Ion chromatography sample preparation method for detecting fluorine and chlorine in neodymium iron boron alloy and waste
Patent Information
- Application Number
- CN202611340238.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-09-01
- Publication Date
- 2026-10-27
AI Technical Summary
本发明提供了一种燃烧炉与离子色谱联用的样品制备方法，通过系统研究助燃剂比例、燃烧温度、燃烧时间及补水速度等关键参数对检测结果的影响，发现各参数之间存在非线性的协同关系，并在此基础上筛选出与钕铁硼基体相匹配的最优条件组合：样品与三氧化钨按质量比1:5混合，于1050℃燃烧700s，以0.35mL/min水蒸气将燃烧产生的气体带入纯水吸收池，其中样品先在氩气环境中裂解、再于氧气环境中氧化，使氟氯转化为易溶于水的HX或X2后被纯水完全吸收，最后采用离子色谱同步测定，多参数协同对比实验表明，任一参数偏离本发明限定范围均导致加标回收率显著下降（不足73%），而本发明组合可达到98%以上。
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Abstract
Description
Technical Field
[0001] This invention relates to the field of analytical chemistry, specifically to a method for preparing ion chromatography samples for the detection of fluorine and chlorine in neodymium iron boron alloys and waste. Background Technology
[0002] Neodymium iron boron (NdFeB) permanent magnet materials are widely used in new energy vehicles, wind power generation, electronic information, and aerospace. With the expansion of the industry, NdFeB waste (including production waste and end-of-life products) is increasing year by year, making its recycling of significant resource and environmental value. However, the fluorine and chlorine elements present in NdFeB and its waste can interfere with the separation and recovery of rare earth elements, corrode smelting equipment, and pose risks to the environment and human health. Therefore, accurately determining their content is a necessary prerequisite for ensuring recycling processes, controlling product quality, and reducing environmental risks.
[0003] However, NdFeB alloys possess high magnetic properties, high rare earth content (especially containing large amounts of neodymium, praseodymium, dysprosium, and other rare earth elements), and complex intermetallic compound structures. Their high-temperature combustion behavior differs significantly from that of ordinary metals, ores, or polymer materials, posing a unique challenge for detection: First, rare earth elements in NdFeB readily form high-melting-point oxides (such as Nd2O3 with a melting point of approximately 2270℃) at high temperatures. These oxide slags can encapsulate the internal sample, hindering the complete release of halogens, making complete oxidation difficult to achieve under conventional combustion conditions. Second, rare earth elements have strong coordination capabilities and may form stable rare earth halide oxides or complexes with fluorine and chlorine, causing the target elements to be trapped by the matrix during combustion, resulting in incomplete release. Third, the magnetic properties of NdFeB make the sample prone to agglomeration during grinding and weighing, affecting the uniformity of mixing with the combustion aid and further exacerbating the problem of incomplete combustion.
[0004] Existing detection methods include ion-selective electrode methods, titration methods, spectrophotometry, and turbidimetry, among others. Sample pretreatment often employs offline methods such as alkali fusion, strong acid dissolution, or steam distillation. However, all of these methods require cumbersome sample pretreatment. The use of strong acids and alkalis can easily cause personal injury and environmental damage, and the various reagents introduced can contaminate the detection system. Furthermore, the pretreatment process is time-consuming and difficult to adapt to the demands for rapid, accurate, and sensitive detection.
[0005] In recent years, combustion furnace-ion chromatography (CLC) technology has been attempted to be applied to the determination of halogens in other materials (such as coal, textiles, and copper-zinc ore). However, the sample matrix targeted by this type of method is completely different from that of NdFeB. The reported combustion accelerant ratio, combustion temperature, combustion time, and absorption conditions are all based on materials with physicochemical properties that are very different from those of NdFeB. Due to the unique high rare earth content, high melting point, and magnetic agglomeration problem of NdFeB, existing methods cannot be directly applied to the detection of fluorine and chlorine in NdFeB and its waste. For a long time, there has been a lack of mature and efficient online combustion-absorption-detection integrated solutions for NdFeB matrices. Summary of the Invention
[0006] The purpose of this invention is to provide an ion chromatography sample preparation method for the detection of fluorine and chlorine in neodymium iron boron alloys and waste, so as to realize the continuous automation of the entire process of sample combustion, absorption and ion chromatography determination.
