Clay Admixtures Research Articles

Time Dependent Evolution of Heat and Stress Field in Granite–clay System Representing Geological Disposal Scheme for High Level Radioactive Wastes

Abstract A reference Geological Disposal System (GDS) for high level long lived heat emitting radioactive waste with dimension 20 x 10 x 6.25 m has been evaluated for time dependent heat field distribution, stress build up and possibility of micro-fracturing. The GDS comprises of three cylindrical heat sources (0.30 m diameter and 2 m length) mimicking radioactive waste loaded canisters emplaced within Jalore granite (JG) with barrier layers of Barmer bentonite (BB) clays, from Rajasthan. The methodology adopted in the study includes thermo- mechanical characterization of the granites and clays, followed by finite difference method (FDM) based numerical analysis for time dependent buildup of thermal and mechanical stresses, evolution of temperature field and micro fracturing phenomena within the studied GDS. The study reveals that three heat sources (waste filled SS canisters) of 500 watt intensity with spacing of 2.5 m and clay granite (CG) ratio of 60:40 and 70:30 produces maximum temperature of 92.42 and 94.69 °C and total stress (thermal and mechanical) of 24.77 and 24.97 MPa respectively within the system. 3.32 and 3.31 mm maximum displacement observed in the GDS for 60:40 and 70:30 CG ratio respectively which is within design limit. Analysis further establishes that clay admixture having bentonite clay and granite ratio in the range of 70:30 and 60:40 is capable of smooth dissipation of heat thorough them with resultant maximum temperature of < 100 °C throughout the entire duration of the time periods analysed. Based on these results it is concluded that JG and BB clay in 60:40 and 70:30 ratio with waste canister spacing of 2.5 m have appropriate characteristics suitable for hosting geological disposal system for heat emitting high level waste canisters. The study marks first analysis of multi-canister geological disposal system in Indian context.

Analysis of the vertical distribution of 137Cs and 239,240Pu in waterlogged and non-boggy soils by the sequential extraction method

Mobile capabilities of 137Cs, 239,240Pu and some stable element physicochemical forms were studied in soil layers at a depth of 6–8 cm (maximum concentrations of radionuclides) of non-boggy and waterlogged soil cores sampled on the shores of Lake Bedugnis (Lithuania). Soil samples were acidic with small amount of clay (muscovite). The radionuclide activity concentrations were about 2.5 times higher in non-boggy soil. It was explained by different conditions of deposition of radioactive fallout at these sampling sites and density of the soil samples. The value of the exchangeable fraction of radionuclides is shown to be an indicator of their migration capabilities in the soil. Under anaerobic conditions in waterlogged soil (stagnant pore water conditions) and due to the presence of clay admixture, ∼90% of 137Cs was concentrated in the residual fraction and its mobility was low. 239,240Pu was concentrated mainly in organic matter with rather large exchangeable fractions (∼9.6–∼13.9%). Under oxidizing conditions in non-boggy soil (dynamic pore water conditions in the case of rain), 239,240Pu was mostly concentrated in the oxide fraction. Its exchangeable fractions were less than those in waterlogged soil and, respectively, its mobility was lower. In non-boggy soils, exchangeable fractions of 137Cs were large and varied in the range of 10.1–12.2%, which indicated its high mobility. In the case, 137Cs adsorption by clay materials was reduced and its residual fraction did not exceed 71.3%. The obtained data show that in the area of Lake Bedugnis, the migration capabilities of 137Cs and 239,240Pu change in antiphase.

