Method for determining tin content in fuming furnace waste residue through composite alkali fusion ICP-AES

Abstract

The invention provides a method for determining the tin content in fuming furnace waste residues through composite alkali fusion ICP-AES, and belongs to the technical field of chemical analysis and testing. The fuming furnace waste residues to be treated are taken, a composite alkali flux is added into the fuming furnace waste residues to be treated and mixed to be uniform, and the composite alkali flux is a mixture of sodium peroxide and sodium carbonate; the method comprises the following steps: heating a mixture containing fuming furnace waste residues and a composite alkali flux to 400-700 DEG C, and carrying out gradient melting; after fusion is completed, transferring a melt into water for leaching, acidizing a product obtained by leaching, filtering, and fixing the volume of filtrate to obtain a solution to be detected; and preparing a standard solution and a blank solution, determining in an inductively coupled plasma emission spectrometer, and obtaining the tin content in the fuming furnace waste residue according to the obtained working curve. The method is applied to determination of low tin content, and the tin content in the tin-containing waste slag of the fuming furnace can be rapidly and accurately determined.

Description

Technical Field

[0001] This application relates to a method for determining the tin content in fuming furnace slag using a composite alkali fusion ICP-AES, which belongs to the field of chemical analysis and testing technology. Background Technology

[0002] Tin, as an important metallic element, has wide applications in various industrial fields such as electronics, chemicals, and food, both in its elemental form and in its compounds. In recent years, with the continuous depletion of tin resources, its price has gradually increased, and the composition of raw materials has become increasingly complex. Fuming tin smelting technology has made significant progress in extracting tin resources from tin-containing slag and tailings, becoming an economically feasible method. A certain amount of tin usually remains in the slag from fuming furnaces; the tin content not only directly affects the control of the fuming furnace process but is also an important indicator for judging the economic benefits of resource extraction and utilization. Therefore, developing a rapid and accurate method for determining the tin content in tin-containing slag from fuming furnaces is of great significance.

[0003] Methods for determining tin mainly include iodometric titration, atomic absorption spectrometry, and ICP-AES. These methods suffer from drawbacks such as long sample preparation and testing cycles, complex processes, and low efficiency. Current methods for detecting low-content tin have the following limitations.

[0004] (I) Iodometric method: The national standard method for determining the tin content in minerals is the iodometric method, which is cumbersome to operate and only applicable to minerals with a content of more than 0.2%. Especially in the determination of low tin content, such as tin-containing waste slag from fuming furnaces (Sn≤0.25%), the detection limit of the iodometric method is high and cannot meet the determination requirements. The color change at the endpoint of some samples is not obvious, which can easily lead to over- or under-titration. The error in judging the titration endpoint affects the accuracy of the determination results. Moreover, the main chemical components of tin-containing waste slag from fuming furnaces include Fe 27-32%, SiO2 27-32%, CaO 13-17%, and S 0.2-0.4%. Tin in it mainly exists in the form of SnO (“Current Status and Prospect of Tin Smelting Technology Development”, Wang Hongbin, China Nonferrous Metals, 2017, 2(1)), which is difficult to dissolve in common inorganic acids. Using HF to treat the sample will lead to the loss of tin.

[0005] (II) Photometric Method: Photometric determination of tin has significant limitations. The sensitivity and selectivity of the colorimetric reaction are insufficient, some colorimetric reagents have slow reaction rates and poor product stability, and are easily affected by light / temperature, leading to fading. Coexisting ions (such as Fe) 3+ Cu 2+ It easily complexes with colorimetric reagents, interfering with the colorimetric system, requiring masking or pre-separation, and making the analytical operation highly complex.

[0006] (III) Atomic Absorption Spectrometry: When determining low-content tin using atomic absorption spectrometry, matrix effects cause significant interference. Other components can alter the atomization conditions or form non-volatile compounds with tin, reducing the sensitivity of the determination. Furthermore, this method is complex to operate, limiting its widespread application.

[0007] Therefore, considering the composition and structural characteristics of tin-containing waste slag from fuming furnaces, sample pretreatment becomes a crucial step. To date, there are no literature reports on methods suitable for determining low tin content in tin-containing waste slag from fuming furnaces. Summary of the Invention

[0008] In view of this, this application provides a method for determining the tin content in fuming furnace slag using a composite alkaline fusion ICP-AES, which enables rapid and accurate determination of tin-containing slag with a tin content of less than 0.2%, thereby solving the problems of long determination cycle, complex process, low efficiency, and unsuitability for determining low tin content in existing methods.

