Smectite Content Research Articles

Density Normal Compaction Trend in the Peciko Field, Lower Kutai Basin, Indonesia

DOI:10.17014/ijog.7.3.253-265The density normal compaction trend is the mandatory parameter in order to calculate contribution of disequilibrium compaction to overpressure, in the presence of unloading to total overpressure. In this paper, mudrock compaction behaviour is studied in the Peciko Field. The density normal compaction trend was constructed in a normally pressured section, where the temperature is <1200C, within the transformation of smectite–illite zone. The compaction trend includes not only vertical effective stress, but also diagenesis, especially smectite-illite transformation, as dependant factor for compaction, both termed as β. This compaction trend is also known as Skempton-Duta compaction model. Quardros-Linares fifth-order kinetic reaction was found that could model smectite-illite transformation in the studied area fairly well. The plot between β and smectite content shows a very good match, confirming that Skempton-Dutta compaction model is valid for the entire range of smectite-illite transformation. In the area where the density log is unavailable, the density normal compaction can be constructed from temperature history acting as a proxy for smectite-illite transformation, with some local calibration.

Hydrophobicity and surface free energy to assess spent coffee grounds as soil amendment. Relationships with soil quality

The aim of this work was to evaluate the effects of spent coffee grounds (SCG), a highly hydrophobic raw material, on the hydrophobicity of two Mediterranean agricultural soils. Physical, chemical, mineralogical and biological soil properties, most of them used to evaluate soil quality, were studied and related to the main hydrophobicity parameters. The in vitro assay was performed with two SCG doses (2.5 and 10%), two soils and two incubation times (30 and 60 days). Hydrophobicity was determined by the water drop penetration time test (WDPT), the contact angle (CA) with H2O, formamide and diiodomethane, and the surface free energy components (SFE) calculated using the Van Oss model. The addition of SCG increased the WDPT, CA and SFE, being the latter which was related to a greater number of soil quality variables. Hydrophobicity was related to lower humus quality index (HQI), and a higher proportion of labile organic matter, as shown by Infrared and UV–vis spectroscopy. An increase in hydrophobicity was related to an improvement of soil physical quality: a high aggregate stability index, saturated hydraulic conductivity, porosity (total and macro), water retention, and a less bulk density. The most critical effect related to the increase in hydrophobicity was the significant decrease in the available water content. The SEM images showed a greater occlusion and stabilization mechanism of the SCG particles incorporated in Vega soil, probably due to its higher content of smectite and carbonates. The appearance of fungal biomineralizations of calcium carbonate is associated with SCG addition and could be considered as an interesting and little studied process of inorganic carbon fixation and secuestration. These results showed that hydrophobicity can afford relevant information that can help to asses soil quality status after an amendment with SCG.

Clay-carbonate aggregation in alluvial calcareous soils, Central Anatolia, Turkey

An unexpectedly high infiltration capacity was determined for heavy-textured, clayey alluvial calcareous soils (Calcic Haploxerepts) in central Anatolia, Turkey, presumably due to the specific mineralogical contents. In order to unravel the phenomenon, clay mineralogy and morphology, soil microaggregate composition, and carbonate accumulations were studied in these soils via X-ray diffractometry, scanning electron microscopy, and energy-dispersive analyses. Calcite and layered minerals were the principal components of the fine fraction. The percentages of clay, silt, and sand were 45, 54, and 1%, respectively. Illites were dominant in the clay fraction – 43–49%, whereas the content of smectites was rather small – 4– 6%. The results indicated that the principal factors of the high hydraulic capacity of the soils were (1) illitization, a process that is typical for arid and semi-arid soils, and (2) microaggregation involving pedogenic calcite, resulted in the formation of clay–calcite ultra-microaggregates maintaining elongated 3–10 μm in diameter micropores.

