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1.
Heavy metal retention in secondary precipitates from a mine rock dump and underlying soil, Dalarna, Sweden 总被引：7，自引：2，他引：7
This study investigates the retention of heavy metals in secondary precipitates from a sulfidic mine rock dump and underlying
podzolic soils by means of mineralogical and chemical extraction methods. The rock dump, which is at least 50 years old, consists
of a 5–10-cm-thick leached zone and an underlying 110–115-cm-thick accumulation zone. Optical microscopy and electron microprobe
analyses confirm that pyrrhotite weathering has proceeded much further in the leached horizon relative to the accumulation
horizon. The weathering of sulfides in the leached zone has resulted in the migration of most heavy metals to the accumulation
zone or underlying soils, where they are retained in more stable phases such as secondary ferric minerals, including goethite
and jarosite. Some metals are temporarily retained in hydrated ferrous sulfates (e.g., melanterite, rozenite).
Received: 28 October 1996 · Accepted: 24 February 1997 相似文献
2.
Continuous monitoring of a 15 m high heavily instrumented experimental waste rock pile (0.053 wt.% S) since 2006 at the Diavik diamond mine in northern Canada provided a unique opportunity to study the evolution of fresh run-of-mine waste rock as it evolved over annual freeze–thaw cycles. Samples were collected from soil water solution samplers to measure pore water properties, from twelve 4 to 16 m2 basal collection lysimeters to measure basal leachate properties in the region underlying the crest of the pile (the core), and from basal drains to measure aggregate total pile leachate properties. By 2012, monitoring of pore water geochemistry within the core structure of the test pile revealed an apparent steady state with respect to weathering geochemistry, represented by (i) a flush of pre-existing blasting residuals and applied tracers, (ii) declining pH, (iii) a stepwise progression and subsequent equilibrium with acid-neutralizing phases (depletion of available carbonates; equilibrium with respect to aluminum hydroxide phases and subsequent iron (III) hydroxide phases), and (iv) concordant release of SO4, major cations (Ca, Mg, K, Na, Si), and trace metals (Al, Fe, Ni, Co, Cu, Zn). Distinct, high concentration ‘spring flushes’, characteristic of drainage in northern environments and primarily explained by a combination of fluid residence time and the build-up of oxidation products over the winter, were released from core drainage each season. Following the initial flush, the concentration of all dissolved constituents steadily declined, with distinct minimums prior to freeze-up. The opposite trend was observed in the cumulative pile drainage, in which early season leachate dominated by snowmelt and batter flow had low concentrations and late season leachate dominated by contributions from the core of the pile (indicated by season end merging of core and cumulative drainage geochemistry) had higher concentrations. Northern waste rock pile drainage geochemistry is strongly influenced by freeze–thaw cycling and varying core and batter subsystem contributions to total drainage. A comprehensive understanding of thermal cycling in waste rock piles is an important component of temporal predictions of drainage water composition based on up-scaling or reactive transport modeling. 相似文献
3.
This study reports on the transfer of contaminants from waste rock dumps and mineralised ground into soils, sediments, waters
and plants at the rehabilitated Mary Kathleen uranium mine in semi-arid northwest Queensland. Numerous waste rock dumps were
partly covered with benign soil and the open pit mine was allowed to flood. The mineralised and waste calc-silicate rock in
the open pit and dumps has major (>1 wt%) Ca, Fe and Mg, minor (>1,000 ppm) Ce, La, Mn, P and S, subminor (>100 ppm) Ba, Cu,
Th and U, and trace (<100 ppm) As, Ni, Pb, Y and Zn values. Consequently, chemical and physical weathering processes have
acted on waste rock and on rock faces within the open pit, mobilising many elements and leading to their dispersion into soils,
stream sediments, pit water and several plant species. Chemical dispersion is initiated by sulfide mineral breakdown, generation
of sulfuric acid and formation of several soluble, transient sulfate minerals as evaporative efflorescent precipitates. Radiation
doses associated with the open pit average 5.65 mSv year−1; waste dumps commonly have lower values, especially where soil-covered. Surface pit water is slightly acid, with high sulfate
values accompanied by levels of U, Cu and Ni close to or above Australian water guideline values for livestock. Dispersion
of U and related elements into soils and stream sediments occurs by physical (erosional) processes and from chemical precipitation.