[0009] Specifically, this application is implemented through the following scheme:

[0010] A method for determining the tin content in fuming furnace waste residue using a composite alkaline fusion ICP-AES method comprises the following steps:

[0011] Step 1: Take the waste residue from the fuming furnace to be treated, add a composite alkali flux to it and mix it evenly. The composite alkali flux is a mixture of sodium peroxide and sodium carbonate.

[0012] Step 2: The mixture containing the fuming furnace waste and the composite alkali flux is heated to 400-700℃ and subjected to gradient melting.

[0013] Step 3: After melting is complete, transfer the molten material to water for extraction at a temperature of 70-80℃.

[0014] Step 4: Acidify the product obtained from leaching, filter it, and dilute the filtrate to a final volume to obtain the solution to be tested.

[0015] Step 5: Prepare standard solution and blank solution, and measure them in an inductively coupled plasma atomic emission spectrometer. Based on the obtained working curve, obtain the tin content in the fuming furnace waste residue.

[0016] Furthermore, as a preferred option:

[0017] In step one,

[0018] In the composite alkali flux, the mass ratio of sodium peroxide to sodium carbonate is 8-9:1.

[0019] In step two,

[0020] The gradient melting refers to: raising the temperature to 400-500℃ for the first stage of melting, with the first stage melting lasting 10-15 minutes, and then raising the temperature to 600-700℃ for constant melting until complete melting. More preferably, the first stage melting temperature is 400℃, and the second stage melting temperature is 700℃.

[0021] In step four,

[0022] The pH value in the acidification treatment is 1 to 2, and the acidification treatment time is 10 to 20 minutes.

[0023] The acidification process involves the addition of hydrochloric acid, with a concentration of 40-50%.

[0024] The acidification process involves heating to a gentle boil to promote dissolution.

[0025] The concentration of hydrochloric acid in the solution to be tested is 10-15%.

[0026] In step five,

[0027] The standard solutions include tin standard storage solutions and tin standard solutions.

[0028] The tin standard storage solution is a hydrochloric acid solution of pure tin, with 0.5 mg of tin per ml.

[0029] The preparation process of tin standard storage solution is as follows: Weigh 0.5000g of pure tin (mass fraction ≥99.99%) and add 200ml of dilute hydrochloric acid (50%). After it is completely dissolved, transfer it to a 1000ml volumetric flask, add 50ml of hydrochloric acid (commercially available analytical grade), dilute with water to the mark, and shake well.

[0030] The tin standard solution is obtained by diluting the tin standard storage solution, and 1 ml of the solution contains 50 μg of tin.

[0031] The preparation process of tin standard solution is as follows: Transfer 10.00 ml of tin standard stock solution into a 100 ml volumetric flask, add 10 ml of hydrochloric acid (commercially available analytical grade), dilute with water to the mark, and shake well.

[0032] The method for preparing the blank solution is as follows:

[0033] S1, without adding the waste residue from the fuming furnace to be tested, obtain a blank sample solution following steps one through four.

[0034] S2. Add 0 ml, 0.20 ml, 0.50 ml, 1.00 ml, and 2.00 ml of tin standard solution (1 ml of tin standard solution contains 50 μg of tin) to five 100 ml volumetric flasks respectively. Then add blank test solution and 20 ml of hydrochloric acid (1+1) to each flask. Finally, add water to dilute to the mark and mix well to obtain the blank solution.

[0035] The measurement parameters of the inductively coupled plasma atomic emission spectrometer are set as follows:

[0036] The radio frequency power is 1400-1450W.

[0037] The observation method is axial.

[0038] Atomizer back pressure <280kPa.

[0039] The atomization chamber gas flow rate is 0.6–0.7 L / min, the pump flow rate is 1.5–1.8 ml / min, the plasma flow rate is 15–17 L / min, and the auxiliary gas flow rate is 0.2–0.3 L / min.

