The diffusion of exchanged Yb, Ho, and Eu from interlayer positions in montmorillonite was studied using infrared spectroscopy (IR), X-ray powder diffraction, and cation-exchange measurements. Dehydration of exchanged montmorillonite between 100° and 280°C caused the ions to diffuse into the hexagonal rings of surface oxygens. Subsequent migration into vacant octahedral sites was small regardless of the radius of the cation. Considerable ion fixation in excess of the cation-exchange capacity of the clay was observed at 20°C in both water and a 1:1 water:95% ethanol mixture. Evidence for hydrolysis as a possible mechanism for cation fixation was obtained by observing frequency shifts for deuterated hydroxyl groups using IR spectroscopy. A major IR band centered at 2680 cm−1 was observed for all three lanthanide-exchanged montmorillonites studied and assigned to the OH-stretching frequency of a lanthanide hydroxide. This band intensified on heating at 300°C for 1 hr. An IR band between 690 and 710 cm−1 also was observed for all three lanthanide-exchanged montmorillonites and was assigned to a lanthanide-hydroxyl deformation mode. No hydrolysis was observed for Na-montmorillonite, as expected from the very low hydration energy of Na+.

X-ray diffraction, infrared, and cation-exchange capacity measurements of the reaction products of montmorillonites with YbCl3.6H2O show that at 1 atm irreversible sorption of Yb3+ increases with increasing temperature in the range 20° to 280°C, whereas at 110 atm it decreases with increasing temperature. Above 100°C, less irreversible sorption occurs at 110 atm than at 1 atm. The decreased sorption at high pressure is attributed to reduced cation hydrolytic fixation and to rapid expulsion of interlayer Yb3+ by interlayer water at higher temperatures, with a concomitant decrease in Yb3+ migration to octahedral sites. At 110 atm, 160° and 200°C treatments cause changes in infrared absorption bands (884 cm-1, 848 cm-1) suggesting that sorbed Yb3+ is charge compensated by the deprotonation of Fe3+- and Mg2+-hydroxyl groups. At 290°C deprotonation is restricted to Fe3+-hydroxyl groups.

Various secondary phases formed during alteration/dissolution of HLW (high-level nuclear waste) borosilicate glass represent a significant retention potential for radionuclides including divalent actinides. The trioctahedral smectite, hectorite, Na0.7[Li0.7Mg5.3Si8O20(OH)4], is one of the secondary phases identified within the alteration layer of corroded HLW glass. Numerous studies have clearly shown that many radionuclides are associated with clay minerals and the migration of radionuclides is strongly reduced by complexation. Due to the structural complexity and chemical variability of smectites, sorption of radionuclides involves several sorption mechanisms: (1) adsorption via inner-sphere and outer-sphere complexation; (2) cation exchange in the interlayer; and (3) incorporation into the smectite structure. Up to now, it was not known whether trivalent actinides such as Cm(III) and Am(III) become incorporated into the crystal structure of clay minerals like hectorite. We have used a new method, developed by Carrado et al. (1997b), to synthesize a Eu- and a Cm-containing hectorite, utilizing Cm(III) and chemically homologous Eu(III) coprecipitated with Mg(OH)2 as a precursor. X-ray diffraction, Fourier transform infrared spectroscopy and atomic force microscopy identified the reaction products unambiguously as hectorite. The sorption mechanisms of Eu associated with the synthesized hectorite were investigated by time-resolved laser fluorescence spectroscopy (TRLFS). An unhydrated Eu species (fluorescence lifetime 930 µs) and a partly hydrated Eu species (fluorescence lifetime 381 µs) could be identified. The unhydrated Eu species can be interpreted as incorporating Eu(III) into the hectorite structure or a remaining X-ray amorphous silica phase. The spectra of Eu hectorite and the Eu silica complexation are too similar to permit differentiation between these species, but dialysis experiments demonstrated the close association of the unhydrated Eu species with the crystalline hectorite phase. Time-resolved laser fluorescence spectroscopy (TRLFS) measurements identified the same incorporated Eu species as long as the Eu hectorite was stable under acidic conditions. The stability of the Eu hectorite could be shown by the dialysis experiment over a time period of 160 h. Between 160 und 500 h, hectorite became unstable and a new silica phase was detected. In addition, TRLFS measurements of the Cm-containing hectorite confirmed the incorporation of actinides in the smectite structure. The Cm-hectorite and Cm-silica species can be differentiated unambiguously by TRLFS. In order to differentiate between coprecipitated and surface-sorbed Eu species, batch sorption studies were performed with synthetic Eu-free hectorite. For the surface-sorbed Eu species, a fluorescence lifetime of 284 µs (3.1 H2O molecules) was found, which clearly differs from the coprecipitated species with a fluorescence lifetime of 930 µs. The different lifetimes indicate a different chemical environment. Based on all observations it seems to be very likely that trace amounts of Cm/Eu occupy a distorted octahedral site in the hectorite.

In the search for rare earth and other critical elements in coal measures, the coals are emphasized with lesser consideration for the accompanying rocks. In this investigation, the focus is on a lanthanide-rich, 315–317 Ma (after Machlus et al., Chemical Geology, 539, art. no. 119485, 2020) volcanic ash-fall trachyandesite to trachyte tonstein which occurs in association with the Middle Pennsylvanian Duckmantian-age Fire Clay coal in eastern Kentucky. The tonstein was deposited largely during peat accumulation, although it is known to occur at the base of the coal or within the underclay. The mineralogy is dominated by kaolinite with illite and quartz as minor to major minerals. A number of accessory minerals, as detected by X-ray diffraction + Siroquant XRD software and scanning and transmission electron microscopy (S/TEM), include REE-bearing phosphates (apatite, crandallite, florencite, monazite), and Y-bearing zircon. The highest rare earth element + Y concentrations occur in the weathered tonsteins, probably due to the concentration of these minerals after weathering of kaolinite from the rock.

