Clay Phases Research Articles

Pyrophyllite clay-derived porous geopolymers for removal of methylene blue from aqueous solutions

This study reports the synthesis and characterization of a porous geopolymer systems based a naturally occurring Moroccan pyrophyllite clay. The contribution of pyrophyllite in geopolymerization reaction was very low, the geopolymer matrix formed was assured by alkaline activation of the metakaolin present in the sample. The pyrophyllite role is forming of disordered and heterogeneous geopolymer promote the pore creation. The structure and morphology of the raw natural clay, calcined meta-pyrophyllite phase and prepared geopolymer samples are characterized by several methods namely, X-ray Diffraction (XRD), 29Si and 27Al magic-angle-spinning nuclear magnetic resonance (MAS NMR) analysis, Fourier Transform Infra-Red (FTIR) spectroscopy, Differential Thermal Analysis (DTA) and Thermal Gravimetric Analysis (TGA), N2 adsorption/desorption isotherm analysis by the Brunauer-Emmett-Teller (BET) method and Scanning Electron Microscopy (SEM). The specific surface area (SBET) and pore volume (Vp) measured from products utilizing the calcined meta-pyrophyllite precursor (SBET = 86 m2/g and Vp = 0.08 cm3/g) have both increased markedly compared to those values determined using a raw pyrophyllite clay phase (SBET = 30 m2/g and Vp = 0.05 cm3/g). The methylene blue (MB) molecular adsorption experiment realized in water medium exhibited Pseudo Second Order (PSO) rate kinetics and adopted a Langmuir adsorption model. The thermodynamics data shows that the chemisorption is spontaneous, irreversible, and endothermic, with the quantity of MB molecules retained by the porous geopolymer specimen reaching 64.10 mg/g.

Hydrologic regulation of clay-mineral transformations in a redoximorphic soil of subtropical monsoonal China

Abstract Clay-mineral evolution in supergene environments is commonly a complex process subject to hydrologic influences on clay-mineral transformations, yet these influences remain insufficiently investigated to date. A quaternary red soil profile with evident redoximorphic features in subtropical monsoonal China was investigated with a focus on processes of secondary clay-mineral transformation. Evidence provided by soil physical and chemical descriptions, clay-mineral analysis, spectroscopic characterization, extractions of pedogenic Al and Fe species, and geochemical compositions reveals a complex relationship of clay minerals and iron phases to pedogenic weathering conditions as a function of depth in the studied soil profile. The soil profile can be divided into a homogenous horizon (HH; 0–2.0 m), a redoximorphic horizon (RH; 2.0–6.0 m), and a basal layer (BL; 6.0–7.2 m), and these three horizons are dominated by various intermediate clay phases. The HH is characterized by moderately acidic conditions (mean pH = 5.2) and low total organic content (TOC; TOC ≤2.1 g kg–1). More importantly, compared with the lower horizons, the HH contains significantly more active acid-forming cations, as reflected by a greater abundance of Al phases and higher aluminum saturation levels. We infer that the occurrence of hydroxy-interlayered vermiculite (HIV) in the HH is tightly coupled with the nature of the soil acidic pools, which include both H+ ions (i.e., pH) and active acid-forming cations (e.g., Al3+ and Fe3+). The reaction pathway from primary minerals to final weathering products appears to be highly sensitive to dynamic hydrological processes. HIV is favored in generally oxic, well-drained soil systems with adequate acidic cations to maintain acidic weathering. When soils are more waterlogged and the aqueous solution is dominated by base cations, primary minerals tend to transform to smectite group minerals. Therefore, discrete smectite, interstratified illite-smectite (I-S), and interstratified kaolinite-smectite (K-S) were observed only in the RH and BL. We present a novel framework that links clay-mineral transformation pathways to soil hydrological disturbances, providing new insights into understanding the kinetics of water-mineral interactions in natural soil systems.