Thermodynamic Interpretation on the Rheology of Aqueous Bentonite Suspensions

Since their exceptional rheological behavior, bentonite suspensions are widely used in engineering, industrial, agricultural, and drilling applications. So, the aim of the present study is to investigate the rheological properties of three types aqueous suspensions prepared with calcium bentonite (CaB), sodium bentonite (NaB) obtained from that by Na2CO3 activation, and NaB with the excess soda. The CaB taken from Giresun/Turkey region contains calcium smectite (CaxS) as clay mineral and opal CT (SiO2.nH2O) as impurity which is paracrystalline silica. Soda content by the activation and bentonite content in the suspension were changed in the interval of 2.5-15.0% and 5-20% by mass, respectively. CaxS completely converted to sodium smectite (Na2xS) by the activation with the soda content of 2.5% and then Na2xS+Na2CO3 mixtures formed. Rheological properties of these aqueous suspensions were measured using a Fann Viscometer. These properties reached their maxima by the most thixotropic Na2xS suspensions and greatly increased with the increasing of smectite content. Rheological plots drawn of the shear rate vs. shear stress in the interval of 170-1020 s-1 showed that the suspensions flow as a Bingham Plastic. Change in rheological properties depending on the smectite type and content as well as excess soda content was explained thermodynamically based on the chemical potential gradient between interlayer and dispenser waters.

Influence of (3–Aminopropyl) triethoxysilane on entrapped polypropylene at nanosilica composite for shale swelling and hydration inhibition

The unforgiving shale formations require special shale inhibitors to mitigate wellbore instability problems. (3–Aminopropyl) triethoxysilane polypropylene-nanosilica composite (PNSC + NH2) was evaluated in water-based drilling muds (WBDMs) as a clay swelling and hydration inhibitor. The size distribution, functional groups, morphology, and thermal stability of the PNSC + NH2 were studied. Rheological and filtrate volume tests were carried out to determine the influence of the PNSC + NH2 on WBDMs. The clay swelling inhibition performance of the PNSC + NH2 mud system was examined and compared with that of potassium chloride (KCl) and KCl + partially hydrolyzed polyacrylamide (KCl + HPAM) through clay swelling inhibition test, extended clay swelling inhibition test (inhibition longevity test), and BET analysis test. Four shale specimens were prepared with compactor cell for the measurement of clay swelling using the Linear Swell Meter. Drilling muds were examined on 16 mm thick-compacted shale pellets using the highest concentration of smectite. A shale rolling recovery test was conducted to determine the shale hydration-retardation. Results showed that the PNSC + NH2 particle has good dispersibility, with a size distribution predominantly distributed between 80 and 390 nm. The inclusion of 1.5w/v% PNSC + NH2 concentration enhanced the plastic viscosity and yield point of WBDM from 11 to 15 mPa s and 9–14 Pa, respectively. Also, it reduced the API filtrate volume of the WBDM from 10.2 to 7.8 ml. The clay swelling inhibition performance of the WBDM for 36 h showed 62% swelling and was reduced to 42% by KCl, 33% by KCl + HPAM, and 28% by PNSC + NH2. When the inhibition test was extended to 60 h, the swelling increased to 44% for KCl, 40% for KCl + HPAM, and 29% for PNSC + NH2 mud systems. These results revealed that the PNSC + NH2 has the best inhibition performance due to its ability to provide the greatest long-lasting inhibiting effect on the clay surface. When the shale cuttings with the various mud systems were subjected to 150 °C for 16 h in an ageing steel cell, the shale recovery rate at 1.5w/v% concentration confirmed that the PNSC + NH2 exhibited 75.3 wt%, while that of the base mud, KCl, and KCl + HPAM systems demonstrated 33.6, 58.4, and 63.1 wt%, respectively. The BET surface area of the shale reduced significantly by 52.3% with 1.5w/v% PNSC + NH2 from 14.72 to 7.02 m2/g. The wettability determination of the shale surface showed a contact angle of 36.8° which improved to 68.4° by 81.0% with 2.0w/v% PNSC + NH2 concentration. The application of PNSC + NH2 for clay swelling and hydration inhibition proved to be promising and could be effective for drilling shales.

