The Origin of Saline Groundwaters in Granitic Rocks: Evidence From Hydrothermal Experiments

1985 ◽  
Vol 50 ◽  
Author(s):  
David Savage ◽  
Mark R. Cave ◽  
Antoni E Milodowski
Keyword(s):  
Fluid Phase ◽  
Granitic Rocks ◽  
Plagioclase Feldspar ◽  
Natural Systems ◽  
Stability Diagrams ◽  
Hydrothermal Experiments ◽  
Mineral Stability ◽  
Solid Phases ◽  
Chemical Conditions ◽  
The Stability

AbstractHydrothermal rock-water experiments at 80°, 150° and 250° C have been carried out to investigate the origin of saline groundwaters in the Carnmenellis Granite, Cornwall, UK which have previously been attributed to be derived via dissolution of biotite and plagioclase feldspar by dilute meteoric groundwaters. The nature of product fluid and solid phases in the experiments was dominated by the dissolution of plagioclase and potassium feldspars, coupled with the precipitation of laumontite, calcite and smectite. However, the release of chloride from the rock was minimal, suggesting minor dissolution of the major chloride bearing mineral, biotite. The relative inertness and stability of biotite during the experiments was borne out by direct physical observation of reacted biotites and by consideration of the fluid phase composition in terms of thermodynamic mineral stability diagrams. It is concluded that the experimental and natural systems are buffered under different chemical conditions, which may be due to acidity generated via oxidation of localised sulphide zones within the granite and absent in the experiments. Dissolution of biotite may be an important mechanism for enhancing the salinity of groundwaters in granitic rocks if groundwaters are buffered to be outside the stability of biotite and convective circulation is significant.

Application of a thermodynamic model to predict the mineral stability of titaniferous smectites from soils on volcanic rocks

Clay Minerals ◽  
1986 ◽  
Vol 21 (3) ◽  
pp. 389-400
Author(s):  
J. L. Martin de Vidales ◽  
J. Casas ◽  
J. Sanz
Keyword(s):  
Thermodynamic Model ◽  
Soil Depth ◽  
Volcanic Rocks ◽  
Soil Matrix ◽  
Ciudad Real ◽  
Weathering Processes ◽  
Stability Diagrams ◽  
Mineral Stability ◽  
The Stability ◽  
Octahedral Substitution

AbstractWeathering processes in the Piedrabuena volcano, Ciudad Real province, Central Spain, have produced a smectitic phyllosilicate in four profiles on porphyritic-holocrystalline basalts consisting mainly of titaniferous augites, olivine and pigeonite. Chemical analysis of the purified smectites gave TiO2 contents of 1·89–3·77%. Apart from one profile, the smectites showed high tetrahedral Al-for-Si substitution, with the lattice charge arising from this source exceeding that from octahedral substitution, and thus could be termed beidellites. Octahedral Ti contents ranged from 0·21 to 0·41 per 24 O. A thermodynamic model was used to estimate the ΔG° of formation of these titaniferous smectites. Values ranged between −2503·30 and −2543·26 Kcal/mol. Suitable equilibria were established by calculating their ΔG° of reaction and log Ksp and, from these, the stability diagrams pH - 1/2pMg2+ against log H4SiO4 were derived. Correlations found were: (i) strong and positive between AlVI-X+ (0·91), AlIV-FeVI (0·85), AlVI-FeVI (0·85) and AlVI-MgVI (0·76); (ii) strong and negative between AlIV-octahedral charge; (iii) solubility product (log Ksp) positively correlated with X+ (0·73), AlIV (0·89), FeVI (0·67) and MgVI (0·84). Smectites showing higher tetrahedral charges were the least stable. Conversely, the stabilities of titaniferous smectites were favoured by high values of pH - 1/2pMg2+ and/or activities in soil-matrix solution. When the activities of H4SiO4 decreased, the montmorillonitic smectites became less stable than those showing beidellitic characteristics. Variations in composition and stability of the titaniferous smectites were not correlated with soil depth.

scholarly journals Influence of biopolymers on the rheological properties of seafloor sediments and the runout behavior of submarine debris flows

