GB/T 5195.6-2017Fluorspar - Determination of phosphorus content - Photometric method (English PDF)

3.1 Principle

The sample is dissolved in hydrofluoric acid and perchloric acid, and ammonium molybdate is added to the hydrochloric acid medium of about 1mol/L to form phosphomolybdenum heteropolyacid with phosphorus to resist damage

Blood acid-hydroxylamine hydrochloride reduces the phosphomolybdenum heteropoly acid to phosphomolybdenum blue, and the absorbance is measured at a wavelength of 800nm with a spectrophotometer.

3.2 Reagents

Unless otherwise specified in the analysis, only use approved analytical reagents and distilled water above grade 2 or above that meet the requirements of GB/T 6682.

Water of comparable purity.

3.2.1

Hydrofluoric acid, rho=1.13g/mL.

3.2.3

Hydrobromic acid, rho=1.38g/mL.

3.2.4

Hydrochloric acid, rho=1.19g/mL.

3.2.6

Ammonium molybdate solution, 40g/L.

Weigh 4.0g ammonium molybdate [(NH4)6Mo7O24·4H2O] in a beaker, add an appropriate amount of water, heat to dissolve, cool to room temperature, use

Dilute with water to 100mL. Mix well and filter.

3.2.7

Ascorbic acid solution, 50g/L, ready to use.

3.2.8

Hydroxylamine hydrochloride solution, 50g/L, ready to use.

3.2.9 Phosphorus standard stock solution

1mg/mL.

Put potassium dihydrogen phosphate (KH2PO4) in an oven and dry at 105°C±5°C for more than 2h. After taking it out of the oven, put it in dry

Cool to room temperature in a desiccator. Weigh accurately 4.3937g (accurate to 0.2mg), dissolve it in water, and then transfer it into a 1000mL volumetric flask.

Dilute to the mark and mix well. The standard solution 1mL contains 1mg phosphorus. Commercially available certified standard solutions can also be used.

3.2.10 Phosphorus standard solution

10µg/mL.

Pipette 10.00mL phosphorus standard stock solution (3.2.9) in a 1000mL volumetric flask, dilute to the mark with water and mix. The standard solution

1mL solution contains 10µg phosphorus.

3.3 Apparatus

3.3.1 Oven

The temperature can be controlled at 105°C±5°C.

3.3.3 Single-marked volumetric flask

should meet the requirements of GB/T 12806.

3.3.4 Indexing pipette

should meet the requirements of GB/T 12807.

3.4 Sampling and sample preparation

3.4.1

Carry out sampling and sample preparation according to GB/T 22564.

3.4.2

The sample should be processed to a particle size less than 0.063mm.

3.4.3

Dry the sample at 105°C ± 5°C for 2h before analysis, and place it in a desiccator to cool to room temperature.

3.5 Analysis steps

3.5.1 Number of determinations

For the same sample, at least two independent determinations.

3.5.2 Sample quantity

Weigh the sample according to Table 1, accurate to 0.0002g.

Table 1 Sample quantity

Phosphorus mass fraction/% sample amount/g

0.002~0.020 0.20

>0.020~0.50 0.10

3.5.3 Blank test

Do a blank test with the sample.

3.5.4 Measurement

3.5.4.1

Place the sample (3.5.2) in a polytetrafluoroethylene beaker or platinum crucible, add 4 mL of hydrofluoric acid (3.2.1), heat to dissolve at low temperature, and then steam

When it is nearly dry, add 2mL of hydrofluoric acid (3.2.1), continue to evaporate until it is nearly dry, and cool slightly. Add 3mL hydrochloric acid (3.2.4) (if the sample contains arsenic, then

Add 0.5mL hydrobromic acid (3.2.3)], evaporate to near dryness, and cool slightly. Add 2mL perchloric acid (3.2.2), evaporate to near dryness, cool slightly. Join

7mL hydrochloric acid (3.2.5), heated until the salts are dissolved, cooled to room temperature, and transferred to a 50mL volumetric flask.

3.5.4.2

Take the sample solution according to Table 2, add hydrochloric acid (3.2.5), place it in another 50mL volumetric flask, dilute with water to about 30mL,

Add 4mL ammonium molybdate solution (3.2.6), 2mL ascorbic acid solution (3.2.7), 1mL hydroxylamine hydrochloride solution (3.2.8), mix, and blow with water

Wash the bottle neck, place it on a hot water bath and heat for 5 minutes, remove the running water and cool to room temperature, dilute to the mark with water, and mix well.

Table 2 Dispensed amount and added hydrochloric acid 3.5.4.3 Move part of the solution into a 1cm cuvette and use the accompanying blank as a reference. Measure the absorbance at a wavelength of 800nm with a spectrophotometer

Luminosity, find the corresponding phosphorus content from the calibration curve.

