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1.
In this work, the effectiveness of native and chemically modified rice bran to remove heavy metal Pb(II) ions from aqueous solution was examined. Chemical modifications with some simple and low-cost chemicals resulted in enhancement of the adsorption capacities and had faster kinetics than native rice bran. Experiments were conducted in shake flasks to monitor the upshot of parameters over a range of pH, initial Pb(II) concentrations and contact times using a batch model study. The sorption capacities q (mg g?1) increased in the following order: NaOH (147.78), Ca(OH)2 (139.08), Al(OH)3 (127.24), esterification (124.28), NaHCO3 (118.08), methylation (118.88), Na2CO3 (117.12) and native (80.24). The utmost uptake capacity q (mg g?1) was shown by NaOH-pretreated rice bran. The results showed that, using NaOH-modified rice bran, the chief removal of Pb(II) was 74.54 % at pH 5, primary Pb(II) concentration 100 mg L?1 and contact time 240 min. Equilibrium isotherms for the Pb(II) adsorption were analyzed by Langmuir and Freundlich isotherm models. The Langmuir isotherm model, showing Pb(II) sorption as accessible through the high value of the correlation coefficient (R 2 = 0.993), showed a q max value of 416.61 mg g?1. The kinetic model illustrated adsorption rates well, depicted by a second order, which gives an indication concerning the rate-limiting step. Thermodynamic evaluation of the metal ion ?G o was carried out and led to the observation that the adsorption reaction is spontaneous and endothermic in nature. NaOH chemically modified rice bran was a superb biosorbent for exclusion of Pb(II) and proved to be excellent for industrial applications.  相似文献   

2.
Unsafe lead (Pb) concentrations in leafy vegetables raised in urban and peri-urban agricultural production systems have been reported across cities in Northern Nigeria, even though Pb concentrations in soils are within regulatory safe levels. This study examined the soil enrichment, adsorption and chemical species of Pb in urban garden fields irrigated with untreated wastewater at three industrial locations in Kano, northern Nigeria. Total Pb in the soil profiles ranged from 9 to 91 mg kg?1 and decreased rapidly from the surface to the subsurface layer, but attaining nearly constant concentration at depth ≥1.2 m in the profiles. The potentially labile Pb maintained fairly constant concentration with depth up to 0.9 m, but decreased fairly rapidly with depth thereafter. There was a significant Pb enrichment of the soils, extending up to 30–60 cm depth in the soil profiles. The adsorption of Pb by the soils increased drastically with pH, and attained maximum adsorption at pH ≥ 7.0 in the surface layer, and at pH ≥ 6 in the subsurface layer. The surface soils adsorbed between 85 and 97 % of added Pb at pH ≤ 5. Free Pb2+ activities in soil solution accounted for between 46 and 87 % at pH 5–7 of total dissolved Pb (PbT). The quantifiable chemical species of Pb in solution consisted mainly of PbOH+, PbSO 4 · , PbCl+ and PbOH 2 · which accounted for between 0.9 and 26 % of PbT in soil solution at pH ≥ 5.0, but declining to between 0.1 and 2.1 % at pH ≥ 7.5. There was no apparent equilibrium between Pb2+ activities and known Pb-compounds in the soils. It was concluded from the data that reports of excess Pb concentrations in leafy vegetables raised in these soils are consistent with high free Pb2+ activities maintained in soil solution by these predominantly sandy-textured soils.  相似文献   

