CN110231375B - Method for detecting fluorine content in phosphoric acid and phosphoric acid salt thereof by standard addition method - Google Patents
Method for detecting fluorine content in phosphoric acid and phosphoric acid salt thereof by standard addition method Download PDFInfo
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Abstract
A method for detecting the fluorine content in phosphoric acid and phosphate thereof by a standard addition method is characterized in that a sample is dissolved by hydrochloric acid, a saturated calomel electrode is used as a reference electrode, a fluorine ion selective electrode is used as an indicating electrode in a solution with the pH value of 5.5-6.0, the electrode potential of the solution is directly measured, the fluorine content is measured by the standard addition method, and the result is calculated by a formula. The detection method of the invention does not need to draw a fluorine standard working curve, but has detection limit and accuracy equivalent to those of a working curve method, and compared with the working curve method, the detection method of the invention has the advantages of simpler and quicker operation, low analysis cost, wide measurement range and wide application range. The invention is not only suitable for phosphorite with higher fluorine content and wet-process dihydrate/semi-hydrated phosphoric acid; also suitable for phosphogypsum with slightly low fluorine content, defluorinated phosphoric acid and fertilizer grade/feed grade phosphate samples; it is also suitable for purified phosphoric acid, food phosphoric acid, industrial phosphoric acid, etc. with fluorine content as low as 0.001% or more.
Description
Technical Field
The invention belongs to the technical field of analysis and detection, and particularly relates to a method for detecting fluorine content in phosphoric acid and phosphate thereof by a standard addition method, which is suitable for measuring the fluorine ion content in phosphoric acid samples and phosphate samples thereof with different fluorine contents at different stages and samples such as phosphorite, phosphogypsum and the like.
Background
Fluorine is a nonmetallic chemical element, has very active chemical property, can hardly exist independently, exists in various compound states in nature, and widely exists in rocks, soil and oceans; taking phosphorus chemical industry as an example, fluorine is a main component of phosphate ore, and in the preparation process of phosphoric acid, most of fluorine enters atmosphere in the form of hydrogen fluoride, a small part of fluorine enters phosphogypsum, and the rest of fluorine enters phosphoric acid completely, so that a large amount of fluorine exists in phosphoric acid, phosphide and other phosphate products; its content in external environment and various living bodies is an important mark for measuring ecological environment quality and human health. Therefore, the analytical measurement of fluorine is an important issue, and heretofore, the analysis of fluorine has been generally performed by colorimetry, spectrophotometry, titration, a fluoride ion selective electrode method, and modern ion chromatography; the detection method provided by the invention has the advantages of no need of drawing a fluorine standard working curve, detection limit and accuracy equivalent to those of a working curve method, simplicity and rapidness in operation compared with the working curve method, low analysis cost, wide measurement range and wide method application range. The detection method provided by the invention is suitable for phosphorite with high fluorine content and wet-process dihydrate/semi-hydrated phosphoric acid; also suitable for phosphogypsum with slightly low fluorine content, defluorinated phosphoric acid and fertilizer grade/feed grade phosphate samples; it is also suitable for purifying phosphoric acid, food phosphoric acid, industrial phosphoric acid, etc. with fluorine content as low as 0.0010%.
