Method to differentiate red rust (Fe2O3) from black rust(Fe3O4)

[Red rust identification]

Does someone know about a chemical procedure to differentiate these phases? If not chemical, do you have another?

[Sensei]

Did you tried centrifuge?

https://en.wikipedia.org/wiki/Centrifuge

 

http://www.ebay.com/sch/Centrifuges-/26232/i.html

 

ps. I interpreted your "differentiate" as "separation". I hope so right?

Edited July 8, 2015 by Sensei

[John Cuthber]

It reminds me of the story of Jack the village idiot, who had two horses but didn't know how to tell them apart.

Someone suggested he measured their heights.

Jack was delighted when he found that the black one was two inches taller than the white one.

[Red rust identification]

I have use an etchant to tell if a part is rusted, but this etchant reacts for both fe2O and fe3O4. I was mostly looking for a method to truly tell when we have one or the other.

[pavelcherepan]

Does someone know about a chemical procedure to differentiate these phases? If not chemical, do you have another?

 

Fe₃O₄, or more precisely Fe²⁺Fe₂³⁺O₄ is magnetite and the "red dust" is hematite. The former is ferromagnetic and the latter is anti-ferromagnetic, hence a piece of iron would work fine to separate those.

[John Cuthber]

 

Fe₃O₄, or more precisely Fe²⁺Fe₂³⁺O₄ is magnetite and the "red dust" is hematite. The former is ferromagnetic and the latter is anti-ferromagnetic, hence a piece of iron would work fine to separate those.

Do you realise that both those materials stick to a magnet, and that the difference is in relation to an obscure property of the spin states?

[pavelcherepan]

Do you realise that both those materials stick to a magnet, and that the difference is in relation to an obscure property of the spin states?

 

Yes, John, I do. That's why I said "piece of iron", not a magnet. Maybe I should've made it more clear. Black dust will stick to the iron, red dust shouldn't, as it's very weakly magnetic.

[John Cuthber]

There are too many other variables.

Notably,why would either of them stick to a piece of (un-magnetised) iron?

[pavelcherepan]

Actually, you can also use magnet for separation of those. For example in iron ore beneficiation, for magnetite magnets are used to separate it from waste rock, but for hematite is so weakly magnetic that magnets are not used for separation, instead density flotation separation is used.

[John Cuthber]

So, now yo are back to using a magnet. OK.

[pavelcherepan]

There are too many other variables.

Notably,why would either of them stick to a piece of (un-magnetised) iron?

 

"Normal magnetite is attracted to a magnet but some specimens are automagnetized and have the ability to attract small pieces of iron, small pieces of magnetite and other magnetic objects. This form of magnetite, known as "lodestone", was man's first encounter with the property of magnetism. Lodestone is easily identified because it is usually covered with small particles of magnetite and other magnetic minerals (see photo). "

 

http://geology.com/minerals/magnetite.shtml

 

So, now yo are back to using a magnet. OK.

 

Of course, why wouldn't I?

 

Mineral Composition Magnetic Order T_c(°C) σ_s (Am²/kg)

 

Magnetite Fe₃O₄ ferrimagnetic 575-585 90-92

Hematite αFe₂O₃ canted AFM 675 0.4

 

Where [latex]\sigma[/latex] is saturation magnetisation at room temperature.

 

http://www.irm.umn.edu/hg2m/hg2m_b/hg2m_b.html

Edited July 11, 2015 by pavelcherepan

[John Cuthber]

That's fine. it's just that earlier you said "Yes, John, I do. That's why I said "piece of iron", not a magnet. Maybe I should've made it more clear. Black dust will stick to the iron, red dust shouldn't, as it's very weakly magnetic. "

And I'm still waiting for a reply to my question "why would either of them stick to a piece of (un-magnetised) iron?"

 

Of course, there's still a problem.

The particle size for example.

A bigger problem is the fact that the particles will stick to each other in the presence of any applied magnetic fiels.

​None of this will help if there are particles containing a mixture of the materials (as I suspect would often be the case)

[CharonY]

Is it certain that only one or the other exists? Either case, in order to assess purity of iron preparations powder x-ray diffraction is a relatively quick way and also allows a rough estimate of contamination, provided it is relatively pure.

[pavelcherepan]

That's fine. it's just that earlier you said "Yes, John, I do. That's why I said "piece of iron", not a magnet. Maybe I should've made it more clear. Black dust will stick to the iron, red dust shouldn't, as it's very weakly magnetic. "

And I'm still waiting for a reply to my question "why would either of them stick to a piece of (un-magnetised) iron?"

 

I guess I have to re-post it.

 

"Normal magnetite is attracted to a magnet but some specimens are automagnetized and have the ability to attract small pieces of iron, small pieces of magnetite and other magnetic objects. This form of magnetite, known as "lodestone", was man's first encounter with the property of magnetism. Lodestone is easily identified because it is usually covered with small particles of magnetite and other magnetic minerals (see photo). "

 

 

 

Of course, there's still a problem.

The particle size for example.

A bigger problem is the fact that the particles will stick to each other in the presence of any applied magnetic fiels.

​None of this will help if there are particles containing a mixture of the materials (as I suspect would often be the case)

 

This.

 

 

 

Hematite is not magnetic and should not respond to a common magnet. However, many specimens of hematite contain enough magnetite that they are attracted to a common magnet.

 

http://geology.com/minerals/hematite.shtml

Edited July 13, 2015 by pavelcherepan

[Red rust identification]

 

Fe₃O₄, or more precisely Fe²⁺Fe₂³⁺O₄ is magnetite and the "red dust" is hematite. The former is ferromagnetic and the latter is anti-ferromagnetic, hence a piece of iron would work fine to separate those.

 

Thank you! So just to clarify, I have Fe2O3 (hematite) attached to a surface and I used iron or a magnet, it will not happen anything? Compare to having Fe3O4 attached to a surface (in which iron will be attracted? )

[John Cuthber]

 

I guess I have to re-post it.

 

"Normal magnetite is attracted to a magnet but some specimens are automagnetized and have t...

no, you have to read, and understand it.

"Normal magnetite is attracted to a magnet but some specimens are automagnetized "

Clearly, some are not.