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jun Kameda ◽  
Hamada Yohei
Keyword(s):  
Rheological Properties ◽  
Debris Flows ◽  
Extracellular Polymeric Substances ◽  
Flow Behavior ◽  
Mass Movement ◽  
Rheological Parameters ◽  
Natural Environments ◽  
Natural Systems ◽  
Chemical Conditions ◽  
Seafloor Sediments

AbstractSubmarine debris flows are mass movement processes on the seafloor, and are geohazards for seafloor infrastructure such as pipelines, communication cables, and submarine structures. Understanding the generation and run-out behavior of submarine debris flows is thus critical for assessing the risk of such geohazards. The rheological properties of seafloor sediments are governed by factors including sediment composition, grain size, water content, and physico-chemical conditions. In addition, extracellular polymeric substances (EPS) generated by microorganisms can affect rheological properties in natural systems. Here we show that a small quantity of EPS (~ 0.1 wt%) can potentially increase slope stability and decrease the mobility of submarine debris flows by increasing the internal cohesion of seafloor sediment. Our experiments demonstrated that the flow behavior of sediment suspensions mixed with an analogue material of EPS (xanthan gum) can be described by a Herschel–Bulkley model, with the rheological parameters being modified progressively, but not monotonously, with increasing EPS content. Numerical modeling of debris flows demonstrated that the run-out distance markedly decreases if even 0.1 wt% of EPS is added. The addition of EPS can also enhance the resistivity of sediment to fluidization triggered by cyclic loading, by means of formation of an EPS network that binds sediment particles. These findings suggest that the presence of EPS in natural environments reduces the likelihood of submarine geohazards.

Stability of a Binary Colloidal Suspension and its effect on Colloidal Processing

1989 ◽  
Vol 155 ◽  
Author(s):  
Wan V. Shih ◽  
Wei-Heng Shih ◽  
Jun Liu ◽  
Ilhan A. Aksay
Keyword(s):  
Particle Size ◽  
Hard Sphere ◽  
Colloidal Particles ◽  
Colloidal Suspension ◽  
Fluid Phase ◽  
Ceramic Processing ◽  
Colloidal Processing ◽  
Interparticle Interactions ◽  
The Stability ◽  
Binary Suspension

The stability of a colloidal suspension plays an important role in colloidal processing of materials. The stability of the colloidal fluid phase is especially vital in achieving high green densities. By colloidal fluid phase, we refer to a phase in which colloidal particles are well separated and free to move about by Brownian motion, By controlling parameters such as pH, salt concentration, and surfactants, one can achieve high packing (green) densities in the repulsive regime where the suspension is well dispersed as a colloidal fluid, and low green densities in the attractive regime where the suspensions are flocculated [1,2]. While there is increasing interest in using bimodal suspensions to improve green densities, neither the stability of a binary suspension as a colloidal fluid nor the stability effects on the green densities have been studied in depth as yet. Traditionally, the effect of using bimodal-particle-size distribution has only been considered in terms of geometrical packing developed by Furnas and others [3,4]. This model is a simple packing concept and is used and useful for hard sphere-like repulsive interparticle interactions. With the advances in powder technology, smaller and smaller particles are available for ceramic processing. Thus, the traditional consideration of geometrial packing for the green densities of bimodal suspensions may not be enough. The interaction between particles must be taken into account.

scholarly journals Thermodynamic Stabilities of U(VI) Minerals: Estimated and Observed Relationships

1996 ◽  
Vol 465 ◽  
Author(s):  
Robert J. Finch
Keyword(s):  
Gibbs Energy ◽  
Reaction Pathways ◽  
Free Energies ◽  
Fine Grained ◽  
Surface Energies ◽  
Stability Diagrams ◽  
Activity Diagrams ◽  
Mineral Stability ◽  
Mineral Compositions

