YS/T 555.1-2009Methods for chemical analysis of molybdenum concentrate. Determination of molybdenum content. Lead molybdenum gravimetry (English PDF)

3.1 Mixed flux. weigh 500 g of anhydrous sodium carbonate and 250 g of zinc oxide.

Mix well and grind finely. Store in a ground glass bottle.

3.2 Ammonium nitrate.

3.3 Hydrochloric acid (rho 1.19 g/mL).

3.4 Nitric acid (rho 1.42 g/mL).

3.5 Ammonia solution (rho 0.90 g/mL).

3.6 Saturated potassium nitrate-chlorate solution.

3.7 Hydrochloric acid (1+1).

3.8 Hydrochloric acid solution (1+19).

3.9 Sulfuric acid (1+1).

3.10 Ammonia solution (1+1).

3.11 Ammonia solution (3+97).

3.12 Sodium hydroxide solution (200 g/L).

3.13 Acetic acid-ammonium acetate buffer solution. weigh 250 g of ammonium acetate

into a 1000 mL beaker. Dissolve in 500 mL of water, then add 150 mL of acetic acid.

Filter and dilute with water to 1000 mL. Mix well.

3.14 Ferric chloride solution (48 g/L). weigh 48 g of ferric chloride (FeCl3·6H2O) and

dissolve it in 50 mL of hydrochloric acid (3.3). Dilute with water to 1000 mL. Mix well.

3.15 Ammonium nitrate solution (30 g/L). weigh 30 g of ammonium nitrate and

dissolve it in 1000 mL of water. Adjust the pH to 8~9 with ammonia water (3.10).

3.16 Ammonium acetate solution. measure 25 mL of acetate-ammonium acetate buffer

solution (3.13). Dilute with water to 500 mL. Mix well.

3.17 Lead acetate solution (18 g/L). weigh 18 g of lead acetate into a 1000 mL beaker.

Add 15 mL of glacial acetic acid and 80 mL of water to dissolve. Filter and dilute with

water to 1000 mL.

3.18 Potassium thiocyanate solution (300 g/L).

3.19 Thiourea solution (50 g/L).

3.20 Sulfuric acid-copper sulfate solution. weigh 1 g of copper sulfate (CuSO4·5H2O)

into a 1000 mL beaker. Add 1000 mL of sulfuric acid (3.9) to dissolve. Mix well.

3.21 To make the filter paper pulp, tear quantitative filter paper into pieces. Place it in

a 500 mL beaker. Add water, and boil it into a paste.

3.22 Molybdenum standard stock solution (100 µg/mL). weigh 0.1500 g of

molybdenum trioxide (primary standard reagent) into a 300 mL beaker. Add 2 mL of

sodium hydroxide solution (3.12) and 100 mL of water. Heat to dissolve. Cool. Transfer

to a 1000 mL volumetric flask. Dilute to the mark with water. Mix well. This solution

contains 100 µg of molybdenum per mL.

3.23 Molybdenum standard solution. transfer 10.00 mL of molybdenum standard stock

solution (3.22) into a 100 mL volumetric flask. Dilute to the mark with water. Mix well.

This solution contains 10 µg of molybdenum per mL.

3.24 Methyl orange solution (1 g/L).

3.25 Tannin solution (10 g/L, used as an external indicator).

3.26 Phenolphthalein solution (1 g/L). prepared with ethanol (1+1).

6.1 Test material

Weigh approximately 0.20 g of the specimen, accurate to 0.0001 g. Perform two

independent determinations and take the average value.

6.2 Blank test

Conduct a blank test along with the test material.

6.3 Determination

6.3.1 Determination of molybdenum in specimens with tungsten content less than

0.25%

6.3.1.1 Place the test material (6.1) in a 400 mL beaker. Add 20 mL of saturated

potassium nitric acid-chlorate solution (3.6). Cover with a watch glass. Dissolve by

heating at low temperature. Evaporate to 3 mL~5 mL. Add another 5 mL of saturated

potassium nitric acid-chlorate solution (3.6). Continue evaporating to 3 mL. Remove

and let cool slightly. Add 10 mL of hydrochloric acid (3.3). Continue heating and

evaporating to 3 mL~4 mL. Remove.

6.3.1.2 Add 10 mL of hydrochloric acid (3.3) to the test solution. Rinse the glass and

beaker walls with water. Dilute to approximately 80 mL. Boil. Add a small amount of

paper pulp. Remove and let cool slightly. Slowly add ammonia (3.5) while stirring.

Allow the hydroxide to precipitate, then add an excess of 20 mL. Boil for 5 min.

Remove and filter while hot using rapid filter paper. Wash the precipitate 4~5 times

with hot ammonia solution (3.11). Add 10 mL of hydrochloric acid (3.7) to dissolve the

precipitate in the original beaker. Rinse the filter paper with hot water until no yellow

color remains. Dilute the filtrate to 50 mL with water. Add 25 mL of ammonia (3.5).

Boil for 5~6 min. Filter the precipitate into the first filtrate using the original filter paper,

then wash the precipitate 4~5 times with hot ammonia solution (3.11). Retain the

residue for the correction determination of molybdenum.

