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1.
《Chemical Geology》2006,225(1-2):156-171
Groundwater samples were collected along a groundwater flow path in the Carrizo Sand aquifer in south Texas, USA. Field measurements that included pH, specific conductivity, temperature, dissolved oxygen (DO), oxidation–reduction potentials (Eh in mV), alkalinity, iron speciation, and H2S concentrations were also conducted on site. The geochemistry (i.e., concentrations, shale-normalized patterns, and speciation) of dissolved rare element elements (REEs) in the Carrizo groundwaters are described as a function of distance along a flow path. Eh and other redox indicators (i.e., DO, Fe speciation, H2S, U, and Re) indicate that redox conditions change along the flow path in the Carrizo Sand aquifer. Within the region of the aquifer proximal to the recharge zone, groundwaters exhibit both highly oxidizing and localized mildly reducing conditions. However, from roughly 10 km to the discharge zone, groundwaters are reducing and exhibit a progressive decrease in redox conditions. Dissolved REE geochemical behavior exhibits regular variations along the groundwater flow path in the Carrizo Sand aquifer. The changes in REE concentrations, shale-normalized patterns, and speciation indicate that REEs are not conservative tracers. With flow down-gradient, redox conditions, pH and solution composite, and adsorption modify groundwater REE concentrations, fractionation patterns, and speciation.  相似文献   

2.
Arsenic and Antimony in Groundwater Flow Systems: A Comparative Study   总被引：3，自引：0，他引：3  
Arsenic (As) and antimony (Sb) concentrations and speciation were determined along flow paths in three groundwater flow systems, the Carrizo Sand aquifer in southeastern Texas, the Upper Floridan aquifer in south-central Florida, and the Aquia aquifer of coastal Maryland, and subsequently compared and contrasted. Previously reported hydrogeochemical parameters for all three aquifer were used to demonstrate how changes in oxidation–reduction conditions and solution chemistry along the flow paths in each of the aquifers affected the concentrations of As and Sb. Total Sb concentrations (SbT) of groundwaters from the Carrizo Sand aquifer range from 16 to 198 pmol kg−1; in the Upper Floridan aquifer, SbT concentrations range from 8.1 to 1,462 pmol kg−1; and for the Aquia aquifer, SbT concentrations range between 23 and 512 pmol kg−1. In each aquifer, As and Sb (except for the Carrizo Sand aquifer) concentrations are highest in the regions where Fe(III) reduction predominates and lower where SO4 reduction buffers redox conditions. Groundwater data and sequential analysis of the aquifer sediments indicate that reductive dissolution of Fe(III) oxides/oxyhydroxides and subsequent release of sorbed As and Sb are the principal mechanism by which these metalloids are mobilized. Increases in pH along the flow path in the Carrizo Sand and Aquia aquifer also likely promote desorption of As and Sb from mineral surfaces, whereas pyrite oxidation mobilizes As and Sb within oxic groundwaters from the recharge zone of the Upper Floridan aquifer. Both metalloids are subsequently removed from solution by readsorption and/or coprecipitation onto Fe(III) oxides/oxyhydroxides and mixed Fe(II)/Fe(III) oxides, clay minerals, and pyrite. Speciation modeling using measured and computed Eh values predicts that Sb(III) predominate in Carrizo Sand and Upper Floridan aquifer groundwaters, occurring as the Sb(OH)30 species in solution. In oxic groundwaters from the recharge zones of these aquifers, the speciation model suggests that Sb(V) occurs as the negatively charged Sb(OH)6− species, whereas in sufidic groundwaters from both aquifers, the thioantimonite species, HSb2S4 − and Sb2S4 2−, are predicted to be important dissolved forms of Sb. The measured As and Sb speciation in the Aquia aquifer indicates that As(III) and Sb(III) predominate. Comparison of the speciation model results based on measured Eh values, and those computed with the Fe(II)/Fe(III), S(-II)/SO4, As(III)/As(V), and Sb(III)/Sb(V) couples, to the analytically determined As and Sb speciation suggests that the Fe(II)/Fe(III), S(-II)/SO4 couples exert more control on the in situ redox condition of these groundwaters than either metalloid redox couple.  相似文献   

