Thiocyanate anion exchange process

Thiocyanate anion-exchange systems have been used to purify americium from rare earths until recently supplanted, a plant-scale thiocyanate ion-exchange process was in long use at the Rocky Flats plant (1960-75) for routine purification of Am recovered from aged plutonium metal [16], This purification scheme was developed at the Los Alamos Scientific Laboratory by Coleman et al. [59]. 

A cation-anion exchange process has recently replaced the hydroxide precipitation and thiocyanate ion-exchange systems formerly used at the Rocky Flats plant for recovering Am from solutions of spent NaCl-KCl-MgCl2 salt residues [63]. 

Ion exchange techniques have been widely applied in the separation process. In the large-scale ammonium thiocyanate process, the metal is retained on strong base anion exchanger thus, separating it from the lighter lanthanide elements which are not strongly absorbed on the resin. 

Trivalent americium forms relatively unstable complexes with Cl and NOs and more stable complexes with the thiocyanate ion CNS. These americium complexes are more stable than those of the corresponding lanthanide compounds, so that americium can be separated from trivalent lanthanides by anion exchange with concentrated solutions of liQ, liNOs, or NH4CNS. Trivalent americium can be extracted with TBP from a concentrated nitrate solution. It can also be extracted with TBP from a molten LINO3 -KNOs eutectic at 150°C, with much higher distribution coefficients than in extraction from aqueous solutions. Americium is more readily extracted by this process than is trivalent curium [K2]. 

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