ASTM E246-21

Standard Test Methods for Determination of Iron in Iron Ores and Related Materials by Dichromate Titrimetry

SIGNIFICANCE AND USE
3.1 The determination of the total iron content is the primary means for establishing the commercial value of iron ores used in international trade.  
3.2 These test methods are intended as referee methods for the determination of iron in iron ores. It is assumed that all who use these test methods will be trained analysts capable of performing common laboratory procedures skillfully and safely. It is expected that work will be performed in a properly equipped laboratory and that proper waste disposal procedures will be followed. Appropriate quality control practices must be followed, such as those described in Guide E882.
SCOPE
1.1 These test methods cover the determination of total iron in iron ores, concentrates, and agglomerates in the concentration range 30 % to 95 % iron.  
1.2 The test methods in this standard are contained in the sections indicated as follows:    
Test Method A— Iron by the Hydrogen Sulfide Reduction Dichromate Titration Method (30 % to 75 % Fe)  
Test Method B—Iron by the Stannous Chloride Reduction Dichromate Titration Method (35 % to 95 % Fe)  
Test Method C—Iron by the Silver Reduction Dichromate Titration Method (35 % to 95 % Fe)  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific hazards statements are given in Section 5 and in special “Warning” paragraphs throughout these test methods.  
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Sep-2021
• ICS: 73.060.10 - Iron ores
• Technical Committee: E01 - Analytical Chemistry for Metals, Ores, and Related Materials
• Drafting Committee: E01.02 - Ores, Concentrates, and Related Metallurgical Materials

Relations

• Refers: ASTM E50-17 - Standard Practices for Apparatus, Reagents, and Safety Considerations for Chemical Analysis of Metals, Ores, and Related Materials
• Effective Date: 01-Sep-2017
• Refers: ASTM E882-10(2016)e1 - Standard Guide for Accountability and Quality Control in the Chemical Analysis Laboratory
• Effective Date: 01-Dec-2016
• Refers: ASTM E882-10(2016) - Standard Guide for Accountability and Quality Control in the Chemical Analysis Laboratory
• Effective Date: 01-Dec-2016
• Refers: ASTM E50-11(2016) - Standard Practices for Apparatus, Reagents, and Safety Considerations for Chemical Analysis of Metals, Ores, and Related Materials
• Effective Date: 01-Aug-2016
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2011
• Refers: ASTM E50-11 - Standard Practices for Apparatus, Reagents, and Safety Considerations for Chemical Analysis of Metals, Ores, and Related Materials
• Effective Date: 15-Oct-2011
• Refers: ASTM E882-10 - Standard Guide for Accountability and Quality Control in the Chemical Analysis Laboratory
• Effective Date: 01-Oct-2010
• Refers: ASTM E877-08 - Standard Practice for Sampling and Sample Preparation of Iron Ores and Related Materials for Determination of Chemical Composition
• Effective Date: 01-Nov-2008
• Refers: ASTM E29-08 - Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
• Effective Date: 01-Oct-2008
• Refers: ASTM E691-08 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Oct-2008
• Refers: ASTM E276-03(2008)e1 - Standard Test Method for Particle Size or Screen Analysis at No. 4 (4.75-mm) Sieve and Finer for Metal-Bearing Ores and Related Materials
• Effective Date: 01-Sep-2008
• Refers: ASTM E29-06b - Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
• Effective Date: 15-Nov-2006
• Refers: ASTM E29-06a - Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
• Effective Date: 15-Sep-2006
• Refers: ASTM E29-06 - Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
• Effective Date: 01-May-2006

Overview

ASTM E246-21 is the internationally recognized standard that provides referee test methods for the determination of total iron content in iron ores, concentrates, and agglomerates, using dichromate titrimetry. Developed by ASTM International, this standard is essential for the assessment of commercial value, quality control, and trade of iron ore materials. The methods outlined in ASTM E246-21 cover iron concentrations ranging from 30% to 95%, supporting a wide range of sample types commonly encountered in the iron and steel industry.

Key Topics

• Purpose and Significance

  • Establishes trusted methods for quantifying total iron, a critical metric for commercial evaluation and trading of iron ores internationally.
  • Serves as a referee method, intended to resolve disputes or validate results from other test procedures.
  • Emphasizes the need for trained analysts, proper laboratory setup, and robust quality control practices.

• Scope of Methods

  • Applicable to iron ores, concentrates, and agglomerates with iron content from 30% to 95%.
  • Describes all procedures and safety considerations in SI units to ensure consistency and compliance with international practice.

• Test Methods Included

  • Test Method A: Hydrogen Sulfide Reduction Dichromate Titration for samples with 30%-75% iron.
  • Test Method B: Stannous Chloride Reduction Dichromate Titration for higher-range samples (35%-95% iron).
  • Test Method C: Silver Reduction Dichromate Titration, also suitable for 35%-95% iron content.
  • Each method features detailed sample preparation, reagent specifications, interference management, and calculation guidelines.

• Quality and Safety

  • Strong focus on laboratory safety, chemical handling, and waste disposal.
  • Quality control practices in accordance with ASTM Guide E882.
  • Clear warnings for toxic and hazardous materials involved, such as hydrogen sulfide and sodium peroxide.

Applications

• Iron Ore Quality Assessment:
  Used by mining companies, exporters, and importers to determine iron content as a basis for pricing and contractual agreements in international trade.

• Metallurgical Laboratories:
  Reference procedures for quality control and research laboratories where accurate iron quantification is required.

• Material Certification:
  Supports the certification process of iron ore products by providing standardized, repeatable measurement methods.

• Regulatory and Compliance:
  Assists industry stakeholders in meeting regulatory, environmental, and trade compliance requirements related to iron content in ores and related materials.

• Dispute Resolution:
  As referee methods, these procedures offer a clear path for settling analytical disputes between parties.

