Lion850
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Report on making praseodymium sulphate
I was keen to try a praseodymium salt because my favourite colour is green! Praseodymium oxide was purchased from a pottery supplier. This is the dark
brown oxide, Pr6O11. The oxide was reacted with sulphuric acid in stages, and the sulphate crystallized out by making use of the drop in solubility of
praseodymium sulphate in water as the temperature increases. The equation:
1Pr6O11 + 9H2SO4 = 3Pr2(SO4)3 +1O2 + 9H2O.
The sulphate obtained was hydrated, probably a mix of the octahydrate and pentahydrate (refer to http://praseodymium.atomistry.com/praseodymium_sulphate.html). Procedure followed:
- 15g water and 10g H2SO4 (98%) in beaker
- Add 10g Pr6O11 and stir
- After an hour, a green solution but lots of unreacted oxide remaining.
- Decant off and filter the green solution.
- Add 10ml water and 10ml H2SO4 (98%) to the beaker with the remaining oxide and gentle heating.
- At a certain temperature a reaction started and quickly completed, all brown oxide consumed and now a grey suspension in solution.
- Add the previously decanted green solution back into the beaker.
- Solution slowly became more green as the dehydrated sulphate could dissolve in the bigger water volume.
- Add another 10g Pr6O11 (acid was in excess) and heat.
- Again a sudden reaction near boiling point, gas appeared to have been released. Solution now grey.
- Add water to increase total volume to 400ml (Pr2(SO4)3 is not that soluble at my ambient temp of 30 C).
- All dissolved, clear green solution. Acid still in excess.
- Add 5g Pr6O11. Solution turns dark, and slowly lightens as oxide reacts.
- Add 4g Pr6O11 and boil down to 200ml. Leave to stir overnight while cooling.
- Next day: Green solution with some unreacted oxide remaining and some undissolved sulphate (whitish).
- Decant off green solution and filter.
- Add 5g H2SO4 (98%) to the remains in beaker, nearly all oxide converted to whitish sulphate.
- Add water in 50ml lots with stirring in-between until all sulphate dissolved. Filter the solution, now a total of 400ml lovely green solution. See
photo.
- Heat to boiling – light green suspension of sulphate falling out of solution. Boil down from 400 to 200ml volume. Observed that this compound can
be boiled down while in suspension with very little bumping (as long as it is also being stirred).
- Filter the 200ml boiling solution in the buchner vacuum filter. Wash the remainder twice with boiling water to remove acid that may still be
present.
- Left to dry overnight. Moved into the sun in the morning under a stainless dish. Left in the sun for 8 hours.
- 36g of dry green crystals. See photos.
  
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Bezaleel
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Hi Lion850,
I guess you learned what I learned also when I tried to make Pr sulphate.
* Use dilute sulphuric acid. Some 15% is good, stronger not recommended.
* Stir at standard temperature until no further oxide will dissolve (the solution needs excess acid to dissolve the oxide)
* Decant / filter
* Heat until boiling to crystallise the Pr-sulphate
* Solutions of the crystallised Pr-sulphate will be acid when dissolved in pH 7 water. One way to create a neutral solution is to add Pr(OH)3, which
you can make by adding excess ammonia solution to the Pr-sulphate solution; another way is to calcine your Pr-Sulphate. After 2 rounds of intense
calcination (over 400C) and subsequent dissolving, the pH of the solution of Pr-sulphate will be around 6.
* Pr-sulphate forms beautiful crystals, check here.
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Lion850
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Hi Bezaleel I’ve not tried to grow big crystals but they do look beautiful! Thanks for the other info.
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Herr Haber
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Did you take a picture of your crystals ?Please share if you have.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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Boffis
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Have you tried adding a little hydrogen peroxide to the sulphuric to assist with dissolution of the praseodymium oxide. It acts by reducing the PrIV
part of the oxide making the whole more readily soluble.
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Bezaleel
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Did you ask me or Lion850? Mine are in the link I gave.
BTW The crystal keep well: 3 years later, it's still as shiny as were when I took the pictures in 2017.
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