Method for digesting calcium fluoride and measuring metal ions in calcium fluoride

Abstract

The invention relates to a method for digesting calcium fluoride and measuring metal ions in calcium fluoride, and belongs to the technical field of digestion treatment methods. The method specifically comprises the following steps: (1) mixing calcium fluoride, hydrofluoric acid and perchloric acid, heating until liquid in a system is completely evaporated to dryness to obtain solid residues, and cooling; (2) adding nitric acid into the solid residues obtained in the step (1), and mixing to obtain transparent liquid; whether the transparent liquid contains insoluble substances or not is observed, and if the transparent liquid does not contain the insoluble substances, digestion is completed; and if insoluble substances are contained, heating is performed until the insoluble substances disappear, and digestion is completed. The method disclosed by the invention can be used for thoroughly digesting calcium fluoride and has the advantages of high digestion speed, simplicity in operation and no influence on later metal ion detection.

Description

Technical Field

[0001] The invention relates to a method for digesting calcium fluoride and measuring metal ions in calcium fluoride, belonging to the technical field of digestion treatment methods. Background Art

[0002] Calcium fluoride (CaF2) is an inorganic compound that is a colorless crystal or white powder. It is insoluble in water, slightly soluble in inorganic acids, and reacts with hot concentrated sulfuric acid to generate hydrofluoric acid. Laboratories generally use calcium carbonate to react with hydrofluoric acid or use concentrated hydrochloric acid or hydrofluoric acid to repeatedly treat fluorite powder to prepare calcium fluoride. The calcium fluoride mineral in nature is fluorite or fluorspar. In recent years, with the revival of my country's semiconductor industry, the demand for semiconductor materials has also increased. Calcium fluoride, as a new type of electro-optical raw material, is widely used in the production of fluorine and fluoride. Therefore, the detection of metal ions in calcium fluoride is crucial.

[0003] At present, the main methods for detecting metal ions include atomic absorption spectroscopy, atomic fluorescence spectroscopy, inductively coupled plasma atomic emission spectroscopy (ICP-OES), etc. Among these methods, inductively coupled plasma atomic emission spectroscopy is widely used in the detection of metal ion residues in battery raw materials due to its advantages such as wide linear range, high sensitivity, low interference, and ability to detect multiple ions at the same time. Sample pretreatment is the primary link in analysis and testing, and the quality of the pretreatment process directly affects the accuracy and reliability of the analysis and test results.

[0004] The commonly used pretreatment methods include microwave digestion, high temperature melting, wet digestion and dry ashing. Among them, wet digestion is widely used in sample pretreatment before ICP-OES detection due to its advantages such as fast digestion speed, short processing time, less element loss, simple equipment and suitability for large-scale sample processing.

[0005] In the original implementation standard GB / T 27804-2011 (calcium fluoride), calcium fluoride is digested with a hydrochloric acid-boric acid-sulfuric acid mixture. The specific process is: 0.50g of the calcium fluoride sample to be tested is moistened with anhydrous ethanol, 50mL of hydrochloric acid-boric acid-sulfuric acid mixture is added, and heated to a slight boil for 30 minutes, and shaken every 5 minutes. After cooling, dilute with water to 100mL, continue to heat to a slight boil, filter with fast filter paper into a volumetric flask, wash the container with warm water containing hydrochloric acid 5 times, wash the insoluble matter 10 times, and dilute and mix the test solution with water after cooling. The digestion method of calcium fluoride in the implementation standard is a relatively complicated process, which is not suitable for large-scale high-throughput digestion. At the same time, the digestion is not thorough, and more impurities are introduced, which has a great impact on the subsequent detection of metal ions in calcium fluoride. Summary of the invention

[0006] The first object of the present invention is to provide a method for digesting calcium fluoride to solve the problem that the wet digestion method used in the prior art for digesting calcium fluoride is complicated in operation, takes a long time, and cannot achieve complete digestion.

[0007] The second object of the present invention is to provide a method for measuring metal ions in calcium fluoride, and to provide a measuring method with less influence on the detection of metal ions in calcium fluoride.

