ASTM E342-11 Test Method for Determination of Chromium Oxide in Chrome Ores by Permanganate Titrimetry

Scope:

ASTM E342-11 test method covers the determination of chromium oxide (Cr₂O₃₎ in chrome ores from 25 % to 60 % in the compositional range. The values stated in SI units are to be regarded as standard.

Test Procedure:

The sample is decomposed by fusion with sodium peroxide. After leaching in water and boiling to decompose peroxides, the solution is acidified with nitric and sulfuric acids. Residual chromium is oxidized to chromate with silver nitrate, potassium permanganate, and peroxy-disulfate. The addition of sodium chloride destroys the excess of permanganate. After cooling, the chromate is reduced by the addition of a measured excess of ferrous ammonium sulfate, and the excess is titrated with a permanganate solution.

 Figure 1: A simple titration Apparatus for the titration Process

Test Specimen:

Pulverised Chrome Ores of size 150 μm and dried to 105º to 110º for 1 hr.

Data: 

Calculate the chromium oxide content as follows

Where,

A = milliliters of KMnO4 solution equivalent to the total amount of FeSO₄(NH₄)₂SO₄·6H₂O added to the sample solution.

B = millilitres of KMnO₄ solution required to titrate the excess FeSO₄(NH₄)₂SO₄·6H₂O,

C = normality of KMnO₄ solution, and

D = grams of sample used