3.
《International Geology Review》2012,54(13):1626-1640
Dolerite dike swarms are widespread across the North China Craton (NCC) of Hebei Province (China) and Inner Mongolia. Here, we report new geochemical, Sr–Nd–Pb isotope, and U–Pb zircon ages for representative samples of these dikes. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb analysis yielded consistent Permian ages of 274.8 ± 2.9 and 275.0 ± 4.5 Ma for zircons extracted from two dikes. The dolerites have highly variable compositions (SiO2 = 46.99–56.18 wt.%, TiO2 = 1.27–2.39 wt.%, Al2O3 = 14.42–16.20 wt.%, MgO = 5.18–7.75 wt.%, Fe2O3 = 8.03–13.52 wt.%, CaO = 5.18–9.75 wt.%, Na2O = 2.46–3.79 wt.%, K2O = 0.26–2.35 wt.%, and P2O5 = 0.18–0.37 wt.%) and are light rare earth element (LREE) and large ion lithophile element (LILE, e.g. Rb, Ba, and K, and Pb in sample SXG1-9) enriched, and Th and high field strength element (HFSE, e.g. Nb and Ta in sample SXG1-9, and Ti) depleted. The mafic dikes have relatively uniform (87Sr/86Sr)i values from 0.7031 to 0.7048, (206Pb/204Pb)i from 17.77 to 17.976, (207Pb/204Pb)i from 15.50 to 15.52, (208Pb/204Pb)i from 37.95 to 38.03, and positive ?Nd(t) (3.6–7.3), and variable neodymium model ages (TDM1 = 0.75–0.99 Ga, TDM2 = 0.34–0.74 Ga). These data suggest that the dike magmas were derived from partial melting of a depleted region of the asthenospheric mantle, and that they fractionated olivine, pyroxene, plagioclase, K-feldspar, and Ti-bearing phases without undergoing significant crustal contamination. These mafic dikes within the NCC formed during a period of crustal thinning in response to extension after Permian collision between the NCC and the Siberian Block.  相似文献   

4.
Zircon, monazite, and xenotime have proven to be valuable chronometers for various geological processes due to their commonly high-U–Th and low common Pb contents. However, zircons that have crystallized in highly fractionated granites often have such high-U contents that radiation damage can lead to scattered U–Pb ages when measured with secondary ion mass spectrometry (SIMS). In this study, monazite and xenotime were separated from a number of highly fractionated granites at the Xihuashan tungsten mine, Southeast China, for alternative dating methods by SIMS. For monazite analysis, obvious excess 204Pb signal (mainly from interference of 232Th144Nd16O2 ++) was observed in high-Th (>2 wt%) monazite, which hinders 204Pb-based common Pb corrections. A 207Pb-based common Pb correction method was used instead. By employing power law relationships between Pb+/U+ versus UO2 +/U+, Pb+/Th+ versus ThO2 +/Th+ and suitable exponentials, monazites with ThO2 contents in the range of ~3–19 % do not exhibit this matrix effect. Independent SIMS U–Pb ages and Th–Pb ages of three phases of Xihuashan granite samples were consistent with each other and yielded dates of 158.7 ± 0.7, 158.0 ± 0.7, and 156.9 ± 0.7 Ma, respectively. Xenotime does show marked matrix effects due to variations of U, Th, and Y [or total rare earth element (REE), referred as ΣREE hereafter] contents. Suitable correction factors require end-member standards with extremely high or low U, Th, and Y (or ΣREE) contents. No excess 204Pb was observed, indicating that the 204Pb-based common Pb correction method is feasible. Independent 207Pb/206Pb ages can be obtained, although multi-collector mode is necessary to improve precision. The main difficulties with dating xenotime are when high-Th (U) mineral inclusions are ablated. We can identify when this occurs, however, by comparing the measured UO2 +/U+ and ThO2 +/Th+ with those in xenotime standards. Three xenotime samples from the first phase of Xihuashan granite yielded a weighted mean 207Pb/206Pb date of 159.5 ± 4.4 Ma (MSWD = 1.0) and a 206Pb/238U date of 159.4 ± 0.9 Ma (MSWD = 1.6), which are consistent with monazite U–Pb and Th–Pb ages from the same granites. This study demonstrates that monazite and xenotime are better SIMS chronometers for highly fractionated granites than zircon, which can yield doubtful ages due to high-U contents.  相似文献   

