Thermodynamic and structural properties of Gd(III) complexes with polyamino-polycarboxylic ligands: basic compounds for the development of MRI contrast agents

Magnetic (Fe3O4) and nonmagnetic (SiO2 and TiO2) nanoparticles were decorated on their surface with N-[(3-trimethoxysilyl)propyl]ethylenediamine triacetic acid (TMS-EDTA). The aim was to investigate the influence of the substrate on the behavior of these immobilized metal coordinating groups. The nanoparticles functionalized with TMS-EDTA were used for the adsorption and separation of trivalent rare-earth ions from aqueous solutions. The general adsorption capacity of the nanoparticles was very high (100 to 400 mg/g) due to their large surface area. The heavy rare-earth ions are known to have a higher affinity for the coordinating groups than the light rare-earth ions but an additional difference in selectivity was observed between the different nanoparticles. The separation of pairs of rare-earth ions was found to be dependent on the substrate, namely the density of EDTA groups on the surface. The observation that sterical hindrance (or crowding) of immobilized ligands influences the selectivity could pr...

Selective Uptake of Rare Earths from Aqueous Solutions by EDTA-Functionalized Magnetic and Nonmagnetic Nanoparticles

The TALSPEAK Process (Trivalent Actinide Lanthanide Separation with Phosphorus-Reagent Extraction from Aqueous Komplexes) was originally developed at Oak Ridge National Laboratory by B. Weaver and F.A. Kappelmann in the 1960s. It was envisioned initially as an alternative to the TRAMEX process (selective extraction of trivalent actinides by tertiary or quaternary amines over fission product lanthanides from concentrated LiCl solutions). TALSPEAK proposed the selective extraction of trivalent lanthanides away from the actinides, which are retained in the aqueous phase as aminopolycarboxylate complexes. After several decades of research and development, the conventional TALSPEAK process (based on di-(2-ethylhexyl) phosphoric acid (extractant) in 1,4-di-isopropylbenzene (diluent) and a concentrated lactate buffer containing diethylenetriamine-N,N,N’,N”,N”-pentaacetic acid (actinide-selective holdback reagent)) has become a widely recognized benchmark for advanced aqueous partitioning of the trivalent 4f/5f e...

The Chemistry of TALSPEAK: A Review of the Science

To better understand the bonding in complexes of f-elements by polydentate N-donor ligands, the complexation of americium(III) and lanthanide(III) cations by 2-amino-4,6-di-(pyridin-2-yl)-1,3,5-triazine (ADPTZ) was studied using a thermodynamic approach. The stability constants of the 1:1 complexes in a methanol/water mixture (75/25 vol %) were determined by UV−visible spectrophotometry for every lanthanide(III) ion (except promethium), and yttrium(III) and americium(III) cations. The thermodynamic parameters (ΔH°, ΔS°) of complexation were determined from the temperature dependence of the stability constants and by microcalorimetry. The trends of the variations of ΔG°, ΔH°, and ΔS° across the lanthanide series are compared with published results for other tridentate ligands and confirm strongly ionic bonding in the lanthanide−ADPTZ complexes. Comparison of the thermodynamic properties between the Am− and Ln−ADPTZ complexes highlights an increase in stability of the complexes by a factor of 20 in favor of...

Thermodynamic study of the complexation of trivalent actinide and lanthanide cations by ADPTZ, a tridentate N-donor ligand.

The aqueous geochemistry of the rare-earth elements: Critical stability constants for complexes with simple car☐ylic acids at 25°C and 1 bar and their application to nuclear waste management

M.P. Goedken

Papers

The complexation of lanthanides by aminocarboxylate ligands—I: Stability constants

The complexation of lanthanides by aminocarboxylate ligands—II: Thermodynamic parameters