the lithium content in the aluminum electrolyte sample to be tested is obtained, and the lithium fluoride content in the aluminum electrolyte sample to be tested is calculated.

[0022] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.

[0023] In this invention, the aluminum electrolyte sample to be tested is mixed and ground with a grinding aid, and then dried and pressed into tablets to obtain a sample tablet to be tested; the grinding aid includes ethanol.

[0024] In this invention, the aluminum electrolyte sample to be tested is preferably crushed before use, and the particle size of the crushed sample is preferably 2 to 5 mesh.

[0025] In this invention, the preferred ratio of the aluminum electrolyte sample to the grinding aid is 10g:4-10 drops, specifically 10g:5-8 drops (each drop approximately 0.05mL); the preferred ethanol is anhydrous ethanol. This invention preferably adds anhydrous ethanol dropwise to the surface of the aluminum electrolyte sample. The amount of grinding aid described in this invention ensures effective grinding and dispersion of the sample.

[0026] In this invention, the grinding is preferably performed using a vibratory mill, and the grinding time is preferably 70-110 seconds, specifically 80 seconds, 90 seconds, or 100 seconds. The grinding speed is 1300-1500 r / min, specifically 1400 r / min. The particle size of the sample after grinding is preferably 40-48 μm. The grinding time specified in this invention ensures effective grinding and dispersion of the sample.

[0027] In this invention, the drying temperature is preferably 105~115℃ (110±5℃), and the drying time is preferably 15~25min, specifically 20min.

[0028] In this invention, the preferred pressure for pressing the tablet is 5-15 MPa, specifically 10 MPa, and the preferred holding time is 15-25 seconds, specifically 20 seconds. The pressure and time specified in this invention result in a compact tablet.

[0029] The present invention performs LIBS detection on the sample to be tested, and obtains the lithium content in the aluminum electrolyte sample based on the obtained lithium element light intensity value and a predetermined standard curve, and then calculates the lithium fluoride content in the aluminum electrolyte sample.

[0030] In this invention, the LIBS detection preferably uses a handheld LIBS spectrometer. LIBS (Laser-Induced Breakdown Spectroscopy) uses an ultrashort pulse laser to focus a plasma onto the sample surface, and then analyzes the plasma emission spectrum to identify the elemental composition of the sample for quantitative analysis.

[0031] In this invention, when performing LIBS detection, the probe of the LIBS spectrometer is preferably vertically aligned with the sample surface. In this embodiment, the steps are as follows: place the sample to be tested on a stable stage, use a handheld LIBS spectrometer to vertically align the probe with the sample surface, and measure each sample three times at different positions. The preferred parameters for LIBS detection include: lithium characteristic spectral line 670.78 nm; spectral resolution: ≤0.05~0.1 nm (at 670 nm); spectrometer delay time: 1~3 μs; spectrometer integration time: 1~5 ms.

[0032] In this invention, the predetermined standard curve is obtained by LIBS detection of standard sample pieces, wherein the Li mass content in the standard sample pieces is preferably 0.235~1.907%. The standard sample pieces are obtained by mixing high-purity lithium carbonate and aluminum electrolyte standard samples in different proportions, followed by drying and pressing. The purity of the high-purity lithium carbonate is preferably ≥99.99%, and the aluminum electrolyte standard sample is preferably a certified standard sample GDJ-3 aluminum electrolyte X-ray fluorescence spectroscopy standard sample, standard sample number: GSB 04-2607-2010, with a lithium mass content of 0.235%. The mass ratio of the high-purity lithium carbonate to the aluminum electrolyte standard sample is preferably 0~9:91~100, specifically 0:100, 1:99, 2:98, 3:97, 4:96, 5:95, 6:94, 7:93, 8:92, or 9:91; the mixture is preferably ground after mixing. The drying temperature is preferably 105~115℃ (110±5℃), and the drying time is preferably 15~25min, specifically 20min. The tableting pressure is preferably 5~15MPa, specifically 10MPa, and the pressure holding time is preferably 15~25s, specifically 20s.

[0033] In this invention, the predetermined standard curve preferably uses the light intensity value of lithium element as the X-axis and the lithium element mass content (%) of the standard sample as the Y-axis.