Novel method of ancient pottery analysis based on radioactive isotope ratios: a pilot study

The proposed method has been applied to a multi-phased settlement complex and pottery manufacturing centre in Ostrowite in northern Poland. In this study the radioactive isotope ratios method has been applied to a set of ceramic pottery specimens from the same multi-layered archaeological site and probably produced from local raw material. The pilot radiometric research was based on: 24 Neolithic (5200–5000 BCE), 21 Early Iron Age (800–600 BCE), 4 Roman Period (100–400 CE), and 13 Middle Ages (1030–1320 CE) pottery fragments, and also 8 samples of local clay (glacial till) and 3 burned clay samples. The method shows the similarities within the ceramic material used to manufacture the pottery. The variations in the quantitative and qualitative compositions of the basic products (clay, silt, loam, sand, ash and organic admixtures) used in the preparation of the ceramic paste change the isotopic composition and activity ratios. Pottery from each ceramic manufacturing centre, based on the specific composition of the raw materials, have characteristic isotope ratios. Radioactive isotope ratios as fingerprints of ancient ceramic manufacturing centres have not yet been applied as an archaeometric method. In this study two isotope ratios have been selected and applied: 40K/228Ac and 226Ra/208Tl. All analysis have been done using gamma spectrometry system, with quality and quantity analysis of the spectrums. Low-background passive shield was used for obtain improvement of results quality. The pilot study confirms the grouping of isotope ratio results for each sample type, even in terms of similarities with the base clay material collected in this region.

DFT Study on the Compatibility Between Bentonite Clay Mineral and Hydration Products With the Polycarboxylate Water Reducer in the Cement Hydration Process

As one of the most used grouting materials, cement has the characteristics of low price and a wide resource of raw material. With the in-depth research and application of cement admixture, the compatibility between different water-reducing agents and clay has become one of the critical factors that affects the cement hydration process. Due to the adsorption of clay on cement additives, the dispersion efficiency of the water reducer will be reduced, also the strength and impermeability of hydration products will be adversely affected. This paper studies the adsorption characteristics of different PCE superplasticizers on bentonite clay minerals and hydration products using a molecular simulation technique. Results showed that there is competitive adsorption between the clay and hydration products when the admixture participates in the hydration reaction, the additives are likely to adsorb on the CH rather than the clay minerals, while the adsorption energy of the hydration product C-S-H is the highest, thus the preferential adsorption order and compatibility between clay minerals and hydration products on admixtures could also be obtained. PDOS (partial density of states) analysis concluded that some new characteristic peaks and rearrangement of the bonding orbitals may appear after the adsorption, with the peak value of the minerals higher than that of jennite, which is also consistent with the adsorption energy. This study aims to reveal the interaction mechanism and compatibility between the hydration product and clay minerals, hoping to fully utilize the advantages of both clay minerals and admixtures in the cement hydration process.

Limestones of the Uk Formation (Upper Riphean, the Southern Urals): Effect of contamination and diagenetic fluids on the distribution of rare-earth elements and yttrium

Research subject. A study was conducted into the geochemical features of various lithotypes of carbonate rocks (granular and clastic limestones, limestones with planar, planar-columnar and columnar stromatolites) from the upper subformation of the Uk Formation. This formation crowns the Upper Riphean Karatau Group on the Western slope of the Southern Urals (Bashkir meganticlinorium). Material and methods. The research material was two collections of carbonate rocks (11 and 32 samples), the general geochemical features of which were previously considered in publications in 2019. The main research method was the analysis of the correlation relationships of the main rock-forming components, trace elements and their indicator relationships. Research results. It was established that all lithotypes are characterized by a significant content of both the main rock-forming components and the trace elements that make up the insoluble residue/fine-grained terrigenous admixture. This suggests that the area of accumulation of carbonate sediments was located near the continent, which served as a source of a significant amount of fine-grained/clay suspension. Conclusions. A strong positive correlation was observed between K2O and REE in the carbonate rocks of the Upper Uk Subformation, and a strong negative correlation was observed between REE and CaO. This suggests that the REE content in carbonate rocks is controlled mainly by terrigenous/clay admixture. A positive correlation is also observed between REE and Th, Zr, and Al2O3. All this shows that REE in carbonate rocks are mainly present in clay admixtures. The correlation coefficient between Ce/Ce* and (Dy/Sm)N is 0.20, while this coefficient for Eu/Eu* and (Pr/Sm)N equals 0.12. Thus, a definite conclusion about the effect of diagenetic fluids on the distribution of REE cannot be made. The data obtained show that the distribution of REE and Y in our collection of carbonate rocks of the Upper subformation of the Uk Formation of the Southern Urals is controlled mainly by clay admixtures.