[0008] In order to achieve the above object, a technical solution of a method for digesting calcium fluoride in the present invention is:

[0009] A method for digesting calcium fluoride comprises the following steps:

[0010] (1) mixing calcium fluoride, hydrofluoric acid and perchloric acid and heating until all the liquid in the system is evaporated to dryness to obtain a solid residue, and cooling;

[0011] (2) adding nitric acid to the solid residue obtained in step (1) and mixing to obtain a transparent liquid; observing whether the transparent liquid contains insoluble matter, and if not, digestion is completed; if contained, heating until the insoluble matter disappears, and digestion is completed.

[0012] The beneficial effect of the above technical scheme is that the method for digesting calcium fluoride of the present invention is a pioneering invention. Under normal conditions, calcium fluoride is a colorless crystal or white powder, which is insoluble in water and slightly soluble in inorganic acid. The present invention is aimed at the chemical properties of calcium fluoride. Through repeated experiments, it is found that by adjusting the ratio of hydrofluoric acid and perchloric acid in the digestion process, calcium fluoride can be transformed from a solid powder sample into a fluffy substance that is agglomerated together and then cooled to room temperature, and concentrated nitric acid is added again for heating, so that calcium fluoride can be completely digested. After the digestion, the sample is subjected to multiple ICP-OES tests, and the content of each metal ion can be accurately detected. At the same time, the instrument can be used normally, and there is no blockage or flameout in the instrument. It shows that the method of the present invention can thoroughly digest calcium fluoride, and has the advantages of fast digestion speed, simple operation, and no effect on the detection of metal ions in the later stage.

[0013] Specifically, the hydrofluoric acid and perchloric acid used in the present invention are both electronic grade.

[0014] As a further improvement, the mixing in step (1) is to mix calcium fluoride and hydrofluoric acid and then add perchloric acid.

[0015] The beneficial effect of the above technical solution is that: in actual operation, if calcium fluoride and perchloric acid are mixed first, a more violent heat release will occur and there will be splashing. However, mixing calcium fluoride and hydrofluoric acid first to form calcium hydrogen fluoride and then adding perchloric acid to replace anions helps to improve the safety of the digestion process.

[0016] As a further improvement, in step (1), for every 0.1-0.2 g of calcium fluoride, the corresponding amount of hydrofluoric acid used is (4-6) mL, and the amount of perchloric acid used is at least 1 mL.

[0017] As a further improvement, the volume ratio of hydrofluoric acid to perchloric acid in step (1) is (4-6):(1-2).

[0018] As a further improvement, the heating temperature in step (1) is 180-200°C.

[0019] As a further improvement, for every 0.1-0.2 g of solid residue formed by calcium fluoride, the amount of nitric acid added in step (2) is (5-6) mL.

[0020] As a further improvement, the nitric acid is a mixture of 98% concentrated nitric acid and water in a volume ratio of 1:1.

[0021] As a further improvement, the heating temperature in step (2) is 50-200°C.

[0022] In order to achieve the above object, a technical solution of a method for measuring metal ions in calcium fluoride in the present invention is:

[0023] A method for measuring metal ions in calcium fluoride comprises the following steps: using the method for digesting calcium fluoride to digest the calcium fluoride to be tested, and then detecting the metal ion content.

[0024] The beneficial effect of the above technical solution is that after the digestion, the sample is subjected to multiple ICP-OES tests, and the content of each metal ion can be accurately detected. At the same time, the instrument can be used normally without clogging or flameout.

[0025] As a further improvement, the detection method includes inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. DETAILED DESCRIPTION

[0026] At present, in the implementation standard GB / T 27804-2011 (calcium fluoride), the digestion process of calcium fluoride is a complex process and introduces a lot of impurities, which affects the subsequent detection of its metal ions. However, the present invention finds that by adjusting the ratio of hydrofluoric acid and perchloric acid in the digestion process, it can be thoroughly digested, and the digestion speed is fast, the operation is simple, and there is no effect on the subsequent detection of metal ions.

[0027] Below, the present invention is further described in conjunction with specific embodiments. It should be noted that, under the premise of no conflict, the embodiments described below or the technical features can be arbitrarily combined to form new embodiments. The equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments are all conventional methods in the art unless otherwise specified.

[0028] 1. A specific embodiment of a method for digesting calcium fluoride according to the present invention:

[0029] Example 1

[0030] The method for digesting calcium fluoride in this embodiment comprises the following steps:

[0031] (1) Weigh 0.1011 g of high-purity calcium fluoride (purity: 98.5%) into a beaker, add 4 mL of electronic grade hydrofluoric acid (HF) and 1 mL of perchloric acid (HClO4) in sequence at room temperature, transfer the beaker to an electric furnace, and heat at 180°C.