[0034] In this invention, the conversion formula used is LiF(%) = Li(%) × 3.737 × 100%; In the formula, LiF(%) is the lithium fluoride content in the sample to be tested; Li(%) is the lithium element content in the sample to be tested; and 3.737 is the coefficient for converting 1 mole of lithium to 1 mole of lithium fluoride.

[0035] To further illustrate the present invention, the method for detecting lithium fluoride content in aluminum electrolytes 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.

[0036] The following embodiments are in accordance with Figure 1The flowchart shown illustrates the detection of lithium fluoride content in aluminum electrolytes.

[0037] Example 1 The method for detecting lithium fluoride content in aluminum electrolytes includes the following steps: 1. Preparation of standard samples: The national certified standard sample GDJ-3 aluminum electrolyte X-ray fluorescence spectroscopy standard sample (standard sample number: GSB 04-2607-2010, lithium mass content: 0.235%) was ground and mixed with high-purity lithium carbonate (content ≥99.99%) in a certain proportion. After drying, a portion of the sample was placed into a tablet press to obtain standard sample tablets with different lithium contents. The other portion was analyzed and determined by flame atomic absorption spectrometry (FAAS). See Table 1 for details.

[0038] The preparation steps for standard sample tablets with different lithium contents are as follows: Take 10g of the mixed standard sample and spread it evenly in a mortar. Add 5 drops of anhydrous ethanol to different positions on the sample surface and grind it for 80s (1400r / min). Place the ground sample in an oven and dry it in an oven at 110±5℃ for 20min. Then pour the dried sample into a mold and lining it with edging material (boric acid (analytical grade), aluminum ring, polyethylene ring, etc.). Press it to 10MPa with a tablet press and maintain the pressure for 20s (the resulting tablet thickness is about 3mm).

[0039] Table 1. Standard Sample Preparation Table

[0040] 2. Establishing a standardized curve: Place the standard sample on a stable platform. Using a handheld LIBS spectrometer, align the probe vertically with the sample surface and measure each sample three times at different locations. Collect the spectrum (lithium characteristic spectral line 670.78 nm; spectral resolution at 670 nm: ≤0.1 nm; spectrometer delay time: 1 μs; spectrometer integration time: 1 ms). Then, set the corresponding lithium mass content (%) in the LIBS spectrometer's built-in software according to Table 1. Using the LIBS spectrometer's built-in software, automatically generate a standard curve with the lithium light intensity value as the X-axis (horizontal axis) and the lithium mass content (%) of the standard sample as the Y-axis (vertical axis).

[0041] The equation for the linear working curve of the standard curve is: Y = 1.88 × 10⁻⁶ -5 X = 0.0013, correlation coefficient is R. 2 =1.0000, standard curve graph as follows Figure 2 As shown.

[0042] 3. Sample determination (1) Sample preparation: Crush the electrolyte sample to be tested (2~5 mesh), take 10g of sample and spread it evenly in a mortar, add 5 drops of anhydrous ethanol to different positions on the sample surface, grind with a grinder for 80s (speed 1400r / min), put the ground sample into an oven and dry it in an oven at 110±5℃ for 20min, then pour the dried sample into a mold, edging it with edging material (boric acid (analytical grade), aluminum ring, polyethylene ring, etc.), press it to 10MPa with a tablet press and maintain the pressure for 20s.

[0043] (2) Sample measurement: Start the handheld LIBS analysis program, align the probe vertically with the sample surface, and measure each sample 3 times at different positions.

[0044] (3) Result calculation: The built-in software of the LIBS spectrometer automatically acquires the spectrum and automatically calculates the lithium content according to the established standard curve. Then, the lithium content is converted into lithium fluoride content according to the following formula (the result is retained to two decimal places): LiF (%) = Li (%) × 3.737 × 100%; In the formula, LiF(%) is the mass content of lithium fluoride in the sample to be tested; Li(%) is the lithium content in the sample to be tested; and 3.737 is the coefficient for converting 1 mole of lithium to 1 mole of lithium fluoride.