Trade-off between ‘new’ SOC stabilisation from above-ground inputs and priming of native C as determined by soil type and residue placement

Due to the geographical expanse of grasslands with depleted organic matter stocks, there has been growing interest in the management of these ecosystems for C sequestration to help mitigate climate change. It is generally accepted that management practices intending to increase forage production (e.g. decreasing grazing density) result in increased soil C stocks by increasing the return of biomass inputs to the soil organic carbon (SOC) pool. However, the contribution of C inputs to stable SOC versus GHG losses, and how this is affected by soil properties, remains largely unknown, particularly within subtropical biomes. To investigate the role of soil texture and mineralogy on SOC stabilisation, we identified three different soil types with varying physical properties in close proximity (< 2 km2) to each other. We used isotopically labelled plant material (13C), placed on the soil surface versus incorporated within the mineral soil, to trace the fate of fresh residue inputs into SOM fractions that differed in their degree of protection and mechanistic interactions with the soil matrix. Weekly GHG measurements (CO2, N2O and CH4) were taken to understand the overall GHG balance resulting from C inputs (i.e. SOC accrual versus GHG losses in CO2 equivalents). In finer textured soils with a greater smectite content, SOC accrual was greater but was significantly outweighed by GHG losses, primarily from native SOC priming. The incorporation of residue within the soil increased residue-derived SOC accrual by 4- to 5-fold, whilst also suppressing the priming of native SOC. This improved understanding of how soil texture and residue placement affect the global warming mitigation potential of subtropical grassland soils will be important in determining identifiable regions that should be targeted for SOC restoration efforts by increasing C inputs.

The geochemical and mineralogical fingerprint of West Antarctica's weak underbelly: Pine Island and Thwaites glaciers

The marine-based West Antarctic Ice Sheet (WAIS) is considered the most unstable part of the Antarctic Ice Sheet, with particular vulnerability in the Amundsen Sea sector where glaciers are melting at an alarming rate. Far-field sea-level data and ice-sheet models have pointed towards at least one major WAIS disintegration during the Late Quaternary, but direct evidence for past collapse(s) from ice-proximal geological archives remains elusive. In order to facilitate geochemical and mineralogical tracing of the two most important glaciers draining into the Amundsen Sea, i.e. Pine Island Glacier (PIG) and Thwaites Glacier (TG), we here provide the first multi-proxy provenance analysis of 26 seafloor surface sediment samples from Pine Island Bay.Our data show that the fingerprints of detritus delivered by PIG and TG are clearly distinct near the ice-shelf fronts of both ice-stream systems for all grain sizes and proxies investigated. Glacial detritus delivered by PIG is characterised by low εNd values (~−9), high 87Sr/86Sr ratios (~0.728), low smectite content (<10%), and hornblende and biotite grains with Late Permian to Jurassic (170–270 Ma) cooling ages. In contrast, glacigenic detritus delivered by TG is characterised by higher εNd values (~−4), lower 87Sr/86Sr ratios (0.714), higher smectite (20%) and kaolinite content (37%), biotite and hornblende grains with 40Ar/39Ar cooling ages of <40 Ma and ~115 Ma, and high content of mafic minerals.The geochemical and mineralogical fingerprints for PIG and TG reported here provide novel insights into sub-ice geology and allow us to trace both drainage systems in the geological past, under environmental conditions more similar to those envisioned in the next 50 to 100 years.

