UnintentionalChaos
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Stability of Chromium Salts in Aqueous Soln.
The situation is simple. I dissolved some stainless steel into sulfuric acid by electrolysis and precipitated everything with NaOH. Now, I presumably
have a heap of iron hydroxide, chromium hydroxide and nickel hydroxide. I am aware that redissolving this stuff and aerating will expel the majority
of the iron salts as Fe(OH)3. If I'm not mistaken, Nickel is also stable in solution, much like copper (II). My only question is if chromium salts
hydrolyze anywhere near as easily as the iron/ Is letting the iron "rust" itself out of solution a feasile method of seperation? I have a nice heap
of brown sludge awaiting separation and will (hopefully) have some chromium salts to play with (Also making nickel salts seperately from this, so the
focus is on salvaging the chromium).
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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guy
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Oh cool, stainless steel has a minimum of 16% Cr. Im gonna start extracting that stuff!
Cr(OH)3 will dissolve in excess NaOH. K = 8×10<sup>29</sup>
http://www.public.asu.edu/~jpbirk/qual/qualanal/chromium.htm...
Also has 10% Ni, which can be removed by ammonia.
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12AX7
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Could also fuse the mixed oxides with KOH and an oxidizer (KNO3 preferred) and leach the chromate. Assuming it doesn't form an insoluble iron or
nickel chromate.
Tim
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UnintentionalChaos
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Excellent info guy...I don't seem to have added too much NaOH since the drainwater is yellow for some reason (probably iron (III) hydroxide on a
colloidial level).
I'd go the brute force 12AX7 way, but other than cans, I don't have any decent crucibles and my only good heat source is a large torch that runs on
disposable tanks (ow my wallet) and isn't very easy to control the temp with.
Anyone trying this should realize that it has to be electrolyzed into the acid. I left a small piece in ~60% sulfuric overnight and not a bit of it
dissolved. Not even H2O2 mixed into the acid could attack it (I used this mix to rip up some US nickels much faster than just sulfuric acid could ever
accomplish).
[Edited on 4-23-07 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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12AX7
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I've got a hunk of horribly badly pitted stainless bar due to leaving it sit in concentrated HCl for weeks.
I don't think H2SO4 forms much of a complex, but HCl does, which is likely the reason the Cr2O3 passivation layer on the metal has given us two
different results for these two acids.
Tim
[Edited on 4-24-2007 by 12AX7]
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guy
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| Quote: | Originally posted by 12AX7
I've got a hunk of horribly badly pitted stainless bar due to leaving it sit in concentrated HCl for weeks.
I don't think H2SO4 forms much of a complex, but HCl does, which is likely the reason the Cr2O3 passivation layer on the metal has given us two
different results for these two acids.
Tim
[Edited on 4-24-2007 by 12AX7] |
so HCl works?
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woelen
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HCl + H2O2 definitely works. HCl alone is VERY slow.
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guy
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So any update on the separation?
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Pyridinium
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I think your strategy sounds good, keep air bubbling into the solution to speed the rusting-out of the Fe. Keep the pH high with excess NaOH so the
Cr hydroxo complex stays in solution.
Sounds like it should work just fine.
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