Pretreatment method of fluorine-containing sample for measuring fluorine content by ion selective electrode method

Abstract

The invention provides a pretreatment method of a fluorine-containing sample for determining fluorine content by an ion selective electrode method, and belongs to the technical field of fluorine content detection. The pretreatment method provided by the invention comprises the following steps: mixing a fluorine-containing sample, absolute ethyl alcohol and an alkali reagent, and carrying out heat treatment to obtain a heat-treated sample; the heat treatment comprises first heat treatment and second heat treatment which are sequentially carried out; the temperature of the first heat treatment is 150-170 DEG C; the temperature of the second heat treatment is 650-750 DEG C; and leaching the heat-treated sample with water, and fixing the volume of the obtained leachate to obtain the fluorine-containing sample to be detected. According to the method, the fluorine-containing sample can be prevented from splashing during alkali fusion, the safety is good, the problem that the fluorine content of the fluorine-containing sample is low in the ion selective electrode method detection process is solved, and meanwhile, the time consumption is short, the efficiency is high, and the cost is low.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluorine content detection, and particularly relates to a pretreatment method for fluorine-containing samples for determining fluorine content by an ion-selective electrode method. Background Art

[0002] Fluoride-rich areas are mainly distributed in North China, Northwest China, Northeast China and the Huang-Huai-Hai Plain in China. The high fluorine in these areas mainly exists in shallow or deep groundwater in arid and semi-arid areas. When there are high-fluorine minerals or high-fluorine bedrocks in the strata, the fluorine content in groundwater is relatively high. Fluorine content is an important parameter for healthy geology and will affect the human teeth, skin mucosa, bones, etc. Therefore, the detection of fluorine content has received increasing attention.

[0003] The ion-selective electrode method is widely used because of its advantages such as good selectivity, wide application range, fast and accurate, simple operation, and ability to overcome color interference. It is currently the most commonly used method for determining fluorine content. For example, Part 12 of "GB / T 14506.12-2010 Methods for Chemical Analysis of Silicate Rocks", Part 15 of "GB / T1819.15-2017 Methods for Chemical Analysis of Tin Concentrates" and Part 5 of "GB / T 3884.5-2012 Methods for Chemical Analysis of Copper Concentrates". Taking the description in Part 5 of "GB / T 3884.5-2012 Methods for Chemical Analysis of Copper Concentrates" as an example, the conditions for determining fluorine content by the ion-selective electrode method in the prior art mainly include: the test sample should be dried in an oven at 105°C ± 5°C for 1 h, placed in a desiccator and cooled to room temperature. The test material is added to a 6 g sodium hydroxide nickel crucible, heated and melted to dehydrate on an electric furnace, mixed evenly, placed in a high-temperature furnace preheated to 600°C and melted for 10 min, taken out, the melt is evenly shaken on the inner wall of the crucible, slightly cooled, leached with hot water, heated to boiling, and cooled to a constant volume. However, when determining the fluorine content in fluorine-containing samples by the above method, the sample will splash outside the crucible during the alkali fusion process, resulting in a low fluorine content in the actual sample detection process.

[0004] Compared with Part 12 of "GB / T 14506.12-2010 Methods for Chemical Analysis of Silicate Rocks", the latter adds the step of "heating and melting to dehydrate and mixing evenly on an electric furnace" to avoid splashing of the sample due to directly putting the sample into a high-temperature muffle furnace during the alkali fusion process, thereby avoiding the situation of low fluorine content in the actual sample detection process. Similarly, Part 15 of "GB / T 1819.15-2017 Methods for Chemical Analysis of Tin Concentrates" also sets the operation step of "heating to flow on a hot plate or in a high-temperature furnace (about 400°C)" to avoid high-temperature splashing of the sample.