Paleoclimate change since the Miocene inferred from clay-mineral records of the Jiuquan Basin, NW China

Global cooling and the uplift of the Tibetan Plateau have long been considered the crucial controls of the climate change in inland Asia since the Cenozoic. However, which of these factors has played the leading role is unknown. To understand climate change and the controlling factors in inland Asia, here, we present new records of clay mineralogy and trace elements of clay fractions from the Neogene sedimentary sequence in the Jiuquan Basin of the northeastern Tibetan Plateau. The clay-mineral records reveal four stages of paleoclimate changes. From ca. 24 Ma to 17 Ma, the low total smectite and (smectite+I/S mixed layers+kaolinite)/(illite+chlorite) and high illite contents suggest weak chemical weathering and hence arid climatic conditions. For ca. 17–14 Ma, the high total smectite and (total smectite+kaolinite)/(illite+chlorite) and low illite contents suggest strong chemical weathering, indicating a change in climate from cold and dry to warm and humid. There was no palygorskite during this warm and humid period. From ca. 14 Ma to 8 Ma, the low total smectite content, high illite content and the appearance of palygorskite indicate that the climate turned to cold and dry. Since 8 Ma, low total smectite as well as high illite and chlorite contents suggest a colder and drier period. The records of clay mineralogy illustrate that the Jiuquan Basin has experienced increasing aridity since ca. 14 Ma, synchronous with the inland Asian aridification. Given the synchroneity with the global cooling, we suggest that the climate evolution in the Jiuquan Basin from the late Oligocene to middle-late Miocene was mainly controlled by global climate change. Since the late Miocene, the uplift of the Tibetan Plateau and global cooling have significantly influenced the decreasing temperature and humidity of the Jiuquan Basin. The uplift of Tibetan Plateau may intensify the aridity by blocking moisture from reaching the Jiuquan Basin.

Adsorption of lead and cadmium from aqueous solution by Gunungkidul zeolitic tuff, Indonesia

This study focuses on utilizing zeolitic tuff as a novel adsorbent for lead and cadmium solution. Two zeolitic tuff samples were obtained from Tegalrego and Bantengwareng village, Gunungkidul, Yogyakarta, Indonesia. Zeolitic tuff sample characterization was carried out by conducting microscopic and X-ray diffraction analysis, cation exchange capacity, and chemical measurement. Batch adsorption tests were carried out for the study of isotherms with the Langmuir model. The results of characterization showed that the Bantengwareng and Tegalrejo zeolitic tuff sample consist dominantly of mordenite mineral and other impurities. Bantengwareng zeolitic sample revealed had higher mordenite and smectite content compared to Tegalrejo zeolitic tuff sample which effects to the adsorption capacity. The batch adsorption test showed the adsorption ability of the Bantengwareng zeolitic tuff sample achieved for 76% of lead and 69% of cadmium; however, the Tegalrejo zeolitic tuff sample achieved for 51% of lead and 26% of cadmium. The result of isotherm study based on Langmuir equation revealed that the adsorption capacity of Bantengwareng and Tegalrejo zeolitic tuff samples has a value of 416.67, 384.61 and 277.77, 243.91 mg/g for lead and cadmium, respectively. The correlation coefficient based on Langmuir model varied from 0.866 to 0.956, which suggests that isotherm models fit very well. The reusability study revealed that the efficiency decreased reduce up to 30% after third cycles; however, the zeolitic tuff samples in study area are considered as part of its adsorption potential for lead and cadmium solution.

Key factors controlling radiocesium sorption and fixation in river sediments around the Fukushima Daiichi Nuclear Power Plant. Part 1: Insights from sediment properties and radiocesium distributions

