This invention relates to a method for the determination of metallic and total
chromium content in Sponge Chrome and Nuggets.
BACKGROUND OF THE INVENTION:
Smelting-reduction process is generally used for production of high-carbon
ferrochrome from chromite ores. This process is highly energy intensive and
requires low-ash coke as a reducing agent. Low-ash coke and electricity are both
expensive and there is also scarcity of these resources. Therefore cost of
production of ferrochrome is high. In past various processes were tried for prereduction
of Indian chromite but these processes never achieved required
percentage of metallization and hence not considered for commercialization.
Therefore, a novel process route is designed by reduction of pre-oxidized
chromite ore for production of the 70% metallized chromite ore product. The
preliminary experimental feasibility studies revealed that the reduction of preoxidized
chromite ore to produce the 70% metallized product which after smelting
in SAF will reduce the cost of production of ferrochrome by 20%. The process will
also reduce the power and coke consumption.
During these studies the sponge chrome samples are generated which are
basically partially reduced chromites at lower temperature of 1400C. These
sponge chrome samples contain Cr in metallic form (as a result of reduction) and
also some chromium in oxide form which is not reduced completely. Hence there
is a necessity to develop a new method for analysis of metallic Cr and oxide Cr in
sponge chrome samples.
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OBJECTS OF THE INVENTION:
An object of this invention is to propose a method for the determination of
metallic and total chromium content;
Another object of this invention is to propose a simple method for the estimation
of metallic and total chrominum content in sponge chrome and nuggets.
BRIEF DESCRIPTION OF THE INVENTION:
According to this invention there is provided a method for the estimation of
metallic chromium comprising:
subjecting finely ground partially reduced chromite sample and an acid mixture to
the step of refluxing;
cooling and then filtering the contents;
washing the filtrate with hot water for a number of times;
measuring the metallic chromium content.
In accordance with this invention there is also provided a method for the
estimation of total chromium comprising:
Igniting the residue as produced by the method as claimed in claim 1 to remove
all carbonaceous matter;
mixing the residue with sodium carbonate and borax;
dissolving the mixture in 1:1 acid by warming till a clear solution is obtained and
removing the total chromium content.
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DETAILED DESCRIPTION OF THE INVENTION:
ICP emission spectroscopic method for the estimation of metallic chromium:
0.100-1.000g of the finely ground «100mesh) of the partially reduced chromite
sample is taken in a round bottomed flask fitted with a reflux condenser. An acid
mixture is prepared by adding 100ml of ortho-phosphoric acid and 400 ml of
sulfuric acid to 500 ml of water. 100-150ml of the acid mixture is added to the
sample and the contents are refluxed for 90-150 minutes. The contents are
cooled and filtered through Whatman No. 41 filter paper and the residue washed
3-5 times with hot water. The filtrate and the washings are made up to 250m I in a
volumetric flask and the chromium concentration is measured by IC? emission
spectrometric method.
For the calibration of ICP spectrometer five synthetic standards in the range 0-
500 ppm of chromium were prepared by diluting a standard 1000ppm chromium
ICP calibration solution. The calibration standards were added with the required
amount of acid mixture to match their acid concentration to that of the sample
solutions. 267.716 nm line is used for making the measurements in ICP.
The method is validated by analyzing a certified reference material of Ferro
chrome having a known concentration of metallic chromium. The recovery of
metallic chromium is found to be complete. When a pre-oxidized chromite ore
sample containing only Cr203 and no metallic chromium is treated in a similar
manner, the chromium content of the solution is found to be less than 0.5%,
indicating that only a negligible amount of Cr203 passes into solution in the
treatment process given above and the method given is highly selective for the
determination of metallic chromium.
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ICP emission spectroscopic method for the estimation of total chromium:
The residue remaining after the filtration above is ignited to remove all the
carbonaceous matter in a platinum crucible. The remaining residue is fused with
a mixture of 1.0-2.0g of sodium carbonate and 0.5-1.0g of borax. After the
completion of the fusion the contents are dissolved in 50-100ml 1:1 hydrochloric
acid by warming till a clear solution is obtained. The solution is then transferred
to a 250ml volumetric flask and after cooling the volume is made up with distilled
water.
For the calibration of ICP spectrometer five synthetic standards in the range 0-
500 ppm of chromium were prepared by diluting a standard 1000ppm chromium
ICP calibration solution. The calibration standards were added with the required
amount of acid and fusion mixture to match their matrix to that of the sample
solutions. 267.716 nm line is used for making the measurements in ICP. The
method is validated by analyzing certified reference material chrome ore treated
in a similar manner to that of the samples. The chromium content obtained is the
oxide chromium present in the sample. The total chromium cont~nt of the sample
is the sum of metallic chromium and the oxide chromium from the residue.