[0045] 4. Verification of method accuracy One aluminum electrolyte sample was taken from each of the five aluminum electrolytic cells. After cooling, the sample was crushed and divided into two parts. One part was measured using a LIBS spectrometer according to "3. Sample Determination". The other part was measured using the industry standard YS / T 739.5-2023 "Chemical Analysis Methods for Aluminum Electrolytes Part 5: Determination of Lithium Fluoride Content by Flame Atomic Absorption Spectrometry". The results of the two methods are detailed in Table 2.

[0046] Table 2 Results of Method Accuracy Verification

[0047] The data in Table 2 show that when the same sample was tested multiple times using the LIBS method, the RSD (relative standard deviation) of the detection results was ≤2%. RSD mainly reflects the precision and repeatability of the analytical method, indicating that the detection method of this invention has high precision and good repeatability. The absolute difference between the LIBS and FAAS determination results was ≤0.05%, indicating that the accuracy of the method of this invention is basically the same as that of the industry standard YS / T 739.5-2023 "Chemical Analysis Methods for Aluminum Electrolytes Part 5: Determination of Lithium Fluoride Content by Flame Atomic Absorption Spectrometry". In summary, the LIBS method used in this invention to detect the lithium fluoride content in aluminum electrolytes has high precision, good repeatability, and accurate results.

[0048] Example 2 Using the controlled variable method (unlisted conditions are the same as in Example 1), DJL-10 standard samples were prepared by changing the grinding time and the amount of grinding aid (anhydrous ethanol) added. The samples were then measured using a handheld LIBS spectrometer. The results are detailed in Tables 3 to 6.

[0049] Table 3. Effect of grinding aid addition (grinding for 40 s) on measurement results

[0050] Table 4. Effect of grinding aid addition (grinding for 60 s) on measurement results

[0051] Table 5. Effect of grinding aid addition (grinding for 80 seconds) on measurement results

[0052] Table 6. Effect of grinding aid dosage (grinding for 100 s) on measurement results

[0053] As shown in Tables 3 to 6, when the grinding time is 80 s and the amount of grinding aid (anhydrous ethanol) added is 5 drops, the RSD (relative standard deviation) of the test results is the smallest, proving that under the sample preparation conditions, the method of the present invention has high precision and good repeatability.

[0054] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for detecting lithium fluoride content in aluminum electrolytes, characterized in that, Includes the following steps: The aluminum electrolyte sample to be tested is mixed and ground with a grinding aid, and then dried and pressed into tablets to obtain the sample tablets to be tested; the grinding aid includes ethanol; The sample to be tested is subjected to LIBS detection. Based on the obtained lithium element light intensity value and the predetermined standard curve, the lithium content in the aluminum electrolyte sample to be tested is obtained, and the lithium fluoride content in the aluminum electrolyte sample to be tested is calculated.

2. The detection method according to claim 1, characterized in that, The grinding time is 70~110s, and the rotation speed is 1300~1500r / min.

3. The detection method according to claim 1 or 2, characterized in that, The ratio of the aluminum electrolyte sample to the grinding aid is 10g:4~10 drops.

4. The detection method according to claim 1, characterized in that, The drying temperature is 105~115℃, and the time is 15~25min.

5. The detection method according to claim 1 or 4, characterized in that, The tablet is compressed at a pressure of 5-15 MPa and held for 15-25 seconds.

6. The detection method according to claim 1, characterized in that, When performing LIBS testing, the probe of the LIBS spectrometer is vertically aligned with the surface of the sample to be tested.

7. The detection method according to claim 1 or 6, characterized in that, The LIBS detection was performed using a handheld LIBS spectrometer.

8. The detection method according to claim 1, characterized in that, The predetermined standard curve is obtained by LIBS testing of standard sample pieces, wherein the Li mass content in the standard sample pieces is 0.235~1.907%.

9. The detection method according to claim 8, characterized in that, The standard sample is obtained by mixing high-purity lithium carbonate and aluminum electrolyte standard sample in a certain proportion, followed by drying and tableting; the purity of the high-purity lithium carbonate is ≥99.99%, and the lithium mass content in the aluminum electrolyte standard sample is 0.235%; the mass ratio of the high-purity lithium carbonate to the aluminum electrolyte standard sample is 0~9:91~100.

10. The detection method according to claim 8, characterized in that, The predetermined standard curve uses the light intensity of lithium as the X-axis and the lithium mass content of the standard sample as the Y-axis.

Images