GB/T 223.13-2025Iron, steel and alloy - Determination of vanadium content - Titrimetric method and spectrophotometric method (English PDF)

4.1 Principle

After the test material is dissolved in a suitable acid, vanadium is oxidized with potassium permanganate at room temperature in a sulfuric acid-phosphoric acid medium. Excess potassium permanganate is reduced with sodium nitrite. Excess sodium nitrite is decomposed with urea. Vanadium is titrated with a standard ferrous ammonium sulfate solution using benzoic acid as an indicator.

4.2 Reagents and materials

In the analysis, unless otherwise specified, only analytically pure reagents and Grade II water or water of equivalent purity as specified in GB/T 6682 shall be used.

4.2.1 Hydrochloric acid. rho is approximately 1.19 g/mL.

4.2.2 Nitric acid. rho is approximately 1.42 g/mL.

4.2.3 Sulfuric acid (5+95). diluted with sulfuric acid (rho approx. 1.84 g/mL).

4.2.4 Phosphoric acid. rho is approximately 1.69 g/mL.

4.2.5 Sulfuric acid-phosphoric acid mixture. while stirring, slowly add 200 mL of

sulfuric acid (rho is approximately 1.84 g/mL) to 400 mL of water. Let cool slightly. Add

100 mL of phosphoric acid (4.2.4). Mix well.

4.2.6 Potassium permanganate solution. 3 g/L.

4.2.7 Sodium nitrite solution. 20 g/L.

4.2.8 Urea solution. 200 g/L.

4.2.9 Ferrous ammonium sulfate [(NH4)2Fe(SO4)2·6H2O] solution. 40 g/L.

Weigh 40.0 g of ferrous ammonium sulfate hexahydrate [(NH4)2Fe(SO4)2·6H2O].

Dissolve in sulfuric acid (4.2.3) and dilute to 1000 mL. Mix well.

4.2.10 Benzyl anthranilic acid solution. 2 g/L.

Weigh 0.2 g of benzo (o-aminobenzoic acid) into a 300 mL beaker. Add 0.2 g of anhydrous sodium carbonate. Add 20 mL of water and heat to dissolve. Dilute with water to 100 mL. Mix well.

4.2.11 Sodium arsenite solution. 5 g/L.

Weigh 0.38 g of arsenic trioxide. Dissolve in 50 mL of sodium hydroxide solution (50 g/L). Neutralize with sulfuric acid (rho is approximately 1.84 g/mL, 1+1) until the solution is neutral. Dilute with water to 100 mL. Mix well.

Alternatively, sodium arsenite can be used. Weigh 0.5 g of sodium arsenite and dissolve it in water. Dilute to 100 mL. Mix well.

4.2.12 Potassium dichromate standard solution [c(1/6K2Cr2O7) = 0.01000 mol/L].

Weigh 0.4903 g of potassium dichromate, which has been pre-dried at 150°C for 1 h and cooled to room temperature in a desiccator. Place it in a 300 mL beaker. Dissolve it in water. Transfer the solution to a 1000 mL volumetric flask. Dilute to the mark with water. Mix well.

4.2.13 Ferrous ammonium sulfate standard solution {c[(NH4)2Fe(SO4)2·6H2O] = 0.01

mol/L}.

4.2.13.1 Preparation.

Weigh 4.0 g of ferrous ammonium sulfate hexahydrate [(NH4)2Fe(SO4)2·6H2O].

Dissolve in sulfuric acid (4.2.3) and dilute to 1000 mL. Mix well.

4.2.13.2 Calibration and indicator calibration.

Take three 250 mL Erlenmeyer flasks. Add 15 mL of sulfuric acid (rho is approximately

1.84 g/mL) and 10 mL of phosphoric acid (4.2.4) to each. Heat to evaporate until sulfuric acid fumes are emitted. Let cool slightly. Add 50 mL of water. Cool to room

The specimens used, the raw data of the precision tests, and the statistical results are listed in Tables C.1, C.2, and C.3 of Annex C. A graph of the precision data is shown in

Figure C.1.