Disclosure of Invention
The invention solves the technical problem of providing a fluorine content detection method which has high detection precision, large detection range, simple and quick operation and can quickly obtain accurate data without expensive detection equipment;
in view of the above, the present invention provides a method for detecting fluorine content in phosphoric acid and its phosphate by a standard addition method, which comprises the following steps:
step 1, providing a fluorine standard solution with the concentration of 1 mg/ml; the preparation method comprises the following specific steps: accurately weighing 0.221g of standard sodium fluoride by using an electronic balance, completely transferring the standard sodium fluoride after dissolving in water into a 100ml volumetric flask, diluting the standard sodium fluoride to a scale with water, and shaking up;
step 2, providing (1+1) hydrochloric acid solution, (1+19) nitric acid solution, (200g/L) sodium hydroxide solution, citric acid-sodium citrate buffer solution with the pH value of 5.5-6.0, and (1g/L) bromocresol green indicating solution;
the preparation method comprises the following steps: (1+1) hydrochloric acid solution: measuring 500ml of analytically pure hydrochloric acid solution by using a glass measuring cup, uniformly mixing with 500ml of pure water, and placing in a 1000ml narrow-mouth glass bottle; (1+19) nitric acid solution: measuring 25ml of analytically pure nitric acid solution by using a glass measuring cup, uniformly mixing with 475ml of pure water, and placing in a 500ml brown thin-mouth glass bottle to be protected from light for storage; 200g/L sodium hydroxide solution: weighing 200g (accurate to 0.02g) of analytically pure sodium hydroxide, adding water for dissolving, cooling, fixing the volume to a 1000ml volumetric flask, shaking up, and placing in a 1000ml narrow-mouth polyethylene bottle; a citric acid-sodium citrate buffer solution with pH of 5.5-6.0: weighing 24g of analytically pure citric acid monohydrate and 270g of analytically pure trisodium citrate dihydrate, dissolving in water, diluting to 1000ml, and mixing uniformly; 1g/L bromocresol green indicator fluid: weighing 0.1g of bromocresol green, dissolving in 20ml of absolute ethyl alcohol, diluting with water to 100ml, and uniformly mixing;
step 3, preparing a sample solution to be detected:
liquid phosphoric acid sample treatment: accurately weighing 0.5-5 g of phosphoric acid sample (accurate to +/-0.0002 g) by using an electronic balance, adding 1-10 ml (1+1) of hydrochloric acid solution for dissolving, and placing in a 50ml volumetric flask to ensure that the content of fluorine ions in the liquid to be measured in the 50ml volumetric flask is 50-150 mu g; if the fluorine content of the phosphoric acid sample is too high, diluting the phosphoric acid sample; if the fluorine content of the sample is too low, the sample weighing mass is properly increased;
② solid phosphate sample treatment: accurately weighing 1-1.5 g of phosphate sample (accurate to +/-0.0002 g) in a 100ml beaker by using an electronic balance, adding 10-15 ml of (1+1) hydrochloric acid solution, heating to completely dissolve the sample, and transferring to v2Volumetric flask, diluting with water to scale, shaking, and accurately transferring v with pipette1The volume of the solution is 50ml volumetric flask;
processing phosphate rock and phosphogypsum samples: weighing 0.1-0.5 g of sample (accurate to +/-0.0002 g), placing the sample in a 100ml plastic beaker, wetting the sample with a small amount of water, adding 8-12 ml of (1+1) hydrochloric acid solution, stirring the mixture on a magnetic stirrer for 30min, and transferring the mixture to a v2Volumetric flask, diluting with water to scale, shaking, dry filtering, and accurately transferring v with pipette1The volume of clear filtrate is transferred to a 50ml volumetric flask;
step 4, adjusting the pH value of the solution to be detected: adding 3-6 drops of citric acid-sodium citrate buffer solution with the pH value of 5.5-6.0 and 2-5 drops of 1g/L bromocresol green indicator solution into a solution to be tested, adjusting the solution to be blue or blue-green with 200g/L sodium hydroxide solution, adjusting the solution to be yellow with (1+19) nitric acid solution, adding 15-20 ml of citric acid-sodium citrate buffer solution, diluting with water to a scale, and uniformly mixing;
step 5, potential measurement: pouring the liquid to be tested obtained in the step 4 into a dry 50ml plastic beaker, inserting a fluorine ion selective electrode and a saturated calomel electrode, measuring the potential value during balancing under magnetic stirring, adding 0.5ml of fluorine standard solution (1mg/ml), recording the potential value after rebalancing, and measuring the temperature of the solution;
step 6, calculating fluorine content: the fluorine content was calculated from Δ U using the formula: the formula is as follows:
wherein, the delta U is the difference of the potential values measured in two times, and is preferably 40-60; m is a numerical value of the mass of the weighed sample, and the unit is g; antilog refers to Antilog; 0.0005 means that the fluorine standard solution added corresponds to the fluorine content in g; k is the actual slope or the theoretical value of the Nernst slope obtained by a laboratory and is obtained by checking an attached table according to the temperature of the solution; v. of1/v2Is the dilution factor, v1Is the volume taken, v2The volume is determined by volume, and the unit is ml.
