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1.
Two synthetic series of spinels, MgCr2O4–Fe2+Cr2O4 and MgCr2O4–MgFe2 3+O4 have been studied by Raman spectroscopy to investigate the effects of Fe2+ and Fe3+ on their structure. In the first case, where Fe2+ substitutes Mg within the tetrahedral site, there is a continuous and monotonic shift of the Raman modes A1g and Eg toward lower wavenumbers with the increase of the chromite component into the spinel, while the F2g modes remain nearly in the same position. In the second series, for low Mg-ferrite content, Fe3+ substitutes for Cr in the octahedral site; when the Mg-ferrite content nears 40 %, a drastic change in the Raman spectra occurs as Fe3+ starts entering the tetrahedral site as well, consequently pushing Mg to occupy the octahedral one. The Raman spectral region between 620 and 700 cm?1 is associated to the octahedral site, where three peaks are present and it is possible to observe the Cr–Fe3+ substitution and the effects of order–disorder in the tetrahedral site. The spectral range at 500–620 cm?1 region shows that there is a shift of modes toward lower values with the increase of the Mg-ferrite content. The peaks in the region at 200–500 cm?1, when observed, show little or negligible Raman shift.  相似文献   

2.
Natural barbosalite Fe2+Fe3+ 2 (PO4)2(OH)2 from Bull Moose Mine, South Dakota, U.S.A., having ideal composition, was investigated with single crystal X-ray diffraction techniques, Mössbauer spectroscopy and SQUID magnetometry to redetermine crystal structure, valence state of iron and evolution of 57Fe Mössbauer parameter and to propose the magnetic structure at low temperatures. At 298?K the title compound is monoclinic, space group P21/n, a o ?= 7.3294(16)?Å, b o ?=?7.4921(17)?Å, c o ?=?7.4148 (18)?Å, β?=?118.43(3)°, Z?=?2. No crystallographic phase transition was observed between 298?K and 110?K. Slight discontinuities in the temperature dependence of lattice parameters and bond angles in the range between 150?K and 180?K are ascribed to the magnetic phase transition of the title compound. At 298?K the Mössbauer spectrum of the barbosalite shows two paramagnetic components, typical for Fe2+ and Fe3+ in octahedral coordination; the area ratio Fe3+/Fe2+ is exactly two, corresponding to the ideal value. Both the Fe2+ and the Fe3+ sublattice order magnetically below 173?K and exhibit a fully developed magnetic pattern at 160?K. The electric field gradient at the Fe2+ site is distorted from axial symmetry with the direction of the magnetic field nearly perpendicular to Vzz, the main component of the electric field gradient. The temperature dependent magnetic susceptibility exhibits strong antiferromagnetic ordering within the corner-sharing Fe3+-chains parallel to [101], whereas ferromagnetic coupling is assumed within the face-sharing [1?1?0] and [?1?1?0] Fe3+-Fe2+-Fe3+ trimer, connecting the Fe3+-chains to each other.  相似文献   

