Separating Chromium from Stainless Steel

[elementcollector1]

I would like to know if anyone can give me a confirmation on the following:

If you take stainless steel, dissolve it in concentrated HCl to get a green solution, and add excess alkali, the chromium will be the only thing left in solution because it forms a complex while nickel, iron, etc. do not.

Is this true? I have a beaker of HCl eating away at the end of a SS fork as we speak, so if it's possible, I'd like to attempt it.

The final product I'd like is chromium (III) oxide.

And also, I'd like to avoid someone telling me "It's easier to buy your own". This is for the educational purposes, people!

[yaracuyKirkhoff]

I would like to know if anyone can give me a confirmation on the following:

If you take stainless steel, dissolve it in concentrated HCl to get a green solution, and add excess alkali, the chromium will be the only thing left in solution because it forms a complex while nickel, iron, etc. do not.

Is this true? I have a beaker of HCl eating away at the end of a SS fork as we speak, so if it's possible, I'd like to attempt it.

The final product I'd like is chromium (III) oxide.

And also, I'd like to avoid someone telling me "It's easier to buy your own". This is for the educational purposes, people!

 

by adding excess alkali will you not get Cr2O3 ?

[elementcollector1]

by adding excess alkali will you not get Cr2O3 ?

 

It'll precipitate out at first along with all the impurities, but if you add a bunch more alkali it will redissolve to give a sodium-chromium double salt (sodium chromate/dichromate). In practice, this didn't really work, everything redissolved.

[elementcollector1]

Actually re-doing this experiment now. The SS is dissolving much slower than it usually does... still yellow from the iron, not green. Give it a few weeks...

Anyway, you will get a pure solution of sodium-chromium salt, but you also have hexavalent chrome on your hands.

Seeing as I plan to use this for chrome plating, this is not much of a problem, but I'd really like a way to convert this back to trivalent chrome (for health reasons).

Upon further research, a potential better method is to use a stainless steel anode in an NaCl solution, as the iron will precipitate out as iron (III) hydroxide from the NaOH / NaOCl formed, while the chromium forms it's usual double-salt.

[John Cuthber]

Sodium metabisulphite ( available from home brewing shops or the web) will convert Cr(VI) to Cr(III).

[elementcollector1]

Excellent, thanks! Is there an exact reaction between Na2CrO4 and Na2S2O5? (Just to see what impurities and precipitates I'd have to deal with).

[chilled_fluorine]

If you're not too afraid, add in 30% hydrogen peroxide until you get a 4:1 hcl to h2o2 ratio. This is MUCH more corrosive, the hcl will dissolve any oxides that might be formed. I got a big piece of SS to dissolve in less than 10 minutes. Piraña bath is much more effective, if you like metal sulphates. It's the same, at least conceptually, but much more dangerous. Stay safe.