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1.
Due to the unique chemical properties that are similar but still progressively change, the rare earth elements （REEs） are useful tracers of various geochemical processes in the lithosphere and hydrosphere. However, despite many studies of REE geochemistry in the ocean, the aqueous geochemistry of REEs in lake waters has been poorly documented. In the present study, two special karst lakes are chosen as case studies to investigate the distributions of dissolved REEs in lake water. Although the two lakes, Hongfeng and Aha, are both alkaline and have high pH from 7.9 to 8.7 and high carbonate concentrations, the Aha Lake has been more severely affected by acidic mining drainage with high Fe, Mn and SO42 concentrations. In the present study, the concentrations of dissolved rare-earth elements in lake waters were determined by inductively coupled plasma mass spectrometry. The result shows that the concentrations of dissolved REEs in the studied alkaline karst lakes, as compared to the concentrations of REEs in seawater, are much lower than the other investigated terrestrial surface waters in previous studies. The key factor controlling dissolved REE distributions is pH value which is negatively correlated with REE concentrations. Due to high concentration of carbonate ion and alkaline character of water chemistry, the shale （PAAS） normalized patterns of dissolved REEs show marked HREE enrichment in all water samples. This is primarily the result of the preferential formation of stronger carbonate complexes with the HREEs. In alkaline or intermediate waters, REE-carbonate complexes are the dominant and typical species, which account for about more than 90% of the total dissolved REEs.  相似文献   

2.
The accessory minerals apatite and sphene are the main carriers of REE in alkaline rocks.Their chondrite-normalized REE patterns decline sharply to the right as those of the host rocks,In the patterns an obvious negative Eu anomaly and a positive Ce anomaly can be seen in apatite and sphene,respectively.Zircon from alkaline rocks is different in REE pattern,I,e,. a nearly symmetric“V“-shaped pattern with a maximum negative Eu anomaly.Compared with the equivalents from granites,apatite,sphene and zircon from alkaline rocks are all characterized by higher (La/Yb)N ratio and less Eu depletion,As to the relative contents of REE in minerals,apatite,sphene and zircon are enriched in LREE,MREE and HREE respectively,depending on their crystallochemical properties.  相似文献   

3.
In the coastal aquifers of Kaluvelly （Bengal coast, India）, the over exploitation of the main aquifer （the Vanur sandstone） has created a piezometric depression. Water flows from the sea towards inland. A salinization problem is questioned. The geochemical study was dedicated to major, minor and trace elements as well as isotope ratios （δ^18O, δD, δ^37Cl and ^87Sr/^86Sr）. The catchment comprises a crystalline bedrock hinterland （chamockites） overlaid by sediment. The Vanur and Cuddalore sandstones, the two main layers, are issued from the decay of chamockites upland. The geochemical feature of a water body is linked both to the composition of the hosted rock and the interaction time between water and rock. In the deeper parts of the Vanur aquifer, a mixture with long-residence time groundwaters has been evidenced. These waters can originate from a pocket of water entrapped in the Vanur or from the charnockites downward. No seawater intrusion could be assessed. Piezometric data suggest a possible hydraulic connection between the Cuddalore and the Vanur aquifers. Major, minor element data and isotope ratios do not allow to distinguish between old waters from the different aquifers. Data evidence the heterogeneity of the charnokite formation which is characterized by high Ba contents. On the whole, the two sandstones are depleted compared to charnockites in alkaline and earth-alkaline elements, and enriched in less soluble element such as Th or Zr. Trace elements in groundwaters waters from the chamockite aquifer exhibit a high concentration of Ba as compared to Vanur and Cuddalore waters. As Ba is a soluble element, the concentration of Ba in waters is related to the concentration in the hosted rocks. The Li concentration, slightly higher in Vanur rocks, allows to distinguish waters from the deeper parts of the Vanur aquifer. For insoluble elements such as Ti, the hosted rock signature cannot be seen. The Ti concentration in water samples seems to rely on the reaction progress rather than on the available amount. Trace element data show that waters recovered from chamockites and sandstone aquifers present different geochemical features. The host rock signature can be seen in the chamockite and Vanur aquifers for some alkaline and alkaline-earth elements （mainly Ba and Li）.  相似文献   

