Minimal alteration of montmorillonite following long-term interaction with natural alkaline groundwater: Implications for geological disposal of radioactive waste     

《Applied Geochemistry》2016

Bentonite is one of the more safety-critical components of the engineered barrier system in the disposal concepts developed for many types of radioactive waste. Bentonite is utilised because of its favourable properties which include plasticity, swelling capacity, colloid filtration, low hydraulic conductivity, high retardation of key radionuclides and stability in geological environments of relevance to waste disposal. However, bentonite is unstable under the highly alkaline conditions induced by Ordinary Portland Cement (OPC: initial porewater pH > 13) and this has driven interest in using low alkali cements (initial porewater pH9-11) as an alternative to OPC. To build a robust safety case for a repository for radioactive wastes, it is important to have supporting natural analogue data to confirm understanding of the likely long-term performance of bentonite in these lower alkali conditions. In Cyprus, the presence of natural bentonite in association with natural alkaline groundwater permits the zones of potential bentonite/alkaline water reaction to be studied as an analogy of the potential reaction between low alkali cement leachates and the bentonite buffer in the repository. Here, the results indicate that a cation diffusion front has moved some metres into the bentonite whereas the bentonite reaction front is restricted to a few millimetres into the clay. This reaction front shows minimal reaction of the bentonite (volumetrically, less than 1% of the bentonite), with production of a palygorskite secondary phase following reaction of the primary smectites over time periods of 10⁵–10⁶ years.  相似文献   

电化学检测器—离子色谱法测定水中微量氰离子     

吴铁夫  吕凌峰  孔祥胜 《国土资源》1988,(2)

本文探讨了HPIC—AS_3分离柱分离,Dionex2020i型离子色谱仪—电化学检测器测定水中微量CN~-的诸条件,并考察了干扰离子及CN~-络合物对CN~-测定的影响。采用两根AS_3分离柱串联的方法提高分辨率,150ppmCl~-对5ppbCN~-无干扰。方法检出限0.14PPb。5ppbCN~-11次测定结果相对标准偏差为1.2％。本法可用于地表水、地下水、污水及工业废水中氰离子的分析。  相似文献   

A comparative analysis of enzyme leach and mobile metal ion selective extractions; case studies from glaciated terrain, northern Ontario   总被引：1，自引：0，他引：1  

A. F. Bajc 《Journal of Geochemical Exploration》1998,61(1-3)

The enzyme leach and MMI (mobile metal ion) selective digestions are rapidly gaining popularity in the exploration community because of their successful track record in non-glaciated, arid and tropical climatic regions. Few successful case studies from high-latitude, temperate regions have been published to date. Also lacking is a comprehensive discussion of the constraints and limitations of these geochemical methods and how they affect the successful interpretation of selective-leach survey results in glaciated regions. This paper evaluates each method using specific examples from four case studies undertaken in the glaciated region of northern Ontario. The case studies clearly demonstrate that both the MMI and enzyme leach selective digestions provide the explorationist with useful information, which, when used in conjunction with other exploration tools, can assist with the identification of potential diamond drill targets. Notwithstanding this, the techniques do not appear to work well as ‘stand alone' methods. The importance of following strict sampling protocols and obtaining high-quality observational information on the sampling site and media collected cannot be overstressed. It is only by filtering out the many variables that arise in any sampling program that a sound interpretation of the data can be made. The case studies have drawn attention to some of the apparent shortfalls of the techniques. Of these, issues such as the ability to reproduce survey results from year to year and the recognition of anomalous element associations which specifically target blind mineralisation are probably those which require significant follow-up work. Clearly, additional case studies are required from the glaciated regions of the world to assist with the optimisation of geochemical response of MMI and enzyme leach selective extractions. The mechanisms responsible for the formation of surface geochemical anomalies over deeply buried mineralisation are not well understood. The observed patterns of geochemical response in surface soils and both shallow and deep ground waters over concealed mineralisation should assist with the development of new dispersion models.  相似文献   

New perspectives on radium behavior within a subterranean estuary   总被引：2，自引：0，他引：2  

Meagan Eagle Gonneea  Paul J. Morris  Henrieta Dulaiova  Matthew A. Charette 《Marine Chemistry》2008,109(3-4):250