[0040] The beneficial effects of this application can be summarized as follows:

[0041] First, in the sample pretreatment method, a composite alkaline flux of sodium peroxide (Na2O2) and sodium carbonate (Na2CO3) is used to melt and decompose the tin-containing waste slag from the fuming furnace. This not only solves the problem of incomplete sample decomposition by a single Na2O2 flux, but also effectively solves the problem that tin in the sample exists in the form of SnO and is difficult to dissolve in common inorganic acids. It avoids tin loss caused by HF treatment of the sample, improves the efficiency and accuracy of sample pretreatment, eliminates the need for hazardous chemicals such as hydrofluoric acid and potassium iodide, and reduces the difficulty of waste liquid treatment.

[0042] Secondly, the melting process employs gradient temperature control. The first stage of melting is at a relatively low temperature, effectively reducing sample splashing during heating and ensuring the stability and safety of the experimental operation. Subsequent isothermal melting ensures complete melting of the sample, improving melting efficiency and thorough sample decomposition, providing a solid foundation for subsequent analysis and detection. Combined with dynamic matrix matching (such as standard solutions and blank solutions), high concentrations of Na are effectively excluded. + Matrix interference problem.

[0043] Third, the obtained sample is acidified in steps by hot water leaching, cooling, slow acidification to pH 1-2, and finally acidification to 10-15% in the test solution. The reaction rate and acidity gradient are controlled during the stepwise acidification process. Combined with the settings of parameters such as radio frequency and observation method in inductively coupled plasma atomic emission spectrometry (ICP-AES), rapid and accurate determination of low-content tin in tin-containing waste slag from fuming furnaces is achieved. Compared with traditional iodometric and atomic absorption methods, the reliability and repeatability of the results obtained by this invention are significantly improved, enhancing its application and accuracy. It features a short determination cycle, simple operation, high efficiency, and applicability to samples with tin content below 0.2%, broadening the determination range. The detection limit reaches 0.001% (mass fraction), a 200-fold increase in sensitivity compared to the traditional iodometric method (0.2%), filling the technological gap in low-content tin detection. The spiked recovery rate is 98.26-101.74%, with RSD < 2.0%, demonstrating significant advantages over other methods. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the measurement process for this application;

[0045] Figure 2 This is the working curve in this application. Detailed Implementation

[0046] In the following embodiments:

[0047] I. Reagents:

[0048] The analytical grade hydrochloric acid used was 50% by volume.

[0049] II. Detection Methods:

[0050] 1) Tin content test method: Refer to the "National Standard of the People's Republic of China, Chemical Analysis Method for Tin Ore, Determination of Tin Content by Qualitative Method" (GB / T15924-1995, Beijing: China Standards Press, 1996).

[0051] Expressed as mass fraction (ω), it is calculated using the following formula:

[0052]

[0053] In the formula:

[0054] ω — the mass fraction of tin, expressed as a percentage (%);

[0055] ρ—The mass concentration of tin in the test solution, in micrograms per milliliter (μg / mL);

[0056] ρ0 — The mass concentration of tin in the blank solution, in micrograms per milliliter (μg / mL);

[0057] V—Total volume of the test solution, in milliliters (mL);

[0058] V1 — Volume of test solution dispensed, in milliliters (mL);

[0059] V2 — The volume of the test solution measured, in milliliters (mL);

[0060] m — the mass of the sample, in grams (g).

[0061] 2) Operation of inductively coupled plasma atomic emission spectrometer: Refer to the "National Standard of the People's Republic of China, General Rules for Inductively Coupled Plasma Atomic Emission Spectrometry of Chemical Reagents" (GB / T23942-2009, Beijing: China Standards Press, 2010).

[0062] Example 1

[0063] In this embodiment, a Na2O2-Na2CO3 composite flux was used to melt and decompose the sample, and the tin content was determined by ICP-AES. Figure 1 The measurement process is as follows:

[0064] (1) The sample to be tested is crushed to a particle size ≤100μm, dried at around 100℃ for 2h, and then placed in a desiccator to cool to room temperature for later use.

[0065] (2) Weigh 0.3g of the sample after step (1) accurately, to the nearest 0.0001g.

[0066] (3) Using a ratio of 90wt% sodium peroxide (Na2O2) + 10wt% sodium carbonate (Na2CO3), 3g of composite alkali flux was prepared.

[0067] (4) Add composite alkali flux in a layered manner: First, take 1g of the composite alkali flux obtained in step three and place it at the bottom of a 25ml corundum crucible. Then, place the sample from step (2) on the composite alkali flux, add 1g of composite alkali flux, stir with a glass rod 7-10 times to ensure that the sample and composite alkali flux are fully mixed and uniform, and finally cover with 1g of composite alkali flux.