5.
We investigate the geology of Altar North (Cu–Au) and Quebrada de la Mina (Au) porphyry deposits located in San Juan Province (Argentina), close to the large Altar porphyry copper deposit (995 Mt, 0.35% Cu, 0.083 g/t Au), to present constraints on the magmatic processes that occurred in the parental magma chambers of these magmatic-hydrothermal systems. Altar North deposit comprises a plagioclase-amphibole-phyric dacite intrusion (Altar North barren porphyry) and a plagioclase-amphibole-biotite-phyric dacite stock (Altar North mineralized porphyry, 11.98 ± 0.19 Ma). In Quebrada de la Mina, a plagioclase-amphibole-biotite-quartz-phyric dacite stock (QDM porphyry, 11.91 ± 0.33 Ma) crops out. High Sr/Y ratios (92–142) and amphibole compositions of Altar North barren and QDM porphyries reflect high magmatic oxidation states (fO2 = NNO +1.1 to +1.6) and high fH2O conditions in their magmas. Zones and rims enriched in anorthite (An37–48), SrO (0.22–0.33 wt.%) and FeO (0.21–0.37 wt.%) in plagioclase phenocrysts are evidences of magmatic recharge processes in the magma chambers. Altar North and Quebrada de la Mina intrusions have relatively homogeneous isotopic compositions (87Sr/86Sr(t) = 0.70450–0.70466, εNd(t) = +0.2 to +1.2) consistent with mixed mantle and crust contributions in their magmas. Higher Pb isotopes ratios (207Pb/204Pb = 15.6276–15.6294) of these intrusions compared to other porphyries of the district, reflect an increase in the assimilation of high radiogenic Pb components in the magmas. Ages of zircon xenocrysts (297, 210, 204, 69 Ma) revealed that the magmas have experienced assimilation of Miocene, Cretaceous, Triassic and Carboniferous crustal rocks.Fluids that precipitated sulfides in the Altar deposit may have remobilized Pb from the host rocks, as indicated by the ore minerals being more radiogenic (207Pb/204Pb = 15.6243–15.6269) than their host intrusions. Au/Cu ratio in Altar porphyries (average Au/Cu ratio of 0.14 × 10?4 by weight in Altar Central) is higher than in the giant Miocene porphyry deposits located to the south: Los Pelambres, Río Blanco and Los Bronces (Chile) and Pachón (Argentina). We suggest that the increase in Au content in the porphyries of this region could be linked to the assimilation of high radiogenic Pb components in the magmas within these long-lived maturation systems.  相似文献   

6.
The crystal structure of Pb6Bi2S9 is investigated at pressures between 0 and 5.6 GPa with X-ray diffraction on single-crystals. The pressure is applied using diamond anvil cells. Heyrovskyite (Bbmm, a = 13.719(4) Å, b = 31.393(9) Å, c = 4.1319(10) Å, Z = 4) is the stable phase of Pb6Bi2S9 at ambient conditions and is built from distorted moduli of PbS-archetype structure with a low stereochemical activity of the Pb2+ and Bi3+ lone electron pairs. Heyrovskyite is stable until at least 3.9 GPa and a first-order phase transition occurs between 3.9 and 4.8 GPa. A single-crystal is retained after the reversible phase transition despite an anisotropic contraction of the unit cell and a volume decrease of 4.2%. The crystal structure of the high pressure phase, β-Pb6Bi2S9, is solved in Pna2 1 (a = 25.302(7) Å, b = 30.819(9) Å, c = 4.0640(13) Å, Z = 8) from synchrotron data at 5.06 GPa. This structure consists of two types of moduli with SnS/TlI-archetype structure in which the Pb and Bi lone pairs are strongly expressed. The mechanism of the phase transition is described in detail and the results are compared to the closely related phase transition in Pb3Bi2S6 (lillianite).  相似文献   

7.
The total lead content in the soil itself is insufficient as a measure to indicate the actual environmental risks related to the presence of lead in the soil. Understanding the mobility of lead and its chemical speciation in soil solution is of great importance for accurately assessing environmental risks posed by lead. Therefore, a laboratory study was carried out to evaluate the effect of inorganic amendments (gypsum, rock phosphate and di-ammonium phosphate) on lead mobility and chemical speciation under different moisture regimes (flooding regime and 75 % field capacity) in normal and salt-affected lead-contaminated soils. After 2, 7, 15, 30, 100 and 110 days of incubation, pore water samples were collected by using Rhizon soil moisture samplers. In order to estimate the chemical speciation of lead in pore water, Visual MINTEQ 3.0 modeling approach was used. The results showed that presence of free Pb2+, PbCl+, Pb(SO4) 2 2? , and PbH2PO4 + was significantly (P ≤ 0.05) affected by the soil moisture regime, incubation time and applied amendments in lead-contaminated soils. The Visual MINTEQ 3.0 predicted free Pb2+ species concentration was found higher in lead-contaminated soils, while PbCl+ was more pronounced in salt-affected soils. Gypsum increased the occurrence of Pb(SO4) 2 2? , while di-ammonium phosphate and rock phosphate enhanced the PbH2PO4 + species formation and decreased free Pb2+ species in pore water. Thus, gypsum is the most effective in reducing lead and free Pb2+ species concentrations in the pore water under different soil moisture regimes and incubation times in normal and salt-affected lead-contaminated soils.  相似文献   