In the invention, the concentration of the liquid solution is expressed by v1+ v2 (for example, the concentration of hydrochloric acid solution is 1+1, and the concentration of nitric acid solution is 1+19), which means that solute with v1 volume and solvent with v2 volume are mixed and shaken up, and the same solution format appears in the invention, which is the same as the description, and the repeated description is not repeated;
in the step 3 of the invention, if the fluorine content of the phosphoric acid sample is too high in the preparation of the sample liquid phosphoric acid solution to be detected, the operation of diluting the phosphoric acid sample is as follows: accurately weighing 1-1.5 g of sample (accurate to +/-0.0002 g) by using an electronic balance, adding 10-15 ml of (1+1) hydrochloric acid solution for dissolving, and transferring to a v2In a volumetric flask with the volume, accurately transferring v by a pipette after shaking up with water to a constant volume1Placing the volume of the solution in a 50ml volumetric flask to ensure that the content of the fluorine ions in the solution to be measured in the 50ml volumetric flask is between 50 and 150 mu g;
in the step 3, the preparation of the liquid to be tested of the solid phosphate sample and the phosphate rock and phosphogypsum sample is carried out by adopting different sample treatment methods or adding a heating or dry filtering process according to the difference of the properties of the samples, so that the liquid to be tested entering a 50ml volumetric flask cannot contain undissolved samples or colors so as to avoid interfering with the subsequent measurement.
The step 4 of the invention for adjusting the (1+19) nitric acid solution to be yellow is to slowly add the (1+19) nitric acid solution to adjust the color, the color can be stopped when the color is changed to be yellow, and the excessive amount cannot be caused, so that the problem that the subsequent added citric acid-sodium citrate buffer solution exceeds the buffering range to influence the analysis result due to the overhigh acidity of the solution is avoided;
in the step 4 of the invention, the pH range of the added 15-20 ml citric acid-sodium citrate buffer solution is 5.5-6.0, because the activity of fluorine ions is reduced when the pH is less than 5.0 and the equilibrium time is prolonged when the pH is more than 8, the acidity of the solution to be measured is controlled to be 5.5-6.0. The acidity of the solution to be detected can be controlled and the interference of iron and aluminum plasma can be eliminated by adding the citric acid-sodium citrate buffer solution;
the core requirement in the preparation of the solution to be tested in the step 3 of the invention is as follows: the fluorine ion content of the liquid to be measured in a 50ml volumetric flask is between 50 and 150 mu g; the specific operation is to adjust the sample weighing mass and v1/v2The value of Δ U is preferably 40 to 60.
The core requirement in the potential measurement of step 5 of the invention is as follows: a measuring scale capable of accurately sucking the solution by using a calibrated graduated pipette or a pipette with a large belly can accurately suck 0.5ml of fluorine standard solution (1mg/ml), and records the value after the equipotential value is balanced.
The invention has the advantages that the fluorine content is measured by using the fluorine ion selective electrode standard addition method, a fluorine standard working curve does not need to be drawn, but the detection limit and the accuracy are equivalent to those of a working curve method, and compared with the working curve method, the detection method provided by the invention has the advantages of simpler and faster operation, low analysis cost, wide measurement range and wide application range.
The detection method provided by the invention is suitable for phosphorite with high fluorine content and wet-process dihydrate/semi-hydrated phosphoric acid; also suitable for phosphogypsum with slightly low fluorine content, defluorinated phosphoric acid and fertilizer grade/feed grade phosphate samples; it is also suitable for purified phosphoric acid, food phosphoric acid, industrial phosphoric acid, etc. with fluorine content as low as 0.001% or more.
Attached K value table for calculation of the invention
The theoretical K value of the actual slope or Nernst slope determined experimentally in the determination of the fluorine content.
