Method for determining ultra-low content of thallium in iron ore

Abstract

The application provides a method for determining ultra-low content thallium in iron ore, which adopts an extraction separation method to extract thallium from a multi-component test solution containing iron, calcium, aluminum and silicon, realizes separation and enrichment, and then determines by using an inductively coupled plasma emission spectrometer; the application utilizes the chemical properties of thallium and alkane compounds containing active oxygen substituents represented by 4-methyl-2-pentanone, adopts an extraction method for separation and enrichment, establishes a suitable analysis method, and completes the detection of ultra-low content thallium in ore.

Description

Technical Field

[0001] This invention relates to the field of determining ultra-low content of thallium, an environmentally friendly element, in iron ore, belonging to the fields of chemistry and metallurgy. Specifically, it relates to a method for determining the thallium content in iron ore, and more particularly to a method for determining ultra-low content of thallium in iron ore. Background Technology

[0002] Thallium (Tl) is a highly toxic element. Thallium pollutants in the environment mainly originate from smelting residues of thallium-rich ores (such as zinc, iron, and copper ores), including dust and slag. In recent years, the environmental hazards caused by thallium have increasingly attracted attention. Due to its high toxicity, thallium has been listed as one of the priority toxic elements for pollution control in my country. Steel plants consume approximately ten million tons of iron ore annually, and production water is recycled. Even if the thallium content in the iron ore is extremely low, it will accumulate continuously during the steelmaking process due to the use of different raw materials and the recycling of production processes. This eventually leads to the accumulation of thallium in industrial wastewater or waste residue, causing significant harm to the environment and human health. Therefore, the determination of thallium content in iron ore is imperative. Establishing an accurate, simple, efficient, and low-investment method for thallium determination as soon as possible is of great significance for production material control, procurement planning, and environmental protection. Currently, thallium is mainly determined by spectrophotometry, electrochemical methods, titration, atomic absorption spectrometry (graphite furnace method), and inductively coupled plasma mass spectrometry (ICP-MS). Among the existing standards, ICP-MS is used for the determination of ultra-low thallium content. The national standard GB / T 6730.81-2020, "Determination of Multiple Trace Elements in Iron Ore by Inductively Coupled Plasma Mass Spectrometry," specifies a thallium detection range of 0.10 mg / kg to 100 mg / kg. However, due to the high cost of ICP-MS instruments, many testing institutions and production laboratories lack the necessary equipment. Other analytical methods suffer from drawbacks such as cumbersome operation, high skill requirements for operators, failure to meet detection limits, and unstable results. It should be noted that the thallium content in smelting raw materials such as iron ore in the steel industry is generally extremely low (Tl% < 0.0001% or Tl concentration < 1 ug / g), which is far beyond the minimum detection limit of inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0003] In summary, the existing technologies have the following problems: the inductively coupled plasma mass spectrometry method for the determination of ultra-low thallium content is expensive, while the inductively coupled plasma atomic emission spectrometry (ICP-AES) method results in the detection limit not meeting the requirements. In addition, other analytical methods have drawbacks such as cumbersome operation, high requirements for operators, and unstable measurement results. Summary of the Invention

[0004] This invention provides a method for determining ultra-low thallium content in iron ore, which solves the problems of the prior art where inductively coupled plasma mass spectrometry is expensive for determining ultra-low thallium content, and the detection limit is not met when using inductively coupled plasma atomic emission spectrometry (ICP-AES). It also avoids the drawbacks of other analytical methods, such as cumbersome operation, high requirements for operators, and unstable measurement results.

[0005] Therefore, this invention proposes a method for determining the thallium content in iron ore, and more particularly a method for determining ultra-low thallium content in iron ore.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for determining ultra-low thallium content (Tl% < 0.0001% or Tl concentration < 1 μg / g) in iron ore, wherein the method employs an extraction separation method to extract thallium from a multi-component sample solution containing iron, calcium, aluminum, and silicon, achieving separation and enrichment, and then performs determination using inductively coupled plasma atomic emission spectrometry. The specific steps of the method for determining ultra-low thallium content in iron ore are as follows:

[0008] S1: Preparation of sample mother liquor: Add aqua regia and hydrofluoric acid to the sample until it is completely dissolved to obtain a solution. Evaporate the solution until the brown fumes are completely removed and the sample is in the form of wet salt. Then add hydrochloric acid to dissolve, filter, and heat to evaporate and reduce the volume of the solution to obtain the sample mother liquor.

