guy
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Cannot separate Cr(III)
I hoped to get Cr separated out of stainless steel by formation of [Cr(OH)4]-. It is not working. I used HCl to dissolve the steel so I have CrCl3,
in which the chloride is not labile. So it cannot form the chromate(III) because I get an oxychloride.
H2O2 produces chromate(VI) but is this a good way to separate it? Or should I fuse the precipitate with KNO3?
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12AX7
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If all the chrome is converted to (VI), sure.
Tim
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not_important
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What about adding excess alkali and bubbling air through the mix to take Fe(II) to Fe(III), Cr(III) forming soluble chromites. Filter off the Fe(III)
hydroxide, bubble CO2 through the filtrate to generate Cr(OH)3.
The powdered mineral chromite, approximately F3Cr2O4 with some magnesium replacing iron, sold at potters supply shops, is a better source of chromium
that stainless steel; especially if you are going to be doing alkaline oxidising fusion anyway.
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guy
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| Quote: | Originally posted by not_important
What about adding excess alkali and bubbling air through the mix to take Fe(II) to Fe(III), Cr(III) forming soluble chromites. Filter off the Fe(III)
hydroxide, bubble CO2 through the filtrate to generate Cr(OH)3.
The powdered mineral chromite, approximately F3Cr2O4 with some magnesium replacing iron, sold at potters supply shops, is a better source of chromium
that stainless steel; especially if you are going to be doing alkaline oxidising fusion anyway. |
Well I addressed that in my first post. It won't work; I suspect the very non-labile chloride is preventing the formation of the chromite.
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chromium
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Sorry if it looks like i want to steal the thread but has anyone ever seen any documented and succesful procedure for separating chromium, nickel and
Fe from each other in solution?
It would be great way to get some nice salts (and more than one member has started with this but AFAIK with no success). Everything what i have seen
so far are just ideas that could (or should) work but no actual experimental data on successful procedures.
Some of those that "should" work are of course fractional crystallisation from sulfate solutions, precipitating with NaOH on strictly controlled pH
values, selective plating with controlled voltages etc. but has anyone seen actual experimental data on some of such procedures?
[Edited on 21-7-2007 by chromium]
When all think alike, then no one is thinking. - Walter Lippmann
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S.C. Wack
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Of course, this is well established in the analytical literature. The chlorides in solution are boiled with a large amount of NH4Cl with dropwise
addition of the minimum amount of NH4OH, Ni remaining in solution. Boiling NaOH + H2O2 gives chromate. If you don't care about separating the Fe and
Ni from each other, precipitate with NaOH directly.
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guy
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So I just have done the fusion of the oxide with KNO3 and NaOH and it works very well. However I wonder if oxidation by H2O2 works well too. Would
Fe(OH)3 catalyze the decomposition of H2O2 too much?
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S.C. Wack
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H2O2 is not the most pleasant method to chromate, especially on a large scale. This becomes evident in the doing, but it certainly works and is very
convenient as a fast qualitative test for Cr. If one is going to try to obtain hexavalent Cr by this method, KOH is probably to be recommended over
NaOH, for ease of isolation as dichromate on concentration and acidification.
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