Related Standards

To support comprehensive testing and compliance, ASTM E246-21 references several related ASTM standards:

• ASTM D1193: Specification for Reagent Water
• ASTM E29: Practice for Using Significant Digits in Test Data
• ASTM E50: Practices for Apparatus, Reagents, and Safety in Chemical Analysis of Metals, Ores, and Related Materials
• ASTM E276: Particle Size Analysis for Metal-Bearing Ores
• ASTM E691: Conducting Interlaboratory Studies for Test Method Precision
• ASTM E877: Sampling and Sample Preparation of Iron Ores
• ASTM E882: Guide for Accountability and Quality Control in the Chemical Analysis Laboratory

Practical Value

Implementing ASTM E246-21 ensures consistent, high-quality analysis of iron content in iron ores, supporting fair pricing, reliable quality control, and regulatory adherence. Its detailed methodologies and focus on safety and quality management make it a cornerstone for laboratories and organizations that need reliable iron determination in the global iron ore market.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E246 − 21
Standard Test Methods for
Determination of Iron in Iron Ores and Related Materials by
Dichromate Titrimetry
This standard is issued under the fixed designation E246; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E29Practice for Using Significant Digits in Test Data to
Determine Conformance with Specifications
1.1 These test methods cover the determination of total iron
E50Practices for Apparatus, Reagents, and Safety Consid-
in iron ores, concentrates, and agglomerates in the concentra-
erations for Chemical Analysis of Metals, Ores, and
tion range 30% to 95% iron.
Related Materials
1.2 The test methods in this standard are contained in the
E276TestMethodforParticleSizeorScreenAnalysisatNo.
sections indicated as follows:
4 (4.75-mm) Sieve and Finer for Metal-Bearing Ores and
Test Method A— Iron by the Hydrogen Sulfide Reduction Dichromate
Related Materials
Titration Method (30% to 75% Fe)
E691Practice for Conducting an Interlaboratory Study to
Test Method B—Iron by the Stannous Chloride Reduction Dichromate Determine the Precision of a Test Method
Titration Method (35% to 95% Fe)
E877Practice for Sampling and Sample Preparation of Iron
Ores and Related Materials for Determination of Chemi-
Test Method C—Iron by the Silver Reduction Dichromate Titration
Method (35% to 95% Fe)
cal Composition and Physical Properties
E882Guide for Accountability and Quality Control in the
1.3 The values stated in SI units are to be regarded as
Chemical Analysis Laboratory
standard. No other units of measurement are included in this
E1028Test Method for Total Iron in Iron Ores and Related
standard.
Materials by Dichromate Titrimetry (Withdrawn 2003)
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3. Significance and Use
responsibility of the user of this standard to establish appro-
3.1 The determination of the total iron content is the
priate safety, health, and environmental practices and deter-
primary means for establishing the commercial value of iron
mine the applicability of regulatory limitations prior to use.
ores used in international trade.
Specific hazards statements are given in Section 5 and in
special “Warning” paragraphs throughout these test methods.
3.2 These test methods are intended as referee methods for
1.5 This international standard was developed in accor- thedeterminationofironinironores.Itisassumedthatallwho
dance with internationally recognized principles on standard-
use these test methods will be trained analysts capable of
ization established in the Decision on Principles for the
performing common laboratory procedures skillfully and
Development of International Standards, Guides and Recom-
safely. It is expected that work will be performed in a properly
mendations issued by the World Trade Organization Technical
equipped laboratory and that proper waste disposal procedures
Barriers to Trade (TBT) Committee.
will be followed.Appropriate quality control practices must be
followed, such as those described in Guide E882.
2. Referenced Documents
2.1 ASTM Standards: 4. Apparatus, Reagents, and Instrumental Practices
D1193Specification for Reagent Water
4.1 Apparatus—Specialized apparatus requirements are
listed in the “Apparatus” Section in each test method.
These test methods are under the jurisdiction of ASTM Committee E01 on
4.2 Reagents:
Analytical Chemistry for Metals, Ores, and Related Materials and are the direct
responsibility of Subcommittee E01.02 on Ores, Concentrates, and Related Metal-
4.2.1 Purity of Reagents—Reagent grade chemicals shall be
lurgical Materials.
used in all tests. Unless otherwise indicated, it is intended that
Current edition approved Oct. 1, 2021. Published October 2021. Originally
all reagents conform to the specifications of the Committee on
approvedin1964.Lastpreviouseditionapprovedin2015asE246–10(2015).DOI:
10.1520/E0246-21. Analytical Reagents of theAmerican Chemical Society where
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
E246 − 21
such specifications are available. Other grades may be used, copper, and small amounts of molybdenum, which occasion-
provided it is first ascertained that the reagent is of sufficiently ally occur in iron ores.
high purity to permit its use without lessening the accuracy of
10. Apparatus
the determination.
10.1 Hydrogen Sulfide Generator—H S shall be obtained
4.2.2 Purity of Water—Unless otherwise indicated, refer-
from a cylinder of the compressed gas or from a Kipp
ences to water shall be understood to mean reagent water
generator.Aconsistentflowof1L⁄minshallbemaintainedand
conforming to Type I or Type II of Specification D1193. Type
the gas passed through a water trap to remove any salts.
IIIorTypeIVmaybeusediftheyeffectnomeasurablechange
10.1.1 Warning—H S is extremely toxic. All procedures
in the blank or sample.
involving its use must be performed in an efficient fume hood.
5. Hazards
Refer to Hazards section in Practices E50.
5.1 For precautions to be observed in the use of certain
10.2 Crucibles, platinum, 25-milliliter (mL) capacity.
reagents and equipment in this test method refer to Practices
11. Reagents and Materials
E50.
11.1 Ferrous Ammonium Sulfate Solution (approximately
6. Sampling and Sample Preparation
0.10 N)—Dissolve 40 g of ferrous ammonium sulfate
6.1 Collect and prepare the test sample in accordance with
(FeSO ·(NH ) SO ·6H O) in H SO (1+19). Transfer to a
4 4 2 4 2 2 4
Practice E877.
1-L flask and dilute to volume with the same acid. When the
sample solution is ready for titration, standardize the