8.
This study analyses the adsorption of Pb(II) and Cr(III) in soils. These metals are commonly found together in nature in urban wastes or industrial spillages, and the theoretical approach of the work was to evaluate the response of the soil to continuous Cr and Pb spillages to soil in terms of several physicochemical parameters. The influence of an anthropogenic input of phosphorus was evaluated. Continuous flow experiments were run in duplicates in acrylic columns (25 cm × 3.2 cm). The influent Cr(III) and Pb(II) solutions of 10 mg l?1 and 25 mg l?1 at pH 5 were pumped upward through the bottom of the columns to ensure saturation flow conditions. Also, successive experiments were run with the above concentrations of Cr(III) and Pb(II) and NaH2PO4, keeping metal to phosphorus ratio of 1:0, 1:0.1 and 1:1. Modelling parameters included Freundlich and Langmuir equations, together with the Two-site adsorption model using CXTFIT code. Results obtained allowed concluding that Pb(II) adsorption presents a certain degree of irreversibility and the continued spillages over soil increment the fraction which is not easily desorbed. Cr(III) desorption was almost complete, evidencing its high mobility in nature. The presence of an anthropogenic input of phosphorus leads to a marked increase of both Pb(II) and Cr(III) adsorption in soils. Z-potential measurements allow to discard the electrostatic attraction of Cr(III) and Pb(II) with the surface charged soil as the dominant process of metal sorption. Instead, CheaqsPro simulation allows to identify PbH2PO4 +, PbHPO4 (aq) and CrHPO4 + as the dominant species which regulate Cr(III) and Pb(II) transport in soils.  相似文献   

9.
Pollution by heavy metals presents an environmental concern, and their toxicity threats soil, water, animals and human health. Phytoremediation can be used as a solution to remediate contaminated soils. The aim of this study was to identify native plants collected from tailings: material of Pb–Zn mine sites of Fedj Lahdoum and Jebel Ressas (two abandoned mines located, respectively, in the northwest of Tunisia and in the south of Tunis City). The tolerance of plant to heavy metals (lead, zinc and cadmium) is evaluated. Soil samples were collected and analyzed for Pb, Zn and Cd concentration. The total soil Pb, Zn and Cd are, respectively, reached 6132 mg kg?1, 11,052 mg kg?1 and it doesn’t exceed 479 mg kg?1 for Cd. The highest content of Zn in plants was detected in shoots of Rumex bucephalophorus (1048 mg kg?1), and the highest Pb concentration was detected in roots of Chrysopogon zizanioides (381 mg kg?1), while for Cd Silene colorata it accumulated the highest content in roots (51 mg kg?1). From all plants, only 12 have a translocation factor for Pb which is higher than one. Among all plants, only 17 have a translocation factor that is higher than one for Zn, while for Cd only 13 plants indicate TF > 1. As for the biological absorption coefficient, all samples indicate a rate which is lower than one. These plants can be primarily hyper accumulators and useful in remediation of lead- and zinc-contaminated soils after further biochemistry researches in mechanism of accumulation and translocation of heavy metals in plants.  相似文献   

10.
The Gulf Killifish (Fundulus grandis) is one of the most abundant nekton species in the US Gulf of Mexico (GOM) salt marshes, providing an important trophic link in these systems. Recently, the use of F. grandis as an indicator species of salt marsh health in the region has been suggested because its Atlantic coast congener, the Mummichog (Fundulus heteroclitus) has filled such a role due to its demonstrated high site fidelity and small-scale movements. Given the similar life histories between species, F. grandis was assumed to exhibit the same type of small-scale movements, although this has not been documented. During summer 2013, we collected and marked 1,719 fish from a northern Gulf of Mexico estuary, recapturing 959 (56 % recapture rate). Of these recaptured fish, only 31 moved from their original tagging location, and of these, 29 moved only 100 m between sites connected by salt marsh. Based on these results, F. grandis appears to exhibit high site fidelity and make only small-scale movements, similar to F. heteroclitus, supporting its role as an indicator species.  相似文献   