In order to elucidate the radiocesium transport behaviors in natural environment, we systematically investigated sediments from the highly contaminated rivers of Ukedo and Odaka around the Fukushima Daiichi Nuclear Power Plant. We focused on determining the key factors controlling the radiocesium sorption and fixation, such as variations in the particle size, clay mineralogy, and organic matter (OM). The distribution patterns of the 137Cs concentration and particle size fractions were found to be similar for the two rivers, indicating that both clay and silt fractions contributed almost equally to the Cs sorption. The clay mineralogical composition evaluated using X-ray diffraction analysis showed that the relative contents of micaceous minerals were higher in the Ukedo River samples, whereas the relative contents of smectite and kaolinite were higher in the Odaka River samples. This implies that the sediments in both rivers were likely at different weathering stages due to the different geological settings in both catchments. The effects of OM on the sediment properties were also investigated by comparing the cation exchange capacity (CEC) and the radiocesium interception potential (RIP) of the two samples both with and without OM present. The CEC values were controlled by both the clay minerals and OM, and the RIP values increased significantly in the absence of OM. Such trends were correlated to the total organic carbon values, which may be used to understand the direct and indirect roles of OM in the sorption and fixation of Cs. These key differences in river sediment were attributed to the differences in the geological settings and weathering stages. These properties may contribute to the different sorption and fixation behaviors of radiocesium. In the second part paper, we further examined these behaviors and identified key factors by investigating their relationship to the sediment properties of both rivers.

Evolution of Elastic and Mechanical Properties During Fault Shear: The Roles of Clay Content, Fabric Development, and Porosity

AbstractPhyllosilicates weaken faults due to the formation of shear fabrics. Although the impacts of clay abundance and fabric on frictional strength, sliding stability, and porosity of faults are well studied, their influence on elastic properties is less known, though they are key factors for fault stiffness. We document the role that fabric and consolidation play in elastic properties and show that smectite content is the most important factor determining whether fabric or porosity controls the elastic response of faults. We conducted a suite of shear experiments on synthetic smectite‐quartz fault gouges (10–100 wt% smectite) and sediment incoming to the Sumatra subduction zone. We monitored Vp, Vs, friction, porosity, shear and bulk moduli. We find that mechanical and elastic properties for gouges with abundant smectite are almost entirely controlled by fabric formation (decreasing mechanical and elastic properties with shear). Though fabrics control the elastic response of smectite‐poor gouges over intermediate shear strains, porosity is the primary control throughout the majority of shearing. Elastic properties vary systematically with smectite content: High smectite gouges have values of Vp ~ 1,300–1,800 m/s, Vs ~ 900–1,100 m/s, K ~ 1–4 GPa, and G ~ 1–2 GPa, and low smectite gouges have values of Vp ~ 2,300–2,500 m/s, Vs ~ 1,200–1,300 m/s, K ~ 5–8 GPa, and G ~ 2.5–3 GPa. We find that, even in smectite‐poor gouges, shear fabric also affects stiffness and elastic moduli, implying that while smectite abundance plays a clear role in controlling gouge properties, other fine‐grained and platy clay minerals may produce similar behavior through their control on the development of fabrics and thin shear surfaces.

EFFECT OF PLANT COVERAGE ON MINERALOGICAL CHANGES OF MICA IN RHIZOSPHERE

Three soil sites were chosen in sulaymaniyah governorate, for three types of trees (pine, oak and pear), in order to study the effect of biochemical activities in rhizosphere on weathering of mica and potassium availability comparing with Bulk soil. Results of X-ray showed that the transformation process of mica to 2:1 expandable minerals in rhizosphere was exceeded than in Bulk soil of all type of trees. While the superiority of mica weathering, and increase of smectite content in all rhizosphere were taken a followed sequence. Pine &gt; oak &gt; pear. Results of SEM for clay samples of Bulk soil showed there was no cracks, splitting, Exfoliation, and no separation of the layers on the surfaces of minerals. While the inspection results confirmed two types of mica edges weathering: first, was a complete edge weathering of mica in Bulk soil of pine trees, and second, was un completed edge weathering in Bulk soil of oak and pear. Also a complete pal colour of mica particle surfaces were found in clay samples of rhizosphere soil under pine trees. While the surfaces and edges of mica were less affected by the weathering processes, was found in clay samples of rhizosphere soil of oke and pear trees.