Detailed Description
In the following, the technical solutions in the embodiments of the present invention will be clearly and completely described according to different samples in combination with the embodiments of the present invention, including detailed descriptions of the detection range, detection limit, allowable deviation, etc. of the method. The described embodiments are only a few embodiments of the present invention, not all embodiments of the present invention.
The following are specific embodiments, which illustrate specific embodiments of the present invention in detail.
Example 1
Determination of fluoride content (in F) in industrial wet-process purified phosphoric acid and food-grade phosphoric acid
1. Analytical instrument and reagent
A conventional analytical instrument, a mettler ME204E electronic balance, an acidimeter or potentiometer (precision 2 mV/grid), a magnetic stirrer; 1mg/ml fluorine standard solution, (1+1) hydrochloric acid solution concentration, (1+19) nitric acid solution, 200g/L sodium hydroxide solution, citric acid-sodium citrate buffer solution with pH of 5.5-6.0, and 1g/L bromocresol green indicator solution;
2. concrete preparation steps of reagent
1mg/ml fluorine standard solution: accurately weighing 0.221g of standard sodium fluoride by using an electronic balance, completely transferring the standard sodium fluoride after dissolving in water into a 100ml volumetric flask, diluting the standard sodium fluoride to a scale with water, and shaking up;
(1+1) hydrochloric acid solution: measuring 500ml of analytically pure hydrochloric acid solution by using a glass measuring cup, uniformly mixing with 500ml of pure water, and placing in a 1000ml narrow-mouth glass bottle; (1+19) nitric acid solution: measuring 25ml of analytically pure nitric acid solution by using a glass measuring cup, uniformly mixing with 475ml of pure water, and placing in a 500ml brown thin-mouth glass bottle to be protected from light for storage; 200g/L sodium hydroxide solution: weighing 200g (accurate to 0.02g) of analytically pure sodium hydroxide, adding water for dissolving, cooling, fixing the volume to a 1000ml volumetric flask, shaking up, and placing in a 1000ml narrow-mouth polyethylene bottle; a citric acid-sodium citrate buffer solution with pH of 5.5-6.0: weighing 24g of analytically pure citric acid monohydrate and 270g of analytically pure trisodium citrate dihydrate, dissolving in water, diluting to 1000ml, and mixing uniformly; 1g/L bromocresol green indicator fluid: 0.1g of bromocresol green is weighed and dissolved in 20ml of absolute ethanol, diluted to 100ml with water and mixed evenly.
3. Preparing a solution to be detected: accurately weighing 2.5-5 g of phosphoric acid sample (accurate to 0.0002g) by using an electronic balance, adding 1-2 ml (1+1) of hydrochloric acid solution, and placing in a 50ml volumetric flask to ensure that the fluorine ion content of the liquid to be measured in the 50ml volumetric flask is 50-150 mu g;
4. the determination step comprises:
adding 3-6 drops of citric acid-sodium citrate buffer solution with the pH value of 5.5-6.0 and 2-5 drops of 1g/L bromocresol green indicator solution into a solution to be detected, adjusting the solution to be blue or blue-green with 200g/L sodium hydroxide solution, adjusting the solution to be yellow with (1+19) nitric acid solution, adding 15-20 ml of citric acid-sodium citrate buffer solution, diluting the solution to a scale with water, and uniformly mixing; pouring all the materials into a dry 50ml plastic beaker, inserting a fluorine ion selective electrode and a saturated calomel electrode, measuring the potential value during balancing under magnetic stirring, adding 0.5ml of fluorine standard solution, recording the potential value after rebalancing, and measuring the temperature of the solution;
5. and (3) calculating the fluorine content: the values are expressed in% in mass fraction of the mass of fluorine (F) and are calculated according to the following formula:
wherein, the delta U is the difference of the potential values measured in two times, and is preferably 40-60; m is a numerical value of the mass of the weighed sample, and the unit is g; antilog refers to Antilog; 0.0005 means that the fluorine standard solution added corresponds to the fluorine content in g; k is the actual slope or the theoretical value of the Nernst slope obtained by a laboratory and is obtained by checking an attached table according to the temperature of the solution; v. of1/v2Is the dilution factor, v1Is the volume taken, v2The volume is determined by volume, and the unit is ml.
