I have commented before about uranium and its affinity for carbonate. The reaction of uranium(VI) cations with water can form uranyl dications (O=U=O)2+ which are able to bind to carbonate. Both mononuclear and polynuclear complexes are possible, the term polynuclear means a metal complex where more than one metal atom is present in it.
In a paper by P.G. Allen, J.J. Bucher, D.L. Clark, N.M. Edelstein, S.A. Ekberg, J.W. Gohdes, E.A. Hudson, N. Kaltsoyannis, W.W. Lukens, M.P. Neu, P.D. Palmer, T. Reich, D.K. Shuh, C.D. Tait and B.D. Zwick (Inorganic Chemistry, 1995, 34, 4797) a complex containing three uranium atoms has been reported. Below I am showing the structure of the [(UO2)3(CO3)6]6- anion first here is a ball and stick view.
Now here is the space filling view of the same complex.
I hope to be able to write more on the subject of uranium and carbonate later.