Genesis Exploration of White Clays Deposited in Thimi Area of Kathmandu Valley

The geological genesis of the Thimi-Sanothimi white clay deposits of Kathmandu Valley was explored employing mineralogical and chemical analyses in this research. For the study, two sample specimens of the clay having two types of particle size, i.e., about < 63 µm (bulk) and < 2 µm (fine), were separated with the help of standard sieve mesh which further modified using high-temperature heat, and 1 M HCl and 1 M KCl solution treatments. For the most part, both the clay fractions constituted of 2:1 type of vermiculite and mica (mainly of K-mica type) clay minerals with different feldspars and quartz phases as clay admixtures from the results of the mineralogical phase analysis. The chemical constituents of the clay particles with < 63 µm, < 2 µm, and the HCl-treated sample specimens confirmed the existence of a high quantity of SiO2 with comparatively low Al2O3 which indicates the presence of fewer amounts of the vermiculite and mica minerals comparatively with feldspars and quart admixtures in the analyzed white clay samples. Moreover, the clay sample contained a considerable quantity of Fe2O3 and MgO chemicals which are not favorable raw material constituents for good quality porcelains and white-wares products without refining and chemical-modifications. The present work could be the first step to explore its potentiality in various industrial sectors like table-ware, sanitary-ware, brick and tile ceramics, paper and pulp, petrochemical, pharmaceutical including environmental pollution controlling agents in Nepal.

Some reflections on Buckingham’s viscous grain shearing model

Sediment geoacoustic properties are of considerable interest for commercial, industrial, and naval applications. In order to make geoacoustic inferences from acoustic data, the practitioner must choose a sediment acoustics model. The ‘Hamilton model’ is the most common, which assumes a frequency-independent sound speed, density, and an attenuation varying linearly with frequency, f1. Buckingham’s Viscous Grain Shearing (VGS) model offers a practical alternative with important benefits. For example, since it obeys causality, it provides fundamental bounds to the parameter space that the Hamilton model does not. Furthermore, if the acoustic data are sufficiently informative, the model provides insight into the frequency dependence of sound speed and attenuation. The central physics in VGS are expressed in high-level (material impulse response) functions, which consider both viscous and friction loss mechanisms and lead to attenuation varying between f1/2 to f1 to f2. Geoacoustic inference from seabed reflection measurements using the VGS model provides insight into the frequency dependence of naturally occurring marine sediments, i.e., admixtures of clay, silt, sand. At present, the VGS model is likely the most general (causal) sediment acoustics model, i.e., can reasonably treat the broadest range of sediment fabrics. [Research supported by the ONR Ocean Acoustics Program.]

Physico-chemical and surface properties of air plasma treated PVDF/PMMA/Attapulgite/hexagonal-Boron Nitride blends

In our present study, we synthesized and characterized a series of Poly (vinylidene fluoride) (PVDF)/Poly (methyl methacrylate) (PMMA) polymer blends modified by the admixtures of attapulgite clay (AT) and hexagonal-Boron Nitride (h-BN) by weight ratio. The surface of the modified polymer blends was treated with air plasma. The samples were further characterized by polarizing optical microscopy (POM), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) to visualize and understand the morphology of the surfaces before and after the plasma treatment. The air plasma induced an alteration in the surface chemical compositions, functional groups and the elemental ratio which was analyzed in detail by Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS). The contact angle measurements were performed to envisage the wetting property of the untreated and plasma treated surfaces and their physical and chemical properties were correlated to address the nature of the surfaces. This study can be helpful to develop, future protective barriers and advanced functional surface coatings.

