condennnsa
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chromium extraction from SS
Hi everyone. Is it possible to extract chromium from stainless steel using a process similar to the electrorefining of copper? I remember that one
time i was playing with salt water electrolysis and i used a SS anode and the solution turned a deep violet color, which i think was CrCl3. Will there
be a deposit of chromium on the cathode?
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not_important
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There isn't a whole lot of chromium in most stainless steels, so they're not the best source.
Chromium is fairly electropositive and somewhat difficult to electroplate. The less reactive metals such as iron and nickle will likely plate out
instead.
Electrowinning and electrorefining generally work best when the metal you want is noticeably less electropositive than contaminating metals, and/or
where contaminating metals are much less electropositive and less reactive than the metal being refined. Generally the metal makes up 90% or better
of the anode.
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chief
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I wondered about that too; a single waching-machine-drum will contain maybe 15% of its mass in chromium ...
==> which makes several 100 g
The whole could be anodically dissolved in some NaCl-solution, within no time ...
==> then after decanting 2 or 3 times with water there could be filtered and dried an oxide-mixture, consisting of various Fe-and
Cr-Oxides/hydroxides etc. ...
=======================
Then plain old chemistry would have to be applied to separate the oxides ...; maybe the mixture could be glowed up to some themperature which would
leave the iron-oxides in a Fe2O3-state, for later magnetical separation ?
Somehow the Fe-Oxides would have to be eliminated ...
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not_important
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Remember that the alloys generally contain Mo, Ni, Mn, an/or other metals. This makes the separation a bit more difficult.
Heating mixed iron and chromium oxides is a decent way to make chromite, or similar minerals if there's also nickle or manganese oxides. Standard wet
chemistry is more likely to work.
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condennnsa
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So what exactly will the electrolysis of nacl solution with stainless steel anodes yield?
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The WiZard is In
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Run chromium recovery scrap through Google.com/patents.
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blogfast25
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Cr [+III] is slightly amfoteric, so that would help separating from non-amfoterics... Lixiviate as chromites...
[Edited on 9-5-2010 by blogfast25]
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Melgar
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I actually did this. I had some scrap stainless steel tubing and broke it up into short pieces. Then I took one of those chemical hand warmers and
opened it up into some hydrochloric acid. Those things are mostly reduced iron powder, so my theory was the iron would scavenge all the free O2 and
there wouldn't be any to form a chromium oxide layer, thus exposing the metal to the HCl. It worked, and the acid gradually turned dark green, though
now I'm not sure if the iron powder was necessary. Of course, there was a yellow color too from the iron chloride. The jar of acid bubbled for a
couple weeks, though I probably could have sped it up by heating it. I think it would be possible to separate the metals by electroplating them out,
then switching electrodes as the different metals are depleted. At least I think it should work to separate iron and chromium.
Still, bottom line is it's definitely possible to dissolve stainless steel in hydrochloric acid, saving you from messing around with wires and power
supplies. Also, if you're going to go through all that trouble, start with stainless steel of known composition. For example, 304 stainless steel.
That way you know exactly what metals you have to deal with.
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chief
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Stainless steel dissolves in hot HCl: When I used to boil down freshly-made chloride-solutions (HCl+ carbonate) in stainless-steel-vessels
==> the residual HCl engaged in dissolving the steel, roughening up the surface ... ; solutions turned yellow-green ...
Anyhow with the 5 V @ 20 A from a computer-supply and some plain NaCl-solution it will be a matter of minutes/few hours to dissolve larger amounts of
stainless steel ...
==> The chromium-plating from something can be stripped as well ... : Once I had no other means to break a lock in ther basement, of which the key
was lost: After 1 h at 3 A ther chromium-plating as well as the 7mm-steel was history ...
==> usually the metals dissolve and ppt. as some very fine hydroxides ..., when e- and NaCl-soluition is used ...; they don't stay in the liquid
phase...
[Edited on 10-5-2010 by chief]
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