Rare earth element profile

Trace elements also exhibit systematic changes in concentration with depth. Figure 8.37 shows, for instance, concentration profiles of rare earth elements (REE) determined by De Baar et al. (1985) in Pacific and Atlantic waters. Note that the concentration profiles differ for the various elements in the series in particular, the amount of Ce is quite high in surface waters of the Atlantic Ocean. 

Fig. 2. Line profiles of some rare earth element atomic emission lines in inductively coupled plasma atomic emission spectrometry (photographic measurements obtained with a high-resolution grating spectrograph) ...

Authigenic Deposits. Carbon Cycle. Cenozoic Climate - Oxygen Isotope Evidence. Cenozoic Oceans - Carbon Cycle Models. Cosmogenic Isotopes. Mid-Ocean Ridge Geochemistry and Petrology. Rare Earth Elements and their Isotopes in the Ocean. River Inputs. Stable Carbon Isotope Variations in the Ocean. Uranium-Thorium Series Isotopes in Ocean Profiles. 

Land, M., Ohlander, B., Ingri, J., Thunberg, J., 1999. Solid speciation and fractionation of rare earth elements in a spodosol profile from northern Sweden as revealed by sequential extraction. Chem. Geol. 160, 121-138. 

Previously reported bis(amidate)- and tethered-amidate-supported zirconium complexes can be used for alkene hydroamination catalysis, and all substrate scope and mechanistic investigations of these systems are consistent with the [2+2] cycloaddition mechanistic profile [61, 62). However, more recent catalyst systems that can be used with secondary amines show broader substrate scope, similar to that attained by rare earth elements and suggest a mechanistic similarity to that observed for previously intensely investigated rare earth hydroamination catalyst systems [7j. Such complexes are proposed to achieve ring closure via o-bond insertion, and thus, consideration of such a mechanistic profile in this case demanded further investigation. 

Once again, this proton-assisted mechanistic profile allows for previously unattainable reactivity, in that this overall neutral complex is capable of achieving alkene hydroamination at room temperature with standard gem-disubstituted substrates, much Hke rare earth elements. This enhanced reactivity may be attributable to the formally cationic metal center in this zwitterionic species, thereby realizing a catalytic species that is isoelectronic with the more reactive rare earth elements. Interestingly, while previously reported cationic Zr species have had a... 

Late transition metals are particularly useful for enantioselective transformations with protected amines and in some cases arylamines however, simple alkylamines have rarely been addressed using these metal centers. Considering the mechanistic profiles for these reactions and the competitive coordination of amine and alkene with these systems, it would seem that late transition metals are preferred for less nucleophilic amines, while early transition metals and rare earth elements will be preferred for unprotected amines. As such, the development of hydroamination catalysts from different regions of the periodic table can result in complementary synthetic solutions. 

Chemical diffusion of the rare-earth element was measured in natural calcite under anhydrous conditions, using rare-earth carbonate powders as the sources. Experiments were run in sealed silica capsules together with finely ground calcite to ensure stability of the single-crystal samples during diffusion anneals. Rutherford back-scattering spectroscopy was used to measure diffusion profiles. The Arrhenius relationship at 600 to 850C was ... 

The diffusion of rare-earth elements was studied in yttrium aluminum garnet. The source of the diffiisant was a mixture of alumina and the rare-earth element oxide. The diffusion profiles were measured using Rutherford back-scattering spectrometry. The Arrhenius relationship was ... 

The profiles of spectral lines from plasma sources at atmospheric pressure are illustrated by the high-resolution spectra of a number of rare-earth elements in an inductively coupled plasma (ICP)(Fig. 2) [12]. 

Benkhedda et al demonstrated the unique performance of ICP-TOF-MS for the simultaneous multi-element detection of 22 isotopes of rare earth elements (REEs) in a El peak of about 5 s width (at 50% height) without the introduction of any spectral skew. Eigure 2.24 represents the profiles obtained by USN-ICP-TOE-MS for three replicates of 250 ptL injections of a 0.1 mg/L multi-elemental standard of REE s after FI on-line pre-concentration in a fkr (KR) pre-coated with the chelating reagent l-phenyl-3-methyl-4-benzoyl-pyrazol-5-one (PMBP). 

Immobility of Nb has also been documented in other laterite profiles (100,112,113). The correlation of Nb with Ti and Fe suggests that Nb is hosted by relict rutile and Fe-oxides. Molybdenum and Pb are probably adsoibed by goethite (JI4), whereas the accumulation of phosphate minerals in the ferruginous zone leads to the enrichment of Y and some light rare earth elements (La, Ce). However, the positive Ce anomaly is maiidy due to formation of cerianite (Ce02) in laterite (I0(. ... 

Duddy, I. R. 1980. Redistribution and fractionation of rare earth and other elements in a weathering profile. Chemical Geology, 30, 363-381. 

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