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1.
The magnetic properties of the synthetic Cu3SnS4 (kuramite)–Cu2FeSnS4 (stannite) pseudobinary series were investigated by means of electron paramagnetic resonance (EPR) spectroscopy, at room temperature, and by magnetometry, in the range 2–300 K. The system is particularly complex, from both chemical and crystal chemical points of view, in particular with respect to the metal valence states and the local ordering in the different terms of the series. Nevertheless, recent successes in synthesising nanostructured kuramite foster the interest to ascertain the bulk magnetic properties of these important semiconducting phases. The obtained results allowed to ascertain that a variable lack of local ordering in the Cu3–x Fe x SnS4 (x < 0.85) samples induce the raise of strong metal–sulphur–metal superexchange interactions, that result in the appearance of marked deviations from the single-ion behaviour, typical for pure stannite. Ferro- and antiferromagnetic interactions are in fact observed at relatively high temperatures (~150 K). A possible role played by Cu(I)–Fe(III) was revealed by the EPR measurements. The Cu-rich terms of the series (x < 0.1) are characterised by dynamic resonant disorder (i.e. time-evolving delocalisation of the formally divalent valence state for Cu among the nearest neighbouring Cu-sites), in addition to the Cu–Fe–Sn static disorder verified along the whole series. Both factors concurring to a non-periodic arrangement of paramagnetic ions in the lattice have the main effect to drastically broaden the EPR lines.  相似文献   

2.
An EPR and SQUID magnetometry study of Cu2FeSnS4 (stannite) and Cu2ZnSnS4 (kesterite) has been performed in order to gain a deeper insight into the crystal chemistry of these minerals, in which the mixed character of bonds lends uncertainty to the determination of the metal valence states. EPR investigations were performed down to almost liquid nitrogen temperature on both natural and synthetic samples of stannite and kesterite. The interpretation of their parameters (g- and T-tensors) was refined by computer simulation. The main feature of all the spectra is the unstructured signal centered at about 0.310 T due to the presence of Cu(II). The absence of structure in the signal is due to spin-spin exchange interaction between Cu(II) and Fe(II), pointing to a diluted distribution of Cu(II). The temperature dependence of the Cu(II) signal can be related to a topological variation of the first-neighbors coordination. The SQUID measurements, while allowing a more precise interpretation of the EPR data, led to a full characterization of magnetic behavior of stannite and kesterite down to liquid helium temperature, evidencing antiferromagnetic interactions between the Fe(II) ions in all samples but in synthetic kesterite. From the EPR and SQUID experimental data no evidence was provided for the existence of two different structures for stannite and kesterite. Received: 2 August 1999 / Accepted: 7 January 2000  相似文献   

3.
The successful synthesis of nanoparticles of Fe-bearing kuramite, (Cu,Fe)3SnS4, is reported in this study. Nanocrystalline powders were obtained through a mild, environmentally friendly and scalable solvothermal approach, in a single run. The sample was the object of a multidisciplinary investigation, including X-ray diffraction and absorption, scanning electron microscopy and microanalysis, electron paramagnetic resonance, diffuse reflectance and Mössbauer spectroscopy as well as SQUID magnetometry. The nanoparticles consist of pure Fe-bearing kuramite, exhibiting tetragonal structure. The valence state of the metal cations was assessed to be Cu+, Sn4+ and Fe3+. The material presents a band gap value of 1.6 eV, which is fully compatible with solar cell applications. The uptake of Fe by nanokuramite opens a compositional field where the physical properties can be tuned. We thus foster the application of Fe-bearing nanokuramite for photovoltaics and energy storage purposes.  相似文献   

4.
A wide investigation of the synthetic analogue of tetrahedrite, Cu12Sb4S13, has been performed by a combination of several techniques, magnetisation and differential scanning calorimetric measurements, cw, and pulsed EPR spectroscopy, to obtain complementary information about the presence and the distribution of Cu(II). The high temperature susceptibility of the sample accounts for two Cu(II) per formula unit, in agreement with the charge balance. However, strong antiferromagnetic interactions, observed even at room temperature, are associated with a transition at 83(3) K. At lower temperatures a residual susceptibility is observed. At 4.2 K ESEEM experiments enabled observation of the chemical environment of the residual paramagnetic species. Cu(II) was found randomly distributed in the M(1) site. The statistical presence of nearest neighbouring Cu(II) ions justify the observed antiferromagnetic interactions and transition. Nevertheless, isolated paramagnetic ions have been determined below the Néel temperature: they are mainly located near the surface of the grains. A colour centre, previously observed in natural samples, has been also identified.  相似文献   

