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Major category, Sub-category (small third size): Coal – Determination of total sulfur (Eisler method). 1. Scope of application: This standard applies to lignite, bituminous coal, anthracite, and coking coal, as well as to dried coal samples from coal slurry. 2. Method summary: Coal is mixed with Eisler’s reagent and burned; the sulfur in the coal is converted into sulfates, after which the sulfate ions are turned into barium sulfate precipitate. The total sulfur content in the coal is calculated based on the mass of barium sulfate. 3. Reagents 3.1 Aeschar reagent (hereinafter referred to as aeschar): 2 parts by mass of chemically pure light magnesium oxide and 1 part by mass of chemically pure anhydrous sodium carbonate are mixed together and ground to a particle size of less than 0.2 mm, after which it is stored in a sealed container. 3.2 Hydrochloric acid solution (1+1): 1 volume of hydrochloric acid mixed with 1 volume of water. 3.3 Barium chloride solution: 100 g/L; 10 g of barium chloride is dissolved in 100 mL of water. 3.4 Methyl orange solution: 10 g/L; 0.2 g of methyl orange is dissolved in 100 mL of water. 3.5 Silver nitrate solution: 10 g/L; silver nitrate is dissolved in 100 mL of water, with a few drops of nitric acid added, and the solution is stored in a dark bottle. 3.6 Porcelain crucibles: available in capacities of 30 mL and (10–12) mL. 3.7 Filter paper: medium-speed qualitative filter paper and dense, ash-free quantitative filter paper. 4. Experimental procedure 4.1 In a 30 mL porcelain crucible, weigh coal samples that are air-dried and have a particle size of less than 0.2 mm, in an amount of (1.00 ± 0.1) g (accurate to 0.0002 g), along with 2 g of aeschar (accurate to 0.1 g). Mix them thoroughly, then cover the coal sample with another 1 g of aeschar (accurate to 0.1 g). 4.2 Place the crucible containing the coal sample in a well-ventilated muffle furnace. Heat it gradually from room temperature to (800–850)°C over a period of (1–2) hours, and maintain this temperature for another (1–2) hours. 4.3 Remove the crucible from the muffle furnace and allow it to cool to room temperature. Use a glass rod to carefully loosen the burned residue within the crucible and crush it; if any unburned coal particles remain, continue burning for another 30 minutes. Then transfer the burned residue to a 400 mL beaker. Rinse the inner walls of the crucible with hot water, add the rinse liquid to the beaker, and then add (100–150) mL of freshly boiled distilled water. Stir thoroughly. If any black coal particles are still floating on the surface of the liquid, the test result is invalid. 4.4 Filter using medium-speed qualitative filter paper by the pouring method. Rinse three times with hot water, then transfer the residue to the filter paper and wash it carefully at least 10 times. The total volume of the wash liquid should be approximately (250–300) mL. 4.5 Add (2–3) drops of methyl orange indicator to the filtrate. Neutralize it with hydrochloric acid solution (1+1), adding an excess of 2 mL so that the solution becomes slightly acidic. Heat the solution to boiling, then slowly add 10 mL of barium chloride solution while stirring continuously. Maintain the solution at a gentle boil for about 2 hours; the final volume of the solution should be approximately 200 mL. 4.6 After the solution has cooled or been left to stand overnight, filter it using dense, ash-free quantitative filter paper. Wash it with hot water until no chloride ions remain (no turbidity should occur when tested with silver nitrate). 4.7 Transfer the filter paper containing the precipitate to a porcelain crucible of known mass. Ash the filter paper at low temperature, then burn it in a muffle furnace at (800–850)°C for (20–40) minutes. After removing the crucible from the furnace, allow it to cool slightly in the air before placing it in a desiccator to cool to room temperature, after which it can be weighed. 4.8 For each batch of aldrin prepared or whenever any other reagent is replaced, more than 2 blank tests shall be conducted (all in accordance with Section 4 of this standard, except without adding coal samples); the mass variation of the barium sulfate precipitate shall not exceed 0.0010 g, and the arithmetic mean value shall be used as the blank value. 5 Result Calculation The measurement results are calculated using Equation (1) …………………………(1) The repeatability limit and reproducibility critical difference for total sulfur determination by the Ashcroft method are specified in Table 1. Table 1 Precision of determining total sulfur in coal by the Esca method. Total sulfur mass fraction St%; Repeatability limit %; Reproducibility critical difference %: ≤1.50: 0.05; 0.10; 1.50 (not included) – 4.00: 0.10; 0.20; >4.00: 0.20; 0.30. Source of the method: The method is based on GB/T 214-2007, Method for determining total sulfur in coal