Plants growing in the mine void, on waste dumps and contaminated soil display evidence of biological uptake of U, LREE, Cu
and Th and to a lesser degree of As, Ni, Pb, Y and Zn, with values being up to 1–2 orders of magnitude above background sites
for the same species. Although rehabilitation procedures have been partly successful in reducing dispersion of U and related
elements into the surrounding environment, it is apparent that 20 years after rehabilitation, there is significant physical
and chemical mobility, including transfer into plants. 相似文献
4.
《Applied Geochemistry》1994,9(5):583-595
A steady-state geochemical model has been developed to study water-rock interactions controlling metal release from waste rock heaps at the Aitik Cu mine in northern Sweden. The Cu release in drainage waters from the site is of environmental concern. The waste rock heaps are treated as single completely mixed flow-through reactors. The geochemical model includes kinetices of sulphide and primary silicate mineral weathering, heterogeneous equilibrium with secondary mineral phases and speciation equilibrium. Field monitoring of drainage water composition provides a basis for evaluation of model performance.The relative rate of oxidative weathering of sulphides and dissolution of primary silicate minerals, using published kinetic data, are consistent with net proton and base cation fluxes at the site. The overall rate of Fe2+ oxidation within the heap is three orders of magnitude faster than that which could be explained by surface-catalysed reaction kinetics. This suggests significant activity of iron-oxidizing bacteria. The absolute weathering rates of sulphides and silicate minerals, normalized to a measured BET surface area, are approximately two orders of magnitude lower at field scale than published rates from laboratory experiments. Because of the relative absence of carbonate minerals, the weathering of biotite and plagioclase feldspar are important sources of alkalinity. 相似文献
5.
The physicochemical processes that affect acid mine drainage (AMD) in unsaturated waste rock piles and the capabilities of small-scale laboratory experiments to predict AMD from waste rock are not well understood. An integrated laboratory and field study to measure and compare low sulfide waste rock and drainage characteristics at various scales has been initiated. This paper describes the design, construction and instrumentation of three field-scale experimental waste rock piles (test piles), and six active zone lysimeters at the Diavik diamond mine in the Northwest Territories, Canada. The test piles are comprised of granitic and sulfide-bearing metasedimentary waste rock excavated during open pit mining operations. One test pile contains waste rock with a target S content of <0.04 wt.% S; the second test pile contains waste rock with a target S content of >0.08 wt.% S; and the third test pile contains the higher sulfide waste rock (>0.08 wt.% S) and was re-sloped and capped with a low permeability till layer and a low sulfide waste rock cover. The first two test piles are approximately 15 m high with bases of 50 m by 60 m, and the re-sloped test pile has a larger base of 80 m by 125 m. Instrumentation was selected to measure matrix flow, geochemistry of pore water and drainage, gas-phase O2 concentration, temperature evolution, microbiological populations, waste rock permeability to air, and thermal conductivity, as well as to resolve mass and flow balances. Instrument locations were selected to characterize coupled physicochemical processes at multiple scales and the evolution of those processes over time. Instruments were installed at a density such that the number of instruments that survived construction (40% to >80% by instrument type) was sufficient to allow adequate characterization of the physicochemical processes occurring at various scales in the test piles. 相似文献
6.