5.
Equilibrium reactions involving Cu(II) and As(V) have been studied with respect to formation of complexes in aqueous solutions as well as formation of solid phases. Potentiometric titrations performed at 25 °C (I = 0.1 M Na(Cl)) and at different Cu to As ratios gave no evidence for the existence of Cu(II) arsenate complexes in solution below the pH of the precipitation boundaries (pH ≈ 4), irrespective of the Cu to As ratio and pH. Mixing of solutions of Cu(II) and As(V) at different proportions and adjusting pH to values ranging from 4 to 9 resulted in precipitation of five different solid phases. The elemental composition of the solids was determined using X-ray Photoelectron Spectroscopy, and Environmental Scanning Microscopy-Field Emission Gun equipped with an energy dispersive spectroscopy detector. The average Cu/As ratio was determined by dissolving the solids. Total soluble concentrations of the components Cu(II) and As(V), as well as the basicity of the solid phases were determined by analysis of aqueous solutions. Based upon these experimental data the stoichiometric composition of the solid phases and their stability were determined. The resulting equilibrium model includes the solid phases Cu3(AsO4)2, Cu3(AsO4)(OH)3, Cu2(AsO4)(OH), Cu5Na(HAsO4)(AsO4)3 and Cu5Na2AsO4)4, where Cu5Na(HAsO4)(AsO4)3 and Cu5Na2(AsO4)4 have not been reported previously. In 0.1 M Na(Cl), Na+ was found to be a significant component in two of the solid phases. The Cu5Na2(AsO4)4 was formed in weakly alkaline conditions with pNa < 2.5. Stability constants for all solid phases have been determined. Distribution diagrams as well as predominance area (pNa-pH) diagrams are presented to illustrate stability fields of the different solid phases.  相似文献   

6.
A magnetic and spectroscopic characterisation has been performed on a natural bornite sample from the Natural History Museum of the University of Florence. The combination of magnetic measurements and continuous-wave electron paramagnetic resonance (cw-EPR) spectroscopy at different temperatures and frequencies provided information about the distribution and valence states of Cu and Fe in bornite. The studied sample was found to obey the Curie–Weiss law with a transition from a paramagnetic to an antiferromagnetic phase at 64 K; its possible attribution to a disordered spin glass phase was ruled out by ac susceptibility measurements. Q- and X-band cw-EPR measurements confirmed the presence of Fe(III) as fundamental valence state in bornite: the single EPR line registered in the temperature range from 300 to 65 K can be assigned, in fact, to the Fe(III) single ions. Some Cu(II) signals were revealed in the low temperature EPR spectra and attributed to an early stage of the surface alteration. The width of the Fe(III) EPR spectrum, which hinders any characteristic spectral structure, can be ascribed to the exchange interaction. The pure antiferromagnetic character of the magnetic transition confirms the ordering between Fe and Cu in the bornite structure, at least at low temperature (≤70 K). Moreover, the relatively high Nèel temperature suggests the accepted model of Collins et al.’s (Can J Phys 59:535–539, 1981) to conveniently explain the overall magnetic properties in the range 298–4 K. Despite the increasing of the susceptibility in the paramagnetic range, in fact, the integrated EPR line area decreases by lowering the temperature, thus suggesting a progressive rising of the antiferromagnetic interactions among next-nearest-neighbouring paramagnetic centres.  相似文献   

