ANALYSIS OF DIFFERENT OXIDATION STATES OF CHROMIUM

Ferro alloys like ferro chrome are mostly produced in submerged electronic arc furnace. This process generates large amounts of slag. The slag is basically M2O3-MgO-SiO2 based with constituent of CaO and Cr (OX). Therefore slag contains chromium in different oxidation states besides Cr0:

Procedure:

Total Cr, Cr3+ and Cr0 was done by volumetric method and Cr+6 were done by ICP-OES.

Metallic Cr (Cr0):

Sample extracted with anhydrous bromine and anhydrous methanol mixture to convert zerovalent Cr to CrBr3 which is soluble in methanol. Methanol solution was separated by filtration and washing. Solution is evaporated to remove methanol, solution made acidic with dil H2SO4 followed by Chromium determination with Std KMnO4 soln.

Hexavalent Cr (Cr+6):

The residue left on the filter paper was treated with 5% NaOH solution in order to bring Cr+6 as Na2CrO4 in solution. Solution is separated by filtration and washing. The solution is made acidic with dil HCl followed by Cr determination with ICP-AES.

Trivalent Cr (Cr+3):

The residue left on the filter paper was burnt and fused with Na2O2, the solution made acidic with dil H2SO4, followed by Cr determination with std KMnO4 solution.

One ferro chrome slag sample was analysed and results are given below:

Sl. No. Total Cr (%) Metallic Cr (%) Hexavalent Cr (%) Trivalent Cr (%)
1 9.30 0.45 0.0020 8.75
2 9.40 0.55 0.0030 8.80
3 9.30 0.50 8.70

Conclusion:

It was found that slag also contains Cr+6 with Cr3+ and Cr0 which may produced in the slag due to oxidizing condition prevailing in the slag.

Contributed by : Mr. Pintu Hazra & Mr. Kajal Ray

Leave a Reply

Your email address will not be published. Required fields are marked *