6.3.1.3 Dilute the filtrate with water to approximately 300 mL. Add 2 drops of methyl

orange solution (3.24). Neutralize with hydrochloric acid (3.7) until the solution turns

orange-red. Add an excess of 10~12 drops. Add 50 mL of acetate-ammonium acetate

buffer solution (3.13). Heat to a gentle boil. Remove from heat. Add lead acetate

solution (3.17) with stirring using a burette. Add lead acetate evenly at 1 mL/3 s until

the tannin external indicator solution (3.25) no longer turns yellow. Add an excess of

2~3 mL. Add a small amount of filter paper pulp (3.21). Heat to a gentle boil, then let

stand at room temperature for 30 min. Remove from heat. Filter with medium-speed

quantitative filter paper. Wipe away any precipitate adhering to the beaker and glass rod

with a small piece of filter paper. Wash the precipitate 10~12 times with hot ammonium

acetate solution. Transfer the precipitate and filter paper to a pre-weighed porcelain

crucible. Dry. Ash. Heat in a furnace at 550°C~600°C until constant weight (weigh after

cooling in a desiccator).

6.3.2 Determination of molybdenum in specimens with a tungsten content of

0.25%~2%

6.3.2.1 Place the test material (6.1) in a 300 mL beaker. Add 20 mL of nitric acid (3.4).

Cover with a watch glass. Heat to dissolve. Evaporate to a volume of 3 mL~5 mL.

Remove and let cool slightly. Add 10 mL of hydrochloric acid (3.3) and continue

heating to a volume of 3 mL~4 mL. Remove from heat.

6.3.2.2 Add 10 mL of hydrochloric acid (3.3) and 50 mL of water to the test solution.

Boil. Filter while hot using rapid filter paper. Wash the precipitate 7~8 times with

hydrochloric acid solution (3.8), and the beaker 2~3 times. Transfer the residue

adhering to the beaker into the filtrate using ammonia water (3.10). Wash with water.

Retain the filter paper and residue. Add 6 mL of ferric chloride solution (3.14) and 2~3

g of ammonium nitrate (3.2) to the filtrate. Boil. Let cool slightly. Slowly add ammonia

water (3.5) while stirring, allowing the hydroxide to precipitate, then add an excess of

6.3.2.3 Add 10 mL of hydrochloric acid (3.7) to dissolve the precipitate in the original

beaker. Rinse the filter paper with hot water until no yellow color remains. Dilute the

filtrate with water to 50 mL. Add 15 mL of ammonia (3.5). Boil until a slight ammonia

odor is detected. Adjust the pH of the solution to 8~9 with hydrochloric acid (3.7) or

ammonia (3.10). Filter the solution into the filtrate using the original filter paper. Wash

4~5 times with hot ammonium nitrate solution (3.15). Combine the precipitate and

residue for the correction determination of molybdenum.

6.3.2.4 Dilute the filtrate with water to approximately 300 mL. The following

procedures shall be performed according to 6.3.1.3.

6.3.3 Molybdenum correction

6.3.3.1 Place the residue and filter paper obtained in 6.3.1.3 or 6.3.2.2 into a 30 mL

porcelain crucible. Carefully ash. Add 2 g~3 g of mixed flux (3.1). Stir well. Cover the

surface with another 1 g~2 g of mixed flux (3.1). Sinter in a high-temperature furnace

at 700°C~750°C for 30 min~40 min. Remove and cool. Carefully transfer the crucible

and sintered block into a 300 mL beaker. Wash the crucible with 30 mL~40 mL of hot

water and remove. Heat to boiling to dissolve the soluble salts. Remove. After cooling,

transfer to a 100 mL volumetric flask. Dilute to the mark with water. Mix well. Filter

dry.

6.3.3.2 Transfer 20.00 mL of the filtrate (6.3.3.1) to a 50 mL volumetric flask. Add 1

drop of phenolphthalein solution (3.26). Neutralize with sulfuric acid (3.9) until the

solution is colorless. Add 8 mL of sulfuric acid-copper sulfate solution (3.20) and 5 mL

of thiourea solution (3.19) and mix well. Let stand for 5 min. Add 5 mL of potassium

thiocyanate solution (3.18). Dilute to the mark with water. Mix well. Let stand for 30

min.

6.3.3.3 Transfer a portion of the solution into a 3 cm cuvette. Use the blank test solution

as a reference. Measure the absorbance at 460 nm using a spectrophotometer. Determine

the corresponding mass of molybdenum from the working curve.

6.3.3.4 Drawing the working curve

Transfer 0 mL, 2.00 mL, 4.00 mL, 6.00 mL, 8.00 mL, and 10.00 mL of molybdenum

standard solution (3.23) into a set of 50 mL volumetric flasks. Add water to a final

volume of 20 mL. Perform the following operations as per 6.3.3.2.Transfer a portion

of the solution into a 3 cm cuvette. Measure the absorbance using a reagent blank as a

reference. Plot a working curve with the mass of molybdenum on the x-axis and

absorbance on the y-axis.

0.2613 - Conversion factor from lead molybdate to molybdenum.

The calculation result is expressed to two decimal places.

8.1 Repeatability

For two independent determination results obtained under repeatability conditions, the

absolute difference between the two determination results should not exceed the

repeatability limit (r) within the range of the average values given below, and the

occurrence of differences exceeding the repeatability limit (r) should not exceed 5%.

The repeatability limit (r) is obtained by linear interpolation using the following data.

Molybdenum mass fraction / %. 40.00 50.00 57.00

Repeatability limit (r) / %. 0.30 0.35 0.40

NOTE. The repeatability limit (r) is 2.8Sr, where Sr is the repeatability standard deviation.

8.2 Allowable difference

The difference between laboratory analytical results should not exceed the allowable

difference listed in Table 1.

Table 1

Molybdenum mass fraction / % Allowable difference / %