[0005] However, whether it is the step of "heating, melting, dehydrating, and mixing on an electric furnace" or the step of "heating to flow on a hot plate or in a high-temperature furnace", the operations in actual production are relatively complex. Moreover, in order to avoid the high-temperature splashing of the sample as much as possible, the operator needs to continuously operate near the high-temperature sample, which is somewhat dangerous, time-consuming, and inefficient. Summary of the Invention

[0006] The object of the present invention is to provide a pretreatment method for fluorine-containing samples for determining fluorine content by the ion-selective electrode method. The present invention can avoid the splashing of fluorine-containing samples during alkali fusion, has good safety, solves the problem of low fluorine content in the process of detecting fluorine-containing samples by the ion-selective electrode method, and at the same time is time-saving, efficient, and low-cost.

[0007] In order to achieve the above-mentioned invention object, the present invention provides the following technical solutions:

[0008] The present invention provides a pretreatment method for fluorine-containing samples for determining fluorine content by the ion-selective electrode method, including the following steps:

[0009] Mix a fluorine-containing sample, absolute ethanol, and an alkali reagent, and perform heat treatment to obtain a heat-treated sample; the heat treatment includes a first heat treatment and a second heat treatment carried out in sequence; the temperature of the first heat treatment is 150-170 °C; the temperature of the second heat treatment is 650-750 °C;

[0010] Extract the heat-treated sample with water, and make up the volume of the obtained leaching solution to obtain a fluorine-containing sample to be measured.

[0011] Preferably, the source of the fluorine-containing sample includes geological samples.

[0012] Preferably, the geological sample includes a rock sample or a soil sample.

[0013] Preferably, the material-liquid ratio of the fluorine-containing sample to absolute ethanol is 0.2-1.0 g: 3.0-10 mL.

[0014] Preferably, the alkali reagent includes alkali metal hydroxides.

[0015] Preferably, the alkali reagent includes at least one of sodium hydroxide and potassium hydroxide; the mass ratio of the fluorine-containing sample to the alkali reagent is 0.2-1.0: 4-8.

[0016] Preferably, the heat preservation time of the first heat treatment is 15-30 min.

[0017] Preferably, the heat preservation time of the second heat treatment is 15-30 min.

[0018] Preferably, the heat treatment is carried out in a nickel crucible.

[0019] Preferably, the temperature of the water is 90 - 100 °C.

[0020] The present invention provides a pretreatment method for a fluorine-containing sample for determining the fluorine content by an ion selective electrode method, comprising the following steps: mixing the fluorine-containing sample, absolute ethanol and an alkali reagent, and performing heat treatment to obtain a heat-treated sample; the heat treatment includes a first heat treatment and a second heat treatment performed in sequence; the temperature of the first heat treatment is 150 - 170 °C; the temperature of the second heat treatment is 650 - 750 °C; extracting the heat-treated sample with water, and making the obtained leaching solution to a constant volume to obtain a fluorine-containing sample to be measured, thereby realizing the pretreatment for determining the fluorine content of the fluorine-containing sample by the ion selective electrode method. The present invention uses absolute ethanol to remove the moisture in the fluorine-containing sample, so that the fluorine-containing sample can be directly mixed with the alkali reagent for melting, avoiding the situation of violent boiling and splashing due to the presence of moisture in the fluorine-containing sample, and solving the problem of low fluorine content in the process of detecting the fluorine-containing sample by the ion selective electrode method. Moreover, the method of the present invention does not need to heat up from room temperature for alkali fusion, reduces the alkali fusion time, improves the efficiency and reduces the cost; at the same time, there is no need for the operator to continuously operate near the high-temperature sample, and the safety is good. Detailed embodiments

[0021] The present invention provides a pretreatment method for a fluorine-containing sample for determining the fluorine content by an ion selective electrode method, comprising the following steps:

[0022] Mixing the fluorine-containing sample, absolute ethanol and an alkali reagent, and performing heat treatment to obtain a heat-treated sample; the heat treatment includes a first heat treatment and a second heat treatment performed in sequence; the temperature of the first heat treatment is 150 - 170 °C; the temperature of the second heat treatment is 650 - 750 °C;

[0023] Extracting the heat-treated sample with water, and making the obtained leaching solution to a constant volume to obtain a fluorine-containing sample to be measured.

