GB/T 6730.5-2022 PDF in English
GB/T 6730.5-2022 (GB/T6730.5-2022, GBT 6730.5-2022, GBT6730.5-2022)
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Iron ores -- Determination of total iron content -- Titrimetric methods after titanium(III) chloride reduction
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Standards related to: GB/T 6730.5-2022
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GB/T 6730.5-2022: PDF in English (GBT 6730.5-2022) GB/T 6730.5-2022
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 73.060.10
CCS D 31
Replacing GB/T 6730.5-2007
Iron Ores - Determination of Total Iron Content -
Titrimetric Methods after Titanium (III) Chloride
Reduction
[ISO 2597-2:2019, Iron Ores - Determination of Total Iron Content - Part 2:
Titrimetric Methods after Titanium (III) Chloride Reduction, MOD]
ISSUED ON: APRIL 15, 2022
IMPLEMENTED ON: NOVEMBER 1, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 3
Introduction ... 5
1 Scope ... 6
2 Normative References ... 6
3 Terms and Definitions ... 7
4 Principle ... 7
5 Reagents ... 7
6 Instruments ... 9
7 Specimen Collection and Preparation ... 10
8 Analytical Procedures ... 11
9 Result Calculation and Expression... 14
10 Test Report ... 16
Appendix A (informative) Constituent Documents of GB/T 6730 ... 18
Appendix B (normative) Acceptance Procedure of Specimen Analysis Results ... 23
Iron Ores - Determination of Total Iron Content -
Titrimetric Methods after Titanium (III) Chloride
Reduction
WARNING: personnel adopting this document shall have practical experience with
formal laboratory work. This document does not point out all possible security issues. It
is the user’s responsibility to take appropriate safety and health measures, and to ensure
the compliance with the conditions stipulated by relevant national regulations.
1 Scope
This document specifies the method for the determination of total iron content by potassium
dichromate titration method after reduction of iron with titanium trichloride.
This document is applicable to the determination of total iron content in natural iron ores, iron
ore concentrates and agglomerates, including sintered products, and the determination range
(mass fraction) is: 30.00% ~ 72.00%.
2 Normative References
The contents of the following documents constitute indispensable clauses of this document
through the normative references in this text. 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 601 Chemical Reagent - Preparations of Reference Titration Solutions
GB/T 6682 Water for Analytical Laboratory Use - Specification and Test Methods (GB/T 6682-
2008, ISO 3696:1987, MOD)
GB/T 6730.1 Iron Ores - Preparation of Predried Test Samples for Chemical Analysis (GB/T
6730.1-2016, ISO 7764:2006, MOD)
GB/T 6730.3 Iron Ores - Determination of Hydroscopic Moisture in Analytical Samples -
Gravimetric, Karl Fischer and Mass-loss Methods (GB/T 6730.3-2017, ISO 2596:2006, MOD)
GB/T 8170 Rules of Rounding off for Numerical Values & Expression and Judgement of
Limiting Values
GB/T 10322.1 Iron Ores - Sampling and Sample Preparation Procedures (GB/T 10322.1-2014,
ISO 3082:2009, IDT)
GB/T 12805 Laboratory Glassware - Burettes (GB/T 12805-2011, ISO 385:2005, NEQ)
GB/T 12806 Laboratory Glassware - One-mark Volumetric Flasks (GB/T 12806-2011, ISO
1042:1998, NEQ)
GB/T 12808 Laboratory Glassware - One-mark Pipettes
3 Terms and Definitions
This document does not have terms or definitions that need to be defined.
4 Principle
4.1 Decomposition of Specimen
4.1.1 Acid decomposition
For specimen containing no more than 0.05% vanadium, use hydrochloric acid to dissolve the
specimen; after filtering and burning the residue, use hydrofluoric acid and sulfuric acid to treat
the specimen; use potassium pyrosulfate to melt it; leach the melt and combine it with the main
liquid; use potassium permanganate solution for oxidation.
4.1.2 Melting-filtration
For specimen containing over 0.05% vanadium, use alkali to melt it; use water to leach the
cooled melt and filter it; after using sodium hydroxide solution to rinse the precipitate, use
hydrochloric acid to dissolve the precipitate.
4.2 Titration
Most of the iron is reduced by stannous chloride, and the remaining iron is reduced by titanium
trichloride. Use dilute potassium dichromate solution to oxidize the excess reducing agent. Take
sodium diphenylamine sulfonate as the indicating agent and use potassium dichromate solution
to titrate the reduced iron.
5 Reagents
Unless it is otherwise specified in the analysis, only approved analytically pure reagents, and
distilled water that complies with the stipulations of GB/T 6682, or water of equivalent purity
can be used.
5.1 Potassium pyrosulfate, fine powder.
5.2 Sodium carbonate, anhydrous or pre-burned at 500 C.
5.3 Sodium peroxide (Na2O2), dry powder. Sodium peroxide shall be stored as dry as possible
dissolved. After cooling, slowly add 5 mL of hydrogen peroxide solution (5.15); heat it to
boiling, and boil until excess hydrogen peroxide decomposes, then, remove chlorine. After
cooling to room temperature, transfer it into a 1,000 mL volumetric flask; use water to dilute to
the scale; mix it up.