Clay minerals of surface sediments from the lower Bengal Fan: Implications for provenance identification and transport processes

Based on the clay mineral assemblages of 98 surface sediments from the lower Bengal Fan, we carried out a quantitative provenance identification and discussed the potential transport processes of fine fractions with the support of the hydrodynamic environment. Illite is the dominant clay mineral in the study area, with an average of 51%, followed by kaolinite, with an average of 20%, while chlorite and smectite account for averages of 17 and 11%, respectively. The study area can be divided into two provinces based on the clay mineral assemblages: Province I, located in the western part of the study area, has relatively higher smectite content, while province II, located in the eastern part, shows higher illite content. The Ganges–Brahmaputra (Himalayan) and the Godavari–Krishna (Indian Peninsula) are suggested to be the major provenances, and the average relative contributions of the Himalayan source and the Indian source are 76 and 24%, respectively. Sediments in province II receive more sediment from the Himalayan source, with an average contribution of 84%, while the Indian source mainly contributed to province I, with an average contribution rate of 32%. The Indian Peninsula materials are predominantly conveyed to the study area by the northeast monsoon circulation, and the relative contribution gradually decreases from northwest to southeast in the lower Bengal Fan. However, most of the Himalayan material is transported to the study area by the southwest monsoon. Our research indicates that the seasonal hydrodynamic pattern of the Northeast Indian Ocean plays an important role in controlling modern sediment transport in the Bay of Bengal, causing terrestrial materials from different sources to show significantly different spatial distribution characteristics.

Clay mineralogy of Miocene mudstones from the Lower Austrian Molasse Basin

Abstract Recent studies established the lithological and chemical sediment evolution in the Lower Austrian Molasse Basin (LAMB), a part of the North Alpine foreland basin, during the Early Miocene. In this study, we aim to integrate the clay mineralogy of seven wells across the LAMB with a newly proposed lithostratigraphy, and to infer implications for provenance, palaeo-geography and palaeoclimate. The results of our qualitative and quantitative evaluation of the clay-sized fraction with x-ray diffractometry largely support the stratigraphic model. The early stage of foreland basin formation (Egerian/Eggenburgian?) is represented by kaolinite contents up to 93 % in the clay sized fraction. This indicates an orogen-external source, i.e. the Bohemian Massif, and erosion of intensively chemical weathered products during this early Molasse basin stage. The over-lying marine Robulus Schlier (lower/middle Ottnangian) is characterized by a distinctly reduced kaolinite content and overall increased illite content compared to the other formations. Illite was predominantly provided from denudation of the rising Eastern Alps, i.e. characterizing the orogen-internal provenance. The pelites of the overlying carbonate poor Traisen Formation (upper Ottnangian) show again a higher kaolinite and smectite content. In the largely coeval basinal Wildendürnbach Formation, smectite reaches up to 70 % in the clay sized fraction. Peak smectite values may be linked to volcanic ash input from the nearby Carpathian volcanic arc. Generally rising smectite versus illite ratios during the Ottnangian-Karpatian could point to a warming and intensified chemical weathering of the rising Alpine orogen.

Swelling clay minerals and containment risk assessment for the storage seal of the Peterhead CCS project

