ASTM E342-23

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Designation: E342 − 11 (Reapproved 2016) E342 − 23
Standard Test Method for
Determination of Chromium Oxide in Chrome Ores by
Permanganate Titrimetry
This standard is issued under the fixed designation E342; 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 This test method covers the determination of chromium oxide (Cr O ) in chrome ores in the compositional range from 25 %
2 3
to 60 %.
NOTE 1—As used in this test method, “%” refers to a mass fraction (wt/wt %) (g/100g).
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 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 and healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use.
1.4 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
E135 Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
E276 Test Method for Particle Size or Screen Analysis at 4.75 mm (No. 4) Sieve and Finer for Metal-Bearing Ores and Related
Materials
E882 Guide for Accountability and Quality Control in the Chemical Analysis Laboratory
3. Terminology
3.1 Definitions—For definitions of terms used in this test method, refer to Terminology E135.
This test method is under the jurisdiction of ASTM Committee E01 on Analytical Chemistry for Metals, Ores, and Related Materials and is the direct responsibility of
Subcommittee E01.02 on Ores, Concentrates, and Related Metallurgical Materials.
Current edition approved Nov. 15, 2016April 1, 2023. Published December 2016April 2023. Originally approved in 1967. Last previous edition approved in 20112016
as E342 – 11.E342 – 11 (2016). DOI: 10.1520/E0342-11R16.10.1520/E0342-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
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E342 − 23
4. Summary of Test Method
4.1 The sample is decomposed by fusion with sodium peroxide. After leaching in water and boiling to decompose peroxides, the
solution is acidified with HNO and H SO . Residual chromium is oxidized to chromate with silver nitrate, potassium
3 2 4
permanganate, and peroxydisulfate. The excess of permanganate is destroyed by the addition of NaCl. After cooling, the chromate
is reduced by the addition of a measured excess of a ferrous ammonium sulfate, and the excess is titrated with a permanganate
solution.
5. Significance and Use
5.1 This test method is intended to be used for compliance with compositional specifications for chromium oxide content in
chromium-bearing ores. It is assumed that all who use these procedures 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.
6. Interferences
6.1 None of the elements normally found in chrome ores interfere with this test method.
7. Reagents and Materials
7.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents conform to the specifications of the 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 the reagent is of sufficiently high purity
to permit its use without lessening the accuracy of the determination.
7.2 Purity of Water—Unless otherwise indicated, references to water shall be understood to mean reagent water conforming to
Type I or II of Specification D1193. Type III or IV may be used if they effect no measurable change in the blank or sample.
7.3 Ammonium Peroxydisulfate Solution (250 g/L)—Dissolve 25 g of ammonium persulfate (ammonium peroxydisulfate)
((NH ) S O ) in water, and dilute to 100 mL. Prepare fresh as needed.
4 2 2 8
7.4 Ferrous Ammonium Sulfate Solution (0.2 N)—Dissolve 78.4 g of ferrous ammonium sulfate (FeSO (NH ) SO ·6H O) in 1 L
4 4 2 4 2
of cool H SO (5 + 95). Because the ferrous ammonium sulfate solution gradually weakens in reducing power, it is necessary to
2 4
standardize the ferrous ammonium sulfate solution daily or at the same time that the chrome ore is analyzed. To standardize,
transfer 100 mL of FeSO (NH ) SO ·6H O to a 600-mL beaker, dilute to 300 mL with cold H SO (5 + 95), add 2 mL of H PO
4 4 2 4 2 2 4 3 4
and 2 drops of ortho-phenanthroline ferrous sulfate (ferroin). Titrate immediately with 0.2 N KMnO solution (7.8) to a faint,
permanent pink color.
7.5 Ferrous Sulfate Solution (0.025 M)—Dissolve 6.95 g of ferrous sulfate (FeSO ·7H O) in 500 mL of water and dilute to 1 L.
4 2
7.6 Ortho-Phenanthroline Ferrous Sulfate Indicator Solution—(0.025 M)—Dissolve 1.485 g of 1,10-phenanthroline monohydrate
in 100 mL of ferrous sulfate solution (FeSO ·7H O) prepared in 7.5.
4 2
7.7 Potassium Permanganate Solution (20 g/L)—Dissolve 20 g of potassium permanganate (KMnO ) in water and dilute to 1 L.
7.8 Potassium Permanganate Solution (0.2 N)—Dissolve 6.4 g of KMnO in 1 L of water. Standardize against a National Institute
of Standards and Technology Reference Material for sodium oxalate (Na C
...