[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing ion chromatography samples for the detection of fluorine and chlorine in neodymium iron boron alloys and waste, comprising the following steps: Step (1): Grind and pretreat the neodymium iron boron and its waste samples; Step (2): Weigh samples of neodymium iron boron and its waste materials, and perform online combustion; Step (3): Set the online combustion conditions. The sample is first cracked in an argon environment and then oxidized in an oxygen environment to convert halogens into water-soluble HX or X2. The combustion temperature is 1050℃ and the combustion time is 700s. At the same time, water vapor at a flow rate of 0.35mL / min carries the gas generated by combustion into the absorption cell. The absorbent in the absorption cell is pure water, which is used to absorb fluoride ions and chloride ions. Step (4): Collect the absorption liquid and determine the content of fluoride and chloride ions in the sample by ion chromatography; Furthermore, the grinding pretreatment conditions in step (I) are as follows: the neodymium iron boron and its waste samples are calcined at 300℃-500℃ for 1 hour, and after cooling, they are ground with a grinder until they all pass through a 200-mesh analytical sieve.
[0008] Further, in step (ii), neodymium iron boron and its waste samples are weighed and mixed with tungsten trioxide, the combustion aid, at a mass ratio of 1:5.
[0009] Furthermore, the ion chromatography method employs an anion exchange column and uses a carbonate system as the eluent for isocratic elution.
[0010] Compared with the prior art, the present invention has the following significant advantages: This invention provides a sample preparation method using a combustion furnace coupled with ion chromatography. Through a systematic study of the effects of key parameters such as the proportion of combustion aid, combustion temperature, combustion time, and water replenishment rate on the detection results, a nonlinear synergistic relationship was discovered among these parameters. Based on this, the optimal combination of conditions matching the NdFeB matrix was selected: the sample is mixed with tungsten trioxide at a mass ratio of 1:5 and burned at 1050℃ for 700s. The combustion gases are then carried into a pure water absorption cell using 0.35mL / min water vapor. The sample is first pyrolyzed in an argon environment and then oxidized in an oxygen environment, converting fluorine and chlorine into water-soluble HX or X2, which are then completely absorbed by pure water. Finally, ion chromatography is used for simultaneous determination. Multi-parameter synergistic comparison experiments show that any parameter deviating from the limits defined in this invention leads to a significant decrease in the spiked recovery rate (less than 73%), while the combination of this invention can achieve over 98%.
[0011] 2. Method validation results show that the detection limits for fluorine and chlorine are as low as 1.3 mg / kg and 5.9 mg / kg, respectively, with relative standard deviations between 1.1% and 2.1%, which are significantly better than the current standard methods. This method achieves continuous automation of the entire process of sample combustion, absorption, and ion chromatography determination without the need for strong acids or bases, avoiding pollution and loss from offline pretreatment. It fills the method gap in the field of online combustion-ion chromatography detection of NdFeB matrix and provides rapid, accurate, and reliable detection technology support for rare earth resource recycling and product quality control. Attached Figure Description
[0012] Figure 1 Comparative ion chromatograms of sample absorption solutions under different combustion conditions (with / without combustion improvers); Figure 2 A graph showing the effect of the mass ratio of combustion improver to sample on the test results; Figure 3 The graph shows the effect of combustion temperature on the measurement results. Figure 4 This is a graph showing the effect of combustion time on the measurement results. Figure 5 A graph showing the effect of water replenishment rate on the measurement results; Figure 6 A comparison graph showing the measurement results for different absorption solutions; Table 1 shows the comparison data of precision experiments and methods; Table 2 shows the spike recovery rates under different parameter combinations. Detailed Implementation
[0013] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.
[0014] Example 1
[0015] Feasibility experiment of WO3 combustion accelerant: At high temperatures, the NdFeB sample underwent pyrolysis and combustion in an atmosphere of argon and oxygen, converting the fluorine and chlorine compounds in the sample into gaseous X2 (F2, Cl). ２ ) or HX (HF, HCl), and is absorbed by the water in the absorption tank, thereby converting into F. - and Cl - The sample was then analyzed using an ion chromatograph. In this study, considering the incomplete combustion of neodymium iron boron, tungsten trioxide was used as a combustion aid.
