Effect of phosphate on Uranium speciation

[Dien Li]

HI, Brian

 

Could you please give a quick shot on this simple question. In a simple U-water system, at 2e-6 M, schopite is precipitated at near neutral pH. However, with addtion of HPO4-- at 2e-4 M into the system, the modeling indicated that U became dorminantly soluble U-phosphate species, rather than conventional concept that U would form U phosphate precipitation. Could you please instruct. Thanks.

 

 

DL

U-phosphate speciation-phase diagram.ac2

[Brian Farrell]

Hi DL,

 

It's hard to say what the problem is here. On the one hand, complexes can increase solubility (carbonate reacts strongly with uranium to form aqueous complexes). On the other hand, I know people who have done experimental work with microbial uranium reduction, and they needed to limit the amount of phosphorous in their growth media to prevent precipitation.

 

Uranium chemistry is really complex and an area of active research. It's very possible that important minerals and species are not included in some of the thermodynamic datasets.

 

If possible, I would try to find out what phase or phases people are identifying under similar conditions in the literature. Then check to see whether they are included in any of the datasets, and whether the logK values for their reactions seem appropriate.

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions LLC

[Dien Li]

HI, Brian

 

Thanks you so much. From experimental work it appears that addition of P would reduce the U species solubility and trigger U-P phase precipitation. However, GWB phase disgram showed the opposite way. Yes, it is good to check the database to see if the appropriate U-P phase data were in there. I will check and contact with you again. Thanks.

 

DL