SN/T 5256-2020Determination of phosphorus content in coal microwave ashing-spectrophotometric method (English PDF)

Foreword

This standard was drafted in accordance with the rules given in GB/T 1.1-2009.

This standard was proposed and managed by the General Administration of Customs of the People's Republic of China.

Drafting organization of this standard. Taiyuan Customs of the People's Republic of China.

1 Scope

This standard specifies the microwave ashing-spectrophotometric method to determine the phosphorus content in coal.

This standard applies to the determination of phosphorus content in lignite, bituminous coal, anthracite and coke. The measurement range (mass fraction) is 0.005%~0.7%.

2 Normative references

The following documents are indispensable for the application of this document. For dated reference documents, only the dated version applies to this article Pieces. For undated reference documents, the latest version (including all amendments) is applicable to this document.

GB/T 212 Coal Industrial Analysis Method GB/T 474 Coal sample preparation method GB/T 1274 Chemical reagent potassium dihydrogen phosphate GB/T 6379.2 Accuracy of measurement methods and results (accuracy and precision) Part 2 Determine the repeatability of standard measurement methods Basic methods of sex and reproducibility GB/T 6682 Analytical laboratory water specifications and test methods

3 Method summary

After microwave ashing, the coal sample is decomposed with hydrofluoric acid-sulfuric acid to remove silicon dioxide, and ammonium molybdate, potassium antimony tartrate and ascorbic acid are added.

The mixed solution produces phosphomolybdenum blue, and the absorbance is measured with a spectrophotometer, and the standard curve method is used for quantification.

4 Reagents and materials

Unless otherwise specified, the reagents used in this standard are of analytical grade, and the test water is the secondary water specified in GB/T 6682.

4.1 Hydrofluoric acid. rho(HF)=1.15 g/mL, analytically pure.

4.2 Sulfuric acid solution. c (12 H2SO4) = 10 mol/L, measure 278 mL of concentrated sulfuric acid, slowly add an appropriate amount of water, stir while adding, and then use the volume of water is adjusted to 1 000 mL.

4.3 Sulfuric acid solution. 14.Measure.200 mL of concentrated sulfuric acid and slowly add an appropriate amount of water, stirring while adding, and then dilute the volume to 1 000 mL with water.

4.4 Ammonium molybdate-sulfuric acid solution. Dissolve 17.2 g of ammonium molybdate in an appropriate amount of sulfuric acid solution (4.3), and dilute with sulfuric acid solution (4.3) to 1 000 mL.

4.5 Ascorbic acid solution. Weigh 5 g of ascorbic acid, dissolve it in 1,000 mL of water, and make it ready for use.

4.6 Potassium antimony tartrate solution. Weigh 0.34 g of potassium antimony tartrate and dissolve it in 250 mL of water.

4.7 Mixed solution. add 10 mL of ascorbic acid solution (4.5) and 5 mL of potassium antimony tartrate to 35 mL of ammonium molybdate-sulfuric acid solution (4.4) Solution (4.6), mix well and prepare before use.

4.8 Phosphorus standard stock solution (0.1 mg/mL). accurately weigh the premium grade pure potassium dihydrogen phosphate dried at 110 °C for 1 h (see GB/T 1274) 0.439 2 g is dissolved in water and diluted with water to 1000 mL. A solution of certified reference materials can also be used.

4.9 Phosphorus standard series working solution. Draw the phosphorus standard stock solution (4.8) 0 mL, 1.00 mL, 2.00 mL, 3.00 mL, 4.00 mL in a 100 mL volumetric flask, dilute to the mark with water, the phosphorus content of the standard series of working solutions are 0.00 mg/L, 1.00 mg/L, 2.00 mg/L, 3.00 mg/L, 4.00 mg/L, ready to use.

5 Apparatus and equipment

5.1 Analytical balance. Sensitivity 0.1 mg.

5.2 Microwave ashing furnace. with program temperature adjustment device, can maintain the temperature (815±10) °C.

5.3 Spectrophotometer.

5.4 Electric heating plate. adjustable temperature.

5.5 Porcelain boat or quartz crucible. Porcelain boat, 45 mm×22 mm×14 mm; quartz crucible, 35 mm×15 mm or equivalent.

5.6 Platinum or PTFE crucible. the capacity is 25 mL~30 mL.

6 Analysis steps

7 Result calculation

The mass fraction Cad (%) of phosphorus in the air-dried coal sample is calculated according to formula (1).

Cad-the mass concentration of phosphorus in the sample, %;

X - Check the phosphorus content of the test solution from the working curve, the unit is milligram (mg);

V --The volume of the test solution divided from the total solution of the test solution, in milliliters (mL);

m1-the mass of the ash sample, in grams (g);

Aad-ash content of air-dried coal samples (see GB/T 212), %;

m2 - The mass of the air-dried coal sample, in grams (g).

The calculation result retains two significant digits.

8 Precision

Nine laboratories conduct method precision tests on 3 levels of samples, and perform statistics in accordance with GB/T 6379.2.

See Table 2.