Improved Platinum-Group Element Extraction by NiS Fire Assay from Chromitite Ore Samples Using a Flux Containing Sodium Metaphosphate   总被引：1，自引：0，他引：1  

L. Paul Bédard  Sarah-Jane Barnes 《Geostandards and Geoanalytical Research》2004,28(2):311-316

Many chromite-rich rocks contain relatively high concentrations of the platinum-group elements (PGE). In many cases, the phases carrying PGE occur as either platinum-group minerals (PGM) or as base metal sulfides in solid solution in sulfides. In some cases, such as the UG-2 unit of the Bushveld Complex, the PGM are occluded inside chromite grains. Chromites are notably difficult to dissolve in most fluxes and if the chromite contains some PGM the possibility exists that not all the PGE will be recovered during fusion. In this work, shortcomings in published methods of analysis based on the nickel sulfide fire assay procedure were investigated and a new procedure developed based on the addition of sodium metaphosphate to the fusion mixture. Optimum composition of the fusion mixture was found to be 10 g sodium metaphosphate and 9 g silica to 10 g sample, 15 g sodium carbonate, 30 g lithium tetraborate, 7.5 g nickel and 4.5 g sulfur to achieve complete dissolution of chromite grains. The new flux mixture was evaluated by the analysis of reference material CHR-Pt+ (which is known to contain PGM inside chromite grains) and no undissolved chromite grains were found in the glassy slag. Analysis of the nickel sulfide beads from this fire assay using neutron activation analysis showed similar results for Rh and Ru when compared with published conventional true (or accepted) values, while Au, Ir, Os, Pd and Pt values determined here were 10 to 30% higher than the corresponding published conventional true values. It was concluded that the addition of sodium metaphosphate improved chromite dissolution in the flux and appears to improve PGE recovery.  相似文献   

Optimisation de la quantification des flux de matière en suspension d'un cours d'eau alpin : l'Isère à Grenoble (France)     

Dominique Dumas 《Comptes Rendus Geoscience》2004,336(13):1149-1159

This study seeks to determine suspended-matter flux of the Isère at Grenoble, one of the most important rivers of the northern French Alps. Since 1994, and especially 1996, systematic samplings of the left bank make it possible to follow in one point the variations of suspended particles and matter (SPM) of this river. But from a single measurement, sometimes not very representative of the whole observable concentrations within the section, it remains still difficult to estimate precisely the SPM flux. The results of this study show in particular the successive appearance of several turbidity gradients, whose occurrence is explained mainly by the hydrological and hydro-sedimentary dynamics of this river. The estimate of these gradients thus makes it possible to extrapolate specific measurements more easily and consequently to daily define the quantities of suspended matter exported by the Isère. Since 1996, the results show a very high flow, specific of the Isère at Grenoble, variable between 124 and more than 460 t km^?2 yr^?1. To cite this article: D. Dumas, C. R. Geoscience 336 (2004).  相似文献   

内蒙古温带半干旱羊草草原N₂O通量及其影响因素   总被引：5，自引：2，他引：5  

董云社  齐玉春  Manfred Domroes  耿元波  杨小红  刘立新  刘杏认 《地理研究》2004,23(6):776-784

利用静态箱 -气相色谱法于 2 0 0 1～ 2 0 0 3年对内蒙古锡林河流域羊草草原进行了连续 2年的野外定位试验 ,获得羊草草原原状群落与土壤N2 O年排放通量分别在 3 91～ 4 71μgm- 2h- 1以及 5 5 0～ 10 0 3μgm- 2 h- 1范围内变动 ,证明内蒙古温带半干旱羊草草原生态系统是大气中N2 O的源 ;系统分析了羊草草原N2 O通量的季节变化、源汇特征以及关键的环境因子对草地N2 O通量的影响等 ,建立了N2 O通量与环境因子间的回归方程 ;并利用两年连续完整的观测数据对羊草草原N2 O年排放量进行了估算  相似文献   

基于通量均衡基准的地壳垂直形变场分析模型   总被引：1，自引：0，他引：1  

张勤  范一中  赵超英 《武汉大学学报(信息科学版)》2004,29(3):231-234

根据全球通量均衡假说建立了地壳垂直形变场的分析模型，在球面近似下求得了该模型的球谐函数级数解并拟合了两个不同区域的地壳垂直形变场，编绘了等值线图，继而在密切平面坐标系下导出了该模型的Fourier级数解。结果表明，该方法不仅具有几何意义，而且具有一定的地球动力学意义。  相似文献   

