Sciencemadness Discussion Board

Seperating chrome from iron and nickel, stainless steel

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JJay - 4-4-2018 at 13:45

You'll have sodium and/or potassium bisulfate if the pH is low enough and enough sulfuric acid is present... not sure exactly how that will make a difference....

Fulmen - 4-4-2018 at 15:51

That's an excellent point, and both of these are far more soluble than the sulfates. I think it's worth a shot.

JJay - 4-4-2018 at 22:58

I'm thinking about dissolving some impure calcium chromate in water and dripping in sulfuric acid until I see no precipitate, filtering, and then adding an excess of sulfuric acid to see if I can get any chromium trioxide to precipitate. This seems like it might be a fairly dangerous experiment (especially if there are a lot of chlorides present), and I think a lot of sulfuric acid may be required, but I am pretty sure it will work....

Fulmen - 4-4-2018 at 23:49

Don't see why not. I don't see any reason for "titrating" the calcium, a slight excess of acid should be enough. With 10% sulfuric acid the precipitation was quite slow, producing a very dense ppt that was easy to filter off.
I would also concentrate the solution before trying to produce the trioxide, chromic acid is far more soluble than calcium chromate. This should remove more dissolved salts and reduce the amount of acid required.

Fulmen - 6-4-2018 at 07:52

I give up. After acidifying it with sulfuric acid I added potassium carbonate in hope of precipitating potassium dichromate. No such luck. I did get a whiteish precipitate, but now the solution has turned an odd brown-green color. I don't know what I have anymore or how to deal with it, so I'm mothballing the project for now.

Peterae - 24-4-2018 at 11:53

I've been following the process from here
http://lanthanumkchemistry.over-blog.com/article-how-to-sepa...

I'm at the Bleach stage which is incredibly slowwwww.

I'm getting a nice yellow though, with yellow crystals of Sodium Chromate on evaporation mixed with Sodium Chlorate from the bleach, maybe a little Sodium Chloride from the electrolysis process.

I need some ammonium hydroxide and have Ammonium Sulphate, I electrolytically made some Sodium hydroxide and will combine this with the Ammonium Sulphate and bubble the Ammonia gas through water and add this to my dried filtrate to get Nickle Amine.

[Edited on 24-4-2018 by Peterae]

[Edited on 24-4-2018 by Peterae]

Fantasma4500 - 12-8-2018 at 06:15

Peterae - i would suggest you to be very careful with adding ammonia to chlorate mixtures as ammonium chlorate is a potentially unstable explosive
chlorate has commonly been eliminated from perchlorate solutions by gassing the solution with SO2, this step would seem like a good idea if youre tossing ammonium ions into it and your goal isnt masochistic

however i dont know what SO2 would do to chromate.... fractionally crystallizing NaCrO4 NaClO3 and NaCl to get you mostly NaCrO4 and NaClO3 then reducing that with SO2 could possibly give off some insoluble chromium? this could potentially be a great way to purify chromium, wonder if ascorbic acid could be used instead as its less toxic and has many other benifits

theres a chance that iron chromate could ppt the chromate ion, though iron being in lower density than copper - i recall copper chromate being somewhat unstable in solution and also creating very volumnous ppt years back when i tried isolating the chrome from stainless steel chlorides in solution.
barium chromate could seperate the sodium chromate and chlorate.

from a sodium chlorochromate solution was added some NaOH, the dilute lightly orange solution shifted to a bright yellow.
a pinch of barium peroxide was added to some concentrated HCl, H2O2 and oxygen likely formed along with BaCl2, warm solution crystal clear.
addition of slightly basic NaCrO4 (possibly chlorate and chloride impurities) caused solution to turn deep blue, surprisingly this cleared up after 10 seconds - slight excess of HCl in the now slightly green turbid solution, but no notable precipitate, quite dilute and warm

iron sulfate solution added to basic sodium chromate solution, iron hydroxide precipitated, adding some hydrochloric acid turned the solution back into dichromate - pH seems to be quite an issue in precipitating chromate.

lead however: a bit of the sodium chlorochromate solution was pulled into a flask, diluted a slight bit and upon adding concentrated leadacetate solution with some acetic acid and copper acetate impurities a beige white ppt was immediatedly seen, however it doesnt settle very fast, and appears a slight bit spongy.

i could turn the chlorochromate into chromate dessicating the acid vapours with sodium carbonate and dilute sodium hydroxide but it seems that the impure mix ive got responds to lead acetate already, however lead chloride is most likely among the ppt, redissolving the ppt in acid should get around this, possibly with hydrochloric acid to keep the PbCl2 out of dissolution giving you a solution of hydrochloric acid and chromate (chromic acid??) which may then again be neutralized with sodium hydroxide or carbonate to finally be seperable by fractional crystallization

maybe reducing the chromium earlier on would be a better idea after all?

Abromination - 13-8-2018 at 11:30

Hexavalent chromium isn't involved in the extraction, right? All trivalent?

JJay - 13-8-2018 at 12:19

Chromate is hexavalent.

Keras - 20-8-2018 at 06:12

Hey – chiming in out of nowhere (well, I’ve been lurking -for a long while but it’s not until this summer that I really got back my hands into the hard stuff and so had actually anything to say).

I’ve tried myself separating chrome 3+ salts from iron 3+ salts. I had that idea, but I’m not it works: reduce Fe3+ and Cr3+ to Fe and Cr using Al (aluminium foils?). That should work given the respective potentials of the redox couples (Al 3+/Al is very low).