Lithium and strontium isotopic systematics in the Nalenggele River catchment of Qaidam basin, China: Quantifying contributions to lithium brines and deciphering lithium behavior in hydrological processes

The salt lakes fed by the Nalenggele River in the Qaidam Basin, located on the northeastern Qinghai Tibetan Plateau (QTP), are major brine lithium reservoirs in China. The quantitative identifications of the Li sources and their dynamic behavior shed light on the formation mechanism of the brine Li deposits in closed-basin of arid regions. This study presents Li and Sr isotope ratios (δ7Li, 87Sr/86Sr) and other hydrogeochemical parameters for river waters, springs, spring river waters, shallow groundwaters, surface brines, and intercrystalline brines around the Nalenggele River Basin (NRB) and its adjacent small watersheds. The results indicate that the Nalenggele River water is a mixing product of hot springs and regional surface meltwater, and the source of dissolved Li in the NRB is mainly supplied by the hot springs. With multi-tracer models, it is confirmed that around 84.9 %−93.4 % of dissolved Li is provided by the Li-rich hot spring waters, which account for only 3–5 % of the total water input. Furthermore, the dissolved Li in the streams of different hydrological regions shows various isotopic fractionation behavior. In general, the lower average δ7Li values (average of +5.6 ‰) with more enriched Li with respect to Na in the waters of the piedmont Gobi region indicates a significant additional input of dissolved Li from bedrock and sediments. The second-stage alluvial fan of the NRB produces 7Li enrichments and Li-depleted waters (compared with Na), which can be explained by the adsorption of clay or Fe (Mn) oxide phases that fractionate Li isotopes. The highest average δ7Li values (+12.76 ‰) are observed when Li is not adsorbed by the scarce fine clastic sediments in the hypersaline environment of the salt lake region. It can be concluded that the continuous halite precipitation during the brine evolution not only causes the abnormal enrichment of Li in the brine (compared with Na) but also continuously sequesters the 6Li from the brines, resulting in a significant 7Li enrichment. Overall, these findings advance the understanding of the lithium sources of Li-rich brines and its enrichment and metallogenic process during water migration in hyper-arid regions and have crucial indicative significance for lithium cycling under a strong evaporation environment.

Soil crusting: New insight from synchrotron 2D micro X-ray diffraction mapping of clay-particle orientation and mineralogy

Our understanding of soil crusting and its detrimental consequences is mainly based on the analysis of morphological changes occurring at the soil surface. Such changes are usually assessed at spatial scales ranging from a few millimeters to that of the field. The inner-reorganisation within the topsoil during soil crusting primarily involves the redistribution of clay particles. Their mineralogy and arrangement remain however delicate to determine by the sole use of microscope observations. To overcome these limitations, we developed an innovative methodology based on synchrotron 2D micro X-ray diffraction (2D-µXRD) to map relevant parameters related to the organisation of all types of soil clay minerals, i.e. relative diffracted intensities, degree of preferential orientation, mean deviation angle from the surface. Our methodological strategy was first validated on a laboratory-made model sample, composed of various pure clay phases with clear preferential orientations. Then, a vertical section of soil crust from long-term bare fallow (LTBF) experiment of the France's National Research Institute for Agriculture, Food and Environment (INRAE, Versailles, France) was studied. Micromorphological features of the soil crust were first described by using conventional scanning electron microscopy. Synchrotron 2D-µXRD analyses were then successfully applied on the same region of interest. The in-depth analysis provided by the synchrotron 2D-µXRD approach revealed the presence of clay microlayers that were not observed on SEM images. Additionally, clay mineralogy as well as preferred clay-particle orientation and overall alignment highlighted specific quantitative structural signatures. These signatures involved the discrimination between clay microlayers associated to the settling of clay particles in microdepressions and clayey microaggregates resulting from transportation of pre-existing soil crusts. This new technique has led to re-interpretation of the deposition mechanisms in the natural soil investigated here and opens wide perspectives for in-depth detailed characterization of clay mineralogy in soil crusts.