Predicting the future DOC flux from upland peat catchments   总被引：6，自引：0，他引：6  

Fred Worrall  Tim Burt 《Journal of Hydrology》2005,300(1-4):126-139

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Rainfall partitioning through a mixed cedar swamp and associated C and N fluxes in Southern Ontario,Canada     

Tim P. Duval 《水文研究》2019,33(11):1510-1524

Partitioning of rainfall through a forest canopy into throughfall, stemflow, and canopy interception is a critical process in the water cycle, and the contact of precipitation with vegetated surfaces leads to increased delivery of solutes to the forest floor. This study investigates the rainfall partitioning over a growing season through a temperate, riparian, mixed coniferous‐deciduous cedar swamp, an ecosystem not well studied with respect to this process. Seasonal throughfall, stemflow, and interception were 69.2%, 1.5%, and 29.3% of recorded above‐canopy precipitation, respectively. Event throughfall ranged from a low of 31.5 ± 6.8% for a small 0.8‐mm event to a high of 82.9 ± 2.4% for a large 42.7‐mm event. Rain fluxes of at least 8 mm were needed to generate stemflow from all instrumented trees. Most trees had funnelling ratios <1.0, with an exponential decrease in funnelling ratio with increasing tree size. Despite this, stand‐scale funnelling ratios averaged 2.81 ± 1.73, indicating equivalent depth of water delivered across the swamp floor by stemflow was greater than incident precipitation. Throughfall dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) averaged 26.60 ± 2.96 and 2.02 ± 0.16 mg L^?1, respectively, which were ~11 and three times above‐canopy rain levels. Stemflow DOC averaged 73.33 ± 7.43 mg L^?1, 35 times higher than precipitation, and TDN was 4.45 ± 0.56 mg L^?1, 7.5 times higher than rain. Stemflow DOC concentration was highest from Populus balsamifera and TDN greatest from Thuja occidentalis trees. Although total below‐canopy flux of TDN increased with increasing event size, DOC flux was greatest for events 20–30 mm, suggesting a canopy storage threshold of DOC was readily diluted. In addition to documenting rainfall partitioning in a novel ecosystem, this study demonstrates the excess carbon and nitrogen delivered to riparian swamps, suggesting the assimilative capacity of these zones may be underestimated.  相似文献   

Dynamic river–groundwater exchange in the presence of a saline,semi‐confined aquifer          下载免费PDF全文

N. P. Unland  I. Cartwright  E. Daly  B. S. Gilfedder  A. P. Atkinson 《水文研究》2015,29(23):4817-4829

Understanding groundwater–surface water exchange in river banks is crucial for effective water management and a range of scientific disciplines. While there has been much research on bank storage, many studies assume idealized aquifer systems. This paper presents a field‐based study of the Tambo Catchment (southeast Australia) where the Tambo River interacts with both an unconfined aquifer containing relatively young and fresh groundwater (<500 μS/cm and <100 years old) and a semi‐confined artesian aquifer containing old and saline groundwater (electrical conductivity > 2500 μS/cm and >10 000 years old). Continuous groundwater elevation and electrical conductivity monitoring within the different aquifers and the river suggest that the degree of mixing between the two aquifers and the river varies significantly in response to changing hydrological conditions. Numerical modelling using MODFLOW and the solute transport package MT3DMS indicates that saline water in the river bank moves away from the river during flooding as hydraulic gradients reverse. This water then returns during flood recession as baseflow hydraulic gradients are re‐established. Modelling also indicates that the concentration of a simulated conservative groundwater solute can increase for up to ~34 days at distances of 20 and 40 m from the river in response to flood events approximately 10 m in height. For the same flood event, simulated solute concentrations within 10 m of the river increase for only ~15 days as the infiltrating low‐salinity river water drives groundwater dilution. Average groundwater fluxes to the river stretch estimated using Darcy's law were 7 m³/m/day compared with 26 and 3 m³/m/day for the same periods via mass balance using Radon (²²²Rn) and chloride (Cl), respectively. The study shows that by coupling numerical modelling with continuous groundwater–surface water monitoring, the transient nature of bank storage can be evaluated, leading to a better understanding of the hydrological system and better interpretation of hydrochemical data. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Variability in bedform morphology and kinematics with transport stage          下载免费PDF全文

Jeremy G. Venditti  C.‐Y. Martin Lin  Moslem Kazemi 《Sedimentology》2016,63(4):1017-1040