3.
《Applied Geochemistry》2001,16(9-10):1067-1082
Thermodynamic data for all fate-determining processes are needed in order to predict the fate and transport of metals in natural systems. The surface complexation properties of a synthetic MnO2, δ-MnO2, have accordingly been investigated using glass electrode potentiometry. Experimental data were interpreted according to the surface complexation model in conjunction with the diffuse double layer model of the solid/solution interface. Adsorption constants were determined using the non-linear optimisation program FITEQL. Surface complexation parameters determined in this way were validated against results obtained from the literature. Best fits of alkalimetric titration data were obtained with a 2-site, 3 surface-species model of the δ-MnO2 surface. Site concentrations of 2.23×10−3 mol g−1 and 7.66×10−4 mol g−1 were obtained. Corresponding logarithms of formation constants for the postulated surface species are −1.27 (≡XO−), −5.99 (≡YO−) and 3.52 (≡YOH2+) at I=0.1 M. The surface speciation of δ-MnO2 is dominated by ≡XO− over the pH range investigated. Metal adsorption was modelled with surface species of the type ≡XOM+, ≡XOMOH, ≡YOM+, ≡YOMOH (M=Cu, Ni, Zn, Cd and Pb) and ≡XOM2OH2+ (M=Pb). For Cu, Ni and Zn, titration data could be modelled with ≡XOM+, ≡XOMOH, ≡YOM+ and ≡YOMOH, whereas for Cd, ≡XOM+ and ≡YOM+ were sufficient. Lead data were best modelled by assuming the dinuclear species ≡XOM2OH2+ to be the only surface species to form. Adsorption constants determined for Ni, Cu and Zn follow the Irving-Williams sequence. The model suggests an adsorption order of (Pb, Cu) > (Ni, Zn) > Cd. The discrepancy between model predictions and published adsorption results is similar to the variability observed in experimental results from different laboratories.  相似文献   

4.
Detailed phase relations have been determined within the systems Fe2O3-MgO-TiO2 and FeO-MgO-TiO2. Experiments were performed over the temperature interval 1173–1473 K by equilibrating pelletized, fine-grained oxide mixtures in either inert calcia-stabilized zirconia pots (Fe2O3-MgO-TiO2 system) or evacuated silica tubes (FeO-MgO-TiO2 system). Equilibrium phase assemblages were determined by combined optical microscope, X-ray diffraction and EMP examination. Phase relations in the Fe2O3-MgO-TiO2 ternary are dominated by the instability of the M2O3 solid solution relative to the phase assemblage M3O4 + M3O5. A miscibility gap along the M2O3 binary also gives rise to two, 3-phase fields (α-M2O3 + M3O5 + M3O4 and α′-M2O3 + M3O5 + M3O4) separated by the M3O4 + M3O5 phase field. Phase relations in the FeO-MgO-TiO2 ternary were divided into two sub-systems. For the FeTiO3-MgTiO3-TiO2 sub-ternary, there is complete solid solution along the M2O3 and M3O5 binary joins at high temperature. At low temperatures (T < 1373 K) the M3O5 pseudobrookite solid solution decomposes to M2O3 + TiO2. Increasing the concentration of MgO in M3O5 phase results in a decrease in the temperature at which M3O5 becomes unstable and compositional tie lines linking M2O3 and TiO2 fan out, before the appearance of a three-phase region where M2O3, M3O5, and TiO2 coexist. Within the expanded FeO-MgO-TiO2 system, at temperatures above ∼1273 K there is a continuous solid solution along the M3O4 binary. At low temperatures (T < 1273 K) the Mg2TiO4 end-member breaks down to MgO and MgTiO3. The M3O4 phase shows significant non-stoichiometry, down to at least 1173 K. Fe2+-Mg partitioning data were obtained for coexisting M2O3-M3O5 and M2O3-M3O4 pairs in the FeO-MgO-TiO2 ternary. Assuming a regular solution mixing model for all phases, the M2O3 and M3O4 solid solutions were both found to exhibit moderate positive deviations from ideality (∼2600 J/mol), whereas the data for the M3O5 binary suggest close to ideal behaviour. Received: 22 May 1998 / Accepted: 3 November 1998  相似文献   

