Sciencemadness Discussion Board

An effective method for stipping uranyl nitrate from TBP

Gammatron - 20-10-2022 at 20:37

When using tributyl phosphate to extract uranium it takes several washings to recover the uranyl nitrate from the TBP layer. This is annoying, slow and creates large amounts of dilute solutions that can be difficult to handle. I've been wanting to come up with a method to convert the nitrate into a different salt that won't be soluable in the TBP, won't contaminate the product, wont degrade the TBP and won't create a precipitate because that will cause an emulsion that cant be recovered. I came up with a short list of compounds that could possibly achieve this (oxalate, formate, acetate and citrate) and the first one I tried worked exceptionally well which is the oxalate.

I made an arbitrary concentration by dissolving 1g of oxalic acid in 15ml of water, a little heating was used to help dissolve. I combined 5ml of it with 5ml of the TBP and after a bit of mixing I could see the yellow going into the aq phase with a small amount of bubbling at the phase boundary. I heated the aq phase to near boiling and shook vigorously and it effectively cleared out the TBP and successfully moved most of the U into the aq phase.

You can see that even after an attempt to wash with hot water almost all of the the U nitrate stayed in the upper TBP layer in the flask but in my test tube reaction it has gone into the bottom phase. The TBP still looks yellow because of light reflecting from the flask. Uranyl oxalate decomposes on strong heating to UO3 in the presence of oxygen and UO2 without it which is also an advantage because the standard method of creating UO2 is with hydrogen at high temperature, a little scary...

This is a pretty exciting discovery for me as an amateur chemist because I have never read about using any method like this in literature. Industrially they use dilute nitric acid which has been very ineffective for me.

20221021_002436.jpg - 1.1MB

[Edited on 10-21-2022 by Gammatron]

violet sin - 4-11-2022 at 11:15

What procedure are you using? I have not heard of this untill reading your post the other day; interesting stuff. I haven't done any chem with U/Th minerals, but the paper I was reading claimed they had problems stripping the solution effectively after some breakdown products were created in the TBP layer.. they had a clean up prep, runs it with an acid and then a base then water iirc, claimed good as new. here's the document:

I only got to page 22 the other night, so that info isn't hard to find

They talk about diluting with different substances like hexane and some more tailored ones, that influences the total handshake of U from mineral leach solution to the TBP and finally to aqueous collection.

It also talks about bringing over the Pu content with ferrous sulfamate in the U containing fraction? Think that's illegal for us normies iirc Pu is strictly forbidden. I did not get time to fully read up on the paper or anything else. Figured I comment before loosing traction on what I learned the other day.

Interesting stuff you are doing. Have you tried replicating any mineralization with your extracted U compounds? Be cool to have some home made crystals if any were doable.

The Plutonium Bunny - 30-11-2022 at 09:56

Very nice to see some PUREX-type chemistry at the home scale! Quick side question: where did you get the uranium? Love the yellow color.

It wasn't clear from your original post, but are you using pure TBP or diluted TBP? Industrially, the extractant solution is typically 20-30% TBP in a hydrocarbon diluent such as kerosene or n-dodecane. This is done because pure TBP will actually extract metals too strongly, leading to non-selective extraction and impurities. For example, pure TBP will extract Ce(IV), which would be undesirable in industrial PUREX. I would expect that using pure TBP would also extract uranyl more strongly, potentially leading to issues with the stripping step.

Also, with regard to breakdown products in the TBP, those definitely do impact the extraction and stripping of metals. The radiolysis product dibutyl phosphoric acid (HDBP) has very strong extraction for the higher oxidation states (i.e. U(VI), Np(VI), Ce(IV) to name a few), and this can greatly hinder stripping. In PUREX on used nuclear fuel (UNF) with high radiation fields, the TBP is recycled through a base scrub contact (they may use sodium carbonate for this) to scrub HDBP before the TBP is contacted with more dissolved fuel.

I wouldn't expect freshly purchased TBP to have much HDBP, but if you wanted to be sure, one purification process for the 30% TBP in dodecane commonly used is this:
- Wash with 0.25 M sodium carbonate, 2:1 organic:aqueous by volume, 3x
- Wash with 0.1 M nitric acid, 1:1 organic:aqueous, 1x

Indeed, ferrous sulfamate is used to recover the Pu from the organic phase. Fe(II) reduces the Pu(IV) to Pu(III) (a beautiful blue-purple color), which is not well extracted by TBP and strips into the aqueous phase.

Gammatron - 30-11-2022 at 18:59

I got the TBP from a buddy who is a professional chemist but I'm not sure where he got it from, the cheapest source ive found online is Alibaba at $80/Kg. I used 70% kerosene from ace hardware as it was the cheapest readily available source. I'm not sure how pure it is but it seems pretty clean.

I know the TBP breaks down after several uses and I noticed it becoming more difficult to extract and recover the U nitrate with each use. With my last run I wasn't even able to recover it with the oxalic acid so I think it's pretty much expired. I doubt radiolysis played much of a role since U is a weak source and I've only done pretty small batches but I think I will try to cleanit up to see if i can get any more use out of it. I would honestly say the process is not that practical for a home lab since extracting with a carbonate leach and peroxide precipitation is extremely effective on its own.

Unfortunately Pu will probably never be in reach for me but U ore is abundantly available in the American west.

Gammatron - 30-11-2022 at 19:01

Also I have written about my extraction process on my WordPress site if anyone is interested but it's pretty much the same as the industrial process just using lab glassware.