4.
Water samples from the Wujiang River, a typical karst river system, were analyzed for major ion concentrations and δ^34S values of dissolved sulfate in order to identify the sources of sulfate, quantify the sulfate export flux and understand the role of sulfur cycling in chemical weathering rate of carbonate. Spatial variations in sulfate concentration and sulfur isotopic composition of tributaries over the catchment area are obvious, allowing to decipher S sources between rocks and atmosphere. According to the variations in sulfate concentration and isotopic composition, it is inferred that sulfate ions in the upper-reach river waters may have three sources, rain water, sulfate resultant from oxidation of pyrite in coal, and sulfate from sulfide deposits. In the lower reaches, the S isotopic composition of the samples lies mainly on a mixing trend between evaporite sulfate and rainwater sulfate, the contribution of sulfate from oxidation of pyrite being lesser. A pronounced seasonal variation in both content and isotopic composition of sulfate characterizes the Wujiang River. The average sulfate concentration of the waters is 0.65 mmol/L in winter, 0.17 mmol/L higher than that in summer. River water δ^34S values range from -15.7‰ to 18.9‰ in winter, while the δ^34S values of river waters in summer vary to a lesser extent than in winter, from -11.5‰ to 8.3‰. The δ^34S values of the main stream range from -6.7‰ to -3.9‰ in summer, averaging 3‰ lower than in winter. This indicates that in summer, when the discharge increases, the contribution of a source enriched in light isotopes to the atmosphere or the oxidation of pyrite in coal is more important.  相似文献   

5.
Based on REE abundances in megacrysts and host basalts and their equilibrium conditions,it has proved that megacrysts may have been produced from the magma derived from the host rocks or of more basic composition.The REE ratios of megacrysts to host rocks may be taken as partition coefficients when both are equilibrium with each other.The crystal fractionation of megacrysts has caused the evolution of REE in the magma.It is obvious that some host basalts are the product of magma evolution after crystal fractionation.According to REE abundances in the host rocks and the partition coefficients between crystal and liquid,the history of crystal fractionation of magma can be traced.  相似文献   

6.
The formation depth of metamorphic rocks in the Dabie ultrahigh pressure metamorphic (UHPM) zone influences not only our understanding of formation mechanism and evolution processes of collision orogenic belt, but also the studies on earth's interior and geodynamic processes. In this study, the isotopic data of metamorphic rocks in the Dabie UHPM zone are discussed to give constraints on the formation depth in the Dabie UHPM zone. The εSr of eclogite in the Dabie UHPM zone varies from 18 to 42, and the εNd varies from -6.1 to -17, both of them show the characters of isotopic disequilibrium. The oxygen isotope studies indicate that the protoliths of these UHPM rocks have experienced oxygen isotope exchange with meteoric water (or sea water) before metamorphism and no significant changes in the processes of metamorphism on their oxygen isotope composition have been recorded in these rocks. Except for one sample from Bixiling, all samples of eclogite from Dabie UHPM zone show the 3He/4He ratios from 0.79×10-7 to 9.35×10-7, indicating the important contribution of He from continental crust. All Sr, Nd, O and He isotopic studies indicate that the UHPM rocks retain the isotopic characteristics of their protoliths of crust origin. No significant influence of mantle materials has been found in these metamorphic rocks. Trying to explain above isotopic characteristics, some researchers assume that the speeds of dipping thrust and uplifting of rocks were both very high. In this condition, there will not be enough time for isotopic exchange between crust protolith and mantle materials. Therefore, we can not see the tracer of mantle materials in these UHPM rocks. However, this assumption can not be justified with available knowledge. Firstly, it was estimated that the whole process of UHPM took at least 15 Ma. During such a long period, and at the metamorphic temperature of ≥700 ℃, the protolith of crust origin can not escape from isotopic exchange with mantle materials if the UHPM have happened in the mantle depth of ≥100 km. In contrast, all problems will be dismissed if we assume that the UHPM have happened at the depth still in crust.  相似文献   