6. The fluoride content (in terms of F) of industrial wet-cleaned phosphoric acid and food grade phosphoric acid is shown in table 1, and when the chloride ion content in the sample is lower than 0.002%, the allowable relative deviation between two parallel samples is not more than 50%; when the content of the chloride ions in the samples is more than 0.002 percent and less than 0.04 percent, the allowable relative deviation between the two parallel samples is not more than 25 percent.
TABLE 1
7. As can be seen from the embodiment 1, the detection method provided by the invention has higher precision and accuracy and lower detection limit when detecting the fluorine content in the phosphoric acid sample.
Example 2
Measuring the fluorine content (counted as F) in an intermediate sample of the industrial wet-process purified phosphoric acid by an organic solvent extraction method;
1. the intermediate sample comprises raw material wet-process phosphoric acid (after defluorination), raffinate phosphoric acid, extracted phosphoric acid, raffinate phosphoric acid and back-extracted phosphoric acid;
2. the areas of this embodiment and embodiment 1 are sample processing, and the weighed mass and dilution factor of each sample are different due to the difference of fluorine content of each intermediate sample;
3. the operations of analyzing instruments, reagents and the liquid to be detected, such as pH adjustment, potential measurement, fluorine content calculation and the like, required by the embodiment are the same as those of the embodiment 1;
4. raw material wet-process phosphoric acid (after defluorination) and raffinate phosphoric acid sample treatment: accurately weighing 1-1.5 g (accurate to 0.0002g) of the sample, placing the sample in a 100ml beaker, adding 10-15 ml (1+1) of hydrochloric acid solution, transferring the solution to a 250ml volumetric flask after dissolution, diluting the solution to a scale with water, and shaking up. Accurately transferring 10ml or 15ml of test solution to a 50ml volumetric flask by using a pipette;
5. and (3) extracting phosphoric acid and washing residual phosphoric acid samples: accurately weighing 0.5-1 g of acid sample (accurate to 0.0002g) by using an electronic balance, adding 2-5 ml (1+1) of hydrochloric acid solution, and placing in a 50ml volumetric flask;
6. and (3) treatment of a back extraction phosphoric acid sample: accurately weighing 2.5-5 g of phosphoric acid sample (accurate to 0.0002g) by using an electronic balance, adding 1-2 ml (1+1) of hydrochloric acid solution, and placing in a 50ml volumetric flask;
7. according to the detection method provided by the invention, the fluorine content measurement data of each sample in the embodiment is shown in table 2; when the content of the fluorine ions in the samples is between 0.002% and 0.01%, the allowable relative deviation between two parallel samples is not more than 25%; when the content of the fluoride ions in the samples is more than 0.01 percent, the allowable relative deviation between two parallel samples is not more than 15 percent;
TABLE 2
8. As can be seen from the embodiment 2, the detection method provided by the invention has strong sample applicability when detecting the content of the fluorine ions in the phosphoric acid sample, can be used for accurately detecting phosphoric acid samples with large fluorine ion content difference, and has the advantages of high data precision and large detection range.