Micro-column testing of the dynamic adsorption of Pb by Fe-Mg clay–quartz beds

AbstractClays have been used widely as sorbents of potentially toxic elements, especially Pb. However, their adsorption efficiency has been studied mostly under static experimental conditions, which are labour-intensive. In this study, dynamic adsorption experiments were established using micro-columns to assess the adsorption behaviour of natural Fe-Mg-rich clays for Pb ions by varying the inlet solution pH, Pb concentration and flow rate. The clays, consisting of varying amounts of palygorskite and Fe-smectite, were diluted with quartz (Qz) sand to enhance their permeability. Greater adsorption capacity was observed for the mixed palygorskite/Fe-smectite-rich clay beds (45.2 ± 0.01 mg g–1) followed by the Fe-smectite-rich (35.7 ± 0.07 mg g–1) and palygorskite-rich (20.0 ± 0.03 mg g–1) clay beds. The results indicated that the greater adsorption efficiency of palygorskite/Fe-smectite-rich clays could be attributed to synergistic effects due to the coexistence of palygorskite and Fe-smectite clay phases, which have distinct physicochemical characteristics. Moreover, the results obtained showed good agreement with the static experiments, implying that the use of micro-columns could describe adsorption adequately over shorter experimental times.

Microscopic molecular insights into methane hydrate growth on the surfaces of clay minerals: Experiments and molecular dynamics simulations

Clay is widely present in hydrate reservoirs and drilling and completion fluids. A quantitative understanding of hydrate growth characteristics on clay solid phase surfaces is vital for predicting hydrate formation and preventing secondary hydrate generation in solid-phase-containing drilling fluid systems. The experiments and nonequilibrium molecular dynamics simulations are performed to investigate the characteristics of methane hydrate growth on the surfaces of kaolinite and montmorillonite. The experiments and dynamics simulated results demonstrate that a large number of bound waters is absorbed on the clay surface. However, the bound water does not participate in hydrate formation. The mechanisms by which clay minerals influence the formation of hydrates are different. Kaolinite reduces the induction time of hydrate formation, but the massive amount of bound water on the kaolinite surface reduces the total amount of free water molecules, which hinders the formation of hydrates, and the inhibition effect on hydrates is more significant than that with montmorillonite. Significantly, the hydrolysis of interlayer cations on the montmorillonite surface inhibits the formation of hydrates. This study will help us to understand the mechanism for gas hydrates formation on reservoir clay minerals, and to predict the amount of hydrate reservoir reserves, which will further aid hydrate resource drilling and exploration.

Diagenesis and controls on reservoir quality of Lower Triassic red bed sandstones (Buntsandstein) from a marginal basin facies, southwest Germany

After decades of hydrocarbon exploration and production in the Lower Triassic Buntsandstein from the Central European Basin center, the marginal southern German Buntsandstein has gained interest as a potential lithology for geothermal applications and lithium brine extractions. For this purpose and in order to better understand reservoir quality, porosity and permeability in combination with point-counted petrographic data of sandstones from SW Germany covering the Lower, Middle, and Upper Buntsandstein are studied. Textural, mineralogical, and petrophysical data show that the eolian and fluvial sandstones represent a heterogeneous reservoir system. Permeabilities vary over six orders of magnitude from 0.001 to 515 mD, while porosities are in the range of 7.9–21.5%. Different controls on reservoir quality exist. Large grain sizes ≥0.31 mm together with total quartz contents are the major controls on reservoir quality. Additional controls on reservoir quality are exerted by authigenic phases. Since porosity loss is dominated by compaction, the influence of authigenic clay phases on reservoir quality is minor. However, illite coatings on detrital quartz efficiently inhibited syntaxial quartz overgrowth. Where illite coatings lack, syntaxial quartz overgrowths locally stabilized the granular framework and, thus, preserved primary porosity. These authigenic phases, however, represent a local control, which cannot be applied on a regional scale. Similarly, enhanced secondary porosity due to feldspar dissolution is locally restricted and minor. The comparison with other studies on the Buntsandstein shows that its reservoir system is highly heterogeneous over small and large scales and within the same stratigraphic levels. In this study, quartz-rich and authigenic clay-poor sandstones with relative large grain sizes interpreted as eolian deposits reveal the best reservoir qualities.