7.
In the last forty years, the rare-earth elements （REEs） have been used as a powerful tool for solving various geological and geochemical problems due to their unique and chemically coherent behavior. The river sediments are produced by weathering, transportation and deposition. Nesbitt suggested that the rare-earth elements had been mobilized and fractionated during supracrustal alteration of the Torrongo granite, southeastern Australia. Nevertheless, recently, our replicate estimation for REE patterns in sediments revealed that there is nearly no variation in REE patterns. This suggests that invariability of REE patterns in weathering and solidification can be used as a tracer for constraining the provenance of stream sediments. In order to trace the pathway of the river sediments geochemically, based on the REE geochemistry from the river sediments and rocks, we have monitored the REE abundance of stream sediments at branch rivers of the Namhan River in South Korea for three years. The branches studied are Bokhacheon, Shinduncheon and Yanghwacheon. The sediments were divided into coarse （〉300 μm） and fine fractions （〈300 μm）. As a result, we could observe that major element compositions were similar to each other regardless of particle size and sampling date. This suggests that it is difficult to deduce a geochemical difference between river sediments based on major element composition and particle size. The geochemical characteristics of surrounding soils were similar to those of fine river sediments. And the chondrite-normalized REE patterns of most of the fine and coarse sediments in combination with grain sizes and drainage area showed very close relationship with the surrounding rocks. However, some sites showed that there were large variations in REE patterns including total REE abundance and Eu anomaly due to feldspars. This variation trend of REE patterns suggests that changes might have happened in sediment supply for the drainage system in the study area due to floods or large-scale construction.  相似文献   

8.
This paper re-describes the characteristics of pre-Ordovician (Pt3) metamorphic volcanic rocks in the Huimin-Manlai region of Yunnan Province from the aspects of petrographic characteristics, rock assemblage, petrochemistry, REE, trace elements, lead isotopes and geotectonic setting. The metamorphic volcanic rocks maintain blasto-intergranular and blasto-andesitic textures; the volcanic rocks are characterized by a basalt-andesite-dacite assemblage; the volcanic rocks are basic-intermediate-intermediate-acid in chemical composition, belonging to semi-alkaline rocks, with calc-alkaline series and tholeiite series coexisting, and they are characterized by low TiO2 contents; their REE distribution patterns are of the LREE-enrichment right-inclined type; the volcanic rocks are enriched in large cation elements and commonly enriched in Th and partly depleted in Ti, Cr and P, belonging to the Gondwana type as viewed from their Pb isotopic composition; petrochemically the data points fall mostly within the field of island-arc volcanic rocks. All these characteristics provided new evidence for the existence of original Tethysan island-arc volcanic rocks in the region studied.  相似文献   

9.
Petrographic and geochemical analyses of three Cretaceous lithostratigraphic sandstone units were undertaken to constrain their provenance and tectonic setting. Petrographic analysis showed that there are differences in composition between the three sandstone bodies, which can be attributed to differences in provenance relief, transport distance and geology of the terrain. Composition of the three lithostratigraphic sandstone bodies fall within the craton interior field.
Framework mode and chemical features indicated their derivation from basaltic volcanics, source rocks during the early rifting stage, and felsic, intermediate and mafic igneous source rocks located at the southeast basement complex terrain, with minor sedimentary components from the uplifted and folded older Cretaceous strata.
The chemical composition of the sandstones is mainly related to source rocks, chemical weathering conditions and transport agents. The source rocks were derived mainly from the southeastern Precambrian basement of Nigeria. Through examination of the sandstones, the tectonic setting was modeled. The Benue Trough belongs to a continental sedimentary basin of the passive margin type.
The tectonic evolution from Albian to Maastrichtain of the trough is contributed to the difference in framework mode and chemical composition of the sandstones. The evolution of the basin was reconstructed in terms of sandstone petrology and geochemistry. The tectonic evolution can be subdivided into three stages from the petrology and geochemistry data. The first stage covers Albian; the second stage the Turonian-Coniacian, and the third stage the Campanian-Maastrichtain. These are the three mega discontinuities in the sandstone composition among these three stages. These three discontinuities signify the influence of tectonism.  相似文献   