3.
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   

4.
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   

5.
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   

6.
对大同盆地典型高砷地下水开展了稀土元素地球化学研究.研究表明: 高砷地下水具有低∑REE含量及富集重稀土(HREEs)特征.地下水中低含量∑REE与含水层沉积物中Fe-Mn氧化物/氢氧化物对REEs的吸附有关.地下水中重稀土元素相对于轻稀土元素的富集可能是吸附作用和碳酸根离子同REEs发生络合作用的共同结果.采用平均大陆上地壳标准化的地下水稀土元素分布表现出显著的Ce及Eu正异常.地下水Ce/Ce*值及Eu含量与Fe+Mn具有显著相关性, 表明铁锰氧化物还原性溶解是控制Ce/Ce*值及Eu含量特征的主要因素.Ce/Ce*值及Eu含量与As浓度的关系表明, Ce异常及Eu含量特征能对地下水中As的富集进行有效指示.   相似文献   

7.
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   

8.
The chemical analysis of 19 water wells in Ferdows area, Northeastern Iran, has been evaluated to determine the hydrogeochemical processes and ion concentration background in the region. In the study area, the order of cation and anion abundance is Na+ > Ca2+ > Mg2+ > K+ and Cl? > SO 4 ?2  > HCO3 ? > NO3 ?, respectively, and the dominating hydrochemical types are Na–Cl. Most metal concentrations in water depend on the mineral solubility, and pH, Eh, and salinity of the solution. Their ΣREE concentrations showed excellent correlations with parameters such as TDS and pH. North American Shale Composite (NASC)-normalized REE patterns are enriched in the HREEs relative to the LREEs for all groundwaters. They all have positive Eu anomalies (Eu/Eu* = 0.752–3.934) and slightly negative Ce anomalies (Ce/Ce* = 0.019–1.057). Reduction–oxidation, complexation, desorption, and re-adsorption alter groundwater REE concentrations and fractionation patterns. The positive Eu anomalies in groundwaters are probably due to preferential mobilization of Eu2+ relative to the trivalent REEs in the reducing condition.  相似文献   

9.
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   

10.
《Applied Geochemistry》2000,15(6):695-723
Ground and surface waters collected from two undisturbed Zn–Pb massive sulphide deposits (the Halfmile Lake and Restigouche deposits) and active mines in the Bathurst Mining Camp (BMC), NB, Canada were analysed for the rare earth elements (REE). REE contents are highly variable in waters of the BMC, with higher contents typical of waters with higher Fe and lower pH. There are significant differences between ground- and surface waters and between groundwaters from different deposits. The REE contents of surface waters are broadly similar within and between deposit areas, although there are spatial variations reflecting differences in pH and redox conditions. Surface waters are characterised by strong negative Ce anomalies ([Ce/Ce*]NASC as low as 0.08), produced by oxidation of Ce3+ to Ce4+ and preferential removal of Ce4+ from solution upon leaving the shallow groundwater environment. Groundwaters and seeps typically lack significant Ce anomalies reflecting generally more reducing conditions in the subsurface environment and indicating that Ce oxidation is a rapid process in the surface waters. Deeper groundwaters at the Halfmile Lake deposit are characterised by REE patterns that are similar to the host lithologies, whereas most groundwaters at the Restigouche deposit have LREE-depleted patterns compared to NASC. Halfmile Lake deposit groundwaters have generally lower pH values, whereas Restigouche deposit groundwaters show greater heavy REE-complexation by carbonate ions. Shallow waters at the Halfmile Lake and Stratmat Main Zone deposits have unusual patterns which reflect either the adsorption of light REE onto colloids and fracture-zone minerals and/or precipitation of REE–phosphate minerals. Middle REE-enrichment is typical for ground- and surface waters and is highest for neutral pH waters. The labile portion of stream sediments are generally more middle REE-enriched than total sediment and surface waters indicating that the REE are removed from solution by adsorption to Fe- and Mn-oxyhydroxides in the order middle REE≥light REE>heavy REE.  相似文献   