Uranium retention in a Callovo-Oxfordian clay rock formation: From laboratory-based models to in natura conditions

For the performance assessment of radioactive waste disposal, it is critical to predict the mobility of radionuclides in the geological barrier that hosts it. A key challenge consists of assessing the transferability of current knowledge on the retention properties deduced from model systems to in natura situations. The case of the redox-sensitive element uranium in the Callovo-Oxfordian clay formation (COx) is presented herein. Extensive experimental work was carried out with respect to parameters affecting uranium speciation (pH, PCO2, [Ca] and redox potential) with illite, COx clay fraction and raw COx claystone. The “bottom-up” approach implemented, with illite and montmorillonite as reactive phases, quantitatively explains the adsorption results of U(VI) and U(IV) on COx. While retention is high for U(IV) (Rd∼104 L kg−1), it remains very low for U(VI) (Rd∼4 L kg−1) due to the formation of soluble ternary Ca(Mg)–U(VI)-carbonate complexes. The applicability of the sorption model was then assessed by comparing predictive analyses with data characterizing the behavior of naturally-occurring U (<3 mg kg−1). The COx clay phase is the largest reservoir of naturally-occurring U (∼65%) but only a small fraction appears to be adsorbed (∼1%). Under representative site conditions (especially with respect to reducing conditions), we have concluded that ternary U(VI) complexes control U speciation in solution while U(IV) surface species dominate U adsorption, with Rd values > 70 L kg−1.

Preliminary characterization and potential use of different clay materials from North-Eastern Morocco in the ceramic industry

The first part of this work relates to the characterization of raw clay materials and the second part is to the evaluation of the potential use of clay-rich raw materials in the region of Nador (northeast, Morocco) to manufacture ceramic products. In this regard, physical (particle size distribution, organic matter), chemical (X-ray fluorescence, XRF), mineralogical (X-ray diffraction, XRD), and geotechnical (Atterberg limits) analyses were carried out on the materials studied. The results show that the main minerals in the samples were feldspars and cristobalite, while carbonates are ubiquitously present. Smectite was present as the dominant clay phase and minor phases of smectite kaolinite, illite, and kaolinite, including chlorite, also appeared in some samples. The results showed that the studied clay materials require the addition of another type of clay or less plastic materials to improve their properties and to be suitable for the production of structural ceramics.

Facies analysis and petrophysical investigation of the Late Miocene Abu Madi sandstones gas reservoirs from offshore Baltim East field (Nile Delta, Egypt)

The Nile Delta has become an economically important region of Egypt, because of large-scale natural gas and oil discoveries in recent decades. The offshore Baltim East field is one of the Nile Delta's major gas producers from the upper Miocene clastic reservoirs, but detailed lithofacies and petrophysical analyses of the Abu Madi gas reservoir have not been conducted to date. This study investigates the petrographical and petrophysical properties of the upper Miocene Abu Madi Formation from the Nile Delta to infer the lithofacies distribution, depositional environments, and reservoir qualities of the Level 3 Main and Lower sands. In this work, we used a variety of data sets, including core samples, petrophysical measurements, and well logs, to identify the most important characteristics of these sandstone reservoirs. Both reservoirs are hydrostatically pressured and exhibit a gas gradient of ∼2.26 MPa/km. We have identified six different lithofacies from the two reservoirs. SEM and thin section analyses indicate that trough cross-bedded (F-1), parallel laminated (F-2), and massive sandstones (F-6) are the primary reservoir lithofacies composed of texturally immature subfeldspathic quartz arenites. These sandstones have sharp bases and exhibit fining-upward trends with ripple laminated siltstone (F-3), heterolithic silt and clay (F-4), and laminated claystone (F-5) facies lying on top. We inferred the reservoir depositional environment as fluvial channels and sequence stratigraphically these incised valley-fills represent low stand systems tract. The reservoir sandstone facies show good porosity (10–28%), mostly interparticle. Chlorite coatings around quartz grains are abundant, while pore-filling kaolinite is the dominant porosity-destroying clay phase. Grain dissolution introduced secondary intergranular porosity along the potassium feldspar cleavage planes within the F-1 lithofacies. Porosity, permeability, and reservoir quality parameters (RQI, NPI, and FZI) calculated from routine core analysis indicate that the F-1 and F-6 lithofacies have excellent hydraulic flow properties with >100 mD permeability, RQI>1 μm and FZI >5 μm, while the fine-to very fine-grained F-2 offers poor to fair reservoir quality defined by a wide permeability range of 0.1–2150 mD. The clay and silt-dominated lithofacies (F-3, F-4, and F-5), due to their impervious nature, act as intra-reservoir vertical permeability barriers. The differences in rock composition and facies control diagenesis and physical properties of the reservoir. The results presented, provide further insight into the exploration of the fluvial channel deposits and regional reservoir quality of the upper Miocene Abu Madi Formation of the Nile Delta.