Example 3
Measuring the fluorine content (counted as F) in the phosphate sample;
1. the present case mainly uses feed-grade calcium hydrogen phosphate and calcium dihydrogen phosphate as examples to describe the detection method provided by the present invention;
2. the difference between the present embodiment and embodiment 1 and embodiment 2 is that the sample described in the present embodiment is a solid sample, the sample treatment is slightly different from that of a liquid sample, and the dilution factor is also determined according to the fluorine content in the sample; an electric heating plate is added on the analyzer, and the rest parts are not different;
3. the analytical instruments required by the embodiment are the same as those in embodiment 2 except that an electric heating plate is added, and the operations of pH adjustment, potential measurement, fluorine content calculation and the like of the required reagent and the liquid to be measured are the same as those in embodiment 2;
4. sample treatment: accurately weighing 1-1.5 g (accurate to 0.0002g) of a test sample, placing the test sample in a 100ml beaker, wetting the test sample with a small amount of water, adding 10-15 ml (1+1) of hydrochloric acid solution, completely dissolving the test sample by using an electric hotplate, transferring the test sample to a 250ml volumetric flask, diluting the test sample to a scale with water, shaking up the test sample, and accurately transferring 20ml of test solution to a 50ml volumetric flask by using a pipette;
5. adjusting the pH value of the solution to be measured and measuring the potential according to the embodiment 1; in the embodiment, the fluorine content is calculated by using a formula, wherein the dilution multiple v1/v2 is 20/250;
6. according to the detection method provided by the invention, the fluorine content measurement data of the sample of the embodiment is shown in table 3; the allowable relative deviation between two parallel samples is not more than 15%;
TABLE 3
7. As can be seen from the embodiment 3, the relative deviation between the detection method provided by the invention and the national standard determination method is not more than 15% when the content of the fluorine ions in the phosphate samples is detected, and the parallelism between the samples is also good, which indicates that the detection method provided by the invention can be used for determining the phosphate samples.
Example 4
Measuring the total fluorine content (calculated as F) in the phosphorite and phosphogypsum samples;
1. the embodiment mainly takes phosphorite and phosphogypsum as examples to describe the detection method provided by the invention;
2. the difference between the present embodiment and the previous three embodiments is the sample weighing quality and the processing method;
3. the operations of other analytical instruments, reagents and the to-be-detected liquid such as pH adjustment, potential measurement and the like required by the embodiment are the same as those of the embodiment 1, and the description is not repeated in the embodiment;
4. and (3) phosphorite sample treatment: weighing 0.1-0.2 g (accurate to 0.0002g) of phosphate rock sample which passes through a 125-micron test sieve and is dried for more than 2 hours at 105-110 ℃, putting the phosphate rock sample into a 100ml beaker, wetting the phosphate rock sample with a small amount of water, adding 8-12 ml (1+1) of hydrochloric acid solution, stirring the phosphate rock sample on a magnetic stirrer for 30min, transferring the phosphate rock sample to a 250ml volumetric flask, diluting the phosphate rock sample to a scale with water, shaking the phosphate rock sample evenly, drying and filtering the phosphate rock sample by using filter paper, and accurately transferring 10ml of clear filtrate to a 50ml volumetric flask by using a transfer pipette;
5. phosphogypsum sample treatment: weighing about 0.4-0.5 g (accurate to 0.0002g) of a dry-base phosphogypsum sample, placing the dry-base phosphogypsum sample in a 100ml beaker, wetting the dry-base phosphogypsum sample with a small amount of water, adding 8-12 ml (1+1) of hydrochloric acid solution, stirring the mixture on a magnetic stirrer for 30min, transferring the mixture to a 250ml volumetric flask, diluting the mixture to a scale with water, shaking the mixture evenly, performing dry filtration by using filter paper, and accurately transferring 10ml of clear filtrate to a 50ml volumetric flask by using a transfer pipette;
6. adjusting the pH value of the solution to be measured and measuring the potential according to the embodiment 1; in the embodiment, the fluorine content is calculated by using a formula, wherein the dilution multiple v1/v2 is 10/250;
7. according to the detection method provided by the invention, the fluorine content measurement data of the sample in the embodiment is shown in table 4; the allowable relative deviation between two parallel samples is not more than 15%;
TABLE 4
8. Through the embodiment 4, the relative deviation between the detection method provided by the invention and the national standard determination method is not more than 15% when the content of the fluorine ions in the phosphate ore and phosphogypsum samples is detected, and the samples are good in parallelism, so that the detection method provided by the invention is completely suitable for determining the phosphate ore and phosphogypsum samples.