[0016] First, the fluorine and chlorine content of tungsten trioxide itself was examined. The experiment revealed that the fluorine and chlorine content in tungsten trioxide and the blank test solution were essentially the same (e.g., ...). Figure 1 As shown in the figure, the fluorine and chlorine content of tungsten trioxide itself has no effect on this experimental study. Comparing the chromatograms of the combustion absorbents of the samples before and after the addition of tungsten trioxide revealed that the peak areas of fluorine and chlorine in the absorbent after the addition of tungsten trioxide were significantly larger than those without tungsten trioxide, indicating that tungsten trioxide has a significant promoting effect on sample combustion. Further combustion of the sample and the tungsten trioxide mixture residue after combustion showed that the fluorine and chlorine content in the absorbent was basically close to the level of the blank sample, indicating that the sample can be completely combusted after the introduction of tungsten trioxide as a combustion aid, and that fluorine and chlorine are fully converted and absorbed.
[0017] Experiments were conducted to determine the proportions of WO3 as a combustion accelerator: WO3 was used as a combustion accelerator, and the effects of different combustion accelerator-to-sample mass ratios on the test results were systematically studied (e.g., ...). Figure 2 (As shown). With the increase of the mass ratio of combustion accelerator to sample, the test results for fluorine and chlorine showed a gradual increasing trend. When the mass ratio was greater than 4:1, the results tended to stabilize. Taking all factors into consideration, this study selected a mass ratio of combustion accelerator to sample of 5:1.
[0018] Combustion temperature experiments were conducted: the changes in fluorine and chlorine content test results of NdFeB samples under different combustion temperatures were investigated (e.g., Figure 3 (As shown). When the combustion temperature increases from 800℃ to 1050℃, the fluorine and chlorine content in the sample increases rapidly. Further increasing the combustion temperature has little effect on the measurement results. Therefore, 1050℃ was selected as the combustion temperature in this experiment.
[0019] Combustion time experiments were conducted to further investigate the effect of different combustion times on the measurement results. (e.g.) Figure 4 As shown, the fluorine and chlorine content of neodymium iron boron and its waste samples gradually increased with the extension of combustion time. When the combustion time was greater than 700s, the fluorine and chlorine determination results tended to be stable. Therefore, 700s was selected as the combustion and absorption time of the sample in this experiment.
[0020] A water replenishment rate experiment was conducted: During the high-temperature combustion and pyrolysis of the sample, the free halogen and hydrogen halide gases generated need to reach equilibrium before being fully absorbed by water vapor. Therefore, the water replenishment rate has a significant impact on gas absorption. (e.g.) Figure 5 As shown, both excessively low and excessively high water replenishment rates during the combustion pyrolysis process are detrimental to gas absorption, leading to lower results. Therefore, this study selected an optimal water replenishment rate of 0.35 mL / min.
[0021] A comparative experiment was conducted using different absorbents: The results of fluoride and chlorine content determination were compared using pure water, 10 mmol / L NaOH solution, and a mixed solution of 3.2 mmol / L Na₂CO₃ and 1.0 mmol / L NaHCO₃ as absorbents. The results showed that the fluoride and chlorine content determination results using water as the absorbent were significantly higher than those using 10 mM sodium hydroxide solution and 3.2 mM Na₂CO₃-1.0 mM NaHCO₃ solution (e.g.,...). Figure 6 As shown in the figure, water was chosen as the absorption liquid in this experiment.
[0022] Example 2
[0023] Based on Example 1, Instruments and reagents: The system employs a combustion furnace-ion chromatography system with a minimum heat resistance of 1100℃; the ion chromatograph is a Metrohm ECOICFlex; the absorption system is a Metrohm 920 Absorber Module; the chromatographic column is a Metrosep ASupp5-150 / 4.0; and the guard column is a Metrosep RP2Guard / 3.5. Fluorine and chlorine standard solutions (1000 mg / L); absorption solutions: pure water, 10 mmol / L NaOH solution, a mixed solution of 3.2 mmol / L Na2CO3 and 1.0 mmol / L NaHCO3; high-purity tungsten trioxide.
[0024] Experimental steps: Step (1): Grind and pretreat the neodymium iron boron and its waste samples; Step (2): Weigh the NdFeB and its waste samples, mix the NdFeB and its waste samples with the combustion aid tungsten trioxide at a mass ratio of 1:5, and perform online combustion; Step (3): Set the online combustion conditions. The sample is first cracked in an argon environment and then oxidized in an oxygen environment to convert halogens into water-soluble HX or X2. The combustion temperature is 1050℃ and the combustion time is 700s. At the same time, water vapor at a flow rate of 0.35mL / min carries the gas generated by combustion into the absorption cell. The absorbent in the absorption cell is pure water, which is used to absorb fluoride ions and chloride ions. Step (4): Collect the absorption liquid and determine the content of fluoride and chloride ions in the sample by ion chromatography; In step (ii), the mass ratio of the sample to tungsten trioxide, the combustion temperature, combustion time, and water vapor flow rate in step (iii) work together to achieve complete combustion of the NdFeB matrix sample and full absorption of fluoride and chloride ions.