We investigated chemical weathering in a high elevation granitic environment in three selected watersheds located in the Pyrenees (France). The sites were located on glacial deposits derived from similar Hercynian (∼300 Ma) granites characterized by the occurrence of zoned plagioclases and trace calcic phases (epidote, prehnite, sphene, apatite). The surface waters at those sites show high Ca/Na molar ratios (>1) which could not be explained by the dissolution of the major plagioclase (oligoclase) present in the rocks. The coupled approach of investigating stream water chemistry and the mineralogy and chemistry of rocks and soils allowed us to explore the role of the weathering of trace calcic minerals in calcium export at the watershed scale. The weathering of the trace calcic minerals which represent ∼ 1% of the total rock volume are responsible for more than 90% of the calcium export at the sites. Annual cationic fluxes (∼ 23.104 eq/km2/yr) calculated for the Estibère watershed are among the highest reported for high elevation systems draining granitic rocks and ∼ 80% of this annual cationic flux can be attributed to the weathering of trace calcic phases. Calculations based on isotopic values (87Sr/86Sr) go in the same direction. Except apatite, the trace calcic phases appear to be mainly silicates, thus the type of chemical weathering observed in the Estibère watershed may have an influence on atmospheric CO2 consumption by granite weathering. However, comparison with other watersheds draining granitic environments worldwide, and with the two other sites in the Pyrenees, indicate that the role of trace calcic phases is important in most young environments exposed to chemical weathering (e.g., high elevation catchments on glacial deposits). Other factors such as the date of glacial retreat, the physical denudation rate, the hydrological functioning of the watershed and the nature and structure of the soil cover are also important. 相似文献
7.
对一近地表铀矿体中某些铀系长寿命核素的放射性平衡状态和１４种微量元素迁移特征研究得出，自该铀矿床６３Ｍａ前生成至今，仅近１Ｍａ来，当上覆花岗岩遭剥蚀使矿体近地表时，矿石中天然放射性核和微量元素才因水－岩反应沿围岩破碎带，裂隙发生迁移；裂隙两侧岩石受水－岩反应影响的范围较小，裂隙面的化学组分以溶失为主，裂隙两侧粘土化花岗岩中则以核素、元素的扩散和吸附为主，最后阐述了本研究结果对高放废物处置库安全评价 相似文献
8.
《Applied Geochemistry》1991,6(6):597-612
A small (4 km2) drainage basin in northeastern Washington contains highly uraniferous groundwater and highly uraniferous peaty sediments of Holocene age. The U is derived from granitic bedrock that underlies the entire drainage basin and that contains 9–16 ppm U. This local bedrock was studied by petrographic, chemical and isotopic methods to determine conditions of its petrogenesis and post-emplacement history that may have contributed to its present high U content and source-rock capability. The original magma was derived by anatexis of Precambrian continental crust of probable mixed metaigneous and metasedimentary character. Mineral-melt partitioning controlled the enrichment of U in chemically evolved phases of the crystallizing melt. Following emplacement in the upper crust at ∼100Ma, the pluton interacted with meteoric-hydrothermal water at ambient temperatures 300°C. Locally intense fracturing promoted alteration, and fracturing and alteration probably continued during later regional uplift in the Eocene. Regional uplift was followed by low-temperature alteration and weathering in the middle to late Tertiary. The combined result of hydrothermal alteration and low-temperature alteration and weathering was the redistribution of U from primary mineral hosts such as allanite to new sites on fracture surfaces and in secondary minerals such as hematite. Zones of highly fractured and altered rock show the most obvious evidence of this process. A model is proposed in which high-angle fractures beneath the drainage basin were the sites of Tertiary supergene enrichments of U. Recent glacio-isostatic uplift has elevated these older enriched zones to shallow levels where they are now being leached by oxidizing groundwater. The chemistry, mineralogy, texture and geological history of this U source-rock suggest criteria for locating other granitic terrane that may contain uraniferous waters and associated young surficial U deposits. The details of U distribution and mobility at this site also apply to the general topic of U mobility in granitic rocks. 相似文献
9.
