Introduction:
The chromite ore is normally having a composition of FeCr2O4 which may be written as FeO.Cr2O3. In some ore Fe is partially replaced by Mg as (Fe, Mg) Cr2O4. The ore may have Fe in other form besides being present in the spinel. An accurate determination of FeO content is extremely important in chromite ores and refractories made with them. The percentage content of FeO and Fe2O3/FeO ratio in sample is used to solve a whole number of theoretical problems dealing with the mineral composition of chromite spinel, chromite massifs and the degree and nature of the ancient weathering they have undergone. The Fe2O3/FeO ratio also plays an important part in developing production techniques for refractories.
FeO analysis in chromite ores and chrome magnesite refractories involves difficulties on account of their high resistance to the reagents uses to decompose the samples. Under the present investigation, vanadate method has been used for determination of FeO as it is very less complicated and can be performed easily.
Method:
During the process 0.5 gm of the chromite ore sample is taken along with 0.25 g V2O5 (added in measured quantity that is enough for complete decomposition of the sample) in a 250ml conical flask. Then 20ml of acid mixture containing conc H2SO4 and H3PO4 in 2:1 ratio is added to it. It is then put on the hot plate for dense fuming. After dense fuming and complete dissolution of the sample, it is allowed to cool and titrated against Mohr salt solution which is already standardized against (N/10) K2Cr2O7 solution. A reagent blank is always to be analyzed under the same condition.
Reactions Involved behind the Process:
Initially, V2O5 hydrolyses in the process as follows:
V2O5 + H2O = 2HVO3 (in presence of acidic condition)
The vanadate (VO3– ) oxidizes ferrous to ferric state as below:
Fe+2 + VO3– + 4H+ = Fe+3 + VO+2 + 2H2O
2FeSO4 + 2 HVO3 + 3 H2SO4 → Fe2(SO4)3 + 2VOSO4 + 4H2O
The remaining excess HVO3 is then back titrated against standardized Mohr’s salt solution. The reaction involve in the process is as follows:
Fe+2 + VO3– + 4H+ = Fe+3 + VO+2 + 2H2O
Calculation:
Results:
|
Sample No. |
Actual Total Fe % |
FeO results in triplicate |
% Average |
Std deviation |
||
|
I |
10.45 |
12.04 |
11.85 |
11.97 |
11.95 |
0.096 |
|
II |
21.11 |
20.35 |
20.10 |
20.23 |
20.23 |
0.125 |
|
III |
11.86 |
15.39 |
15.05 |
15.12 |
15.19 |
0.180 |
Advantages of the process:
- All reagents which are used in this method are easily available in pure state.
- The cost of analysis is also very nominal.
- The method of analysis of FeO from the amount of pentavalent vanadium remaining in the solution by titrating it with Mohr’s salt solution is a very easy as well as accurate technique.
- Dissolution of chromite ore by the vanadate method is less time consuming process.
Conclution:
Estimation of percentage of FeO in chrome ore is a difficult and time consuming process. However, vanadate method for FeO estimation in chrome ore is a better process as it is less time consuming and could be carried out in the laboratory quite comfortably. The accuracy of the process and availability of all reagents is also very good. And most important matter is the cost of the whole process is very nominal. So, we can conclude that vanadate method for estimation of FeO in chrome ore is a very reliable process.