Neodymium iodide synthesis - powder supplied also contains Praseodymium?

I received my neodymium fine powder from China a few months ago and eventually got round to trying to make the iodide. Things did not go as expected, most like due to the powder being contaminated.
The reaction was supposed to be:
2Nd (4g) + 3I2 (11g) = NdI3 (15g).
Water to be used as the reaction solvent.
- 100ml water with 1g Nd powder in beaker on hot plate stirrer. Stir, no heat. Grey solution due to fine metal swirling around.
- Add 2g I2. Just stir, no heat.
- After 5 minutes the solution turned olive green. Which made me excited as some suppliers mentions NdI3 as green crystals.
- After 4 minutes add 1.4g Nd (total now 2.4) and 4g I2 (total now 6).
- At 2 minutes add 2.6g Nd (total now 5) to make sure slight excess and thus consume all the iodine. Solution unexpectedly turned dark brown in a matter of a minute.
- Add 5g I2 (total 8).
- After 10 minutes add 3.7g I2 (total 11.7) and 1.2g Nd (total now 6.2).
Final totals: Nd 6.2g, I2 11.7g. Thus Nd in excess.
- At the 30 minute mark, start to heat. Solution stays dark brown but offgassing iodine fumes when hot.
- Transfer to big beaker and 400ml water (in case low solubility of something was an issue although this was not expected).
- Stir another 3 hours. Stop for the night (no stirring) to see if there is a ppt in the morning.
- Next morning brown solution and brown ppt. Stir and heat again to boiling but no further iodine offgassing.
- Add 1g iodine to confirm offgassing starts again - it did.
- Increase water to 500 and boil strongly for an hour. After this no more iodine offgassing.
- Filer hot. Boil down to 150ml. Filter. Boil down to 50. Filter.
- Left with light brown-gold solution with a hint of lavender.
- Heat the filtrate in steam bath for hours until a crust with very little liquid. Into the desiccator under vacuum overnight.
- Gather together all the brown ppt and dry overnight.
Next day: Dry brown ppt crystals = 6.5g. The Iodide crystals dried nicely in the desiccator and yield was 11g. Color a mix of brown and yellow with some lavender (not so clear on the photo).

But what did I have? The brown ppt made no sense. Time to do some tests.

The "neodymium" powder as received sticks to a magnet. The brown ppt does not. Neodymium (and other rare earths) are indeed magnetic.

- The iodide is very hygroscopic. A weak solution in water is very pale yellow with a hint of lavender. It gives bright yellow PbI2 with Pb(NO3)2. With NaOH a it gives a lavender-whitish ppt. So this is looking promising for being neodymium iodide.

- The brown ppt seems very stable. Insoluble in water. It gravity filters out quite quickly (unlike precipitated iron hydroxide which is very fine).

- The "neodymium" powder dissolves easily in concentrated HCl to give a green solution that slowly turns yellow. In dilute HCl the solution is yellow straight away when the metal powder is dissolved. Yellow should not be the color for neodymium so this is probably due to the presence of another metal.

- The brown ppt dissolves easily in dilute HCl giving a yellow-gold solution. This solution in turn gives a very dark brown ppt with NaOH, still brown but almost looks black. Probably the same ppt as the original ppt.

Assuming there is mostly neodymium in the bottle I received but it is mixed with another rare earth, for now I can only see praseodymium to fit the bill because of the dark brown insoluble ppt and yellow solutions. And green initially with the strong HCl.

Could it be that for some reason the neodymium preferentially reacted with the iodine, forming NdI3 which in turn when dissolved in water give the lavender ppt with NaOH? And the praseodymium, maybe after activation by the iodine, reacted with water to form the brown oxide as ppt?

Any ideas will be very welcome! Photos attached in sequence, I hope the file name comes up when a mouse is over each photo.

False Neodymium

Hi,

Two Neodymium metal powder commands from Ebay China and two false item...