[0032] (2) There is a small amount of smoke during the heating process. After heating for 5 minutes, a large amount of smoke is generated. The high-purity calcium fluoride sample will gradually change from a white solid sample to a white fluffy substance.

[0033] (3) The sample was heated for another 1 min, and the state of the sample completely changed from a white solid sample to a white fluffy substance.

[0034] (4) After a white fluffy substance is generated, continue heating for 1 min and then cool the beaker to 25°C.

[0035] (5) Add 5 mL of electronic grade nitric acid (HNO3) (1:1) at 25°C. After the addition is completed, the sample will change from a white fluffy substance to a transparent liquid.

[0036] (6) Observe whether the transparent liquid contains insoluble matter. If not, digestion is complete. If so, transfer the beaker to an electric furnace and heat it at 50°C until the insoluble matter disappears, and digestion is complete.

[0037] Example 2

[0038] The method for digesting calcium fluoride in this embodiment comprises the following steps:

[0039] (1) Weigh 0.1020 g of high-purity calcium fluoride (purity: 97%) into a beaker, add 4 mL of electronic grade hydrofluoric acid (HF) and 1 mL of perchloric acid (HClO4) in sequence at room temperature, transfer the beaker to an electric furnace, and heat at 180°C.

[0040] (2) There is a small amount of smoke during the heating process. After heating for 5 minutes, a large amount of smoke is generated. The high-purity calcium fluoride sample will gradually change from a white solid sample to a white fluffy substance.

[0041] (3) The sample was heated for another 1 min, and the state of the sample completely changed from a white solid sample to a white fluffy substance.

[0042] (4) After a white fluffy substance is generated, continue heating for 1 min and then cool the beaker to 25°C.

[0043] (5) Add 5 mL of electronic grade nitric acid (HNO3) (1:1) at 25°C. After the addition is completed, the sample will change from a white fluffy substance to a transparent liquid.

[0044] (6) Observe whether the transparent liquid contains insoluble matter. If not, digestion is complete. If so, transfer the beaker to an electric furnace and heat it at 180°C until the insoluble matter disappears, and digestion is complete.

[0045] Example 3

[0046] The method for digesting calcium fluoride in this embodiment comprises the following steps:

[0047] (1) Weigh 0.1008 g of high-purity calcium fluoride (purity: 99%) into a beaker, add 4 mL of electronic grade hydrofluoric acid (HF) and 1 mL of perchloric acid (HClO4) in sequence at room temperature, transfer the beaker to an electric furnace, and heat at 180°C.

[0048] (2) There is a small amount of smoke during the heating process. After heating for 5 minutes, a large amount of smoke is generated. The high-purity calcium fluoride sample will gradually change from a white solid sample to a white fluffy substance.

[0049] (3) The sample was heated for another 1 min, and the state of the sample completely changed from a white solid sample to a white fluffy substance.

[0050] (4) After a white fluffy substance is generated, continue heating for 1 min and then cool the beaker to 25°C.

[0051] (5) Add 5 mL of electronic grade nitric acid (HNO3) (1:1) at 25°C. After the addition is completed, the sample will change from a white fluffy substance to a transparent liquid.

[0052] (6) Observe whether the transparent liquid contains insoluble matter. If not, digestion is complete. If so, transfer the beaker to an electric furnace and heat it at 100°C until the insoluble matter disappears, and digestion is complete.

[0053] 2. Comparison

[0054] Comparative Example 1

[0055] The method for digesting calcium fluoride in this comparative example is different from that in Example 1 only in that 3.5 mL of electronic grade hydrofluoric acid is used in step (1). The specific steps are as follows:

[0056] (1) Weigh 0.1011 g of high-purity calcium fluoride (purity: 98.5%) into a beaker, add 3.5 mL of electronic grade hydrofluoric acid (HF) and 1 mL of perchloric acid (HClO4) in sequence at room temperature, transfer the beaker to an electric furnace, and heat at 180°C.

[0057] (2) There is a small amount of smoke during the heating process. After heating for 5 minutes, a large amount of smoke is generated. The high-purity calcium fluoride sample will gradually change from a white solid sample to a white fluffy substance.

[0058] (3) The sample was heated for another 1 min, and the state of the sample completely changed from a white solid sample to a white fluffy substance.