Theoretical K value of actual slope or Nernst slope obtained by experiment when the fluorine content is measured by attached table
| Temperature of | K | Temperature of | K | Temperature of | K |
| 0 | 54.20 | 15 | 57.17 | 30 | 60.15 |
| 1 | 54.30 | 16 | 57.37 | 31 | 60.35 |
| 2 | 54.59 | 17 | 57.57 | 32 | 60.55 |
| 3 | 54.79 | 18 | 57.77 | 33 | 60.74 |
| 4 | 54.99 | 19 | 57.97 | 34 | 60.94 |
| 5 | 55.19 | 20 | 58.17 | 35 | 61.14 |
| 6 | 55.39 | 21 | 58.36 | 36 | 61.34 |
| 7 | 55.59 | 22 | 58.56 | 37 | 61.54 |
| 8 | 55.78 | 23 | 58.76 | 38 | 61.74 |
| 9 | 55.98 | 24 | 58.96 | 39 | 61.93 |
| 10 | 56.18 | 25 | 59.16 | 40 | 62.13 |
| 11 | 56.38 | 26 | 59.36 | 41 | 62.33 |
| 12 | 56.58 | 27 | 59.55 | 42 | 62.53 |
| 13 | 56.77 | 28 | 59.75 | 43 | 62.73 |
| 14 | 56.97 | 29 | 59.95 |
Claims (7)
1. A method for detecting the fluorine content in phosphoric acid and phosphate thereof by a standard addition method comprises the following detection steps:
step 1, providing a fluorine standard solution with the concentration of 1 mg/ml; the preparation steps are as follows: accurately weighing 0.221g of standard sodium fluoride by using an electronic balance, completely transferring the standard sodium fluoride after dissolving in water into a 100ml volumetric flask, diluting the standard sodium fluoride to a scale with water, and shaking up;
step 2, providing (1+1) hydrochloric acid solution, (1+19) nitric acid solution, 200g/L sodium hydroxide solution, citric acid-sodium citrate buffer solution with the pH value of 5.5-6.0 and 1g/L bromocresol green indicator solution;
the preparation method comprises the following steps: (1+1) hydrochloric acid solution: measuring 500ml of analytically pure hydrochloric acid solution by using a glass measuring cup, uniformly mixing with 500ml of pure water, and placing in a 1000ml narrow-mouth glass bottle; (1+19) nitric acid solution: measuring 25ml of analytically pure nitric acid solution by using a glass measuring cup, uniformly mixing with 475ml of pure water, and placing in a 500ml brown thin-mouth glass bottle to be protected from light for storage; 200g/L sodium hydroxide solution: weighing 200g of analytically pure sodium hydroxide, adding water to dissolve, cooling, metering the volume to a 1000ml volumetric flask, shaking up, and placing in a 1000ml narrow-mouth polyethylene bottle; a citric acid-sodium citrate buffer solution with pH of 5.5-6.0: weighing 24g of analytically pure citric acid monohydrate and 270g of analytically pure trisodium citrate dihydrate, dissolving in water, diluting to 1000ml, and mixing uniformly; 1g/L bromocresol green indicator fluid: weighing 0.1g of bromocresol green, dissolving in 20ml of absolute ethyl alcohol, diluting with water to 100ml, and uniformly mixing;
step 3, preparing a sample solution to be detected:
liquid phosphoric acid sample treatment: accurately weighing 0.5-5 g of phosphoric acid sample by using an electronic balance, adding 1-10 ml (1+1) of hydrochloric acid solution for dissolving, and placing in a 50ml volumetric flask to ensure that the content of fluorine ions in the liquid to be measured in the 50ml volumetric flask is 50-150 mu g; if the fluorine content of the phosphoric acid sample is too high, diluting the phosphoric acid sample; if the fluorine content of the sample is too low, the sample weighing mass is properly increased;
② solid phosphate sample treatment: accurately weighing 1-1.5 g of phosphate sample in a 100ml beaker by using an electronic balance, adding 10-15 ml of (1+1) hydrochloric acid solution to completely dissolve the sample, and transferring the sample to v2Volumetric flask, diluting with water to scale, shaking, and accurately transferring v with pipette1The volume of the solution is 50ml volumetric flask;
processing phosphate rock and phosphogypsum samples: weighing 0.1-0.5 g of sample, accurately weighing to 0.0002g, placing in a 100ml plastic beaker, wetting with a small amount of water, adding 8-12 ml of (1+1) hydrochloric acid solution, stirring on a magnetic stirrer for 30min, transferring to v2Volumetric flask, diluting with water to scale, shaking, dry filtering, and accurately transferring v with pipette1The volume of clear filtrate is transferred to a 50ml volumetric flask;