[0025] Verification of limits of detection and limits of quantitation: A series of mixed standard working solutions were prepared by serially diluting 1000 μg / mL fluoride and chloride ion standard solutions. The fluoride ion concentrations were 50 ng / mL, 100 ng / mL, 200 ng / mL, 500 ng / mL, and 1000 ng / mL, respectively, and the chloride ion concentrations were 100 ng / mL, 200 ng / mL, 400 ng / mL, 1000 ng / mL, and 2000 ng / mL, respectively. The mixed standard solutions were measured sequentially from low to high concentration. A calibration curve was fitted with fluoride and chloride concentrations on the x-axis and peak area on the y-axis. The linear regression equation was y = 1.46 × 10⁻⁶. -5 x-4.12×10 -2 (R=0.9998) and y=1.05×10 -5 x–0.139 (R=0.9990). Eleven consecutive measurements were performed on low-content samples. The limits of detection (LOD) and quantitation (LOQ) were calculated using methods with 3 times and 10 times standard deviations, respectively. The LODs for fluorine and chlorine content in NdFeB and its waste samples were 1.3 mg / kg and 5.9 mg / kg, respectively, and the LODs for quantitation were 4.2 mg / kg and 19.7 mg / kg, respectively. Experimental results show that the ion chromatography detection method established in this invention can accurately and confidently determine whether the fluorine content in NdFeB exceeds 4.2 mg / kg and the chlorine content exceeds 19.7 mg / kg. It has successfully passed rigorous methodological validation and is fully applicable to the routine detection of fluorine and chloride ions in NdFeB and its waste.
[0026] Precision Experiment and Method Comparison: For actual samples of NdFeB and its waste with three different content levels, this method was used to continuously determine the fluorine and chlorine content 11 times. The relative standard deviation of the determination results was between 1.1% and 2.1% (as shown in Table 1). Further, referring to XB / T612.4-2023, the steam distillation-ion selective electrode method was used for determination, and the results of the two methods for determining the fluorine and chlorine content were roughly consistent. Experimental results show that the ion chromatography detection method established in this invention has a relative standard deviation of 1.1%-2.1% and exhibits good consistency with the current standard XB / T612.4-2023 in the determination of fluorine and chlorine, and can replace the standard method for the determination of fluorine and chlorine.
[0027]
[0028] Example 3
[0029] Based on Example 2, this example investigates the effect of different parameter combinations on the spike recovery rate. Using actual sample #2 as the subject, the spiked amounts were 50 mg / kg fluorine and 500 mg / kg chlorine. Each condition was measured in triplicate, and the average recovery rate was taken. Other conditions were kept the same as in Example 2 (including argon / oxygen atmosphere, absorbent as pure water, etc.), while the proportion of combustion accelerant, combustion temperature, combustion time, and water replenishment rate were varied. The results for each combination and the recovery rate are shown in Table 2.
[0030]
[0031] As can be seen from the data in Table 2: (1) The fluorine recovery rate of experimental group 1 (under the conditions of this invention) was 98.5% and the chlorine recovery rate was 99.2%, both of which were the highest values.
[0032] (2) Experimental groups 2-5 reduced the combustion accelerant ratio from 1:5 to 1:3, the combustion temperature from 1050℃ to 950℃, the combustion time from 700s to 500s, and the water replenishment rate from 0.35mL / min to 0.20mL / min, respectively, while keeping the other three parameters the same as experimental group 1. The fluorine recovery rates of the four groups were 72.3%, 68.7%, 64.2%, and 69.5%, respectively, and the chlorine recovery rates were 70.1%, 66.4%, 61.8%, and 67.0%, respectively. Compared with experimental group 1, the fluorine recovery rate decreased by 26.2, 29.8, 34.3, and 29.0 percentage points, respectively, and the chlorine recovery rate decreased by 29.1, 32.8, 37.4, and 32.2 percentage points, respectively. This indicates that changing any one of the four parameters outside the scope defined by this invention significantly reduced the recovery rate, and the degree of recovery rate loss caused by the deviation of each parameter was similar (all reduced the recovery rate to the 61%-73% range).
