用二-2-乙基己基磷酸从盐酸溶液中萃取Th(Ⅳ)

用二-2-乙基己基磷酸(HDEHP)做萃取剂,Na2CO3做反萃剂,234Th为示踪剂,完成了从盐酸溶液中液-液萃取Th(IV)的实验研究。在不同萃取条件下(包括HDEHP和Na2CO3溶液浓度、震荡时间、有机相和水相比值等)对234Th百分萃取(或反萃取)作了一系列实验。发现,随HDEHP浓度的增加,234Th的萃取效率明显增加。当HDEHP的浓度≥20%时,234Th的萃取效率>97%;用Na2CO3溶液能有效地从有机相中反萃出234Th,当Na2CO3溶液的浓度≥0.5mol/L时,234Th的反萃效率>96%;反萃时,震荡周期长于4min时,两相能达到反萃平衡;随有机相和水相比值的增加,234Th的萃取效率也明显地增加,在合适的萃取条件下,有机相与水相比值≥4:1时,高达97%的234Th进入有机相。

用1-苯基-3-甲基-4-苯甲酰基-5-吡唑啉酮萃取~(46)Sc的研究

用1-苯基-3-甲基-4-苯甲酰基-5-吡唑啉酮(PMBP)做萃取剂,氯仿和环己烷为稀释剂,观察了在HCl溶液46Sc的溶剂萃取行为。实验结果表明,从10-3~10-2mol/L的HCl溶液中用PMBP-氯仿(或环己烷)能有效地萃取46Sc,萃取率可达95%以上。另外,对PMBP从HCl溶液中萃取46Sc和234Th的结果也做了比较,结果表明,通过控制水溶液中HCl的浓度,能实现234Th与46Sc的分离。

用1-苯基-3-甲基-4-苯甲酰基-5-吡唑啉酮从硝酸中萃取痕量钍

用1-苯基-3-甲基-4-苯甲酰基-5-吡唑啉酮(PMBP)为萃取剂,~(234)Th作示踪剂,完成了在硝酸介质中痕量钍溶剂萃取行为的研究。在~(234)Th萃取效率与酸度、萃取剂浓度、平衡时间等依赖关系的条件实验的基础上,获得了萃取钍的最佳条件。使用改进的PMBP萃取钍的流程,从~(18)O离子辐照过的铀靶中分离钍,钍样品的γ射线单谱显示绝大部分反应产物和大量铀的去除是满意的。

Implications of groundwater weathered profile interactions to the mobilization of radionuclides

This study reports the nature and extent of open-system interaction between groundwater and a weathered profile developed in the high grade thorium and REE ore body in Morro do Ferro, Pocos de Caldas plateau. The radioelement mobility in the shallow oxidizing environment was considered by using chemical data in conjunction with U-234/U-238, Ra-226/Th-230, Th-230/U-234, Th-228/Th-232, Ra-228/Th-232 and Th-230/Ra-228 activity ratios (AR's) for borehole spoil and groundwater samples.Recharging groundwater from the studied borehole has low salinity values, with total dissolved solids content of 14.7 mg/l and total ionic strength of 0.00018. The ratio of the weight of dissolved radioelement per unit volume of solution to the weight of radioelement in solid phase per unit weight of solid phase showed that the radioelement solubility in the studied waters varied according to the following order: radium> uranium >thorium.U-234/U-238 AR's less than 1 were measured in solid phase and can justify the enhancement of U-234 in solution. Ra-226/Th-230 AR's greater than 1 and Th-230/U-234 AR'S less than 1 were evaluated between 20 and 27 m in depth, where a 2.1-m thick magnetite dike was intersected. These ratios could be justified by deposition of U and Ra associated with Fe-Mn oxides and kaolinite, where mineral saturation indices evaluated from the available data confirm this possibility. Covariations among disequilibria involving Th-228/(228) Ra and Ra-228/Th-232 AR's showed the preferential removal of Ra-228 relative to Tn isotopes, Th-228 and Th-232. The recent deposition of radium within the timescale of at least the last 35 years also is suggested. (C) 1998 Elsevier B.V. Ltd. All rights reserved.

Th-234 and Po-210 as POC flux proxies during the ARK-XXVII/3 expedition (August-October 2012)

The Arctic sea-ice extent reached a record minimum in September 2012. Sea-ice decline increases the absorption of solar energy in the Arctic Ocean, affecting primary production and the plankton community. How this will modulate the sinking of particulate organic carbon (POC) from the ocean surface remains a key question. We use the 234Th/238U and 210Po/210Pb radionuclide pairs to estimate the magnitude of the POC export fluxes in the upper ocean of the central Arctic in summer 2012, covering time scales from weeks to months. The 234Th/238U proxy reveals that POC fluxes at the base of the euphotic zone were very low (2 ± 2 mmol C/m**2/d) in late summer. Relationships obtained between the 234Th export fluxes and the phytoplankton community suggest that prasinophytes contributed significantly to the downward fluxes, likely via incorporation into sea-ice algal aggregates and zooplankton-derived material. The magnitude of the depletion of 210Po in the upper water column over the entire study area indicates that particle export fluxes were higher before July/August than later in the season. 210Po fluxes and 210Po-derived POC fluxes correlated positively with sea-ice concentration, showing that particle sinking was greater under heavy sea-ice conditions than under partially ice-covered regions. Although the POC fluxes were low, a large fraction of primary production (>30%) was exported at the base of the euphotic zone in most of the study area during summer 2012, indicating a high export efficiency of the biological pump in the central Arctic. This article is protected by copyright. All rights reserved.