ABSTRACTGibbs free energies of formation (ΔG°ƒ) for several structurally related U(VI) minerals are estimated by summing the Gibbs energy contributions from component oxides. The estimated ΔG°f values are used to construct activity-activity (stability) diagrams, and the predicted stability fields are compared with observed mineral occurrences and reaction pathways. With some exceptions, natural occurrences agree well with the mineral stability fields estimated for the systems Sio2-Cao-Uo3-UOH2O and Co2-caO-UO3-H2O providing confidence in the estimated thermodynamic values. Activity-activity diagrams are sensitive to small differences in ΔG°f values, and mineral compositions must be known accurately, including structurally bound H2O. The estimated ΔG°f values are not considered reliable for a few minerals for two major reasons: (1) the structures of the minerals in question are not closely similar to those used to estimate the ΔG°f* values of the component oxides, and/or (2) the minerals in question are exceptionally fine grained, leading to large surface energies that increase the effective mineral solubilities.

scholarly journals Stability analysis of magnetic fluids in the presence of an oblique field and mass and heat transfer

2020 ◽  
Vol 330 ◽  
pp. 01035
Author(s):  
Rabah Djeghiour ◽  
Bachir Meziani
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Magnetic Fluids ◽  
Physical Parameters ◽  
Stability Diagrams ◽  
Stability And Instability ◽  
Mass And Heat Transfer ◽  
Model Equations ◽  
The Stability ◽  
Oblique Magnetic Field

In this paper, we investigate an analysis of the stability of a basic flow of streaming magnetic fluids in the presence of an oblique magnetic field is made. We have use the linear analysis of modified Kelvin-Helmholtz instability by the addition of the influence of mass transfer and heat across the interface. Problems equations model is presented where nonlinear terms are neglected in model equations as well as the boundary conditions. In the case of a oblique magnetic field, the dispersion relation is obtained and discussed both analytically and numerically and the stability diagrams are also obtained. It is found that the effect of the field depends strongly on the choice of some physical parameters of the system. Regions of stability and instability are identified. It is found that the mass and heat transfer parameter has a destabilizing influence regardless of the mechanism of the field.

Numerical Modelling of Hydrodynamic Instabilities in Supercritical Fluids

2021 ◽  
pp. 32-54
Author(s):  
Sakir Amiroudine
Keyword(s):  
Boundary Layer ◽  
Thermal Boundary Layer ◽  
Stokes Equations ◽  
Gravitational Instability ◽  
Heat Diffusion ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Stability Diagrams ◽  
The Stability ◽  
Rayleigh Benard

The case of a supercritical fluid heated from below (Rayleigh-Bénard) in a rectangular cavity is first presented. The stability of the two boundary layers (hot and cold) is analyzed by numerically solving the Navier-Stokes equations with a van der Waals gas and stability diagrams are derived. The very large compressibility and the very low heat diffusivity of near critical pure fluids induce very large density gradients which lead to a Rayleigh–Taylor-like gravitational instability of the heat diffusion layer and results in terms of growth rates and wave numbers are presented. Depending on the relative direction of the interface or the boundary layer with respect to vibration, vibrational forces can destabilize a thermal boundary layer, resulting in parametric/Rayleigh vibrational instabilities. This has recently been achieved by using a numerical model which does not require any equation of state and directly calculates properties from NIST data base, for instance.

Stability of Colloidal Dispersions: A Thermodynamic Approach

1993 ◽  
Vol 27 (10) ◽  
pp. 117-129 ◽  
Author(s):  
Raj Rajagopalan
Keyword(s):  
Virial Coefficient ◽  
Second Virial Coefficient ◽  
Colloidal Dispersions ◽  
Chemical Parameters ◽  
Interaction Forces ◽  
Colloidal Forces ◽  
Stability Diagrams ◽  
The Stability ◽  
Physical And Chemical ◽  
Interparticle Collisions

The classical theory of coagulation relies on relating the rate of interparticle collisions to the interaction forces, and thus to the physical and chemical parameters of the dispersion, through kinetic arguments, and is restricted to dilute systems. Here, we present a modern, thermodynamic theory capable of predicting stability diagrams for dense as well as dilute dispersions. Although based on statistical thermodynamics, the method is simple to use and requires only the second virial coefficient of osmotic pressure of the dispersion. All the information necessary for applying the model to arbitrary dispersions is given. The method is illustrated for a model colloidal potential, and it is shown how static light scattering measurements can be used for predicting the stability diagrams when information about the colloidal forces are not known in advance.

