A method for determining the content of metal oxides in cement

Abstract

This invention discloses a method for determining the content of metal oxides in cement, comprising: (1) sample pretreatment: adding hydrofluoric acid and perchloric acid to the sample to be tested, and performing a first digestion at 280-290℃ to obtain a first digestion product; adding perchloric acid to the first digestion product for a second digestion to obtain a second digestion product; adding nitric acid to the second digestion product for a third digestion to obtain a third digestion product; adjusting the volume of the third digestion product to obtain a digestion solution of the sample to be tested; (2) ICP-MS detection: using the internal standard calibration method of ICP-MS to detect the digestion solution of the sample to be tested to obtain the content of the target metal oxides in cement; this method significantly improves the problems of complex and variable interference factors, ionization and interatomic interference that exist in ICP-MS detection, and significantly improves the accuracy and stability of the detection results, making it suitable for large-scale application in cement quality detection.

Description

Technical Field

[0001] This invention relates to the field of material content detection technology, specifically to the field of material content detection technology in cement, and particularly to a method for determining the content of metal oxides in cement by inductively coupled plasma mass spectrometry. Background Technology

[0002] With the needs of China's economic and social development, more and more high-speed railways with higher speeds are gradually being put into construction. To ensure the safe operation of trains, the quality requirements for various raw materials are extremely strict during the construction of high-speed railways. Cement, as an indispensable building material, plays a vital role in the construction process. There are many factors that affect the quality of cement, among which the testing process for metal oxides in the chemical composition of cement has always been cumbersome, with complex analytical steps and long processing times. Therefore, it is particularly urgent to find a way to quickly and accurately detect the metal oxide components in cement.

[0003] Currently, the main methods for testing the metal oxide content in cement, both domestically and internationally, include titration analysis, visible spectrophotometry, atomic absorption spectrophotometry, inductively coupled plasma atomic emission spectrometry (ICP-MS), and infrared spectroscopy. While existing research has explored the use of ICP-MS for detecting metal oxide content in cement, no national or industry standards have been established for this purpose. Furthermore, practical applications have revealed that ICP-MS for cement metal oxide content suffers from several drawbacks. These include the complexity of cement samples (multiple types of impurities) and the variety of metal components, making target element extraction difficult. Additionally, it is subject to severe interference from ionization and multi-atom interactions, resulting in complex and variable interfering factors. Consequently, the accuracy and stability of the measurement results are poor, which is clearly detrimental to the accurate assessment of cement quality. In particular, among the elements K, Na, Ca, Mg, Fe, Al, and Ti in cement, K, Na, Ca, and Mg are widely present in nature, causing serious matrix and background interference; K and Na are low ionization energy elements, causing ionization interference. 38 ArH + , 40 ArH + Will be against K, 12 C 16 O 2+ Will affect Ca, 12 C 2+ , 12 C 14 N + Will affect Mg, 40 Ar 16 O + , 40 Ar 16O 1 H + Will affect Fe, 32 S 16 O + , 32 S 16 O 1 H + It can cause polyatomic interference to Ti, so it is a challenge to more accurately detect the contents of K, Na, Ca, Mg, Fe, Al and Ti in cement at the same time. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of poor accuracy and stability in existing methods for simultaneously detecting the content of seven metal oxides (K, Na, Ca, Mg, Fe, Al, and Ti) in cement using ICP-MS. This invention proposes a new method for determining the content of metal oxides in cement. Through sample pretreatment, this method not only converts the metal elements in cement into inorganic ions but also performs multiple purification processes. This significantly improves the problems of complex and variable interference factors, ionization, and inter-atomic interference encountered in ICP-MS detection. Consequently, the accuracy and stability of the detection results are significantly improved, which is beneficial for the rapid and accurate assessment of cement quality and suitable for large-scale application in cement quality testing.