10.
In natural waters inorganic mercury （Hg） and methylmercury （MeHg） are complexed with a variety of inorganic and organic ligands, such as OH^-, Cl^-, sulfide, thiols, and dissolved organic matter （DOM）. The bioavailability and toxicity of Hg and MeHg are related to their speciation, instead of their total concentrations. Among these species, Hg-DOM and MeHg-DOM complexes are the least known, due to the complexity and site-specificity of DOM in natural waters. Here we report the complexation between DOM and Hg or MeHg using fluorescence spectroscopy. The Suwannee River fulvic acid, peat humic acid, amino acid typotophan, and natural organic matter from the Suwannee River, Nordic River, and Delta Marsh were studied at their respective excitation/emission maxima,  相似文献   

11.
The ability of organic matter as well as carbonate ions to extract rare earth elements (REEs) from sandy sediments of a Coastal Plain aquifer was investigated for unpurified organic matter from different sources (i.e., Mississippi River natural organic matter, Aldrich humic acid, Nordic aquatic fulvic acid, Suwannee River fulvic acid, and Suwannee River natural organic matter) and for extraction solutions containing weak (i.e., CH3COO−) or strong (i.e., ) ligands. The experimental results indicate that, in the absence of strong REE complexing ligands in solution, the amount of REEs released from the sand is small and the fractionation pattern of the released REEs appears to be controlled by the surface stability constants for REE sorption with Fe(III) oxides/oxyhydroxides. In the presence of strong solution complexing ligands, however, the amount and the fractionation pattern of the released REEs reflect the strength and variation of the stability constants of the dominant aqueous REE species across the REE series. The varying amount of REEs extracted by the different organic matter employed in the experiments indicates that organic matter from different sources has different complexing capacity for REEs. However, the fractionation pattern of REEs extracted by the various organic matter used in our experiments is remarkable consistent, being independent of the source and the concentration of organic matter used, as well as solution pH. Because natural aquifer sand and unpurified organic matter were used in our experiments, our experimental conditions are more broadly similar to natural systems than many previous laboratory experiments of REE-humic complexation that employed purified humic substances. Our results suggest that the REE loading effect on REE-humic complexation is negligible in natural waters as more abundant metal cations (e.g., Fe, Al) out-compete REEs for strong binding sites on organic matter. More specifically, our results indicate that REE complexation with organic matter in natural waters is dominated by REE binding to weak sites on dissolved organic matter, which subsequently leads to a middle REE (MREE: Sm-Ho)-enriched fractionation pattern. The experiments also indicate that carbonate ions may effectively compete with fulvic acid in binding with dissolved REEs, but cannot out compete humic acids for REEs. Therefore, in natural waters where low molecular weight (LMW) dissolved organic carbon (DOC) is the predominant form of DOC (e.g., lower Mississippi River water), REEs occur as “truly” dissolved species by complexing with carbonate ions as well as FA, resulting in heavy REE (HREE: Er-Lu)-enriched shale-normalized fractionation patterns. Whereas, in natural terrestrial waters where REE speciation is dominated by organic complexes with high molecular weight DOC (e.g., “colloidal” HA), only MREE-enriched fractionation patterns will be observed because the more abundant, weak sites preferentially complex MREEs relative to HREEs and light REEs (LREEs: La-Nd).  相似文献   

