Trivalent ionic strength dependence

For a given ionic strength, //, depends on the nature of the coextracted anion A-. To allow the formation and extraction of the neutral complex, the coextracted mineral anion A- has to lose part (or all) of its hydration shell. The smaller the hydration energy of the mineral anion is, the easier is its transfer to the organic phase, and thus the higher is the affinity of the solvation extractant toward trivalent 4/ and 5/ elements (29, 76), as observed in the series chloride < nitrate < perchlorate < pertechnetate, which inversely follows the anion hydration energy order AG/CI ) > AG/NO3) > AG(,(CI04) > AG/TcO/. 

At a finite distance, where the surface does not come into molecular contact, equilibrium is reached between electrodynamic attractive and electrostatic repulsive forces (secondary minimum). At smaller distance there is a net energy barrier. Once overcome, the combination of strong short-range electrostatic repulsive forces and van der Waals attractive forces leads to a deep primary minimum. Both the height of the barrier and secondary minimum depend on the ionic strength and electrostatic charges. The energy barrier is decreased in the presence of electrolytes (monovalent < divalent [Pg.355]

Citric acid complexes are soluble in water, but exist also water-insoluble complexes, their speciation and properties are depending on the oxidation state of metal cation, ionic strength, pH and temperature. Citrate complexes were investigated by a variety of experimental methods but evidently the potentiometric titration technique and spectroscopic methods prevailed. Available in the hterature investigations were directed mainly to citrate complexes with alkali metals and alkaline earth metals, Na, K+Ca and Mg % considering that they are major components of natural waters and biological fluids. Other important group of complexes is these with divalent and trivalent metal cations (Cu Ni +, Cu, Ni, Fe % Tl ). 

---