[0005] To achieve the above-mentioned objective, this invention provides a method for determining the content of metal oxides in cement, comprising the following steps:

[0006] (1) Sample pretreatment: Hydrofluoric acid and perchloric acid were added to the sample to be tested, and the first digestion was carried out at 280-290℃ to obtain the first digestion product; perchloric acid was added to the first digestion product for the second digestion to obtain the second digestion product; nitric acid was added to the second digestion product for the third digestion to obtain the third digestion product; the third digestion product was diluted to a certain volume to obtain the digestion solution of the sample to be tested.

[0007] (2) ICP-MS detection: ICP-MS was used to detect the digestion solution of the sample to be tested to obtain the content of the target metal oxide in the cement; when performing ICP-MS detection, the internal standard correction method of HMI mode was used.

[0008] This invention discloses a method for determining the content of metal oxides in cement. First, the metal elements in the cement are ionized using hydrofluoric acid, and the silicon element is removed by the generated volatile silicon fluoride, thus initially purifying the metal elements. Then, perchloric acid is used to replace and remove the hydrofluoric acid in the system, further removing carbon and organic matter, thus further purifying the metal elements. Next, nitric acid is used to remove the perchloric acid in the system, purifying the metal elements again and providing an acidic environment to ensure the stable existence of metal ions. Finally, ICP-MS detection is performed using the HMI mode internal standard calibration method. This method, through the combined effect of sample pretreatment and detection mode, significantly improves the interference of matrix, background, ionization, and polyatomic factors on ICP-MS detection results, significantly improving the accuracy and stability of the detection results. This is beneficial for the rapid and accurate assessment of cement quality. The method is simple, convenient to operate, has good repeatability, and high accuracy, making it suitable for large-scale application in cement quality testing.

[0009] Preferably, the metal oxide is potassium oxide, sodium oxide, calcium oxide, magnesium oxide, ferric oxide, aluminum oxide, or titanium dioxide.

[0010] The hydrofluoric acid has extremely strong chemical activity, capable of converting most inorganic or organic metal elements in cement into inorganic ions. It can also react with silicon in cement to generate silicon fluoride gas, thus removing the metal elements and purifying them. This is beneficial for detecting metal elements using inductively coupled plasma atomic emission spectrometry (ICP-AES). Preferably, the mass fraction of the hydrofluoric acid is not less than 40%. If the hydrofluoric acid concentration is too low, its activity is low, failing to convert all metal elements in the cement into inorganic ions and leaving a large amount of silicon in the test solution, interfering with the detection and reducing the accuracy of the results.

[0011] The perchloric acid can replace and remove hydrofluoric acid, and can also remove carbon elements, organic matter, etc. from cement, thereby further purifying the metal elements. At the same time, perchloric acid is also easy to remove from the solution, which can reduce its interference with the detection results and improve the accuracy of the detection results. Preferably, the mass fraction of the perchloric acid is not less than 70%. If the mass fraction is too low, it cannot completely replace and remove hydrofluoric acid, which will cause hydrofluoric acid to interfere with the detection results and reduce the accuracy of the detection results.

[0012] The nitric acid provides an acidic environment for the stable existence of metal ions, which helps improve the accuracy of detection results. At the same time, it can remove perchloric acid, purify metal elements, and improve the accuracy of detection results. Preferably, the mass fraction of the nitric acid is not less than 65%. If the mass fraction is too low, it cannot completely remove perchloric acid, which will cause perchloric acid to interfere with the detection results and reduce the accuracy of the detection results.

[0013] Preferably, in step (1), before adding hydrofluoric acid and perchloric acid during the first digestion, the cement is wetted with ultrapure water; the wetting treatment can prevent the cement particles from scattering during the transfer process and affecting the test results; preferably, the ultrapure water is water with a resistivity of not less than 18.0 MΩ·cm.

[0014] Preferably, the volume ratio of hydrofluoric acid to perchloric acid is 10:1 during the first digestion. This preferred volume ratio has a better ionization effect on the metal elements in the cement, which is beneficial to improving the accuracy of the test results.