Mineral matter composition of drained floodplain soils in north-eastern Poland

Abstract Soils in two river valleys (Rozoga and Omulew) in north-eastern Poland were investigated. The valleys are located on a sandy outwash plain formed during the Vistulian (Weichelian) Glaciation. The soils are drained, used as meadows and classified as Fluvic Umbric Gleysol, Fluvic Mollic Gleysol, and Eutric Fluvic Histic Gleysol (IUSS Working Group WRB 2015). The aim of the study was to identify the composition of mineral matter and to determine the types of clay minerals and intermediate stages of clay minerals by means of the X-ray diffraction (XRD). The studied floodplain soils are rich in organic matter and contain considerable mineral alluvial admixtures. The content of clay fraction (< 2.0 μm) is low (0.02–5.61% of total mineral matter). Higher content of clay fraction was noted in soils with elevated content of organic matter, which can be evidence of simultaneous accumulation of both components. In deeper depressions occurring in river valleys (oxbow lakes), a specific deposit termed silty telmatic mud (16–24% TOC, 50–75% silt, 3.1–5.6% clay fraction content) was accumulated. On the other hand, in shallow depressions, a muddy deposit was accumulated (5.7–7.7% TOC, sandy texture). The main identified clay minerals were smectite, vermiculite, illite and kaolinite as well as variety of mixed-layer clays. Alluvial clay admixture in studied soil formations showed mineralogical similarity to typical floodplain mineral soils (Fluvisols). Mineral fraction of studied soils is mostly of allochthonous origin.

Effect of silica and clay minerals on rheology of heavy crude oil emulsions

Researchers studying oil-in-water emulsions practically always deal with the oil and water purified of mineral admixtures. In reality, a water/crude oil emulsion obtained from a well contains solid clay- and sand particles, which may act as surfactants. In the present work, the solid particles’ effect on the morphology and rheological behavior of heavy crude oil emulsions are studied. Water-in-oil emulsions are fluids with the weakly non-Newtonian behavior and viscosity exceeding that of the crude oil. Solid particle admixtures have practically no effect on the viscosity of these emulsions. Oil-in-water emulsions, on the contrary, are viscoplastic systems, the yield stress of which increases with silica- and clay admixture content. The transition from water emulsions to the oil ones was realized using surfactants (cetrimonium bromide, sodium dodecyl sulfate, Tween 85, and Triton X-100), the success of the phase inversion depending on the hydrophilic-lipophilic balance of a surfactant. The effective viscosity of the oil-in-water emulsions is demonstrated to depend on the shear rate and solid particle- and surfactant concentrations, this providing the opportunity to optimize the compositions of crude oil emulsions for transportation.

Laboratory evaluation on the effectiveness of polypropylene fibers on the strength of fiber-reinforced and cement-stabilized Shanghai soft clay

This paper presents a laboratory evaluation on the strength behavior of cement–clay admixture improved by polypropylene fiber. Waste polymer textile bags are harmful to the environment and sustainable means to reuse them are urgently being sought. A novel method to recycle these waste polymer textile bags is applying them in soft soil improvement projects, such as compacted-pavement base/subbases. In order to verify the effectiveness of fiber bundles used in soil mixing, a series of laboratory investigation are conducted on fiber-reinforced cement-improved soft Shanghai clay. In the tests, two types of polymer fibers were employed; the first one is monofilament polypropylene fiber and the other is fiber bundles split from polymer textile bags. The tests were conducted using unconfined compressive strength (UCS) test after the specimen of fiber–soil–cement admixture were cured for some period. The results show that fiber additive can significantly improve the strength and ductility of the cement treated Shanghai clay. The UCS of fiber–soil–cement admixture is related to both content and length of fiber. Both two kinds of fiber-reinforced cement clay reached their peak strength at fiber content of 0.5%. UCS will slowly reverse if the fiber content continues to increase. Even though the polypropylene fiber works better than the fiber bundles, the difference is less than 5%. These results indicate that the fiber bundles split from polymer bags can be used as the reinforcement in soil mixing, thus providing a novel approach to treat waste polymer textile bags.

