Soil total silicon determination method based on graphite powder crucible

Abstract

The invention discloses a graphite powder crucible-based soil total silicon determination method, which comprises: 1, preparing a sample, and taking a plurality of groups of soil as an experiment sample; 2, preparing spectrum pure graphite powder; 3, graphite powder is filled into the crucibles, the number of the crucibles is consistent with that of the experimental samples, and smooth concave surfaces are pressed in the middles of the crucibles; 4, preparing a reaction solvent, respectively weighing a soil sample and the reaction solvent, and placing the soil sample and the reaction solvent in the smooth concave surface in the step 3; 5, feeding the crucible into a muffle furnace for melting, taking out the crucible after melting, cooling, and transferring molten balls obtained by melting; and 6, taking the molten balls, adding the molten balls into the dissolving solution, dissolving, diluting the dissolving solution, and measuring. Compared with the prior art, the soil total silicon determination method based on the graphite powder crucible has the advantages of convenience in operation and application, low cost and easiness in separation and use.

Description

Technical Field

[0001] The present invention relates to the technical field of determination of total silicon in soil, and specifically refers to a method for determining total silicon in soil based on a graphite powder crucible. Background Art

[0002] Silicon dioxide in soil accounts for 30%-95% of the soil mineral content and constitutes the main framework of the soil. Silicon dioxide is insoluble in acid, and HF can destroy the soil lattice, causing it to dissolve and precipitate, but the dissolution process will cause SiF4 to volatilize. In response to this problem, relevant scholars have also proposed a high-pressure sealed digestion method to control the volatilization of SiF4, but it is difficult to operate and has low batch efficiency.

[0003] Therefore, the current effective pretreatment method for determining total silicon in soil is the alkali fusion method: alkali fusion-inductively coupled plasma emission spectrometry.

[0004] The high-temperature alkali fusion method is a common pretreatment method for soil agrochemical analysis. By high-temperature alkali fusion, the soil lattice is destroyed to completely melt the organic matter and inorganic minerals in the soil, and then after dissolution with dilute acid, the melt is converted into a soluble test solution for determining the content of various mineral elements;

[0005] However, the platinum crucible used in the high-temperature alkali fusion method is expensive, has low processing efficiency, the melt adheres tightly to the crucible and is not easily dissolved, and it is difficult to transfer without damage. There are multiple difficulties and error-prone points such as strong acid being easy to consume the platinum crucible. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the above technical defects and provide a method for determining total silicon in soil based on a graphite powder crucible that is convenient for operation and application, has a low price, and is easy to separate and use.

[0007] To solve the above technical problem, the technical solution provided by the present invention is: A method for determining total silicon in soil based on a graphite powder crucible, comprising the following steps:

[0008] Step 1: Prepare samples, and take multiple groups of soil as experimental samples;

[0009] Step 2: Prepare spectroscopically pure graphite powder;

[0010] Step 3: Fill the graphite powder into the crucible. The number of crucibles is the same as the number of experimental samples, and a smooth concave surface is pressed in the middle;

[0011] Step 4: Configure the reaction solvent, weigh the soil sample and the reaction solvent respectively and place them in the smooth concave surface in Step 3;

[0012] Step 5: Send the crucible into a muffle furnace for melting, take out the crucible and cool it after melting, and transfer the melted melt ball;

[0013] Step 6: Take the fused beads, add them to the dissolution solution for dissolution, dilute the dissolution solution, and then conduct measurements.

[0014] Preferably, the preparation of the spectroscopically pure graphite powder includes putting the graphite powder in a ceramic mortar, sending it into a muffle furnace for calcination, taking it out, and then packing it into a self-sealing bag for sealing and standby after cooling to room temperature.

[0015] Preferably, in step 4, the reaction solvent includes weighing anhydrous sodium carbonate, lithium metaborate, and lithium tetraborate and mixing them evenly, with a mass ratio of 10:4:1.

[0016] Preferably, in step 4, the ratio of the soil sample to the reaction solvent is 6:0.9 - 1.

[0017] Preferably, the temperature of the muffle furnace is 1000 - 1100 °C and the calcination time is 30 min.