[0009] S2: Extraction with the organic solvent 4-methyl-2-pentanone to obtain 4-methyl-2-pentanone extract;

[0010] S3: Separation and Enrichment

[0011] The 4-methyl-2-pentanone extract was evaporated to dryness, then nitric acid was added, and the mixture was heated on a hot plate until there was a volume remaining. After cooling, the solution was diluted to volume in a volumetric flask and shaken well to prepare the test solution for analysis.

[0012] S4: The content of thallium in the test solution was determined by inductively coupled plasma atomic emission spectrometry.

[0013] Furthermore, the preparation of the sample mother liquor in S1 specifically includes: weighing 0.5-2g of sample into a beaker, adding 40-200mL of aqua regia and 2-4mL of hydrofluoric acid to completely dissolve it at high temperature, evaporating the solution until the remaining volume is 3mL, when the brown fumes have completely evaporated and the sample is in the form of wet salt, removing it, cooling it, adding 2-10mL of hydrochloric acid to dissolve the salts, removing it, cooling it, filtering it, and heating it to evaporate and shrink the solution volume to 10-20mL as the sample mother liquor.

[0014] Furthermore, step S2 specifically includes the following steps:

[0015] A. Transfer the sample mother liquor from S1 into a colorimetric tube, add ascorbic acid, and shake until the ascorbic acid is completely dissolved to obtain solution one;

[0016] B. Weigh ammonium iodide and ascorbic acid into a beaker, add water to dissolve, mix and dilute to obtain ammonium iodide-ascorbic acid solution. Add the ammonium iodide-ascorbic acid solution to solution one, shake and mix to obtain solution two.

[0017] C. Add the organic solvent 4-methyl-2-pentanone to solution 2 and perform fractional extraction to obtain 4-methyl-2-pentanone extract.

[0018] Further, step A specifically includes: adding 0.5-2g of ascorbic acid to the sample mother liquor in S1 in a 50mL colorimetric tube, and shaking until the ascorbic acid is completely dissolved;

[0019] The preparation of the ammonium iodide-ascorbic acid solution in step B specifically includes: weighing 26g of ammonium iodide and 20g of ascorbic acid into a beaker, adding an appropriate amount of water to dissolve and mix, and then diluting to 100mL.

[0020] Furthermore, step B also includes: adding 5-10 mL of ammonium iodide-ascorbic acid solution to solution one and shaking well.

[0021] Further, step C specifically includes: adding the organic solvent 4-methyl-2-pentanone to solution two for a first extraction, allowing it to stand until the layers separate, and separating the first extract of 4-methyl-2-pentanone and the lower mother liquor; extracting the lower mother liquor twice more using the same method to obtain the second extract of 4-methyl-2-pentanone and the third extract of 4-methyl-2-pentanone, respectively; and finally combining the first extract of 4-methyl-2-pentanone, the second extract of 4-methyl-2-pentanone, and the third extract of 4-methyl-2-pentanone to obtain the combined extract of 4-methyl-2-pentanone.

[0022] Furthermore, in the first extraction, the amount of 4-methyl-2-pentanone used was 1 / 5 of the volume of the mother liquor in S1, and in the second and third extractions, the amount of 4-methyl-2-pentanone used was the same as in the first extraction.

[0023] Furthermore, each extraction was performed for 2 minutes, followed by a 15-minute standing period.

[0024] Further, the separation and enrichment in S3 specifically includes: placing the 4-methyl-2-pentanone extract from step C into a boiling water bath or a fully enclosed heating plate at 100°C and evaporating it to dryness, then adding 3-5 mL of nitric acid, heating and digesting on the heating plate until the volume remains at 1-2 mL, cooling, and making up to 10 mL in a volumetric flask.

[0025] Furthermore, when using inductively coupled plasma atomic emission spectrometry to determine the thallium content in the test solution, the wavelength was set to 190.856 nm.