1.00 mL of this solution is equivalent to 1.00 mL of potassium dichromate standard solution
(5.21).
5.21 Potassium dichromate standard solution, 0.01667 mol/L.
Weigh-take 4.904 g of potassium dichromate (standard reagent) that has been pre-dried at 140
C ~ 150 C for 2h and cooled to room temperature in a desiccator into a 300 mL beaker. Add
100 mL of water to dissolve it, transfer it to a 1,000 mL volumetric flask; cool it to 20 C, then,
use water to dilute to the scale; mix it up.
The used volumetric flask shall comply with the requirements of Level-A volumetric flasks in
GB/T 12806. If necessary, the volumetric flask shall be calibrated in advance. For each
application, the actual temperature shall be measured, and the volume of the used solution shall
be corrected. Mark the temperature, at which, the solution was diluted (20 C) on the storage
bottle.
The water used to prepare the standard solution shall be subjected to the temperature and
humidity balance treatment at room temperature in advance. Immerse the calibrated mercury
thermometer with a division value of 0.1 C in the pipetted standard solution; after over 60 s,
read the temperature, accurate to 0.1 C.
5.22 Sodium tungstate solution, 250 g/L.
Weigh-take 25 g of sodium tungstate and dissolve it in an appropriate amount of water (if it is
turbid, filter it). Add 5 mL of phosphoric acid (5.11) and use water to dilute to 100 mL.
5.23 Sodium diphenylamine sulfonate indicating agent, 2 g/L.
Dissolve 0.2 g of sodium diphenylamine sulfonate (C6H5NHC6H4SO3Na) in a small amount of
water, then, dilute it to 100 mL. Store this solution in a brown glass bottle.
5.24 Ammonia water, is about 0.90 g/mL.
5.25 Ammonia water, 5 + 95.
6 Instruments
Unless it is otherwise specified, the used one-mark volumetric flasks and one-mark pipettes
shall comply with the stipulations of GB/T 12806 and GB/T 12808.
6.1 Corundum crucible, with a capacity of 25 mL ~ 30 mL.
6.2 Burette, Grade-A, comply with the stipulations of GB/T 12805.
6.3 Platinum crucible, with a capacity of 25 mL ~ 30 mL, with a lid.
6.4 Weighing spoon, made of non-magnetic material or demagnetized stainless steel.
6.5 High-temperature furnace, with a temperature preferably controlled within the range of 500
C ~ 800 C.
6.6 Balance, with a division value of 0.0001 g.
7 Specimen Collection and Preparation
7.1 Laboratory Specimen
In accordance with GB/T 10322.1, carry out specimen collection and preparation. Generally
speaking, the particle size of the specimen shall be less than 100 m. If the content of
chemically combined water or readily oxidizable substance in the specimen is high, the particle
size shall be less than 160 m.
NOTE 1: the stipulation of high content of chemically combined water and readily oxidizable
substance is shown in GB/T 6730.1.
NOTE 2: if the determination of total iron content involves reducibility test, the specimens reserved
for chemical analysis in the whole reducibility test shall be crushed and ground to be less
than 100 m to prepare laboratory specimens.
7.2 Specimen Preparation
7.2.1 Ores with high content of chemically combined water or readily oxidizable substance
For the following types of ores, in accordance with GB/T 6730.3, prepare air balance specimens:
a) processed ores containing metallic iron;
b) natural or processed ores containing more than 0.2% sulfur;
c) natural or processed ores containing more than 2.5% chemically combined water.
7.2.2 Ores beyond the scope of 7.2.1
Thoroughly mix the laboratory specimens; adopt the fraction method to perform sampling. In
accordance with the stipulations of GB/T 6730.1, dry the specimens at a temperature of 105 C
2 C.
Use water jetting to rinse the watch glass; use warm water to dilute it to 50 mL. Use medium-
speed filter paper to filter the insoluble residue. Use a wipe stick to clean the wall of the beaker;
use warm hydrochloric acid (5.7) to wash the beaker for 3 times. Use warm hydrochloric acid
(5.7) to rinse the residue, until the yellow ferric chloride is no longer visible. Then, use warm
water to rinse for 6 ~ 8 times. Collect the filtrate and cleansing solution in a 400 mL beaker.
Put the filter paper and residue into a platinum crucible (6.3); dry it and ash the filter paper.
Finally, burn it at 750 C ~ 800 C. Cool the crucible; add 4 drops of sulfuric acid (5.10) to wet
the residue. Add about 5 mL of hydrofluoric acid (5.8) and slowly heat it, so as to remove silicon
dioxide and sulfuric acid (until the white smoke of sulfur trioxide is exhausted). Add 2 g of
potassium pyrosulfate (5.1) to the cooled crucible and cover the crucible; firstly, slowly heat it,
then, heat it at a high temperature, until the melt becomes clear (melt at 650 C for about 5 min).
Cool it, put the crucible and the crucible lid into the original 250 mL beaker; add about 25 mL
of water and about 5 mL of hydrochloric acid (5.4); warm to dissolve the melt. Wash the crucible
and the crucible lid; combine this solution with the main solution.