Heat the resulting mixed metal powder over 40 °C (or 100 °F). At that temperature, chrome magnetism is lost. Sort with a magnet?

I’m sure it’s awfully wrong, but I wonder if it’s not worth trying?

Fantasma4500 - 31-8-2018 at 02:40

it seems to work for chromium chloride with aluminium metal, the aluminium foil has turnt into a darker grey and the chromium solution went from green to light blue, it requires a bit of heating, i would suggest running some aluminium foil through a coffee grinder for 10 seconds to get some workable pieces and reacting excess aluminium with sodium hydroxide
i believe having actual steel (powder) in contact with water could turn quite messy so that must be taken into account although caustic soda somehow tends to inhibit corrosion of steel (per my own personal experience)

maybe one could react the steel with some weak acid, leaving behind chromium?

however you would be left with nickel and chromium at this point - if you dont use it while steel is present
actually i think you got nickel and chromium mixed up in terms of magnetism, 316 steel isnt magnetic due to its higher content of nickel and chromium, chromium being main alloying metal, nickel being ~half of the chromium content - nickel is magnetic, but not very much (IIRC)

so you propose:
stainless steel --> HCl --> StainlessSteelClx --> react with aluminium, metal powders ppt. --> magnet, discard steel, nickel --> chromium

pure chromium seems to react quite vigorously with hydrochloric acid, so it might actually be possible to leach the chromium from the steel (unsure about nickel HCl reactivity vs chrome) without even getting all magnetic.

if you react stainless steel with water through electrolysis (a bit of NaCl for conductivity) you will mostly turn the steel into Fe3O4 - magnetite, this metal oxide is .. magnetic, that would leave you with a sludge of chromium and nickel hydroxides and a slight bit of chlorides, of my experience pretty much all the steel went into Fe3O4 - however i used carbon steel, but the steel in SS should react similarily

Peterae - 28-11-2018 at 12:42

Thanks for the ideas chaps, been a while, I got a bit chicken with the sodium chromate, it was getting messy with all the decanting and bleaching, so I bottled it and ditched it after turning to chrome iii using ascorbic acid.


But I have now built myself a 3D printer from scratch and have designed a system where I can electrolyse, filter, wash, drain and decant with zero chance of spillage.


I have also been thinking of a way to drop a pure Chrome compound out of solution, and am wondering what happens if I add Calcium Hydroxide to Sodium Chromate, would I get Chromium Hydroxide?? I'm sure i read this somewhere, if so that would drop out and can then be washed as much as I want, I could then heat to make chrome oxide and then thermite it with aluminium powder to get chrome metal.


[Edited on 28-11-2018 by Peterae]

fusso - 28-11-2018 at 12:56

Quote: Originally posted by Peterae  
I have also been thinking of a way to drop a pure Chrome compound out of solution, and am wondering what happens if I add Calcium Hydroxide to Sodium Chromate, would I get Chromium Hydroxide?? I'm sure i read this somewhere, if so that would drop out and can then be washed as much as I want, I could then heat to make chrome oxide and then thermite it with aluminium powder to get chrome metal.
[Edited on 28-11-2018 by Peterae]
How is it possible to make Cr(III) from Cr(VI) w/o a reducing agent?

clearly_not_atara - 28-11-2018 at 13:03

If barium is available, barium chromate has an extremely low solubility, about 3 milligrams per liter. This allows chromium to be obtained without trying to acidify anything. Instead, you just add baryta to a strongly alkaline solution containing Fe/Ni/Cr. Cf:

https://books.google.com/books?id=bZQrAAAAYAAJ&pg=PA19&a...

There are a couple of possible ways to obtain chromium from BaCrO4, but my favorite is just to thermally decompose it (210 C) and then remove the barium with e.g. acetic acid. Cr6+ should be thoroughly destroyed by prolonged heating.

Peterae - 28-11-2018 at 14:02

I can convert the Sodium Chromate using Ascorbic Acid to turn light green chromium(iii), which is part of the process in the link i originally posted, if that would allow me to drop the hydroxide.

Infact i believe i have Chromium Hydroxide after electrolysis but offcourse this is mixed with iron and nickle as well, adding bleach converts the Chromium iii to Sodium Chromate to allow me to seperate the chrome by filtration, but at this stage it is contaminated by chlorate and chlorides left over from electrolysis and bleaching, hence i would like to find a way to drop a solid from the Sodium Chromate.

Barium looks good.
Need to look at a Copper Chromate route as well maybe.


fusso - 28-11-2018 at 15:35

But Cr3+ will dissolve in excess OH-, you need CO3 2- to precipitate Cr(OH)3.

Peterae - 28-11-2018 at 22:24

I can convert the Sodium Chromate using Ascorbic Acid to turn light green chromium(iii), which is part of the process in the link i originally posted, if that would allow me to drop the hydroxide.

Infact i believe i have Chromium Hydroxide after electrolysis but offcourse this is mixed with iron and nickle as well, adding bleach converts the Chromium iii to Sodium Chromate to allow me to seperate the chrome by filtration, but at this stage it is contaminated by chlorate and chlorides left over from electrolysis and bleaching, hence i would like to find a way to drop a solid from the Sodium Chromate.

Barium looks good.
Need to look at a Copper Chromate route as well maybe.


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