[0059] (4) After a white fluffy substance is generated, continue heating for 1 min and then cool the beaker to 25°C.

[0060] (5) Add 5 mL of electronic grade nitric acid (HNO3) (1:1) at 25°C. After the addition is completed, the sample will change from a white fluffy substance to a transparent liquid.

[0061] (6) The transparent liquid is observed to contain obvious white insoluble matter. The beaker is transferred to an electric furnace and heated at 50°C. After heating, the white insoluble matter is still present.

[0062] Comparative Example 2

[0063] The method for digesting calcium fluoride in this comparative example is different from that in Example 1 only in that 0.95 mL of perchloric acid is used in step (1). The specific steps are as follows:

[0064] (1) Weigh 0.1011 g of high-purity calcium fluoride (purity: 98.5%) into a beaker, add 4 mL of electronic grade hydrofluoric acid (HF) and 0.95 mL of perchloric acid (HClO4) in sequence at room temperature, transfer the beaker to an electric furnace, and heat at 180°C.

[0065] (2) There is a small amount of smoke during the heating process. After heating for 5 minutes, a large amount of smoke is generated. The high-purity calcium fluoride sample will gradually change from a white solid sample to a white fluffy substance.

[0066] (3) The sample was heated for another 1 min, and the state of the sample completely changed from a white solid sample to a white fluffy substance.

[0067] (4) After a white fluffy substance is generated, continue heating for 1 min and then cool the beaker to 25°C.

[0068] (5) Add 5 mL of electronic grade nitric acid (HNO3) (1:1) at 25°C. After the addition is completed, the sample will change from a white fluffy substance to a transparent liquid.

[0069] (6) The transparent liquid is observed to contain obvious white insoluble matter. The beaker is transferred to an electric furnace and heated at 50°C. After heating, the white insoluble matter is still present.

[0070] Comparative Example 3

[0071] This comparative example uses the method in the implementation standard GB / T 27804-2011 (calcium fluoride) to digest calcium fluoride (purity of 97%). To avoid the introduction of impurities, the reagents and water used in this comparative example are electronic grade high-purity reagents and first-class water. Five groups of experiments were carried out at the same time. After the digestion was completed, it was observed that two of the five groups of experiments had insoluble precipitation and needed to be filtered.

[0072] 3. Experimental Example A method for measuring metal ions in calcium fluoride

[0073] Experimental Example 1

[0074] The calcium fluoride digested in Example 1 was subjected to ICP-OES detection. The conditions of ICP-OES detection were: plasma gas 12 L / min, auxiliary gas 0.4 L / min, nebulizer gas 0.7 L / min, power 1500 W, observation distance 15 mm, axial observation mode, peak calculation method three-point area method, and standard curve with four standard points (ppm) of 0.02501, 0.04994, 0.25, and 0.5001.

[0075] The specific process of ICP-OES detection is as follows: after preheating, perform optical initialization. After the initialization value is passed, run the calibration blank with fresh ultrapure water. When the calibration blank is less contaminated (optical intensity Na<1000, As<300), use the above-mentioned standard sample points to establish a calibration curve. When the linear fit of all elements to be detected is above 0.999, start detection.

[0076] The results are shown in Table 1, where the cations are the average of ten results detected by ICP-OES.

[0077] Table 1 Average results of ten tests of calcium fluoride samples prepared in Example 1

[0078] Detection elements Fe As Na K Co Mn Pb Cr Cu Zn Al Cd Element results (ppm) 0.09 0.41 0.55 0.33 0 0.02 0 0 0.11 0 0 0 variance <![CDATA[1.6e -4 ]]> <![CDATA[6.9e -4 ]]> <![CDATA[5.4e -4 ]]> <![CDATA[9.1e -4 ]]> 0 <![CDATA[6.7e -5 ]]> 0 0 <![CDATA[4.2e -4 ]]> 0 0 0

[0079] Experimental Example 2

[0080] The calcium fluoride digested in Example 2 was subjected to ICP-OES detection, and the specific operation was as shown in Experimental Example 1.

[0081] The results are shown in Table 2, where the cations are the average of ten results detected by ICP-OES.

