GB/T 8704.5-2020Ferrovanadium—Determination of vanadium content—The ammonium ferrous sulfate titrimetric method and the potentiometric titrimetric method (English PDF)

3.2.9 Sodium nitrite solution, 20g/L

3.2.10 Manganese sulfate solution, 10g/L

3.2.11 Potassium dichromate standard solution, c(1/6K2Cr2O7) = 0.07000mol/L

Weigh 3.4322g of benchmark potassium dichromate that has been dried in an electric oven at 120°C to constant weight. Place in a 300mL beaker. Use water to dissolve. Move into a 1000mL volumetric flask. Use water to dilute to the scale. Mix well.

3.2.12 Ferrous ammonium sulfate standard solution (about 0.07mol/L)

3.2.12.1 Preparation

Weigh 27.45g of ferrous ammonium sulfate [(NH4)2Fe(SO4)2·6H2O] in a 300mL beaker. Dissolve in appropriate amount of sulfuric acid (5+95). Use sulfuric acid (5+95) to dilute to 1000mL. Mix well.

3.2.12.2 Calibration and indicator calibration

Dispense 5.00mL of potassium dichromate standard solution (see 3.2.11) into three portions. Respectively place in 500mL Erlenmeyer flasks. Successively add 20mL of sulfuric acid (see 3.2.5), 5mL of phosphoric acid (see 3.2.3), 70mL of water, 3 drops of N-phenylanthranilic acid indicator solution (see 3.2.14). Use ferrous ammonium sulfate standard solution (see 3.2.12) to titrate the solution from purple-red to bright yellow-green as the end point. The volume of ferrous ammonium sulfate standard titration solution is not counted. Add 20.00mL (V01) of potassium dichromate standard solution (see 3.2.11). Use ferrous ammonium sulfate standard titration solution (see 3.2.12) to titrate the solution from purple-red to bright yellow-green as the end point. Record the consumed volume of ferrous ammonium sulfate standard titration solution V1.

The difference in the volume of ferrous ammonium sulfate standard titration solution consumed by three potions of potassium dichromate standard solutions does not exceed 0.05mL. Take the average. Calculate the concentration of ferrous ammonium sulfate standard titration solution according to formula (1):

Where, c1 - Concentration of ferrous ammonium sulfate standard titration solution, in Mole per liter (mol/L);

3.5.5.2 Ammonium persulfate oxidation

b) In the test solution (see 3.5.5.1), add 4g~5g of ammonium persulfate (see 3.2.1). Add 5mL of manganese sulfate solution (see 3.2.10). Mix well. Heat and boil until big bubbles appear. Remove. Use a little water to rinse the bottle wall. Boil for another 2min~3min. Remove and cool to room temperature.

3.5.5.3 Titration

In the test solution (see 3.5.5.2), add 3 drops of N-phenylanthranilic acid indicator solution (see 3.2.14). Immediately use ferrous ammonium sulfate standard titration solution (see 3.2.12) to titrate the solution from purple-red to bright yellow-green as the end point. The volume of the consumed ferrous ammonium sulfate standard titration solution is V4.

3.6 Calculation and expression of analysis result

3.6.1 Calculation of vanadium content

Calculate vanadium content wv according to formula (2), in mass fraction (%):

Where, c1 - Concentration of ferrous ammonium sulfate standard titration solution, in Mole per liter (mol/L);

V4 - Volume of ferrous ammonium sulfate standard titration solution consumed to titrate the test material solution, in milliliters (mL);

V0 - Volume of ferrous ammonium sulfate standard titration solution consumed to titrate the blank test solution, in milliliters (mL);

50.94 - Molar mass of vanadium, in grams per mole (g/mol);

m - Amount of test material, in grams (g).

3.6.2 Determination and expression of analysis results

If the absolute value of the difference between two independent analysis results of the same sample is not greater than the repeatability limit r, then take the arithmetic mean as the analysis result. If the absolute value of the difference between the two independent analysis results is greater than the repeatability limit r, then increase the number of determinations and determine the analysis

4.2.3 Phosphoric acid, rho 1.70g/mL

4.2.4 Sulfuric acid, 1+1

4.2.5 Sodium nitrite solution, 10g/L

4.2.6 Potassium permanganate solution, 6.3g/L

4.2.7 Potassium dichromate standard solution, c(1/6K2Cr2O7) = 0.2000mol/L

Precisely weigh 9.8064g of benchmark potassium dichromate that has been pre-dried at 150°C for 2h and cooled to room temperature in a dryer. Place in a 300mL beaker. Use water to completely dissolve. Move into a 1000mL volumetric flask. Use water to dilute to the scale. Mix well.

4.2.8 Ferrous ammonium sulfate standard titration solution

c[(NH4)2Fe(SO4)2·6H2O] = 0.2mol/L.

4.2.8.1 Preparation

Weigh 78.4g of ferrous ammonium sulfate [(NH4)2Fe(SO4)2·6H2O] in a 500mL beaker. Use an appropriate amount of sulfuric acid (5+95) to completely dissolve. Move into a 1000mL volumetric flask. Use sulfuric acid (5+95) to dilute to the scale. Mix well.

4.2.8.2 Calibration

In a 600mL beaker that is filled with 270mL of water, 10mL of phosphoric acid (see 4.2.3) and 20mL of sulfuric acid (see 4.2.4), use a burette to add 40.00mL of potassium dichromate standard solution (see 4.2.7). Use ferrous ammonium sulfate standard titration solution (see 4.2.8) to conduct potentiometric titration.

Under the potentiometer check, use ferrous ammonium sulfate standard titration solution (see 4.2.8) to slowly titrate to the end point. Continue to add 0.05mL each time or add drop by drop. Record the potential reading and titration volume every time the potential is balanced. Continue to drip till it exceeds the end point. Determine the end point from potentiometric titration curve or dE/dV curve. Record the volume of ferrous sulfate standard solution consumed at the end of the titration, V5.

Calculate the concentration of ferrous ammonium sulfate standard titration solution (4.2.8) according to formula (3):

Where, c2 - Concentration of ferrous ammonium sulfate standard titration solution, in Mole per liter (mol/L);

c02 - Concentration of potassium dichromate standard solution, in Mole per liter (mol/L);

V02 - Volume of potassium dichromate standard solution, in milliliters (mL);

V5 - Volume of ferrous ammonium sulfate standard titration solution consumed when calibrating, in milliliters (mL).

4.3 Instruments

4.3.1 Magnetic stirrer.

4.3.2 Automatic potentiometric titrator, equipped with platinum electrode and calomel electrode.

4.4 Sample extraction and preparation

Extract and prepare samples according to GB/T 4010. All samples shall pass through the 0.180mm sieve.

4.5 Analysis steps

4.5.1 Number of determinations

For the same sample, at least independently determine twice.

4.5.2 Test material

Weigh 0.50g of test material, to the nearest of 0.0001g.

4.5.3 Blank test

Conduct the blank test with test material. The reagents used shall be taken from the same reagent bottle.

4.5.4 Verification test

Analyze the same type of standard sample along with test material.

4.5.5 Determination

4.5.5.1 Place the test material (see 4.5.2) in a 400mL beaker. Add 10mL of water, 10mL of nitric acid (see 4.2.2), 50mL of sulfuric acid (see 4.2.4). Heat till all the test material is dissolved. Evaporate to emit sulfuric acid white smoke. Remove and cool. […]