Dispersive Particle Transport: Identification of Macroscale Behavior in Heterogeneous Stratified Subsurface Flows     

Ali Fadili  Rachid Ababou  Roland Lenormand 《Mathematical Geology》1999,31(7):793-840

Dispersive mass transport processes in naturally heterogeneous geological formations (porous media) are investigated based on a particle approach to mass transport and on its numerical implementation using LPT3D, a Lagrangian Particle Tracking 3D code. We are currently using this approach for studying microscale and macroscale space–time behavior (advection, diffusion, dispersion) of tracer plumes, solutes, or miscible fluids, in 1,2,3-dimensional heterogeneous and anisotropic subsurface formations (aquifers, petroleum reservoirs). Our analyses are based on a general advection-diffusion model and numerical scheme where concentrations and fluxes are discretized in terms of particles. The advection-diffusion theory is presented in a probabilistic framework, and in particular, a numerical analysis is developed for the case of advective transport and rotational flows (numerical stability of the explicit Euler scheme). The remainder of the paper is devoted to the behavior of concentration, mass flux density, and statistical moments of the transported tracer plume in the case of heterogeneous steady flow fields, where macroscale dispersion occurs due to geologic heterogeneity and stratification. We focus on the case of perfectly stratified or multilayered media, obtained by generating many horizontal layers with a purely random transverse distribution of permeability and horizontal velocity. In this case, we calculate explicitly the exact mass concentration field C(x, t), mass flux density field f(x, t), and moments. This includes spatial moments and dispersion variance ² _x (t) on a finite domain L, and temporal moments on a finite time scale T, e.g., the mass variance of arrival times ² _T (x). The moments are related to flux concentrations in a way that takes explicitly into account finite space–time scales of analysis (time-dependent tracer mass; spatially variable flow through mass). The multilayered model problem is then used in numerical experiments for testing different ways of recovering information on tracer plume migration, dispersion, concentration and flux fields. Our analyses rely on a probabilistic interpretation that emerges naturally from the particle approach; it is based on spatial moments (particle positions), temporal moments (mass weighted arrival times), and probability densities (both concentrations and fluxes). Finally, as an alternative to direct estimations of the flux and concentration fields, we formulate and study the Moment Inverse Problem. Solving the MIP yields an indirect method for estimating the space–time distribution of flux concentrations based on observed or estimated moments of the plume. The moments may be estimated from field measurements, or numerically computed by particle tracking as we do here.  相似文献   

Natural occurrence of a (Fe,Mn, Mg) tetrasilicic potassium mica     

J. -L. Robert  R. C. Maury 《Contributions to Mineralogy and Petrology》1979,68(2):117-123

A mica whose structural formula: (K_1.76Na_0.31)(Fe_2.22Mn_1.29Mg_0.99Ti_0.28Al_0.240.98) ·(Si_7.33Al_0.67)O_20.26(F_2.16OH_1.58) closely approximates that of tetrasilicic potassium mica K₂(M ₅ ²⁺ )Si₈O₂₀(OH,F)₄ where M²⁺ represents Mg²⁺, Fe²⁺, Mn²⁺, ..., has been discovered in the matrix of a peralkaline rhyolite (comendite) of the Mont-Dore massif (France). These micas had been obtained previously by synthesis only. In the groundmass of the rock, the micaceous phase is accompanied by a manganoan arfvedsonite, pyrophanite, magnetite, apatite, sphene, zircon and fluorite. The crystallographic properties of the mica are typically that of a tetrasilicic mica, with d ₀₆₀ = 1.533Å and space group C2/m. There is a regular decrease of d ₀₆₀ (parameter b) with the ionic radius of the octahedral cation in synthetic micas containing Fe²⁺, Co²⁺, Mg²⁺, Ni²⁺. The purely Mn²⁺ end-member could not be synthesised; its instability is discussed on the basis of structural considerations. The conditions of crystallization of the micaceous phase are estimated to be 760 ° C, 800 bars with a f _{o 2}=10^–14.7 bar. This mica has crystallized from a residual liquid, with high activity of silica and low activity of alumina, whose origin is discussed. The name MONT-DORITE is proposed for this natural tetrasilicic mica having Fe/Fe+Mg >1/2 and Fe/Fe+Mn >1/2. This name is from the stratovolcano Mont-Dore.  相似文献   

