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GB/T 6730.8-2016 English PDF (GBT6730.8-2016)

GB/T 6730.8-2016 English PDF (GBT6730.8-2016)

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GB/T 6730.8-2016: Iron ores -- Determination of iron (???) content -- Potassium dichromate titrimetric method

This Part of GB/T 6730 specifies the determination of iron (II) content by potassium dichromate titrimetric method. This Part applies to the determination of iron (II) content in iron ores, iron concentrates, sinters, and pellets. Determination range (mass fraction): 0.700%~30.00%.
GB/T 6730.8-2016
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 73.060.10
D 31
Replacing GB/T 6730.8-1986
Iron ores - Determination of iron (II) content -
Potassium dichromate titrimetric method
ISSUED ON: OCTOBER 13, 2016
IMPLEMENTED ON: SEPTEMBER 01, 2017
Issued by: General Administration of Quality Supervision, Inspection and Quarantine of the PRC;
Standardization Administration of the PRC.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Principle ... 6
4 Reagents and materials ... 6
5 Apparatus ... 7
6 Sampling and sample preparation ... 7
7 Analytical procedures ... 8
8 Analysis results and their representation ... 10
9 Test report ... 12
Appendix A (Normative) Flow chart for acceptance procedure of sample
analysis value ... 13
Appendix B (Informative) Additional information on joint precision test ... 14 Appendix C (Informative) Graphical representation of precision result ... 15 Iron ores - Determination of iron (II) content -
Potassium dichromate titrimetric method
WARNING: The personnel using this Part shall have practical experience
in regular laboratory work. This Part does not point out all possible safety problems. It is the responsibility of the user to take appropriate safety and health measures and to ensure compliance with the conditions stipulated by relevant national regulations.
1 Scope
This Part of GB/T 6730 specifies the determination of iron (II) content by potassium dichromate titrimetric method.
This Part applies to the determination of iron (II) content in iron ores, iron concentrates, sinters, and pellets. Determination range (mass fraction): 0.700%~30.00%.
2 Normative references
The following documents are indispensable for the application of this document. For the dated references, only the editions with the dates indicated are applicable to this document. For the undated references, the latest edition (including all the amendments) are applicable to this document.
GB/T 6379.1 Accuracy (trueness and precision) of measurement methods
and results - Part 1: General principles and definitions
GB/T 6379.2 Accuracy (trueness and precision) of measurement methods
and results - Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method
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
POUR 400 mL of phosphoric acid (??=1.70 g/mL), while stirring, into 400 mL of water; then slowly add 200 mL of sulfuric acid (??=1.84 g/mL) and mix well. 4.8 Ferric trichloride solution, 30 g/L.
WEIGH 30.0 g of ferric trichloride (FeCl3 ?€? 6H2O); dissolve it in 1000 mL of water and mix well. If the solution is turbid, it shall be used after filtering. 4.9 Potassium dichromate standard titration solution c(1/6K2Cr2O7)=0.03000 mol/L.
WEIGH 1.4709 g of potassium dichromate (reference reagent) which is pre- dried at 150 ??C for 1 h and cooled to room temperature; dissolve it in water; TRANSFER to a 1000 mL volumetric flask; USE water to dilute to the mark and mix well.
4.10 Ammonium ferrous sulfate solution, about 0.03 mol/L.
WEIGH 11.8 g of ammonium ferrous sulfate [(NH4)2Fe(SO4)2 ?€? 6H2O] dissolved in a certain volume of sulfuric acid (5+95); TRANSFER to a 1000 mL volumetric flask; USE sulfuric acid (5+95) to dilute to the mark and mix well.
4.11 Sodium diphenylamine sulfonate indicator solution, 2 g/L.
WEIGH 0.1 g of sodium diphenylamine sulfonate; dissolve it in 50 mL of water; ADD 2 drops~3 drops of concentrated sulfuric acid (??=1.84 g/mL); USE it after the solution is clear.
5 Apparatus
In the analysis, only ordinary experimental apparatus are used. The burette, one-mark volumetric flask, and one-mark pipette used shall meet the
requirements of GB/T 12805, GB/T 12806, and GB/T 12808, respectively.
5.1 Non-magnetic metal iron core stir bar.
5.2 Adjustable-speed magnetic stirrer.
