GB/T 214-2007Determination of total sulfur in coal (English PDF)

5.1 Principle

The coal sample was mixed with Eschka reagent and burned. The sulfur in the coal was converted into sulfate; and then the sulfate ions were precipitated as barium sulfate. The total sulfur content in the coal was calculated based on the mass of barium sulfate.

5.2 Reagents and materials

Unless otherwise specified, only reagents confirmed to be of analytical pure and distilled or deionized water or water of equivalent purity shall be used in the analysis.

5.2.1 Eschka reagent (hereinafter referred to as Aldrin). Evenly mix 2 portions by weight of chemically pure light magnesium oxide with 1 portion by weight of chemically pure anhydrous sodium carbonate; grind them into substance with a particle size of less than 0.2 mm; and store in a sealed container. Commercially available Aldrin may also be used.

5.2.2 Hydrochloric acid solution. (1+1) (V+V), 1 volume of hydrochloric acid mixed evenly

with 1 volume of water.

5.2.3 Barium chloride solution. 100 g/L; take 10 g of barium chloride (BaCl2·2H2O); dissolve in water; and dilute to 100mL.

5.2.4 Silver nitrate solution. 10 g/L; dissolve 1 g of silver nitrate in 100 mL of water; add 3~4 drops of nitric acid; and store in a brown bottle.

5.2.5 Methyl orange solution. 2 g/L; dissolve 0.2 g of methyl orange in 100 mL of water.

5.2.6 Porcelain crucibles. Capacities of 30 mL and 10~20 mL, respectively.

5.2.7 Filter paper. Medium-speed qualitative filter paper and dense ashless quantitative filter

paper.

5.3 Instruments and equipment

5.3.1 Analytical balance. Graduation value 0.1 mg.

5.3.2 Muffle furnace. Equipped with a temperature control device, capable of heating to 900 °C, temperature adjustable and ventilated.

5.4 Determination

5.4.1 Weigh (1.00±0.01) g (accurate to 0.0002 g) of general analytical test coal sample and 2.0 g (accurate to 0.1 g) of Aldrin into a 30 mL porcelain crucible. Mix carefully and thoroughly;

then cover the top of the mixed coal sample with 1.0 g (accurate to 0.1 g) of Aldrin. Take 0.5 g of coal sample when the total sulfur content is 5%~10%; and take 0.25 g of coal sample when the total sulfur content is greater than 10%.

5.4.2 Transfer the crucible containing the coal sample into a well-ventilated muffle furnace.

Gradually heat the sample from room temperature to 800°C~850°C over 1h ~ 2h; and maintain this temperature for 1h ~ 2h.

5.4.3 Remove the crucible from the muffle furnace and allow it to cool to room temperature.

Carefully loosen and break up (if any unburned particles are found, continue igniting for 30 min) the ignited material in the crucible with a glass rod. Then transfer the ignited material to a 400 mL beaker. Rinse the inside of the crucible with hot water; collect the washings in the beaker; and add 100 mL~150 mL of freshly boiled water; stir thoroughly. If black particles are still floating on the surface of the liquid, then the determination is invalid.

5.4.4 Filter the solution using medium-speed qualitative filter paper via decantation. Rinse 3

times with hot water. Transfer the residue to the filter paper and wash thoroughly with hot water at least 10 times, producing a total washing solution volume of 250mL ~ 300mL.

5.4.5 Add 2 ~ 3 drops of methyl orange indicator to the filtrate. Neutralize with hydrochloric acid solution, adding an excess of 2 mL, to make the solution slightly acidic. Heat the solution to boiling and slowly titrate 10 mL of barium chloride solution while stirring constantly.

Maintain this gentle boiling state for approximately 2 h, until the final solution volume is approximately 200mL.

5.4.6 After cooling or allowing the solution to stand overnight, filter it using dense, ashless quantitative filter paper; and wash with hot water until no chloride ions are present (the solution shall not be turbid when tested with silver nitrate solution).

5.4.7 Transfer the filter paper with precipitate to a known-mass porcelain crucible. After low- temperature ashing of the filter paper, ignite it in a muffle furnace at 800°C~850°C for 20 min

~ 40 min. Remove the crucible; cool it slightly in air; and then place it in a desiccator to cool to room temperature before weighing.