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Some of the typical results obtained are given below.
Known Obtained Known Obtained
Concentration of Concentration Concentration Concentration
S.No Metallic of Metallic of Total of Total
Chromium Chromium Chromium Chromium
BCS 203-1 72.1% 72.50% 72.1% 72.55%
BCS308
0% <0.5% 28.40% 28.52%
Chrome
Ore
Preoxidized
0% <0.5% - 32.5%
Ore
1 - 21.4% - 29.0%
2 - 10.7% - 30.8%
3 - 24.5% - 32.5%
4 - 21.9% - 32.1%
5 - 7.5% - 30.5%
Example 1:
Method for the estimation of metallic chromium:
0.25g of the finely ground «100mesh) of the partially reduced chromite sample is
taken in a round bottomed flask fitted with a reflux condenser. An acid mixture is
prepared by adding 100ml of ortho-phosphoric acid and 400 ml of sulfuric acid to
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500 ml of water. 100ml of the acid mixture is added to the sample and the
contents are refluxed for 90 minutes. The contents are cooled and filtered
through Whatman No. 41 filter paper and the residue washed five times with hot
water. The filtrate and the washings are made up to 250ml in a volumetric flask
and the chromium concentration is measured by ICP emission spectrometric
method.
For the calibration of ICP spectrometer five synthetic standards having
0,50,100,200 and 300 ppm of chromium were prepared by diluting a standard
1000ppm chromium ICP calibration solution. The calibration standards were
added with the required amount of acid mixture to match their acid concentration
to that of the sample solutions 267.716 nm line is used for making the
measurements in ICP.
The method is validated by analyzing a certified reference material of Ferro
chrome having a known concentration of metallic chromium. The recovery of
metallic chromium is found to be complete. When a pre-oxidized chromite ore
sample containing only Cr203 and no metallic chromium is treated in a similar
manner, the chromium content of the solution is found to be less than 0.5%,
indicating that only a negligible amount of Cr203 passes into solution in the
treatment process given above and the method given is highly selective for the
determination of metallic chromium.
Example 2:
Method for the estimation of total chromium:
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The residue remaining after the filtration above is ignited to remove all the
carbonaceous matter in a platinum crucible. The remaining residue is fused with
a mixture of 2.0g of sodium carbonate and 1.0g of borax. After the completion of
the fusion the contents are dissolved in 100ml 1:1 hydrochloric acid by warming
till a clear solution is obtained. The solution is then transferred to a 250ml
volumetric flask and after cooling the volume is made up with distilled water.
For the calibration of ICP spectrometer five synthetic standards having 0, 50,
100, 200 and 300 ppm of chromium were prepared by diluting a standard
1000ppm chromium ICP calibration solution. The calibration standards were
added with the required amount of acid and fusion mixture to match their matrix
to that of the sample solutions 267.716 nm line is used' for making the
measurements in ICP. The method is validated by analyzing certified reference
material chrome ore treated in a similar manner to that of the samples. The
chromium content obtained is the oxide chromium present in the sample. The
total chromium content of the sample is the sum of metallic chromium and the
oxide chromium from the residue.
WE CLAIM:
1. A method for the estimation of metallic chromium comprising:
subjecting finely ground partially reduced chromite sample and an acid
mixture to the step of refluxing;
cooling and then filtering the contents;
washing the filtrate with hot water for a number of times;
measuring the metallic chromium content.
2. The method as claimed in claim 1, wherein the said reduced chromite
sample is finely ground to <100mesh.
3. The method as claimed in claim 1, wherein the acid mixture is prepared
by adding ortho-phosphoric acid and of sulfuric acid in a ratio of 1:4 to
water.
4. The method as claimed in claim 1, wherein the chromite sample and the
acid mixture is refluxed for 90-150 minutes.
5. The method as claimed in claim 1, wherein the said residue is washed for
3 to 5 time with hot water.
6. A method for the estimation of total chromium comprising:
igniting the residue as produced by the method as claimed in claim 1 to
remove all carbonaceous matter;
mixing the residue with sodium carbonate and borax;
dissolving the mixture in 1:1 acid by warming till a clear solution is
obtained and removing the total chromium content.
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7. The method as claimed in claim 6, wherein the said acid is hydrochloric
acid.