Georges Calas 《Geochimica et cosmochimica acta》1979,43(9):1521-1531
Depending upon oxygen fugacity, uranium exists in three different oxidation states in magmatic silicate liquids. The hexavalent state, present as the uranyl group, UO2+2, is stable under highly oxidizing conditions, but can still be detected in the presence of the NiNiO buffer. Under the same conditions the pentavalent state forms about 30–40% of total uranium and is also characteristic of relatively high oxygen fugacities. Optical absorption spectra obtained on granitic and basaltic glasses synthesized in the presence of the NiNiO buffer are very different: this is interpreted as being due to the presence of UO+2 complexes in the former and 6-coordinated U(V) in the latter. The tetravalent state is the most stable under reducing conditions: at the FeFeO buffer, it is the only one present. An 8-coordinated U(IV) species seems the most probable, by comparison of the spectra with those of crystallized U(IV) compounds. The trivalent state was not detected, even under the most reducing conditions. Interpretation of the spectra obtained in the glasses in terms of coordination and bonding is however difficult, due to the lack of knowledge of 5f-systems in iono-covalent systems such as oxide glasses. The presence of the pentavalent state must be taken into account in discussing partition coefficients of uranium and trans-uranium compounds in natural and synthetic systems (because of the effect of oxygen fugacity and oxide ion activity on the U(IV) U(V) system). During postmagmatic hydrothermal processes U(V) is destroyed, resulting in the early precipitation of U(IV) containing minerals and possible migration of uranyl ions. 相似文献
10.
华南花岗岩中铀活化转移的地球化学证据 总被引：10，自引：2，他引：10
采用诱发裂变径迹法研究，发现华南产铀花岗岩副矿物中的铀沿微裂隙活化转移和交代蚀变矿物的自洁作用迫使载体矿物中的铀活化再分配的地球化学现象。与经过０．０５ｍＨＣ１溶液浸泡的花岗样品进行第二次诱发裂变径迹照射结果对比，确认为活化铀的存在，并具有易转移的特点。蚀变轩上岩取订及铅同位素组成研究提供了铀在热液蚀变过程中活化转移的佐证。γ能谱测量结果证实，花岗岩中的部分铀在风化作用过程中已活化转移而钍则基本存 相似文献
11.
铀的地球化学性质与成矿——以华南铀成矿省为例 总被引：1，自引：1，他引：1
铀是强不相容元素,随着岩浆演化而不断富集,在岩浆演化末期受结构氧增加影响进入独居石、磷钇矿等副矿物中。岩浆演化通常无法直接形成达到工业品位的铀矿床。铀是对氧逸度敏感的变价元素。在表生风化过程中岩体(层)中的铀被氧化为UO_2~(2+)而极易溶解进入水体中,并可在还原环境沉淀而富集成矿,氧化还原界面是找矿的理想选区。大气水可通过断裂构造系统进入一定深度,并受热源作用形成高氧逸度的热液而萃取出岩体(层)中的铀在还原位置沉淀富集形成矿床。新元古代氧化事件以及Marinoan冰期结束使得表生风化过程中更多的U进入水体;而寒武纪生命大爆发,易在沉积盆地底部形成还原环境,有利于U的沉淀富集。受上述三方面因素控制,在华南形成了广泛分布的富铀黑色页岩层,并被之后的沉积物覆盖,成为华南各型铀矿床的铀源层。印支期构造运动使部分富铀黑色页岩层发生部分熔融形成了富铀的S型花岗岩,该类岩石亦是之后铀成矿作用的铀源岩。燕山运动后期华南发生伸展构造背景下的岩浆热事件为以大气水为主的高氧逸度热液的形成并作用于铀源岩(层)提供了有利条件,促使华南各类型铀矿床开始在白垩纪集中形成。 相似文献
12.
连山关地区位于华北克拉通北缘铀成矿省辽东铀成矿带,已知铀矿床（点）均发育在韧性剪切带附近。为了解韧性剪切带运动学、几何学构造变形机制及与铀矿的关系,本文以连山关岩体周缘韧性剪切带为研究对象,通过野外宏观调查和室内微观研究相结合的研究方法,探讨构造变形期次、韧性剪切带形成机理及其对铀成矿的控制作用。研究表明：连山关岩体周缘发育的韧性剪切带与近南北向挤压构造变形有关,其右行韧性剪切带应变类型为压扁应变,属于一般压缩-平面应变范围,Flinn指数K值在0.19~0.69之间,岩石类型属于S/SL型构造岩。研究区内铀矿体均为隐伏盲矿体,主要赋存于沿着连山关岩体和辽河群接触带右行剪切作用形成的背斜褶皱核部,和北东东向断裂关系密切。综合分析认为,连山关岩体南缘北西向韧性剪切带为一级控矿构造,是区内铀矿热液运移的通道,而剪切带边部的晚期北东东向断裂则是铀矿储存空间;铀源可能来自于太古宙古风化壳,并在大型韧性剪切活动（提供热液运移通道）和基性脉岩侵入（提供热源和还原剂）等综合因素作用下运移、富集成矿。 相似文献
13.
