[i.jasheel]

I'm currently working in a project in which I have to convert the iron oxides present in iron ore slime into ferric nitrate. Iron ore slime is which has the particle size of below 0.15 mm is being discarded as waste during the mining and processing stages iron ore and it will be stored at the tailing dam. It is estimated that 18% - 25% of tailing will be generated during the processing of iron ore. The major compositions of iron ore slime are hematite, quartz, alumina, mica. SO basically it consists of ferric oxide and alumina, silica, magnesia, calcia,etc impurities. I wanted to extract the iron part of the slime by converting it into water soluble ferric nitrate leaving behind the insoluble impurities. Even if some soluble impurities like clacium nitrate is formed then its not a problem. I tried treating the slime with nitric acid both conc. and dilute but no reaction was observed.
Please suggest me some useful ways to get ferric nitrate from iron ore slime.(or any other steel industry waste product like mill scale, slag etc.)

[Arkcon]

OK.  In you paragraph you list, twice, the composition of the ore waste.  Now, you have two (or three) problems to work on:

How do you know its reacting or not?  How can you tell.  If the ore waste is 0.1% iron, how will you find it, and in how much dilute acid?

Does iron, pure, as filing or steel wool, react with your chosen acid concentration?  Can you put it fine iron, in a test tube, and get a reaction?  What sort of reaction do you get?  Can you get a reaction form a solid piece?  If you coat a pellet of iron, with cement, covering 90% of the surface area, can the acid still reach the iron?  Try it and see.

[i.jasheel]

Firstly the visual confirmation. I used 60# size of iron ore slime and the powder was passive to the acid. To get a better idea i conducted a physical mass test in which I used 1M nitric acid in excess and put a measured amount of slime in it. The I used a pre-weighted filter paper to filtrate out the slime from the acid. And filter paper was dried afterwards. The mass of the filter paper after drying was very slightly less than the combined mass of slime taken and filter paper. I know this method is lame but still assuming that slime contains 40% of iron oxide, we would have experienced a significant weight loss.

I even tried the same with conc acid(15.6M approx) but the results were no different.

I read in a forum somewhere that I can get iron nitrate from iron shreddings and I'm sharing it with you but it would be of no use since my aim to form ferric nitrate from ferric OXIDE is getting lost.

<Method of converting iron to ferric nitrate>
"Adding some H2O2 does help. It assures that ALL Fe(2+) is oxidized to Fe(3+) very quickly. But if the acid is hot, then garage chemist's suggestion also works well. Use a large excess amount of acid and keep it hot, or use only a small excess amount of acid, but then you need to add H2O2. Keep in mind though, that the reaction with H2O2 also consumes some acid, albeit less than the reaction in which the acid alone works as oxidizer.

In order to keep things practical, first try on a small scale, e.g. a testtube to get a feeling for the reaction and allow some experimenting without wasting 100's of ml of precious chemicals.

If I wanted to make pure ferric nitrate, then I would go for 30% HNO3, to which some H2O2 (30%) is added. E.g. 5 parts acid mixed with 1 part of H2O2. This mix I would add to iron with weak heating. Use excess amounts of the mix and after all iron has dissolved, boil down in order to destroy all unreacted H2O2 and make the liquid more concentrated. It will be hard though to isolate pure ferric nitrate, because nitric acid will strongly adhere to your product and you almost certainly end up with a strongly acidic product, which still contains quite a lot of HNO3.

Good pure ferric nitrate is very pale brown/purple. It is VERY hygroscopic and if you put a crystal of the solid on a watch glass, then a few minutes later it has turned into a brown/orange droplet of liquefied salt. The brown/orange color is due to partial hydrolysis of the ferric ions. A solution of ferric ions is nearly colorless, the brown/orange and sometimes somewhat turbid solutions, which are so well-known have this color due to hydrolysis of ferric ions. Only at very low pH you will have such colorless solutions."
http://www.sciencemadness.org/talk/viewthread.php?tid=19837

[Arkcon]

OK.  You have a lot of diverse knowledge and observations, and some research.  That's good.  Now, what we need from you is a discussion of your application, the scale of your application and the technical level.