Integrating petrography, mineralogy and hydrochemistry to constrain the influence and distribution of groundwater contributions to baseflow in poorly productive aquifers: Insights from Gortinlieve catchment, Co. Donegal, NW Ireland

Identifying groundwater contributions to baseflow forms an essential part of surface water body characterisation. The Gortinlieve catchment (5km2) comprises a headwater stream network of the Carrigans River, itself a tributary of the River Foyle, NW Ireland. The bedrock comprises poorly productive metasediments that are characterised by fracture porosity. We present the findings of a multi-disciplinary study that integrates new hydrochemical and mineralogical investigations with existing hydraulic, geophysical and structural data to identify the scales of groundwater flow and the nature of groundwater/bedrock interaction (chemical denudation). At the catchment scale, the development of deep weathering profiles is controlled by NE-SW regional scale fracture zones associated with mountain building during the Grampian orogeny. In-situ chemical denudation of mineral phases is controlled by micro- to meso-scale fractures related to Alpine compression during Palaeocene to Oligocene times. The alteration of primary muscovite, chlorite (clinochlore) and albite along the surfaces of these small-scale fractures has resulted in the precipitation of illite, montmorillonite and illite-montmorillonite clay admixtures. The interconnected but discontinuous nature of these small-scale structures highlights the role of larger scale faults and fissures in the supply and transportation of weathering solutions to/from the sites of mineral weathering. The dissolution of primarily mineral phases releases the major ions Mg, Ca and HCO3 that are shown to subsequently form the chemical makeup of groundwaters. Borehole groundwater and stream baseflow hydrochemical data are used to constrain the depths of groundwater flow pathways influencing the chemistry of surface waters throughout the stream profile. The results show that it is predominantly the lower part of the catchment, which receives inputs from catchment/regional scale groundwater flow, that is found to contribute to the maintenance of annual baseflow levels. This study identifies the importance of deep groundwater in maintaining annual baseflow levels in poorly productive bedrock systems.

Stability of kaolin sand from the Vyšný Petrovec deposit (south Slovakia) in an acid environment

Abstract Comprehensive characterization of kaolin sand from the Vyšný Petrovec (VP) deposit in Slovakia by a variety of experimental methods was performed. The quantitative XRD analysis (RockJock software) revealed that the acid-untreated sample contained mainly kaolinite (~60 wt. %), a considerable amount of dioctahedral micas (~32 wt. %) and quartz (~ 7 wt. %). The Hinckley index (HI) and Aparicio-Galán-Ferrel index (AGFI) calculated from the 02l and 11l reflections showed medium-defect kaolinite to be present in the VP kaolin. The influence of the mineral composition of VP kaolin on its stability in 6 mol · dm-3 HCl at 95 °C was investigated. The solid reaction products were examined by chemical analysis; XRD and infrared spectroscopy in both middle (MIR) and near (NIR) regions. Considerably higher dissolution rate of Fe compared to Al indicated that Fe was bounded in a readily soluble phase rather than in kaolinite. While the MIR spectra confirmed the gradual release of the central atoms from the clay minerals layers and creation of amorphous silica upon acid treatment, the NIR spectra revealed the formation of Si-OH groups in the solid reaction product. Relatively high dissolution rate of VP kaolin resulted from the presence of small-grains of mediumdefect kaolinite and clay admixtures in VP kaolin sand.

Mineralogical characterization of ceramic tiles prepared by a mixture of Cretaceous and Mio-Pliocene clays from Tunisia: factory and laboratory products

Thermal transformations in ceramic products at high temperatures were studied for admixture of Cretaceous and Mio-Pliocene clays, either carbonatic or with plastic behaviour, used for Lab-tiles and factory biscuits with amounts (25%) of quartz-sand added as temper. Clay admixtures contained illites, smectites series, interstratified I/S species and kaolinite. Firing steps of pastes in the factory took place in a tunneled gas kiln at 1080°C; whereas, tiles used for laboratory experiments were fired in an electric kiln (600–1050°C). SEM and XRD patterns help identify minerals disseminated in a glassy matrix as well as idiomorphic crystals formed in pored ceramic tiles, including feldspars (anorthite, sanidine), wollastonite, diopside and melilite (gehlenite). In the fired products, minerals form preferably in pores and crystal genesis is mainly controlled by melt flow. Wollastonite, diopside and gehlenite appear at 800°C. Gehlenite amounts remain nearly constant or may diminish slightly above 1000°C. Enough calcite amounts favor formation of anorthite, gehlenite and wollastonite; whereas gehlenite doesn’t appear necessarily as a precursor for anorthite. It is worthy of noting that gehlenite persists at 1100°C and coexists with anorthite. The later crystallizes above 850°C and its amounts increase abruptly above 1000°C. Following mineral crystallization at elevated temperature, the melt precursor can be either completely consumed or remains as relicts in biscuits.

