ASTM E246 Determination of Iron in Iron Ores and Related Materials

Scope:

ASTM E246 defines the standard test methods to estimate iron concentration in iron ores, concentrates, and agglomerates. The methods are suitable for determining iron concentrations between 30% to 95% iron. This standard describes three methods using dichromate titration for estimating iron content. Hydrogen sulfide reduction, stannous chloride reduction, and silver reduction dichromate titration methods are the standard methods contained in ASTM E246.

Test procedure:

For ASTM E246 testing, the sample is dissolved in HCl. This results in the formation of an insoluble residue which is filtered, ignited, and treated for the recovery of iron. It is then added to the main solution.

Test Method A-Iron by Hydrogen Sulfide Reduction Dichromate Titration Method

To the solution containing all the iron, H₂SO₄ is added and the solution is evaporated into fumes to expel chlorides. The salts are made to dissolve in water. The resultant solution is boiled, and the iron is reduced by a rapid stream of hydrogen sulfide (H₂S). The precipitated sulfides are filtered and washed with an acid sulfide wash solution until they are free of iron. The filtrate is then boiled to expel the H₂S, cooled, and titrated with K₂Cr₂O₇ solution, using sodium diphenylamine sulfonate as the indicator.

Test Method B- Iron by Stannous Chloride Reduction Dichromate Titration Method

In this ASTM E246 method, 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 HClO₄. The solution is cooled and the reduced iron is titrated with a standard K₂Cr₂O₇ solution using sodium diphenylamine sulfonate as the visual endpoint indicator.

Test Method C- Iron by Silver Reduction Dichromate Titration Method

The test sample is passed through a silver reductor. After the addition of the H₂SO₄–H₃PO₄ mixture and diphenylamine sulfonate indicator, the total iron is determined by titration with a standard solution of K₂Cr₂O₇.

Video 01: Redox titration (Dichromate titration)

Specimen size:

The following table provides specimen sizes for the three ASTM E246 testing methods:

Test method	Test specimen weight (g)
A	0.5
B	0.4
C	0.3

Data:

For ASTM E246, the percentage of iron is calculated as follows;

Test Method A 

where:

A = milliliters of K₂Cr₂O₇ required for titration of the sample,

B = milliliters of K₂Cr₂O₇ required for titration of the blank,

C = iron equivalent of the K₂Cr₂O₇, g/mL, and

D = grams of sample used.

Test Method B

where:

V₁ = volume of K₂Cr₂O₇ standard solution used for the

titration of the analytical sample, mL,

V₂ = volume of K₂Cr₂O₇ standard solution used for the

titration of the blank test, mL, and

m = mass of the test portion, g.

Test Method C

where:

T = the volume in milliliters of K₂Cr₂O₇ standard solution

used for the titration, and

m = the mass, in grams of the test portion.

Conclusion:

ASTM E246 defines the standard test methods to estimate iron concentration in iron ores, concentrates, and agglomerates.