12.
The aquatic chemistry of rare earth elements in rivers and estuaries   总被引：17，自引：0，他引：17  
Laboratory experiments were carried out to determine how pH, colloids and salinity control the fractionation of rare earth elements (REEs) in river and estuarine waters. By using natural waters as the reaction media (river water from the Connecticut, Hudson and Mississippi Rivers) geochemical reactions can be studied in isolation from the large temporal and spatial variability inherent in river and estuarine chemistry. Experiments, field studies and chemical models form a consistent picture whereby REE fractionation is controlled by surface/solution reactions. The concentration and fractionation of REEs dissolved in river waters are highly pH dependent. Higher pH results in lower concentrations and more fractionated composition relative to the crustal abundance. With increasing pH the order of REE adsorption onto river particle surfaces is LREEs > MREEs > HREEs. With decreasing pH, REEs are released from surfaces in the same order. Within the dissolved (<0.22 µm) pool of river waters, Fe-organic colloids are major carriers of REEs. Filtration through filters and ultrafilters with progressively finer pore sizes results in filtrates which are lower in absolute concentrations and more fractionated. The order of fractionation with respect to shale, HREEs > MREEs > LREEs, is most pronounced in the solution pool, defined here as <5K and <50K ultrafiltrates. Colloidal particles have shale-like REE compositions and are highly LREE enriched relative to the REE composition of the dissolved and solution pools. The addition of sea water to river water causes the coagulation of colloidal REEs within the dissolved pool. Fractionation accompanies coagulation with the order of sea water-induced removal being LREEs > MREEs > HREEs. While the large scale removal of dissolved river REEs in estuaries is well established, the release of dissolved REEs off river particles is a less studied process. Laboratory experiments show that there is both release and fractionation of REEs when river particles are leached with seawater. The order of sea water-induced release of dissolved REE(III) (LREEs > MREEs > HREEs) from Connecticut River particles is the same as that associated with lowering the pH and the same as that associated with colloidal particles. River waters, stripped of their colloidal particles by coagulation in estuaries, have highly evolved REE composition. That is, the solution pool of REEs in river waters are strongly HREE-enriched and are fractionated to the same extent as that of Atlantic surface seawater. This strengthens the conclusions of previous studies that the evolved REE composition of sea water is coupled to chemical weathering on the continents and reactions in estuaries. Moreover, the release of dissolved Nd from river particles to sea water may help to reconcile the incompatibility between the long oceanic residence times of Nd (7100 yr) and the inter-ocean variations of the Nd isotopic composition of sea water. Using new data on dissolved and particle phases of the Amazon and Mississippi Rivers, a comparison of field and laboratory experiments highlights key features of REE fractionation in major river systems. The dissolved pool of both rivers is highly fractionated (HREE enriched) with respect to the REE composition of their suspended particles. In addition, the dissolved pool of the Mississippi River has a large negative Ce-anomaly suggesting in-situ oxidation of Ce(III). One intriguing feature is the well developed maximum in the middle REE sector of the shale normalized patterns for the dissolved pool of Amazon River water. This feature might reflect competition between surface adsorption and solution complexation with carbonate and phosphate anions.  相似文献   

13.
Rare earth element (REE) concentrations in alkaline lakes, circumneutral pH groundwaters, and an acidic freshwater lake were determined along with the free carbonate, free phosphate, and free sulfate ion concentrations. These parameters were used to evaluate the saturation state of these waters with respect to REE phosphate and carbonate precipitates. Our activity product estimates indicate that the alkaline lake waters and groundwaters are approximately saturated with respect to the REE phosphate precipitates but are significantly undersaturated with respect to REE carbonate and sulfate precipitates. On the other hand, the acidic lake waters are undersaturated with respect to REE sulfate, carbonate, and phosphate precipitates. Although carbonate complexes tend to dominate the speciation of the REEs in neutral and alkaline waters, our results indicate that REE phosphate precipitates are also important in controlling REE behavior. More specifically, elevated carbonate ion concentrations in neutral to alkaline natural waters tend to enhance dissolved REE concentrations through the formation of stable REE-carbonate complexes whereas phosphate ions tend to lead to the removal of the REEs from solution in these waters by the formation of REE-phosphate salts. Removal of REEs by precipitation as phosphate phases in the acid lake (pH=3.6) is inconsequential, however, due to extremely low [PO 4 3– ] F concentrations (i.e., 10–23 mol/kg).  相似文献   