5.5 Blank test

When preparing each batch of Aldrin or changing any other reagent, 2 or more blank tests shall be performed (without adding coal samples, follow 5.4). The mass range of barium sulfate precipitate in the blank tests shall be less than 0.0010 g. Take the arithmetic mean of the blank test results as the blank value.

5.6 Calculation and expression of results

5.6.1 Calculation of results

The determination results are calculated according to Formula (1).

Where.

St,ad - total sulfur mass fraction in coal samples for general analysis, expressed by %;

m1 - mass of barium sulfate, in g;

m2 - mass of barium sulfate in blank tests, in g;

0.1374 - coefficient for converting barium sulfate to sulfur;

m - mass of coal sample, in g.

5.6.2 Expression of results

The total sulfur content (mass fraction, %) of the tested coal sample is the average of repeated determinations, rounded off to 0.01% according to GB/T 483.

5.7 Precision of method

The precision of the Eschka method for determining total sulfur in coal is specified in Table 1.

6.1 Principle

Coal sample is combusted and decomposed in an air stream under the action of a catalyst. Sulfur in the coal is converted into sulfur oxides, of which sulfur dioxide is absorbed by potassium iodide solution. The iodine produced by the electrolysis of potassium iodide solution is used for titration. The total sulfur content in the coal is calculated based on the amount of electricity consumed in the electrolysis.

6.2 Reagents and materials

Unless otherwise specified, only reagents confirmed to be of analytically pure and distilled water, deionized water, or water of equivalent purity are used in the analysis.

6.2.1 Electrolyte. Take 5.0 g each of potassium iodide and potassium bromide; dissolve in 250 mL ~ 300 mL of water; and add 10 mL of glacial acetic acid.

6.2.2 Tungsten trioxide.

6.2.3 Sodium hydroxide. Chemically pure.

6.2.4 Color-changing silica gel.

6.2.5 Certified coal reference material.

6.2.6 Combustion boat. Made of ceramsite or corundum, with a sample loading section

approximately 60 mm long, and heat resistant to temperatures above 1200°C.

6.2.7 Quartz tray. Capable of holding the combustion boat, allowing it to move in and out of the combustion tube according to a programmed sequence and to a designated position.

6.2.8 Glass wool.

6.2.9 Aluminosilicate wool.

6.3 Instruments and equipment

6.3.1 Coulometric sulfur analyzer

It mainly includes a controller, tubular high-temperature furnace, coulometric integrator, electrolytic cell, electromagnetic stirrer, and air supply and purification device. The reducing combustion tubes of the tubular high-temperature furnace shall be tightly connected end-to-end to the piston and electrolytic cell; and sealed with silicone rubber tube.

a) Tubular high-temperature furnace. Capable of heating to above 1200 °C, with a high- temperature isothermal zone of at least 70 mm long at (1150±10) °C; equipped with a platinum-rhodium-platinum thermocouple temperature measurement and control device;

and containing a reducing combustion tube with a temperature resistance of above

1300 °C. The outlet of the combustion tube is filled with clean, dry glass wool; at a distance of 80 mm ~ 100 mm from the outlet end, it is filled with a layer of aluminosilicate wool with a thickness of approximately 3 mm.

b) Electrolytic cell and electromagnetic stirrer. The electrolytic cell is 120 mm ~ 180 mm high, with a capacity of no less than 400 mL, and contains a platinum electrolytic electrode pair with an area of approximately 150 mm² and a platinum indicator electrode pair with an area of approximately 15 mm². The response time of the indicator electrode shall be less than 1 s; and the speed of the electromagnetic stirrer shall be approximately

500 r/min and continuously adjustable.

c) Coulometric integrator. The linearity error of the integral shall be less than 0.1% within the electrolysis current range of 0 mA ~ 350 mA.

d) Sample injection program controller. Capable of advancing, stopping, and reversing according to a prescribed program, placing the coal sample at the 500 °C pre- decomposition and 1150 °C high-temperature decomposition positions in the combustion tube.

e) Air supply and purification device. Composed of an electromagnetic pump and a purification tube. The air supply rate is approximately 1500 mL/min; and the extraction

......