Estimation of mean trace length of discontinuities   总被引：18，自引：0，他引：18  

P. H. S. W. Kulatilake  T. H. Wu 《Rock Mechanics and Rock Engineering》1984,17(4):215-232

Summary Trace lengths of discontinuities observed on finite exposures are biased due to sampling errors. These errors should be corrected in estimating mean trace length. A technique, which takes into account the sampling errors, is proposed for estimating the mean trace length on infinite, vertical sections from the observations made on finite, rectangular, vertical exposures. The method is applicable to discontinuities whose orientation is described by a probability distribution function. The method requires that the numbers of discontinuities with both ends observed, one end observed, and both ends censored be known. The lengths of observed traces and the density function of trace length are not required. The derivation assumes that midpoints of traces are uniformly distributed in the vertical plane. Also independence between trace length and orientation is assumed. Data on a Pennsylvania shale in Ohio, U. S. A., were used as an example.Notations dip direction - direction of sampling plane - acute angle between dip direction and sampling plane - dip angle - _A apparent dip angle - mean density of trace mid-points per unit area - mean trace length - D diameter of discontinuity - f (.),g (.) probability density function - h height of rectangular window - estimator of mean trace length - m sample size, number of discontinuities intersecting window - m ₀ number of discontinuities intersecting window with both ends censored - m ₂ number of discontinuities intersecting window with both ends observed - n, N expected number of discontinuities intersecting the window - n ₀,N ₀ expected number of discontinuities intersecting the window with both ends censored - n ₂,N ₂ expected number of discontinuities intersecting the window with both ends observed - Pr (.) probability - w width of rectangular window - x trace length  相似文献   

Use of the lattice parameter b 0 of dioctahedral illite/muscovite for the characterization of P/T gradients of incipient metamorphism     

Ady Padan  Hanan J. Kisch  Reginald Shagam 《Contributions to Mineralogy and Petrology》1982,79(1):85-95

The P/T gradient or baric type of low-grade metamorphic terranes can be characterized on the basis of cumulative frequency curves of the lattice parameter b ₀ of dioctahedral micas (Sassi and Scolari 1974), which essentially reflects celadonite content and increases with pressure. The method is here applied to illite/muscovite of sub-greenschist (incipient metamorphism) and low-greenschist facies terranes from the marginal zones of the Swedish Caledonides, Swiss Alps and Venezuelan Andes, where the grade of metamorphism was determined on the basis of illite crystallinity.Complications in the determinations of b ₀ arising from (a) shifts in the spacing of the apparent 060 diffraction peaks of the illites due to the presence of inter-stratified expandable layers, and (b) persistence of more crystalline clastic micas are pointed out.In contrast to the earlier-reported decrease of b ₀ with progressive metamorphism at higher grades, b ₀ tends to increase with grade during incipient metamorphism: it is markedly lower in the diagenetic and low-grade anchimetamorphic grades in the Cambro-Silurian of the Caledonides of Jämtland, western Sweden (zone A), and the Lower Tertiary of the Helvetic zone of the Swiss Alps, than in the higher grade anchizone and epizone of the former terrane.Mean b ₀ values for the intermediate and highest (epizone) grades of the Swedish Caledonides are respectively 9.030 and 9.037 Å compared to the mean value of 9.035 Å for the medium-high pressure, Barrovian-type, terrane of Otago, N.Z. Mean b ₀ of 9.005 Å for the mainly epizonal slates of the Venezuelan Andes lies between those for the low-pressure terranes of Bosost ( 8.992 Å), and the low-medium pressure terrane of northern New Hampshire (9.010 Å). These baric estimates agree well with those for the metamorphic facies series at higher grade produced by the same events.Cumulative b ₀ curves are concluded to be useful for the characterization of P/T gradients of incipient metamorphism, particularly in the higher grade part of the anchizone and the epizone.  相似文献   

