GB/T 6730.65-2009Iron ores - Determination of total iron content - Titanium(III) chloride reduction potassium dichromate titration methods (routine methods) (English PDF)

4.15 Ammonia water

5+95.

4.16 Sodium hydroxide solution

10 g/L.

4.17 Sodium fluoride solution

50 g/L, stored in a plastic bottle.

4.18 Stannous chloride solution

60 g/L.

Dissolve 6 g of stannous chloride in 20 mL of hot concentrated hydrochloric acid. Use water to dilute to 100 mL. Mix well. Add several tin particles.

4.19 Sodium tungstate solution

250 g/L.

Weigh 25 g of sodium tungstate and dissolve it in an appropriate amount of water. Add

5 mL of phosphoric acid. Use water to dilute to 100 mL.

4.20 Titanium trichloride solution

1+14.

Take 2 mL of titanium trichloride solution (approximately 15% mass volume concentration). Use hydrochloric acid (1+5) to dilute to 30 mL.

4.21 Copper sulfate

5 g/L.

4.22 Potassium dichromate solution

1 g/L.

4.23 Potassium permanganate solution

4 g/L.

4.24 Sodium diphenylamine sulfonate indicator solution

2 g/L.

4.25 Ammonium ferrous sulfate solution, c(Fe

2+

) = 0.05 mol/L.

Weigh 19.7 g of ammonium ferrous sulfate [(NH4 ) 2 Fe(SO4 ) 2 ·6H 2 O]. Dissolve in sulfuric acid (5+95). Transfer to a 1000 mL volumetric flask. Use sulfuric acid (5+95) to dilute to the scale. Mix well.

4.26 Potassium dichromate standard titration solution

c(1/6K2 Cr 2 O 7 ) = 0.05000 mol/L.

Weigh 2.4515 g of potassium dichromate (reference reagent) that has been pre dried at

140°C~150°C for 2 h and cooled to room temperature in a dryer. Put it in a 250 mL beaker. Add water to dissolve. Transfer to a 1000mL volumetric flask. Dilute to the scale. Mix well. Note down the temperature at which the standard titration solution is prepared.

The volumetric flasks used shall meet the requirements for Grade A volumetric flasks in GB/T 12806. Calibrate the volumetric flask beforehand if necessary.

NOTE 1: Certain potassium dichromate standard substances have determined their potassium dichromate content. The mass of potassium dichromate can be calculated and weighed according to its content.

NOTE 2: Attention shall be paid to the ambient temperature of potassium dichromate standard titration solution. The temperature during titration shall be as consistent as possible with the temperature of the prepared standard titration solution.

6.1 Laboratory specimens

Prepare laboratory specimens in accordance with the provisions of GB/T 10322.1.

Generally, the particle size of the specimen shall be less than 100 µm. If the content of hydrated water or easily oxidized substances in the specimen is high, the particle size shall be less than 160 µm.

6.2 Pre-dried specimens

Mix the laboratory specimens thoroughly. Use fractional division method to sample. In accordance with the provisions in GB/T6730.1, dry the specimen at a temperature of

105°C ± 2°C.

7.1 Number of determinations

For the same pre-dried specimen (6.2), conduct at least 2 independent determinations.

NOTE: "Independent" means that in the same laboratory, the same operator uses the same equipment and uses the same test method to independently test the same measured object within a short period of time.

when the fume of sulfuric acid is 5 cm ~ 6 cm away from the liquid surface.

NOTE 1: When the amount of silicon in the specimen is high, 0.5 g of sodium fluoride (4.4) can be added to aid for dissolution.

NOTE 2: For iron ore samples with high silicon and low iron content, in general, the mass fraction of total iron is less than 50%. Decomposition method by sulfuric acid-phosphoric acid shall not be used.

7.4.2.2

Cool for a little while. Add 20 mL of hydrochloric acid (4.9) along the beaker wall. Add stannous chloride solution (4.18) dropwise while hot until the test solution turns slightly yellow. Cool to room temperature. Add about 50 mL of water, 1 mL of sodium tungstate solution (4.19). Add titanium trichloride solution (4.20) dropwise until the test solution turns blue.

7.4.2.3 Add potassium dichromate solution (4.22) dropwise until the blue color

disappears. Or wait until the oxygen in the air is oxidized until the blue color disappears.

Add 5 drops of sodium diphenylamine sulfonate indicator solution (4.24). Use potassium dichromate standard titration solution (4.26) to titrate until the test solution turns from green to blue-green. When the last drop turns purplish red, it shall be the end point.

