GB/T214 Determination of Total Sulfur in Coal (GB/T 214-1996, eqv ISO 334:1992)

Determination of sulfur sulfate

3.1 Method Summary

Boil the coal sample with dilute hydrochloric acid, extract sulfate from the coal and generate barium sulfate precipitate. Calculate the sulfate sulfur content in the coal based on the mass of barium sulfate.

3.2 Reagents and Materials

The water used is Grade II laboratory water (GB/T6682).

3.2.1 Hydrochloric acid solution: c (HCl)=5mol/L, take 417mL of hydrochloric acid (GB/T622), dilute with water to 1L, shake well and set aside.

3.2.2 Ammonia solution (GB/T631): Volume ratio of 1+1.

3.2.3 Barium chloride solution: 100 g/L, weigh 10g of barium chloride (GB/T652) and dissolve it in 100mL of water.

3.2.4 Hydrogen peroxide (GB/T6684).

3.2.5 Potassium thiocyanate solution: 20g/L, weigh 2g of potassium thiocyanate (GB/T648) and dissolve it in 100mL of water.

3.2.6 Silver nitrate solution: 10g/L, weigh 1g of silver nitrate (GB/T670) and dissolve it in 100mL of water. Add several drops of nitric acid (GB/T626) dropwise, mix well, and store in a brown bottle.

3.2.7 Ethanol (GB/T679): Over 95%.

3.2.8 Methyl orange solution: 2g/L, weigh 0.2g of methyl orange (HG/T3-3089) and dissolve it in 100mL of water.

3.2.9 Aluminum powder: analytically pure.

3.2.10 Zinc powder: analytically pure.

3.2.11 Filter paper: slow qualitative filter paper and slow quantitative filter paper.

3.3 Instruments and equipment

3.3.1 Analytical balance: with a sensitivity of 0.1mg.

3.3.2 Muffle furnace: capable of heating up to 900 ℃ and adjusting the temperature, with good ventilation.

3.3.3 Electric heating plate or sand bath: The temperature is adjustable.

3.3.4 Beaker: Capacity (250~300) mL.

3.3.5 Surface vessel: diameter 100mm.

3.3.6 Porcelain crucible: Smooth, with a capacity of (10-20) mL.

3.4 Measurement steps

3.4.1 Accurately weigh (1 ± 0.1) g of air dried coal sample with a particle size less than 0.2mm (accurate to 0.0002g), place it in a beaker (3.3.4), add (0.5-1) mL of ethanol (3.2.7) for wetting, then add 50mL of hydrochloric acid solution (3.2.1), cover with a petri dish (3.3.5), shake well, heat on an electric heating plate, and simmer for 30 minutes.

3.4.2 After slightly cooling, first filter the coal sample through a slow qualitative filter paper using the pouring method, wash the coal sample several times with hot water, then transfer all the coal samples to the filter paper and wash with hot water until there are no iron ions [check with potassium thiocyanate solution (3.2.5), if the solution is colorless, it indicates no iron ions]. If there is coal powder passing through the filter paper during filtration, it should be re filtered. If the filtrate is yellow, 0.1g of aluminum powder (3.2.9) or zinc powder (3.2.10) should be added. After slightly heating to make the yellow color disappear, filter again and wash with water until there are no chloride ions [check with silver nitrate solution (3.2.6), if the solution is not turbid, it indicates that there are no chloride ions]. After filtration, stack the coal sample with filter paper and place it in the original beaker for the determination of iron sulfide and sulfur.

3.4.3 Add (2-3) drops of methyl orange indicator (3.2.8) to the filtrate, neutralize with ammonia (3.2.2) until slightly alkaline (the solution turns yellow), then add hydrochloric acid to adjust the solution to slightly acidic (the solution turns red), add an excess of 2mL, heat until boiling, and add 10 mL of 10% barium chloride solution (3.2.3) with continuous stirring. Place it on an electric heating plate or sand bath for slightly boiling for 2 hours or overnight, and finally maintain the volume of the solution at around 200mL.

3.4.4 Filter with slow quantitative filter paper and wash with hot water until there are no chloride ions.

3.4.5 Transfer the precipitate and filter paper into a constant weight porcelain crucible, first ash the filter paper at low temperature, and then burn it in a muffle furnace at a temperature of (800-850) ℃ for 40 minutes. Take out the crucible, cool it slightly in air, then place it in a dryer to cool to room temperature and weigh it.

3.4.6 Perform blank measurements according to the steps specified in 3.4.1 to 3.4.5 (without adding coal samples), and take the average of the two measurements as the blank value.

3.5 Result Calculation

Calculate the mass fraction (%) of sulfate sulfur (Ss, ad) in air dried coal samples using formula (1):

(1)

In the formula:

- The mass of barium sulfate measured in coal samples, in grams (g);

- The mass of barium sulfate measured in blank, in grams (g);

- Coal sample mass, in grams (g);

0.1374? The coefficient for converting barium sulfate to sulfur.

