Sciencemadness Discussion Board

Uranyl acetate to nitrate

oberkarteufel - 7-7-2020 at 02:29

Some time ago I got interested in an old photography technique called uranotype. For now, the only U source I may have an access to is uranyl acetate, however the technique mentioned calls for the nitrate (probably due to better solubility and thus better color saturation).

I did some reading and came with the following routes:
uranyl acetate -(H2O2)-> peroxide -(heat)-> oxide -(HNO3)-> uranyl nitrate
acetate -(NH4HCO3, heat)-> ammonium uranate -(heat)-> oxide -(HNO3)-> nitrate
Both of them are a bit unfavorable to me, as they require thermal decomposition and I do not quite fancy radioactive powders getting airborne with convection drafts. Not that I cannot countermeasure it, I just prefere not having to; hence wet routes would be favorable.

I thought about a direct reaction of uranyl peroxide with dilute HNO3, but I suspect such mixture could suddenly boil out on its own at best and simply blow up at worst. Given how H2O2 and HNO3 can react I suspect similar behavior with other peroxides.
Also thought about direct conversion acetate -> nitrate by heating with HNO3 and boiling off the acetic acid. I see however 2 drawbacks here - acetic acid has comparable boiling point as 65% nitric (so an excess of the latter would be required), and I am a bit suspicious about heating nitric with organic salts.

Has anyone already done such conversion and can advise on this topic?

Heptylene - 7-7-2020 at 10:45

I have done the purification of uranyl nitrate by the first method:
impure nitrate --> peroxide --> oxide --> purer nitrate. The impure nitrate was obtained from nitric acid dissolution of the mineral autunite. I think acetate will work the same way.

Some advice:

- The reaction with peroxide must be done at a pH of around 3. Below that the peroxide dissolves. Much above you can get uranates. The uranates formed in basic solution redissolve in acidic solutions, so you can adjust the pH with ammonia and nitric acid. I recommend adding the peroxide with an addition funnel into a RBF equipped with a reflux condenser. With such a closed system you avoid spraying a mist of uranium salts everywhere and you can digest the precipitate before filtration. Otherwise the precipitate is very fine and difficult to filter.

- Decompose the peroxide in a crucible with a lid, but do so over several hours by slowly raising the temperature. You want to first decompose the peroxide hydrates to anhydrous peroxide at around 100 °C. Then decompose this to uranium trioxide. I found a final temperature of 400 °C worked well. The preparation and stoichiometry of the oxide is discussed in the article attached below.

- Do not open the crucible while it's hot, as tempting as it may be. As you mentionned, convection currents will carry find uranium oxide dust in the air. I didn't even transfer the product from the crucible afterwards; I added nitric acid directly to avoid dealing with fine powder.

- Uranium has the nice property of being sufficiently radioactive to be detected, but not so much that it poses a radiological hazard (unless inhaled or ingested). So use a geiger counter to find and remove contaminations when you clean up after the reaction.

I do not think dissolving the peroxide with nitric acid will work. As I mentionned, the peroxide dissolves in acidic solution. The paper below also mentions the hydrolysis of uranyl salts as a route to hydrate uranium trioxide.

Attachment: wheeler1964 uranium trioxide preparation.pdf (1MB)
This file has been downloaded 378 times

oberkarteufel - 8-7-2020 at 00:13

Kindly thank you for your answer. Your advice provides a good insight, it can be seen that you've really done this (somehow I'm convinced that you couldn't resist opening the hot crucible ;)).

30% H2O2 needs to be used, or will 3% be sufficient?

UC235 - 8-7-2020 at 19:25

If the uranyl acetate is already pure, just boil it with an excess of nitric acid. The displaced acetic acid should evaporate.

Heptylene - 8-7-2020 at 23:20

Quote: Originally posted by oberkarteufel  
Kindly thank you for your answer. Your advice provides a good insight, it can be seen that you've really done this (somehow I'm convinced that you couldn't resist opening the hot crucible ;)).

30% H2O2 needs to be used, or will 3% be sufficient?

I used 30 % to keep the volumes down. I haven't tried with 3 %.

oberkarteufel - 9-7-2020 at 00:04

@Heptylene - thank you for the information. I might try with 3% first, as it is much less hassle to buy it than 30%, even if it's more expensive per pure H2O2. In case it doesn't work, I'll resolve to 30%. If the solubility is low enough, the concentration of precipitant shouldn't matter that much.

@UC235 - I thought about this, and mentioned it already and stated my concerns. Have you done this on your own or can you provide me with the paper on this topic? I did search on direct uranyl acetate -> nitrate route, but found only some articles on complexes formation, nothing really relevant. I would deal with toxic/corrosive/potentially dangerous mixture, so I want to know beforehand as much about risk/safety as possible. Thus, verified information is really appreciated.

oberkarteufel - 27-8-2020 at 02:03

A little update with a couple conclusions.

3% H2O2 works fine for precipitating uranyl peroxide. As soon as I added it to uranyl acetate solution, a white-yellowish precipitate started to form and the solution started fading into a colorless one.

My hotplate is crap. I couldn't bring the mixture after the reaction to proper boiling, so later the filtration was frustratingly slow. Just as Heptylene had written.

The nitrate is now slowly crystalizing. Unfortunately, it looks like sunny days with proper light intensity are over for this year :D So either I buy some UV lamp or wait till next spring.