Progressive and polyphase deformation of the Schistes Lustrés in Cap Corse, Alpine Corsica     

Lyal Harris   《Journal of Structural Geology》1985,7(6):637-650

In Cap Corse, progressive deformation during Late Cretaceous obduction of the ophiolitic Schistes Lustrés (sensu lato) as a pile of imbricate, lens-shaped units during blueschist facies metamorphism was non-coaxial. Two zones are recognized: a lower series emplaced towards the west is overlain by a series emplaced towards the south-southwest in Cap Corse. Equivalent structures (differing only in orientation) occur in both zones. The change in thrust direction was responsible for local refolding and reorientation of previously formed structures, parallel to the new stretching direction immediately below the thrust contact between the two zones, and within localized shear zones in the underlying series.Both zones are refolded about E-overturned F₂ folds trending between 350 and 025°. Local minor E-directed thrusts occur associated with the F₂ folds. This second deformation of Middle Eocene age is considered to be related to the backthrusting of an overlying klippe containing gneisses of South Alpine origin, and is followed by a third Late Eocene phase of upright 060°-trending F₃ folds accompanied by greenschist facies metamorphism.  相似文献   

新疆阿拉套山花岗岩类高ε_Nd值的成因探讨   总被引：13，自引：0，他引：13       下载免费PDF全文

周泰禧  陈江峰 《地质科学》1996,31(1):71-79

新疆阿拉套山广泛出露的华力西期花岗岩类的一般岩石学和地球化学性质可与我国以及世界上大部分地区出露的花岗岩相类比,但其ε_Nd(t)高,为+2.2-+3.2,其中一部分花岗岩的⁸⁷Sr/⁸⁶Sr(t)也高,可达0.715.这可能是壳幔物质AFC式混合的结果,也可能是准噶尔地块及其两缘特殊地质环境的反映。  相似文献   

Finite element analysis of consolidation of layered clay soils using an elastic visco-plastic model     

Guofu Zhu  Jian-Hua Yin 《国际地质力学数值与分析法杂志》1999,23(4):355-374

This paper presents a general one-dimensional (1-D) finite element (FE) procedure for a highly non-linear 1-D elastic visco-plastic (1-D EVP) model proposed by Yin and Graham for consolidation analysis of layered clay soils. In formulating the 1-D FE procedure, a trapezoidal formula is used to avoid the unsymmetry of the stiffness matrix for a Newton (modified Newton) iteration scheme. Unlike many other 1-D FE approaches in which the initial in situ stresses (or stress/strain states) are considered indirectly or even not considered, the initial in situ stress/strain states are taken into account directly in this paper. The proposed FE procedure is used for analysis of 1-D consolidation of a clay with published test results in the literature. The FE modelling results are in good agreement with the measured results. The FE model and procedure is then used to analyse the consolidation of a multi-layered clay soils with a parametric study on the effects of the variations of creep parameters in Yin and Graham's 1-D EVP model. It is found that the creep parameters ψ/V and t₀ have significant influence on the compression and porewater pressure dissipation. For some boundary conditions, changes of parameters in one layer will have some effects on the consolidation behaviour of another layer due to the different consolidation rates. Finally, the importance of initial stress/strain states is illustrated and discussed. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Interaction of bentonite colloids with Cs, Eu, Th and U in presence of humic acid: A flow field-flow fractionation study   总被引：2，自引：0，他引：2  

Muriel Bouby  Horst Geckeis  Silvia Mihai  Thorsten Schäfer 《Geochimica et cosmochimica acta》2011,75(13):3866-3880