11.
The solubility of all possible Zn and Pb species in aqueous chloride fluids was evaluated by means of thermodynamic simulations in systems ZnO(PbO)-aqueous solution of NaCl (KCl, NaCl + HCl) within broad ranges of temperature (600–900°C), pressure (0.7–5 kbar), and chloride concentrations, under parameters corresponding to the crystallization and degassing of granitoid magmas in the Earth’s crust. Our simulation results demonstrate that the addition of Cl to the fluid phase in the form of Na(K)Cl and HCl significantly increases the concentrations of Cl-bearing Zn and Pb complexes and the total concentration of the metals in the solutions in equilibrium with the solid oxides. In Zn-bearing fluids, the Zn(OH) 2 0 , ZnOH+, and Zn(OH) 3 ? —hydroxyl complexes and the ZnCl 2 0 , and ZnCl+ chlorocomplexes, which are predominant at low Cl concentrations (CCl < 0.05–0.1 m) give way to ZnCl 4 2? with increasing CCl, which becomes the predominant Zn species of the fluid at CCl > 0.1–0.5 m throughout the whole temperature range in question and pressures higher than 1 kbar. For Pb-bearing fluids, the T-P-X region dominated by the Pb(OH) 2 0 , and Pb(OH) 3 ? hydroxyl complexes is remarkably wider than the analogous region for Zn, particularly at elevated temperatures (≥700°C) in alkaline solutions. An increase in CCl is associated with an increase in the concentration and changes in the speciation of Pb chlorocomplexes: PbCl 2 0 → PbCl 3 ? → PbCl 4 2? . The concentrations of Zn and Pb chlorocomplexes increase with increasing pressure, decreasing temperature, and decrease pH with the addition of HCl to the system. It is demonstrated that the solubility of ZnO at any given T-P-X in alkaline solutions with low chloride concentrations are lower than the solubility of PbO. The Zn concentration increases more significantly than with the Pb concentration with increasing CCl and decreasing pH, so that the Zn concentration in acidic solutions is higher than the Pb concentration over broad ranges of temperature, pressure, and Cl concentration. Chloride complexes of Zn (ZnCl 2 0 , and ZnCl 4 2? ) and Pb (PbCl 2 0 , and PbCl 3 ? are proved to be predominant within broad T-P-X-pH ranges corresponding to the parameters under which magmatic fluid are generated. Our simulation results confirm the hypothesis that chlorocomplexes play a leading role in Zn and Pb distribution between aqueous chloride fluids and granitic melts. These simulation results are consistent with experimental data on the Zn and Pb distribution coefficients (D(Zn)f/m and D(Pb)f/m, respectively) between aqueous chloride fluids and granitic melts that demonstrated that (1) D(Zn)f/m and D(Pb)f/m increase with increasing Na and K chloride concentrations in the aqueous fluid, (2) both D(Zn)f/m and D(Pb)f/m drastically increase when HCl is added to the fluid, and (3) (D(Zn)f/m is higher than D(Pb)f/m at any given T-P-X parameters. The experimentally established decrease in D(Zn)f/m and D(Pb)f/m with increasing pressure (at unchanging temperature and Cl concentration) is likely explained by an increase in the alkalinity of the aqueous chloride fluid in equilibrium with granite melt and, correspondingly, a decrease in the Zn and Pb solubility in this fluid.  相似文献   

12.
Wadeite-type K2Si4O9 was synthesized with a cubic press at 5.4 GPa and 900 °C for 3 h. Its unit-cell parameters were measured by in situ high-T powder X-ray diffraction up to 600 °C at ambient P. The T–V data were fitted with a polynomial expression for the volumetric thermal expansion coefficient (αT = a 0 + a 1 T), yielding a 0 = 2.47(21) × 10?5 K?1 and a 1 = 1.45(36) × 10?8 K?2. Compression experiments at ambient T were conducted up to 10.40 GPa with a diamond-anvil cell combined with synchrotron X-ray radiation. A second-order Birch–Murnaghan equation of state was used to fit the P–V data, yielding K T = 97(3) GPa and V 0 = 360.55(9) Å3. These newly determined thermal expansion data and compression data were used to thermodynamically calculate the P–T curves of the following reactions: 2 sanidine (KAlSi3O8) = wadeite (K2Si4O9) + kyanite (Al2SiO5) + coesite (SiO2) and wadeite (K2Si4O9) + kyanite (Al2SiO5) + coesite/stishovite (SiO2) = 2 hollandite (KAlSi3O8). The calculated phase boundaries are generally consistent with previous experimental determinations.  相似文献   