[0015] Preferably, during sample pretreatment, the mass ratio of the sample to the volume of hydrofluoric acid + perchloric acid, perchloric acid, and nitric acid is 0.1g:5ml + 0.5ml:2ml:5ml. This preferred mass-to-volume ratio, while meeting the digestion requirements, helps to shorten the detection time.

[0016] Preferably, the first digestion time is 1.5-3 hours; the preferred digestion time has good digestion effect and short time.

[0017] Preferably, the second digestion time is 0.5-1.5 hours; the preferred digestion time results in good digestion effect and short time.

[0018] Preferably, the third digestion time is 0.5-1.5 hours; the preferred digestion time results in good digestion effect and short time.

[0019] Preferably, after the third digestion, the digestion container is rinsed with ultrapure water 5 to 8 times and then used to make up the volume; this can make the test results more accurate.

[0020] Preferably, in step (2), the specific instrument parameters for ICP-MS detection are as follows:

[0021] Sensitivity: Plasma mode HMI;

[0022] Mode: Collision Reaction Pool Mode;

[0023] RF power: 1550W;

[0024] RF matching: 1.80V;

[0025] Sampling depth: 10.0 mm;

[0026] Atomizing gas (Ar): 0.34 L / min;

[0027] Peristaltic pump: 0.10 rps;

[0028] Atomization chamber temperature: 2℃;

[0029] Diluent gas (Ar) inlet rate: 0.59 L / min;

[0030] Assist gas (Ar) intake rate: 0.90 L / min;

[0031] Plasma gas (Ar) inlet velocity: 15.0 L / min;

[0032] The tuning equipment was selected with Co (mass number 59), Y (mass number 89), and Tl (mass number 205). The tuning oxide content was 0.534% and the double charge content was 2.772%. Sc was selected as the internal standard element.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. The method for determining the content of metal oxides in cement according to the present invention not only converts the metal elements in cement into inorganic ions through sample pretreatment, but also performs multiple purifications, thereby significantly improving the problems of complex and variable interference factors, ionization and inter-atomic interference that exist in ICP-MS detection. This significantly improves the accuracy and stability of the results of simultaneous detection of the contents of seven metal oxides, namely K, Na, Ca, Mg, Fe, Al and Ti.

[0035] 2. The method for determining the content of metal oxides in cement according to the present invention further improves the interference of matrix, background, ionization and polyatomic factors on the ICP-MS detection results by selecting the ICP-MS detection mode, thereby further improving the accuracy and stability of the detection results.

[0036] 3. The method for determining the content of metal oxides in cement according to the present invention is simple, easy to operate, has good repeatability and high accuracy, which is conducive to the rapid and accurate evaluation of cement quality and is suitable for large-scale application in cement quality testing. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to experimental examples and specific embodiments. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0038] 1. Instruments and reagents

[0039] Inductively coupled plasma mass spectrometer (7800, Agilent); electronic balance (PX224ZH / E); ultrapure water system (UPR-II-10T); digital display heating plate (DB-type).

[0040] K, Na, Ca, Mg, Fe, Al, Ti single-element standard solutions (1000 μg / mL, National Center for Analysis and Testing of Nonferrous Metals and Electronic Materials); Bi, Ge, In, Li6, Sc, Tb, Y mixed internal standard solution (10 μg / mL, Agilent); Ce, Co, Li, Tl, Y ICP-MS tuning solution (10 μg / mL, Agilent); HClO4 (70% by mass); HNO3 (65% by mass); HF (40% by mass).

[0041] The laboratory pure water was all ultrapure water with a resistivity of 18.2 MΩ·cm; cement standard materials: fly ash silicate cement composition analysis standard material GBW 03208a-2012 and ordinary silicate cement composition analysis standard sample GSB 08-1356-2017.

[0042] 2. Instrument parameters

[0043] Sensitivity was plasma; mode was HMI; collision cell mode; RF power was 1550W; RF matching was 1.80V; sampling depth was 10.0mm; nebulizer gas (Ar) was 0.34L / min; peristaltic pump was 0.10rps; nebulizer temperature was 2℃; dilution gas (Ar) was 0.59L / min; auxiliary gas (Ar) was 0.90L / min; plasma gas (Ar) was 15.0L / min; a tuning device with mass numbers of 59 Co, 89 Y and 205 Tl was used, with a tuning oxide content of 0.534%; double charge was 2.772%, and Sc was used as the internal standard element.