[0018] Preferably, the temperature of the muffle furnace is 1000 - 1100 °C, the calcination time is 40 min, and the cooling time is 30 min.

[0019] Preferably, the dissolution solution is a 20% nitric acid solution. Transfer the fused beads and the graphite powder in contact with the fused beads within the smooth concave surface to the 20% nitric acid solution and completely dissolve them using an ultrasonic instrument;

[0020] After dissolution, let it stand for 1 h, suck out the supernatant, dilute it 10 times, and conduct measurements using rhodium as an internal standard.

[0021] The advantages of the present invention compared with the prior art are as follows: In the present invention, a graphite powder crucible is used, which is inexpensive. Through the application of graphite powder, advantages such as the fused beads being naturally separated from the crucible after melting are achieved, exactly overcoming the difficulties of platinum crucibles. At the same time, in the present invention, a graphite powder crucible is used for melting operations, so batch melting operations can be carried out, thereby reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic structural diagram of a four-layer crucible rack.

[0023] Figure 2 is a schematic diagram showing the influence of the dosage of the mixed flux on the measurement results of reference substances.

[0024] Figure 3 is a schematic diagram showing the influence of the dosage of the mixed flux on the determination results of total silicon in soils with different sand particle contents.

[0025] Figure 4 is a schematic diagram showing the influence of the sand particle content of different texture soils on the determination results of total silicon. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be further described in detail below with reference to the accompanying drawings.

[0027] In the specific implementation of the present invention:

[0028] Six certified reference materials GBW07407a, GBW07401a, GBW07390, GBW07557, GBW07572, and GBW07568 were selected; 4 groups of soils with different textures, including 12 soils with different sand particle contents; the basic conditions of the tested soils are shown in Table 1

[0029] Table 1 Particle size composition and texture of studied soils

[0030]

[0031] An inductively coupled plasma optical emission spectrometer (ICP-OES), an ultrasonic cleaner, a muffle furnace, and an electronic balance were selected during the operation.

[0032] Consumables selected: anhydrous sodium carbonate, lithium metaborate, lithium tetraborate, graphite powder (spectral pure), 20% nitric acid solution, 30 ml porcelain crucible, 250 mL plastic beaker, grooved shaping rod, weighing paper (7.5*7.5 cm).

[0033] The graphite powder was placed in a ceramic mortar (1 L), put into a muffle furnace, the temperature was set at 1050 °C, the constant temperature time was 30 min, and impurities were removed by high-temperature burning. After the constant temperature ended, the graphite powder was taken out after the muffle furnace cooled down. After cooling to room temperature, it was sealed in a self-sealing bag for standby.

[0034] Or spectral pure graphite powder was selected.

[0035] During the operation, the graphite powder was filled into a 250 ml plastic beaker, filled and compacted repeatedly, a 30 ml porcelain crucible was inverted on the graphite powder, and both hands were used to press down the crucible until the bottom, then the crucible was dug out with a stainless steel spoon, and a smooth concave surface was slowly pressed out in the graphite powder with a 50 ml round-bottom smooth plastic centrifuge tube. If it was not flat, the graphite powder was refilled and pressed.

[0036] Weigh 20 g of anhydrous sodium carbonate, 8 g of lithium metaborate, and 2 g of lithium tetraborate (when the dosage is large, an appropriate amount is weighed according to the ratio of 10:4:1) and place them in a 1000 mL plastic bottle. After covering the bottle, shake it vigorously to mix well;

[0037] Weigh 0.6 g of flux with weighing paper, then weigh 0.09 g - 0.1 g (accurate to 0.0001 g) of soil on the flux, and swing the weighing paper diagonally back and forth with both hands to mix the soil and the flux evenly. Wrap it carefully and place the paper ball in the graphite pit of the crucible. Pay attention to the discharge order to avoid confusing the samples;

[0038] Place the crucibles (without lids) on the four - layer crucible rack in sequence and use the sample - feeding fork to send the entire crucible rack into the muffle furnace. This has the advantages of efficiently utilizing the space of the muffle furnace, fixed position, not being prone to misnumbering, and at the same time reducing the risk of high - temperature operation.