6.2 The test sample shall be pulverized to pass a No.100
FeSO ·(NH ) SO ·6H O solution against the standard
(150-µm) sieve in accordance with Test Method E276.To
4 4 2 4 2
K Cr O (0.1000 N), as described in 12.5. Calculate the
facilitate decomposition some ores, such as specular hematite, 2 2 7
milliliters of standard K Cr O equivalent to 1mL of the
require grinding to pass a No.200 (75-µm) sieve.
2 2 7
FeSO ·(NH ) SO ·6H O solution.
4 4 2 4 2
TEST METHOD A—IRON BY THE HYDROGEN
11.2 Potassium Dichromate, Standard Solution (0.1000
SULFIDE REDUCTION DICHROMATE TITRATION
N)—Transfer 4.9031g of primary standard grade potassium
METHOD
dichromate (K Cr O ); previously ground in an agate mortar,
2 2 7
and dried at 105°C to 110°C, to a 1-L volumetric flask.
7. Scope
Dissolve in water and dilute to 1L. If preferred, this solution
7.1 This test method covers the determination of total iron
maybepreparedfromreagentgradeK Cr O ,bypurifyingthe
2 2 7
in iron ores, concentrates, and agglomerates in the range from
salt twice by recrystallizing from water, drying at 110°C,
30% to 75% by mass.
pulverizinginanagatemortar,anddryingat180°Ctoconstant
7.2 This international standard was developed in accor-
weight. The titer of this solution shall be confirmed by means
dance with internationally recognized principles on standard-
of standard sample similar in type and composition to the test
ization established in the Decision on Principles for the
sample.
Development of International Standards, Guides and Recom-
11.3 Potassium Permanganate Solution (25g⁄L)—Dissolve
mendations issued by the World Trade Organization Technical
25g of potassium permanganate (KMnO ) in water and dilute
Barriers to Trade (TBT) Committee.
to 1L.
8. Summary of Test Method
11.4 Sodium Diphenylamine Sulfonate Indicator Solution—
8.1 ThesampleisdissolvedinHCl.Theinsolubleresidueis Dissolve 0.3g of sodium diphenylamine sulfonate in 100mL
removed by filtration, ignited, treated for the recovery of iron, of water. Store in a dark-colored bottle.
and added to the main solution. To this solution containing all
11.5 Sodium Pyrosulfate (Na S O ).
2 2 7
of the iron, H SO is added and the solution evaporated to
2 4
11.6 Sulfuric Acid-Hydrogen Sulfide Wash Solution—Add
fumes to expel chlorides. The salts are dissolved in water, the
20mLof concentrated H SO (H SO , sp gr 1.84) to 900mL
2 4 2 4
solution heated to boiling, and the iron reduced by a rapid
water, cool, dilute to 1L, and pass a rapid stream of H S
stream of hydrogen sulfide (H S).The precipitated sulfides are
through it for at least 10min.
filtered and washed with an acid-sulfide wash solution until
freeofiron.ThefiltrateisthenboiledtoexpeltheH S,cooled,
2 12. Procedure
and titrated with K Cr O solution, using sodium diphenylam-
2 2 7
12.1 Transferapproximately0.50gofthetestspecimentoa
ine sulfonate as the indicator.
small weighing bottle previously dried at about 105°C. Dry
the bottle and contents for 1h at 105°C to 110°C (Note 1).
9. Interferences
Cap the bottle and cool to room temperature in a desiccator.
9.1 None of the elements normally found in iron ores
Momentarilyreleasethecaptoequalizethepressureandweigh
interfere with this test method. These include vanadium,
the capped bottle and sample to the nearest 0.1mg. Repeat the
drying and weighing until there is no further mass loss.
Reagent Chemicals, American Chemical Society Specifications, American
Transferthetestspecimentoa250-mLbeakerandreweighthe
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
cappedbottletothenearest0.1mg.Thedifferencebetweenthe
listed by theAmerican Chemical Society, see the United States Pharmacopeia and
National Formulary,U.S.PharmacopeialConvention,Inc.(USPC),Rockville,MD. two masses is the mass of the sample taken for analysis.
E246 − 21
NOTE 1—Most ores yield their hygroscopic moisture at this tempera-
5). Remove from the source of heat, cover the flask with a
ture.Ifadryingtemperatureotherthanthatspecifiedisrequired,thisshall
small watch glass, and cool in running water to 20°C.
be determined by mutual agreement between manufacturer and purchaser.
NOTE 4—If the sample contains much calcium, prolonged fuming with
12.2 Decomposition of the Sample—Moisten the sample
H SO may lead to the formation of salts that are difficult to dissolve.
2 4
with a few (mL) of water and add 25mL of HCl. Cover the
Therefore,inthepresenceofconsiderablecalcium,fumejustlongenough
beaker and heat, maintaining a temperature below boiling until
toexpelthechloridesandnitrates.Cool,washthesidesofthebeakerwith
water, and again evaporate to light fumes.
most of the dark particles are dissolved and no further attack is
NOTE5—Ifthesamplecontainsanappreciableamountofmolybdenum,
apparent. Add 5mL of HNO and digest for another 15min.
further precipitation may occur in the filtrate when boiling out the H S.
Remove from the source of heat, wash the sides and cover of
The effect of residual molybdenum is not significant and may be
the beaker, and dilute to 50mL with warm water. Filter the
neglected.
insolubleresidueonafine-texturepaper.Washtheresiduewith
12.4 Titration—Add to the cooled solution 5mL of phos-
warm HCl (1+50) until the yellow color of ferric chloride is
phoric acid (H PO ) and five drops of the sodium diphenylam-
3 4
nolongerobservedandthenwithwarmwatersixtimestoeight
ine sulfonate indicator solution. Dilute to 350mL and titrate
times.Collectthefiltrateandwashingsina600-mLbeakerand
with the standard K Cr O solution to a distinct purple
2 2 7
reserve as the main solution (Note 2). Place the paper and
endpoint.
residue in a platinum crucible. Char the paper at a low
TABLE 1 Precision Data
Repeatability Reproducibility
Number of Iron Found
Sample
R R
I 2
Laboratories %
s s
r R
(2.8 s) (2.8 s )
r R
Seine River Ore 9 57.52 0.125 0.35 0.126 0.35
Knob Lake Ore 9 58.45 0.097 0.27 0.136 0.38
NBS 27d (64.96% Fe) 6 65.01 0.057 0.16 0.085 0.24
Chilean Iron Ore 9 66.11 0.102 0.29 0.172 0.48
A
Pooled standard deviations 0.101 0.137
A
Weighted by degrees of freedom, n for s and (n−1)for s where n = number of laboratories.
r R
temperature, then ignite at 950°C.Allow the crucible to cool, 12.5 Determination of Blank—Determinetheblankvalueof
moisten the residue with H SO (1+1), add about 5mL of thereagentsconcurrentlywiththetestdetermination,usingthe
2 4
HF, and heat gently to remove silica and H SO (Note 3). same amount of all reagents and following all the steps of the
2 4
Cool the crucible, add 3g of Na S O , and heat until a clear procedure. Immediately before titrating with the K Cr O
2 2 7 2 2 7