7.
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8.
《Geochimica et cosmochimica acta》1999,63(13-14):1955-1967
The investigation of the Cu2+ uptake by the calcium carbonate minerals vaterite and calcite with continuous wave and pulse electron paramagnetic resonance (EPR) yields information on a molecular scale about the relevant complexation reactions at the mineral–water interface. The structural assignment is based on changes in the coordination geometry of the copper complexes. Magnetic interactions of the unpaired Cu2+ electron with nuclei of 13C-labeled carbonate ligands and protons from water or hydroxyl ligands in the first and second coordination spheres of the cation are detected by pulse EPR techniques. Our results show that the Cu2+ ions are rapidly dehydrated upon adsorption on the mineral surface. The strong surface binding is due to monodentate coordination to three or four carbonate surface ions, comparable to chelate complexation in solution. The formation of square-planar or square-pyramidal copper complexes at exposed surface sites like kinks and steps yields a convincing explanation for the inhibition of calcium carbonate growth and dissolution. Upon recrystallization the Cu2+ ions are integrated into the calcite lattice where they exhibit a dynamic Jahn–Teller effect. The resulting local lattice distortions are expected to destabilize the CuxCa(1−x)CO3(s) solid solution. Our results support the concept of a dynamic calcium carbonate surface, covered by a thin, structured surface layer. The detailed structural information obtained for Cu2+ provides a better understanding of the interaction of other metal ions with calcium carbonate minerals.  相似文献   

9.
In many river basins, floodplain soils have accumulated a variety of metal contaminants, which might be released during periods of flooding. We investigated the dynamics of copper, cadmium, lead, zinc, and nickel in a contaminated freshwater floodplain soil under a realistic sulfate-limited flooding regime in microcosm experiments. We found that most contaminants were initially mobilized by processes driven by the reductive dissolution of Fe(III) and Mn(IV, III) (hydr)oxides. Subsequently, bacterial sulfate respiration resulted in the transformation of the entire available sulfate (2.3 mmol/kg) into chromous reducible sulfur (CRS). Cu K-edge X-ray absorption fine structure (XAFS) spectroscopy revealed that the soil Cu speciation changed from predominantly Cu(II) bound to soil organic matter (SOM) intermittently to 14% metallic Cu(0) and subsequently to 66% copper sulfide (CuxS). These CuxS precipitates accounted for most of the formed CRS, suggesting that CuxS was the dominant sulfide phase formed in the flooded soil. Sequential metal extractions, in agreement with CRS results, suggested that easily mobilizable Cd was completely and Pb partially sequestered in sulfide precipitates, controlling their dissolved concentrations to below detection limits. In contrast, Zn and Ni (as well as Fe) were hardly sequestered into sulfide phases, so that micromolar levels of dissolved Zn and Ni (and millimolar dissolved Fe(II)) persisted in the reduced soil. The finding that Cu, Cd, and Pb were sequestered (but hardly any Zn, Ni, and Fe) is consistent with the thermodynamically predicted sulfide ladder following the increasing solubility products of the respective metal sulfides. The observation that Cd and Pb were sequestered in sulfides despite the presence of remaining SOM-bound Cu(II) suggested that the kinetics of Cu(II) desorption, diffusion, and/or CuxS precipitation interfered with the sulfide ladder. We conclude that the dynamics of multiple metal contaminants are intimately coupled under sulfate limitation by the relative thermodynamic stabilities and formation kinetics of the respective metal sulfides.  相似文献   

10.
Infrared and Raman spectra of the basic copper salts malachite, Cu2(OH)2CO3, and brochantite, Cu4(OH)6SO4, as well as of deuterated and 13C substituted samples are presented and discussed in terms of group theory and the hydrogen bonds present. The main results are that (i) the hydrogen donor strengths of the OH? ions are strongly increased due to the very great synergetic effect of the copper ions, (ii) the acceptor strengths of the H-bond acceptor groups (SO4 2-, CO3 2-, and OH? ions) are significantly modified by the linkage and coordination of the acceptor atoms — this complicates true assignment of the OH bands observed to the two and six different OH? ions present in malachite and brochantite, respectively -, and (iii) the Cu — O stretching modes at 430–590 cm?1 and 420–520 cm?1 for malachite and brochantite, respectively, exhibit strong, partially covalent Cu — O bonding.  相似文献   