[0082] Table 2 Average results of ten tests of calcium fluoride samples prepared in Example 2

[0083] Detection elements Fe As Na K Co Mn Pb Cr Cu Zn Al Cd Element results (ppm) 0.12 0.48 0.57 0.28 0 0.01 0 0 0.12 0 0 0 variance <![CDATA[1.7e -4 ]]> <![CDATA[3.5e -4 ]]> <![CDATA[2.3e -4 ]]> <![CDATA[9.2e -4 ]]> 0 <![CDATA[7e -4 ]]> 0 0 <![CDATA[2.2e -4 ]]> 0 0 0

[0084] Experimental Example 3

[0085] The calcium fluoride digested in Example 3 was subjected to ICP-OES detection, and the specific operation was as shown in Experimental Example 1.

[0086] The results are shown in Table 3, where the cations are the average of ten results detected by ICP-OES.

[0087] Table 3 Average results of ten tests of calcium fluoride samples prepared in Example 3

[0088] Detection elements Fe As Na K Co Mn Pb Cr Cu Zn Al Cd Element results (ppm) 0.12 0.48 0.53 0.28 0 0.01 0 0 0.12 0 0 0 variance <![CDATA[2e -4 ]]> <![CDATA[8.5e -4 ]]> <![CDATA[6.3e -4 ]]> <![CDATA[9.7e -4 ]]> 0 <![CDATA[8e -5 ]]> 0 0 <![CDATA[5.2e -4 ]]> 0 0 0

[0089] Experimental Example 4

[0090] The samples that do not need to be filtered (one of the groups without insoluble matter) and the filtered samples (a group of filtered liquids with insoluble matter) in Comparative Example 3 were taken for ICP-OES detection respectively. The specific operation is as shown in Experimental Example 1.

[0091] The results are shown in Tables 4 and 5, where the cations are the average values ​​of ten results detected by ICP-OES.

[0092] Table 4 Average results of ten tests of calcium fluoride samples (without filtration) prepared in Comparative Example 3

[0093]

[0094] Table 5 Average results of ten tests of calcium fluoride samples (after filtration) prepared in Comparative Example 3

[0095]

[0096] From the results of ICP-OES test in the above table, it can be seen that there is a big difference between the calcium fluoride before and after filtration after digestion. The Mn element is not detected after filtration, and the Na element suddenly increases.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The patent protection scope of the present invention shall be based on the claims. All equivalent structural changes made using the contents of the description and drawings of the present invention should also be included in the protection scope of the present invention.

Claims

1. A method for digesting calcium fluoride, characterized in that: The following steps are involved: (1) Mix calcium fluoride, hydrofluoric acid and perchloric acid and heat until all the liquid in the system is evaporated to dryness to obtain a solid residue, which is then cooled; (2) adding nitric acid to the solid residue obtained in step (1) and mixing to obtain a transparent liquid; Observe whether the transparent liquid contains insoluble matter. If not, digestion is completed. If contained, heat until the insoluble matter disappears, and digestion is completed.

2. The method for digesting calcium fluoride according to claim 1, characterized in that: The mixing in step (1) is to mix calcium fluoride and hydrofluoric acid and then add perchloric acid.

3. The method for digesting calcium fluoride according to claim 1, characterized in that: In step (1), for every 0.1-0.2 g of calcium fluoride, the corresponding amount of hydrofluoric acid used is (4-6) mL, and the amount of perchloric acid used is at least 1 mL.

4. The method for digesting calcium fluoride according to claim 3, characterized in that: The volume ratio of hydrofluoric acid to perchloric acid in step (1) is (4-6):(1-2).

5. The method for digesting calcium fluoride according to claim 1, characterized in that: The heating temperature in step (1) is 180-200°C.

6. The method for digesting calcium fluoride according to claim 1, characterized in that: For every 0.1-0.2 g of solid residue formed by calcium fluoride, the amount of nitric acid added in step (2) is (5-6) mL.

7. The method for digesting calcium fluoride according to claim 6, characterized in that: The nitric acid is prepared by mixing 98% concentrated nitric acid and water in a volume ratio of 1:

1.

8. The method for digesting calcium fluoride according to any one of claims 1 to 7, characterized in that: The heating temperature in step (2) is 50-200°C.

9. A method for measuring metal ions in calcium fluoride, characterized in that: After the calcium fluoride to be tested is digested using the method for digesting calcium fluoride according to any one of claims 1 to 8, the metal ion content is detected.

10. The method for measuring metal ions in calcium fluoride according to claim 9, characterized in that: The detection method includes inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry.

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