melt is obtained. Cool, place the crucible in a 250-mL beaker, solution, add 1.0 mL, accurately measured, of the
add about 25mL of water and 5mL of HCl, and warm to FeSO ·(NH ) SO ·6H O solution. In another beaker place
4 4 2 4 2
dissolve the melt. Rinse and remove the crucible. Add the 350mLofcoldH SO (1+9)andaddanaccuratelymeasured
2 4
solution and washings to the main solution. 1mL of the FeSO ·(NH ) SO ·6H O solution. Add 5mL of
4 4 2 4 2
H PO and five drops of the sodium diphenylamine sulfonate
3 4
NOTE 2—If the residue is small in amount and perfectly white, the
indicator solution and titrate with the K Cr O solution.
2 2 7
filtration, and treatment of the residue may be omitted without causing
Recordthistitrationandsubtractfromthetitrationoftheblank
significant error.
solution to obtain the corrected blank.
NOTE 3—The treatment of the residue depends upon the nature of the
minerals present. Many ores require only an H SO −HF treatment to
2 4
NOTE 6—In the absence of iron, the diphenylamine sulfonate indicator
decompose the residue.
does not react with the K Cr O solution. The addition of the
2 2 7
12.3 Reduction—To the combined solution add 10mL of FeSO ·(NH ) SO ·6H O is, therefore, necessary to promote indicator
4 4 2 4 2
response in the blank solution.Acorrection must be made in terms of its
H SO (1+1) and evaporate to copious fumes of sulfur
2 4
equivalent in mL of K Cr O solution.
2 2 7
trioxide (SO)(Note 4). Cool, dilute to approximately 100mL
withwater,andheattoboiling.AdddropwiseKMnO solution
13. Calculation
until the permanganate color persists. Dilute the solution to
13.1 Calculate the percentage of iron as follows:
250mLand again heat to boiling for several minutes. Remove
fromthesourceofheatandpassarapidstreamofH Sthrough
iron, % 5 A 2 B 3 C/D 3100 (1)
2 @~ ! #
the solution for 15 min. (Warning—Hydrogen sulfide is
where:
extremely toxic. All procedures involving its use must be
A =mLofK Cr O required for titration of the sample,
performed in an efficient fume hood. Refer to Hazards section 2 2 7
B =mLofK Cr O required for titration of the blank,
inPracticesE50.)Digestat60°Cfor15minandfilterthrough 2 2 7
C = iron equivalent of the K Cr O , g/mL, and
2 2 7
a medium-texture paper, collecting the filtrate in a 500-mL
D = grams of sample used.
Erlenmeyer flask. Wash the precipitated sulfides thoroughly
with the H SO −H S wash solution. Add 10mL of H SO 13.2 Roundingoftestresultsobtainedusingthistestmethod
2 4 2 2 4
(1+1) to the solution in the flask and add glass beads to shall be performed as directed in Practice E29, Rounding
prevent bumping. Boil for 10min to expel H S (lead acetate Method, unless an alternative rounding method is specified by
test paper) and continue boiling for an additional 10min (Note the customer or applicable material specification.
E246 − 21
14. Precision and Bias containing molybdenum or vanadium, or both, these elements
are removed by water leach and filtration of the cooled sodium
14.1 Precision—From six to nine laboratories analyzed four
carbonate/sodium peroxide fusion melt. Other elements nor-
ironoresamplestodetermineiron.Thereplicationmadebythe
mally found in iron ores do not interfere.
different laboratories ranged from two to four, averaging three
replicates. The data was studied by the interlaboratory test
18. Apparatus
procedureofPracticeE691–87modifiedbyweightingcertain
sums to accommodate the unequal replication. Table 1 shows
18.1 Crucibles, platinum, 25-mL to 30-mL capacity.
a summary of these results. From pooled standard deviations,
18.2 Crucibles, zirconium, 25-mL to 30-mL capacity.
the overall between-laboratory reproducibility coefficient, R,
was calculated as being 0.38.
18.3 Weighing Spatula, of a nonmagnetic material or de-
magnetized stainless steel.
14.2 TheagreementofthedeterminationofironintheNBS
Standard Reference Material with the certified value shows no
19. Reagents
evidence of bias, well within a 95% confidence level:
(R = 0.24)
19.1 Iron (III) Ammonium Sulfate (approximately 0.1 N)—
Dissolve 40 g of iron (II) ammonium sulfate
TEST METHOD B—IRON BY THE STANNOUS
[FeSO ·(NH ) SO ·6H O] in H SO (1+19). Transfer to a
4 4 2 4 2 2 4
CHLORIDE REDUCTION DICHROMATE
1-Lvolumetric flask, dilute to volume with the same acid, and
TITRATION METHOD
mix. Standardize against standard K Cr O solution using
2 2 7
15. Scope diphenylamine sulfonate as indicator.
15.1 This test method covers the determination of total iron
19.2 Potassium Dichromate, Standard Solution (0.1 N)—
in iron ores, concentrates, and agglomerates in the range from
Pulverizeabout6gofK Cr O reagentinanagatemortar,dry
2 2 7
35% to 95% by mass.
in an air-bath at 140°C for 3h to 4h, and cool to room
temperature in a desiccator. Dissolve 4.9031g of the dry
15.2 This international standard was developed in accor-
reagent in water and dilute the solution with water to exactly
dance with internationally recognized principles on standard-
1Lin a volumetric flask. Record the temperature at which this
ization established in the Decision on Principles for the
dilution was made.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
19.3 Potassium Permanganate Solution (KMnO ), 25g⁄L.
Barriers to Trade (TBT) Committee.
19.4 Potassium Pyrosulfate Fine Powder (K S O ).
2 2 7
16. Summary of Test Method
19.5 Sodium Carbonate Anhydrous Powder (Na CO ).
2 3
16.1 This test method provides two alternative dissolution
19.6 Sodium Diphenylaminesulfonate Solution—Dissolve
procedures.
0.2g of the reagent (C H NC H ·SO Na) in water and dilute
6 5 6 4 3
16.2 Acid Decomposition—The sample is dissolved in HCl.
to 100mL. Store the solution in a brown glass bottle.
The insoluble residue is removed by filtration, ignited, treated
for the recovery of iron, and added to the main solution.
19.7 Sodium Hydroxide Solution (NaOH), 20g⁄L.
16.3 Decomposition by Fusion—The sample is fused with a
19.8 Sodium Peroxide (Na O ), dry powder. (Warning—
2 2
mixture of sodium carbonate and sodium peroxide (Na O ).
2 2 Use proper safety practices and equipment when performing
The melt is leached with water. For samples containing more
Na O fusions. )
2 2
than 0.1% of vanadium or molybdenum, or both, the solution
19.9 Sulfuric Acid-Phosphoric Acid Mixture—Pour 150mL
is filtered and the insoluble residue is dissolved in HCl. For
of H PO (6.12) into about 400mL of water. While stirring,
3 4
other samples the leachate is acidified with HCl.
add 150mL of H SO (6.20). Cool in a water bath and dilute
2 4
16.4 Reduction of the Iron—Mostoftheironisreducedwith
with water to 1L.
stannous chloride, followed by the addition of a slight excess
