通讯机构：
Key Discipline Laboratory for National Defense for Biotechnology in Uranium Mining and Hydrometallurgy, University of South China, Hengyang, China
摘要：
In this paper, we synthesized and characterized a di-tetradentate macrocyclic ligand as a novel resonance fluorescence probe for the determination of uranium. The ligand contains two tetradentate ligand moieties and can chelate two cations to form binuclear complex. We found that when the ligand only chelates a uranyl ion or europium (III) ion, the formed complex can only produce weak resonance fluorescence. When the ligand chelates simultaneously uranyl and europium (III) to form heterobinuclear complex, the formed complex can produce strong resonance fluorescence due to the cation-cation interaction between uranyl and europium (III). Based on this finding, we established a resonance fluorescence chemosensor for the determination of uranium (VI) by utilizing the formation of the heterobinuclear complex. Under optimal conditions, the linear range for the determination of uranium (VI) is 0.008-1.2 nmol mL(-1) with a detection limit of 0.002 nmol mL(-1). The method has been applied to determine uranium (VI) in environmental water samples with the recoveries between 95.7% and 103.6%. (C) 2018 Elsevier B.V. All rights reserved.
作者机构：
[刘红娟; 谢水波] Institute of Nuclear Science and Technology, University of South China, Hengyang;Hunan;421001, China;Key Discipline Laboratory for National Defence for Biotechnology in Uranium Mining and Hydrometallurgy, University of South China, Hengyang;[张希晨; 刘迎九; Zeng, Tao-Tao] Hunan Province Key Laboratory of Pollution Control and Resources Reuse Technology, University of South China, Hengyang
通讯机构：
[Xie, S.-B.] I;Institute of Nuclear Science and Technology, University of South China, Hengyang, Hunan, China
摘要：
Oceanic subduction zones are important channels for carbon exchange between the Earth's crust and mantle. However, the nature of carbon cycles at depths from 120 to 410 km in the subduction zone remains unknown. To decipher this issue, high-precision stable Mg isotopes of arc-like volcanic rocks from Tengchong, Southwestern China, have been investigated. The Tengchong volcanic rocks comprise basalts and andesites, with Mg0 content varying from 2.41 to 8.48 wt.%. Both the basalts and andesites exhibit homogeneous and light Mg isotopic compositions with delta Mg-26 ranging from -0.51 to -0.45 parts per thousand and -0.49 to -0.33 parts per thousand, respectively. Their delta Mg-26 values are lower than the average mantle (delta Mg-26 = -0.25 +/- 0.07 parts per thousand) and island arc lavas (delta Mg-26 = -0.35 to +0.06%e), but similar to the <110 Ma intra-continental basalts from eastern China (delta Mg-26 = -0.60 to 0.30 parts per thousand). This light Mg isotopic composition could not originate from the accumulation of ilmenite in their mantle source because both the Nb/Ta and delta Mg-26 values of the basalts are invariant with TiO2 content. The recycling of carbonated eclogites is also unlikely because of the lack of any correlation between delta Mg-26 and either (Gd/Yb)(N) or Fe/Mn ratios in the Tengchong basalts. Alternatively, the most probable explanation for the light Mg isotopic composition is the recycling of sedimentary carbonates in the mantle source. This is supported by the high Na2O + K2O/TiO2 ratios (3.3-4.1), low Ti/Ti* and Hf/Hf* values in the basalts, which are consistent with the partial melting trend of carbonated peridotite. Additionally, the high Ba/Th, low Rb/Cs and enriched Sr-Nd isotopes (EMII-like endmember) of the Tengchong basalts indicate the presence of Indian sediments in their mantle source. Furthermore, the extremely high Th/U (6.5-8.3) ratios in basalts suggest the higher mobility of Th than U, which is a unique characteristic of slab-derived supercritical liquids in subduction zones with pressures greater than 6 GPa. Based on the quantitative modeling of Mg-Sr-Nd-Pb isotopes and trace elements, the mantle source of the Tengchong basalts lies along mixing lines of the DMM with 1% supercritical liquids and 15-19% recycled mixture containing 66-72% dolomite, 22-26% calcite and 2-12% Indian sediments. Given that the recycled mixture is mainly dolomite (66-72%), we proposed that the slab-derived supercritical liquids can dissolve dolomite and then metasomatized the overlying mantle to form carbonated peridotite. Partial melting of this mantle source should be located at a depth of similar to 120 to 300 km under which supercritical liquids can occur, which is supported by seismic tomographic observations. The Tengchong andesites display many geochemical features similar to the basalts, such as enrichments in LILEs (Large Ion Lithophile Elements), LREEs (Light Rare Earth Elements) and Sr-Nd-Pb isotopes, as well as low delta Mg-26 values, suggesting a petrogenetic link between these two rock types. Our detailed study suggests that the andesites evolved from the Tengchong basalts via assimilation and fractional crystallization (AFC) processes. This interpretation is also supported by the geophysical tomography, which reveals a low-velocity anomalous zone in the continental crust. This study reveals a new carbon cycle in which Mg-rich carbonate - dolomite - can be dissolved by supercritical liquids and subducted into a deep mantle wedge to depths of 120-300 km in the oceanic subduction zone. This deep metasomatic mantle wedge mixed with the upwelling mantle beneath the Tengchong volcano and partially melted to form the low delta Mg-26 volcanic rocks. (C) 2018 Elsevier Ltd. All rights reserved.
作者机构：
[Dai Bing] Univ South China, Nucl Resources Engn Coll, Hengyang 421001, Peoples R China.;[Zhao Guo-yan; Dai Bing] Cent S Univ, Sch Resources & Safety Engn, Changsha 410001, Hunan, Peoples R China.;[Konietzky, H.; Wasantha, P. L. P.; Dai Bing] TU Bergakad, Geotech Inst, D-09599 Freiberg, Germany.
通讯机构：
[Dai Bing] U;[Dai Bing] C;[Dai Bing] T;Univ South China, Nucl Resources Engn Coll, Hengyang 421001, Peoples R China.;Cent S Univ, Sch Resources & Safety Engn, Changsha 410001, Hunan, Peoples R China.
关键词：
damage evolution;loading and unloading;granitic rock;triaxial testing
摘要：
In-situ rock failures can result from stress changes due to pure loading and/or unloading. Understanding of the damage evolution behavior in brittle rocks during loading and unloading is imperative for the designs of rock structures. In this paper, we investigate the damage evolution characteristics of a granitic rock during loading and unloading after a series of triaxial experiments performed at different confining pressures. The axial stress-axial strain variations of the tested specimens revealed that the specimens undergoing unloading fail with a lower axial strain compared to the specimens failed purely by loading. Higher confining pressures were observed to exacerbate the difference. Volumetric strain versus axial strain curves indicated that the curves reverse the trend with the beginning of major damage of specimens. We suggest here a new form of equation to describe the secant modulus variation of brittle rocks against the axial stress for the unloading process. Failure mechanisms of tested specimens showed two distinct patterns, namely, specimens under pure loading failed with a single distinct shear fracture while for the unloading case specimens displayed multiple intersecting fractures. In addition, analysis of the evolution of dissipation and elastic energy during deformation of the specimens under loading and unloading conditions showed differentiable characteristics. Moreover, we evaluated the variations of two damage indices defined based on the energy dissipation and secant modulus evolution during deformation and observed that both of them satisfactorily distinguish key stages of damage evolution.
