110,208 research outputs found
REE fractionation during granite weathering and removal by waters and suspended loads: Sr and Nd isotopic evidence
No full textVery few studies deal with REE (rare earth element) mobility within the system soil–soil solution–streamwater. In this article, we try to characterize the fractionation and the migration of the REE in a granite-derived soil system located in a small catchment of the Vosges mountains. ICP-MS and TIMS measurements were performed on both solid samples (“fresh” granite, soil, and suspended load of the stream) and waters (soil solutions, springwater, and streamwater) to determine their respective REE concentrations and Sr and Nd isotopic compositions. The PAAS-normalized REE pattern of the bedrock is characterized by a strong depletion in HREE (heavy REE) and a negative Eu anomaly (0.46). Similarly, the granite-normalized REE distribution patterns of the soil samples show HREE depletions that become more important with decreasing depth. The correlative behavior between P2O5, Th, and REE with depth indicates that, besides apatite, other phosphate minerals such as monazite are the most important phases controlling the Th and REE budget in the soil profile. On the other hand, at greater depth, zircon seems to be another important mineral phase controlling especially the HREE enrichment as shown by the positive relationship between Zr content and the Yb/Ho ratio. Different grain size fractions show similar REE distribution patterns and are only weakly fractionated, compared with bulk soil sample. However, the finest fraction (0–20 mm) is more enriched in Sr and REE, suggesting a stronger concentration of REE-carrying minerals in this fraction. The suspended and dissolved load of the stream show as a whole an enrichment in HREE if compared with the granite or with the different soil samples. However, compared with the uppermost soil samples, the suspended load is significantly more enriched in HREE. Its REE distribution pattern is more similar to that of the finest fraction of the deeper soil sample and to the “fresh” granite. Thus, most probably the REE of the suspended load originated from a source with REE characteristics found in the deep soil horizons. This source might have been situated in the uppermost soil profile, which is actually REE depleted. The weathering process can be compared with a leaching experiment where the waters correspond to the leachate and the soil to the residual phase of the granite. The Sr isotope data indicate that the suspended load originates from the finest soil fraction. The Sr and Nd isotopic data of the suspended load suggest that it contains up to 3% Sr and Nd from apatite and up to 97% from feldspar. Most of the Sr and Nd in the waters originate from apatite leaching or dissolution
Distribution and origin of major and trace elements (particularly REE, U and Th) into labile and residual phases in an acid soil profile (Vosges Mountains, France).
No full textA seven step sequential extraction procedure has been conducted on a podzolic soil profile from the Vosges Mountains in order to determine the ability of several elements to be released to the environment. Very little Si, K and Al were extractable ( 10% of the total soil concentration) of Ca, P, metals (Fe, Pb), REE and actinides (Th, U) could be leached. For each element, preferential binding sites can be recognized. High recovery of P and Ca in the acid soluble fraction (AS) suggests that phosphate minerals are highly involved in this step of the extraction. Organic matter appears to control the adsorption of Ca, Fe, Th, U and REE, even at depths in the soil profile where organic matter content is particularly low (0.5%). Weak acid leaching experiments (with HCl and acid acetic 0.001 N) were also performed in order to characterize the origin of the insoluble material in this soil profile. The leachable REE distributions indicate that a large part of the labile REE in the surface horizon has an atmospheric origin whereas at greater depth phosphate mineral (apatite) alteration is the main factor controlling REE release in the leachate. Our study further suggests that adsorbed material holding actinides and REE are not strictly the same. So, caution should be taken when using REE as analogues for actinides in soils systems
Origin and fluxes of atmospheric REE entering an ombrotrophic peat bog in Black Forest (SW Germany): Evidence from snow, lichens and mosses