Formation and preservation of pedogenic carbonates in South India, links with paleo-monsoon and pedological conditions: Clues from Sr isotopes, U-Th series and REEs

The influence of the pedogenic and climatic contexts on the formation and preservation of pedogenic carbonates in a climosequence in the Western Ghats (Karnataka Plateau, South West India) has been studied. Along the climosequence, the current mean annual rainfall (MAR) varies within a 80 km transect from 6000 mm at the edge of the Plateau to 500 mm inland. Pedogenic carbonates occur in the MAR range of 500-1200 mm. In the semi-arid zone (MAR: 500-900 mm), carbonates occur (i) as rhick hardpan calcretes on pediment slopes and (ii) as nodular horizons in polygenic black soils (i.e. vertisols). In the sub-humid zone (MAR: 900-1500 mm), pedogenic carbonates are disseminated in the black soil matrices either as loose, irregular and friable nodules of millimetric size or as indurated botryoidal nodules of centimetric to pluricentimetric size. They also occur at the top layers of the saprolite either as disseminated pluricentimetric indurated nodules or carbonate-cemented lumps of centimetric to decimetric size. Chemical and isotopic (Sr-87/Sr-86) compositions of the carbonate fraction were determined after leaching with 0.25 N HCl. The corresponding residual fractions containing both primary minerals and authigenic clays were digested separately and analyzed. The trend defined by the Sr-87/Sr-86 signatures of both labile carbonate fractions and corresponding residual fractions indicates that a part of the labile carbonate fraction is genetically linked to the local soil composition. Considering the residual fraction of each sample as the most likely lithogenic source of Ca in carbonates, it is estimated that from 24% to 82% (55% on average) of Ca is derived from local bedrock weathering, leading to a consumption of an equivalent proportion of atmospheric CO2. These values indicate that climatic conditions were humid enough to allow silicate weathering: MAR at the time of carbonate formation likely ranged from 400 to 700 mm, which is 2- to 3-fold less than the current MAR at these locations. The Sr, U and Mg contents and the (U-234/U-238) activity ratio in the labile carbonate fraction help to understand the conditions of carbonate formation. The relatively high concentrations of Sr, U and Mg in black soil carbonates may indicate fast growth and accumulation compared to carbonates in saprolite, possibly due to a better confinement of the pore waters which is supported by their high (U-234/U-238) signatures, and/or to higher content of dissolved carbonates in the pore waters. The occurrence of Ce, Mn and Fe oxides in the cracks of carbonate reflects the existence of relatively humid periods after carbonate formation. The carbonate ages determined by the U-Th method range from 1.33 +/- 0.84 kyr to 7.5 +/- 2.7 kyr and to a cluster of five ages around 20 kyr, i.e. the Last Glacial Maximum period. The young occurrences are only located in the black soils, which therefore constitute sensitive environments for trapping and retaining atmospheric CO2 even on short time scales. The maximum age of carbonates depends on their location in the climatic gradient: from about 20 kyr for centimetric nodules at Mule Hole (MAR = 1100 mm/yr) to 200 kyr for the calcrete at Gundlupet (MAR = 700 mm/yr, Durand et al., 2007). The intensity of rainfall during wet periods would indeed control the lifetime of pedogenic carbonates and thus the duration of inorganic carbon storage in soils. (C) 2010 Elsevier Ltd. All rights reserved.

La sacra doctrina y el gnosticismo : (S. Th., I, q. 1, art. 1)

El estudio de la falsa gnosis es algo de lo cual varios pensadores católicos ya han escrito y lo siguen haciendo. Sin embargo, la consideración de este argumento a la luz del pensamiento de Santo Tomás de Aquino no es algo común. El concepto de gnosis (gnw/sij, conocimiento), en sí mismo, no significa algo peyorativo. Por el contrario, Jesucristo hace referencia a los doctores de la ley que han quitado la llave de la ciencia (Lc 11, 52). Por su parte san Pablo confiesa que «no hay sino un solo Dios y Padre, de quien proceden todas las cosas, y nosotros estamos destinados hacia él; y un solo Señor Jesucrito, por quien son todas las cosas, y nosostros también por él. Pero no en todos se halla esa ciencia (h` gnw/sij)». Este conocimiento o gnosis que toma la Revelación en la fe por regla y guía es la gnosis verdadera Nos proponemos en este trabajo realizar una lectura del art. 1º de la Iª Pars de la Suma Teológica y compararlo ante todo con el fundamento mismo de aquello que san Pablo denomina como «la mal llamada ciencia»...