NOTE: Add 1~2 drops of copper sulfate solution (4.21). Shake well. Blue color immediately fades away. Titrate immediately after adding the indicator solution.

7.4.3 Melting by sodium carbonate-boric acid mixed flux, decomposition by

hydrochloric acid

7.4.3.1 Put the test material (7.2) in a platinum crucible (5.1) that is filled with 2.5 g of sodium carbonate-boric acid mixed flux (4.5). Mix well. Cover with the platinum lid.

Place the platinum crucible in a high-temperature furnace (5.4) at 950 °C for 10 min ~

20 min for melting. Remove the crucible from the high temperature furnace and shake it. Cool.

7.4.3.2 Put the platinum crucible in a 300 mL beaker that is filled with 100 mL of hydrochloric acid (4.9). Cover the watch glass. Heat slowly until the test material is dissolved. During the dissolution process, add stannous chloride solution (4.18) continuously dropwise. Keep the test solution slightly yellow. Wash out the platinum crucible and lid. Transfer the test solution into a 500 mL Erlenmeyer flask. Add water to about 150 mL. Add 1 mL of sodium tungstate solution (4.19). Add titanium trichloride solution (4.20) dropwise until the test solution turns blue.

7.4.3.3 The following operations are the same as 7.4.1.3.

NOTE: If you are used to titration analysis in a beaker, you don’t need to transfer it to a 500 mL

Erlenmeyer flask. Carry out subsequent steps directly in the beaker.

7.4.4 Melting by sodium carbonate, sodium peroxide mixed flux

7.4.4.1 Specimens with vanadium content less than 0.1%

7.4.4.1.1 Put the test material (7.2) in the corundum crucible (5.2) that is pre-added with

0.5 g of anhydrous sodium carbonate (4.1). Add 2 g of sodium peroxide (4.2). Mix well.

Use a small amount of sodium peroxide to cover the surface. Bake on a hot plate until browned. Place in the high temperature furnace (5.4). Slowly heat up from 400°C to

700°C~750°C. Melt for 5 min ~ 10 min until it is clear. Cool.

7.4.4.1.2 Put the corundum crucible in a 300 mL beaker that is filled with 100 mL of hydrochloric acid (4.9). Cover the watch glass. Heat slowly until the test material is dissolved. During the dissolution process, the stannous chloride solution (4.18) is continuously added dropwise. Keep the test solution slightly yellow. Wash out the corundum crucible. Cool to room temperature.

7.4.4.1.3 The following are the same as 7.4.1.2 and subsequent steps.

7.4.4.2 Specimens with vanadium content greater than 0.1%

7.4.4.2.1 Same as 7.4.4.1.1.

7.4.4.2.2 Put the corundum crucible in a 400 mL beaker. Add 150 mL of hot water to soak. Wash out the crucible. Use medium speed filter paper to filter. Use sodium hydroxide solution (4.16) to rinse the beaker and precipitate for 5~6 times.

7.4.4.2.3 Use 20 mL of hydrochloric acid (4.8) to dissolve the precipitate in the original beaker. Use a small amount of hot hydrochloric acid (4.10) to wash the filter paper until it is colorless. Clean the original corundum crucible. The washing liquid is combined in the original beaker. Heat slowly until the precipitate is dissolved. During the dissolution process, the stannous chloride solution (4.18) is continuously added dropwise. Keep the test solution slightly yellow. Cool to room temperature. Transfer the test solution into a 500 mL Erlenmeyer flask. Add water to about 150 mL. Add 1 mL of sodium tungstate solution (4.19). Add titanium trichloride solution (4.20) dropwise until the test solution turns blue.

7.4.4.2.4 The following operations are the same as 7.4.1.3.

NOTE: If you are used to titration analysis in a beaker, you don’t need to transfer it to a 500 mL

Erlenmeyer flask. Carry out the subsequent steps directly in the beaker.

7.4.5

Sintering by sodium carbonate, potassium nitrate and oxalic acid mixed flux, decomposition by hydrochloric acid

7.4.5.1 Put the test material in a porcelain crucible that is filled with 0.8 g of mixed flux of sodium carbonate, potassium nitrate and oxalic acid (4.6). Mix well. Transfer them all to a conical filter paper. Pack into a small packet. Place in a porcelain crucible that is lined with magnesium oxide (4.3). Open the furnace door in the high-temperature