The interaction of Cs(I), Eu(III), Th(IV) and U(VI) with montmorillonite colloids was investigated in natural Grimsel Test Site groundwater over a 3 years period. The asymmetric flow field-flow fractionation combined with various detectors was applied to study size variations of colloids and to monitor colloid association of trace metals. The colloids suspended directly in the low ionic strength (I), slightly alkaline granitic groundwater (I = 10⁻³ mol/L, pH 9.6) showed a gradual agglomeration with a size distribution shift from initially 10-200 nm to 50-400 nm within over 3 years. The Ca²⁺ concentration of 2.1 × 10⁻⁴ mol/L in the ground water is believed to be responsible for the slow agglomeration due to Ca²⁺ ion exchange against Li⁺ and Na⁺ at the permanently charged basal clay planes. Furthermore, the Ca²⁺ concentration lies close to the critical coagulation concentration (CCC) of 10⁻³ mol L⁻¹ for clay colloids. Slow destabilization may delimit clay colloid migration in this specific groundwater over long time scales. Eu(III) and Th(IV) are found predominantly bound to clay colloids, while U(VI) prevails as the UO₂(OH)₃⁻ complex and Cs(I) remains mainly as aquo ion under our experimental conditions. Speciation calculations qualitatively represent the experimental data. A focus was set on the reversibility of metal ion-colloid binding. Addition of humic acid as a competing ligand induces rapid metal ion dissociation from clay colloids in the case of Eu(III) even after previous aging for about 3 years. Interestingly only partial dissociation occurs in the case of Th(IV). Experiments and calculations prove that the humate complexes dominate the speciation of all metal ions under given conditions. The partial irreversibility of clay bound Th(IV) is presently not understood but might play an important role for the colloid-mediated transport of polyvalent actinides over wide distances in natural groundwater.  相似文献   

X射线衍射旋转撒样法分析氟金云母多型组成与含量     

陈爱清  何宏平  谭伟  杨宜坪  陶奇 《岩矿测试》2021,(4):504-511

合成氟金云母多型种类与含量对云母的物理化学性质具有重要的影响.然而在X射线粉晶衍射(XRD)制样过程中云母00l基面极易产生择优取向,严重制约了云母多型组成和含量的分析.传统撒样法可促使晶体取向随机分布,但制备的试样表面不够平坦.本文对传统撒样法进行改进,在撒样过程中使样品架均匀旋转,从而获得表面平坦的试样.XRD测试...  相似文献   

Über den Hügelit     

Prof. Dr. K. Walenta 《Mineralogy and Petrology》1979,26(1-2):11-19

Zusammenfassung Der Hügelit, das Arsenat-Analogon zum Dumontit, gehört zu den Sekundärmineralien der Grube Michael im Weiler bei Lahr im Schwarzwald (Bundesrepublik Deutschland), wo er zusammen mit Hallimondit, Widenmannit, Mimetesit, Cerussit und Zeunerit in Drusen von hornsteinartigem Quarz auftritt. Beobachtete kristallographische Formen: {100}, {110}, {001}, {011} sowie (?) {010}.Spaltbarkeit nach {100} sehr gut, nach {110} unsicher. Bruch muschelig. Härte etwa 2 1/2; spröde.Farbe braun bis orangegelb; durchsichtig bis durchscheinend. Strich hellgelb. Keine UV-Fluoreszens. Brechungsindizes:n =1,898(5),n =1,915(5), 2V =25° (für =592 nm); sehr starke Achsenwinkeldispersion.Gitterkonstanten:a ₀=8,13,b ₀=17,27,c ₀=7,01 Å, =109°. Raumgruppe:P2₁/m oderP2₁.D _x=5,80 g·cm^–3 (mit der Formel Pb₂(UO₃)₃(AsO₄)₂(OH)₄·3H₂O undZ=2). Stärkste Linien des Pulverdiagramms: 3,73(10), 3,06(9), 3,00(7) und 2,89(7).

