The measurement procedure of iron sulfide powder in coal is as follows:

(1) Add 50 ml of nitric acid solution to the coal sample extracted from iron sulfide powder with hydrochloric acid, cover the surface plate, boil for 30 minutes, and wash the surface with water.

(2) Add 2 ml of hydrogen peroxide to the filtrate and boil for about 5 minutes to eliminate the color generated by the decomposition of the coal sample (in the coal with a low degree of coalification, you can add more hydrogen peroxide until the brown color disappears).

(3) Add the ammonia solution until the ferric hydroxide precipitates in the boiling solution, add 2 ml until the precipitation is complete. Boil the solution, filter with quick qualitative filter paper, and rinse the sediment and the wall of the beaker with hot water 1-2 times. Break the filter paper, wash the sediment into the original beaker with hot water, transfer the sediment to the filter paper, rinse around the filter paper with 10 ml of hydrochloric acid solution, dissolve a small amount of iron in the filter paper, rinse the filter paper with hot water until there is no iron Ion until several times.

(4) Cover the surface plate, let the solution boil until the volume of the solution reaches about 20-30 ml, add 2 drops of the tin dichloride solution dropwise while stirring, and after rapid cooling, wash the surface with water. Leave it for a while, dilute to 100 ml with water, add 15 ml of sulfuric acid-phosphoric acid mixture and 5 drops of sodium diphenylamine sulfonate indicator, and use potassium dichromate standard solution.

(5) Carry out blank measurement in accordance with the prescribed sequence (no coal sample), and use the average of the two measurements as the blank value.

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