13.
Two samples of hydroxyl-clinohumite, sample SZ0407B with approximate composition Mg8.674(14)Fe0.374(4)(Si0.99(1)O4)4(OH)2 and sample SZ0411B with composition Mg9(SiO4)4(OH)2, were synthesized at 12 GPa and 1,250 °C coexisting with olivine. Unit-cell parameters determined by single-crystal X-ray diffraction are given as follows: a = 4.7525(4) Å, b = 10.2935(12) Å, c = 13.7077(10) Å, α = 100.645(9)°, V = 659.04(9) Å3 for SZ0407B, and a = 4.7518(6) Å, b = 10.2861(12) Å, c = 13.7008(9) Å, α = 100.638(9)°, V = 658.15(9) Å3 for SZ0411B. Single-crystal X-ray intensity data were collected for crystal structure refinements of both samples. Relative to the pure-Mg sample, Fe decreases M3–OH bond lengths by ~0.010(3) Å, consistent with some ferric iron ordering into M3. Raman spectroscopy shows two strong bands in the lattice-mode region at 650 and 690 cm?1 in the Fe-bearing sample, which are not observed in the pure-Mg sample. Spectra in the H2O region show at least five bands, which are deconvolved into seven distinct O–H-stretching modes. Thermal expansion measurements were carried out for both samples from 153 to 787 K by single-crystal X-ray diffraction. The average a-, b-, c-axial and volumetric thermal expansion coefficients (10?6 K?1) are 10.5(1), 12.3(2), 12.5(2) and 34.9(5) for SZ0407B, respectively, and 11.1(1), 12.6(3), 13.7(3), 36.8(6) for SZ0411B, respectively. After heating, the unit-cell parameters were refined again for each sample at ambient condition, and no significant changes were observed, indicating no significant oxidation or dehydration during the experiment. For the DHMS phases along the brucite–forsterite join, linear regression gives a systematic linear decrease in expansivity with increasing density. Further, substitution of ferrous iron into these structures decreases thermal expansivity, making the Fe-bearing varieties slightly stiffer.  相似文献   

14.
ABSTRACT

The east–central part of Jilin Province, NE China, hosts an important polymetallic metallogenic district that contains more than 10 recently discovered large-, medium-, and small-scale Mo deposits. The Mo deposits in this area include porphyry-, skarn-, and quartz vein-type mineralization, of which the porphyry-type deposits dominate. Few studies of these mineralization-related granitoids have been undertaken. Here, we present the results of a systematic regional survey of the geochemistry and geochronology of Mo mineralization-related granites in this area. Zircon U–Pb dating of the Fuanpu, Jidetun, Shuangshan, and Jiapigou granites, all of which are associated with Mo mineralization, yielded weighted mean 206Pb/238U ages of 167.05 ± 0.81, 170.91 ± 0.83, 183.8 ± 1.1, and 182.3 ± 2.2 Ma, respectively, indicating that these plutons were emplaced during the Early–Middle Jurassic. They have SiO2 = 62.59–73.5 wt.%, Al2O3 = 13.74–16.19 wt.%, and K2O/Na2O = 0.8–2.18. Chemically, they are metaluminous to peraluminous and belong to the high-K calc-alkaline to shoshonitic series. Moreover, they are enriched in large ion lithophile elements and light rare earth elements, and are depleted in high field strength elements, which are characteristics of I type granite. Whole rock Sr–Nd–Pb isotopic compositions of these granitoids are similar (initial 87Sr/86Sr = 0.70404 to 0.70554; εNd(t) = –0.9 to 2.4; (206Pb/204Pb)t = 15.549–15.567, (207Pb/204Pb)t = 18.035–18.530, (208Pb/204Pb)t = 37.966–38.229) and altogether suggest that the magmas from which the Mo deposits were generated originated from the mantle or juvenile crust. Combining our results with regional Jurassic tectonic setting, we conclude that the mineralization of these granitoids reflected Pacific plate subduction which induced magma underplating and promoted the remelting of the juvenile crust, resulting in voluminous granitic magma.  相似文献   