11.
A luminol chemiluminescence (CL) detection/flow injection analysis technique coupled with ion chromatography (IC) has been employed for the determination of low levels of Cu(II) and Co(II) in drinking water samples. The detection system was the CL of luminol/perborate or luminol/percarbonate in alkaline medium catalyzed by these transition metals. Oxalic acid in a solution of KOH and N(CH3)4OH was used as an eluent in the IC to improve the column selectivity (Dionex CS5A). Concentration and pH of the eluent affected simultaneously the CL intensity and the retention times (t R). Under the elution conditions used here, the retention times of both metal ions were much greater when the concentration of oxalic acid was decreased. Thus, R t(Cu) = 2.15 min and t R(Co) = 4.50 min were measured at 80 mM oxalic acid concentration, while t R raised to 4.12 and 18 min for Cu(II) and Co(II), respectively, using a 10-mM concentration, but on the other hand, the CL signals showed substantially higher values when the concentration of oxalic acid was lesser in the eluent. An optimum oxalic acid concentration of 20 mM and an eluent pH = 4.7 were selected in order to have reproducible signals with a total analysis time of 10 min. The optimum flow rate for the mobile phase was 1.5 mL min?1. The concentration and pH of the postcolumn reagents also affected the CL signal, obtaining optimum concentrations of 5 mM for both oxidants (perborate or percarbonate) and luminol, this last dissolved in a 0.1-M borate buffer at pH 12. The optimum flow rate for the postcolumn reagents was 1 mL min?1. Linear calibrations for both transition metal ions were established, with calculated detection limits of 0.15 ng mL?1 for Co(II) and 0.20 μg mL?1 for Cu(II). Others ions commonly present in natural waters showed little or no interference. The method was successfully applied to water samples spiked with Cu(II) and Co(II), obtaining recoveries in the range of 85–128%, depending on the metal concentrations.  相似文献   

12.
We measured the adsorption of Cu(II) onto kaolinite from pH 3-7 at constant ionic strength. EXAFS spectra show that Cu(II) adsorbs as (CuO4Hn)n−6 and binuclear (Cu2O6Hn)n−8 inner-sphere complexes on variable-charge ≡AlOH sites and as Cu2+ on ion exchangeable ≡X--H+ sites. Sorption isotherms and EXAFS spectra show that surface precipitates have not formed at least up to pH 6.5. Inner-sphere complexes are bound to the kaolinite surface by corner-sharing with two or three edge-sharing Al(O,OH)6 polyhedra. Our interpretation of the EXAFS data are supported by ab initio (density functional theory) geometries of analog clusters simulating Cu complexes on the {110} and {010} crystal edges and at the ditrigonal cavity sites on the {001}. Having identified the bidentate (≡AlOH)2Cu(OH)20, tridentate (≡Al3O(OH)2)Cu2(OH)30 and ≡X--Cu2+ surface complexes, the experimental copper(II) adsorption data can be fit to the reactions
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13.
Secondary minerals formed in tailings derived from a W-rich deposit were investigated in detail using transmission electron microscopy (TEM). The study focused on secondary minerals that formed in the vicinity of oxidized sphalerite [ZnS] and tennantite [Cu10(Fe,Zn)2As4S13] grains. Samples for TEM analysis were prepared directly from petrographic thin sections using a focused ion beam instrument. This method insured that spatial relationships among primary grains, secondary minerals and the pore spaces were maintained. The results from this study indicate that the secondary coatings associated with sphalerite and tennantite are composed of several discrete phases. The phases identified in this study include an Fe–Zn–As–O phase, secondary sulfides, native Cu, an Fe–Si–O phase, an In–O phase, and wulfenite [PbMoO4]. The Fe–Zn–As–O phase precipitates directly from the pore water and the nearby primary mineral grains act as a source for some of the elements (e.g., Zn from sphalerite, As from tennantite). Secondary Cu sulfides were found at the outer margins of sphalerite and roquesite [CuInS2] grains. It is likely that these Cu sulfides form as a result of interactions between the primary grain and aqueous Cu(II) present in the pore water, similar to what occurs in supergene environments. A secondary sulfide that was composed of variable amounts of Cu, Zn, As, Fe and S was also identified along the outer margins of tennantite. Native Cu was found in association with chalcopyrite [CuFeS2] inclusions that were present in one of the sphalerite grains and probably represents a low-temperature secondary phase. The oxidation of chalcopyrite in the presence of aqueous Si leads to the formation of a nanocrystalline or amorphous Fe–Si–O phase. Roquesite oxidation leads to the formation of a crystalline In–O phase, which is likely dzhalindite [In(OH)3]. Wulfenite was found in the interstitial voids present in the Fe–Zn–As–O phase suggesting that it forms by direct precipitation from the local pore water. The results from this study indicate that secondary coatings consist of complex secondary phases that may only be distinguished at the nanoscale. The TEM investigations reveal details regarding mineralogical sinks and sources for aqueous components that may otherwise be overlooked.  相似文献   