3.5.5 Drawing of calibration curve

Pipette 0, 0.50mL, 1.00mL, 2.00mL, 3.00mL, 4.00mL, 5.00mL phosphorus standard solution (3.2.10) into a group respectively

In a 50mL volumetric flask, add 7mL hydrochloric acid (3.2.5) to each, follow 3.5.4.2 to develop the color, take the reagent blank (without phosphorus standard solution) as the reference

Compared with, the absorbance was measured at a wavelength of 800nm with a spectrophotometer, and the phosphor content was used as the abscissa and the absorbance as the ordinate to draw a calibration curve.

3.6 Calculation and presentation of results

3.6.1 Calculation of analysis results

Calculate the mass fraction WP of phosphorus in the sample according to formula (1), and the value is expressed in %.

3.6.2 Determination and presentation of analysis results

According to the procedures in Appendix A, calculate the results of independent repeated determinations according to formula (1) and compare them with the allowable deviations to determine the analysis results.

The final result is the arithmetic mean of the acceptable values of the sample, or other values measured according to the operation specified in Appendix A. Analysis result

Round off according to GB/T 8170, and round the value to three decimal places.

3.7 Allowance

The difference between the two determination results should not be greater than the allowable difference listed in Table 3.

Table 3 Allowable difference

4.1 Principle

The sample was melted with a mixed flux of sodium carbonate, boric acid, and sodium nitrate, leached with excess nitric acid, added iron ions, and precipitated iron phosphate with ammonia water.

filter. Dissolve the precipitate with nitric acid, add ammonium molybdate to generate a phosphomolybdate complex, and extract with a mixed solvent of ethyl acetate and butyl acetate.

Add stannous chloride to the phase to reduce the complex to molybdenum blue in the organic phase, and measure the absorbance at a wavelength of 710nm with a spectrophotometer.

4.2 Reagents

Unless otherwise specified in the analysis, only use approved analytical reagents and distilled water above grade 2 or above that meet the requirements of GB/T 6682.

Water of comparable purity.

4.2.1

Anhydrous sodium carbonate-boric acid mixed flux.

Mix anhydrous sodium carbonate and boric acid at a mass ratio of 2.1, grind and mix well.

4.2.2

Sodium nitrate.

4.2.3

Nitric acid, rho=1.42g/mL.

4.2.5

Mixed solvent of ethyl acetate and butyl acetate.

Ethyl acetate and butyl acetate are mixed in a volume ratio of 7.3.

4.2.6

Ammonia, rho=0.90g/mL.

4.2.7

Ammonia solution, 1,200.

Ammonia (4.2.6) is mixed with water in a volume ratio of 1.200.

4.2.8

Ammonium molybdate solution, 30g/L.

Dissolve 30g ammonium molybdate tetrahydrate [(NH4)6Mo7O24·4H2O] and 10g sulfamic acid (NH4OSO2NH4) in 500mL water,

Transfer this solution into a 1000mL volumetric flask, dilute to the mark with water, and mix.

4.2.9

Stannous chloride solution, 20g/L.

Dissolve 20g of stannous chloride (SnCl2·2H2O) in.200mL hydrochloric acid (3.2.4), and shake it until the dissolution is complete. This solution

Transfer to a 1000mL volumetric flask, dilute to the mark with water, and mix.

4.2.10

Iron solution, 4g/L.

Weigh 0.4 g of high-purity iron (phosphorus content < 0.002%), add 10 mL of hydrochloric acid (3.2.4) to heat and dissolve on the electric hot plate, and add 3 mL of nitrate

The acid (4.2.3) is heated to boiling, cooled to room temperature, this solution is transferred to a 100mL volumetric flask, diluted with water to the mark, and mixed.

4.2.11 Phosphorus standard stock solution

0.060g/L.

Put potassium dihydrogen phosphate (KH2PO4) in an oven and dry at 105°C±5°C for more than 2h. After taking it out of the oven, put it in dry

Cool to room temperature in a desiccator. Accurately weigh 0.2637g (accurate to 0.2mg), dissolve it in water, and then transfer it into a 1000mL volumetric flask.

Release to the mark and mix well. The standard solution 1mL contains 60µg phosphorus. Commercially available certified standard solutions can also be used.

4.2.12 Phosphorus standard solution

0.006g/L.

Pipette 100mL phosphorus standard stock solution (see 4.2.11) in a 1000mL volumetric flask, dilute to the mark with water and mix. The standard

The solution 1mL contains 6µg phosphorus.

4.3 Apparatus

4.3.1 Oven

The temperature can be controlled at 105°C±5°C.

4.3.3 Platinum dish

45mm in diameter and 25mm in depth.

4.3.5 Single-marked volumetric flask

should meet the requirements of GB/T 12806.

4.3.6 Indexing pipette

should meet the requirements of GB/T 12807.

4.4 Sampling and sample preparation

4.4.1

Carry out sampling and sample preparation according to GB/T 22564.

4.4.2

The sample should be processed to a particle size less than 0.063mm.

4.4.3

Dry the sample at 105°C ± 5°C for 2h before analysis, and cool it to room temperature in a desiccator.

4.5 Analysis steps

4.5.1 Number of determinations

For the same sample, at least two independent determinations.