15.
Athyrium wardii (Hook.) is a promising herbaceous plant species for phytostabilization of cadmium (Cd)-contaminated sites with large biomass and fast growth rate. However, little information is available on its tolerance mechanisms toward Cd. To further understand the mechanisms involved in Cd migration, accumulation and detoxification, the present study investigated subcellular distribution and chemical forms of Cd in the mining ecotypes and corresponding non-mining ecotypes of A. wardii via greenhouse pot experiment. Subcellular fractionation of Cd-containing tissues demonstrated that the majority of the element was mainly located in soluble fraction in cell walls. This indicated that both the vacuoles and cell walls might be evolved the Cd tolerance mechanisms to protect metabolically active cellular compartments from toxic Cd concentrations. Meanwhile, Cd taken up by the plant existed in different chemical forms. Results showed that the majority of Cd in plant was in undissolved Cd–phosphate complexes (extracted by 2 % CH3COOH), followed by water-soluble Cd–organic acid complexes, Cd(H2PO4)2, pectates and protein form (extracted by deionized water and 1 M NaCl), whereas only small amount of Cd in roots was in inorganic form (extracted by 80 % ethanol), which suggests low capacity to be transported to aboveground tissues. It could be suggested that Cd integrated with undissolved Cd–phosphate complexes in cell wall or compartmentalization in vacuole might be responsible for the adaptation of the mining ecotypes of A. wardii to Cd stress.  相似文献   

16.
Pb-contaminated water is a dangerous threat occurring near metallurgic and mining industries. This circumstance produces serious environment concern, due to Pb(II) high toxic effects. Several reactive materials have been reported for Pb(II) adsorption, but not all reached final Pb(II) suitable concentrations, or they are expensive and rejected in massive remediation technologies; hence, natural materials are good options. The adsorption behavior of a volcanic scoria (two sieved fractions 1425 and <425 µm) was studied toward synthetic Pb(II) water solutions in batch experiments (170.4–912.3 mg L?1) with high removal efficiencies (97%). The Langmuir model fits both fractions with high linear correlation coefficients (0.9988 and 0.9949) with high maximum capacity values (588.23 and 555.55 mg g?1). Separation factor R L parameter varies with initial concentration, and the empirical equation predicts the limits of the material usefulness, a criterion proposed in this paper for conditions’ selection. The Lagergren pseudo-second-order analysis demonstrates chemisorption; calculated rate constant (416.66 mg g?1 min?1). Weber–Morris intraparticle model proves that the adsorption phenomena occur fast on the material surface (k inst = 72 g mg?1 min?0.5). The characterization of the volcanic material afforded the elemental composition (X-ray fluorescence), and the empirical formula was proposed. X-ray diffraction patterns verify the material structure as basalt, with a plagioclase structure that matches anorthite and albite, mostly composed of quartz. The presence of oxides on the material surface explain the high Pb(II) adsorption capacity, observed on the surface by scanning electronic microscopy. The studied volcanic scoria has potential use as a Pb(II) adsorbent in water remediation technologies.  相似文献   

17.
Farming is the major source of income for the villagers of North-central Sri Lanka. However, chronic kidney disease of unknown etiology is a major health hazard in the area and it is assumed that agricultural contaminants are the major causative agents. This study focuses on the geochemistry of soils in the area to determine possible natural and anthropogenic impacts of the problem. X-ray fluorescence analysis was used to determine the abundance of selected major and trace elements. Results show that geo-enrichment for many elements indicates slight to significant variations between agricultural and non-agricultural soils. Geoaccumulation index (I geo) shows higher pollution levels of Pb and V (2 < I geo < 3) and very lower pollution levels of As, Zn, Cu, Fe and Mn (1 < I geo < 2) in agricultural soils. However, I geo for non-agricultural soils implies lack of contaminations (I geo < 1). Positive correlations of As with Pb and Zn and negative correlations with Cu, Ni and Cr suggest that they may have derived from different sources such as sulfide minerals of basement rocks, fertilizers and agrochemicals. The results of this study suggest that there is no significant threat from As and other trace elements to soils. The accumulation of these elements in agricultural fields may have been effectively controlled by seasonal farming practices. However, there is a potential environmental risk from elements such as Pb and V due to their significant enrichment in soils.  相似文献   