11.
Rare earth element (REE) concentrations were determined in acid mine drainage (AMD), bedrock, pyrite, and coal samples from the Sitai coal mine and the Malan coal mine in Shanxi province, China. The AMD displayed high REE concentrations with typical convex shale-normalized patterns. The REE concentrations in the bedrock samples are one order of magnitude higher than those found in pyrite and coal samples. The high REE concentrations in AMD most likely come from the acidic solution leached out REE in bedrock. Results from laboratory and field experiments show that pH is the most important factor controlling the fractionation of REE; but Fe, Al, and Mn colloids and secondary minerals also affects their fractionation. As the pH increased from 4 to 6, the concentrations of total dissolved REE decreased from 520 to 0.875???g?L?1. Fe and Al in AMD has less influence on the fractionation of dissolved REE than low concentrations of Mn. HREE were preferentially removed by secondary minerals and colloids, followed by MREE. Rare earth element??s speciation modeling indicates that sulfate complexes (LnSO4 + and Ln(SO4) 2 ? , 79?C91%) and free-metal species (Ln3+, 8.8?C21%) are the dominant REE species in the AMD, but the REE-sulfate complexation could not explain the MREE-enriched patterns.  相似文献   

12.
The competitive binding of rare earth elements (REE) to purified humic acid (HA) and MnO2 was studied experimentally using various HA/MnO2 ratios over a range of pH (3 to 8). MnO2, humic acid and REE solutions were simultaneously mixed to investigate the kinetics of the competitive reactions. Aqueous REE–HA complex is the dominant species whatever the experiment time, pH and HA/MnO2 ratio. The value of the distribution coefficients between MnO2 and solution (log KdRee/Mno2) increases with the HA/MnO2 ratio, indicating that part of the REE–HA complexes are adsorbed onto MnO2. The development of a Ce anomaly appears strongly limited in comparison with inorganic experimental conditions. Throughout the experimental run time, for HA/MnO2 ratios of less than 0.4, MnO2 acts as a competitor leading to a partial dissociation of the REE–HA complex. The majority of the dissociated REE is readsorbed onto the MnO2 surface. The readsorption of REE is expressed by an increased Ce anomaly on the log KdRee/Mno2 pattern as well as a change in shape of the coefficient distribution of REE between soluble HA and solution pattern (log KdRee/HA decrease for the heavy rare earth elements — HREE). Thus, REE are not only bound to MnO2 as a REE–HA complex, but also as REE(III). Moreover, the competition between HA and MnO2 for REE binding is shown to be higher at low pH (< 6) and low DOC/Mn ratio. This study partially confirms previous work that demonstrated the control of REE adsorption by organic matter, while shedding more light on the impact of pH as well as complexation reaction competition on long-term REE partitioning between solid surface and organic solutions. The latter point is important as regards to REE speciation under conditions typical of rock and/or mineral alteration.  相似文献   

13.
The thorium and rare-earth element (Th-REE) deposit at Morro do Ferro formed under supergene lateritic weathering conditions. The ore body consists of shallow NW-SE elongated argillaceous lenses that extend from the top of the hill downwards along its south-eastern slope. The deposit is capped by a network of magnetite layers which protected the underlying highly weathered, argillaceous host rock from excessive erosion. The surrounding country rocks comprise a sequence of subvolcanic phonolite intrusions that have been strongly altered by hydrothermal and supergene processes.From petrological, mineralogical and geochemical studies, and mass balance calculations, it is inferred that the highly weathered host rock was originally carbonatitic in composition, initially enriched in Th and REEs compared to the surrounding silicate rocks. The intrusion of the carbonatite caused fenitic alteration in the surrounding phonolites, consisting of early potassic alteration followed by a vein-type Th-REE mineralization with associated fluorite, carbonate, pyrite and zircon. Subsequent weathering has completely decomposed the carbonatite forming a residual supergene enrichment of Th and REEs.Initial weathering of the carbonatite has created a chemical environment that might have been conductive to carbonate and phosphate complexing of the REEs in groundwaters. This may have appreciably restricted the dissolution of primary REE phases. Strongly oxidic weathering has resulted in a fractionation between Ce and the other light rare earth elements (LREEs). Ce3+ is oxidized to Ce4+ and retained together with Th by secondary mineral formation (cerianite, thorianite), and by adsorption on poorly crystalline iron- and aluminium-hydroxides. In contrast, the trivalent LREEs are retained to a lesser degree and are thus more available for secondary mineral formation (Nd-lanthanite) and adsorption at greater depths down the weathering column. Seasonally controlled fluctuations of recharge waters into the weathering column may help to explain the observed repetition of Th-Ce enriched zones underlain by trivalent LREE enriched zones.  相似文献   