[0026] Compared with existing technologies, this invention uses 4-methyl-2-pentanone extraction and separation method, which can effectively extract thallium from multi-component test solutions containing large amounts of iron, calcium, aluminum, silicon, etc., eliminating the interference of the matrix on the determination of low-content thallium. At the same time, it enriches the thallium in the solution, improving the detection limit of the method. It can determine and analyze ultra-low content thallium in iron ore samples. The detection limit of thallium in this invention is 0.1 μg / g, while the detection limit of thallium in existing technologies that do not use the extraction and separation method of this invention is 10 μg / g. Therefore, this invention greatly improves the detection limit of thallium. This invention uses inductively coupled plasma atomic emission spectrometry (ICP-AES) to determine ultra-low thallium content in iron ore. The measured data are compared with those obtained by inductively coupled plasma mass spectrometry (ICP-MS). The results meet the tolerance requirements for thallium in the national standard GB / T6730.81-2020 "Determination of Multiple Trace Elements in Iron Ore by Inductively Coupled Plasma Mass Spectrometry". This invention can compensate for the lack of a mass spectrometer in the laboratory. It can effectively detect thallium in iron ore, providing accurate data for environmental protection and research. The operation is simple, easy to promote and apply in production, and saves detection and analysis costs. Attached Figure Description

[0027] Figure 1 This is a comparison diagram of laterite nickel ore before extraction and separation with a pure water matrix, as presented in this invention.

[0028] Figure 2 This is a comparison diagram of the laterite nickel ore extraction and separation process and the pure water matrix of the present invention.

[0029] Explanation of reference numerals: 1. Spectrum of water-based matrix; 2. Spectrum of laterite nickel ore matrix;

[0030] in Figure 1 , Figure 2 In the mid-spectrum, wavelength is the horizontal axis (in nm) and light intensity is the vertical axis (in cps). Detailed Implementation

[0031] To provide a clearer understanding of the technical features, objectives, and effects of this invention, the invention is now described.

[0032] This invention addresses the limitations of existing laboratory inductively coupled plasma atomic emission spectrometry (ICP-AES). It explores the use of an organic solvent to effectively extract and enrich thallium from materials, enabling the quantitative determination of trace amounts of ultra-low thallium in iron ore. This provides accurate data for environmental control, research, and raw material procurement. Through extensive experiments, we determined that by utilizing the chemical properties of thallium and alkanes with active oxygen substituents, such as 4-methyl-2-pentanone, an extraction method can be employed for separation and enrichment. Excess iodide ions can form a stable complex with thallium(III) (thallium(III) is in its trivalent chemical state). Using 4-methyl-2-pentanone as the extractant in a strongly acidic system, thallium in the solution is extracted to the organic phase, effectively eliminating matrix background interference. Simultaneously, the thallium in the solution is enriched, thus achieving the goal of determining low-content thallium.

[0033] I. The method of this invention is used for the determination of ultra-low thallium content in iron ore, is easy to promote and apply in production, and has positive guiding significance for smelting production. This invention has the following key technical points and points to be protected:

[0034] 1. This invention utilizes alkane compounds containing active oxygen-substituted groups, such as 4-methyl-2-pentanone, to achieve the separation and enrichment of thallium. The thallium content in iron ore samples is generally as low as 0.1 μg / g, and the matrix is ​​complex with significant background interference. This invention employs an extraction separation method, using 4-methyl-2-pentanone to effectively extract ultra-low concentrations of thallium from the solution, eliminating the interference of the matrix on the determination of low-content thallium. The chemical structural formula of 4-methyl-2-pentanone is shown below.

[0035]

[0036] 2. This invention utilizes the combined action of ascorbic acid and iodide ions to achieve sufficient complexation of thallium(III) in the test solution. First, excess ascorbic acid is used to reduce the high content of oxidizing substances such as ferric iron in the solution, ensuring that iodide ions react fully with thallium(III) in a stable state, while avoiding interference from other metal ions, which is beneficial to the smooth progress of subsequent extraction and enrichment.

[0037] 3. This invention proposes a method for removing organic solvents after extraction and before ICP-AES determination. By evaporating the solvent to dryness at 100–140°C and then using concentrated nitric acid, the organic structure is completely destroyed, eliminating the need for a dedicated organic sample introduction system for ICP-AES and improving the method's applicability.

