An Investigation of Digestion Methods for Trace Elements in Bauxite and Their Determination in Ten Bauxite Reference Materials Using Inductively Coupled Plasma‐Mass Spectrometry

Trace elements from samples of bauxite deposits can provide useful information relevant to the exploration of the ore‐forming process. Sample digestion is a fundamental and critical stage in the process of geochemical analysis, which enables the acquisition of accurate trace element data by ICP‐MS. However, the conventional bomb digestion method with HF/HNO₃ results in a significant loss of rare earth elements (REEs) due to the formation of insoluble AlF₃ precipitates during the digestion of bauxite samples. In this study, the digestion capability of the following methods was investigated: (a) ‘Mg‐addition’ bomb digestion, (b) NH₄HF₂ open vessel digestion and (c) NH₄F open vessel digestion. ‘Mg‐addition’ bomb digestion can effectively suppress the formation of AlF₃ and simultaneously ensure the complete decomposition of resistant minerals in bauxite samples. The addition of MgO to the bauxite samples resulted in (Mg + Ca)/Al ratios ≥ 1. However, adding a large amount of MgO leads to significant blank contamination for some transition elements (V, Cr, Ni and Zn). The NH₄HF₂ or NH₄F open vessel digestion methods can also completely digest resistant minerals in bauxite samples in a short period of time (5 hr). Unlike conventional bomb digestion with HF/HNO₃, the white precipitates and the semi‐transparent gels present in the NH₄HF₂ and NH₄F digestion methods could be efficiently dissolved by evaporation with HClO₄. Based on these three optimised digestion methods, thirty‐seven trace elements including REEs in ten bauxite reference materials (RMs) were determined by ICP‐MS. The data obtained showed excellent inter‐method reproducibility (agreement within 5% for REEs). The relative standard deviation (% RSD) for most elements was < 6%. The concentrations of trace elements in the ten bauxite RMs showed agreement with the limited certified (Li, V, Cr, Cu, Zn, Ga, Sr, Zr and Pb) and information values (Co, Ba, Ce and Hf) available. New trace element data for the ten RMs are provided, some of which for the first time.     

Effects of key components of <Emphasis Type="Italic">S. triqueter</Emphasis> root exudates on fractions and bioavailability of pyrene–lead co-contaminated soils

The key components of S. triqueter root exudates involved 4-oxo-pentanoic acid, succinic acid, glutaric acid, phthalate acid, citric acid, vanillic acid, myristic acid, pentadecanoic acid, decanoic acid, 14-methyl-pentadecanoic acid, hexadecanoic acid, octadecanoic acid and oleic acid, and the content of the water-soluble organic acids (citric acid, succinic acid and glutaric acid) significantly increased in pyrene and lead co-contaminated rhizosphere soil. These three water-soluble organic acids including citric acid, succinic acid and glutaric acid were detected as the specific root exudates of S. triqueter under stress of pollutants for pyrene and lead, so they were chosen as the research objects, and they were added into the bioremediation systems of pyrene and lead co-contaminated wetland soils. Compared with the control, the treatments added the three organic acids always improved the quantity of the bioavailable fraction of pyrene and lead in wetland soils and greatly influenced other chemical states of pyrene and lead fractions in the test concentration range. Under the 50 g kg^?1 of organic acids concentration, the amount of the bioavailable fraction of pyrene and lead increased 41.0 and 872.7 % by citric acid, respectively. The enhancement of bioavailability of pyrene and lead in the wetland soil by adding organic acids generally decreased in the following order: citric acid > succinic acid > glutaric acid. Enhancing effects of organic acids on the bioavailability improvement of pyrene and lead is remarkable.     

Applying disk-based discontinuous deformation analysis (DDA) to simulate Donghekou landslide triggered by the Wenchuan earthquake

In this paper, for the first time, disk-based discontinuous deformation analysis (DDA) is applied to simulate a real landslide triggered by an earthquake. For this purpose, the kinematic behaviour of the Donghekou landslide triggered by the Wenchuan earthquake is simulated and the results obtained using disk-based DDA are compared with actual data. The comparisons show that there is a good agreement between the results obtained using disk-based DDA and observed data. The simulation results provided an understanding of the failure behaviour and temporal evolution of the landslide. This study shows that disk-based DDA is a practical numerical tool that can be used to simulate the post-failure behaviour of landslides triggered by an earthquake.     

阿尔金北缘岩石变形机制——来自X光组构分析的证据

对阿尔金北缘地区变形蚀变花岗岩、花岗质糜棱岩、变形酸性火山岩和变形英安质凝灰岩中石英和绢云母2种矿物进行X光岩石组构分析,认为本区岩石变形比较明显,宏观面理近于东西向展布,绢云母变形较强,平行于面理定向排列;而石英以底面或近底面滑移为主,部分样品兼有柱面Ⅰ型滑移和柱面Ⅱ型滑移,反映本区岩石变形机制为中浅层次的脆-韧性变形(10~15km、250~350℃、0.25~0.40GPa)。通过岩石组构特征与宏观面理产状,推断本区韧性变形以右行运动为主,与板块碰撞在阿尔金北缘大平沟地区产生的韧性变形带特征一致。