YT2095 - 18-7-2007 at 06:56
I`m trying to obtain UO2 via the Oxalate route from Uranyl Nitrate, a source says that the simple addition of Oxalic acid to Uranyl Nitrate soln will
ppt the oxalate.
well I tried this and it didn`t, so I thought how about Sodium Oxalate (that seemed to make more sense to me) and it still didn`t ppt.
I don`t want to directly decomp the nitrate, a wet reaction only is what I`m after.
sadly I seem to be having a blonde moment!
anyone have any ideas?
12AX7 - 18-7-2007 at 13:55
Uranyl nitrate is probably acidic? Adding a few percent oxalic acid will just make that worse, and oxalate is a weak acid compared to nitric. So, it
just sits there with protons hanging on, not able to cling to Uranus-named atoms.
(I had to put in some sort of "cling to Uranus" reference, and even made grammatical sense with it! 
)
Tim
not_important - 18-7-2007 at 21:15
Uranium forms complexes with oxalic acid, and with many other anions as well. LANL sez to do it in 2-3N HCl, no more than a 10% excess of oxalic acid,
chill the solution and let it stand for some time.
There is a basic problem with what you propose to do. Uranyl nitrate is [U(VI+)O2](2+)(NO3)2 Just adding oxalic acid gives UO2(C2O4).3H2O, still
hexavalent uranium. Heating it will give U3O8. To get UO2 you would have to ignite the oxalate in a stream of hydrogen, heating UO2 in air gives
U3O8, the hydrated forms can be oxidised to hydrated UO3 by air.
Exposing a solution of a uranyl salt and oxalic acid to sunlight results in a dark green precipitate of U(C2O4)2. It's proably best to have enough
ammonium oxalate to combine with 1/2 to 3/4 of the anion of the uranyl salt, and an excess of oxalic acid over what is needed to reduce U(VI) to
U(IV).
.