[0038] 4. This invention uses inductively coupled plasma atomic emission spectrometry to determine ultra-low thallium content in iron ore. The measurement results are stable and accurate. The measured data are compared with those obtained by inductively coupled plasma mass spectrometry and meet the tolerance requirements for thallium in the national standard GB / T 6730.81-2020 "Determination of the content of multiple trace elements in iron ore by inductively coupled plasma mass spectrometry".

[0039] 5. For iron ore samples with thallium content as low as 0.1 μg / g, this method can effectively achieve accurate detection of ultra-low thallium content in iron ore, providing accurate data for environmental protection and research.

[0040] II. The present invention will now be described in detail with reference to specific embodiments.

[0041] This invention provides a method for determining ultra-low thallium content in iron ore, comprising the following steps:

[0042] S1: Preparation of sample mother liquor: Add aqua regia and hydrofluoric acid to the sample until it is completely dissolved to obtain a solution. Evaporate the solution until the brown fumes are completely removed and the sample is in the form of wet salt. Then add hydrochloric acid to dissolve it, filter it, and heat it to evaporate and reduce the volume of the solution to obtain the sample mother liquor.

[0043] S2: Extraction with the organic solvent 4-methyl-2-pentanone to obtain 4-methyl-2-pentanone extract;

[0044] S3: Separation and Enrichment

[0045] The 4-methyl-2-pentanone extract was evaporated to dryness, then nitric acid was added, and the mixture was heated on a hot plate until a volume remained. After cooling, the solution was diluted to 10 mL in a volumetric flask and shaken well to prepare the test solution for analysis.

[0046] S4: The content of thallium in the test solution was determined by inductively coupled plasma atomic emission spectrometry.

[0047] The experiment will be conducted according to the steps described above, as follows:

[0048] 1. Experimental Materials and Methods

[0049] 1.1 Reagents and Equipment

[0050] Reagents: Lithium carbonate (analytical grade), nitric acid (analytical grade), hydrofluoric acid (analytical grade), hydrochloric acid (analytical grade), hydrogen peroxide (30%), nitric acid (1+3) (meaning 1 volume of concentrated nitric acid added to 3 volumes of water), ascorbic acid (analytical grade), 4-methyl-2-pentanone (99.5%); ammonium iodide.

[0051] The equipment used in this invention is an inductively coupled plasma atomic emission spectrometer.

[0052] 1.2 Experimental Methods

[0053] 1.2.1 Preparation of sample stock solution

[0054] Weigh 0.5–2 g of sample using a balance and place it in a beaker. Rinse the beaker walls with water and disperse the sample. The sample volume is m (g). Add 40–200 mL of aqua regia to the beaker and dissolve it at high temperature for a period of time. Then add 2–4 mL of hydrofluoric acid and continue heating for 10–20 minutes. Slowly add 2–4 mL of hydrogen peroxide. After the hydrogen peroxide has completely decomposed and the sample bubbles vigorously again, if a precipitate forms in the solution, add another 1–3 mL of hydrogen peroxide to clarify the solution. Evaporate the sample until the remaining volume is approximately 3 mL and the brown fumes have completely dissipated. Continue heating until the sample is in a wet salt state (do not evaporate it to dryness). Remove the sample, cool it, rinse the beaker walls with water, add 2–10 mL of hydrochloric acid to dissolve the salts, remove the sample, cool it, filter it, and heat to evaporate the solution to reduce the volume to 10–20 mL as the sample stock solution.

[0055] Note: If the sample is not completely dissolved, the residue can be mixed with lithium carbonate at a mass ratio of 1:4. The mixture is then placed in a muffle furnace at 800-950℃ for alkali dissolution for 20-40 minutes, followed by leaching with hydrochloric acid, filtration, and combination of the filtrate and the sample solution obtained by acid dissolution. The mixture is then filtered, heated and evaporated to reduce the solution volume to 10-20 mL as the sample mother liquor.