Jens Søndergaard Bo Elberling Gert Asmund Claus Gudum Karl Martin Iversen 《Applied Geochemistry》2007
It is well known that oxidation of sulphide-containing coal mine waste has considerable environmental impacts due to generation of acid mine drainage (AMD) containing high dissolved metal concentrations. This study is the first to evaluate seasonal trends in the release of AMD from high arctic coal mine waste rock. Runoff from an abandoned coal mine waste pile in Svalbard (78°N) was studied during the entire 3–4 month period with running water in 2005. Temporal variation in concentrations and fluxes of dissolved elements were quantified based on daily water sampling and used to evaluate weathering processes and estimate element budgets on a daily, seasonal and annual basis. Apart from alkali- and alkaline earth metals; Fe, Al, Mn, Zn and Ni were found to be the most abundant metals in the runoff. Element concentrations were highly correlated and suggest that the processes of sulphide oxidation, ion exchange and silicate weathering occurring within the waste pile were linked throughout the measuring period. Observed pH values varied from 2.8 to 5.2 and SO4 concentrations from 21 to 1463 mg L−1. Manganese and Al concentrations were observed above phytotoxic levels (up to 4 and 23 mg L−1, respectively) and were considered the most critical elements in terms of environmental impact. Throughout the summer a total dissolved quantity of 58 kg Mn, 238 kg Al and 13,700 kg SO4 was released from the pile containing approximately 200,000 m3 of pyritic waste material (<1% FeS2). The highest concentrations of metals, lowest pH values and a very high daily release of H2SO4 (up to twice as high as the following month) were observed during the first week of thaw. This is considered a result of an accumulation of weathering products, generated within the waste pile during winter and released as a pollution-flush during early spring. Similar accumulation/flush sequences were observed later in the summer where rain events following relatively long dry periods caused high daily metal fluxes and on some occasions also elevated dissolved metal concentrations. Despite highly variable weather/climate conditions during the rest of the summer the investigated waste rock pile acted like a relative constant pollution-source during this period. Future investigations regarding the environmental impact of mine waste in the region should include measurements of bioavailable metals in order to provide further details on the seasonal trends in environmental impact. 相似文献
14.
There are wide areas of granitic rocks in the Japanese orogenic belt. These granitic bodies inevitably contain fracture and fault systems associated with alteration zones. However, relatively little attention has been given to the possible influence of such widely distributed alteration zones on the migration of radionuclides from any radioactive waste repository that might in future be sited within granitic rock. In particular, the influences of alteration products and micro-fractures, due to chemical sorption and/or physical retardation require further consideration. In order to understand the retardation capacity of the altered deep granitic rocks, detailed geometrical characterization of pores, geochemical analysis, and batch sorption and flow-through experiments have been carried out. Those results show that the altered granite has a large volume of accessible pores, particularly in potassium-feldspar grains, which would influence nuclide retardation more than the accessible porosity in other minerals present, such as biotite. The distribution coefficients, Kd estimated from batch sorption tests and flow-through experiments suggest that altered granite has a high capability to retard the migration of nuclides. The retardation would probably be due to sorption on altered minerals such as sericite and iron hydroxides formed along grain boundaries and in pores created by dissolution, in addition to sorption on primary sorptive minerals. These results provide confidence that even altered and fractured parts of any granitic rock that might be encountered in a site for the disposal of high level radioactive waste may still retard radionuclide migration and thereby help the geosphere to function as a barrier. 相似文献
15.
