Interpretation of Third Phase Formation in the Th(IV)-HNO_3,TBP-n-Octane System with Baxter's 'Sticky Spheres' Model

摘要

Small-angle neutron scattering (SANS) data for the tri-n-butylphosphate (TBP)-n-octane,HNO_3-Th(NO_3)_4 solvent extraction system,obtained under a variety of experimental conditions,have been interpreted using two different models.The particle growth model led to unrealistic results.The Baxter model for hard-spheres with surface adhesion,on the other hand,was more successful.According to this model,the increase in scattering intensity in the low Q range observed when increasing amounts of Th(NO_3)_4 are extracted into the organic phase,has been interpreted as arising from interactions between small reverse micelles containing three TBP molecules.Upon extraction of Th(NO_3)_4,the micelles interact through attractive forces between their polar cores with a potential energy of up to about 2k_BT.The intermicellar attraction,under suitable conditions,leads to third phase formation.Upon phase splitting,most of the solutes of the original organic phase separate in a continuous phase containing interspersed layers of n-octane.