scholarly journals Chemical, Mineralogical, and Refractory Characterization of Kaolin in the Regions of Huayacocotla-Alumbres, Mexico

2018 ◽  
Vol 2018 ◽  
pp. 1-11
Author(s):  
L. M. Romero-Guerrero ◽  
R. Moreno-Tovar ◽  
A. Arenas-Flores ◽  
Y. Marmolejo Santillán ◽  
F. Pérez-Moreno
Keyword(s):  
Thermogravimetric Analysis ◽  
Decomposition Temperature ◽  
X Ray Diffraction ◽  
Polarization Optical Microscopy ◽  
Plagioclase Feldspar ◽  
X Ray ◽  
Mullite Phase ◽  
Significant Difference ◽  
The Stability

In the present work, the chemical, mineralogical, refractory, and microstructural characterizations of kaolinites from the Huayacocotla-Alumbres region, which is between Veracruz and Hidalgo border, by X-ray diffraction (XRD), polarization optical microscopy (POM), scanning electron microscopy (SEM), refractoriness proof (pyrometric cone equivalent), and thermogravimetric analysis (TGA) were carried out. The analysis by POM showed that the kaolinization degree in this region is variable due to the presence of primary minerals, such as plagioclase, feldspar, and quartz. Additionally, hydrothermal alteration of the epithermal type was determined by oxidation of sulfides (pyrite and galena) and chlorite association. With the X-ray diffraction technique, andalusite and kaolinite were identified as the majority phases in Huayacocotla and quartz was identified as the majority phase in Alumbres. The minority phases, such as dickite, kaolinite, and cristobalite, were observed in both zones. The SEM technique was useful in the determination of the morphology of kaolinite and impurities of Na, Mg, K, and Fe of the complex clay illite-andalusite-dickite group. Thermogravimetric analysis was useful to discover the decomposition temperature and reveal the significant difference between 400 and 800°C, which showcases the greatest mass loss due to dehydration and carbonates decomposition. The mullite phase was detected at approximately 1000°C in the kaolin samples. The refractoriness tests were important to determine the stability temperature of kaolin, which is between 1300 and 1600°C. This stability temperature makes it feasible to use the kaolin as a refractory material for both low and high temperatures. The variables that affect the kaolin stability temperature were determined by principal components with the XLSTAT free program.

scholarly journals Journal of Food Quality Thermal Degradation of Plum Anthocyanins: Comparison of Kinetics from Simple to Natural Systems

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Mihaela Turturică ◽  
Nicoleta Stănciuc ◽  
Claudia Mureșan ◽  
Gabriela Râpeanu ◽  
Constantin Croitoru
Keyword(s):  
Antioxidant Activity ◽  
Citric Acid ◽  
Thermal Degradation ◽  
Fluorescence Spectra ◽  
Degradation Rate ◽  
Natural Systems ◽  
Degradation Rate Constant ◽  
Higher Temperature ◽  
Lower Temperature ◽  
The Stability

The stability of anthocyanin was assessed over a temperature range of 50–120°C in different simulated plum juices in order to compare the thermal behavior in the presence of certain compounds. The results were correlated with the antioxidant activity and intrinsic fluorescence spectra. The results suggested significant changes, especially at higher temperature; hence, increase in the fluorescence intensity and some bathochromic and hypsochromic shifts were observed. Anthocyanins in natural matrices presented the highest rate for degradation, followed by the anthocyanins in juices with sugars. Values of the activation energies were 42.40 ± 6.87 kJ/mol for the degradation in water, 40.70 ± 4.25 kJ/mol for the juices with citric acid, 23.03 ± 3.53 kJ/mol for the juices containing sugars, 35.99 ± 3.60 kJ/mol for simulated juices with mixture, and 14.19 ± 2.39 kJ/mol for natural juices. A protective effect of sugars was evidenced, whereas in natural matrices, the degradation rate constant showed lower temperature dependence.

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