If this is an undergraduate class assignment, we're going to send you to a textbook, and ask you to understand the particular chemistry involved.

If you intend to do this industrially, then from a chemical engineering perspective, and are trying it out on the bench top with a small sample, we'd like to see some more controlled experiments, and that you can talk about how much material you intend to work with, when you get started.

If you're a citizen chemist, and you're thinking, "Hey, why don't we just use a bunch of acid to make a soluble solution,"  then we still want to see good science concepts done by you.

Firstly the visual confirmation. I used 60# size of iron ore slime and the powder was passive to the acid.

Try to determine that more quantitatively.

To get a better idea i conducted a physical mass test

You mean you weighed it before and after acid addition?  Then say it like that, not as you have above -- that's over pretentious, and off putting.

in which I used 1M nitric acid in excess and put a measured amount of slime in it. The I used a pre-weighted filter paper to filtrate out the slime from the acid. And filter paper was dried afterwards. The mass of the filter paper after drying was very slightly less than the combined mass of slime taken and filter paper.

Please be more quantitative.  Actual percentage lost compared with actual tailing composition.  You can determine quantitatively yourself, or you can accept published values for theoretical composition.

I know this method is lame but still assuming that slime contains 40% of iron oxide, we would have experienced a significant weight loss.

Good.  You have some numbers.  Are they correct?  Also, can you purposely make 50%, 40%, 30% iron oxide in slag, and get the required mass lost?  Or does this method have analytical limitations?

I even tried the same with conc acid(15.6M approx) but the results were no different.

Yes.  Do look up "passivation."  Although that may not be the case here, as referenced above.
 

I read in a forum somewhere that I can get iron nitrate from iron shreddings and I'm sharing it with you but it would be of no use since my aim to form ferric nitrate from ferric OXIDE is getting lost./quote]

That's some good research, and it may profit you better as we advance with this problem.  We just need to know exactly what your question is.

[lawhitesell]

Although chromium (Cr), iron (Fe), and aluminium (Al) readily dissolve in dilute nitric acid, the concentrated acid forms a metal-oxide layer that protects the bulk of the metal from further oxidation. The formation of this protective layer is called passivation. Typical passivation concentrations range from 20% to 50% by volume (see ASTM A967-05). Metals that are passivated by concentrated nitric acid are iron, cobalt, chromium, nickel, and aluminium.[8]
 Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 15: The group 15 elements". Inorganic Chemistry, 3rd Edition. Pearson. ISBN 978-0-13-175553-6.

You are running into the same problem that occurs with almost all mine tailings:  separation of the individual oxides from a slurry is extremely difficult.  The amounts of calcia, alumina, and silica themselves act like small amounts of concrete, and in the slurry there is a large amount of intermolecular attraction from hydroxy groups in the extremely basic oxides.  Theis means that simple dissolving becomes extremely unlikely for separating one material from another. 

There are many scholarly articles on these problems, including this 2004 colloquium:
Canadian Geotechnical Journal, 2007, Vol. 44, No. 9 : pp. 1019-1052

Colloquium 2004: Hydrogeotechnical properties of hard rock tailings from metal mines and emerging geoenvironmental disposal approaches
Bruno Bussière
https://doi.org/10.1139/T07-040
ABSTRACT

Tailings are ground rock particles from which the valuable minerals or metals have been extracted. An historical overview on hard rock mines shows that since the 1930s, it has become current practice to pump the tailings into storage areas circumscribed by dykes made of the tailings themselves. However, numerous physical and chemical stability problems were observed mainly owing to the particular hydrogeotechnical and mineralogical properties of the tailings. Therefore, modifications to the conventional methods were proposed, but these were relatively costly, not always efficient, and sometimes difficult to implement. New management methods that improve the physical and (or) chemical stability have hence been developed to reduce environmental risks associated with tailings storage, namely, densified tailings, environmental desulphurization, covers built with tailings, and co-disposal of tailings and waste rock. Even if many aspects need to be optimized, these approaches can be considered today as interesting alternatives to conventional tailings management approaches.

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