Lanthane metal powder XRF certified insteade Neodymium metal power

Quote: Originally posted by Bezaleel

When I made this from magnets, I precipitated the rare earth with oxalic acid. Iron oxalate will stay in solution. If you calcine the RE oxalate, and the colour is brown, then you will have Pr mixed in with you Nd. Calcination of pure Nd oxalate yields a bluish oxide.

Thanks to all the suggestions. Poormanschemist suggested acetic acid may also be worth a try: if iron can get to iron (iii) acetate it should ppt out. I did not have a lot of free time the last 2 days but tried with both oxalic acid and acetic acid.

Acetic acid:
- 60ml glacial acetic acid
- 5g powder
- Stir and heat
- Solution initially silver-grey from metal but quickly turned purple
- Soon afterwards turned brown
- Stir vigorously to get air to mix in plus bubble in air
- Very dark brown. Stop after another 30 minutes of stirring.
- Filter twice. Dark wine-red solution (see photo) and very dark brown ppt on filter paper. With NaOH this red solution gives a dark grey ppt. All metal powder seems to have been consumed.
- The filtrate was boiled down and is now drying under vacuum in the desiccator overnight. But it appears to be very dark purple-red almost black, I have no idea what this is.

Oxalic acid:
- 25g oxalic acid in 100ml water.
- 5g powder
- Some bubbles initially but then nothing.
- Add 5ml 6% H2O2
- Stir and heat a bit. Stop every so often to check color. Steadily becoming greener.
- Filer a bit of the solution and check with NaOH. Pale grey ppt - see photo.
- Stir another hour - green solution and still appears to be lots of metal left. But the metal is not sticking to the stir as easily as before - maybe because wet. Iron filings whether wet or dry is much more difficult to remove from the stir bar.
- Stirring will continue overnight.

Gents please tell me what you think and what I should be doing different. With the amounts of acid I used I though the oxalic acid was more in excess than the acetic acid but the reaction in the acetic acid proceeded to the point of consuming all the powder quite fast. I had some trouble to get equations into the app I use for stoichiometry maybe I messed up.

The supplier in China said he would contact his supplier and get back to me.....let's see.

The supplier eventually said the powder should be neodymium, but maybe not at the published purity. So I wanted to have another go at extracting neodymium. I decided to try and make use of the fact that the solubility of neodymium sulfate in water drops off dramatically as the water approached 100C.

I dissolved 15g powder in 15ml of 98% H2SO4 diluted with 15ml water. The powder quickly reacted and formed a grey ppt. I then added water 50ml at a time with stirring in-between until all the ppt dissolved. This resulted in a 400ml solution with a blackish lavender solution.

This solution was filtered, yielding a clear lavender filtrate. There was some black powder remaining on the filter paper, but not much. The filtrate was heated to boiling and boiled down. A copious amount of lavender ppt quickly fell out and by the time the volume was reduced (by boiling) to 300ml I abandoned more boiling as the bumping became excessive (and I was in a hurry.....)

I filtered the near boiling solution under vacuum, and washed the remainder 3 times with boiling water to get rid of excess acid. The remainder started forming beautiful lavender crystals while it was still in the filter. It was then further dried under a steel dish in the sun. This gave hard dry lavender crystals. See photo. These crystals looks exactly like the neodymium sulfate I made from the oxide I purchased, so I was reasonably happy I managed to get good sulfate from the powder.

I then used a bit of the sulfate to make neodymium oxalate (double displacement with potassium oxalate) and neodymium carbonate (double displacement with ammonium carbonate). Both are pale purple powders, see photo but the photo does not do the color justice. It's more purple to the eye.

The only test I did with the oxalate and carbonate was to test how they react with concentrated hydrochloric acid = the oxalate does nothing, and the carbonate reacts vigorously with lots of bubbles and dissolves into a lavender solution.

I cannot find much info on neodymium carbonate, other than some supplier offers. If anyone can point me towards online info about the carbonate I will appreciate it.

Quote: Originally posted by Lion850

I cannot find much info on neodymium carbonate, other than some supplier offers. If anyone can point me towards online info about the carbonate I will appreciate it.