GB/T 6730.9-2016 English PDF (GBT6730.9-2016)

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GB/T 6730.9-2016: Iron ores -- Determination of silicon content -- Silicomolybdic blue spectrophotometric method reduced by ammonium ferrous sulfate
GB/T 6730.9-2016
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 73.060.10
D 31
Replacing GB/T 6730.9-2006
Iron Ores - Determination of Silicon Content -
Silicomolybdic Blue Spectrophotometric Method Reduced
by Ammonium Ferrous Sulfate
ISSUED ON: OCTOBER 13, 2016
IMPLEMENTED ON: SEPTEMBER 1, 2017
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine of the People’s Republic of China;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative References ... 4
3 Principle ... 5
4 Reagents ... 5
5 Instruments ... 6
6 Sampling and Sample Preparation ... 6
7 Analytical Procedures ... 6
8 Result Calculation ... 8
9 Test Report ... 11
Appendix A (normative) Flowchart of Specimen Analytical Value Acceptance Program
... 12
Appendix B (informative) Iron Ore Specimens for Precision Test ... 13
Iron Ores - Determination of Silicon Content -
Silicomolybdic Blue Spectrophotometric Method Reduced
by Ammonium Ferrous Sulfate
WARNING---the personnel adopting this Part shall have formal laboratory experience.
This Part does not address all possible safety issues. It is the user’s responsibility to take
appropriate safety and health measures and ensure the compliance with the conditions
stipulated in the relevant national laws and regulations.
1 Scope
This Part of GB/T 6730 specifies the determination of silicon content through the
silicomolybdic blue spectrophotometric method reduced by ammonium ferrous sulfate.
This Part is applicable to the determination of silicon content in natural iron ore, iron
concentrate, sinter and pellets. The range of determination (mass fraction) is: 0.10% ~ 5.00%.
2 Normative References
The following documents are indispensable to the application of this document. In terms of
references with a specified date, only versions with a specified date are applicable to this
document. In terms of references without a specified date, the latest version (including all the
modifications) is applicable to this document.
GB/T 6682 Water for Analytical Laboratory Use - Specification and Test Methods
GB/T 6730.1 Iron Ores - Preparation of Predried Test Samples for Chemical Analysis
GB/T 8170 Rules of Rounding off for Numerical Values and Expression and Judgement of
Limiting Values
GB/T 10322.1 Iron Ores - Sampling and Sample Preparation Procedures
GB/T 12806 Laboratory Glassware - One-mark Volumetric Flasks
GB/T 12807 Laboratory Glassware - Graduated Pipettes
GB/T 12808 Laboratory Glassware - One Mark Pipettes
3 Principle
Use sodium carbonate-boric acid mixed flux to melt the specimen, use dilute sulfuric acid to
leach it, under acidic conditions, silicic acid and ammonium molybdate form yellow
molybdenum silicon heteropoly acid, then, add oxalic acid to eliminate the interference of
phosphorus and arsenic, and use ferrous ammonium sulfate to reduce silicon molybdenum
heteropoly to silicon molybdenum blue. At a wavelength of 760 nm, measure the absorbance,
thereby, determining the silicon content.
4 Reagents
Unless it is otherwise specified, only use the recognized reagents of analytical purity and
distilled water complying with the stipulations of GB/T 6682, or water of equivalent purity in
the analysis.
4.1 Mixed flux, take 3 portions of anhydrous sodium carbonate and 1 portion of boric acid,
evenly grind and mix them.
4.2 Sulfuric acid: ρ = 1.89 g/mL.
4.3 Sulfuric acid: 5 + 95.
4.4 Oxalic acid solution, 50 g/L.
4.5 Ammonium ferrous sulfate solution, 30 g/L.
Weigh-take 3 g of ferrous ammonium sulfate [(NH4)2Fe(SO4)2  6H2O], add 1 mL of sulfuric
acid (1 + 1), use water to dilute to 100 mL; dissolve and filter for use. It shall remain valid for
1 week.
4.6 Ammonium molybdate solution, 50 g/L. Store it in a plastic bottle.
4.7 Silicon standard solution.
4.7.1 Silicon stock solution, 200.0 g/mL.
Weigh-take 0.2140 g of silicon dioxide (above 99.9%) that has been burned to a constant mass
at 1,000 C, place it in a platinum crucible containing 4 g of mixed flux (4.1), carefully and mix
it well, then, use 1 g of mixed flux (4.1) to cover it. Cover the platinum cover, melt and
decompose it at 900 C ~ 950 C for 30 min, take it out, slowly turn it to make the molten liquid
evenly distributed on the inner wall of the crucible and cool it down. Put the crucible and the
cover into a polytetrafluoroethylene beaker filled with water, at a low temperature, heat and
leach it, then, wash the crucible and the cover. Cool it to room temperature, transfer the leaching
solution into a 500 mL volumetric flask; use water to dilute to the mark, mix it well, then,
immediately transfer it to a plastic bottle for storage.
7.2 Amount of Specimen
Weigh-take 0.20 g of specimen, accurate to 0.0001 g.
7.3 Blank Test and Verification Test
7.3.1 Blank Test
Weigh-take the same amount of high-purity ferric oxide (iron content greater than 99.98%) as
the specimen; along with the specimen, conduct a blank test.
7.3.2 Verification test
Along with the specimen, analyze the same type of reference sample.
7.4 Determination
7.4.1 Specimen decomposition
Place the specimen in a platinum crucible containing 4 g of mixed flux (4.1), carefully and mix
it well, then, use 1 g of mixed flux (4.1) to cover it. Cover the platinum cover, melt and
decompose it at 900 C ~ 950 C for 15 min ~ 30 min, take out the crucible, slowly turn it to
make the molten liquid evenly distributed on the inner wall of the crucible and cool it down.
Put the cooled crucible in a beaker filled with 200 mL of sulfuric acid (4.3), at a low temperature,
heat and leach it, then, wash the platinum crucible and the cover, and cool to room temperature.
Transfer the leaching solution into a 250 mL volumetric flask, use water to dilute to the mark,
mix it well and reserve it for later use. If there is precipitation, adopt the dry filtration method
to filter it.
7.4.2 Color development
Respectively take two portions of 5.00 mL (when the silicon content is less than 1%,
respectively take 10.00 mL) of the solution (7.4.1) in 100 mL volumetric flasks. One is used as
a color developing solution, and the other is used as a reference solution.
a) Color developing solution
Take one portion of the test solution, add 5 mL of ammonium molybdate solution
(4.6), add 30 mL of water to mix it well, and let it stand for 15 min (when the room
temperature is lower than 15 C, let it stand for 40 min or heat it in a boiling water
bath for 30 s, then, immediately cool it). Add 10 mL of oxalic acid solution (4.4) and
mix it well; within 30 s after the solution becomes clear, add 10 mL of ammonium
ferrous sulfate solution (4.5), use water to dilute to the mark and mix it well.
b) Reference solution
Take the other portion of the test solution, add 10 mL of oxalic acid solution (4.4), 5
mL of ammonium molybdate solution (4.6) and 10 mL of ammonium ferrous sulfate
solution (4.5); use water to dilute to the mark and mix it well.
7.4.3 Absorbance measurement
At a wavelength of 760 nm of the spectrophotometer, use an appropriate cuvette to measure the
absorbance, subtract the absorbance of the blank test solution, and find out the content of silicon
in the test solution on the calibration curve. For specimens with a silicon content lower than
0.5%, the absorbance may be measured at a wavelength of 810 nm.
7.4.4 Preparation of calibration cu...