Scope:

This test method covers the determination of chromium oxide (Cr2O3) in chrome ores in the compositional range from 25 % to 60 %.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 peroxydisulfate. The excess of permanganate is destroyed by the addition of sodium chloride. 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.

  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 = millilitres 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