This standard specifies the reagents and materials, apparatus and equipment used for determining the transmittance of low rank coal as well as the determination procedures and the expression and precision of determination result.
This standard is applicable to lignite and low coal rank bitumite.
2 Methods and Principles
The low rank coal will react with the mixed acid of nitric acid and phosphoric acid at certain test conditions and generate colored solution. Taking potassium bichromate solutions in sulfuric acid of different concentrations as standard, the transmittance of coal sample is determined by visual colorimetry according to the color of the solution.
3 Reagents and Materials
3.1 10% sulfuric acid (GB / T 625, chemically pure) solution (volume fraction).
3.2 Potassium bichromate (GB / T 642, analytically pure): it shall be dried for 2h at 110℃~120℃ before use.
3.3 (1+9) phosphoric acid (GB / T 1282, chemically pure) solution (volume fraction).
3.4 Nitric acid (GB / T 626, chemically pure): the nitric acid in a color of yellow shall not be used.
3.5 Mixed acid: prepared by mixing nitric acid, phosphoric acid and distilled water in a volume ration of 1:1:9.
3.6 Primary potassium bichromate solution
3.6.1 Weigh 2.5000g (accurate to 0.0002g) potassium bichromate powders (3.2) in a volumetric flask and add in 10% sulfuric acid solution (3.1) to prepare into 250mL solution. This solution will be used as the standard series of solution for preparing the potassium bichromate solution with a transmittance at 30%~100%.
3.6.2 Weigh 5.0000g (accurate to 0.0002g) potassium bichromate powders (3.2) in a volumetric flask and add in 10% sulfuric acid solution (3.1) to prepare into 250mL solution. This solution will be used as the standard series of solution for preparing the potassium bichromate solution with a transmittance less than 30%.
3.7 Standard series of potassium bichromate solution
Pipet primary solutions in required volume with 1mL, 2mL, 5mL or 10mL graduated straight pipette (or micro-buret) from the primary potassium bichromate solution (3.6.1 and 3.6.2) and place them into 50mL volumetric flask, and then dilute the solution with 10% sulfuric acid solution (3.1) to the scale to prepare to the standard series of solution and shake well for use. The corresponding relationship between the concentration of prepared standard solution and the required primary potassium bichromate solution is provided in Appendix A.
Rinse the dry colorimetric tube (4.2) with a small amount of prepared standard series of solution and then pour the solution into the colorimetric tube until it reaches the 10mL scale division place (the elevation of the liquid column of the colorimetric tubes shall be the same).
In general, the standard series of solution may be used for 2~3 months. In the colorimetric analysis, if the temperature changes more than 10 ℃ than that when preparing the standard series of solution, the solution shall be re-prepared.
3.8 Qualitative filter paper: dense.