Coupled modelling, based on laboratory data, indicated that the storage seal above the Captain reservoir of the Peterhead CCS project could be affected by stresses caused by clay swelling due to CO2 interaction. In particular, calculations indicate that, over a period of 100 – 10,000 years, local shear failure in rock exposed to CO2 may occur under unfavourable stress conditions. The likelihood and consequences of local shear failure are however difficult to assess. We therefore defined passive safeguards against this potential risk to seal integrity. The basis for these safeguards is data and information given in the Peterhead CCS Storage Permit Application (storage seal thicknesses, lithologies, reservoir conditions etc.), chemical, thermodynamic and mechanical data from laboratory measurements, as well as the coupled model built and described earlier by Wentinck and Busch (2017).The passive safeguards provided in this study address the mineralogy of the caprock and more specifically its swellable clay content. Furthermore, the geometry of the reservoir is addressed, particularly with respect to the presence of pre-existing faults. Our model shows that for shear failure to be a risk a fault offset on the order of the thickness of the sealing layer needs to be present and in contact with the CO2 plume. It should be noted that swelling stress build-up may relax by creep of the surrounding shale matrix, thereby buffering this effect. Finally, the risk of CO2 to escape the storage container only exists when slip on pre-existing faults leads to permeability enhancement as well as reduction of capillary entry pressures along the fault.Our analyses show that the smectite contents of the unit at the base of the caprock is significant with an average of 57 %, substantiating the threat of clay swelling. Taking the locations of interpreted faults and the total storage seal thickness of 117−165 m, we find no potential offsets similar to this thickness, as identified offsets are up to 33 m. Unquantified uncertainties remain in the creep behaviour of the caprock as well as the fault permeability. Given however that a maximum fault offset is lower than the seal thickness, we classify loss of containment due to fault reactivation caused by swelling clays, and concomitant fluid leakage, to be a low geological risk for the Peterhead CCS project.

Clay mineralogy of the upper Miocene-Pliocene red clay from the central Chinese Loess Plateau and its paleoclimate implications

Study of clay mineral is one of effective methods for reconstruction of the paleoclimate and paleoenvironment. Here we represent clay mineral records from an upper Miocene–Pliocene red clay succession in the central Chinese Loess Plateau (CLP). On the basis of the existing age model, we employ X-ray diffraction and scanning electron microscopy to carry out clay mineral analyses, the results indicated that illite was the dominant clay mineral and the contents of smectite, chlorite and kaolinite were minor. From the analysis of contents of clay minerals, illite crystallinity, illite 5 Å/10 Å, smectite/(illite+chlorite) ratio, magnetic susceptibility, summer monsoon intensity and deep-sea δ18O values, the paleoclimatic evolution between 7.5 and 2.6 Ma can be divided into three intervals: interval I, from 7.5 to 6.9 Ma, it was cool and dry; interval II, from 6.9 to 4.1 Ma, was cool-warm oscillations; interval III, from 4.1 to 2.6 Ma, was significantly warm and humid stage of the seasonal climate conditions. The proxy records display a large amplitude transition in the later interval III, from 2.8 to 2.6 Ma, which implied an abrupt climate and environment variability. Through comparison the local and global paleoclimatic records, we found that clay minerals reflect regional paleoclimatic change superimposing global climatic records during the late Miocene–Pliocene period. We conclude that the regional tectonic activity and global cooling had affected East Asia Monsoon, which was characterized by the different temperature and precipitation in the central CLP.

Influence of smectite and salinity on the imaginary and surface conductivity of volcanic rocks

ABSTRACTWe investigate the complex conductivity behaviour of natural volcanic rocks containing variable amounts of smectite in multi‐salinity experiments. We compare the results with relationships established for sandstones. Considering only samples with little volume of metallic particles, we observe similar and small phase‐angles at low frequency for all samples at all salinities (less than 25 mrad at 1 Hz). Yet, a wide range of cation exchange capacity, porosity and formation factor is covered by the sample set: 0.5–50 meq/100 g, 4–40% and 18–780, respectively. Our results show that, in the absence of metallic particles, the ratio between imaginary conductivity and surface conductivity is significantly lower for altered volcanic rocks than for sandstones and decreases with the smectite content. These observations indicate that an increased smectite content causes more conduction and less polarization, which could be explained by the onset of a continuous conduction pathway throughout connected interfoliar spaces of smectite. Due to this pathway, cations from the pore fluid may penetrate the solid lattice, for example through connected smectite aggregates clogging the fracture network, thus preventing polarization. We also observe that the relationship between imaginary conductivity and surface conductivity, at one salinity or over the whole salinity range, is not more significant than the relationship between the imaginary conductivity and the total real conductivity. Therefore, we suggest that the imaginary conductivity cannot be used to discriminate the contributions from smectite and pore water to the total conductivity of altered volcanic rocks.