[0068] (5) Gradient melting: Place the corundum crucible containing the composite alkali flux and the sample into a muffle furnace that has been heated to 400°C. After processing for about 15 minutes, raise the temperature to 700°C and continue to melt at a constant temperature for 25 minutes. After the melting is complete, remove the corundum crucible, shake the melt evenly, and cool it.

[0069] (6) Place the corundum crucible and the molten material together in a 250ml beaker containing 100ml of hot water at approximately 80℃. Heat the beaker on a hot plate (temperature controlled at around 250℃) to allow the molten material to leach out completely. After the solution cools to room temperature, slowly add 50% hydrochloric acid (volume concentration) until the solution is acidified (pH value around 1) and add an excess of 60mL. Simmer the solution on the hot plate (temperature controlled at around 250℃) for 10 minutes, then remove and cool.

[0070] (7) Volume adjustment and acidity control: Transfer the solution obtained in step (6) along with the precipitate into a 250 mL volumetric flask, dilute with water to the mark, and mix well. Filter dry, discard the initial filtrate, and retain the intermediate filtrate. Take 5.00 mL of the filtrate into a 100 mL volumetric flask, add 25 mL of hydrochloric acid, dilute with water to the mark, and mix well to obtain the test solution. The acidity of the test solution should be controlled at approximately 13%.

[0071] (8) Preparation of a series of standard solutions:

[0072] 1. Tin Standard Stock Solution: Weigh 0.5000g of pure tin (mass fraction not less than 99.99%) into a 200ml beaker, add 100ml of hydrochloric acid, and after it is completely dissolved, transfer it to a 1000ml volumetric flask, add 50ml of hydrochloric acid, dilute with water to the mark, and mix well. 1ml of this solution contains 0.5mg of tin.

[0073] 2. Tin Standard Solution: Transfer 10.00 ml of tin standard stock solution to a 100 ml volumetric flask, add 10 ml of hydrochloric acid, dilute to the mark with water, and mix well. 1 ml of this solution contains 50 μg of tin.

[0074] 3. Sample blank and working curve series of standard solutions: Transfer 0 mL, 0.40 mL, 0.80 mL, 1.20 mL, 1.60 mL and 2.00 mL of tin standard solution (1 mL contains 50 μg of tin) into a set of 100 mL volumetric flasks, add 5 mL of sample blank solution (3.0 g of Na2O2-Na2CO3 formulation flux was weighed in a 25 mL corundum crucible and processed according to the sample processing method in steps (1) to (7), add 25 mL of hydrochloric acid, dilute with water to the mark, and mix well.

[0075] (9) Detection parameter settings: The detection was performed on an AVIO 220MAX inductively coupled plasma atomic emission spectrometer (PerkinElmer, USA).

[0076] The parameters of the AVIO 220MAX inductively coupled plasma atomic emission spectrometer were optimized (see Table 1), and the RF power and observation height of the instrument were optimized under the best operating conditions.

[0077] Table 1: Parameter Settings for Inductively Coupled Plasma Emission Spectrometer

[0078]

[0079] (10) Sample determination and working curve plotting

[0080] At the selected analytical spectral line of 189.99 nm, the emission intensity of tin in the test solution and the accompanying blank solution was measured, and the instrument calculated the mass concentration of tin based on the working curve.

[0081] Under the instrument operating conditions selected in Table 1, the emission intensity of a series of standard solutions was measured. A working curve was plotted with the tin mass concentration on the x-axis and the emission intensity on the y-axis (see Table 1). Figure 2 ).

[0082] The linear correlation coefficient R of the working curve 2 ≥0.999, the working curve equation is expressed as: x=0.0004y-0.0006.

[0083] 1) Determination of detection limit

[0084] The detection limit of the instrument was set at three times the standard deviation of 10 consecutive determinations of the blank solution of the sample. The detection limit was 0.001% (mass fraction), which is 200 times more sensitive than the traditional iodometric method (0.2%).

[0085] 2) Precision test

[0086] The tin content in tin-containing waste slag from a certain fuming furnace was measured in parallel five times using this method. The relative standard deviation of the measurement results was then calculated, and the results are shown in Table 2.