Changes in water quality in the North Fork of the Humboldt River, Nevada are caused by weathering of waste rock from an inactive Carlin-type gold mine. Review of historical water-quality data, monthly water sampling, and continuous monitoring of water-quality parameters were used to quantify these impacts. River water pH, which ranged between 7 and 8, did not show statistically significant variation from upstream of the mine to downstream. Several constituents, most notably sulfate, calcium, and magnesium, showed statistically significant increases in dissolved-ion concentrations. These data, along with geochemical modeling, suggest that oxidation of sulfide minerals and in situ acid neutralization by carbonate host rocks are occurring. Large increases in dissolved-ion concentrations were observed twice a year—during spring snow melt and the onset of the winter precipitation season. These spikes are likely caused by flushing of pore waters that have reacted with waste rock during months-long periods when shallow groundwater recharge is not occurring. 相似文献
16.
伟晶岩型铀矿是北秦岭成矿带东段重要的铀矿类型,本文介绍了该类型铀矿的矿体特征、矿石特征、副矿物特征和年代学特征.铀矿体产于淡色含榴花岗岩体内外接触带伟晶岩脉中,围绕花岗岩体产出,形态复杂,随伟晶岩脉的形态而变化,呈似脉状、透镜状和不规则状,晶质铀矿为最主要的工业矿物.通过LA-ICP-MS锆石U-Pb定年获得含铀伟晶岩年龄为404.3±1.4 Ma,略晚于淡色含榴花岗岩体年龄,矿岩时差小,显示了岩浆成矿的特征.综合分析表明早泥盆世丹凤地区进入后碰撞构造环境,秦岭岩群发生部分熔融形成富铝含榴花岗质岩浆,随着岩浆结晶分异演化的不断进行,铀元素以U4+形式与O2-结合形成晶质铀矿,在岩体内外接触带黑云母富集部位沉淀成矿.三叠纪后接受长期隆升剥蚀,侵入岩呈岩株出露地表,围绕岩株外带产出的含铀伟晶岩脉,表现为光石沟式铀矿床.随着隆升剥蚀作用的进一步加剧,侵入岩顶部相遭受剥蚀之后以岩基出露地表,在岩体的内接触带不规则形态的含铀伟晶岩出露地表,表现为陈家庄式铀矿床.依据成矿模式,预测伟晶岩型铀矿成矿远景区2片,分别为大毛沟地区和纸房沟地区. 相似文献
17.
Chemical weathering was investigated by collecting samples from five selected weathering profiles in a high elevation granitic
environment located in Seoul, Korea. The overall changes of chemistry and mineralogical textures were examined reflecting
weathering degrees of the samples, using polarization microscopy, X-ray diffraction (XRD), electron probe micro analysis (EPMA),
X-ray fluorescence spectroscopy (XRF), and inductively coupled plasma–mass spectroscopy (ICP–MS). The chemical distribution
in the weathering profiles shows that few trace elements are slightly immobile, whereas most major (particularly Ca and Na)
and trace elements are mobile from the beginning of the granite weathering. On the other hand, there were mineralogical changes
initiated from a plagioclase breakdown, which shows a characteristic circular dissolved pattern caused by a preferential leaching
of Ca cation along grain boundaries and zoning. The biotite in that region is also supposed to be sensitive to exterior environmental
condition and may be easily dissolved by acidic percolated water. As a result, it seems that some rock-forming minerals in
the granitic rock located in Seoul are significantly unstable due to the environmental condition of acidic rainfall and steep
slopes, where they are susceptible to be dissolved incongruently leading some elements to be highly depleted. 相似文献
18.
Philippe Ildefonse Jean-Pierre Muller Blandine Clozel Georges Calas 《Engineering Geology》1990,29(4):413-439
U-deposit hosted in hydrothermally altered tuffs in Mexico, together with weathering profiles from Cameroon were studied as natural analogues of radionuclide release and migration. Using petrological and spectroscopic methods (infrared and electron paramagnetic resonance), we have distinguished successive secondary mineral parageneses and the behaviour of radionuclides.