[0056] 1.2.2 Extraction, separation and enrichment to prepare test solution

[0057] 1.2.2.1 Preparation of ammonium iodide-ascorbic acid solution: Weigh 26g of ammonium iodide and 20g of ascorbic acid into a beaker, add a small amount of water to dissolve and mix well, and dilute to 100mL;

[0058] 1.2.2.2 Preparation of the test solution: Take the sample stock solution into a 50 mL colorimetric tube, add 0.5–2 g of ascorbic acid, shake well until the ascorbic acid is completely dissolved, add 5–10 mL of ammonium iodide-ascorbic acid solution, shake well; add 1 / 5 volume of 4-methyl-2-pentanone of the sample stock solution, shake to extract for about 2 min, let stand for 15 min, carefully pipette most of the upper organic phase into a 50 mL beaker, and then add the above solution in the same manner. Extract the same volume of 4-methyl-2-pentanone twice more, combine the organic phases, and evaporate the mixture to dryness in a boiling water bath or a fully enclosed heating plate at 100°C (avoid open flame). Then add 3-5 mL of nitric acid to the beaker and heat on the heating plate until the volume is reduced to 1-2 mL (avoid evaporation to dryness during this process). Cool and dilute to a 10 mL volumetric flask as the test solution. The volume of the test solution is V (mL). If the test solution is turbid, it should be filtered dry before the determination.

[0059] 1.2.2.3 Preparation of Standard Working Curve

[0060] Pipette 1.00 mL of thallium standard solution GBW(E)082135 (1000 μg / L) into a 100 mL volumetric flask and dilute to the mark. GBW(E)082135 is the national standard material for thallium. Shake well. Then, pour 0.00, 0.40, 1.00, 2.00, 5.00, and 10.00 mL of thallium standard solution into 100 mL volumetric flasks respectively, dilute to the mark with nitric acid (1+10) (meaning 1 volume of concentrated nitric acid added to 10 volumes of water), and shake well. Using the instrument operating parameters shown in Table 1, inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to determine the results, and a working curve was plotted. The curve R... 2 ≥0.999 (The concentration of the standard solution can be adjusted according to the sensitivity of different instruments and the concentration range of the sample to be tested).

[0061] Table 1 Instrument Operating Parameters

[0062]

[0063]

[0064] 1.2.2.4 Preparation of blank matrix solution

[0065] Except for the absence of a sample, the other steps are the same as those for preparing the test solution.

[0066] 1.2.2.5 Measurement and Data Processing

[0067] Before the determination, select the optimal operating conditions according to the properties of the analyte and the instrument's operating manual. Refer to Table 1 for the operating condition settings of the inductively coupled plasma atomic emission spectrometer (ICP-AES). The recommended analytical wavelength for thallium is 190.856 nm. Under specific instrument operating conditions, determine a series of standard solutions in ascending order of concentration and plot a standard curve. Measure the blank solution (blank matrix) and the sample solution (test sample) under the same conditions. Obtain the concentration C (μg / mL) of the test sample solution Tl from the standard curve, which is used to calculate the content of the analyte in the actual sample. The formula for calculating the thallium content in the sample is as follows (unit: μg / g):

[0068]

[0069] In the formula:

[0070] W --- Thallium content (μg / g);

[0071] C---The concentration of Tl in the test solution (μg / mL) measured by the instrument;

[0072] V --- The total volume (mL) of the test solution measured by the instrument;

[0073] m --- Sample size (g)

[0074] 2. Effectiveness of the detection method

[0075] 2.1 This method has high recovery rate and good repeatability.

[0076] Since there is no standard sample of thallium in iron ore, we used the following two methods to perform spiked recovery experiments on the solution.

[0077] 2.1.1 Weigh 1.0000g of iron ore sample and add 65% iron matrix (the iron matrix is ​​a high-purity iron solution; the iron content in the iron ore is about 65%, so a 65% high-purity iron solution is added as the iron matrix) using the method of this invention. Prepare standard solutions for low, medium, and high thallium content, and after processing with the same extraction, separation, and enrichment method, perform repeatability tests. The average values ​​of low, medium, and high thallium content were measured to be 0.041μg / g, 0.50μg / g, and 1.01μg / g, respectively, with RSD≦7%. The spiked recovery rate can reach 95.00~106.00%, and the results are shown in Table 2.

[0078] Table 2. Record of thallium standard solution spiked recovery and repeatability test data.