Influence of clays on the rheology of cement pastes

The fresh state of concrete is becoming increasingly important in furthering the types of applications of today's construction world. Processing techniques have resulted in technologies such as self-consolidating concrete and depend on the microstructural changes that take place during and immediately after mixing and placing. These changes to the microstructure reflect the flocculation behavior between the particles in suspension. The ability to modify this behavior allows control over the balance among flowability and shape-stability of concrete. This study investigates how clay admixtures affect the microstructure of cement pastes from a rheological stand point. Shear and compressive rheology techniques are used to measure how the solids volume fraction of suspensions with different admixtures evolves with stress. Based on these relationships, the effectiveness of clays on the balance between flowability and shape-stability is measured. Results are consistent with green strength tests performed on concrete mixes derived from the cement paste mixes.

Geotechnical Survey, Dredgeability Of Soil Sediments And Siltation Volume Of Brimsu Water Reservoir

The water supply for the Cape Coast Metropolis of Ghana comes from Brimsu reservoir. The accumulation of soil sediments in the reservoir since construction and commissioning in 1928 has resulted in a drastic reduction of the storage capacity of the reservoir leading to perennial water shortages to the community. A dredging syst-em to desilt the sediments and to improve the storage capacity was investigated. The volume of siltation was determined by hydrographic and topographical surveys using Global Positioning System and Total Station Tec-hniques to obtain data on the area and thickness of the sediments. The rate of siltation had more than doubled since the construction. The geotechnical characteristics of the sediments showed the sediments were of unifor-mly graded sand with admixtures of clay and silt. The dredgeability of the sediments was characterized by geo-technical descriptor terms, indicating that the sediments could be dredged using cutter-type dredger for excava-tion, and transported by hydraulic pipelines to disposal sites. The study established that sustainable environme-ntal management is required to minimize the siltation of the reservoir and ensure regular water supply. Journal of Applied Science and Technology Vol. 12 (1&2) 2007: pp. 71-77

Modelling elastic properties of impure chalk from South Arne Field, North Sea

ABSTRACTIn impure chalk, the elastic moduli are not only controlled by porosity but also by contact‐cementation, resulting in relatively large moduli for a given porosity, and by admixtures of clay and fine silica, which results in relatively small moduli for a given porosity. Based on a concept of solids suspended in pore fluids as well as composing the rock frame, we model P‐wave and S‐wave moduli of dry and wet plug samples by an effective‐medium Hashin–Shtrikman model, using chemical, mineralogical and textural input. For a given porosity, the elastic moduli correspond to a part of the solid (the iso‐frame value) forming the frame of an Upper Hashin–Shtrikman bound, whereas the remaining solid is modelled as suspended in the pore fluid. The iso‐frame model is thus a measure of the pore‐stiffness or degree of cementation of the chalk.The textural and mineralogical data may be assessed from logging data on spectral gamma radiation, density, sonic velocity and water saturation in a hydrocarbon zone, whereas the iso‐frame value of a chalk may be assessed from the density and acoustic P‐wave logs alone. The iso‐frame concept may thus be directly used in conventional log‐analysis and is a way of incorporating sonic‐logging data.The Rigs‐1 and Rigs‐2 wells in the South Arne field penetrate the chalk at the same depth but differ in porosity and in water saturation although almost the entire chalk interval has irreducible water saturation. Our model, combined with petrographic data, indicates that the difference in porosity is caused by a higher degree of pore‐filling cementation in Rigs‐1. Petrographic data indicate that the difference in water saturation is caused by a higher content of smectite in the pores of Rigs‐1. In both wells, we find submicron‐size diagenetic quartz.

