Solvent extraction techniques stability constant determination

The stepwise stability constants for zirconium and hafnium thiocyanato-complexes have been determined by solvent-extraction techniques. The values ) i = 12.1 2.2, = 215 11, P4. = 205 + 20 for zirconium, and Pi =... 

This is a study of the complexation of zirconium by hydroxide using the solvent extraction technique. Experimental work in the study was conducted at 25°C and in 1.96 M (Li, H)C104. Benzene was used as the organic phase and thenoyltrifluoroacetone (TTA) as the extractant. The hydrolysis data was analysed using the previously determined stability constants determined by Solovkin and Ivantsov [66SOL/IVA] using the same technique. The study therefore suffers from the same deficiencies as before and as such cannot be recommended. 

Tanner and Choppin [133] have determined by solvent extraction techniques the first stability constants and thermodynamic parameters for glycine-M complexation at pH 3.64 and ionic strength 2.0 m (NaC104). The results indicate that the amino acid is coordinated predominantly in the zwitterionic (NH3 CH2CO2) form, in contrast to previous reports claiming the glycine ligand to be in the cationic form. 

Desire, Hussonnois and GuUlaumont (1969) determined stability constants for the species AnOH + for the actinides, plutonium(III), americium(III), curium (III), berkelium(III) and californium (III) using a solvent extraction technique. The stability constants obtained for americium(III) and curium(III) are two orders of magnitude larger than other similar data available in the literature. The stability constants of the lanthanide(III) and actinide(III) ions are very difficult to obtain using solvent extraction due to problems associated with attainment of maximum extraction into the solvent phase before the narrow band of pH between the onset of hydrolysis reactions and the precipitation of solid hydroxide phases. Consequently, the data of Desire, Hussonnois and GuUlaumont (1969) are not retained in this review. 

The physical nature of the sulfate complexes formed by plutonium(III) and plutonium(IV) in 1 M acid 2 M ionic strength perchlorate media has been inferred from thermodynamic parameters for complexation reactions and acid dependence of stability constants. The stability constants of 1 1 and 1 2 complexes were determined by solvent extraction and ion-exchange techniques, and the thermodynamic parameters calculated from the temperature dependence of the stability constants. The data are consistent with the formation of complexes of the form PuSOi,(n-2)+ for the 1 1 complexes of both plutonium(III) and plutonium(IV). The second HSO4 ligand appears to be added without deprotonation in both systems to form complexes of the form PuSOifHSOit(n"3) +. ... 

The free energy is calculated from the stability constant, which can be determined by a number of experimental methods that measure some quantity sensitive to a change in concentration of one of the reactants. Measurement of pH, spectroscopic absorption, redox potential, and distribution coefficient in a solvent extraction system are all common techniques. 

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