[0033] (3) Experimental groups 6 and 7 simultaneously changed two parameters: Group 6 reduced the oxidizer ratio to 1:3 and the combustion temperature to 950℃, with fluorine and chlorine recovery rates of 45.6% and 43.1%, respectively; Group 7 reduced the oxidizer ratio to 1:3 and shortened the combustion time to 500s, with fluorine and chlorine recovery rates of 41.3% and 38.9%, respectively. The recovery rates of these two groups were lower than those of experimental groups 2-5, which deviated from either single parameter. For example, the fluorine recovery rate of Group 2 (single deviation from oxidizer ratio) was 72.3%, and that of Group 3 (single deviation from temperature) was 68.7%, while that of Group 6 (simultaneous deviation from oxidizer ratio and temperature) was only 45.6%, which was 26.7 and 23.1 percentage points lower than that of Group 2 and Group 3, respectively; the fluorine recovery rate of Group 7 (simultaneous deviation from oxidizer ratio and time) was 41.3%, which was 31.0 percentage points lower than that of Group 2 (72.3%) and 22.9 percentage points lower than that of Group 4 (single deviation from time, 64.2%). The chlorine recovery rate showed the same trend.
[0034] (4) When three parameters were changed simultaneously in experimental group 8 (the ratio of combustion aid to fuel remained unchanged at 1:5, but the temperature was reduced to 950℃, the time was shortened to 500s, and the water replenishment rate was reduced to 0.20mL / min), the recovery rates of fluorine and chlorine further decreased to 29.8% and 27.2%, respectively, which were the lowest among all combinations. This recovery rate was 38.9 percentage points lower than that of experimental group 3 (single deviation from temperature, 68.7%), 34.4 percentage points lower than that of experimental group 4 (single deviation from time, 64.2%), and 39.7 percentage points lower than that of experimental group 5 (single deviation from water replenishment rate, 69.5%).
[0035] (5) Comparing the recovery rates of experimental groups 6, 7 and 8: Group 6 (double deviation) was 45.6%, Group 7 (double deviation) was 41.3% and Group 8 (triple deviation) was 29.8%, showing that the more deviation parameters there were, the more significant the decrease in recovery rate.
[0036] In summary, under the experimental conditions, the recovery rate can reach over 98% only when the accelerant ratio, combustion temperature, combustion time, and water replenishment rate are simultaneously within the values specified in this invention (1:5, 1050℃, 700s, 0.35mL / min). Any single parameter deviating from this value reduces the recovery rate to the 61%-73% range; two parameters deviating simultaneously reduces it to 38%-46%; and three parameters deviating simultaneously reduces it to 27%-30%. This data indicates that the effects of each parameter on the recovery rate are cumulative, and the optimal recovery rate is obtained only when all parameters are at the values specified in this invention.
[0037] In the embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of the system is only a logical functional division, and there may be other division methods in actual implementation. For example, multiple systems or components may be combined or integrated into another system, or some features may be ignored or not executed.
[0038] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method for preparing ion chromatography samples for the detection of fluorine and chlorine in NdFeB alloys and waste, characterized in that, Includes the following steps: Step (1): Grind and pretreat the neodymium iron boron and its waste samples; Step (2): Weigh samples of neodymium iron boron and its waste materials, and perform online combustion; Step (3): Set the online combustion conditions. The sample is first cracked in an argon environment and then oxidized in an oxygen environment to convert halogens into water-soluble HX or X2. The combustion temperature is 1050℃ and the combustion time is 700s. At the same time, water vapor at a flow rate of 0.35mL / min carries the gas generated by combustion into the absorption cell. The absorbent in the absorption cell is pure water, which is used to absorb fluoride ions and chloride ions. Step (4): Collect the absorption liquid and determine the content of fluoride and chloride ions in the sample by ion chromatography.
2. The method according to claim 1, characterized in that, The grinding pretreatment conditions in step (I) are as follows: place the NdFeB and its waste samples at 300℃-500℃ for 1 hour, and after cooling, grind them with a grinder until they all pass through a 200-mesh analytical sieve.
3. The method according to claim 1, characterized in that, In step (ii), neodymium iron boron and its waste samples are weighed and mixed with tungsten trioxide, the combustion aid, at a mass ratio of 1:
5.
4. The method according to claim 1, characterized in that, The ion chromatography method employs an anion exchange column and uses a carbonate system as the eluent for isocratic elution.