No full textThe fate of the Rare Earth Elements (REE) were investigated in different types of archives of atmospheric deposition in the Black Forest, Southern Germany: (1) a 70 cm snow pack collected on the domed part of a raised bog and representing 2 months of snow accumulation, (2) a snow sample collected close to the road about 500 m from the peat bog, (3) two species of lichens and (4) a peat profile representing 400 years of peat accumulation as well as a “preanthropogenic” sample and the living moss layer from the top of the core. REE concentrations in peat are significantly correlated to Ti which is a lithogenic conservative element suggesting that REE are immobile in peat bog environments. Snow, lichens and peat samples show similar PAAS (Post Archean Australian Shale) normalized REE distributions suggesting that the complete atmospheric REE signal is preserved in the peat profile. However, the annual flux of REE accumulated by the peat is ca. 10 times greater than that of the bulk winter flux of REE. This difference probably indicates that the REE concentrations in the snowpack are not representative of the average REE flux over the whole year. Despite the pronounced geological differences between this site (granite host-rock) and a previously studied peat bog in Switzerland (limestone host-rock) similar REE distribution patterns and accumulation rates were found at both sites. Given that both sites confirm an Upper Continental Crust signature, the data suggests both sites are influenced by regional and not local, soil-derived lithogenic aerosols
Characterization and migration of atmospheric REE in soils and surface waters
No full textRainwater and snow collected from three different sites in France (Vosges Mountains, French Alps and Strasbourg) show more or less similar shapes of their REE distribution patterns. Rainwater from Strasbourg is the most REE enriched sample, whereas precipitations from the two mountainous, less polluted catchments are less REE enriched and have concentrations close to seawater. They are all strongly LREE depleted. Different water samples from an Alpine watershed comprising snow, interstitial, puddle and streamwater show similar REE distributions with LREE enrichment (rainwater normalized) but MREE and HREE depletion. In this environment, where water transfer from the soil to the river is very quick due to the low thickness of the soils, it appears that REE in streamwater mainly originate from atmospheric inputs. Different is the behaviour of the REE in the spring- and streamwaters from the Vosges Mountains. These waters of long residence time in the deep soil horizons react with soil and bedrock REE carrying minerals and show especially significant negative Eu anomalies compared to atmospheric inputs. Their Sr and Nd isotopic data suggest that most of the Sr and Nd originate from apatite leaching or dissolution. Soil solutions and soil leachates from the upper soil horizons due to alteration processes strongly depleted in REE carrying minerals, have REE distribution patterns close to those of lichens and throughfall. Throughfall is slightly more enriched especially in light REE than filtered rainwater probably due to leaching of atmospheric particles deposited on the foliage and also to leaf excretion. Data suggest that Sr and Nd isotopes of the soil solutions in the upper soil horizons originate from two different sources: 1) An atmospheric source with fertilizer, dust and seawater components and 2) A source mainly determined by mineral dissolution in the soil. These two different sources are also recognizable in the Sr and Nd isotopic composition of the tree’s throughfall solution. The atmospheric contributions of Sr and Nd to throughfall and soil solution are of 20 to 70 and 20%, respectively. In springwater, however, the atmospheric Sr and REE contribution is not detectable
Luminescence spectroscopy of natural and synthetic REE-bearing minerals
No full textThis study investigates the photoluminescence (PL), cathodoluminescence (CL), radioluminescence (RL) and ionoluminescence (IL) of natural and synthetic minerals. The natural minerals (fluorapatite, leucophanite, meliphanite and zircon) are mostly from Ilímaussaq Alkaline Complex in South Greenland, Langesundsfjord in Norway and from different localities within Scotland. Synthetic fluorapatite (manufactured as part of the present study) and zircon doped with rare earth elements (REE) were used to compare single and multidoped materials.
This study has shown that many of the generally accepted applications of luminescence are not as straightforward as often suggested by the current literature. For example, the study demonstrates how site distribution of REE, based on luminescence, is greatly affected by the dopant level and structural changes, and that different conclusions can be drawn on the same sample depending on method applied. Furthermore, it is clearly demonstrated that using luminescence as a tool for quantitative trace element determination is not going to be a standard technique in the near future if ever. The two main findings supporting this conclusion are the non-linear intensity decrease between different REE activators in the same sample and a large variation between activators at the concentration at which self-quenching starts.