5.
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6.
A number of different impurities are located in the open channels of natural beryl crystals. The rare Maxixe beryl contains an unusual amount of NO2. The isoelectronic CO2 − radical is found in the irradiated Maxixe-type beryl. The NO2 radicals are distributed in the Be–Al plane of the crystal, with the nitrogen atom close to the oxygens of the beryl cavity wall. These oxygens repel the negative CO2 − radical, which is located at the center of the beryl cavity and rotates around its O–O axis, which is parallel to the crystal c-axis. When there is a nearby alkali ion at the center of the beryl channel, it reorients the CO2 − radical so that its bisector is parallel to the c-axis and points toward the positive ion. Different signals are analyzed for Li+, Na+, and another counter-ion, which probably is Cs+. The related NO3 and CO3 − radicals are the color centers in the investigated deep blue beryls. The slow decay of the color, which makes these beryls useless as gem stones, is related to the decay of the hydrogen atoms which are present in these crystals. Evidence is given that NO3 is created in Maxixe beryl by a natural process, while CO3 − in Maxixe-type beryl has been created by irradiation. The temperature dependence of the EPR signals of these two radicals was investigated, but a definitive proof that they rotate at the center of the beryl cavity could not be given. EPR signals from some other radicals in beryl have been observed and described.  相似文献   

7.
The mechanism of thermally induced oxidation of Fe2+ from natural pyrope has been studied at 1000 and 1100 °C using 57Fe Mössbauer spectroscopy in conjunction with XRD, XRF, AFM, QELS, TG, DTA and electron microprobe analyses. At 1000 °C, the non-destructive oxidation of Fe2+ in air includes the partial stabilization of Fe3+ in the dodecahedral 24c position of the garnet structure and the simultaneous formation of hematite particles (15–20 nm). The incorporation of the magnesium ions to the hematite structure results in the suppression of the Morin transition temperature to below 20 K. The general garnet structure is preserved during the redox process at 1000 °C, in accordance with XRD and DTA data. At 1100 °C, however, oxidative conversion of pyrope to the mixed magnesium aluminium iron oxide, Fe-orthoenstatite and cristoballite was observed. During this destructive decomposition, Fe2+ is predominantly oxidized and incorporated into the spinel structure of Mg(Al,Fe)2O4 and partially stabilized in the structure of orthoenstatite, (Mg,Fe)SiO3. The combination of XRD and Mössbauer data suggest the definite reaction mechanism prevailing, including the refinement of the chemical composition and quantification of the reaction products. The reaction mechanism indicates that the respective distribution of Fe2+and Fe3+ to the enstatite and spinel structures is determined by the total content of Fe2+ in pyrope.  相似文献   

8.
正1 Introduction Lithium resources are widely distributed in the oilfield brine from the Nanyishan district in the Qaidam Basin(Fan et al.,2007).The investigation of the thermodynamics and phase diagram of the brine system is valuable in providing the theoretic foundation and scientific guidance in the comprehensive exploitation of the mixture salts effectively.Comprehensive  相似文献   

9.
1Introduction Researchontheapplicationofnaturalminerals(zeolite,montmorillonite,etc.)inenvironmentalpro tectionisattractinggreatattentionofmoreandmorere searchers(WuPingxiaoetal.,2001;Suhasetal.,2000).Asthenaturalmineralshavelargenumbersof micro poresandbigsurfaceareas,thezeolite/TiO2compositephotocatalystcanbepreparedbycombining TiO2withzeolite.Nucleus formationfreeenergyof TiO2crystaldecreasesinamulti phasesystemofzeo lite,whichhelpsformnanometerTiO2crystalanden richstructuralhydroxyl;op…  相似文献   

10.
Zeolite/TiO2 composite photocatalysts were prepared by adding a certain amount of mordenite in TiO2, and degradation experiments on toluene through photocatalytic reactions were implemented. In this paper, these photocatalysts were characterized by using SEM, IR, RAMAN, XRD and UV-Vis to shed light on the microstructure and photocatalytic performance of the composite photocatalysts. The results indicated that the structural hydroxy of zeolite can participate in bonding reaction with TiO2, the addition of zeolite can greatly reduce the diameter of nanometer TiO2 particles in the composite photocatalysts, and enhance the ultraviolet light absorptance of the composite photocatalysts. When the percentage content of zeolite reached 20%, the photocatalytic performance of this catalyst would be highest, with the toluene conversion rate up to 94.58%.  相似文献   