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On Hügelite

Summary Hügelite, the arsenate analogue of dumontite, occurs amongst the secondary minerals of the Michael Mine at Weiler near Lahr in the Black Forest (German Federal Republic), in vugs of dense quartz in association with hallimondite, widenmannite, mimetite, cerussite and zeunerite. Observed crystal forms: {100}, {110}, {001}, {011} and (?) {010}.Cleavage: {100} very good, {110} uncertain. Fracture conchoidal. Hardness about 2 1/2, brittle.Colour brown to orange yellow, transparent to translucent. Not fluorescent in ultraviolet light. Indices of refraction:n =1.898(5),n =1.915(5); 2V =25° (for =592 nm); strong dispersion of the axial angle.Unit-cell dimensions:a ₀=8.13,b ₀=17.27,c ₀=7.01 Å, =109°, space groupP2₁/m orP2₁.D _x=5.80 g·cm^–3 (with the formula Pb₂(UO₂)₃(AsO₄)₂(OH)₄·3H₂O andZ=2). Strongest lines of the powder pattern: 3.73(10); 3.06(9); 3.00(7); 2.89(7).

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Mit 2 Abbildungen

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Herrn Univ. Prof. Dr.H. Meixner zum 70. Geburtstag gewidmet.  相似文献   

Elastic properties of the incommensurate phase of akermanite,Ca2MgSi2O7     

Zhuang Li  Sai-Kit Chan  Subrata Ghose 《Physics and Chemistry of Minerals》1990,17(5):462-466

The crystal structure of akermanite, Ca₂Mg-Si₂O₇, consists of mixed tetrahedral sheets formed by [MgO₄] tetrahedra and [Si₂O₇] groups interleaved along the c axis with Ca²⁺ ions in eight-fold coordination. Above 358 K, the structure is tetragonal , and below it is incommensurate with modulations parallel to [110] and . The elastic stiffness moduli, C ^ij of the incommensurate phase at room temperature were measured from wave velocities in the 20–75 MHz carrier frequency range by the ultrasonic phase comparison method using optically clear synthetic single crystal plates (3×3×2 mm) oriented parallel to (100), (001), (110) and (101) planes. The C _ij values (GPa) are: C ₁₁ 159.40, C ₃₃ 149.43, C ₄₄ 30.26, C ₆₆ 58.10, C ₁₂ 76.58 and C ₁₃ 57.80. In (010) and (001) planes, the compressional modulus, V ²(L) from the longitudinal wave, L is considerably larger than the shear moduli, V ²(T₁, T ₂) both from the in-plane and perpendicular-to-plane shear waves, T ₁ and T ₂. The relatively small values of the shear moduli indicate the ease of tetrahedral rotations in response to in-plane and perpendicular-to-plane shears and may provide preconditions for structural changes involving shear-type atomic movements.  相似文献   

Bearing capacity factor Nc under ϕ=0 condition for piles in clays     

Vishwas N. Khatri  Jyant Kumar 《国际地质力学数值与分析法杂志》2009,33(9):1203-1225

Bearing capacity factor N_c for axially loaded piles in clays whose cohesion increases linearly with depth has been estimated numerically under undrained (?=0) condition. The study follows the lower bound limit analysis in conjunction with finite elements and linear programming. A new formulation is proposed for solving an axisymmetric geotechnical stability problem. The variation of N_c with embedment ratio is obtained for several rates of the increase of soil cohesion with depth; a special case is also examined when the pile base was placed on the stiff clay stratum overlaid by a soft clay layer. It was noticed that the magnitude of N_c reaches almost a constant value for embedment ratio greater than unity. The roughness of the pile base and shaft affects marginally the magnitudes of N_c. The results obtained from the present study are found to compare quite well with the different numerical solutions reported in the literature. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Computation of the seismic stability of rock wedges   总被引：1，自引：0，他引：1  