[0024] In the present invention, unless otherwise specified, the raw materials used are commercially available products well-known to those skilled in the art or prepared by methods well-known to those skilled in the art.

[0025] The present invention mixes the fluorine-containing sample, absolute ethanol and an alkali reagent, and performs heat treatment to obtain a heat-treated sample.

[0026] In the present invention, the source of the fluorine-containing sample may include geological samples; the geological samples may include rock samples, water samples or soil samples. In the present invention, the rock sample may be an ore sample. In the present invention, the particle size of the fluorine-containing sample may not exceed 74 μm (below 200 mesh), referring to Part 12 of "Methods for Chemical Analysis of Silicate Rocks - GB / T 14506.12-2010", Part 15 of "Methods for Chemical Analysis of Tin Concentrates - GB / T1819.15-2017" or Part 5 of "Methods for Chemical Analysis of Copper Concentrates - GB / T3884.5-2012".

[0027] The material-liquid ratio of the fluorine-containing sample to absolute ethanol in the present invention may be 0.2-1.0 g: 3.0-10 mL; in a specific embodiment of the present invention, the material-liquid ratio of the fluorine-containing sample to absolute ethanol is 1.0 g: 10 mL. In the present invention, the alkali reagent may include alkali metal hydroxides. In the present invention, the alkali reagent may include at least one of sodium hydroxide and potassium hydroxide; in a specific embodiment of the present invention, the alkali reagent is sodium hydroxide or potassium hydroxide. The mass ratio of the fluorine-containing sample to the alkali reagent in the present invention may be 0.2-1.0: 4-8; in a specific embodiment of the present invention, the mass ratio of the fluorine-containing sample to the alkali reagent is 1.0: 8. The commonly used alkali fusion reagent in the art, such as sodium peroxide, will react violently with ethanol and even cause combustion under acidic conditions; in contrast, the present invention uses relatively stable potassium hydroxide or sodium hydroxide as the alkali fusion reagent, which has low cost, is safe and convenient to operate. The heat treatment in the present invention includes a first heat treatment and a second heat treatment carried out in sequence. In the present invention, the temperature of the first heat treatment is 150-170 °C; the heat preservation time of the first heat treatment may be 15-30 min. In a specific embodiment of the present invention, the temperature of the first heat treatment is 170 °C; the heat preservation time of the first heat treatment is 20 min. In the present invention, the temperature of the second heat treatment is 650-750 °C; the heat preservation time of the second heat treatment may be 15-30 min. In a specific embodiment of the present invention, the temperature of the second heat treatment is 700 °C; the heat preservation time of the second heat treatment is 15 min. The heat treatment in the present invention may be carried out in a nickel crucible.

[0028] After obtaining the heat-treated sample, the present invention leaches the heat-treated sample with water and makes the obtained leachate constant volume to obtain a fluorine-containing sample to be measured. In the present invention, the temperature of the water may be 90-100 °C; in a specific embodiment of the present invention, the temperature of the water is 100 °C. In the present invention, the conditions for constant volume include: the temperature is 20-35 °C.

[0029] The present invention uses absolute ethanol to remove the moisture in the fluorine-containing sample, enabling the fluorine-containing sample to be directly mixed with an alkali reagent for melting, avoiding the situation of violent boiling and splashing due to the presence of moisture in the fluorine-containing sample, and solving the problem of low fluorine content in the process of detecting the fluorine-containing sample by the ion selective electrode method. Moreover, the method of the present invention does not require heating from room temperature for alkali fusion, reducing the alkali fusion time, improving efficiency, and reducing costs.