[0044] 3. Preparation of standard solutions

[0045] Accurately pipette 0.00, 0.50, 1.00, 1.50, 2.00, 2.50, 3.00, 3.50, 4.00, 4.50, and 5.00 mL of 1000 μg / mL K, Na, Ca, Mg, Fe, Al, and Ti single-element standard solutions into a series of 100 mL volumetric flasks, and dilute to volume with 2% HNO3 solution to prepare mixed standard solutions with mass concentrations of 0 mg / L, 5 mg / L, 15 mg / L, 20 mg / L, 25 mg / L, 30 mg / L, 35 mg / L, 40 mg / L, 45 mg / L, and 50 mg / L, respectively.

[0046] Example 1:

[0047] 1. Sample pretreatment: Accurately weigh 0.1g of the sample to be tested (accurate to 0.0001g) and place it in a 30mL polytetrafluoroethylene crucible. Wet the sample with a few drops of ultrapure water. Transfer 5mL of HF + 0.5mL of HClO4 to a 285℃ hot plate for digestion for 2 hours (starting from a low temperature). After the white fumes are dispelled, remove the plate and cool it to obtain the first digestion product. Add 2mL of HClO4 solution to the first digestion product and digest for 1 hour to obtain the second digestion product. Add 5mL of HNO3 to the second digestion product and digest for 1 hour. Remove the plate and cool it to obtain the third digestion product. Transfer the third digestion product to a 100mL volumetric flask and wash the polytetrafluoroethylene crucible 6 times with ultrapure water. Combine the washing solutions into the 100mL volumetric flask, then dilute to volume with ultrapure water and mix well to obtain the digestion solution of the sample to be tested.

[0048] 2. ICP-MS detection: ICP-MS was used to detect the content of target metal oxides in the cement by analyzing the digestion solution of the sample. The HMI mode internal standard calibration method was used for ICP-MS detection.

[0049] Comparative Example 1:

[0050] The difference from Example 1 is that the HMI mode non-internal standard calibration method is used for ICP-MS detection.

[0051] Comparative Example 2:

[0052] The difference from Example 1 is that, during sample pretreatment, equal volumes of hydrofluoric acid, perchloric acid, and nitric acid are added to the sample to be tested at the same time for digestion.

[0053] Comparative Example 3:

[0054] The difference from Example 1 is that, during sample pretreatment, after the first digestion, nitric acid is added for a second digestion, and then perchloric acid is added for a third digestion.

[0055] Comparative Example 4:

[0056] The difference from Example 1 is that, during sample pretreatment, no perchloric acid was added during the first digestion, and 2.5 ml of perchloric acid was added during the second digestion.

[0057] Comparative Example 5:

[0058] The difference from Example 1 is that, during the sample pretreatment, hydrochloric acid with a mass concentration of 70% was added for the second digestion.

[0059] Experiment Example 1: The Influence of Pattern on Test Results

[0060] The standard reference material GBW 03208a-2012 was tested using the methods described in Example 1 and Comparative Example 1. The test results for seven oxides in cement—potassium oxide, sodium oxide, calcium oxide, magnesium oxide, ferric oxide, aluminum oxide, and titanium dioxide—are shown in Table 1.

[0061] Table 1 Test results under different modes

[0062]

[0063] Analysis of Table 1 shows that, based on the high salt complexity of cement samples, the non-internal standard calibration method (Comparative Example 1) and the internal standard calibration method (Example 1) were used to test the GBW 03208a-2012 standard material. Under the test conditions of the internal standard calibration method, matrix, background, ionization and polyatomic interference can be eliminated, which greatly improves the test accuracy.