step 4, adjusting the pH value of the solution to be detected: adding 3-6 drops of citric acid-sodium citrate buffer solution with the pH value of 5.5-6.0 and 2-5 drops of 1g/L bromocresol green indicator solution into a solution to be tested, adjusting the solution to be blue or blue-green with 200g/L sodium hydroxide solution, adjusting the solution to be yellow with (1+19) nitric acid solution, adding 15-20 ml of citric acid-sodium citrate buffer solution, diluting with water to a scale, and uniformly mixing;
step 5, potential measurement: pouring the liquid to be tested obtained in the step 4 into a dry 50ml plastic beaker, inserting a fluorine ion selective electrode and a saturated calomel electrode, measuring the potential value during balancing under magnetic stirring, adding 0.5ml of fluorine standard solution 1mg/ml, recording the potential value after rebalancing, and measuring the temperature of the solution;
step 6, calculating fluorine content: according to the difference between the two potential values, the value is expressed by delta U; the fluorine content is calculated by using a formula: the formula is as follows:
2. The method for detecting the fluorine content in phosphoric acid and phosphoric acid salt by using the standard addition method as claimed in claim 1, wherein in the step 3, if the fluorine content of the phosphoric acid sample is too high in the preparation of the liquid to be detected of the liquid phosphoric acid sample, the operation of diluting is as follows: accurately weighing 1-1.5 g of sample by using an electronic balance, adding 10-15 ml of (1+1) hydrochloric acid solution for dissolving, and transferring to a v2In a volumetric flask with the volume, accurately transferring v by a pipette after shaking up with water to a constant volume1The volume is placed in a 50ml volumetric flask, so that the content of the fluorine ions in the liquid to be measured in the 50ml volumetric flask is 50 mu g-150 mu g.
3. The method for detecting the content of fluorine in phosphoric acid and phosphate thereof by a standard addition method according to claim 1, wherein in the step 3, different sample treatment methods or heating or dry filtering processes are adopted according to the difference of sample properties to prepare the liquid to be detected of the solid phosphate sample and the phosphate rock and phosphogypsum sample, so that the liquid to be detected entering a 50ml volumetric flask cannot contain undissolved samples or colors, and the subsequent detection is prevented from being interfered.
4. The method for detecting the fluorine content in phosphoric acid and phosphate thereof according to claim 1, wherein the adjustment of the color with the (1+19) nitric acid solution to the yellow color in step 4 is performed by slowly adding the (1+19) nitric acid solution dropwise until the color changes to yellow.
5. The method for detecting the fluorine content in phosphoric acid and phosphoric acid salt by using the standard addition method according to claim 1, wherein the pH range of the citric acid-sodium citrate buffer solution added in the step 4 is between 5.5 and 6.0, and the addition amount is between 15 and 20 ml.
6. The method for detecting the fluorine content in phosphoric acid and phosphoric acid salt by using the standard addition method according to claim 1, wherein the core requirements in the preparation of the solution to be detected in the step 3 are as follows: the fluorine ion content of the liquid to be measured in a 50ml volumetric flask is between 50 and 150 mu g; the specific operation is to adjust the sample weighing mass and v1/v2The value of Δ U is preferably 40 to 60.
7. The method for detecting the fluorine content in phosphoric acid and phosphate thereof by the standard addition method according to claim 1, wherein the core requirements in the potential measurement of the step 5 are as follows: a measuring scale capable of accurately sucking the solution by using a calibrated scale pipette or a pipette with a big belly can accurately suck 1mg/ml of 0.5ml of fluorine standard solution, and the value is recorded after the equipotential value is balanced.
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