14.
Humic Ion-Binding Model V, which focuses on metal complexation with humic and fulvic acids, was modified to assess the role of dissolved natural organic matter in the speciation of rare earth elements (REEs) in natural terrestrial waters. Intrinsic equilibrium constants for cation-proton exchange with humic substances (i.e., pKMHA for type A sites, consisting mainly of carboxylic acids), required by the model for each REE, were initially estimated using linear free-energy relationships between the first hydrolysis constants and stability constants for REE metal complexation with lactic and acetic acid. pKMHA values were further refined by comparison of calculated Model V “fits” to published data sets describing complexation of Eu, Tb, and Dy with humic substances. A subroutine that allows for the simultaneous evaluation of REE complexation with inorganic ligands (e.g., Cl−, F−, OH−, SO42−, CO32−, PO43−), incorporating recently determined stability constants for REE complexes with these ligands, was also linked to Model V. Humic Ion-Binding Model V’s ability to predict REE speciation with natural organic matter in natural waters was evaluated by comparing model results to “speciation” data determined previously with ultrafiltration techniques (i.e., organic acid-rich waters of the Nsimi-Zoetele catchment, Cameroon; dilute, circumneutral-pH waters of the Tamagawa River, Japan, and the Kalix River, northern Sweden). The model predictions compare well with the ultrafiltration studies, especially for the heavy REEs in circumneutral-pH river waters. Subsequent application of the model to world average river water predicts that organic matter complexes are the dominant form of dissolved REEs in bulk river waters draining the continents. Holding major solute, minor solute, and REE concentrations of world average river water constant while varying pH, the model suggests that organic matter complexes would dominate La, Eu, and Lu speciation within the pH ranges of 5.4 to 7.9, 4.8 to 7.3, and 4.9 to 6.9, respectively. For acidic waters, the model predicts that the free metal ion (Ln3+) and sulfate complexes (LnSO4+) dominate, whereas in alkaline waters, carbonate complexes (LnCO3+ + Ln[CO3]2−) are predicted to out-compete humic substances for dissolved REEs. Application of the modified Model V to a “model” groundwater suggests that natural organic matter complexes of REEs are insignificant. However, groundwaters with higher dissolved organic carbon concentrations than the “model” groundwater (i.e., >0.7 mg/L) would exhibit greater fractions of each REE complexed with organic matter. Sensitively analysis indicates that increasing ionic strength can weaken humate-REE interactions, and increasing the concentration of competitive cations such as Fe(III) and Al can lead to a decrease in the amount of REEs bound to dissolved organic matter.  相似文献   

15.
With the aim of contributing to the knowledge of the geochemical behaviour and mobility of the rare earth element (REE) in the natural water systems, the ground and surface waters of the Ottana-Orani area (Central Sardinia, Italy) were sampled. The study area consists of albititic bodies included in Hercynian granodiorites. The waters have pH in the range of 6.0-8.6, total dissolved solid (TDS) of between 0.1 and 0.6 g/l, and major cation composition dominated by Ca and Na, whereas predominant anions are Cl and/or HCO3.The pH and the major-element composition of the waters are the factors affecting the concentration of REE in solution. The concentrations of ∑REE+Y in the samples filtered at 0.4 μm vary between 140 and 1600 ng/l, with La of between 14 and 314 ng/l, and Yb of between <6 and 12 ng/l. A negative Ce anomaly, especially marked at high pH, is observed in the groundwaters. The surface waters show lower REE concentrations, which are independent of pH, and negligible Ce anomaly.Speciation calculations, carried out with the EQ3NR computer program, showed that the complexes with the CO32− ligand are the dominant REE species at pH in the range of 6.7-8.6. The REE3+ ions dominate the speciation at pH <6.7 and only in the light REE (LREE).The relative concentrations of REE in water roughly reflect those in the aquifer host rocks. However, when concentrations of REE in water are normalised relative to the parent rocks, a preferential fractionation of heavy REE (HREE) into the water phase can be observed, suggesting the greater mobility and stability of HREE in aqueous solution.  相似文献   