[0064] Experiment Example 2: Detection Limit Experiment

[0065] The standard solutions were measured using the method in Example 1, and standard curves were plotted. Each element showed a good linear relationship in the range of 0–50 mg / L. The linear equation, correlation coefficient, and detection limit are shown in Table 2.

[0066] Table 2 Linear equations, correlation coefficients, and detection limits

[0067]

[0068] Analysis of Table 2 shows that the linear correlation coefficients of the seven metal element components are all above 0.9991, indicating good linear correlation.

[0069] Experiment Example 3: Accuracy Experiment of Detection Results

[0070] The method described in Example 1 was used to perform six parallel determinations (average results) of seven metal oxide components in two cement standard materials, GBW 03208a-2012 and GSB 08-1356-2017. The results are shown in Tables 3 and 4.

[0071] Table 3. Determination results of cement standard material GBW 03208a-2012

[0072] Components Standard value (%) Mean (%) Relative standard deviation (RSD) (n = 6%) <![CDATA[K2O]]> 0.92±0.04 0.93 1.39 <![CDATA[Na2O]]> 0.27±0.03 0.27 2.20 CaO 47.25±0.09 47.27 0.33 MgO 2.71±0.04 2.70 0.93 <![CDATA[Fe2O3]]> 3.36±0.05 3.36 1.34 <![CDATA[Al2O3]]> 11.25±0.05 11.24 0.93 <![CDATA[TiO2]]> 0.58±0.02 0.57 2.70

[0073] Table 4. Determination results of cement standard material GSB 08-1356-2017

[0074] Components Standard value (%) Mean (%) Relative standard deviation (RSD) (n=6) (%) <![CDATA[K2O]]> 0.72±0.03 0.72 0.94 <![CDATA[Na2O]]> 0.19±0.03 0.19 2.31 CaO 57.10±0.08 57.08 1.09 MgO 3.67±0.04 3.66 1.09 <![CDATA[Fe2O3]]> 3.92±0.03 3.92 1.30 <![CDATA[Al2O3]]> 6.01±0.04 5.99 1.00 <![CDATA[TiO2]]> 0.46±0.03 0.45 1.12

[0075] Analysis of the data in Tables 3 and 4 shows that the relative standard deviation (RSD, n=6) of the detection method in Example 1 is between 0.33 and 2.70%.

[0076] Experiment Example 4: Spike Recovery Experiment

[0077] Spiking tests were conducted on two standard samples using the method described in Example 1. Quantitative amounts of K, Na, Ca, Mg, Fe, Al, and Ti were added to the sample solutions. The spiking amounts and recoveries are shown in Tables 5 and 6.

[0078] Table 5. Recovery Rate of Cement Standard Material GBW 03208a-2012

[0079] element Measured value (mg / L) Dosage (mg) Spiked test value (mg / L) Recovery rate (%) K 8.045 0.2 10.016 98.55 Na 1.858 0.1 2.836 97.80 Ca 34.353 0.5 39.285 98.64 Mg 16.349 0.4 20.296 98.68 Fe 23.625 0.4 27.528 97.58 Al 6.023 0.2 7.959 96.80 Ti 3.498 0.2 5.442 97.20

[0080] Table 6. Cement Standard Material GSB 08-1356-2017 Spike Recovery Rate

[0081] element Measured value (mg / L) Dosage (mg) Test after spiking (mg / L) Recovery rate (%) K 6.568 0.2 8.553 99.25 Na 1.543 0.1 2.514 97.10 Ca 42.751 0.5 47.637 97.72 Mg 23.032 0.4 26.989 98.92 Fe 28.651 0.4 32.590 98.48 Al 33.198 0.4 37.084 97.15 Ti 2.788 0.2 4.762 98.70

[0082] Analysis of the data in Tables 5 and 6 shows that the spiked recovery rate of the detection method in Example 1 is between 96.80% and 99.25%.

[0083] Experiment Example 5: Experiment on Factors Affecting Detection Results

[0084] The seven metal oxide components in cement standard material GBW 03208a-2012 were determined in three parallel trials using the methods described in Example 1 and Comparative Examples 1-5 (the average value of the results was taken). The results are shown in Table 7.