In the U-deposit, the mineral parageneses show that uranium migration is mainly controlled by the redox potential and silica activity of the altering solutions. The high silica content of the solutions is caused by the intense alteration of volcanic rocks. Two types of secondary clay mineral parageneses are evidenced: a kaolinization, intense where uranium is accumulated in the welded tuffs, and a smectitization mainly developed in the underlying weakly welded tuffs.
Several types of kaolinite have been defined according to their genesis (fillings in fissures and feldspar pseudomorphs), their location relative to a breccia pipe where uranium has accumulated (core and rim of the pipe; surrounding rhyolitic tuffs), and particle morphology, structural order and substitutional Fecontent. It is shown that the variations of the concentration of paramagnetic defect centres, always more than ten times as important than those measured in weathering kaolinites, are only correlated to the location of the kaolinites. The highest values correspond to the breccia pipe kaolinites, e.g. kaolinites located in the uranium accumulation zones. Moreover, one or two main defects centres are detected depending on the intimate association of kaolinites with uranium-bearing minerals. Besides, in weathering kaolinites from U-depleted laterites, defect centre concentrations are correlated to the total Fe203 content in bulk samples. This means that the defect centre acts as a memory of the travel of uranium when this element was sorbed onto iron gels in the first stage of weathering.
It is concluded that paramagnetic defect centres in kaolinites might allow an efficient fingerprint of successive irradiations in the natural analogues under study and could be an useful tool to control radionuclides migration through kaolinite-containing clayey materials such as those used for waste repository.
A better understanding of radiation efficiency as well as accurate dose-ratekaolinite-containing clayey materials such as those used for waste reposit estimation are needed for a quantitative tracing of the migration ofA better understanding of radiation efficiency as well as accurate dose-ratekaolin radionuclide elements. With this aim, a simulation has been undertaken withestimation are needed for a quantitative tracing of the migration of various radiations sources. We have determined for each irradiation the parameters of the paramagnetic centres created in order to understand the way they are forming. The knowledge of the parameters governing the formation and the stability of the radiation centres in kaolinites allow to use this mineral as a natural dosimeter. 相似文献
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Mineralization with exchangeable rare earth element (REE) and yttrium (MEX-REY) has been recognized in the weathering profiles in South China since the early 1970's. This type of REY mineralization occurs in weathering profiles of parent rocks ranging in composition from granite to acidic volcanic rocks and lamprophyre. The majority of the known resources occurring in the weathering profiles of granitic rocks. Total resources of this type of REY amount to millions tons of rare earth oxides, and therefore represent one of the most important types of rare earth resources in China, particularly for heavy rare earth elements (HREE) and yttrium.Accumulation of REY in the weathering profiles of granitic rocks is strongly controlled by the resistance to weathering of the principal REY-bearing accessory minerals in the parent rocks; only a limited proportion of total REY (< 30%) is incorporated in the rock-forming minerals. MEX-REY more commonly occur in weathering profiles developed on granitic rocks within which most of the REY are incorporated in accessory minerals weakly resistant to weathering (doverite, parisite, etc.). For the well-developed weathering profiles, three horizons can be distinguished from surface downwards: the lateritic horizon (A), the weathered horizon (B), and the weathering front (C). Continuous leaching, coupled with low rate of denudation, results in the accumulation of REY in the subsurface horizons (the B and C horizons), and thus results in REE differentiation within the well-developed, layered, and mature weathering profiles. Exchangeable REY, which can be replaced by cations like NH4+ and Na+ etc. in electrolyte solutions and can be removed by complexing agents such as EDTA, are commonly the major form of REE occurrence in the B horizon. Cerium is enriched in the top layer (A horizon) and depleted in the subsurface horizons of the weathering profiles, most likely due to the oxidation of Ce(III) to Ce(IV) followed by cerianite formation or absorption onto clays and/or Fe and Al oxyhydroxides. 相似文献