1. Introduction 4208 2. Properties of N-Donors in Solutions 4210 2.1. Basicity 4210 2.1.1. Data on the Protonation of Selected N-Donors 4210 2.2. Protonation in an Organic Solvent 4210 2.3. Protonation of N-Donors in Aqueous Systems 4212 2.3.1. Terpy and Its Derivatives 4212 2.3.2. TPTZ and DMTP 4214 2.3.3. Pyridyl-Substituted Alkaneamines 4214 2.4. Solubility and Distribution between Two Liquid Phases 4214 2.5. Self-Association 4215 2.6. Configuration 4215 2.6.1. Terpy 4215 2.6.2. Other Ligands 4215 2.7. Chemical and Radiation Stability 4216 3. Complexation of Lanthanides(III) and Actinides(III) 4217 3.1. Stability of the Complexes 4217 3.1.1. Dependence of the Complex Stability on the Properties of the Complexant Molecule and the Solvent Properties 4217 3.1.2. Dependencies of Stability Constants on the Atomic Number 4219 3.1.3. Thermodynamics of the Complex Formation 4222 3.2. Composition, Structure, and Reactions of Complexes 4223 3.2.1. Polypyridyls and Their Derivatives 4223 3.2.2. Substituted Di(benzimidazolyl)pyridines 4225 3.2.3. Substituted Di(triazinyl)pyridines and Di(triazinyl)bipyridyl 4226 3.2.4. TPTZ 4226 3.2.5. Heterocycle-Substituted Aliphatic Amines 4227 3.2.6. Electrolyte Behavior 4228 3.2.7. Theoretical Considerations 4228 3.2.8. Kinetics of the Formation and Dissociation of the Complexes 4228 3.2.9. Redox Reactions 4230 3.3. Selective Complexation and Extraction of Actinides(III) over Lanthanides(III) 4230 3.3.1. Selectivity in Homogenous Systems 4230 3.3.2. Selectivity in Two-Liquid-Phase Systems 4231 3.3.3. Effect of Extractant Structure on the Selectivity 4231 3.3.4. Effect of Diluent and Phase Modifier on the Selectivity 4239 3.3.5. Effect of Counterion on the Selectivity 4240 3.3.6. Selectivity with Regard to Other Actinides and Fission Products 4240 3.3.7. The Origin and Prediction of the Selectivity 4240 3.3.8. Significance of Bond Distances 4241 3.3.9. Comparative An(III)-N and Ln(III)-N Bond Distances 4246 3.3.10. Comparative M-N Bond Distances within the Ln(III) and An(III) Series 4247 3.3.11. Application of N-Donors to An(III)/Ln(III) Separation 4250 4. Abbreviations and Symbols 4250 5. References 4250 10.

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Small-angle neutron scattering (SANS) data for the tri-n-butyl phosphate (TBP)-n-octane, HNO(3)-Zr(NO(3))(4) solvent extraction system, obtained under a variety of experimental conditions, have been interpreted using the Baxter model for hard spheres with surface adhesion. The increase in scattering intensity in the low Q range observed when increasing amounts of Zr(NO(3))(4) were extracted into the organic phase was interpreted as arising from interactions between small reverse micelle-like particles containing two to three TBP molecules. Upon extraction of Zr(NO(3))(4), the particles interact through attractive forces between their polar cores with a potential energy that exceeds 2 k(B)T. The interparticle attraction, under suitable conditions, leads to third phase formation. A linear relationship exists between the derivative of the potential energy of attraction with respect to the concentration of nitrate ions in the organic phase and the ionization potential or the hydration enthalpy of the extracted metal cations.

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