14.
Zn-contaminated soils obtained from a steel company in the Republic of Korea were stabilized using Portland cement (PC), cement kiln dust (CKD) and Class C fly ash (FA). The effectiveness of the treatment was evaluated by the United States Environmental Protection Agency toxicity characteristic leaching procedure (TCLP) and the Universal Treatment Standard (UTS) of 4.3 mg/L. X-ray powder diffraction (XRPD) analyses were performed to investigate the crystalline phases associated with Zn immobilization. Scanning electron microscopy (SEM)–energy dispersive X-ray (EDX) analyses were utilized to support the XRPD results. The treatment results showed that the TCLP-Zn concentrations obtained from the 10 wt% PC and 15 wt% CKD treated samples were less than the UTS, after 7 days curing. However, the FA treatment (up to 30 wt%) was not effective in meeting the UTS even after 28 days curing. All PC–CKD treatment combinations were effective in reducing the TCLP-Zn concentrations below the UTS criteria. Moreover, a 20 wt% dose of a PC-FA treatment combination (75/25 PC-FA) was successful in reducing the TCLP-Zn concentrations below 4.3 mg/L after 1 day. The XRPD results showed that ettringite and Zn6Al2(OH)16CO3·4H2O were the possible phases associated with Zn immobilization upon PC and CKD treatment. The SEM–EDX results confirmed the presence of ettringite, while Zn6Al2(OH)16CO3·4H2O was not identified.  相似文献   

15.
We report high precision Cu isotope data coupled with Cu concentration measurements for metal, troilite and silicate fractions separated from magmatic and non-magmatic iron meteorites, analysed for Fe isotopes (δ57Fe; permil deviation in 57Fe/54Fe relative to the pure iron standard IRMM-014) in an earlier study (Williams et al., 2006). The Cu isotope compositions (δ65Cu; permil deviation in 65Cu/63Cu relative to the pure copper standard NIST 976) of both metals (δ65CuM) and sulphides (δ65CuFeS) span much wider ranges (−9.30 to 0.99‰ and −8.90 to 0.63‰, respectively) than reported previously. Metal-troilite fractionation factors (Δ65CuM-FeS = δ65CuM − δ65CuFeS) are variable, ranging from −0.07 to 5.28‰, and cannot be explained by equilibrium stable isotope fractionation coupled with either mixing or reservoir effects, i.e. differences in the relative proportions of metal and sulphide in the meteorites. Strong negative correlations exist between troilite Cu and Fe (δ57FeFeS) isotope compositions and between metal-troilite Cu and Fe (Δ57FeM-FeS) isotope fractionation factors, for both magmatic and non-magmatic irons, which suggests that similar processes control isotopic variations in both systems. Clear linear arrays between δ65CuFeS and δ57FeFeS and calculated Cu metal-sulphide partition coefficients (DCu = [Cu]metal/[Cu]FeS) are also present. A strong negative correlation exists between Δ57FeM-FeS and DCu; a more diffuse positive array is defined by Δ65CuM-FeS and DCu. The value of DCu can be used to approximate the degree of Cu concentration equilibrium as experimental studies constrain the range of DCu between Fe metal and FeS at equilibrium to be in the range of 0.05-0.2; DCu values for the magmatic and non-magmatic irons studied here range from 0.34 to 1.11 and from 0.04 to 0.87, respectively. The irons with low DCu values (closer to Cu concentration equilibrium) display the largest Δ57FeM-FeS and the lowest Δ65CuM-FeS values, whereas the converse is observed in the irons with large values DCu that deviate most from Cu concentration equilibrium. The magnitudes of Cu and Fe isotope fractionation between metal and FeS in the most equilibrated samples are similar: 0.25 and 0.32‰/amu, respectively. As proposed in an earlier study (Williams et al., 2006) the range in Δ57FeM-FeS values can be explained by incomplete Fe isotope equilibrium between metal and sulphide during cooling, where the most rapidly-cooled samples are furthest from isotopic equilibrium and display the smallest Δ57FeM-FeS and largest DCu values. The range in Δ65CuM-FeS, however, reflects the combined effects of partial isotopic equilibrium overprinting an initial kinetic signature produced by the diffusion of Cu from metal into exsolving sulphides and the faster diffusion of the lighter isotope. In this scenario, newly-exsolved sulphides initially have low Cu contents (i.e. high DCu) and extremely light δ65CuFeS values; with progressive equilibrium and fractional crystallisation the Cu contents of the sulphides increase as their isotopic composition becomes less extreme and closer to the metal value. The correlation between Δ65CuM-FeS and Δ57FeM-FeS is therefore a product of the superimposed effects of kinetic fractionation of Cu and incomplete equilibrium between metal and sulphide for both isotope systems during cooling. The correlations between Δ65CuM-FeS and Δ57FeM-FeS are defined by both magmatic and non-magmatic irons record fractional crystallisation and cooling of metallic melts on their respective parent bodies as sulphur and chalcophile elements become excluded from crystallised solid iron and concentrated in the residual melt. Fractional crystallisation processes at shallow levels have been implicated in the two main classes of models for the origin of the non-magmatic iron meteorites; at (i) shallow levels in impact melt models and (ii) at much deeper levels in models where the non-magmatic irons represent metallic melts that crystallised within the interior of a disrupted and re-aggregated parent body. The presence of non-magmatic irons with a range of Fe and Cu isotope compositions, some of which record near-complete isotopic equilibrium implies crystallisation at a range of cooling rates and depths, which is most consistent with cooling within the interior of a meteorite parent body. Our data therefore lend support to models where the non-magmatic irons are metallic melts that crystallised in the interior of re-aggregated, partially differentiated parent bodies.  相似文献   