In contrast to the general perception that luminescence related to REE is mostly independent of the host, this study has shown a strong interaction between host and REE activators. This conclusion is supported by the change in the activator’s coordination polyhedron observed with single-crystal and powder X-ray diffraction combined with full chemical characterisation. When combining the weak interaction between some REE with the strong host interaction this study has shown the potential for designing new types of colour tuneable and “white light” LEDs based on natural minerals. This study also reveals that zircon doped with Gd³⁺ and Eu³⁺ can potentially have quantum-cutting properties
→ DH+H 반응과 → HD+D 반응에 있어서의 텐넬 효과
No full text학위논문(석사) - 한국과학기술원 : 화학과, 1981.2, [ vi, 55 p. ]We considered the tunneling effect on transition-state theory rate-constants for the and reactions. The method for estimating the important parameter (potential barrier height) was proposed. A tunneling correction factor was estimated from experimental data, and compared with the corresponding values obtained from many theoretical methods. We found that our method for calculating the tunneling correction factor is most satisfactory. According to our result, the tunneling effect cannot be neglected around where is ca. 0.8 whereas the factor approaches to unity at where the tunneling completely disappears. In the past, however, the tunneling effect has been considered to be negligible above . We believe that our result is correct and right. In addition to the above fact, we also found that the tunneling correction factor for the two reactions is in the order of in agreement with Truhlar et al.``s result. In contrast to our result, however, Shavitt et al. found that the order is reversed, i.e., . We discussed about the Shavitt et al.``s result.한국과학기술원 : 화학과
Letter from J. H. Skinner to H. J. Reed
No full textLetter regarding inventory of J. C. Arthur's reprints, with annotations from H. J. Ree
Rare earth element systematics in ancient and modem hydrothermal systems
No full textThe geochemical significance of on-axis diffuse fluids, in addition to those formed during the waning phases of hydrothermal systems and off-axis crustal ageing processes, has been investigated through a comparison of the rare earth element (REE) systematics of hydrothermal materials from the ore-forming hydrothermal systems of the TAG vent field, 26 N Mid-Atlantic Ridge, and 90 Myr Troodos Ophiolite, Cyprus. Ophiolites integrate a long (c. 20 Myr) history of seafloor alteration, which reflects both axial and off-axis hydrothermal processes. Spatially-resolved laser ablation inductively coupled plasma-mass spectrometric (LA ICP-MS) REE analyses of individual alteration phases within stockwork-mineralised Troodos lavas have been used to deconvolve the complex alteration processes associated with crustal generation at an oceanic spreading ridge. REE mobility was associated with the development of both high- (-200 to 350 C) and low temperature(<100 C) secondary phases which precipitated within contrasting alteration regimes (discharge- and recharge-dominated respectively). Low-temperature alteration phases are the major repository for the REEs in lavas which are depleted in the light REEEu relative to pristine volcanic glass compositions. These data indicate that much of the REE signature of the alteration pipe is a post-mineralisation overprint acquired in the waning stages of hydrothermal activity and during the protracted alteration of the oceanic basement, rather than on-axis greenschist facies hydrothermal alteration. Submersible and drilling studies of the TAG mound have led to the development of models of mound growth and fluid evolution within an actively-forming seafloor sulphide deposit. The REEs have been used to test the applicability of these models to processes of sulphide mound and metalliferous sediment formation which occurred within the Troodos ophiolite. The REE patterns of umber, ochre and sulphide sampled from a section through the top of the Skouriotissa ore body clearly demonstrate extensive seawater ingress and circulation throughout the upper ore body during waning hydrothermalism and cooling of the mound,which has resulted in the overprinting of any original hydrothermal signatures in both mound sediments and sulphides. This study has demonstrated that the geochemistry of the sulphide mound deposits continues to evolve following the peak of hydrothermal activity, and that the seawater overprinting of the Skouriotissa deposit is the end product of a process which we only see the initiation of on the modern seafloor. At TAG, the origin of far-field Mn and Fe-rich oxide crusts has remained controversial over 25 years of investigations of the vent field. The REE and Nd isotope data presented in this thesis indicate these ferromanganese deposits are forming by a combination of sedimentationof Mn-rich particulates from the TAG hydrothermal plume, and direct precipitation from diffuse hydrothermal fluids seeping from the rift valley wall. The REE data reveal that the separation of manganese from other hydrothermally-derived metals at TAG is due to both plume processes and the spatial distribution of diffuse flow within the vent field.The studies presented in this dissertation have demonstrated the use of REEs as tracers of chemical processes in ancient and modem hydrothermal systems on a wide range of temporal and spatial scales
Zinc glutarate catalyzed synthesis and biodegradability of poly(carbonate-co-ester)s from CO2, propylene oxide, and epsilon-caprolactone
No full textA zinc glutarate (ZnGA) catalyst was prepared from the reaction of zinc oxide and glutaric acid in dry toluene. ZnGA was found to exhibit a catalytic activity for the copolymerization of carbon dioxide (CO2) and propylene oxide (PO) and the homopolymerization of PO but to reveal no catalytic activity for the hornopolymerization of epsilon-caprolactone (CL). The ZnGA-catalyzed polymerization was extended for the terpolymerization of CO2 with PO and CL, producing poly(propylene carbonate-co-epsilon-caprolactone)s (PPCCLs) with a reasonably high molecular weight in high yields. In the terpolymerization, PO and CL were used as both co-monomers and reaction media, after the reaction completed, the excess co-monomers were easily recovered and reused in the next terpolymerization batch. For the synthesized polymers, enzymatic and biological degradability were investigated.X1120sci
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