[0079]

[0080] 2.1.2 We used iron ore sample BD003 (Tl = 0.001 μg / g) (BD003 is the iron ore sample number) for thallium content determination using the national standard GB / T 6730.81-2020 "Determination of Multiple Trace Elements in Iron Ore by Inductively Coupled Plasma Mass Spectrometry" for spike recovery experiments. The average values ​​of low and medium thallium contents were 0.051 μg / g and 0.51 μg / g, respectively, with RSD ≤ 5%. The spike recovery rate reached 94.00–106.00%, confirming that the spike recovery rate of this method with iron ore as the matrix also meets the detection requirements. The results are shown in Table 3.

[0081] Table 3. Record of Thallium Spike Recovery and Repeatability Data in Iron Ore Matrix

[0082]

[0083] 2.2 Good effect in eliminating substrate background

[0084] Iron ore samples have complex matrices and strong background interference. We used inductively coupled plasma atomic emission spectrometry (ICP-AES) to compare the spectra before and after extraction, separation, and enrichment. (The spectra are plotted with wavelength on the x-axis (nm) and light intensity on the y-axis (cps). Before extraction, separation, and enrichment, the sample... Figure 1 As shown, using water-based spectra Figure 1 For comparison, the matrix spectrum of laterite nickel ore Figure 2 High background noise and significant interference; after extraction, separation, and enrichment, such as Figure 2 As shown, water-based spectrum Figure 1 Background and matrix spectrum of lateritic nickel ore Figure 2 The backgrounds are not much different.

[0085] 2.3 Accuracy Verification

[0086] The results obtained by the present invention for iron ore samples were compared with those obtained by mass spectrometry. The data results are shown in Table 4. As can be seen from Table 4, the present invention can effectively detect ultra-low thallium content in the samples. The results obtained by the present invention are within the allowable error range compared with those obtained by mass spectrometry. The analytical results of the present invention are accurate and reliable.

[0087] Table 4. Determination data of thallium in iron ore samples (Note: 1 μg / g = 1 mg / kg; data for BD003 were mentioned above, Tl = 0.001 μg / g, exceeding the detection limit of this method, and was used as the matrix above; Tl for BD006 = 0.003 μg / g, exceeding the detection limit of this method).

[0088]

[0089] 2.4 Precision Verification

[0090] Three iron ore samples were randomly selected, and each sample was measured 10 times according to this method. As shown in Table 5, the RSD of the measurement results is <7%, which proves that the method has good precision.

[0091] Table 5. Precision experimental data of thallium in iron ore samples (Note: 1 μg / g = 1 mg / kg)

[0092]

[0093]

[0094] Iron ore samples often exhibit complex matrices and strong background interference. This invention employs a 4-methyl-2-pentanone extraction method to effectively extract thallium from multi-component solutions containing high levels of iron, calcium, aluminum, and silicon, thus eliminating matrix interference in the determination of low-content thallium. The extraction method enriches thallium in the solution, improving the detection limit and enabling the determination of ultra-low thallium content in iron ore samples. Furthermore, this invention utilizes inductively coupled plasma atomic emission spectrometry (ICP-AES) to determine ultra-low thallium content in iron ore, and the measured data are compared with those obtained by ICP-AES mass spectrometry, conforming to the national standard GB / T. The tolerance requirements for thallium in standard 6730.81-2020, "Determination of the Content of Multiple Trace Elements in Iron Ore by Inductively Coupled Plasma Mass Spectrometry," can compensate for the lack of a mass spectrometer in laboratories and save on testing costs. This invention can effectively detect thallium in iron ore, providing accurate data for environmental protection and research. In addition, this invention is simple to operate and easy to promote and apply in production, and the equipment used is available in conventional iron and steel smelting production laboratories.

