fusso - 22-6-2019 at 10:22
I'm currently extracting Nd from magnets.
I dissolved 150g of magnets in HCl, filtered out the Ni coating and boron, and waited for a few months to oxidise the Fe2+. Now I added far more than
1kg oxalic acid and 1.5L of 25% NH3, which is a huge excess, but there are still alot of iron oxalate undissolved and I suspect not all Fe2+ is
oxidised to Fe3+. I want to use H2O2 to oxidise the Fe(II) oxalate to Fe(III) oxalate, will H2O2 oxidise oxalate/ic acid to CO2? Are there more info
about Nd & Fe oxalates? Those on wiki are limited and don't have much solubility data.
fusso - 23-6-2019 at 05:20
Update: I used HNO3 as the oxidiser trying to oxidise Fe(II) to Fe(III), but now the green soln turned brown. Can Fe oxalate be protonated and
destroyed?
elementcollector1 - 24-6-2019 at 15:25
A few months alone won't do much to Fe (II) oxalate - it needs to be actively oxidized. I left my oxalate alone for an entire year (went to school
elsewhere in the meantime) and came back to find it unchanged and yellow. A few minutes with concentrated hydrogen peroxide turned the precipitate a
beautiful pink color. Nitric acid might be too strong (and introduces more ions to the mix), so you might get better results by neutralizing back to
pH 7 and then adding more oxalic and some freeze-distilled hydrogen peroxide.
Note that Nd magnets are no longer pure Nd/Fe/B - Gd, Ce and Pr are now significant contaminants.
fusso - 25-6-2019 at 21:30
But I added oxalic after the months of waiting…
fusso - 7-9-2019 at 21:18
I want to use H2O2 to oxidise all Fe2+, will the oxalate part be destroyed?
Pumukli - 7-9-2019 at 21:54
Try it on a small sample. But my gut feeling is it won't.
Keep in mind that H2O2 can be catalytically destroyed by various metal ions! So it won't last long. But hopefully it will oxidize Fe2+ in seconds.
If you don't mind waiting: instead of letting the solution alone for months I'd aerate the liquid with a small aquarium bubbler. Wetting the air
before introducing it into the solution may be necessary (to prevent it drying out) for a longer run.
[Edited on 8-9-2019 by Pumukli]
AJKOER - 8-9-2019 at 06:39
Here is an idea on a possible better path way to dissolving a magnet commencing with removing the most anodic iron first, as a possible route to other
alloy metals. The non-iron metals could, in time, be liberated in the form of a pure metal, or as a metal oxide, or less likely, as a metal
hypochlorite, or a decomposition product of the unstable metal hypochlorite (oxide or chloride).
First, from an electrochemical perspective, the magnet, acting as the anode, should be a solid piece so as to have LOW relative surface area.
I would use activated charcoal, with large surface area, as the cathode in place of air, in a solution of only partially acidified chlorine bleach (a
mix of NaOCl and NaCl) with the choice of acid being vinegar or Citric acid or CO2 (created in situ by say the action of vinegar on baking soda).
Using just HOCl from completely acidified bleach is not recommended due to the creation of some operationally problematic chlorine gas (which can
react with unacidified NaOCl forming HOCl,....).
NaOCl + HOAc --> NaOAc + HOCl
Cl2 + H2O = HCl + HOCl
HCl + NaOCl --> NaCl + HOCl
where by last two reactions:
Cl2 + H2O + NaOCl --> NaCl + 2 HOCl
To reduce the inception period associated with electrochemical reactions, I would jump start the reaction in a microwave (perhaps a minute) and just
briefly due to the eventual expected formation of toxic chlorine fumes. The chemistry is, in part, related to my prior comments on the so called
bleach battery (see https://www.sciencemadness.org/whisper/viewthread.php?tid=30... ), but here Aluminum is replaced by the magnet and copper by activated carbon,
with still a cited product of Cl2.
Some not primary, but related effects, associated with a magnetic field on viscosity, dissolved oxygen content, reaction rate,...., is discussed with
sources at http://www.sciencemadness.org/talk/viewthread.php?tid=77204#... .
The reason for employing carbon is that you are actualy NOT working here with iron, but a more noble alloy composition with likely a much lower anodic
index (closer to the more noble oxygen, where the composition of the magnet has been cited previously above).
Unfortunately, my prior experience working with noble alloy compositions appears to not always work! At times, it produces only minor surface related
oxidation of the more anodic metal. For example, a copper-nickel alloys vs. carbon only produces minor amounts of black CuO coating, which suggests
the intervention of mechanical scrubbing to expose fresh alloy for attack.
Nevertheless, I may, in the future, try this experiment myself to confirm my low expectations.
[Edited on 8-9-2019 by AJKOER]