14.
Experiments were conducted to evaluate the impact of organic complexation on the development of Ce anomalies and the lanthanide tetrad effect during the adsorption of rare-earth elements (REE) onto MnO2. Two types of aqueous solutions—NaCl and NaNO3—were tested at pH 5 and 7.5. Time-series experiments indicate that a steady-state is reached within less than 10 h when REE occur as free inorganic species, whereas steady state is not reached before 10 d when REE occur as REE-humate complexes. The distribution coefficients (KdREE) between suspended MnO2 and solution show no or only very weak positive Ce anomaly or lanthanide tetrad effect when REE occur as humate complexes, unlike the results obtained in experiments with REE occurring as free inorganic species. Monitoring of dissolved organic carbon (DOC) concentrations show that log KdREEorganic/KdDOC ratios are close to 1.0, implying that the REE and humate remain bound to each other upon adsorption. Most likely, the Ce anomaly reduction/suppression in the organic experiments arises from a combination of two processes: (i) inability of MnO2 to oxidize Ce(III) because of shielding of MnO2 surfaces by humate molecules and (ii) Ce(IV) cannot be preferentially removed from solution due to quantitative complexation of the REE by organic matter. We suggest that the lack of lanthanide tetrad effect arises because the adsorption of REE-humate complexes onto MnO2 occurs dominantly via the humate side of the complexes (anionic adsorption), thereby preventing expression of the differences in Racah parameters for 4f electron repulsion between REE and the oxide surface. The results presented here explain why, despite the development of strongly oxidizing conditions and the presence of MnO2 in the aquifer, no (or insignificant) negative Ce anomalies are observed in organic-rich waters. The present study demonstrates experimentally that the Ce anomaly cannot be used as a reliable proxy of redox conditions in organic-rich waters or in precipitates formed at equilibrium with organic-rich waters.  相似文献   

15.
分析地质样品中稀土元素的含量,现有的方法都受到基体干扰和共存元素干扰,电感耦合等离子体质谱(ICP-MS)已在痕量元素分析中得到广泛应用,通过条件优化可准确测定稀土元素。本文建立了ICP-MS同时测定铁矿石中钇镧铈镨钕钐铕钆铽镝钬铒铥镱镥15个稀土元素的方法,样品用盐酸、硝酸和氢氟酸高温密闭消解,消解完全后转移定容,在线加入103Rh、115In、185Re内标液进行测定,方法回收率为95%~104%,精密度(RSD)≤3.5%。对12个国家24个代表性主产区进口的铁矿石样品进行检测,分析其稀土元素的配分模式特征为右倾型轻稀土富集,现阶段的进口铁矿粉多为多产区复合配矿。本方法较其他传统方法大幅降低能耗,提高了分析效率,初步探讨的稀土元素丰度特征可为研究主产区铁矿石的矿床成因、提高我国烧结球团矿的加工工艺提供依据。  相似文献   

16.
Soil secondary minerals are important scavengers of rare earth elements (REEs) in soils and thus affect geochemical behavior and occurrence of REEs. The fractionation of REEs is a common geochemical phenomenon in soils but has received little attention, especially fractionation induced by secondary minerals. In this study, REEs (La to Lu and Y) associated with soil-abundant secondary minerals Fe-, Al-, and Mn-oxides in 196 soil samples were investigated to explore the fractionation and anomalies of REEs related to the minerals. The results show right-inclined chondrite-normalized REE patterns for La–Lu in soils subjected to total soil digestion and partial soil extraction. Light REEs (LREEs) enrichment features were negatively correlated with a Eu anomaly and positively correlated with a Ce anomaly. The fractionation between LREEs and heavy REEs (HREEs) was attributed to the high adsorption affinity of LREEs to secondary minerals and the preferred activation/leaching of HREEs. The substantial fractions of REEs in soils extracted by oxalate and Dithionite-Citrate-Bicarbonate buffer solutions were labile (10 %–30 %), which were similar to the mass fraction of Fe (10 %–20 %). Furthermore, Eu was found to be more mobile than the other REEs in the soils, whereas Ce was less mobile. These results add to our understanding of the distribution and geochemical behavior of REEs in soils, and also help to deduce the conditions of soil formation from REE fractionation.  相似文献   