16.
In the present research, the removal of lead(II) and copper(II) from aqueous solutions is studied, using SnO2 nanowires as new adsorbent on solid-phase extraction disk and compared with pine core and buttonwood as biosorbents. Batch adsorption experiments were performed as a function of pH, adsorption time, solute concentration and adsorbent dose for biosorbents. Also, the pH, transfer rate of solution and metal concentration were selected as experimental parameters for the removal of heavy metals by SnO2 nanowires. All of the parameters were optimized by experimental design method for sorbents. The experimental equilibrium adsorption data are tested for the Langmuir and Freundlich equations. Results indicate the following order to fit the isotherms: Langmuir > Freundlich, in case of lead and copper ions. The removal of Cu(II) and Pb(II) was performed by selected sorbents in the presence of interferences ions. This led to no remarkable decrease in the removal efficiency of SnO2 nanowires. Using the SnO2 nanowires in the wastewater treatment indicated 96.8 and 85.28% removal efficiency in only 7 min for Pb(II) and Cu(II), respectively. SnO2 nanowires were found as reusable sorbent. Therefore, SnO2 nanowires have a good potential for application in environmental protection.  相似文献   

17.
Amorphous tin(VI) hydrogen phosphate (ATHP) was synthesized using the liquid phase precipitation method and served as an adsorbent to remove Pb(II), Cu(II), and Zn(II) from aqueous solutions. The ATHP was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption techniques. Adsorption properties were evaluated as a function of pH, reaction time, concentration of reactants, and salinity. Their equilibrium adsorption data were modeled using Freundlich, Langmuir, and Dubinin–Kaganer–Radushkevich isotherms, respectively. The results revealed that adsorption equilibrium reached within 180 min. ATHP indicated good adsorption even below the pHZPC, and best adsorption at pH 5 for Pb(II) and Cu(II) and at pH 5.5 for Zn(II) was observed. Equilibrium data fitted better to the Langmuir model for Pb(II) and Cu(II) and fitted better to the Freundlich model for Zn(II). The saturated adsorption capacities deduced from the Langmuir model were 2.425, 1.801, and 0.600 mmol/g for Cu(II), Pb(II), and Zn(II), respectively, indicating an adsorption affinity order of Cu > Pb > Zn. There is a negative correlation between the concentration of NaCl and adsorption capacity of ATHP, yet ATHP still exhibited excellent adsorption having an adsorption capacity of 19.35, 15.16, 6.425 mg/g when the concentration of NaCl was 0.6 mol/L. The free energy (E) was 12.33, 10.70, and 14.74 kJ/mol for Pb(II), Cu(II), and Zn(II), respectively. An adsorption mechanism based on ion exchange between heavy metal ions and H+ in the ATHP is proposed. Furthermore, the used ATHP was regenerated by HCl solution and the adsorbent was used repeatedly.  相似文献   