Permeation of Sand-Processed Clay Mixtures with Calcium Chloride Solutions

The hypothesis that the substitution of attapulgite clay for bentonite in an otherwise sand-bentonite (S-B) mixture will improve the resistance to change in hydraulic conductivity of the mixture upon permeation with calcium chloride (CaCl\d2) solutions relative to permeation with a processed tap water is tested. For mixtures with the same clay soil content, complete substitution of attapulgite clay for bentonite significantly decreases the change in hydraulic conductivity relative to that observed for the S-B mixtures upon permeation with a 0.5 M CaCl\d2 solution. In addition, the resistance to change in hydraulic conductivity of the sand-attapulgite clay-bentonite (S-AC-B) mixtures containing 20% clay soil is improved by increasing the percentage of attapulgite clay in the clay soil admixture from 50% to 100% and by decreasing the concentration of the CaCl\d2 solution from 0.5 M to 0. The first exposure effect also decreases with increasing amount of attapulgite clay in S-AC-B mixtures containing 20% clay soil. However, the resistance to change in hydraulic conductivity resulting from substituting only half of the bentonite in the S-B mixtures with an equal amount of attapulgite clay is not improved substantially due to the dominating influence of the bentonite portion of the sand-clay mixture.

Influence of amorphous silica and iron hydroxide on interparticle action and soil surface properties

The study of the physicochemical properties of pure amorphous materials (complexes) consisting of Fe2O3 and SiO2 in various proportions indicates that the amorphous complexes will exhibit different properties and characteristics depending on the proportions of Fe2O3 and SiO2. Addition of the amorphous complexes with illitic clay studied shows that the properties of the clay admixture will also vary according to the properties of the amorphous complex, albeit to a lesser degree. The properties and behaviour observed for the amorphous complexes and the clay admixtures can be linked directly to the large specific surface area and high surface charge of the amorphous complexes. The contribution of amorphous complexes to the clay – amorphous complex mixtures (clay admixtures) is twofold: firstly, by the amount of amorphous complex in the clay admixture, and secondly by the composition of the amorphous complex used. The contribution from the amorphous complex is in two forms: water-holding capacity and bonding action. The presence of pH-dependent surface charges associated with the amorphous complexes makes the physicochemical properties and behaviour of the clay admixtures (e.g., liquid limits and zeta potential) sensitive to the pH environment. Coating of amorphous colloids onto clay particle surfaces, shown by scanning electron microscopy, appears to, be enhanced by a decrease in pH of the system, indicating that the enhancement is likely due to the increased electrostatic attraction resulting from the increased amounts of positive charges on the amorphous colloids. Key words : amorphous materials, mass ratio, zeta potential, Bingham yield stress, clay admixtures, hydrogen bonding, specific surface area, cation exchange capacity, anion exchange capacity, fabric and soil structure.

Miocene intensification of upwelling along the California margin as recorded in siliceous facies of the Monterey Formation and offshore DSDP sites

Abstract Diatomaceous sediments and their diagenetic equivalents in the Monterey Formation record a variable history of upwelling along the California margin. Distrinctive dark opal-CT and quartz chertz found in distal basins of the Monterey Formation are the result of burial diagenesis of pure biosiliceous oozes (biosiliceous oozes without significant admixtures of clay) and are therefore evidence of intensified coastal upwelling during the early middle Miocene. Dating of six sections of the Monterey Formation, largely by diatom biostratigraphy, suggests that at the Point Reyes and Point Año Nuevo sections in north-central California, the age of the earliest chert intervals is between 13.8 and 15.0 Ma, and 14.3 and 14.8 Ma, respectively. In south-central California, ages from the Shell Beach, Mussel Rock, and Lions Head sections imply that the age of the base of the chert intervals is between 12.7 and 13.3 Ma. Both ages correlate to an early middle Miocene high latitude cooling step that resulted in more vigorous surface water circulation, upwelling of nutrient-rich waters, and increased biosiliceous sedimentation in the North Pacific. The north-south difference in age of the base of the chert interval probably reflects a progressive intensification of the California Current from 15.0 to 12.7 Ma. The age of the onset of biosiliceous sedimentation at DSDP sites of the northeastern Pacific is also generally younger at the more southern sites; however, these particular DSDP sites were located some distance from the centres of coastal upwelling and are not as reliable indicators of the intensification of upwelling along the California margin.