The line connecting rare earth elements (REE) in chondrite-normalised plots can be represented by a smooth polynomial function using λ shape coefficients as described by O'Neill (2016). In this study, computationally generated λ combinations are used to construct artificial chondrite-normalised REE patterns that encompass most REE patterns likely to occur in natural materials. The dominant REE per pattern is identified, which would lead to its inclusion in a hypothetical mineral suffix, had this mineral contained essential REE. Furthermore, negative Ce and Y anomalies, common in natural minerals, are considered in the modelled REE patterns to investigate the effect of their exclusion on the relative abundance of the remainder REE. The dominant REE in a mineral results from distinct pattern shapes requiring specific fractionation processes, thus providing information on its genesis. Minerals dominated by heavy lanthanides are rare or non-existent, even though the present analysis shows that REE patterns dominated by Gd, Dy, Er and Yb are geologically plausible. This discrepancy is caused by the inclusion of Y, which dominates heavy REE budgets, in mineral name suffixes. The focus on Y obscures heavy lanthanide mineral diversity and can lead to various fractionation processes to be overlooked. Samarium dominant minerals are known, even though deemed unlikely by the computational model, suggesting additional fractionation processes that are not well described by λ shape coefficients. Positive Eu anomalies only need to be moderate in minerals depleted in the light REE for Eu to be the dominant REE, thus identifying candidate rocks in which the first Eu dominant mineral might be found. Here, I present an online tool, called ALambdaR that allows interactive control of λ shape coefficients and visualisation of resulting REE patterns.

The capabilities of the asymmetrical flow field-flow fractionation (AsFlFFF) technique coupled with inductively coupled plasma mass spectrometry and UV–Vis spectrophotometry in the characterization of synthetic and natural colloidal samples are demonstrated in two different systems.The first system is a sol of hectorite which was co-precipitated in the presence of Lu. The results show that hectorite nanoparticles can be mobilized from a bulk sample and that they still contain the dopant Lu, which is homogeneously incorporated into the hectorite crystal structure. Thesecond system is a natural groundwater from the Gorleben site on the northern German plain, which is being tentatively explored to assess its suitability as a nuclear waste repository. Colloidal matter heterogeneity is evident in this system. Alkaline-earth elements are mainly found as ionicspecies. Rare earth elements (REEs) and actinides are distributed in two main colloidal fractions: the heavier REEs and U are concentrated in the <4 nm fraction corresponding to the size range of organic colloidal particles, whereas lighter REEs and Th are concentratedin colloidal particles between 4 and 18 nm in size that are both organic and inorganic in nature. Similar results are reported for another sample from the same site, collected ∼2 km from the first one, demonstrating the homogeneity of the aquifer system and/or a possible colloid migrationpathway. The extent of the reversibility of colloid–radionuclide interactions remains to be evaluated.

The formation of uranyl peroxide phases was identified as a corrosion product of spent fuel by Hanson et al [1]. The subsequent analysis of this phase showed that metastudtite retained 241Am, 237Np and 239Pu [2]. In this study, the retention of radionuclide Pu4+ and An3+, released from the spent fuel matrix into studtite structure, has been evaluated by the precipitation of studtite from uranyl dissolution with variable concentrations of REE (Th, Nd, Sm and Eu). Three different precipitation conditions parameters were studied: media of synthesis, time of synthesis and REE concentration. Synthesized phases were characterized by XRD and the cell parameter was calculated. The REE incorporation was determined by ICP-MS analysis. The results showed that studtite could incorporate 63% of Th in solution during its precipitation. Changes in the “a” cell parameter were identified. The results suggest that studtite coprecipitated with REE could play a role as a limiting for the REE mobility.

Twenty seven new rare earth (Ln) compounds CuLn2 Ge2O8, CuLn2Ge4O12 and CuLn2Si4O12 have been synthesized. The powder diagrams were indexed and solid solutions of silicates and germanates were investigated. Structural variations with temperature, lanthanide contraction and Ge/Si substitution are described. Indications for second order phase transitions were found.

The technique of standard addition in combination with powder X-ray diffraction was used to identify and quantify the amount of Ln3+ segregating into secondary phases from Ln3+doped alkaline earth aluminates. Results indicate that Ln3+ ions are more soluble in CaAl2O4 than SrAl2O4 and BaAl2O4, with this being rationalized by the structural details of the A sites. These results indicate that the enhancement of the luminescence afterglow obtained by doping AAl2O4:Eu2+ samples with Ln3+ ions is a result of much lower doping levels than previously thought.

Lanthanide metals such as terbium have previously been shown to be useful for mapping metal-binding sites in RNA. Terbium binds to the same sites on RNA as magnesium, however, with a much higher affinity. Thus, low concentrations of terbium ions can easily displace magnesium and promote phosphodiester backbone scission. At higher concentrations, terbium cleaves RNA in a sequence-independent manner, with a preference for single-stranded, non-Watson–Crick base-paired regions. Here, we show that terbium is a sensitive probe of human tRNALys,3 tertiary structure and folding. When 1 μM tRNA is used, the optimal terbium ion concentration for detecting Mg2+-induced tertiary structural changes is 50–60 μM. Using these concentrations of RNA and terbium, a magnesium-dependent folding transition with a midpoint (KMg) of 2.6 mM is observed for unmodified human tRNALys,3. At lower Tb3+ concentrations, cleavage is restricted to nucleotides that constitute specific metal-binding pockets. This small chemical probe should also be useful for detecting protein induced structural changes in RNA.