Thorium and Uranium

[chemofun]

Does anybody here know how to separate Uranium from Thorium chemically? I'm not sure how this would be done seeing as how they both have 2 valence electrons. They are pretty close on the periodic table so i don't know if there is enough difference in electronegativity to create different and easy to separate ionic compounds. Any imput from real chemisty buffs would be greatly appreciated. Thanks.

[Marvin]

In terms of practical methods it usually depends on exactly what you have, the metals, nitrates, sulphates etc, what relative amounts of each and what impurities.

Specifically for thorium and uranium only and macroscopic amounts of each, thorium nitrate is more soluable in water than uranium nitrate so fractional crystalisation will seperate them. Uranium nitrate can be extracted from Aq solution to ethyl ether, leaving the thorium nitrate. Thorium can also be precipitated as its sparingly soluable oxalate.

For much smaller amounts of thorium in U solution, again for nitrates, adding ammonium carbonate in large excess and boiling will precipitate thorium as its hydroxide. This can be done fractionally for other contaminants.

U/Th is a fairly easy case and things get more difficult for other members which all have the same problem, s2 p0 outer shell. This is somewhat highlighted by the radioacitivty of this group which demands very high seperation often from a tiny concentrations in one of the other members. Typically the best idea is to oxidise a solution with a mixture of actinides to selectivly force some of them aquire unusual oxidation states (+3, +4 for example). Differences between species can then be exploited, such as solubility in organic solvents, which can vary massivly more according to what oxidation state an ion is in than between two different elements in the same oxidation state. In essence its forcing the f shell differences to come into play by going beyond 2+. This is the basis of the well known dibutyl pthallate based plutonium extraction system.