[0087] Table 2: Precision of the method in this application

[0088]

[0089] 3) Recovery rate experiment

[0090] To evaluate the accuracy and reliability of the assay method, a spiked recovery experiment was conducted on the above samples. A certain amount of high-purity SnO2 was added to the analytical samples, and the samples were processed according to the sample preparation method and measured in parallel five times. The average value was taken. The recovery rate was calculated, and the results are shown in Table 3.

[0091] Table 3: Spike Recovery Rate

[0092] Original content of the sample (%) spiking amount (%) Total amount measured (%) Recovery rate (%) RSD (%) 0.145 0.085 0.226 98.26 1.57 0.145 0.150 0.299 101.36 1.03 0.145 0.256 0.395 98.50 0.97 0.145 0.315 0.468 101.74 1.12 .

[0093] As shown in Table 3, the recovery rate of the samples using the method of this application is 98.26%–101.74%, and the RSD is <2.0%, which meets the analytical requirements.

[0094] In summary, the method described above for determining tin in tin-containing waste slag from fuming furnaces exhibits good precision and accuracy, meeting the measurement requirements and demonstrating high application value. The corundum crucible can be reused multiple times, reducing the cost per sample. The entire process avoids the use of hazardous chemicals such as HF and potassium iodide, simplifying wastewater treatment and conforming to green chemistry analysis standards.

[0095] Comparative Example 1

[0096] The setup of this comparative example is the same as that of Example 1, except that in step (3), the composite alkali flux is replaced with 3g of sodium peroxide (Na2O2).

[0097] Compared to Example 1, Comparative Example 1 used a single alkaline flux. The melting process exhibited the following characteristics: a significantly increased risk of violent splashing; a low decomposition temperature of Na2O2; and a single component violently decomposing and releasing O2 during the preheating stage at 400℃, leading to sample splashing losses (while Na2CO3 could buffer the exothermic rate). Simultaneously, due to the lack of Na2CO3 as a flux, the melt viscosity increased, SnO2 in the tin waste was not completely decomposed, leaving unreacted particles in some areas, and the melting uniformity decreased. The testing process showed that a large amount of colloidal precipitate was generated during acidification. Because excessive NaOH was generated after the single Na2O2 melted, local pH abrupt changes during acidification formed silica gel, which encapsulated tin ions, resulting in incomplete dissolution. The test results are shown in Table 4.

[0098] Table 4:

[0099]

[0100]

[0101] Conclusion: A single flux cannot balance oxidizing properties and melt stability, resulting in a significant deterioration in precision and accuracy. Composite alkaline flux is the core design to ensure accuracy.

[0102] Comparative Example 2

[0103] The setup of this comparative example is the same as that of Example 1, except that in step (5), the step melting is replaced by direct melting at a constant temperature of 700°C for 35 minutes.

[0104] Compared to Example 1, the comparative example used direct melting. The melting process resulted in: intensified corrosion of the corundum crucible, with the crucible weight loss rate increasing several times compared to the example (gradient melting); tin volatilization loss; and partial reduction of SnO2 to volatile SnO (tin-containing waste containing carbonaceous reducing agents) at temperatures above 650°C. The testing process showed that without a 400°C preheating stage, the organic components in the sample carbonized to form coke, which coated metal particles, and the leachate contained black residue. The test results are shown in Table 5.

[0105] Table 5:

[0106] index Comparative Example 2 Example 1 Difference Mechanism Spiked recovery rate 89.5％-94.2％ 98.3％-101.7％ Tin evaporation + package loss Crucible lifespan ≤3 times ≥10 times High-temperature corrosion accelerates

[0107] Conclusion: Gradient melting, by decomposing organic matter / sulfides in stages and avoiding high-temperature side reactions, is key to ensuring low volatility and equipment durability.

[0108] Comparative Example 3

[0109] The setup for this comparative example is the same as that for Example 1, except that the stepwise acidification is replaced with a one-step acidification, i.e., 40 mL of analytical grade hydrochloric acid is added directly.

[0110] Compared to Example 1, the comparative example used a one-step acidification process. The test process showed that the residual Na2O2 in the melt instantly released a large amount of heat and gas upon contact with concentrated hydrochloric acid, resulting in violent boiling and splashing, and significant solution loss. At the same time, the excessively high local acidity promoted the hydrolysis of silicates, producing a large amount of silica gel precipitate, especially in the slow-cooling area. The test results are shown in Table 6.

