Neodymium bromate

It has always been assumed that the hydration numbers for the lanthanides are higher than six, probably between 8 and 10, in analogy with the presence of enneaaquo ion [M(OH2)9 +] in neodymium bromate and ethylsulphate (see later, p. 121). Lanthanide hydration numbers have not been rigorously established, but some attempts have been made to study the problem by NMR technique (13—15). It is rather unfortunate that only low value for the hydration numbers ( 6) have been obtained, except for Er(III) and Yb(III) ions (756), where the hydration number is seven. 

Different, more specific, separation techniques were developed, each one having its special characteristics. It could be separation of other double salts - nitrates, oxalates - composed of a RE metal ion and another cation present in the solution, for example K+, Na+, NH or Mg. Double ammonium nitrate may be used for removal of lanthanum and the separation of neodymium from praseodymium. Members within the cerium group may be separated using double manganese nitrates, while elements in the yttrium group are separated using the differences in solubihty of their bromates. Auer von Welsbach did much work with RE-ammonium oxalate systems. Charles James in the USA developed an effective technique with RE-magne-sium double salts. 

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