4.5.2 Sample quantity

Weigh the sample according to Table 4, accurate to 0.0001g.

4.5.3 Blank test

Do a blank test with the sample.

4.5.4 Measurement

4.5.4.1

Put the sample into a platinum dish containing 2g of anhydrous sodium carbonate-boric acid mixed flux (4.2.1), then add 0.2g of sodium nitrate (4.2.2),

Stir well. Cover with 2g of anhydrous sodium carbonate-boric acid mixed flux (4.2.1), and melt at 900°C~950°C for 10min~20min,

Until the sample melts completely. Take out to cool.

4.5.4.2

Put the platinum dish in a 400mL phosphorus-free beaker (e.g. quartz beaker), add about 20mL water, 10mL nitric acid (4.2.3), and slowly add

Heat until the sample is completely dissolved. Wash the platinum dish with water, and collect the lotion in a beaker.

4.5.4.3

Add 5mL iron solution (4.2.10) and dilute with water to about.200mL, neutralize with ammonia water (4.2.6) and excess 3mL, boil

Cool down after 1 min. Filter with ash-free quick filter paper and wash the precipitate with ammonia solution (4.2.7).

4.5.4.4

Wash the precipitate on the filter paper into a 400 mL beaker with warm water, and rinse the filter paper with 2 mL of warm nitric acid (4.2.3) until the precipitate is dissolved.

Rinse with warm water. Then rinse with 2mL warm nitric acid (4.2.3), then rinse with warm water 4 to 5 times. Heat the solution until the precipitate is completely dissolved. Cool down for use.

4.5.4.5

Drawing of calibration curve.

a) According to Table 5, pipette different volumes of phosphorus standard solutions (4.2.12) into 7 100mL separatory funnels (4.3.4).

b) Preparation of colorimetric solution.

Add about 20mL water, 4mL nitric acid (4.2.3), 10mL ammonium molybdate solution (4.2.8) into each separatory funnel, and dilute with water to

60mL mark and shake, add 10mL mixed solvent (4.2.5), shake for 60s to separate the solution, discard the bottom liquid. Use a small piece of filter paper

Wipe off the water marks in the separatory funnel. Transfer the solution in the separatory funnel to a 50mL volumetric flask, add 20mL stannous chloride solution (4.2.9),

Dilute to the mark with absolute ethanol (4.2.4), shake for about 20s until blue phosphomolybdenum blue complex is formed.

c) Determination of absorbance.

Within 10 minutes of the formation of the phosphomolybdenum blue complex, use a 1cm cuvette and mix with a spectrophotometer (4.3.4) at a wavelength of 710nm.

The solvent (4.2.5) is the reference, adjust the zero point, and measure the absorbance of the organic phase solution.

d) Draw calibration curve.

Take the absorbance of each calibration solution minus the absorbance of the blank calibration solution as the ordinate, and the phosphorus content as the abscissa to draw the calibration curve.

4.5.4.6

Measurement of sample.

a) Preparation of colorimetric complex.

When the phosphorus content in fluorite is <=0.03%, transfer the sample solution (4.5.4.4) into a 100mL separatory funnel, and rinse with about 10mL of water.

Cup, add 10mL ammonium molybdate solution (4.2.8) to the separatory funnel, dilute to 60mL with water and shake well, add 10mL mixed solvent (4.2.5), the following shall be extracted according to the method specified in 4.5.4.5b).

When the phosphorus content in fluorite >0.03%, transfer the sample solution (4.5.4.4) into a 100mL volumetric flask, dilute to the mark with water, and mix well. Of course

Then pipette 20mL into a separatory funnel, add 3.2mL nitric acid (4.2.3), 10mL ammonium molybdate solution (4.2.8), and dilute with water to 60mL

Mark and shake well, add 10mL mixed solvent (4.2.5), and extract according to the method specified in 4.5.4.5b) below.

b) Determination of absorbance.

Take the mixed solvent (4.2.5) as the reference, adjust the zero point, and press 4.5.4.5c) to measure the absorbance and blank of the organic phase solution [see 4.5.4.6a)]

The absorbance of the solution (4.5.3). Find out the phosphorus content corresponding to the absorbance of the sample solution and the blank solution on the calibration curve [see 4.5.4.5d)].

Note. The color temperature is controlled at 20°C~30°C.

4.6 Calculation and presentation of results

4.6.1 Calculation of analysis results

Calculate the mass fraction WP of phosphorus in the sample according to formula (2), and the value is expressed in %.

4.6.2 Determination and presentation of analysis results

According to the procedures in Appendix A, calculate the results of independent repeated determinations according to formula (2) and compare them with the allowable deviations to determine the analysis results.

The final result is the arithmetic mean of the acceptable values of the sample, or other values measured according to the operation specified in Appendix A. Analysis result

Round off according to GB/T 8170, and round the value to three decimal places.

4.7 Allowance

The difference between the two determination results should not be greater than the allowable difference listed in Table 6.

Table 6 Allowable difference