17.
We sampled two box-core sediments from the slope of the eastern South Korea Plateau (SKP) in the East Sea (Sea of Japan) at water depths of 1400 and 1700 m. Two chemical fractions of extractable (hydroxylamine/acetic acid) and residual rare earth elements (REEs) together with Al, Ca, Fe, Mg, Mn, P, S, As, Mo, and U were analyzed to assess the post-depositional redistribution of REEs. Extractable Fe and Mn are noticeably abundant in the oxic topmost sediment layer (<3 cm). However, some trace elements (e.g., S, As, Mo, U) are more abundant at depth, where redox conditions are different. Analysis of upper continental crust (UCC)-normalized (La/Gd)UCC, (La/Yb)UCC, and (Ce/Ce*)UCC revealed that the extractable REE is characterized by middle REE (MREE) enrichment and a positive cerium (Ce) anomaly, different from the case of the residual fraction which shows slight enrichment in light REEs (LREEs) with no Ce anomaly. The extractable MREEs seem to have been incorporated into high-Mg calcite during reductive dissolution of Fe oxyhydroxides. In the top sediment layer, the positive Ce anomaly is attributed to Ce oxide, which can be mobilized in deeper oxygen-poor environments and redistributed in the sediment column. In addition, differential concentrations of Ce and other LREEs in pore water appear to result in variable (Ce/Ce*)UCC ratios in the extractable fraction at depth.  相似文献   

18.
《Applied Geochemistry》2004,19(3):261-271
The distribution of Rare Earth Elements (REE) was investigated in the acidic waters (lake and groundwater) of a lignite mining district (Germany). The Fe- and SO4-rich lake water (pH 2.7) displays high REE contents (e.g. La∼70 μg/l, Ce∼160 μg/l) and an enrichment of light REE (LREE) in the NASC normalised pattern. Considering the hydrodynamic model and geochemical data, the lake water composition may be calculated as a mixture of inflowing Quaternary and mining dump groundwaters. The groundwater of the dump aquifer is LREE enriched. Nevertheless, the leachates of dump sediments generally have low REE contents and display flat NASC normalised patterns. However, geochemical differences and REE pattern in undisturbed lignite (LREE enriched pattern and low water soluble REE contents) and the weathered lignite of the dumps (flat REE pattern and high water soluble REE contents) suggest that lignite is probably the main REE source rock for the lake water.  相似文献   

19.
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   

20.
Geochemical and mineralogical studies were conducted on the 12-m-thick weathering profile of the Kata Beach granite in Phuket, Thailand, in order to reveal the transport and adsorption of rare earth elements (REE) related to the ion-adsorption type mineralization. The parent rock is ilmenite-series biotite granite with transitional characteristics from I type to S type, abundant in REE (592 ppm). REE are contained dominantly in fluorocarbonate as well as in allanite, titanite, apatite, and zircon. The chondrite-normalized REE pattern of the parent granite indicates enrichment of LREE relative to HREE and no significant Ce anomaly. The upper part of the weathering profile from the surface to 4.5 m depth is mostly characterized by positive Ce anomaly, showing lower REE contents ranging from 174 to 548 ppm and lower percentages of adsorbed REE from 34% to 68% compared with the parent granite. In contrast, the lower part of the profile from 4.5 to 12 m depth is characterized by negative Ce anomaly, showing higher REE contents ranging from 578 to 1,084 ppm and higher percentages from 53% to 85%. The negative Ce anomaly and enrichment of REE in the lower part of the profile suggest that acidic soil water in an oxidizing condition in the upper part mostly immobilized Ce4+ as CeO2 and transported REE3+ downward to the lower part of the profile. The transported REE3+ were adsorbed onto weathering products or distributed to secondary minerals such as rhabdophane. The immobilization of REE results from the increase of pH due to the contact with higher pH groundwater. Since the majority of REE in the weathered granite are present in the ion-adsorption fraction with negative Ce anomaly, the percentages of adsorbed REE are positively correlated with the whole-rock negative Ce anomaly. The result of this study suggests that the ion-adsorption type REE mineralization is identified by the occurrence of easily soluble REE fluorocarbonate and whole-rock negative Ce anomaly of weathered granite. Although fractionation of REE in weathered granite is controlled by the occurrence of REE-bearing minerals and adsorption by weathering products, the ion-adsorption fraction tends to be enriched in LREE relative to weathered granite.  相似文献   

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