3.6 Method precision

The repeatability limit and reproducibility critical difference of sulfate sulfur determination are specified in Table 1:

Table 1 Method Precision

Repeatability limit

Ss, ad,% reproducibility critical difference

Ss, d,%

0.03 0.10

4. Determination of iron sulfide sulfur

4.1 Method A - Oxidation method

4.1.1 Method Summary

Leaching iron from non sulfide iron in coal with hydrochloric acid, and the coal after leaching

 

4.1.2 Reagents and materials

The water used is Grade II laboratory water (GB/T6682).

4.1.2.1 Nitric acid solution (GB/T626): Volume ratio of 1+7.

4.1.2.2 Ammonia solution (GB/T631): Volume ratio of 1+1.

4.1.2.3 Hydrogen peroxide (GB/T6684).

4.1.2.4 Hydrochloric acid solution: c (HCl)=5mol/L, take 417mL of hydrochloric acid (GB/T622) and dilute with water to 1L, shake well and set aside.

4.1.2.5 Sulfuric acid phosphoric acid mixture:

Measure 150mL of sulfuric acid (GB625) (relative density 1.84) and 150mL of phosphoric acid (GB/T1282), mix carefully, pour this mixture into 700mL of water, mix well, and set aside.

4.1.2.6 Tin dichloride solution: 100g/L.

Weigh 10g of tin dichloride (GB/T638) and dissolve it in 50mL of concentrated hydrochloric acid (GB/T622). Dilute with water to 100mL (ready to use).

4.1.2.7 Mercury chloride saturated solution: Weigh 80g of mercury chloride (HG/T3-1068) and dissolve it in 1000mL of water.

4.1.2.8 Potassium dichromate standard solution: c (1/6K2Cr2O7)=0.05mol/L.

Accurately weigh 2.4518g of high-grade pure potassium dichromate (GB/T642) that has been pre dried at 150 ℃ to a constant mass, and dissolve it in a small amount of water. Transfer the solution into a 1L volumetric flask and dilute with water to the mark.

4.1.2.9 Sodium diphenylamine sulfonate indicator: 2g/L.

Weigh 0.2g of sodium diphenylamine sulfonate (HG3-621) and dissolve it in 100mL of water. Store it in a brown bottle for later use.

4.1.2.10 Potassium thiocyanate: 20g/L.

Weigh 2g of potassium thiocyanate (GB/T648) and dissolve it in 100mL of water.

4.1.2.11 Filter paper: slow and fast qualitative filter paper.

4.1.3 Instruments and equipment

4.1.3.1 Drying oven: capable of maintaining a temperature of (150 ± 5) ℃.

4.1.3.2 Surface vessel: diameter 100mm.

4.1.3.3 Beaker: Capacity (250-300) mL.

4.1.4 Measurement steps

4.1.4.1 Add 50mL of nitric acid solution (4.1.2.1) to the coal sample (3.4.2) soaked in hydrochloric acid, cover the surface dish (4.1.3.2), boil for 30 minutes, rinse the surface dish with water, filter with slow qualitative filter paper, and wash with hot water until there are no iron ions [check with potassium thiocyanate solution (4.1.2.10)].

4.1.4.2 Add 2mL of hydrogen peroxide (4.1.2.3) to the filtrate and boil for about 5 minutes to eliminate the color caused by coal sample decomposition (for coal with low degree of coalification, add more hydrogen peroxide until the brown color disappears).

4.1.4.3 Add ammonia solution (4.1.2.2) to the boiling solution until iron hydroxide precipitates. When the precipitate is complete, add 2 mL more

 

4.1.4.3 Add ammonia solution (4.1.2.2) to the boiling solution until iron hydroxide precipitates. When the precipitate is complete, add 2 mL more. Boil the solution, filter it with rapid qualitative filter paper, and rinse the precipitate and beaker wall with hot water 1-2 times. Break through the filter paper, wash the precipitate into the original beaker with hot water, transfer the precipitate to the filter paper, and rinse the sides of the filter paper with 10mL hydrochloric acid solution (4.1.2.4) to dissolve the trace iron on the filter paper. Then wash the filter paper several times with hot water until there are no iron ions.

4.1.4.4 Cover the surface vessel and heat the solution to boiling until the volume of the solution is about (20-30) mL. Under continuous stirring, add tin dichloride solution (4.1.2.6) dropwise until the yellow color disappears and add 2 more drops. After rapid cooling, rinse the surface vessel and beaker walls with water and add 10mL of saturated mercuric chloride solution (4.1.2.7) until white filamentous mercuric chloride precipitates. Leave for a moment, dilute with water to 100mL, add 15mL of sulfuric acid phosphate mixture (4.1.2.5) and 5 drops of sodium diphenylamine sulfonate indicator (4.1.2.9), titrate with potassium dichromate standard solution (4.1.2.8) until the solution turns stable purple, and record the volume of standard solution consumed.