19.10 Tin (II) Chloride Solution (100 g ⁄L)—Dissolve 100g
of titanium (III) chloride solution. The excess titanium (III) is
of crystalline tin (II) chloride (SnCl ·2H O) in 200mLof HCl
then oxidized in the hot solution with HClO . The solution is
2 2
by heating the solution in a water bath. Cool the solution and
cooledandthereducedironistitratedwithastandardK Cr O
2 2 7
dilute the water to 1L. This solution should be stored in a
solution using sodium diphenylamine sulfonate as the visual
brown glass bottle with the addition of a small quantity of
endpoint indicator.
granular or mossy tin metal.
17. Interferences
19.11 Titanium (III) Chloride Solution (2 %)—Dissolve 1g
17.1 This test method covers the analysis of iron ores
oftitaniumsponge(99.5%minimumpurity)inabout30mLof
containing less than 0.1% copper. In the case of iron ores
HCl in a covered beaker by heating on a steam bath. Cool the
solution and dilute with water to 50mL. Prepare fresh as
Supporting data giving the results of cooperative testing have been filed at
needed. (If preferred, dilute one volume of commercial tita-
ASTM International Headquarters and may be obtained by requesting Research
nium (III) chloride solution (about 15% w/v) with seven
Report RR:E16-63, datedApril 23, 1968, with an amendment, dated July 27, 1993.
Contact ASTM Customer Service at [e-mail]. volumes of HCl (1+1).)
E246 − 21
20. Procedure place in a muffle furnace at 500°C 610°C for 30min.
NOTE 7—If the procedure is based on acid decomposition, use 20.1.If
Remove from the furnace and heat over a burner until melted.
the procedure is based on an alkaline fusion followed by the filtration of
Continue heating just above the melting point for approxi-
theleachedmelt,(samplescontainingmorethan0.1%bymassvanadium
mately 1.5min.Allow the melt to cool, place the crucible in a
or molybdenum, or both), use 20.2. If the procedure is based on an
400-mL beaker, add about 100mL of warm water, and heat to
alkaline fusion, followed by acidification of the leached melt (samples
leach the melt. Remove the crucible and wash. Reserve the
containing less than 0.1% of molybdenum or vanadium, or both), use
20.3.(Warning—Use proper safety practices and equipment when
crucible. Cool the solution and filter through a filter paper of
performing Na O fusions.)
2 2
dense texture. Wash the paper six times to eight times with
20.1 Acid Decomposition: NaOH solution (20g⁄L) and discard the filtrate and washings.
20.1.1 Weigh approximately 0.40g of sample into a small 20.2.2 Wash the precipitate into the original beaker with
weighingbottlepreviouslydriedatabout105°C(Note8).Dry water,add10mLofHCl,andwarmtodissolvetheprecipitate.
the bottle and contents for 1h at 105°C to 110°C. Cap the Dissolve the iron in the reserved crucible in hot HCl (1+1).
bottle and cool to room temperature in a desiccator. Momen- Wash the crucible with hot HCl (1+10) and add to the main
tarily release the cap to equalize the pressure and weigh the solution. Wash the filter paper three times with warm HCl
capped bottle and sample to the nearest 0.1mg. Repeat the (1+2),severaltimeswithwarmHCl(1+50),andfinallywith
drying and weighing until there is no further mass loss. warm water until the washings are no longer acid, adding the
Transfer the samples to a 250-mL beaker and reweigh the washings to the main solution. Evaporate with low heat to a
cappedbottletothenea
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E246 − 10 (Reapproved 2015) E246 − 21
Standard Test Methods for
Determination of Iron in Iron Ores and Related Materials by
Dichromate Titrimetry
This standard is issued under the fixed designation E246; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 These test methods cover the determination of total iron in iron ores, concentrates, and agglomerates in the concentration range
30 % to 95 % iron.
1.2 The test methods in this standard are contained in the sections indicated as follows:
Test Method A— Iron by the Hydrogen Sulfide Reduction Dichromate
Titration Method (30 % to 75 % Fe)
Test Method B—Iron by the Stannous Chloride Reduction Dichromate
Titration Method (35 % to 95 % Fe)
Test Method C—Iron by the Silver Reduction Dichromate Titration
Method (35 % to 95 % Fe)
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. Specific hazards statements are given in Section 5 and in special “Warning”
paragraphs throughout these test methods.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
E29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
E50 Practices for Apparatus, Reagents, and Safety Considerations for Chemical Analysis of Metals, Ores, and Related Materials
These test methods are under the jurisdiction of ASTM Committee E01 on Analytical Chemistry for Metals, Ores, and Related Materials and are the direct responsibility
of Subcommittee E01.02 on Ores, Concentrates, and Related Metallurgical Materials.
Current edition approved Aug. 15, 2015Oct. 1, 2021. Published August 2015October 2021. Originally approved in 1964. Last previous edition approved in 20102015 as
E246 – 10.E246 – 10(2015). DOI: 10.1520/E0246-10R15.10.1520/E0246-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E246 − 21
E276 Test Method for Particle Size or Screen Analysis at No. 4 (4.75-mm) Sieve and Finer for Metal-Bearing Ores and Related
Materials
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E877 Practice for Sampling and Sample Preparation of Iron Ores and Related Materials for Determination of Chemical
Composition and Physical Properties
E882 Guide for Accountability and Quality Control in the Chemical Analysis Laboratory
E1028 Test Method for Total Iron in Iron Ores and Related Materials by Dichromate Titrimetry (Withdrawn 2003)
3. Significance and Use
3.1 The determination of the total iron content is the primary means for establishing the commercial value of iron ores used in
international trade.
3.2 These test methods are intended as referee methods for the determination of iron in iron ores. It is assumed that all who use
these test methods will be trained analysts capable of performing common laboratory procedures skillfully and safely. It is expected
that work will be performed in a properly equipped laboratory and that proper waste disposal procedures will be followed.
Appropriate quality control practices must be followed, such as those described in Guide E882.
4. Apparatus, Reagents, and Instrumental Practices
4.1 Apparatus—Specialized apparatus requirements are listed in the “Apparatus” Section in each test method.
4.2 Reagents:
4.2.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, all reagents used in these