Over the past decade, radium isotopes have been frequently applied as tracers of submarine groundwater discharge (SGD). The unique radium signature of SGD is acquired within the subterranean estuary, a mixing zone between fresh groundwater and seawater in coastal aquifers, yet little is known about what controls Ra cycling in this system. The focus of this study was to examine controls on sediment and groundwater radium activities within permeable aquifer sands (Waquoit Bay, MA, USA) through a combination of field and laboratory studies. In the field, a series of sediment cores and corresponding groundwater profiles were collected for analysis of the four radium isotopes, as well as dissolved and sediment associated manganese, iron, and barium. We found that in addition to greater desorption at increasing salinity, radium was also closely tied to manganese and iron redox cycling within these sediments. A series of laboratory adsorption/desorption experiments helped elucidate the importance of 1) contact time between sediment and water, 2) salinity of water in contact with sediment, 3) redox conditions of water in contact with sediment, and 4) the chemical characteristics of sediment on radium adsorption/desorption. We found that these reactions are rapid (on the order of hours), desorption increases with increasing salinity and decreasing pH, and the presence of Fe and Mn (hydr)oxides on the sediment inhibit the release of radium. These sediments have a large capacity to sorb radium from fresh water. Combined with these experimental results, we present evidence from time series groundwater sampling that within this subterranean estuary there are cyclic periods of Ra accumulation and release controlled by changing salinity and redox conditions.  相似文献   

赤道附近局地激发LS-TAD的事例观测     

潘建宏  蔡红涛  谷骏  周康俊  罗逸楠  高顺组 《地球物理学报》2022,65(3):853-861

大尺度行进式大气扰动(LS-TAD)通常被认为起源于极区高纬,本文报道了一起激发于低纬赤道地区、在北半球向高纬传播的LS-TAD观测事例.2002年8月10日07:30 UT,CHAMP卫星在30°W磁赤道附近观测到显著的大气密度增强,在随后的2个连续轨道上,该密度增强依次出现在北半球更高纬度上,表现出明显的极向位移,...  相似文献   

Saturn's magnetospheric interaction with Titan as defined by Cassini encounters T9 and T18: New results     

E.C. Sittler Jr.  R.E. Hartle  J.F. Cooper  C. Bertucci  K. Szego  D.G. Simpson 《Planetary and Space Science》2010,58(3):327-1125

We present new results of Cassini's T9 flyby with complementary observations from T18. Based on Cassini plasma spectrometer (CAPS) and Cassini magnetometer (MAG), compositional evidence shows the upstream flow for both T9 and T18 appears composed of light ions (H⁺ and H₂⁺), with external pressures ∼30 times lower than that for the earlier TA flyby where heavy ions dominated the magnetospheric plasma. When describing the plasma heating and sputtering of Titan's atmosphere, T9 and T18 can be considered interactions of low magnetospheric energy input. On the other hand, T5, when heavy ion fluxes are observed to be higher than typical (i.e., TA), represents the limiting case of high magnetospheric energy input to Titan's upper atmosphere. Anisotropy estimates of the upstream flow are 1<T_⊥/T_‖<3 and the flow is perpendicular to B, indicative of local picked up ions from Titan's H and H₂ coronae extending to Titan's Hill sphere radius. Beyond this distance the corona forms a neutral torus that surrounds Saturn. The T9 flyby unexpectedly resulted in observation of two “wake” crossings referred to as Events 1 and 2. Event 2 was evidently caused by draped magnetosphere field lines, which are scavenging pickup ions from Titan's induced magnetopause boundary with outward flux ∼2×10⁶ ions/cm²/s. The composition of this out flow is dominated by H₂⁺ and H⁺ ions. Ionospheric flow away from Titan with ion flux ∼7×10⁶ ion/cm²/s is observed for Event 1. In between Events 1 and 2 are high energy field aligned flows of magnetosphere protons that may have been accelerated by the convective electric field across Titan's topside ionosphere. T18 observations are much closer to Titan than T9, allowing one to probe this type of interaction down to altitudes ∼950 km. Comparisons with previously reported hybrid simulations are made.  相似文献   