4.1.4.5 Perform blank measurements according to the steps specified in 4.1.4.1 to 4.1.4.4 (without adding coal samples), and take the average of the two measurements as the blank value.

4.1.5 Result Calculation

Calculate the mass fraction (%) of iron sulfur sulfide (Sp, ad) in air dried coal samples using formula (2):

(2)

In the formula:

- The amount of potassium dichromate standard solution used for coal sample determination, in milliliters (mL);

- The amount of potassium dichromate standard solution used for blank determination, in milliliters (mL);

- The concentration of potassium dichromate standard solution, in moles per liter (mol/L);

0.05585- millimolar mass of iron, in grams per millimole (g/mmol);

1.148- The coefficient for converting iron to iron sulfide sulfur;

- Coal sample mass, in grams (g).

4.2 Method B - Atomic Absorption Spectroscopy

4.2.1 Method Summary

Using hydrochloric acid to extract iron from non sulfide iron in coal, the extracted coal sample is leached with dilute nitric acid. The iron in the nitric acid leaching solution is determined by atomic absorption spectrophotometry, and the sulfur content of sulfide iron in coal is calculated based on the mass of iron.

4.2.2 Reagents and materials

The water used is Grade I laboratory water (GB/T6682).

4.2.2.1 Nitric acid solution (GB/T626): Volume ratio of 1+7.

4.2.2.2 Nitric acid solution (GB/T626): Volume ratio of 1+1.

4.2.2.3 Iron standard stock solution: 1mg/mL.

Weigh 1.0000g (accurate to 0.0002g) of high-purity iron (99.99%) into a 300mL beaker, add 50mL of nitric acid (4.2.2.2), place on an electric heating plate, slowly heat until completely dissolved, and then cool to room temperature

 

4.1.4.3 Add ammonia solution (4.1.2.2) to the boiling solution until iron hydroxide precipitates. When the precipitate is complete, add 2 mL more. Boil the solution, filter it with rapid qualitative filter paper, and rinse the precipitate and beaker wall with hot water 1-2 times. Break through the filter paper, wash the precipitate into the original beaker with hot water, transfer the precipitate to the filter paper, and rinse the sides of the filter paper with 10mL hydrochloric acid solution (4.1.2.4) to dissolve the trace iron on the filter paper. Then wash the filter paper several times with hot water until there are no iron ions.

4.1.4.4 Cover the surface vessel and heat the solution to boiling until the volume of the solution is about (20-30) mL. Under continuous stirring, add tin dichloride solution (4.1.2.6) dropwise until the yellow color disappears and add 2 more drops. After rapid cooling, rinse the surface vessel and beaker walls with water and add 10mL of saturated mercuric chloride solution (4.1.2.7) until white filamentous mercuric chloride precipitates. Leave for a moment, dilute with water to 100mL, add 15mL of sulfuric acid phosphate mixture (4.1.2.5) and 5 drops of sodium diphenylamine sulfonate indicator (4.1.2.9), titrate with potassium dichromate standard solution (4.1.2.8) until the solution turns stable purple, and record the volume of standard solution consumed.

4.1.4.5 Perform blank measurements according to the steps specified in 4.1.4.1 to 4.1.4.4 (without adding coal samples), and take the average of the two measurements as the blank value.

4.1.5 Result Calculation

Calculate the mass fraction (%) of iron sulfur sulfide (Sp, ad) in air dried coal samples using formula (2):

(2)

In the formula:

- The amount of potassium dichromate standard solution used for coal sample determination, in milliliters (mL);

- The amount of potassium dichromate standard solution used for blank determination, in milliliters (mL);

- The concentration of potassium dichromate standard solution, in moles per liter (mol/L);

0.05585- millimolar mass of iron, in grams per millimole (g/mmol);

1.148- The coefficient for converting iron to iron sulfide sulfur;

- Coal sample mass, in grams (g).

4.2 Method B - Atomic Absorption Spectroscopy

4.2.1 Method Summary

Using hydrochloric acid to extract iron from non sulfide iron in coal, the extracted coal sample is leached with dilute nitric acid. The iron in the nitric acid leaching solution is determined by atomic absorption spectrophotometry, and the sulfur content of sulfide iron in coal is calculated based on the mass of iron.

4.2.2 Reagents and materials

The water used is Grade I laboratory water (GB/T6682).

4.2.2.1 Nitric acid solution (GB/T626): Volume ratio of 1+7.

4.2.2.2 Nitric acid solution (GB/T626): Volume ratio of 1+1.

4.2.2.3 Iron standard stock solution: 1mg/mL.

Weigh 1.0000g (accurate to 0.0002g) of high-purity iron (99.99%) into a 300mL beaker, add 50mL of nitric acid (4.2.2.2), place on an electric heating plate, slowly heat until completely dissolved, and then cool to room temperature