Bedform geometry is widely recognized to be a function of transport stage. Bedform aspect ratio (height/length) increases with transport stage, reaches a maximum, then decreases as bedforms washout to a plane bed. Bedform migration rates are also linked to bedform geometry, in so far as smaller bedforms in coarser sediment tend to migrate faster than larger bedforms in finer sediment. However, how bedform morphology (height, length and shape) and kinematics (translation and deformation) change with transport stage and suspension have not been examined. A series of experiments is presented where initial flow depth and grain size were held constant and the transport stage was varied to produce bedload dominated, mixed‐load dominated and suspended‐load dominated conditions. The results show that the commonly observed pattern in bedform aspect ratio occurs because bedform height increases then decreases with transport stage, against a continuously increasing bedform length. Bedform size variability increased with transport stage, leading to less uniform bedform fields at higher transport stage. Total translation‐related and deformation‐related sediment fluxes all increased with transport stage. However, the relative contribution to the total flux changed. At the bedload dominated stage, translation‐related and deformation‐related flux contributed equally to the total flux. As the transport stage increased, the fraction of the total load contributed by translation increased and the fraction contributed by deformation declined because the bedforms got bigger and moved faster. At the suspended‐load dominated transport stage, the deformation flux increased and the translation flux decreased as a fraction of the total load, approaching one and zero, respectively, as bedforms washed out to a plane bed.  相似文献   

Upper-Tropospheric Environment–Tropical Cyclone Interactions over the Western North Pacific: A Statistical Study     

Yu-Kun QIAN  Chang-Xia LIANG  Zhuojian YUAN  Shiqiu PENG  Junjie WU  Sihua WANG 《大气科学进展》2016,33(5):614-631

Based on 25-year(1987–2011) tropical cyclone(TC) best track data, a statistical study was carried out to investigate the basic features of upper-tropospheric TC–environment interactions over the western North Pacific. Interaction was defined as the absolute value of eddy momentum flux convergence(EFC) exceeding 10 m s~(-1)d~(-1). Based on this definition, it was found that 18% of all six-hourly TC samples experienced interaction. Extreme interaction cases showed that EFC can reach~120 m s~(-1)d~(-1) during the extratropical-cyclone(EC) stage, an order of magnitude larger than reported in previous studies.Composite analysis showed that positive interactions are characterized by a double-jet flow pattern, rather than the traditional trough pattern, because it is the jets that bring in large EFC from the upper-level environment to the TC center. The role of the outflow jet is also enhanced by relatively low inertial stability, as compared to the inflow jet. Among several environmental factors, it was found that extremely large EFC is usually accompanied by high inertial stability, low SST and strong vertical wind shear(VWS). Thus, the positive effect of EFC is cancelled by their negative effects. Only those samples during the EC stage, whose intensities were less dependent on VWS and the underlying SST, could survive in extremely large EFC environments, or even re-intensify. For classical TCs(not in the EC stage), it was found that environments with a moderate EFC value generally below ~25 m s~(-1)d~(-1) are more favorable for a TC's intensification than those with extremely large EFC.  相似文献   

Role of horizontal density advection in seasonal deepening of the mixed layer in the subtropical Southeast Pacific     

Qinyu Liu  Yiqun Lu 《大气科学进展》2016,33(4):442-451

The mechanisms behind the seasonal deepening of the mixed layer(ML) in the subtropical Southeast Pacific were investigated using the monthly Argo data from 2004 to 2012. The region with a deep ML(more than 175 m) was found in the region of(22?–30?S, 105?–90?W), reaching its maximum depth(～200 m) near(27?–28?S, 100?W) in September. The relative importance of horizontal density advection in determining the maximum ML location is discussed qualitatively. Downward Ekman pumping is key to determining the eastern boundary of the deep ML region. In addition, zonal density advection by the subtropical countercurrent(STCC) in the subtropical Southwest Pacific determines its western boundary, by carrying lighter water to strengthen the stratification and form a "shallow tongue" of ML depth to block the westward extension of the deep ML in the STCC region. The temperature advection by the STCC is the main source for large heat loss from the subtropical Southwest Pacific. Finally, the combined effect of net surface heat flux and meridional density advection by the subtropical gyre determines the northern and southern boundaries of the deep ML region: the ocean heat loss at the surface gradually increases from 22?S to 35?S, while the meridional density advection by the subtropical gyre strengthens the stratification south of the maximum ML depth and weakens the stratification to the north. The freshwater flux contribution to deepening the ML during austral winter is limited. The results are useful for understanding the role of ocean dynamics in the ML formation in the subtropical Southeast Pacific.  相似文献