[0095] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the invention. The various components of the present invention can be combined with each other without conflict. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for determining ultra-low thallium content in iron ore, characterized in that, The iron content in the iron ore is 65%. The method for determining the ultra-low thallium content in the iron ore employs an extraction separation method to extract thallium from a multi-component test solution containing iron, calcium, aluminum, and silicon, achieving separation and enrichment. Then, inductively coupled plasma atomic emission spectrometry (ICP-AES) is used for determination. The specific steps of the method for determining the ultra-low thallium content in the iron ore are as follows: S1: Preparation of sample mother liquor: Add aqua regia and hydrofluoric acid to the sample until it is completely dissolved to obtain a solution. Evaporate the solution until the brown fumes are completely removed and the sample is in the form of wet salt. Then add hydrochloric acid to dissolve, filter, and heat to evaporate and reduce the volume of the solution to obtain the sample mother liquor. S2: Extraction with the organic solvent 4-methyl-2-pentanone to obtain 4-methyl-2-pentanone extract; S3: Separation and Enrichment The 4-methyl-2-pentanone extract was evaporated to dryness, then nitric acid was added, and the mixture was heated on a hot plate until there was a volume remaining. After cooling, the solution was diluted to volume in a volumetric flask and shaken well to prepare the test solution for analysis. S4: The content of thallium in the test solution was determined by inductively coupled plasma atomic emission spectrometry. The preparation of the sample mother liquor in S1 specifically includes: weighing 0.5-2 g of sample into a beaker, adding 40-200 mL of aqua regia and 2-4 mL of hydrofluoric acid to completely dissolve it at high temperature, evaporating the solution until the remaining volume is 3 mL, when the brown fumes have completely evaporated and the sample is in the form of wet salt, removing it, cooling it, adding 2-10 mL of hydrochloric acid to dissolve the salts, removing it, cooling it, filtering it, and heating it to evaporate and shrink the solution volume to 10-20 mL as the sample mother liquor; Step S2 specifically includes the following steps: A. Transfer the sample mother liquor from S1 into a colorimetric tube, add ascorbic acid, and shake until the ascorbic acid is completely dissolved to obtain solution one; B. Weigh ammonium iodide and ascorbic acid into a beaker, add water to dissolve, mix and dilute to obtain ammonium iodide-ascorbic acid solution. Add the ammonium iodide-ascorbic acid solution to solution one, shake and mix to obtain solution two. C. Add the organic solvent 4-methyl-2-pentanone to solution 2 and perform fractional extraction to obtain 4-methyl-2-pentanone extract; The specific steps of separation and enrichment in S3 are as follows: the 4-methyl-2-pentanone extract combined solution from step C is placed in a boiling water bath or a 100°C fully enclosed heating plate to evaporate to dryness, then 3-5 mL of nitric acid is added, and the solution is heated and digested on the heating plate until the volume remains 1-2 mL. After cooling, the volume is adjusted to 10 mL in a volumetric flask. When determining the thallium content in the test solution using inductively coupled plasma atomic emission spectrometry, the wavelength was set to 190.856 nm.

2. The method for determining ultra-low thallium content in iron ore according to claim 1, characterized in that, Step A specifically includes: adding the sample mother liquor from S1 into a 50mL colorimetric tube, adding 0.5-2g of ascorbic acid, and shaking until the ascorbic acid is completely dissolved; The preparation of the ammonium iodide-ascorbic acid solution in step B specifically includes: weighing 26g of ammonium iodide and 20g of ascorbic acid into a beaker, adding an appropriate amount of water to dissolve and mix, and then diluting to 100mL.

3. The method for determining ultra-low thallium content in iron ore according to claim 1, characterized in that, Step B further includes: adding 5-10 mL of ammonium iodide-ascorbic acid solution to solution one and shaking well.

4. The method for determining ultra-low thallium content in iron ore according to claim 1, characterized in that, Step C specifically includes: adding the organic solvent 4-methyl-2-pentanone to solution two for a first extraction, allowing it to stand until the layers separate, and obtaining the first extract of 4-methyl-2-pentanone and the lower mother liquor; extracting the lower mother liquor twice more using the same method to obtain the second extract of 4-methyl-2-pentanone and the third extract of 4-methyl-2-pentanone, respectively; and finally combining the first extract of 4-methyl-2-pentanone, the second extract of 4-methyl-2-pentanone, and the third extract of 4-methyl-2-pentanone to obtain the combined extract of 4-methyl-2-pentanone.

5. The method for determining ultra-low thallium content in iron ore according to claim 4, characterized in that, In the first extraction, the amount of 4-methyl-2-pentanone used was 1 / 5 of the volume of the mother liquor in S1. In the second and third extractions, the amount of 4-methyl-2-pentanone used was the same as in the first extraction.

6. The method for determining ultra-low thallium content in iron ore according to claim 1, characterized in that, Extract for 2 minutes each time, then let stand for 15 minutes.

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