16.
《Applied Geochemistry》2000,15(9):1345-1367
Rare Earth Elements (REEs), and Sr and Nd isotope distributions, have been studied in mineralized waters from the Massif Central (France). The CO2-rich springs are characterized by a neutral pH (6–7) associated with total dissolved solids (TDS) from 1 to 7 g l−1. The waters result from the mixing of very mineralized water pools, thought to have equilibrated at a temperature of around 200°C with superficial waters. These two mineral water pools evidenced by Sr isotopes and dissolved REEs could reflect 2 different stages of water–rock interaction and an equilibrium with different mineral assemblages.The concentrations of individual dissolved REEs and total dissolved REEs (ΣREE), in the mineral waters examined, vary over several orders of magnitude but are not dependent on the main parameters of the waters (TDS, T°C, pH, Total Organic C). The dissolved REE concentrations presented as upper continental crust normalized patterns show HREE enrichment in most of the samples. The time evolution of REE patterns does not show significant fluctuations except in 1 borehole, located in the Limagne d’Allier area, which was sampled on 16 occasions over an 18 month period. Ten samples are HREE-enriched, whereas 6 samples show flat patterns.The aqueous speciation of REEs shows that CO2−3 complexes dominate (>80%) over the free metal, F−, SO2−4 and HCO−3 complexes. The detailed speciation demonstrates that the fractionation of REEs (i.e. the HREE enrichment) in CO2-rich and pH neutral fluids is due essentially to the predominance of the CO2−3 complexes.The Sr isotopic composition of the mineral waters in the Massif Central shows different mixing processes; in the Cézallier area at least 3 end-member water types exist. The most dilute end-member is likely to originate as poorly mineralized waters with minimal groundwater circulation. Two other mineralized end-members are identified, although the link between the geographical location of spring outflow and the mixing proportion between the 2 end-members is not systematic. The range in ϵNd(0) for mineralized waters in the Massif Central correlates well with that of the known parent rocks except for 4 springs. One way to explain the ϵNd(0) in these instances is a contribution from drainage of volcanic rocks. The isotopic systematics help to constrain the hydrogeological models for this area.  相似文献   

17.
Acid mine drainage is a major source of water pollution in the Sarcheshmeh porphyry copper mine area. The concentrations of heavy metals and rare earth elements (REEs) in the host rocks, natural waters and acid mine drainage (AMD) associated with mining and tailing impoundments are determined. Contrary to the solid samples, AMDs and impacted stream waters are enriched in middle rare earth elements (MREEs) and heavy rare earth elements (HREEs) relative to light rare earth elements (LREEs). This behavior suggests that REE probably fractionate during sulfide oxidation and acid generation and subsequent transport, so that MREE and HREE are preferentially enriched. Speciation modeling predict that the dominant dissolved REE inorganic species are Ln3+, Ln(SO4)2−, LnSO4+, LnHCO32+, Ln(CO3)2− and LnCO3+. Compared to natural waters, Sarcheshmeh AMD is enriched in REEs and SO42−. High concentrations of SO42− lead to the formation of stable LnSO4+, thereby resulting in higher concentrations of REEs in AMD samples. The model indicates that LnSO4+ is the dissolved form of REE in acid waters, while carbonate and dicarbonate complexes are the most abundant dissolved REE species in alkaline waters. The speciation calculations indicate that other factors besides complexation of the REE's, such as release of MREE from dissolution and/or desorption processes in soluble salts and poorly crystalline iron oxyhydroxy sulfates as well as dissolution of host rock MREE-bearing minerals control the dissolved REE concentrations and, hence, the MREE-enriched patterns of acid mine waters.  相似文献   

18.
《Applied Geochemistry》2004,19(8):1339-1354
Ferrous iron rapidly oxidizes to Fe (III) and precipitates as hydrous Fe (III) oxides in acid mine waters. This study examines the effect of Fe precipitation on the rare earth element (REE) geochemistry of acid mine waters to determine the pH range over which REEs behave conservatively and the range over which attenuation and fractionation occur. Two field studies were designed to investigate REE attenuation during Fe oxidation in acidic, alpine surface waters. To complement these field studies, a suite of six acid mine waters with a pH range from 1.6 to 6.1 were collected and allowed to oxidize in the laboratory at ambient conditions to determine the partitioning of REEs during Fe oxidation and precipitation. Results from field experiments document that even with substantial Fe oxidation, the REEs remain dissolved in acid, sulfate waters with pH below 5.1. Between pH 5.1 and 6.6 the REEs partitioned to the solid phases in the water column, and heavy REEs were preferentially removed compared to light REEs. Laboratory experiments corroborated field data with the most solid-phase partitioning occurring in the waters with the highest pH.  相似文献   