11.
Diffuse X-ray scattering distributions have been recorded for reciprocal layers normal to c * of a synthetic mullite with composition Al2(Al2+2xSi2–2x) O10–xx, where represents an oxygen vacancy and x is close to 0.4. The effect on the diffuse scattering pattern of different schemes for ordering of the oxygen vacancies and the accompanying cation shifts within a single ab-layer of mullite has been investigated using optical diffraction analogue experiments in conjunction with Monte Carlo simulation.A simple scheme in which the only driving force for the ordering is that the Oc oxygens are precluded from being bonded to four T/T* cations, results in a 2D diffuse intensity distribution which displays many of the features that are observed in the x-ray scattering patterns. An alternative scheme in which bonding to four T/T* cations was favoured, resulted in a domain structure consisting of islands of the -alumina structure within a matrix of sillimanite. This gave diffraction patterns bearing no resemblance to the observed x-ray patterns and can, we believe, be discounted completely.  相似文献   

12.
Summary The crystal structure of -Nb2O5, space groupC2/c, a 12.740(2),b 4.8830(6),c 5.5609(6)Å, 105.02(1)°, Z 4, has been refined toR 1.6% for 457 observed reflections (MoK). The coordination polyhedron of the niobium atom is a distorted octahedron; the crystal structure consists of two-octahedron-thick, rutile-like layers separated by crystallographic shear (CS) planes. Relative to the rutile structure, these planes are indexed (101) and adjacent layers are related by the CS vector <a/6b/2c/2>. Members of the thoreaulite-foordite series have topologically identical two-octahedron-thick (101) sheets; however, here the CS vector Zusammenfassung Die Kristallstruktur des -Nb2O5, Raumgruppe C2/c, a 12,740(2),b 4,8830(6),c 5,5609(6) Å, 105,02(1)°,Z 4, wurde mit 457 beobachteten Reflexen (MoK) aufR 1,6% verfeinert. Das Koordinationspolyeder des Niobiumatoms ist ein verzerrtes Oktaeder; die Kristallstruktur besteht aus Rutil-artigen Schichten, die zwei Oktaeder dick sind und von kristallographischen Scher-(CS-)flächen getrennt werden. In bezug auf die Rutilstruktur haben diese Flächen die Indizes (101) und benachbarte Schichten sind durch den CS-Vektor <a/6b/2c/2> verknüpft. Die Glieder der Thoreaulith-Foordit-Reihe haben idente (101)-Schichten einer Dicke von zwei Oktaedern; indessen bewirkt hier der CS-Vektor <a/2> r gekoppelt mit dem Translationsvektor <1,5c> r die Einlagerung von tetragonal-antiprismatischen Lücken zwischen benachbarte Schichten.

With 4 Figures  相似文献   

13.
Hydrocarbons such as CH4 are known to be formed through the Fischer-Tropsch or Sabatier type reactions in hydrothermal systems usually at temperatures above 100°C. Weathering of olivine is sometimes suggested to account for abiotic formation of CH4 through its redox lowering and water splitting properties. Knowledge about the CH4 and H2 formation processes at low temperatures is important for the research about the origin and cause of early Earth and Martian CH4 and for CO2 sequestration. We have conducted a series of low temperature, long-term weathering experiments in which we have tested the CH4 and H2 formation potential of forsteritic olivine.The results show low temperature CH4 production that is probably influenced by chromite and magnetite as catalysts. Extensive analyses of a potential CH4 source trapped in the crystal structure of the olivine showed no signs of incorporated CH4. Also, the available sources of organic carbon were not enough to support the total amount of CH4 detected in our experiments. There was also a linear relationship between silica release into solution and the net CH4 accumulation into the incubation bottle headspaces suggesting that CH4 formation under these conditions could be a qualitative indicator of olivine dissolution.It is likely that minerals such as magnetite, chromite and other metal-rich minerals found on the olivine surface catalyze the formation of CH4, because of the low temperature of the system. This may expand the range of environments plausible for abiotic CH4 formation both on Earth and on other terrestrial bodies.  相似文献   

