Solubility of rare earth metal bromides and iodides in aqueous systems

Assessment of the toxicity of a mixture of five rare earth elements found in aquatic ecosystems in Hydra vulgaris

Rare earth elements (REEs) are considered critical elements for technology and their extraction through mining activities is expected to increase in the future. Due to their chemical similarities, they often co-occur in minerals and thus their ecotoxicity should be assessed as a group/family. However, the available ecotoxicological studies focused mainly on the evaluation of the potential toxicological impacts of individual REEs rather than their mixtures. The aim of this study was therefore to evaluate the toxicity of a representative mixture of five REEs (La, Ce, Pr, Nd and Sm) spanning environmentally relevant concentrations ranging from 0.05X (29 µg REEs L^-1) to 5X (2926 µg REEs L^-1) to the test organism, Hydra vulgaris, at the morphological, reproductive and regenerative levels. The data showed that lethality occurred at concentrations near (2.5 fold) to those inducing sublethal effects after chronic exposure of 7 days. The mixture affected reproduction and head regeneration and even lethality at concentrations even below those reported at environmental concentration (0.5X = 293 µg REEs L^-1) in lakes. This suggests that REEs concentrations found in lakes near mining activities could disrupt regeneration and impair embryonic development. Our data also revealed that combining the 5 REEs results in an antagonistic effect, suggesting that those elements share the same receptor and that low molecular weight and high radius elements (approaching iron) were less toxic. Taken together, hydra could be used as a sensitive model organism for the assessment of aquatic ecotoxicological risks of REE mixtures but further analyses of biochemical and gene expressions should improve our understanding of the long-term effects of REEs mixtures.

Gram-Scale Synthesis of Nanosized Li3 HoBr6 Solid Electrolyte for All-Solid-State Li-Se Battery

Rare earth (RE) based halide solid electrolytes (HEs) are recently considered as research hotspots in the field of all-solid-state batteries (ASSBs). The RE-based HEs possess high ionic conductivity, credible deformability, and good stability, which can bring excellent electrochemical performances for ASSBs. However, the conventional synthetic methods of RE HEs are a mechanochemical process and co-melting strategy, both approaches require expensive raw materials and sophisticated equipment. Therefore, a lot of research work is required to promote the preparation methods for these promising SSEs in ASSBs. Thus, a vacuum evaporation-assisted synthesis method is developed for the massive synthesis of HEs. The as-prepared Li₃ HoBr₆ (LHB) has a high lithium-ion conductivity close to the mS cm^-1 level and the LHB-based Li-Se ASSBs can be assembled by cold pressing. Theoretical calculations have revealed that the Li migrations are highly preferred in Li₃ HoBr₆ owing to the low energy cost and high tolerance of stable structure. The tetrahedral and octahedral pathways are responsible for Li migrations in short and long ranges, respectively. The results show that the LHB-based Li-Se battery has good stability and rate performance, indicating that LHB has potential application in the field of ASSBs.

Ecotoxicity responses of the freshwater cnidarian Hydra attenuata to 11 rare earth elements

Lanthanides are the major family of rare earth elements (REEs) owing to the essential properties these metallic species provide in diverse fields of today's world economy. They are now being mined and produced as never before. This raises new environmental concerns in terms of their expected future discharges notably to aquatic systems. Interspecies studies of their ecotoxicity are sparse and effects on aquatic life are still poorly understood. Absence of such information for cnidarians, an ecologically relevant freshwater community, thus prompted the present research on REEs toxicity using Hydra attenuata as our animal model. Lethal and sublethal ecotoxicity data generated with the 11 REEs displayed LC50 values ranging from 0.21 to 0.77 mg L^-1and EC50 values ranging from 0.02 to 0.27 mg L^-1, thereby confirming the inherent sensitivity of Hydra to REE exposure at environmentally relevant concentrations. Additionally, two properties of REEs were shown to modulate Hydra (sub)lethal toxicity (LC50 and EC50) which decreases with increasing atomic number and with decreasing ionic radius. Compared to studies carried out with different taxonomic groups, Hydra toxicity responses to REEs proved to be among the most sensitive, along with those of other invertebrate species (i.e., Daphnia magna, Ceriodaphnia dubia, Hyalella azteca), suggesting that members of this community are likely more at risk to eventual REE discharges in aquatic environments. Demonstrated Hydra sensitivity to REE exposure strongly justifies their future use in toxicity testing battery approaches to evaluate liquid samples suspected of harbouring REEs.

Solubility and the periodic table of elements

Interesting general tendencies of changes of solubilities of elements and groups of compounds may be observed when the corresponding solubility data are arrayed according to the increasing atomic number of the elements. Such trends are exemplified with the data of various systems (metallic and salt-water type) evaluated in several volumes of the IUPAC-NIST Solubility Data Series. The solubilities of elements in mercury as well as in liquid alkali metals, when ordered according their atomic numbers, change roughly in a corresponding way as the temperatures and energies of melting or boiling points of the elements. However, majority of transition metals dissolved in alkali metals are subject to some side reactions with nonmetallic impurities that may drastically elevate their concentration levels. The solubilities of intermetallic compounds in mercury depend primarily on the energies of formation of these intermetallics in the binary alloys and then on the dissolution energies of the component metals in mercury. It has been observed that the experimental solubilities of metal halates in water show quite well defined periodical changes. The arrayed solubility data of rare earth metal fluorides and chlorides in water display quite smooth changes with the increasing atomic numbers if the solutes are isomorphic. Some exceptions from the smooth changes for rare earth metal bromides and iodides are explained. These general observations are useful in evaluating and predicting solubilities in experimentally unknown systems.