A. Ghosh  W. Haupt 《Rock Mechanics and Rock Engineering》1989,22(2):109-125

Summary Newmark's concept of computing the permanent displacement under seismic loads has been combined with the conventional limit equilibrium analysis to compute the displacements of a rock wedge. The rock wedge formed by the intersecting planes may or may not have a tension crack in the upper slope surface. As the static analysis of a rock wedge is available from the literature, only the seismic problem is treated theoretically in more details.A computer program has been developed to compute the displacements from the digitised input data of the acceleration-time-history. The program can take into account the water pressure on the intersecting planes and on the planes of the tension crack. The effect of rock anchors if present is also taken care of in addition to static surcharge loads. The program calculates the conventional static factor of safety, remaining resistance against sliding, the critical acceleration, exciting force, relative velocity with time and the cumulative displacements.Two model examples are presented: one with simple sinusoidal acceleration and the other one with actual earthquake data considering the different systems of forces acting on the wedge. The results are critically discussed with respect to the different parameters e. g. anchor forces, water pressure and cohesion influencing the magnitude of displacements under seismic loads. It is shown that the critical acceleration is a better index for the seismic stability than the conventional factor of safety.The critical acceleration presented in this paper serves as a very handy tool for a site engineer to get the first hand information about the stability of the wedge for a given acceleration-time-history without going into the details of dynamic analysis.Notations A, B Inclined intersecting planes - C, D Geometric points on the intersection ofA andB - a _cr Critical acceleration - a _h Horizontal acceleration - a _v Vertical acceleration - a _r Relative acceleration of the wedge - DF Driving force - DF _dyn Dynamic driving force - DF _st Static driving force - FS Factor of safety - g Acceleration due to gravity - m Mass of the wedge - RF Resisting force - RF _dyn Dynamic resisting force - RF _st Static resisting force - RS Remaining resisting force against sliding - RS _dyn Total seismic induced force - RS _st Remaining static resisting force against sliding - s _r Cumulative relative displacement of the wedge - TRS Total remaining resisting force against sliding - v _r Relative velocity of the wedge - W Weight of the wedge - W _A ,W _B Weight of the wedge in the planeA andB - Dip of line of intersection of the planesA andB - Average friction angle - _A , _B Friction angle of planeA andB - I, II, III, IV Points in the curve shown in Fig. 6  相似文献   

Computer simulations of the interactions of the (0 1 2) and (0 0 1) surfaces of jarosite with Al, Cd, Cu and Zn     

Karen A. Hudson-Edwards  Kate Wright 《Geochimica et cosmochimica acta》2011,75(1):52-62

Jarosite is an important mineral on Earth, and possibly on Mars, where it controls the mobility of iron, sulfate and potentially toxic metals. Atomistic simulations have been used to study the incorporation of Al³⁺, and the M²⁺ impurities Cd, Cu and Zn, in the (0 1 2) and (0 0 1) surfaces of jarosite. The calculations show that the incorporation of Al on an Fe site is favorable on all surfaces in which terminal Fe ions are exposed, and especially on the (0 0 1) [Fe₃(OH)₃]⁶⁺ surface. Incorporation of Cd, Cu or Zn on a K site balanced by a K vacancy is predicted to stabilize the surfaces, but calculated endothermic solution energies and the high degree of distortion of the surfaces following incorporation suggest that these substitutions will be limited. The calculations also suggest that incorporation of Cd, Cu and Zn on an Fe site balanced by an OH vacancy, or by coupled substitution on both K and Fe sites, is unfavorable, although this might be compensated for by growth of a new layer of jarosite or goethite, as predicted for bulk jarosite. The results of the simulations show that surface structure will exert an influence on uptake of impurities in the order Cu > Cd > Zn, with the most favorable surfaces for incorporation being (0 1 2) [KFe(OH)₄]⁰ and (0 0 1) [Fe₃(OH)₃]⁶⁺.  相似文献   