[0039] During dissolution, in a 250 - mL volumetric flask, add 50 mL of 20% nitric acid solution. Use stainless - steel forceps to pick up the fused beads and put them into the 250 - mL volumetric flask. Then, use a stainless - steel spoon to scoop up the graphite powder at the bottom and around the fused beads that the fused beads have contacted, and transfer them all into the volumetric flask. Flush the graphite powder sticking to the mouth of the volumetric flask with ultrapure water. Then, place the volumetric flask in a fixed rack and place it in an ultrasonic instrument to ultrasonicate until completely dissolved (or place it for 12 hours and then ultrasonicate for 5 minutes to dissolve). Take out the volumetric flask, make up the volume to the scale with ultrapure water, and shake well. After standing for 1 hour, aspirate the supernatant, dilute it 10 times for measurement. Prepare a standard working curve and measure with rhodium as the internal standard. Due to the high salt content, this method uses a Teflon salt - and acid - alkali - resistant injection system.

[0040] Table 2 Standard working curve

[0041]

[0042] In view of the importance of precision and accuracy for the determination method, six certified reference materials: GBW07407a, GBW07401a, GBW07390, GBW07557, GBW07572, GBW07568 are treated by the graphite powder crucible - alkali fusion method. Six repeated experiments are set up, and the relevant results are shown in Table 2.

[0043] Table 3 Precision and accuracy of graphite powder crucible alkali melting method for the determination of soil total silica

[0044] Table3 Accuracy of graphite powder crucible alkali melting method forthe

[0045] determination of soil total silica

[0046]

[0047] Aiming at the interference of the flux dosage of the alkali fusion method on the atomization efficiency and spectrum during the ICP - OES determination process, in order to reduce the measurement error caused by the salt - base effect in the present invention, with the condition of gradually reducing the flux usage, the melting effects of reference materials with different SiO2 contents (high, medium, low) of soil samples and the flux dosages required for soils with different sand particle contents are explored. The usage amounts of the mixed flux are set to be 0.8 g, 0.6 g, and 0.4 g respectively for method verification.

[0048] Figure 2 The results show that the relative errors of the silica content results of the same reference material melted with 0.8 g, 0.6 g, and 0.4 g of the mixed flux are all less than 5%. The results of 0.8 g and 0.6 g are both within the standard certified values. The measurement result of 0.4 g is outside the range, but the relative error is less than 5%. Therefore, when different amounts of the mixed flux are used to treat different reference material soils, the differences in the measurement results are not significant.

[0049] Figure 3 The results show that adding 0.8 g and 0.6 g of the flux can melt the silica in soils with different sand particle contents. The measurement results are not significant (P>0.05), and the RSD<5%, indicating high precision. Therefore, the melting effects of 0.8 g and 0.6 g of the flux are good without loss. When the sand particle content increases to more than 85.6%, the melting effect of 0.4 g of the flux is inferior to that of 0.6 g and 0.8 g of the flux, and the results are all lower by more than 5% and show significant differences (P<0.05). Thus, it can be seen that 0.4 g of the flux cannot completely melt the samples with high sand particle contents, and this addition amount is not suitable for the detection of total silicon in soils. 0.6 g of the flux can not only completely melt the soil silica but also relatively reduce the interference of salts on the measurement results, which is a recommended flux amount.

[0050] Based on the principle that the soil sand particle content is positively correlated with the silica content, this invention uses 0.6 g of the flux to melt different texture types of soils including clay, clay loam, loam, sandy soil, and sandy loam, with the sand particle content ranging from 18.6% to 96.0%, to explore the melting effect of the graphite powder crucible alkali fusion method and its influence on the measurement results of soil total silicon.

[0051] Figure 4 The results show that there is a positive correlation between the sand particle content and the total silicon. When the sand particle content ranges from 18.6% to 96%, the corresponding SiO2 content range is 36.8% to 91.3%. Even when the sand particle content is greater than 85%, the method of this invention can completely melt the silica and the measurement results are above 90%. Thus, it can be seen that 0.6 g of the flux melts completely with good effect, and at the same time, it proves that the graphite powder crucible alkali fusion method is applicable to the analysis and detection of total silicon in different texture types of soils.