14.
In order to determine the mechanisms of formation and properties of natural hydrosilicate liquids (HSLs), which are formed during the transition from magmatic to hydrothermal mineral formation in granitic pegmatites and rare-metal granites, the formation of HSLs was experimentally studied in the Na2O-SiO2-H2O, Na2O-Al2O3-SiO2-H2O, and Na2O-K2O-Li2O-Al2O3-SiO2-H2O systems at 600°C and 1.5 kbar. It was shown that the sequential extension of composition does not suppress HSL formation in the systems and expands the stability field of this phase. However, HSLs formed in extended chemical systems have different structure and properties: the addition of alumina induces some compression of the structure of the silicate framework of HSLs, which results in a decrease in water content in this phase and probably hinders the reversibility of its dehydration. It was demonstrated that HSL can be formed by the coagulation of silica present in a silica-oversaturated alkaline aqueous fluid. It was supposed that the HSL formed during this process has a finely dispersed structure. It was argued that anomalous enrichment in some elements in natural HSLs can be due to their sorption by the extensively developed surface of HSL at the moment of its formation.  相似文献   

15.
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16.
雪玉洞岩溶地下水、地表水Ca2+、Mg2+、Sr2+变化特征研究   总被引：2，自引：1，他引：1  
通过2011年对重庆丰都雪玉洞洞内滴水和地下河河水,上覆岩层中出露的表层岩溶泉水和雪玉洞附近龙河河水等不同类型水中Ca2+、Mg2+、Sr2+浓度及Mg/Ca、Sr/Ca值的研究,发现不同水的Ca2+、Mg2+、Sr2+随外界降水条件的改变而出现明显变化。表层岩溶泉水Ca2+变化能够敏感反应外界降水条件改变,滴水对外界降雨的反应滞后接近1个月,地下河Ca2+可以反应雨季和旱季的变化,地表河水Ca2+全年比较稳定,但是对特殊干旱天气有显著响应。2011年不同类型水的Mg2+、Sr2+全年变化趋势基本一致,在降水较多的3、5、10月呈低值,在其他降水较少的月份浓度相对较高。各离子的这种变化特征主要是受到稀释效应、CO2效应以及所在地层的岩性的影响。雪玉洞不同类型水的Mg/Ca、Sr/Ca值呈现出滴水>地表河>地下河>表层岩溶泉的特点,反映出不同类型水在含水介质中滞留时间的长短,并且Mg/Ca、Sr/Ca值在降水较多的月份降低,在降水较少的月份升高;受碳酸钙的前期沉淀和运移路径差异的影响,不同类型水的Mg/Ca、Sr/Ca值变化稍有不同。因此,不同类型水的离子变化及其比值对外界降水条件变化的响应特征和时间的不同,决定了在利用元素及其比值反映外界环境变化时也要区别对待。   相似文献   

17.
The Chang＇E-1 and Chang＇E-2 missions have successfully obtained a huge amount of ltmar scientific data, through the seven onboard instruments including a CCD stereo camera, a laser altimeter, an interference imag- ing spectrometer, an X-ray spectrometer, a microwave radiometer, a high-energy particle detector and a solar-wind ion detector. Most of the Chang＇E data are now publicly available to the science community, and this article serves as an official guide on how these data are classified and organized, and how they can be retrieved from http：//159.226.88.59：7779/CE1OutENGWeb/. This article also presents the detailed specifications of various instru- ments and gives examples of research progress made based on these instruments.  相似文献   

