One of our team members had bought erbium oxide and chromium oxide (Cr2O3) from a pottery store.
Our goal was to have Er+3 and Cr+3 in aqueous solution, that we could use for additional experiments.
We quickly realized these were heavily calcinated oxides, since adding 31% HCl at room temperature shows no reaction with either after 2 hours.
A thorough use of the search function brought up several old threads. In summary, it seems like no good options have been found. I think for the
moment we are going to pass on the thermite and bisulfate fusing options.
For erbium chloride, the best aqueous options appear to be to boil the oxide with HCl and let it sit for a week. We also have neodymium oxide, and
will attempt the same procedure. The lower solubility of the sulfates make sulfuric acid a less appealing option, and other members seemed to have
poorer results with sulfuric acid.
For chromium oxide, I did not see any good options. We may just buy chromium (III) sulfate as it is not expensive.
As those threads are a little old, if anyone has any updated information on which acid solutions work best, it would be appreciated. Mods feel free to
merge threads if that is appropriate.
[Edited on 2-1-2021 by ChemTalk]njl - 1-2-2021 at 07:05
Which oxides are you referring to? And what is your goal?ChemTalk - 1-2-2021 at 07:12
Which oxides are you referring to? And what is your goal?
We updated the post to clarify your questions, thanks for your reply.Bezaleel - 1-2-2021 at 07:23
Woelen has on his site a method for dissolving hard calcines Cr2O3. I cannot find the link now.
With dissolving hard calcined Nd2O3 by boiling in concentrated H2SO4, I had some (unreported) success. 100ml of H2SO4 with a spoonful of Nd2O3 gives
of water dropwise (1 drop every few seconds) when heated over a gas flame in a flask with a bend and a cooler attached to it. Temperature stayed below
the boiling point of H2SO4, but minor amounts of H2SO4 came over with the water. You will need a way of filtering off the fine Nd2O3 dust which
remains though. This is so fine it will pass through the finest glass frittes.
I dare not melt the oxide in NaHSO4, for fear of the flask cracking on solidification of the bisulphate.
Refluxing in 36% HCl was completely unsuccessful for my Nd2O3.
Besides, treatment with boiling H2SO4 for several hours is one of the two industtrial was of breaking open Bastnäsite, the other being prolonged
treatment with molten lye.ChemTalk - 1-2-2021 at 08:31
As I was hoping for a cost-effective route to convert the Cr2O3 to aqueous Cr+3, Woelen's procedure, while academically interesting, unfortunately is
not useful for our needs.
I think I may consider the Cr2O3 a lot cause. I'll try HCl with the Er2O3, and nitric or sulfuric acid with the Nd2O3 - keeping the sulfuric acid cold
as Woelen suggests.
[Edited on 2-1-2021 by ChemTalk]njl - 1-2-2021 at 08:33
Try NaOH with your Cr2O3 to get hexahydroxychromate, then perhaps you could recrystallize and acidify to get Cr+3 in solution.