The repeatability limit (r) and reproducibility limit (R) are obtained according to the equations given in Table 2.

Under repeatability conditions, the absolute difference between two independent test results shall not exceed the repeatability limit (r), provided that the number of cases exceeding the repeatability limit (r) does not exceed 5%.

Under reproducibility conditions, the absolute difference between two independent test results shall not exceed the reproducibility limit (R), provided that the number of cases exceeding the reproducibility limit (R) does not exceed 5%.

5.1 Principle

Dissolve the test material in a suitable acid. Add phosphoric acid to the solution, so as to eliminate interference from iron. Add potassium permanganate to oxidize vanadium to V(V). Excess permanganate is selectively reduced with sodium nitrite. In the presence of urea, add N-BPHA (tantalum reagent) and hydrochloric acid to form a complex. The mixture is then extracted with chloroform. Measure the absorbance at

535 nm.

5.2 Reagents

Unless otherwise specified, only reagents confirmed to be analytically pure and water of Grade II or equivalent purity as specified in GB/T 6682 shall be used in the analysis.

5.2.1 Hydrochloric acid. rho is approximately 1.19 g/mL.

5.2.2 Hydrochloric acid (4+1). add 400 mL of hydrochloric acid (5.2.1) to 100 mL of water.

5.2.3 Nitric acid. rho is approximately 1.42 g/mL.

5.2.4 Perchloric acid. rho is approximately 1.67 g/mL.

WARNING -- Perchloric acid vapors can typically cause explosions in the presence of ammonia, nitrite fumes, or organic matter.

5.2.5 Phosphoric acid. rho is approximately 1.69 g/mL.

5.2.6 Phosphoric acid (1+1). add 250 mL of phosphoric acid (5.2.5) to 250 mL of water.

5.2.7 Hydrochloric acid/nitric acid mixed acid (3+1). mix 300 mL of hydrochloric acid

(5.2.1) with 100 mL of nitric acid (5.2.3). Prepare when needed.

5.2.8 Hydrogen peroxide solution. 30%.

5.2.9 Sodium nitrite solution. 3 g/L.

5.2.10 Urea solution. 250 g/L.

5.2.11 Sodium tripolyphosphate (Na5P3O10) solution. 100 g/L.

5.2.12 Potassium permanganate solution. 3 g/L.

5.2.13 Chloroform.

5.2.14 N-Benzoylphenyl hydroxylamine [C6H5CON(OH)C6H5] (N-BPHA, also known

as tantalum reagent) - chloroform solution. 2.5 g/L.

Dissolve 0.25 g of N-BPHA in 100 mL of chloroform (5.2.13). The solution shall be stored in a brown bottle. Otherwise, it shall be prepared when needed.

5.2.15 Iron solution. 10 g/L.

Weigh 5.0 g of pure iron (vanadium-free or with the lowest possible and known vanadium content), accurate to 1 mg. Transfer to a 500 mL beaker. Cover with a watch glass. Add 100 mL of a hydrochloric acid/nitric acid mixture (5.2.7). After the vigorous reaction stops, heat slowly until completely dissolved. Add 100 mL of perchloric acid (5.2.4). Heat until white perchloric acid fumes appear and reflux in the beaker. Continue fuming for about 3 min.

Cool. Add 100 mL of hot water. Shake to dissolve the salt. Add a few drops of hydrogen peroxide solution (5.2.8). Heat to boiling. Maintain boiling for about 2 min. After cooling, transfer to a 500 mL volumetric flask. Dilute to the mark with water. Mix well.

5.2.16 Vanadium standard solution. 1.0 g/L.

Dry several grams of ammonium metavanadate (NH4VO3) in an oven at 100°C~105°C for at least 1 h. Then cool to room temperature in a desiccator. Drying at temperatures

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