[0052] The results of measuring the total silicon of the same batch of samples by the graphite powder crucible alkali fusion method among different laboratories show (Table 4) that the relative standard deviation RSD among laboratories is less than 5%, meeting the requirement of the relative deviation of less than 35% in the environmental standard quality assurance of HJ974-2018. Using the SSPS19.0 software to conduct one-way ANOVA and Duncan multiple comparison analysis on the data, the correlation of the measurement results among different laboratories is extremely significant (correlation coefficient r = 0.993, p<0.0001), and there is no significant difference in the measurement results of the same soil samples (P>0.05), indicating that the graphite powder crucible - alkali fusion method has the characteristic of strong portability.

[0053] Table 4 Comparison of Inter-laboratory Results of Graphite Powder Crucible Alkali Melting Method

[0054]

[0055] The research of the present invention shows that the graphite powder crucible alkali melting method is applicable to the determination of total silicon in soil. Adding 0.6 g of flux can completely melt the silicon dioxide in soils of different texture types, while reducing the base effect. The results are accurate, and the determined values of total silicon are consistent with the certified reference material values, with a relative standard deviation RSD < 5%. Compared with the platinum crucible alkali melting method, the melt (melt ball) of the graphite powder crucible alkali melting method naturally detaches from the crucible, having the advantages of being easily soluble in acid, easy to transfer without damage, strong operability and transplantability, and low cost, and is suitable for batch analysis and detection of total silicon in soil.

[0056] The above describes the present invention and its implementation manners. This description is not restrictive. What is shown in the drawings is only one of the implementation manners of the present invention, and the actual structure is not limited thereto. Generally speaking, if those of ordinary skill in the art are inspired by it and design similar structural manners and embodiments without creative efforts without departing from the purpose of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. A method for determining total silicon in soil based on a graphite powder crucible, characterized in that: It includes the following steps: Step 1: Prepare samples. Take multiple groups of soil as experimental samples. Step 2: Prepare spectroscopically pure graphite powder. Step 3: Fill the graphite powder into crucibles. The number of crucibles is the same as the number of experimental samples, and press a smooth concave surface in the middle. Step 4: Prepare the reaction solvent. Weigh the soil sample and the reaction solvent respectively and place them in the smooth concave surface in Step 3. Step 5: Send the crucibles into a muffle furnace for melting. After melting, take out the crucibles and cool them, and transfer the molten globules. Step 6: Take the molten globules, add them to the dissolution solution for dissolution, and dilute the dissolution solution before measurement.

2. The method for determining total silicon in soil based on a graphite powder crucible according to claim 1, wherein: The preparation of the spectroscopically pure graphite powder includes putting the graphite powder in a ceramic mortar, sending it into a muffle furnace for burning and then taking it out, and after cooling to room temperature, packing it into a self-sealing bag and sealing it for standby.

3. A method for determining total silicon in soil based on a graphite powder crucible according to claim 1, characterized in that: In Step 4, the reaction solvent includes weighing anhydrous sodium carbonate, lithium metaborate and lithium tetraborate and mixing them evenly, and the mass ratio is 10:4:

1.

4. A method for determining total silicon in soil based on a graphite powder crucible according to claim 3, characterized in that: In Step 4, the ratio of the soil sample to the reaction solvent is 6:0.9 - 1.

5. The method for determining total silicon in soil based on a graphite powder crucible according to claim 2, wherein: The temperature of the muffle furnace is 1000 - 1100 °C and the burning time is 30 min.

6. The method for determining total silicon in soil based on a graphite powder crucible according to claim 3 or 4, characterized in that: The temperature of the muffle furnace is 1000 - 1100 °C, the burning time is 40 min, and the cooling time is 30 min.

7. A method for determining total silicon in soil based on a graphite powder crucible according to claim 1, characterized in that: The dissolution solution is 20% nitric acid solution. Take the molten globules and the graphite powder in contact with the molten globules in the smooth concave surface and transfer them to the 20% nitric acid solution to completely dissolve them using an ultrasonic instrument. After dissolution, let it stand for 1 h, suck out the supernatant, dilute it 10 times and measure it using rhodium as an internal standard.

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