Add 5 drops of potassium permanganate solution (5.16); heat the solution below the boiling
point. At this temperature, maintain for 5 min; oxidize the organics and arsenic. Without boiling,
continue to evaporate to about 150 mL. In accordance with the steps specified in 8.5.2, continue
the operation.
8.5.1.2 Melting-filtration (for specimens containing over 0.05% vanadium or cannot be
decomposed by acid)
Put the specimen (8.2) into a corundum crucible (6.1); add 1.3 g of sodium carbonate (5.2) and
2.7 g of sodium peroxide (5.3); mix them up. In addition, use a small amount of sodium
peroxide (5.3) to cover the surface; place it in a high-temperature furnace (6.5); gradually heat
it from low temperature to 700 C ~ 750 C, then, melt it for 5 min ~ 10 min, until it becomes
clear.
After cooling, put the crucible into a 400 mL beaker, add about 100 mL of warm water; heat it
for a few minutes, then, leach the melt. Rinse the crucible and add the cleansing solution to the
solution; keep the crucible, cool the solution and use medium-speed filter paper to filter it. Use
sodium hydroxide solution (5.13) to wash the filter paper twice, then, discard the filtrate.
Adopt water jetting to wash the precipitate on the filter paper into the original beaker; add 10
mL of hydrochloric acid (5.4); heat it to dissolve the precipitate. Use the original filter paper to
filter the solution. Use warm hydrochloric acid (5.6) to wash the filter paper for 3 times; use
warm hydrochloric acid (5.7) to rinse it for several times; finally, use warm water to wash it,
until the cleansing solution is acid-free. Collect the filtrate and cleansing solution in a 400 mL
beaker (this is the main solution). In the reserved crucible, use hot hydrochloric acid (5.5) to
dissolve the residual iron and use hot water to wash it into the main solution. Without boiling,
evaporate it to about 150 mL. In accordance with the steps specified in 8.5.2, continue the
operation.
8.5.2 Reduction
8.5.2.1 When the copper content in the specimen is not greater than 0.1%, maintain the solution
obtained in accordance with 8.5.1 at 90 C ~ 95 C, and use a small amount of hot water to
wash the watch glass and the inner wall of the beaker. Immediately dropwise add stannous
chloride solution (5.18) and reduced iron (III); stir the solution in the beaker from time to time,
until the solution remains pale yellow (ferric chloride).
It must be ensured that a small part of iron (III) is not reduced. If the solution becomes colorless
due to the addition of excess stannous chloride solution (5.18), then, hydrogen peroxide (5.15)
or potassium permanganate solution (5.16) must be dropwise added, until the solution becomes
pale yellow.
Use a small amount of hot water to wash the inner wall of the beaker; add 15 drops of sodium
tungstate solution (5.22) as an indicating agent, then, dropwise add titanium trichloride solution
(5.19), and keep stirring the solution, until it turns blue. Put it in a cold-water bath to cool for a
few minutes, then, dropwise add dilute potassium dichromate solution (5.17) to oxidize the
excess titanium trichloride, until the solution is stably colorless (maintain for 5 s).
8.5.2.2 When the copper content in the specimen is greater than 0.1%, add 5 mL of hydrogen
peroxide (5.14) to the test solution. Without boiling, heat the solution; at this temperature,
maintain for 5 min. Use ammonia water (5.24) to neutralize it, until precipitate is generated;
add an excess of 10 mL, boil it; wait till the precipitate drops, then, use fast filter paper to filter
it; use ammonia water (5.25) to rinse the precipitate for 8 ~ 9 times. Use 20 mL of hydrochloric
acid (5.5) to dissolve the precipitate in a 400 mL beaker; use hot hydrochloric acid (5.7) to wash
it, until the filter paper is colorless. Add water to the filtrate to a volume of about 150 mL, then,
boil it to near boiling. The following shall comply with 8.5.2.1; dropwise add stannous chloride
solution (5.18) to perform reduction.
8.5.3 Titration
Immediately add 30 mL of sulfur-phosphorus mixed acid (5.12) to the solution obtained in 8.5.2;
add 5 drops of sodium diphenylamine sulfonate solution (5.23) as the indicating agent; use
potassium dichromate standard solution (5.21) to perform titration. When the solution turns
from green to blue-green, and to the last drop of titration, which makes it purple, it reaches the
end point.
Pay attention to the ambient temperature of the potassium dichromate standard solution. If it
differs by more than 1 C from the temperature during preparation (20 C), in accordance with
the stipulations of GB/T 601, appropriate volume correction shall be performed.
8.5.4 Determination of blank value
Use the same amount of all reagents and follow the same operation procedures as the specimen,
determine the blank test value (8.3.1). Before using stannous chloride solution (5.18) to perform
the reduction (8.5.2), immediately use a one-mark pipette to add 1.00 mL of iron standard
solution (5.20); titrate the solution as described in 8.5.3. Record this titration volume as (V0).
The blank test value (V2) of this titration shall be calculated in accordance with Formula (1):
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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