Vertumnite,a new natural silicate     

Dr. E. Passaglia  Dr. E. Galli 《Mineralogy and Petrology》1977,24(1-2):57-66

Summary A natural calcium aluminum silicate hydrate, vertumnite, is described as a new mineral. It has been found as transparent flattened hexagonal prisms resting on a layer of tobermorite inside a subspherical geode of a phonolite from a quarry at Campomorto, Montalto di Castro, Viterbo, Italy. Most of the crystals are biaxial negative and twinned. The single crystal measurements on an optically homogeneous and biaxial individual gave:a=0.5744 (5) nm,b=0.5766(5) nm,c=2.512(1) nm, =119.72(5)° and space groupP2₁/m orP2₁. The optical properties are:n =1.531(1),n =1.535(1),n =1.541(2) and 2V =62°. The chemical formula is: (Na_0.02K_0.02Ca_3.76Sr_0.06Ba_0.01)_tot=3.87 Al_4.36(P_0.03Si_3.38)_tot=3.41O_5.18 (OH)_24.66·3.09H₂O or schematically Ca₄Al₄Si₄O₆(OH)₂₄ ·3 H₂O. Both the powder data and chemical analysis suggest the mineral to be stronghly related to the synthetic Strätling's compound or hexagonal hydrated gehlenite although the different Si/Al ratios in two inhibit direct correlations.

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Vertumnit, ein neues natürliches Silikat

Zusammenfassung Ein natürliches, wasserhaltiges Calcium-Aluminium-Silikat, Vertumnit, wird als neues Mineral beschrieben. Es kommt in durchsichtigen, flachen, hexagonalen Prismen vor, die auf einer Tobermorit-Schicht in einer kugeligen Geode eines Phonoliths einer Grube in Campomorto, Montalto di Castro, Viterbo, Italien, gefunden wurden. Die meisten Kristalle sind zweiachsig negativ und verzwillingt. Einkristallmessungen an einem optisch homogenen und zweiachsigen Individuum ergaben:a=0,5744(5) nm,b=0,5766(5) nm,c=2.512(1) nm, =119.72(5)° mit RaumgruppeP2₁/m oderP2₁. Die optische Eigenschaften sind wie folgt:n =1,531(1),n =1,535(1),n =1,541(2), 2V =62°. Die chemische Formel ist: (Na_0.02K_0.02Ca_3.76Sr_0.06Ba_0.01)_tot=3.87Al_4.36(P_0.03Si_3.38)_tot=3.41 O_5.18(OH)_24.66·3,09 H₂O oder schematisch Ca₄Al₄Si₄O₆(OH)₂₄·3 H₂O. Sowohl die Pulverdaten als auch die chemische Analyse weisen auf eine Verwandtschaft mit der Strätling-Verbindung oder hexagonal hydrated gehlenite hin, obwohl die verschiedenen Si/Al-Verhältnisse in beiden direkte Beziehungen verhindern.

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With 3 Figures  相似文献   

Investigation of acidic dissolution of mixed clays between pH 1.0 and −3.0 using Si and Al X-ray absorption near edge structure     

Sean A. Shaw  Derek Peak 《Geochimica et cosmochimica acta》2009,73(14):4151-6435

Although widely investigated in relation to acid mine drainage systems at pH > 1.0, we know little about the impact of sulfuric acid (H₂SO₄) on the geochemistry and mineralogy of clays at pH < 1.0 (including negative pH values). Thus, laboratory batch experiments were conducted on three mixed clay samples with different mass ratios of phyllosilicates (smectite, illite, and kaolinite) to investigate the impact of H₂SO₄ from pH 1.0 to −3.0 for exposure periods of 14, 90, 180, and 365 days. Si and Al K- and L_2,3-edge X-ray absorption near edge structure (XANES) spectroscopy were employed on these samples to determine the chemical and structural changes that occur during acidic dissolution of phyllosilicates that cannot be distinguished using X-ray diffraction analyses. A series of silicate, phyllosilicate, and Al-bearing standard compounds were also studied to provide an explanation for the observed changes in the clay samples. The Si XANES results indicated the preferential dissolution of the phyllosilicates (pH ? 1.0, t ? 14 d), the persistence of quartz even at pH ? −3.0 and t ? 365 d, and the formation of an amorphous silica-like phase that was confined to the surface layer of the altered clay samples at pH ? 0.0 and t ? 90 d). Al XANES results demonstrated dissolution of Al-octahedral layers (pH ? 1.0, t ? 14 d), the persistence of four-fold relative to six-fold coordinated Al, and the precipitation of an Al-SO₄-rich phase (pH ? −1.0, t ? 90 d). An existing conceptual model of phyllosilicate dissolution under extremely acidic conditions was modified to include the results of this study.  相似文献