直接沿方向纠正核线影像快速算法     

李冰  耿则勋  魏小峰  郭锐增  王洛飞 《测绘学院学报》2011,(2)

核线几何是数字摄影测量研究与实际生产中常用且有效的约束条件。目前还没有直接在中心投影影像上纠正核线影像的完整算法。推导了中心投影影像上任意两条相邻核线之间的夹角模型,在此基础上给出一种直接在中心投影影像上纠正核线影像的算法,该算法的复杂度小于传统纠正算法的1/2,并且易于对任意多边形区域生成局部核线影像。通过将该算法用于多幅中心投影影像的核线影像生成,都得到正确的试验结果,说明推导的夹角模型正确,所提出的核线影像纠正算法可用并且在计算时间方面优于传统算法。  相似文献   

Some problems of slope development     

C. R. Twidale 《Australian Journal of Earth Sciences》2013,60(2):131-147

Slopes are the fundamental unit of the physiographic landscape. Yet the reasons for variations in their morphology and inferred mode of development are not well understood. The problem is complex, but the slope budget, which results primarily from the interplay of climatically induced factors and structure is significant: where the erosion of the upper slope elements surpasses that on the lower, parallel retreat prevails, but when the reverse is the case, slope decline is dominant. Complications are introduced by such factors as climatic change and fluctuations of baselevel, both local and general. But structural factors can and do override all others.

A knowledge of geomorphic history, and of processes and their effectiveness under various circumstances, in advance of that usually at our disposal at present is necessary before slopes can satisfactorily be analysed. It appears unlikely that there is a universal law of slope development..  相似文献   

Oxygen isotopic distribution along the otolith growth axis by secondary ion mass spectrometry: Applications for studying ontogenetic change in the depth inhabited by deep-sea fishes     

《Deep Sea Research Part I: Oceanographic Research Papers》2014

This study using tuna otoliths as working standards established a high lateral resolution and precision analysis to measure δ¹⁸O_otolith by secondary ion mass spectrometry. This analytical approach of the ion probe was applied to deep-sea fishes to reconstruct the likely depths inhabited by the fishes at different life history stages based on the measured δ¹⁸O_otolith values as a proxy of water temperature. Dramatic increases up to 5–6‰ in δ¹⁸O_otolith, representing a temperature decrease of approximately 20 °C, were detected in a blind cusk eel (Barathronus maculatus) otolith and in the otoliths of Synaphobranchus kaupii during leptocephalus metamorphosis to glass eel, inferred from the drop of otolith Sr/Ca ratios and increase of otolith growth increment width. δ¹⁸O_otolith profiles clearly divided the fish's life history into a planktonic stage in the mixed layer of the ocean and a benthic stage on the deep-sea ocean bottom. The habitat shift signal was recorded within a 150 µm width of otolith growth zone, which was too narrow to be clearly detected by mechanical drilling and conventional isotopic ratio mass spectrometry. However, variations down to −7‰ were found in δ¹⁸O_otolith profiles as the result of Cs²⁺ beam sputter in the core and larval portions of the otoliths. Carbon mapping by electron probe microanalyzer and staining by toluidine blue suggested abundant proteins existed in the areas with anomaly negative δ¹⁸O_otolith values, which cannot be interpreted as a habitat change but due to the isotopic fractionation by O emission from the proteins. These results implied that careful design and understanding of the chemical composition of the analytical areas or tracks on the heterogeneous otolith was essential for highly accurate and precise analysis.  相似文献   

Getting Away with the Stolen Vehicle: An Investigation of Journey-after-Crime*     

《The Professional geographer》2013,65(4):422-433

Abstract

Analyses of criminals' travel patterns can provide significant suggestions to improve crime management. This study extends the investigation of criminals' travel behavior from journey-to-crime to journey-after-crime. Moreover, new methods are developed to examine the spatial patterns of location pairs when restricted by the underlying geographical process. The methods are employed to investigate criminals' journey-after-auto-theft in the city of Buffalo, New York. The analyses reveal that auto thieves' trips from vehicle-theft locations to the corresponding vehicle-recovery locations are local in nature. The travel distances are significantly shorter than the randomly simulated trips; the travel directions are biased from the random directions as well.  相似文献