6 Sampling and sample preparation
6.1 Laboratory sample
Laboratory samples for analysis shall be sampled and prepared in accordance with GB/T 10322.1. The particle size shall be less than 100 ??m. If the sample contains high levels of combined water or readily oxidizable substance, its sodium fluoride (see 4.1), 60 mL of hydrochloric acid (see 4.5), and 0.5 g~1 g of sodium bicarbonate (see 4.2). Quickly use a rubber stopper with a catheter to cover the bottle mouth; HEAT to boiling and maintain a slight boiling for 20 min~40 min, so that the solution volume is evaporated to 20 mL~30 mL.
REMOVE and quickly insert one end of the catheter into a saturated sodium bicarbonate solution (see 4.6); then use running water to cool the conical flask to room temperature. ADD 25 mL of mixture of sulfuric phosphoric acid (see 4.7); ADD water to a volume of about 100 mL; ADD 5 drops of sodium
diphenylamine sulfonate indicator solution (see 4.11); USE potassium
dichromate standard titration solution (see 4.9) to titrate to a stable purple; RECORD the titrimetric volume V3.
7.5.2 Determination of test portion containing metallic iron
The test portion contains metallic iron. ADD 30 mL of ferric trichloride solution (see 4.8); PUT a non-magnetic metallic iron core stir bar (see 5.1) in; COVER the porcelain crucible lid. STIR on a magnetic stirrer (see 5.2) at a speed of 200 r/min for 20 min; WASH out the stir bar; ADD about 0.5 g of sodium fluoride (see 4.1), 30 mL of hydrochloric acid (see 4.3); then, follow the same steps as 7.5.1.
7.5.3 Determination of test portion containing high-valent manganese and no metallic iron
The test portion contains high-valent manganese and does not contain metallic iron. ADD 30 mL of sulfurous acid (see 4.4); PUT a non-magnetic metallic iron core stir bar (see 5.1) in; COVER the porcelain crucible lid. STIR on a magnetic stirrer (see 5.2) at a speed of 200 r/min for 15 min; WASH out the stir bar; ADD about 0.5 g of sodium fluoride (see 4.1), 30 mL of hydrochloric acid (see 4.3); then, follow the same steps as 7.5.1.
7.5.4 Determination of blank value
ADD 6.00 mL of ammonium ferrous sulfate solution (see 4.10) and 25 mL of mixture of sulfuric phosphoric acid (see 4.7) to the blank solution; ADD water to a volume of about 100 mL. ADD 5 drops of sodium diphenylamine sulfonate indicator solution (see 4.11); USE potassium dichromate standard titration solution (see 4.9) to titrate to a stable purple; RECORD the volume V1 of the potassium dichromate standard titration solution consumed. Then add 6.00 mL of ammonium ferrous sulfate solution (see 4.10) to the solution; USE potassium dichromate standard titration solution (see 4.9) to titrate to a stable purple. RECORD the titrimetric volume V2. V0=V1-V2, i.e. the blank value.
8.2.2 Determination of analysis results
According to the procedure in Appendix A, according to formula (1), calculate the independent repeated measurement results. Compare with the repeatability limit r, to determine the analysis results.
8.2.3 Interlaboratory precision
Interlaboratory precision is used to evaluate the consistency between the final results reported by two laboratories. After the two laboratories report the results in accordance with the procedures specified in 8.2.2 respectively, calculate according to formula (2):
Where:
??1 - The final result reported by laboratory 1;
??2 - The final result reported by laboratory 2;
??12 - The average of the final results.
If |??1-??2|???R, the final results are consistent.
8.2.4 Acceptance of analysis values
The acceptance of analysis values is verified using a certified reference material (CRM) or reference material (RM). The final laboratory result is compared with the CRM or RM standard value AC. Two possibilities will appear: a) |??C-AC|???0.7R, in which case there is no significant difference between the reported result and the standard value;
b) |??C-AC|>0.7R, in which case there is significant difference between the reported result and the standard value.
Where:
??C - Measured value of CRM or RM;
AC - Standard value of CRM or RM.
8.2.5 Calculation of final result
The final result is the arithmetic mean of the acceptable values of the sample, or the value measured according to the operation specified in Appendix A. The

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