18.
ABSTRACT

The Anqing region in Lower Yangtze River metallogenic belt is one of the important Cu polymetal producers in China. The origin of Cu polymetallic deposits in the region is closely related to Early Cretaceous adakitic intrusions. To constrain the petrogenetic and metallogenic significance of the adakitic rocks, a detailed geochronological, geochemical, and Sr–Nd–Pb–Hf isotopic study was performed. The Anqing adakitic rocks (SiO2 = 57.4–64.2 wt.%) consist mainly of quartz monzodiorite, formed at 138.2 ± 1.7 Ma (Mean Standard Weighted Deviation (MSWD) = 0.61). They have high MgO, Al2O3, Sr, and low Rb, Y, Yb contents, together with high Sr/Y (50.5–222) and La/Yb (31.9–46.9) ratios. They also show negative whole-rock εNd(t) (?9.8 to ?8.5) and zircon εHf(t) (?10.0 to ?5.4), and high oxygen fugacity (mainly ?17.0 to ?8.01) values and radiogenic Pb isotopic compositions with (206Pb/204Pb)i = 17.692–17.884, (207Pb/204Pb)i = 15.413–15.511, and (208Pb/204Pb)i = 37.611–37.943. Coupled with negative Nb–Ta anomalies, low K2O/Na2O ratios (0.39–0.62), and high Mg# values (0.44–0.71), these data suggest the adakitic rocks and associated large-scale Cu–Au mineralization of the Anqing region resulted from partial melting of the high oxidized subducted oceanic crust. Addition of mantle-derived magmas and assimilation of crustal materials during emplacement are also possible.  相似文献   

19.
Lithian ferrian enstatite with Li2O = 1.39 wt% and Fe2O3 7.54 wt% was synthesised in the (MgO–Li2O–FeO–SiO2–H2O) system at P = 0.3 GPa, T = 1,000°C, fO2 = +2 Pbca, and a = 18.2113(7), b = 8.8172(3), c = 5.2050(2) Å, V = 835.79(9) Å3. The composition of the orthopyroxene was determined combining EMP, LA-ICP-MS and single-crystal XRD analysis, yielding the unit formula M2(Mg0.59Fe 0.21 2+ Li0.20) M1(Mg0.74Fe 0.20 3+ Fe 0.06 2+ ) Si2O6. Structure refinements done on crystals obtained from synthesis runs with variable Mg-content show that the orthopyroxene is virtually constant in composition and hence in structure, whereas coexisting clinopyroxenes occurring both as individual grains or thin rims around the orthopyroxene crystals have variable amounts of Li, Fe3+ and Mg contents. Structure refinement shows that Li is ordered at the M2 site and Fe3+ is ordered at the M1 site of the orthopyroxene, whereas Mg (and Fe2+) distributes over both octahedral sites. The main geometrical variations observed for Li-rich samples are actually due to the presence of Fe3+, which affects significantly the geometry of the M1 site; changes in the geometry of the M2 site due to the lower coordination of Li are likely to affect both the degree and the kinetics of the non-convergent Fe2+-Mg ordering process in octahedral sites.  相似文献   

20.
In this work, accumulation of cosmogenic radionuclide 7Be in seven species of lichens was determined using HPGe detectors in autumn season. Ramsar city which is located in the north of Iran as one of the high-level natural radiation areas in the world was considered. Lichen species represented good potential in accumulation of 7Be radionuclide. The foliose species of Xanthoria parietina with the highest activity concentration value of 112.8 ± 1.8 Bq kg?1 was introduced as bioindicator for accumulation of 7Be radionuclide. Cladonia rangiformis species has got minimum concentration of 64.5 ± 0.8 Bq kg?1. Also from thallus morphology viewpoint, results showed that 7Be accumulation in foliose species is higher than in fruticose and crustose lichens species. Also there was relatively large positive correlation between 7Be and 226Ra activity concentrations in lichens species.  相似文献   

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