Studies on complexation and solvent extraction of lanthanides in the presence of diaza-18-crown-6-di-isopropionic acid.
Stability constants of some lanthanides with K22DAP (diaza-18-crown-6-diisopropionic acid) were determined by potentiometric titration method. The logarithmic values of these constants for La(III), Nd(III), Sm(III), Gd(III), Tb(III), Dy(III), Er(III), and Lu(III) are 11.14, 11.43, 11.78, 11.74, 11.95, 12.09, 11.49, and 10.88, respectively. Solvent extraction studies were carried out on the K22DAP complexes of La(III), Nd(III) and Lu(III) using TTA (thenoyltrifluoroacetone) as an extractant in different diluents. It appears that nitrobenzene, a diluent with high dielectric constant, favors the extraction of the complexes. Extraction rates of the K22DAP complexes of lanthanides were investigated at pH 5.5 and 8.0 with TTA in chloroform. The rates of extraction are found to be dependent upon the nature of the extracted species. Competitive extractions were carried out to see if selective extractions could be achieved.
Enhanced extraction of lanthanides with crown ether carboxylic acids of increasing lipophilicity
sym-Dibenzo-16-crown-5-oxyacetic acid and its modified analogues can extract lanthanides efficiently in solutions with high ionic strength and complex matrices. Increasing the length of the side-arm alkyl group increases the lipophilicity of the macrocyclic polyether and enhances the distribution ratio of the lanthanide complexes in the organic phase. This type of crown ether carboxylic acid is a potential complexing agent for selective extraction and concentration of lanthanides in natural water systems.
Solvent extraction of rare-earth metal ions with thenoyltrifluoroacetone in carbon tetrachloride
Abstract Extraction equilibrium constants for the formation of rare earth ethenoyltrifluoroacetonates, RE(TTA) 3 , have been determined for all rare earths including yttrium. The organic solvent was carbon tetrachloride containing 0·2 M HTTA initially and the aqueous phase was kept at constant ionic strength using 1 M (H,NA)ClO 4 . The liquid-liquid distribution experiments were performed at (23 ± 2)°C, and the values of the extraction equilibrium constants, K 3,0 ∗ , are given in Table 1. The log K 3,0 ∗ , values show the usual increase with atomic number, Z . Additionally, the trend shows a tetrad grouping and is compared with results of early and recent works from the literature. Yttrium is found to have a K 3,0 ∗ value intermediate to those of holmium and erbium.