YS/T 273.4-2020 English PDF (YST273.4-2020)

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YS/T 273.4-2020: Methods for chemical analysis and physical properties test of cryolite - Part 4: Determination of aluminium content - EDTA titration method
YS/T 273.4-2020
YS
NONFERROUS METAL INDUSTRY STANDARD
OF THE PEOPLE’S REPUBLIC OF CHINA
ICS 71.100.10
H 30
Replacing YS/T 273.4-2006
Methods for chemical analysis and physical properties test of
cryolite - Part 4: Determination of aluminum content -
EDTA titration method
ISSUED ON: DECEMBER 09, 2020
IMPLEMENTED ON: APRIL 01, 2021
Issued by: Ministry of Industry and Information Technology of PRC
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Method summary ... 5
3 Reagents ... 5
4 Instruments and equipment ... 6
5 Specimens ... 7
6 Analysis steps ... 7
7 Calculation of test results ... 8
8 Precision ... 8
9 Quality assurance and control ... 9
10 Test report ... 9
Methods for chemical analysis and physical properties test of
cryolite - Part 4: Determination of aluminum content -
EDTA titration method
1 Scope
This Part specifies the method for determination of aluminum content in cryolite.
This section applies to the determination of aluminum content in cryolite. Measurement
range: 9.00% ~ 20.00%.
2 Method summary
The sample is melted with acidic potassium sulfate or potassium pyrosulfate, to remove
fluorine; the frit is dissolved with hydrochloric acid. Take a portion of the test solution.
Add excess Na2EDTA, to form a complex between the aluminum element and EDTA.
Under weakly acidic conditions, use xylenol orange as an indicator. Use zinc nitrate
standard titration solution, to titrate the excess Na2EDTA. Add sodium fluoride. Heat to
displace EDTA. Then use zinc nitrate standard solution, to titrate the released EDTA.
Calculate the aluminum content by using the millimeters of zinc nitrate standard
titration solution, which is consumed in the titration.
3 Reagents
Unless otherwise stated, only reagents and deionized water determined to be of
analytical grade are used in the analysis.
3.1 Acid potassium sulfate or potassium pyrosulfate.
3.2 Sodium fluoride.
3.3 Hydrochloric acid (1 + 1).
3.4 Hydrochloric acid (1 + 3).
3.5 Sodium hydroxide solution (100 g/L).
3.6 Buffer solution (pH value 5.6): Weigh 333 g sodium acetate trihydrate. Dissolve in
water. Add 15 mL of glacial acetic acid. Use water to dilute it to 1000 mL. Mix well.
5 Specimens
Grind and mix the sample, to pass through a 75 μm standard sieve. Bake it in an oven,
at 110 °C ± 5 °C for 2 h. Cool it to room temperature in a desiccator.
6 Analysis steps
6.1 Sample
Weigh 0.25 g of specimen (5), accurate to 0.0001 g.
6.2 Parallel test
Conduct two tests in parallel. Take the average value.
6.3 Determination
6.3.1 Place the sample (6.1) in the platinum crucible (4.1). Add 6 g of acidic potassium
sulfate or potassium pyrosulfate (3.1). Put the platinum crucible into the high-
temperature furnace (4.2) when the temperature is lower than 300 °C. Start timekeeping,
when the furnace temperature reaches 725 °C ± 25 °C. Melt for about 30 minutes, until
the fluorine is completely driven out. Take it out. Cool it to room temperature.
6.3.2 Add 100 mL of water and 5 mL of hydrochloric acid (3.3) in a 250 mL beaker.
Then put the frit (6.3.1) together with the platinum crucible, into the beaker. Heat it.
Use a glass rod to stir, to make the frit fall off. Wash out the platinum crucible. Continue
heating, until the frit is completely dissolved. Remove and cool to room temperature.
Transfer the solution into a 250 mL volumetric flask. Use water to dilute it to the mark.
Mix well.
6.3.3 Pipette 100.00 mL of solution (6.3.2). Add 1 drop of phenolphthalein ethanol
solution (3.9). Dropwise add sodium hydroxide solution (3.5), until the solution turns
red. Dropwise add hydrochloric acid (3.4), until the solution is colorless. Add an excess
of 1.5 mL. Add 15 mL of Na2EDTA solution (3.7). Heat and boil for 2 minutes. Remove
it. Add sodium hydroxide solution (3.5) dropwise, until the solution turns red. Add
hydrochloric acid (3.4) dropwise, until the solution is colorless. Add 20 mL of buffer
solution (3.6). Use running water to cool to room temperature.
6.3.4 Add 3 drops of xylenol orange solution (3.10). Use zinc nitrate standard titration
solution (3.8) for titration, to make the solution change from yellow to rose red.
6.3.5 Add 0.5 g ~ 1 g of sodium fluoride (3.2). Heat and boil for 2 minutes. Then remove
it. Use running water, to cool to room temperature. Use zinc nitrate standard titration
solution (3.8) for titration, until the solution changes from yellow to rose red. Record
the volume of zinc nitrate standard titration solution, which is consumed in the second