test methods shall it is intended that all reagents conform to the reagent grade specifications of the American Chemical
Society.Committee on Analytical Reagents of the American Chemical Society where such specifications are available. Other
grades may be used, provided it is first ascertained that they are of sufficient the reagent is of sufficiently high purity to permit
theirits use without adversely affecting the expected performance of the determination, as indicated in the “Precision and Bias”
Section. Reagent water shall conform to Type II as described in Specification lessening the accuracy of the determination. D1193.
4.2.2 Purity of Water—Unless otherwise indicated, references to water shall be understood to mean reagent water conforming to
Type I or Type II of Specification D1193. Type III or Type IV may be used if they effect no measurable change in the blank or
sample.
5. Hazards
5.1 For precautions to be observed in the use of certain reagents and equipment in this test method refer to Practices E50.
6. Sampling and Sample Preparation
6.1 Collect and prepare the test sample in accordance with Practice E877.
6.2 The test sample shall be pulverized to pass a No. 100 (150-μm) sieve in accordance with Test Method E276. To facilitate
decomposition some ores, such as specular hematite, require grinding to pass a No. 200 (75-μm) sieve.
TEST METHOD A—IRON BY THE HYDROGEN SULFIDE REDUCTION DICHROMATE TITRATION METHOD
7. Scope
7.1 This test method covers the determination of total iron in iron ores, concentrates, and agglomerates in the concentration range
from 30 % to 75 %.75 % by mass.
The last approved version of this historical standard is referenced on www.astm.org.
Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC, www.chemistry.org. DC. For suggestions on the testing
of reagents not listed by the American Chemical Society, see the United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC),
Rockville, MD, http://www.usp.org.MD.
E246 − 21
7.2 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
8. Summary of Test Method
8.1 The sample is dissolved in HCl. The insoluble residue is removed by filtration, ignited, treated for the recovery of iron, and
added to the main solution. To this solution containing all of the iron, H SO is added and the solution evaporated to fumes to expel
2 4
chlorides. The salts are dissolved in water, the solution heated to boiling, and the iron reduced by a rapid stream of hydrogen sulfide
(H S). The precipitated sulfides are filtered and washed with an acid-sulfide wash solution until free of iron. The filtrate is then
boiled to expel the H S, cooled, and titrated with K Cr O solution, using sodium diphenylamine sulfonate as the indicator.
2 2 2 7
9. Interferences
9.1 None of the elements normally found in iron ores interfere with this test method. These include vanadium, copper, and small
amounts of molybdenum, which occasionally occur in iron ores.
10. Apparatus
10.1 Hydrogen Sulfide Generator—H S shall be obtained from a cylinder of the compressed gas or from a Kipp generator. A
consistent flow of 1 L ⁄min shall be maintained and the gas passed through a water trap to remove any salts.
10.1.1 Warning—H S is extremely toxic. All procedures involving its use must be performed in an efficient fume hood. Refer
to Hazards section in Practices E50.
10.2 Crucibles, platinum, 25-mL 25-milliliter (mL) capacity.
11. Reagents and Materials
11.1 Ferrous Ammonium Sulfate Solution (approximately 0.10 N)—Dissolve 40 g of ferrous ammonium sulfate
(FeSO ·(NH ) SO ·6H O) in H SO (1 + 19). Transfer to a 1-L flask and dilute to volume with the same acid. When the sample
4 4 2 4 2 2 4
solution is ready for titration, standardize the FeSO ·(NH ) SO ·6H O solution against the standard K Cr O (0.1000 N), as
4 4 2 4 2 2 2 7
described in 12.5. Calculate the millilitresmilliliters of standard K Cr O equivalent to 1 mL of the FeSO ·(NH ) SO ·6H O
2 2 7 4 4 2 4 2
solution.
11.2 Potassium Dichromate, Standard Solution (0.1000 N)—Transfer 4.9031 g of primary standard grade potassium dichromate
(K Cr O ); previously ground in an agate mortar, and dried at 105 °C to 110 °C, to a 1-L volumetric flask. Dissolve in water and
2 2 7
dilute to 1 L. If preferred, this solution may be prepared from reagent grade K Cr O , by purifying the salt twice by recrystallizing
2 2 7
from water, drying at 110 °C, pulverizing in an agate mortar, and drying at 180 °C to constant weight. The titer of this solution
shall be confirmed by means of standard sample similar in type and composition to the test sample.
11.3 Potassium Permanganate Solution (25 g ⁄L)—Dissolve 25 g of potassium permanganate (KMnO ) in water and dilute to 1 L.
11.4 Sodium Diphenylamine Sulfonate Indicator Solution—Dissolve 0.3 g of sodium diphenylamine sulfonate in 100 mL of water.
Store in a dark-colored bottle.
11.5 Sodium Pyrosulfate (Na S O ).
2 2 7
11.6 Sulfuric Acid-Hydrogen Sulfide Wash Solution—Add 20 mL of concentrated H SO (H SO , sp gr 1.84) to 900 mL water,
2 4 2 4
cool, dilute to 1 L, and pass a rapid stream of H S through it for at least 10 min.
12. Procedure
12.1 Transfer approximately 0.50 g of the test specimen to a small weighing bottle previously dried at about 105 °C. Dry the bottle
and contents for 1 h at 105 °C to 110 °C (Note 1). Cap the bottle and cool to room temperature in a desiccator. Momentarily release
the cap to equalize the pressure and weigh the capped bottle and sample to the nearest 0.1 mg. Repeat the drying and weighing
E246 − 21
until there is no further weightmass loss. Transfer the test specimen to a 250-mL beaker and reweigh the capped bottle to the nearest
0.1 mg. The difference between the two weightsmasses is the weightmass of the sample taken for analysis.
NOTE 1—Most ores yield their hygroscopic moisture at this temperature. If a drying temperature other than that specified is required, this shall be
determined by mutual agreement between manufacturer and purchaser.
12.2 Decomposition of the Sample—Moisten the sample with a few millilitres(mL) of water and add 25 mL of HCl. Cover the
beaker and heat, maintaining a temperature below boiling until most of the dark particles are dissolved and no further attack is
apparent. Add 5 mL of HNO and digest for another 15 min. Remove from the source of heat, wash the sides and cover of the
beaker, and dilute to 50 mL with warm water. Filter the insoluble residue on a fine-texture paper. Wash the residue with warm HCl
(1 + 50) until the yellow color of ferric chloride is no longer observed and then with warm water six times to eight times. Collect