[0085] Table 7. Determination results of cement standard material GBW 03208a-2012 by the methods in Example 1 and Comparative Examples 1-5.

[0086] Components Standard value (%) Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 <![CDATA[K2O]]> 0.92±0.04 0.93 0.90 0.85 0.75 0.83 0.76 <![CDATA[Na2O]]> 0.27±0.03 0.27 0.21 0.23 0.20 0.23 0.22 CaO 47.25±0.09 47.27 47.03 45.54 42.16 43.17 40.82 MgO 2.71±0.04 2.70 2.65 2.53 2.39 2.46 2.36 <![CDATA[Fe2O3]]> 3.36±0.05 3.36 3.27 3.13 2.93 2.96 2.88 <![CDATA[Al2O3]]> 11.25±0.05 11.24 11.16 10.61 9.76 10.05 9.29 <![CDATA[TiO2]]> 0.58±0.02 0.57 0.55 0.50 0.46 0.49 0.47

[0087] Analysis of the data in Table 7 shows that the test results of Example 1, which uses the detection method of the present invention to test the seven metal oxide groups in the cement standard material GBW 03208a-2012, have a small difference from the standard values, indicating high accuracy. In contrast, in Comparative Examples 1-5, any change in the type and order of acid used in the digestion process of the detection method leads to a significant increase in the difference between the test results and the standard values, significantly reducing the accuracy of the test results. It is evident that the method of the present invention for determining the metal oxide content in cement has high accuracy and is suitable for large-scale application in cement quality testing.

Claims

1. A method of determining the content of metal oxides in cement, characterized in that, Includes the following steps: (1) Sample pretreatment: Hydrofluoric acid and perchloric acid were added to the sample to be tested, and the first digestion was carried out at 280-290℃ to obtain the first digestion product; Perchloric acid was added to the first digestion product for a second digestion to obtain the second digestion product; nitric acid was added to the second digestion product for a third digestion to obtain the third digestion product. The third digestion product was diluted to a final volume to obtain the digestion solution of the sample to be tested. (2) ICP-MS detection: ICP-MS was used to detect the digestion solution of the sample to be tested to obtain the content of the target metal oxide in the cement; when performing ICP-MS detection, the internal standard correction method of HMI mode was used.

2. The method for determining the content of metal oxides in cement according to claim 1, characterized in that, The metal oxides are potassium oxide, sodium oxide, calcium oxide, magnesium oxide, ferric oxide, aluminum oxide, and titanium dioxide.

3. The method for determining the content of metal oxides in cement according to claim 1, characterized in that, The mass fraction of the hydrofluoric acid is not less than 40%.

4. The method for determining the content of metal oxides in cement according to claim 1, characterized in that, The mass fraction of the perchloric acid is not less than 70%.

5. The method for determining the content of metal oxides in cement according to claim 1, characterized in that, The mass fraction of the nitric acid is not less than 65%.

6. The method for determining the content of metal oxides in cement according to claim 1, characterized in that, Before adding hydrofluoric acid and perchloric acid during the first digestion, the cement is wetted with ultrapure water.

7. The method for determining the content of metal oxides in cement according to claim 6, characterized in that, The ultrapure water is water with a resistivity of not less than 18.0 MΩ·cm.

8. The method for determining the content of metal oxides in cement according to claim 1, characterized in that, During the first digestion, the volume ratio of hydrofluoric acid to perchloric acid was 10:

1.

9. The method for determining the content of metal oxides in cement according to claim 1, characterized in that, During sample pretreatment, the mass ratio of the sample to the volume of hydrofluoric acid + perchloric acid, perchloric acid, and nitric acid was 0.1g:5ml + 0.5ml:2ml:5ml.

10. The method for determining the content of metal oxides in cement according to any one of claims 1-9, characterized in that, The first digestion time is 1.5-3 hours; the second digestion time is 0.5-1.5 hours; and the third digestion time is 0.5-1.5 hours.

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