What are the dominant uranium species in aqueous nitrate solution in the pH range from 4 to 10?
solution in the pH range from 4 to 10. The U(VI) speciation at a micromolar concentration range at ambient atmosphere has been investigated by computed modeling of updated NEA thermodynamic data and by ATR FT-IR spectroscopy. The significant alterations of the vibrational stretching mode of UO22+ strongly suggest the dominance of mononuclear hydroxo species already at acidic pH. From the spectra recorded at ambient pH several complexes, possibly containing carbonate ligands, can be derived. This is contradictory to the thermodynamic data.I think the following below links may help you in your analysis:
https://pubs.acs.org/doi/abs/10.1021/ic8005103?src=recsys&journalCode=inocaj
https://www.era.lib.ed.ac.uk/bitstream/handle/1842/4267/J74%20ERA.pdf?sequence=1&isAllowed=y
http://eprints.whiterose.ac.uk/1328/2/stewartdi3_Three_resin_based_materials_%28final%29.pdf
Thanks
Dear Isam Eldin Hussein Elgailani ,
I'd not say it is contradictory.
The problem is that heavy metals are not soluble over pH 3 (more or less). So, they became soluble because of complexation with present ions or molecules.
In the case of uranium CO2, it complexes mainly in the form (UO2)+2, Uranyl, because of CO2 that forms (HCO3)-1 and (CO3)-2 in solution.
These CO2 and ions together form a buffer solution effect, proportional to their concentrations of course. remenbering that CO2 is pumped into solution constantly from the air.
It seems that uranyl comes after CO2 interaction with U, and once it is formed, with a +2 charge, it reacts with many other chemical species, but first comes its complexation by CO2.
So, it is possible that uranyl nitrate is also present, in ionic form, but also uranyl sulphates, carbonates, bicarbonates, etc.
In fact, what I have read indicates a lot of chemical complex and ionic species when CO2 is available, but without CO2, uranyl is only formed at very low or very high pH ( 12).
And as you know, complexes are not stable, therefore they have instability constants. Such behaviour destroy and change complexes into new species with pH variation, what I think can be the cause for the apparent contradictory thermodynamic data. I mean something else you didn't take intto accout may be forming or unforming in your solution changing the real thermodynamic value while you think it is a fix group of species.
I hope I've made myself clear.
Good luck!
The thing that I did adsorption test of U using novel adsorbent and found it working very well to adsorb U ions at pH
At pH ≥ 4.8 various oligomeric and monomeric hydrolyzed species of UO22+ are reported. These includes [UO2OH]+, [(UO2)3(OH)4]2+, [(UO2)3(OH)5]+, [(UO2)2(OH)2]2+, , [UO2(OH)4]2- and [(UO2)3(OH)7]– , [(UO2)2OH]3+, [(UO2)3(OH)]5+, [(UO2)4(OH)]7+). In presence of carbonate anions monomeric and oligomeric carbonato species such as [UO2CO3]0, [UO2(CO3)2]2-, [UO2(CO3)3]4- , [(UO2)3(CO3)6]6- , ([UO2(OH)4]2- and [(UO2)3(OH)7]–)may also be formed with different concentrations depending on the pH and the total concentration of UO22+
see: https://www.hindawi.com/journals/je/2016/7214348/
Article Removal of Uranium(VI) from Aqueous Solutions Using Glycidyl...
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