[0030] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0031] The sources of the fluorine-containing samples used in the examples are national standard rock, soil, and ore samples and actual sampling samples;

[0032] The "room temperature" mentioned in the examples is 25 °C.

[0033] Example 1

[0034] Add 0.5 g of the fluorine-containing sample to a nickel crucible, add 5 mL of absolute ethanol to the nickel crucible, then add 4 g of solid sodium hydroxide to the nickel crucible. Place the nickel crucible containing the materials on a hot plate at 170 °C and keep it warm and bake for 20 min at a temperature of 170 °C. After completion, put the nickel crucible containing the materials into a muffle furnace at 700 °C and keep it warm and melt for 15 min at a temperature of 700 °C to obtain a molten material. Extract the molten material with boiling water at 100 °C, and make the obtained leaching solution constant volume to 100 mL at room temperature conditions to obtain a fluorine-containing sample to be measured.

[0035] Test Example 1

[0036] Establishment of the standard curve:

[0037] Take 0 mL, 0.5 mL, 1 mL, 2 mL, 5 mL, and 10 mL of a 10 μg / mL fluoride ion standard solution, and add 10 mL of a blank solution to each of them for ion selective electrode testing to obtain the data shown in Table 1:

[0038] Table 1 Ion selective electrode test results of the fluoride ion standard solution

[0039] Fluorine content m (μg) 0 5 10 20 50 100 x lg m - 0.699 1.000 1.301 1.699 2.000 y Potential (mv) 319.0 293.2 274.8 257.6 234.1 216.5

[0040] Based on the data shown in Table 1, establish a standard curve. The standard curve equation is y = -58.795x + 334.01, R 2 = 0.9999.

[0041] The rock and soil standard samples GSR-5 (GBW07107), GSS-29 (GBW07385), and GSS-7 (GBW07407) were tested respectively according to the pretreatment method in Example 1 for accuracy analysis, and the results are shown in Table 2.

[0042] Table 2 Fluoride content in standard samples

[0043]

[0044] It can be seen from the data in Table 2 that after the standard samples are processed according to the pretreatment method provided by the present invention, the measured values of the fluoride content in the obtained standard samples are within the error range required by the national standard compared with the accurate values, indicating that the test results of the fluoride content in the fluorine-containing samples processed by the pretreatment method provided by the present invention are accurate.

[0045] The results show that no sample splashing occurred during the operation of Example 1, solving the problem of low fluoride content during the detection of fluorine-containing samples by the ion selective electrode method.

[0046] Comparative Example 1

[0047] The temperature of the hot plate in Example 1 was adjusted to 180 °C, and the other conditions were the same as those in Example 1.

[0048] The results show that due to the high heat of absolute ethanol and the too fast evaporation rate, splashing occurred during the melting process of the sample in Comparative Example 1, resulting in a low fluoride content during the actual sample detection process.

[0049] Comparative Example 2

[0050] The amount of absolute ethanol in Example 1 was adjusted to 0 mL, 1 mL, 3 mL, 5 mL, and 7 mL respectively, and the other conditions were the same as those in Example 1 to test whether 0.5 g of fluorine-containing samples could be completely wetted.

[0051] The results show that when the fluorine-containing sample is 0.5 g, the fluorine-containing samples cannot be completely wetted when the amount of absolute ethanol added is 0 mL, 1 mL, and 3 mL. When the amount of absolute ethanol added reaches 5 mL or more, the purpose of complete sample infiltration can be achieved.

[0052] Comparative Example 3

[0053] The temperature of the hot plate in Example 1 was adjusted to 140 °C, 150 °C, 160 °C, 170 °C, and 180 °C respectively, and the time required for the fluorine-containing sample to be completely dried was recorded. The results are shown in Table 3.