18.
 The chemical bonding in the ring silicate mineral dioptase is investigated on the basis of accurate single-crystal X-ray diffraction data. A multipole model is used in the refinements. Static deformation electron density is mapped for the silicon tetrahedron, Cu-octahedron and water molecule in different sections. The silicon tetrahedron exhibits peaks resulting from σ-bonds between Si–sp3 hybrid orbitals and O–p orbitals. The excess density is located on bonds between the Si atom and bridge (in ring) O(1)-, O(1′)-oxygens and across the interior of the Si–O–Si angle. In the Jahn-Teller distorted Cu octahedron, in addition to peaks which result from single Cu–O σ-bonds, there are peaks which are due to 3d electrons. The analysis of crystal-field influence on the Cu charge distribution is made using the tetragonal D 4 d approximation for the low-symmetry (C1) Cu octahedron. The calculation of the occupancies of the 3d atomic orbitals shows that the Cu non-bonding orbitals are most populated (˜20%) and the bonding orbitals least populated (14%), as is typical for the Jahn-Teller octahedron. The effective atomic charge on the Cu atom in dioptase determined from the multipoles is +1.23e: closer to the Cu+1 than to the Cu+2 state. The charge on the Si atom has a value +1.17e, which is in the range typical for Si atoms already determined by this method. The accumulation of density on bridge oxygens and across the interior of the Si–O–Si angle may be explained by additional strain in the bond with the decrease of the Si–O–Si angle in dioptase to 132°. The same effect was found earlier in coesite. A single-crystal neutron diffraction study shows that dioptase becomes antiferromagnetic below a Néel temperature of 15.9(1) K, in contrast to the previously reported specific heat anomaly at 21 K. The magnetic propagation vector is (0, 0, 3/2) on the hexagonal triple cell or (1/2, 1/2, 1/2) in rhombohedral indices. The relation between the antiferromagnetic and the charge-density models for dioptase is discussed. The less occupied Cu d x2−y2 orbitals are responsible for the magnetic properties. These lie in the Cu–O squares, which are approximately perpendicular to c hex, but which are alternately inclined to it by a small angle. The magnetic moments of 0.59(1)μ B on the Cu ions in the same level are ordered ferromagnetically, but between ions in alternate levels the coupling is antiferromagnet. Within experimental error the magnetic moments are perpendicular to the square planes, which make an angle ±13(3)° to the triad axis. Received: 8 June 2001 / Accepted: 10 January 2002  相似文献   

19.
We report on a paramagnetic anisotropy study of three layered phyllosilicates. The mineral samples were characterized through X-ray powder diffraction (XRPD), X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). Based on EPR measurements of samples oriented parallel or perpendicular to the magnetic field lines, we show how the substitutional iron is transformed from Fe(II) (biotite) into Fe(III) (muscovite and kaolinite) species and from axial Fe(III) coordination sites (muscovite) to rhombic (kaolinite) sites in response to weathering.  相似文献   

20.
The X-band EPR and magnetic susceptibility in the temperature range 4.2–300 K study of the shungite-I, natural nanostructured material from the deposit of Shunga are reported. Obtained results allow us to assign the EPR signal to conduction electrons, estimate their number, N P, and evaluate the Pauli paramagnetism contribution to shungite susceptibility. A small occupation (~5%) of the localized nonbonding π states in the zigzag edges of the open-ended graphene-like layers and/or on σ (sp 2+x ) orbitals in the curved parts of the shungite globules has been also revealed. The observed temperature dependence of the EPR linewidth can be explained by the earlier considered interaction of conduction π electrons with local phonon modes associated with the vibration of peripheral carbon atoms of the open zigzag-type edges and with peripheral carbon atoms cross-linking different nanostructures. The relaxation time T 2 and diffusion time T D are found to have comparable values (2.84 × 10−8 and 1.73 × 10−8 s at 5.2 K, respectively), and similar dependence on temperature. The magnetic measurements have revealed the suppression of orbital diamagnetism due to small amount of large enough fragments of the graphene layers.  相似文献   

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