the filtrate and washings in a 600-mL beaker and reserve as the main solution (Note 2). Place the paper and residue in a platinum
crucible. Char the paper at a low temperature, then ignite at 950 °C. Allow the crucible to cool, moisten the residue with H SO
2 4
TABLE 1 Precision Data
Repeatability Reproducibility
Number of Iron Found
Sample
R R
I 2
Laboratories %
s s
R
r (2.8 s ) (2.8 s )
r R
Seine River Ore 9 57.52 0.125 0.35 0.126 0.35
Knob Lake Ore 9 58.45 0.097 0.27 0.136 0.38
NBS 27d (64.96 % Fe) 6 65.01 0.057 0.16 0.085 0.24
Chilean Iron Ore 9 66.11 0.102 0.29 0.172 0.48
A
Pooled standard deviations 0.101 0.137
A
Weighted by degrees of freedom, n for s and (n − 1) for s where n = number of laboratories.
r R
(1 + 1), add about 5 mL of HF, and heat gently to remove silica and H SO (Note 3). Cool the crucible, add 3 g of Na S O ,
2 4 2 2 7
and heat until a clear melt is obtained. Cool, place the crucible in a 250-mL beaker, add about 25 mL of water and 5 mL of HCl,
and warm to dissolve the melt. Rinse and remove the crucible. Add the solution and washings to the main solution.
NOTE 2—If the residue is small in amount and perfectly white, the filtration, and treatment of the residue may be omitted without causing significant error.
NOTE 3—The treatment of the residue depends upon the nature of the minerals present. Many ores require only an H SO −HF treatment to decompose
2 4
the residue.
12.3 Reduction—To the combined solution add 10 mL of H SO (1 + 1) and evaporate to copious fumes of sulfur trioxide (SO )
2 4 3
(Note 4). Cool, dilute to approximately 100 mL with water, and heat to boiling. Add dropwise KMnO solution until the
permanganate color persists. Dilute the solution to 250 mL and again heat to boiling for several minutes. Remove from the source
of heat and pass a rapid stream of H S through the solution for 15 min. (Warning—Hydrogen sulfide is extremely toxic. All
procedures involving its use must be performed in an efficient fume hood. Refer to Hazards section in Practices E50.) Digest at
60 °C for 15 min and filter through a medium-texture paper, collecting the filtrate in a 500-mL Erlenmeyer flask. Wash the
precipitated sulfides thoroughly with the H SO −H S wash solution. Add 10 mL of H SO (1 + 1) to the solution in the flask and
2 4 2 2 4
add glass beads to prevent bumping. Boil for 10 min to expel H S (lead acetate test paper) and continue boiling for an additional
10 min (Note 5). Remove from the source of heat, cover the flask with a small watch glass, and cool in running water to 20 °C.
NOTE 4—If the sample contains much calcium, prolonged fuming with H SO may lead to the formation of salts that are difficult to dissolve. Therefore,
2 4
in the presence of considerable calcium, fume just long enough to expel the chlorides and nitrates. Cool, wash the sides of the beaker with water, and
again evaporate to light fumes.
NOTE 5—If the sample contains an appreciable amount of molybdenum, further precipitation may occur in the filtrate when boiling out the H S. The effect
of residual molybdenum is not significant and may be neglected.
12.4 Titration—Add to the cooled solution 5 mL of phosphoric acid (H PO ) and five drops of the sodium diphenylamine
3 4
sulfonate indicator solution. Dilute to 350 mL and titrate with the standard K Cr O solution to a distinct purple endpoint.
2 2 7
12.5 Determination of Blank—Determine the blank value of the reagents concurrently with the test determination, using the same
amount of all reagents and following all the steps of the procedure. Immediately before titrating with the K Cr O solution, add
2 2 7
1.0 mL, accurately measured, of the FeSO ·(NH ) SO ·6H O solution. In another beaker place 350 mL of cold H SO (1 + 9) and
4 4 2 4 2 2 4
add an accurately measured 1 mL of the FeSO ·(NH ) SO ·6H O solution. Add 5 mL of H PO and five drops of the sodium
4 4 2 4 2 3 4
E246 − 21
diphenylamine sulfonate indicator solution and titrate with the K Cr O solution. Record this titration and subtract from the
2 2 7
titration of the blank solution to obtain the corrected blank.
NOTE 6—In the absence of iron, the diphenylamine sulfonate indicator does not react with the K Cr O solution. The addition of the
2 2 7
FeSO ·(NH ) SO ·6H O is, therefore, necessary to promote indicator response in the blank solution. A correction must be made in terms of its equivalent
4 4 2 4 2
in millilitresmL of K Cr O solution.
2 2 7
13. Calculation
13.1 Calculate the percentage of iron as follows:
iron, %5 @~A 2 B! 3C/D# 3100 (1)
where:
A = millilitres of K Cr O required for titration of the sample,
2 2 7
A = mL of K Cr O required for titration of the sample,
2 2 7
B = millilitres of K Cr O required for titration of the blank,
2 2 7
B = mL of K Cr O required for titration of the blank,
2 2 7
C = iron equivalent of the K Cr O , g/mL, and
2 2 7
D = grams of sample used.
13.2 Rounding of test results obtained using this test method shall be performed as directed in Practice E29, Rounding Method,
unless an alternative rounding method is specified by the customer or applicable material specification.
14. Precision and Bias
14.1 Precision—From six to nine laboratories analyzed four iron ore samples to determine iron. The replication made by the
different laboratories ranged from two to four, averaging three replicates. The data was studied by the interlaboratory test procedure
of Practice E691 – 87 modified by weighting certain sums to accommodate the unequal replication. Table 1 shows a summary
of these results. From pooled standard deviations, the overall between-laboratory reproducibility coefficient, R, was calculated as
being 0.38.
14.2 The agreement of the determination of iron in the NBS Standard Reference Material with the certified value shows no
evidence of bias, well within a 95 % confidence level:
(R = 0.24)
TEST METHOD B—IRON BY THE STANNOUS CHLORIDE REDUCTION DICHROMATE TITRATION
METHOD
15. Scope
15.1 This test method covers the determination of total iron in iron ores, concentrates, and agglomerates in the concentration range
from 35 % to 95 %.95 % by mass.
15.2 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
16. Summary of Test Method
16.1 This test method provides two alternative dissolution procedures.
16.2 Acid Decomposition—The sample is dissolved in HCl. The insoluble residue is removed by filtration, ignited, treated for the
recovery of iron, and added to the main solution.
Supporting data giving the results of cooperative testing have been filed at ASTM International Headquarters and may be obtained by requesting Research Report