Smectite quantification in hydrothermally altered volcanic rocks

In volcanic environments, the presence of smectite may indicate recent hydrothermal circulations. Smectite is also responsible for enhanced rock electrical conductivity, as well as mechanical weakening. Therefore, quantifying smectite is important in geothermal exploration. Smectite identification requires X-ray diffraction (XRD) but quantification based on XRD is time-consuming and not always accurate. In the present study, we investigate the use of an optimized unbuffered Cation Exchange Capacity (CEC) determination, by back-titration of the Copper-triethylenetetramine(II) “Cu-trien” molecule, to quantify the smectite content of altered volcanic rock samples. We establish that a satisfying trade-off between the instrument uncertainty and an independant systematic error is theoretically reached for a fraction of reactants consumed of about 30% at the end of the exchange reaction. We suggest a modification to classical protocols to fall in that range. Finally, we show that optimized CEC determination by Cu-trien are a direct measure of the smectite weight fraction in altered volcanic samples, with an average CEC of pure smectite of 90 ± 5 meq/100 g.

Modeling the risk of U(VI) migration through an engineered barrier system at a proposed Chinese high-level radioactive waste repository

The migration of U(VI) through the engineered barrier system (EBS) and into the natural environment in a geological repository for high-level radioactive waste depends on the chemical and physical environment of the repository. Modeling is widely used to understand the risk associated with migration of U(VI) for different barrier designs for repository sites. In this study, coupled thermal, hydrological, and chemical (THC) models were used to evaluate the risk of U(VI) migration at a proposed deep geological repository in northwestern China. The models incorporated two-site protolysis nonelectrostatic surface complexation, dissolution/precipitation of minerals and cation exchange as the major reactions controlling U(VI) migration. Modeling results showed that the main factors influencing U(VI) migration were pH, and the smectite content in the bentonite, as dissolution of the hydrous uranium oxide mineral schoepite is suppressed at higher pH values, and smectite is the most important adsorbent of dissolved U(VI). Therefore, an alkaline bentonite with a smectite volume fraction of >0.6 is suggested as the backfill material for this EBS. The THC model results also showed that in 100,000 years, U(VI) migration is constrained within EBS if the suggested bentonite is used as backfill in a repository that is hosted within Beishan granite. This study provides a feasible method for selecting a bentonite backfill and predicting the effect of environmental conditions on U(VI) migration.

Measured saline and sodic solutions effects on soil saturated hydraulic conductivity, electrical conductivity and sodium adsorption ratio

Hydraulic conductivity is important in the transport of water and salts in salt affected soils. The objective of this study was to determine how saturation of soil columns with saline and sodic solutions changes soil saturated hydraulic conductivity (Ksat) and subsequent salt leaching on a variety of soil textures and smectite clay content. Soil columns were capillary wetted with solutions of varying electrical conductivity (EC) and sodium adsorption ratio (SAR). Ksat was measured by infiltrating deionized water at the soil surface. Ksat as a function of leachate pore volume was fit with an exponential decay equation and a pedotransfer function was created to predict the decay coefficients. Higher salt contents in waters were more successful at increasing soil SAR as compared to low salt content waters. The pedotransfer functions performed similar to the McNeal and Simunek and Suarez models to predict Ksat change due to solution composition without the need of X-ray diffraction of the soil clay fraction. Soils with a greater clay content and specifically smectite clay content have larger changes in saturated water flow rates whether from one time wetting or under long term use of irrigation waters at high EC and Low SAR. High clay smectitic soils require careful management when they are saline-sodic and have a smaller range of safe irrigation waters to prevent reduction in hydraulic conductivity from SAR.