19.
碳酸盐岩是地球表层岩石圈的重要组成部分,其化学组成可提供沉积环境与海洋水体演化等信息,然而,前人对碳酸盐岩中稀土等元素的分布与变化特征关注不足。本文选择穿越中国东部6个一级大地构造单元的3条地球化学走廊带,系统采集了582件碳酸盐岩地层样品,并准确分析了包括稀土元素(REE)在内的81项指标的含量。结果表明,中国东部地球化学走廊带碳酸盐岩稀土元素(REE＋Y)总量为(0.59～183)×10-6,均值为24.0×10-6,纯净碳酸盐岩(CMC含量≥99％)均值为4.80×10-6。PAAS标准化后其显示具有轻稀土相对于中稀土和重稀土略亏损、δEu轻微正异常、δCe中度负异常等特征。白云岩中稀土含量、LREE/HREE值一般低于石灰岩;砂泥质含量相近时,前中生代各时代碳酸盐岩稀土分布模式相差不大,各构造单元稀土分布特征基本相似;与其他时代相比,中生代及中新元古代碳酸盐岩具有相对较平坦的稀土分布模式。研究表明,碳酸盐岩中稀土分布受碎屑物质影响明显,表现为稀土元素含量与碳酸根负相关,与碎屑物质相关元素(Si、Ti、Rb、Cs、Th、Zr等)、黏土相关元素(Al、Fe、K等)等正相关。成岩过程及白云化过程对较纯净碳酸盐岩中稀土分布特征影响不明显。我国古生代纯净碳酸盐岩分布模式受控于海相环境,其分布模式与现今海水相近;中生代纯净石灰岩受到陆相或海陆交互相的影响,具有较平坦的稀土分布模式。氧化还原条件对δCe的影响较δEu更为明显,δCe值受海相环境控制,极端正异常值(δCe＞1.3)受到还原环境或/和热液影响。若假定海水中REE自中元古代至今无太大变化,各时代稀土元素分配系数均值介于103.55～102.39,分配系数差异是造成碳酸盐岩中轻稀土亏损、Ce负异常及Y正异常的主要原因。微生物(席)可富集稀土等金属元素并改变沉积环境,这可能是造成中新元古界碳酸盐岩较平坦的稀土分布模式的主要原因。  相似文献   

20.
Rare earth element (REE) adsorption onto sand from a well characterized aquifer, the Carrizo Sand aquifer of Texas, has been investigated in the laboratory using a batch method. The aim was to improve our understanding of REE adsorption behavior across the REE series and to develop a surface complexation model for the REEs, which can be applied to real aquifer-groundwater systems. Our batch experiments show that REE adsorption onto Carrizo sand increases with increasing atomic number across the REE series. For each REE, adsorption increases with increasing pH, such that when pH >6.0, >98% of each REE is adsorbed onto Carrizo sand for all experimental solutions, including when actual groundwaters from the Carrizo Sand aquifer are used in the experiments. Rare earth element adsorption was not sensitive to ionic strength and total initial REE concentrations in our batch experiments. It is possible that the differences in experimental ionic strength conditions (i.e., 0.002-0.01 M NaCl) chosen were insufficient to affect REE adsorption behavior. However, cation competition (e.g., Ca, Mg, and Zn) did affect REE adsorption onto Carrizo sand, especially for light rare earth elements (LREEs) at low pH. Rare earth element adsorption onto Carrizo sand can be successfully modeled using a generalized two-layer surface complexation model. Our model calculations suggest that REE complexation with strong surface sites of Carrizo sand exceeds the stability of the aqueous complexes LnOH2+, LnSO4+, and LnCO3+, but not that of Ln(CO3)2- or LnPO4o in Carrizo groundwaters. Thus, at low pH (<7.3), where major inorganic ligands did not effectively compete with surface sites for dissolved REEs, free metal ion (Ln3+) adsorption was sufficient to describe REE adsorption behavior. However, at higher pH (>7.3) where solution complexation of the dissolved REEs was strong, REEs were adsorbed not only as free metal ion (Ln3+) but also as aqueous complexes (e.g., as Ln(CO3)2- in Carrizo groundwaters). Because heavy rare earth elements (HREEs) were preferentially adsorbed onto Carrizo sand compared to LREEs, original HREE-enriched fractionation patterns in Carrizo groundwaters from the recharge area flattened along the groundwater flow path in the Carrizo Sand aquifer due to adsorption of free- and solution-complexed REEs.  相似文献   

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