RR:E16-63, dated April 23, 1968, with an amendment, dated July 27, 1993. Contact ASTM Customer Service at [e-mail].
E246 − 21
16.3 Decomposition by Fusion—The sample is fused with a mixture of sodium carbonate and sodium peroxide (Na O ). The melt
2 2
is leached with water. For samples containing more than 0.1 % of vanadium or molybdenum, or both, the solution is filtered and
the insoluble residue is dissolved in HCl. For other samples the leachate is acidified with HCl.
16.4 Reduction of the Iron—Most of the iron is reduced with stannous chloride, followed by the addition of a slight excess of
titanium (III) chloride solution. The excess titanium (III) is then oxidized in the hot solution with HClO . The solution is cooled
and the reduced iron is titrated with a standard K Cr O solution using sodium diphenylamine sulfonate as the visual endpoint
2 2 7
indicator.
17. Interferences
17.1 This test method covers the analysis of iron ores containing less than 0.1 % copper. In the case of iron ores containing
molybdenum or vanadium, or both, these elements are removed by water leach and filtration of the cooled sodium
carbonate/sodium peroxide fusion melt. Other elements normally found in iron ores do not interfere.
18. Apparatus
18.1 Crucibles, platinum, 25-mL to 30-mL capacity.
18.2 Crucibles, zirconium, 25-mL to 30-mL capacity.
18.3 Weighing Spatula, of a nonmagnetic material or demagnetized stainless steel.
19. Reagents
19.1 Iron (III) Ammonium Sulfate (approximately 0.1 N)—Dissolve 40 g of iron (II) ammonium sulfate [FeSO ·(NH ) SO ·6H O]
4 4 2 4 2
in H SO (1 + 19). Transfer to a 1-L volumetric flask, dilute to volume with the same acid, and mix. Standardize against standard
2 4
K Cr O solution using diphenylamine sulfonate as indicator.
2 2 7
19.2 Potassium Dichromate, Standard Solution (0.1 N)—Pulverize about 6 g of K Cr O reagent in an agate mortar, dry in an
2 2 7
air-bath at 140 °C for 3 h to 4 h, and cool to room temperature in a desiccator. Dissolve 4.9031 g of the dry reagent in water and
dilute the solution with water to exactly 1 L in a volumetric flask. Record the temperature at which this dilution was made.
19.3 Potassium Permanganate Solution (KMnO ), 25 g ⁄L.
19.4 Potassium Pyrosulfate Fine Powder (K S O ).
2 2 7
19.5 Sodium Carbonate Anhydrous Powder (Na CO ).
2 3
19.6 Sodium Diphenylaminesulfonate Solution—Dissolve 0.2 g of the reagent (C H NC H ·SO Na) in water and dilute to
6 5 6 4 3
100 mL. Store the solution in a brown glass bottle.
19.7 Sodium Hydroxide Solution (NaOH), 20 g ⁄L.
19.8 Sodium Peroxide (Na O ), dry powder. (Warning—Use proper safety practices and equipment when performing Na O
2 2 2 2
fusions. )
19.9 Sulfuric Acid-Phosphoric Acid Mixture—Pour 150 mL of H PO (6.12) into about 400 mL of water. While stirring, add
3 4
150 mL of H SO (6.20). Cool in a water bath and dilute with water to 1 L.
2 4
19.10 Tin (II) Chloride Solution (100 g ⁄L)—Dissolve 100 g of crystalline tin (II) chloride (SnCl ·2H O) in 200 mL of HCl by
2 2
heating the solution in a water bath. Cool the solution and dilute the water to 1 L. This solution should be stored in a brown glass
bottle with the addition of a small quantity of granular or mossy tin metal.
E246 − 21
19.11 Titanium (III) Chloride Solution (2 %)—Dissolve 1 g of titanium sponge (99.5 % minimum purity) in about 30 mL of HCl
in a covered beaker by heating on a steam bath. Cool the solution and dilute with water to 50 mL. Prepare fresh as needed. (If
preferred, dilute one volume of commercial titanium (III) chloride solution (about 15 % w/v) with seven volumes of HCl (1 + 1).)
20. Procedure
NOTE 7—If the procedure is based on acid decomposition, use 20.1. If the procedure is based on an alkaline fusion followed by the filtration of the leached
melt, (samples containing more than 0.1 % by mass vanadium or molybdenum, or both), use 20.2. If the procedure is based on an alkaline fusion, followed
by acidification of the leached melt (samples containing less than 0.1 % of molybdenum or vanadium, or both), use 20.3. (Warning—Use proper safety
practices and equipment when performing Na O fusions.)
2 2
20.1 Acid Decomposition:
20.1.1 Weigh approximately 0.40 g of sample into a small weighing bottle previously dried at about 105 °C (Note 8). Dry the
bottle and contents for 1 h at 105 °C to 110 °C. Cap the bottle and cool to room temperature in a desiccator. Momentarily release
the cap to equalize the pressure and weigh the capped bottle and sample to the nearest 0.1 mg. Repeat the drying and weighing
until there is no further weightmass loss. Transfer the samples to a 250-mL beaker and reweigh the capped bottle to the nearest
0.1 mg. The difference between the two weightsmasses is the weightmass of the sample taken for analysis.
NOTE 8—For samples of iron content greater than 68 %, 68 % by mass, weigh approximately 0.38 g.
20.1.2 Carry a reagent blank through all steps of the procedure.
20.1.3 Add 30 mL of HCl, cover the beaker with a watch glass, and heat the solution gently without boiling until no further attack
is apparent. Wash the watch glass and dilute to 50 mL with warm water. Filter the insoluble residue on a close-texture paper. Wash
the residue with warm HCl (1 + 50), until the yellow color or iron (III) chloride is no longer observed, then wash with warm water
six times to eight times. Collect the filtrate and washings in a 400-mL beaker. Start to evaporate this solution.
20.1.4 Place the filter paper and residue in a platinum crucible, dry, and ignite at 750 °C to 800 °C. Allow the crucible to cool,
moisten the residue with H SO (1 + 1), add about 5 mL of HF, and heat gently to remove silica and H SO . Add to the cold
2 4 2 4
crucible 2 g of potassium pyrosulfate, heat gently at first, then strongly until a clear melt is obtained. Cool, place the crucible in
a 250-mL beaker, add about 25 mL of water and about 5 mL of HCl, and warm to dissolve the melt. Remove and wash the crucible.
20.1.5 Adjust the solution to slight alkalinity with ammonia solution. Heat to coagulate the precipitate, filter on a coarse-texture
paper, and wash several times with hot water. Discard the filtrate.
20.1.6 Place the beaker containing the main solution under the funnel and dissolve the precipitate on the filter paper by pouring
over it 10 mL of hot HCl (1 + 2), wash the filter, first six times to eight times with warm HCl (1 + 50), then twice with hot water.
Evaporate the combined filtrates at low heat to a volume of about 30 mL and continue with 20.4.
20.2 Fusion Decompos
...