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# FeOtot recalculation to FeO and Fe2O3 by stoichiometry

Posted by Łukasz Kruszewski

Łukasz Kruszewski
March 16, 2011 08:38AM

Hello everyone!Would like to ask if you know about a "universal" method to recalculate FeOtot to FeO and Fe2O3 by stoichiometry? I know about a method of Carmichael, i.e. recalculation on ulvospinel and ilmenite basis, but it seems to be only for spinels (please correct me if I'm wrong).

Is there a formula for such recalculation for any mineral?

Best regards,

Luke

Johan Kjellman
March 16, 2011 01:24PM

I calculate formulas in xcel-spreadsheats. I then put analysed Fe expressed as FeO* in one column. Then I have one cell for FeO (which is the value I play with) and one for Fe2O3.Then "calculating" FeO and Fe2O3 is done the following way:

First your mineral must have some constraining conditions, i.e. total number of oxygens or cations, etc. which you have as a formula in one of the cells.

Then in the Fe2o3 cell you put the formula

(FeO*-FeO) x 1,11138

In the FeO-cell you now assign a value and check your "constraining condition cell" and adjust until it has the right value.

cheers

Alfredo Petrov
March 16, 2011 02:26PM

If you are starting with microprobe data, Lukasz, there isn't any one method that will work for all minerals. In some cases you won't know O:OH, for example, so you won't be able to calculate it at all by stoichiometry.
Łukasz Kruszewski
March 16, 2011 07:18PM

Thank you very much, Sirs! (-:
Ralph Bottrill
March 16, 2011 11:44PM

Its simple enough for many anhydrous minerals as per Johan, but minerals with vacancies or OH and undetermined elements can be impossible. Schumacher (1997) came up with a method for amphiboles, but it does not always give a good result (Can Min v35 p237-246).Regards,

Ralph

Łukasz Kruszewski
March 17, 2011 08:21AM

Thank you, Ralph! Its all indeed not that simple..Cheers!

Luke

Alfredo Petrov
June 21, 2012 04:16PM

Egbo, Unfortunately this is not possible without knowing the mineralogical purity of the zircon sand itself; in other words, what mineral is the Fe^{3+}present in?

Ralph Bottrill
August 31, 2012 10:52PM

To determine the FeO/Fe2O3 contents there are standard wet chemical methods, based on the dissolution of the soil and titration to determine FeO, then determine Fe2O3 by difference from the total Fe.Regards,

Ralph

John Attard
January 12, 2014 03:54AM

A wet chemical analysis I know involves dissolving a known weight of the dry mineral powder in suitable acids under conditions that exclude oxygen, dilute suitably and titrate with standard permanganate to get the Iron2. If you then pass the resulting solution or an aliquot of the stock solution, through a Jones Reductor (amalgamated zinc in a burette-like tube) the Iron will end up being reduced to Iron2. One then titrates with permanganate again to get the total iron.

Is that what you were looking for?

John Attard, San Diego, California.

Zbynek Burival
January 13, 2014 11:25AM

There is no general way to recalculate Fe2+ and Fe3+. It is too difficult in many silicates. There are undetermined other elements, vacancies, uncertain water/OH content, more elements with different oxidation state etc. Sometimes you can use "brute force" - like calculating garnet on 12 anions and 8 cations with valence calculation - but of course results of this may be quite far from reality. The wet analysis is impossible for mixed, altered or too small minerals. You may avoid undetermined elements by using LA-ICP-MS, sometimes just this helps to get the formula. Sometimes the structure can help, eg. if you can say there is no Fe in position typical for Fe3+ - Raman and IR spectroscopy or xray diffraction help with this. The most efficient method is to use Mossbauer spectroscopy which can directly analyse and distinguish Fe2+ and Fe3+.

To get FeO to Fe2O3 just multiply FeO by 1,11111... Fe2O3 to FeO is just reverse, divide Fe2O3 by 1,11111 (or multiply by 0,899999 as said above).

Maarten VU
January 21, 2014 09:31AM

Zbynek Burival Wrote:-------------------------------------------------------

>

> To get FeO to Fe2O3 just multiply FeO by

> 1,11111... Fe2O3 to FeO is just reverse, divide

> Fe2O3 by 1,11111 (or multiply by 0,899999 as said

> above).

What is the calculation behind this? Where does the number 1,1111 come from?

I have my XRF analysis in Fe2O3, but my modelling program only accepts FeO. So I would like to know how the 1,1111 is calculated.

Johan Kjellman
January 21, 2014 12:33PM

it is the ratio of the molecular weight of half a molecule of Fe2O3 and one molecule of FeOcheers

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