[0054] Table 3 Time required for the fluorine-containing sample to be completely dried at different temperatures

[0055]

[0056] As can be seen from Table 3, the higher the temperature, the faster the evaporation rate of absolute ethanol. However, when the temperature reaches 180 °C, the sample splashes. Considering comprehensively from the perspectives of experimental efficiency and safety, it is most appropriate to select 170 °C as the temperature for drying on the hot plate.

[0057] Comparative Example 4

[0058] The temperatures of the muffle furnace in Example 1 were adjusted to 600 °C, 650 °C, 700 °C, 750 °C, and 800 °C respectively, and other conditions were the same as those in Example 1. The fluorine content in the fluorine-containing sample (standard sample - 1) was recorded, and the results are shown in Table 4.

[0059] Table 4 Fluorine content in fluorine-containing samples at different melting temperatures

[0060]

[0061] According to the national standard, a nickel crucible is used for alkali fusion, and the temperature is generally between 650 and 750 °C. Above 700 °C, the nickel crucible will accelerate oxidation, resulting in a shortened service life of the nickel crucible. As can be seen from Table 4, 700 °C is the most suitable temperature for alkali fusion, which can not only fully melt the fluorine-containing sample but also well protect the nickel crucible.

[0062] Comparative Example 5

[0063] Under the condition of 700 °C, the alkali fusion of fluorine-containing samples (standard sample - 1, standard sample - 2, standard sample - 3) was carried out. The alkali fusion time was adjusted to 10 min, 15 min, 20 min, 25 min, and 30 min respectively, and other conditions were the same as those in Example 1. The fluorine content in the fluorine-containing samples was recorded, and the results are shown in Table 5.

[0064] Table 5 Fluorine content in fluorine-containing samples at different melting times

[0065]

[0066] As can be seen from Table 5, if the alkali fusion time is too short, the fluorine-containing sample will not be completely melted, resulting in a low fluorine content in the fluorine-containing sample. When the alkali fusion time ≥ 15 min, the melting condition of the fluorine-containing sample is good. In addition, in fluorine-containing samples with a low fluorine content, due to the too low fluorine content, the instrument is slow to stabilize, so the detection value will be higher than the standard value.

[0067] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, not all embodiments. People can also obtain other embodiments based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for pre-treating a fluorine-containing sample for determining fluorine content by an ion selective electrode method, characterized in that: The following steps are involved: The fluorine-containing sample, anhydrous ethanol and an alkali reagent are mixed and heat-treated to obtain a heat-treated sample; the heat treatment includes a first heat treatment and a second heat treatment performed in sequence; the temperature of the first heat treatment is 150-170° C.; the temperature of the second heat treatment is 650-750° C.; The heat-treated sample is leached with water, and the obtained leaching solution is fixed to volume to obtain a fluorine-containing sample to be tested.

2. The pre-treatment method according to claim 1, characterized in that: The sources of the fluorine-containing samples include geological samples.

3. The pre-treatment method according to claim 2, characterized in that: The geological sample includes a rock sample or a soil sample.

4. The pretreatment method according to any one of claims 1 to 3, characterized in that: The solid-liquid ratio of the fluorine-containing sample to anhydrous ethanol is 0.2-1.0 g: 3.0-10 mL.

5. The pre-treatment method according to claim 1, characterized in that: The alkaline agent includes an alkali metal hydroxide.

6. The pre-treatment method according to claim 1 or 5, characterized in that: The alkaline reagent includes at least one of sodium hydroxide and potassium hydroxide; the mass ratio of the fluorine-containing sample to the alkaline reagent is 0.2-1:4-8.

7. The pre-treatment method according to claim 1, characterized in that: The holding time of the first heat treatment is 15 to 30 minutes.

8. The pre-treatment method according to claim 1, characterized in that: The holding time of the second heat treatment is 15 to 30 minutes.

9. The pre-treatment method according to claim 1, characterized in that: The heat treatment was performed in a nickel crucible.

10. The pre-treatment method according to claim 1, characterized in that: The temperature of the water is 90-100°C.

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