[0111] Table 6:

[0112] index Comparative Example 3 Example 1 Difference Mechanism RSD 4.6％ 1.1％ Splashing reduces the representativeness of the sample. Spiked recovery rate 85.3％-93.7％ 98.3％-101.7％ Double loss due to sedimentation and splashing linear working curve <![CDATA[R 2 =0.992]]> <![CDATA[R 2 =0.9999]]> Deposits clogging the atomizer cause signal fluctuations

[0113] Conclusion: Stepwise acidification (first hot water leaching → cooling → slow addition of acid to pH 1-2 → final acidification of about 13%) is an important design to ensure accuracy by controlling the reaction rate and pH gradient and avoiding hydrolysis and splashing.

Claims

1. A method for determining the tin content in fuming furnace waste residue using a composite alkaline fusion ICP-AES, characterized in that, The steps are as follows: Step 1: Take the waste residue from the fuming furnace to be treated, add the composite alkali flux, and mix thoroughly. The composite alkali flux is a mixture of sodium peroxide and sodium carbonate; Step 2: The mixture containing the fuming furnace waste and the composite alkali flux is heated to 400-700℃ and subjected to gradient melting. Step 3: After melting is complete, transfer the molten material to water for extraction at a temperature of 70-80℃. Step 4: Acidify the product obtained from leaching, filter, and dilute the filtrate to a final volume to obtain the solution to be tested; Step 5: Prepare standard solution and blank solution, and measure them in an inductively coupled plasma atomic emission spectrometer. Based on the obtained working curve, obtain the tin content in the fuming furnace waste residue.

2. The method for determining the tin content in fuming furnace waste slag using a composite alkali fusion ICP-AES according to claim 1, characterized in that: In the composite alkali flux, the mass ratio of sodium peroxide to sodium carbonate is 8-9:

1.

3. The method for determining the tin content in fuming furnace waste slag using a composite alkali fusion ICP-AES according to claim 1, characterized in that: In step two, the temperature is raised to 400-500℃ for the first stage of melting, which lasts for 10-15 minutes. Then, the temperature is raised to 600-700℃ and kept constant until complete melting.

4. The method for determining the tin content in fuming furnace waste slag using a composite alkali fusion ICP-AES according to claim 1, characterized in that: In step four, the pH of the acidification treatment is 1 to 2, and the acidification treatment time is 10 to 20 minutes.

5. The method for determining the tin content in fuming furnace waste slag using a composite alkali fusion ICP-AES according to claim 1, characterized in that: The acidification process involves the addition of hydrochloric acid, with a concentration of 40-50%.

6. The method for determining the tin content in fuming furnace waste slag using a composite alkali fusion ICP-AES according to claim 1, characterized in that: The concentration of hydrochloric acid in the solution to be tested is 10-15%.

7. The method for determining the tin content in fuming furnace waste slag using a composite alkali fusion ICP-AES according to claim 1, characterized in that, In step five, the standard solution includes a tin standard storage solution and a tin standard solution. The tin standard storage solution is a hydrochloric acid solution of pure tin, containing 0.5 mg of tin per ml. The tin standard solution is obtained by diluting the tin standard storage solution, and 1 ml of the solution contains 50 μg of tin.

8. The method for determining the tin content in fuming furnace waste slag using a composite alkali fusion ICP-AES according to claim 1, characterized in that, In step five, the method for preparing the blank solution is as follows: S1, without adding the waste residue from the fuming furnace to be tested, obtain a blank sample solution following steps one through four. S2, in a 100ml volumetric flask, add the tin standard solution and the blank sample solution, then add 20ml of hydrochloric acid, add water, dilute to the mark, and mix well to obtain the blank solution. S2 contains five volumetric flasks, each containing 0 ml, 0.20 ml, 0.50 ml, 1.00 ml, and 2.00 ml of tin standard solution, respectively. One ml of tin standard solution contains 50 μg of tin.

9. The method for determining the tin content in fuming furnace waste slag using a composite alkali fusion ICP-AES according to claim 1, characterized in that, In step five, the parameters for inductively coupled plasma atomic emission spectrometry (ICP-AES) are set as follows: The radio frequency power is 1400-1450W, the observation mode is axial, the atomizer back pressure is <280kpa, the atomization chamber gas flow rate is 0.6-0.7L / min, the pump flow rate is 1.5-1.8ml / min, the plasma flow rate is 15-17L / min, and the auxiliary gas flow rate is 0.2-0.3L / min.

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