18.
To understand the aqueous species important for transport of rhenium under supercritical conditions, we conducted a series of solubility experiments on the Re–ReO2 buffer assemblage and ReS2. In these experiments, pH was buffered by the K–feldspar–muscovite–quartz assemblage; in sulfur-free systems was buffered by the Re–ReO2 assemblage; and and in sulfur-containing systems were buffered by the magnetite–pyrite–pyrrhotite assemblage. Our experimental studies indicate that the species ReCl4 0 is dominant at 400°C in slightly acidic to near-neutral, and chloride-rich (total chloride concentrations ranging from 0.5 to 1.0 M) environments, and ReCl3 + may predominate at 500°C in a solution with total chloride concentrations ranging from 0.5 to 1.5 M. The results also demonstrate that the solubility of ReS2 is about two orders of magnitude less than that of ReO2. This finding not only suggests that ReS2 (or a ReS2 component in molybdenite) is the solubility-controlling phase in sulfur-containing, reducing environments but also implies that a mixing process involving an oxidized, rhenium-containing solution and a solution with reduced sulfur is one of the most effective mechanisms for deposition of rhenium. In analogy with Re, TcS2 may be the stable Tc-bearing phase in deep geological repositories of radioactive wastes.  相似文献   

19.
Chemical interaction processes among injected CO2, saline fluids and potential reservoir materials are experimentally simulated to derive dissolution rates of natural materials (minerals) that can be used as input parameters for modeling of CO2 storage in deep saline formations and risk analyses. In order to study dissolution processes, mineral aliquots were exposed to CO2-bearing brines at elevated temperature (60, 100, 150 °C) and pressure (85 bar) and at various run durations. Several potential reservoir rocks include carbonates as cement. Calcite and dolomite grains were therefore mainly used as solid starting material. Experiments with the two feldspar varieties alkali feldspar and almost pure anorthite were performed in addition. Grain sizes of the mineral starting materials varied between <63 μm and 500 μm with most experiments performed at grain size fractions of 160 – 250 μm and 250 – 500 μm. All experiments run with a complex synthetic brine (total dissolved solids: ∼156 g/l) according to a natural upper cretaceous formation water. Dry ice was used as CO2-source. All experiments were done in closed batch reactors. These reactors allow mimicking reservoir conditions far from the injection site as well as reservoir conditions after finishing the CO2 injection. The concentration changes during the experiment were monitored by ICP-OES measurements of the initial and the post-run fluids. Dissolution rates were derived based on the concentration changes of the brine.Most of the studied experimental variables and parameters (temperature, run duration, grain size, brine composition – expressed as pH-value and ionic strength) impact alteration of the reacting agents, i.e. they change the chemical composition of the brine, change the surfaces of the mineral aliquots exposed to the CO2-bearing brine, and induce formation of secondary minerals. Hence, all influencing parameters on dissolution processes have to be considered and time-resolved changes of the dissolution behavior have to be implemented in numerical simulations of processes at CO2 injection sites and CO2 storage reservoirs.  相似文献   

20.
This study describes the adsorption features of cadmium on Fe2O3 and MnO2 in alkaline saline conditions. The adsorption reached equilibrium in 6 hours under alkaline conditions. The absorption of cadmium on Fe2O3 and MnO2 was consistent with Freundlich absorption isotherms, and the corresponding adsorption capacities were 16.3 and 16.7 mg·g-1, respectively. Moreover, the adsorption quantity of cadmium on Fe2O3 and MnO2 rose with increasing pH from acidic to neutral, and reached the maximum at pH= 9. The coexisting chlorides reduced the adsorption capacity of Fe2O3 and MnO2. The influence intensities of different cations follow the order of CaCl2>>KCl>NaCl. However, the influence of sodium salts on the capacities of Fe2O3 and MnO2 to adsorb cadmium appeared more complicated: the relatively low concentrations of sodium salts could reduce the adsorption capacity; with increasing concentrations of sodium salts, e.g. NaCl and NaNO3. The adsorption capacity decreased continually. Moreover, due to the competition adsorption and precipitation effects, the adsorption capabilities of Na2CO3, NaH2PO4 and Na2HSO4 could also be reduced and cadmium concentrations in the solution were reduced as well.  相似文献   

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