Self-reactivity of a calcined palygorskite-bearing marlstone for potential use as supplementary cementitious material

This article focuses on the study of the self-reactivity of a 800 °C calcined palygorskite-bearing marlstone which is a complex multi-phase system (including CaO and MgO) whose reactivity in water must be studied before being used as Supplementary Cementitious Material (SCM). The sample was hydrated (w/s = 0.8) for 7, 14, 28 and 180 days and then investigated using X-ray diffraction (XRD), Solid State Nuclear Magnetic Resonance (MAS NMR), and Scanning Electron Microscope (SEM). Crossing the results of XRD and MAS NMR analyses (in particular the phase quantification by spectral integration of 29Si MAS NMR spectra) have revealed the reactivity of the calcined clay phases with the portlandite which leads to the formation of C-(A)-S-H. It also highlighted the reactivity of C2S (neoformed during calcination) within 7 days of hydration. Hydration of this sample showed high self-reactivity (mostly pozzolanic) making it a promising sample for use as SCM.

A simple empirical model for phenanthrene adsorption on soil clay minerals

Soil clay minerals are effective substrate adsorbents of polycyclic aromatic hydrocarbons (PAHs) in natural soil. The adsorbed PAHs result in long-term contamination of soils. In this paper, a typical PAH phenanthrene (Phe) and nine high purity clay minerals are selected as representative PAH pollutants and adsorbents, respectively. A series of experiments have been conducted to disclose the relationship between the Phe adsorption effect of these clay minerals and their physical properties, including specific surface area (SSA), cation exchange capacity (CEC) and contact angle (CA). Molecular simulation methods are performed to explore the mechanism of clay mineral structure on Phe adsorption at the molecular level. Density functional theory (DFT) calculation suggests that the adsorption of Phe on clay minerals is mainly due to the van der Waals effect. The strength of the O-H-π effect is greater than that of the hydrophobic effect of Phe adsorption. Molecular dynamic (MD) simulations imply that the hydration effect of cations hinders the Phe hydrophobic adsorption by occupying the adsorption sites. Based on the mechanism explored, a simple empirical model is proposed, and the adsorption distribution coefficient Kd of clay mineral and water phases can be precisely predicted by the three physical properties of clay minerals, without rigorous quantitative analysis of soil clay minerals.

A Holocene record of floodplain development in the northernmost portion of the Araguaia Belt, southeastern Amazonia

This work aimed to understand the drivers of landscape evolution and floodplain formation in a Precambrian Shield area of southeastern Amazonia. This area evolved during the Quaternary into a denudational system with strong structural control, which produced valley side slopes between the Araguaia Belt (AB) and the topmost Parnaíba basin and narrow floodplains in the lower Vermelho River. These floodplains developed at approximately 11215–11410 cal yr BP with the deposition of muds on the weathered basement rocks of the Couto Magalhães Formation in the Ab (CMF) long before sea-level stabilization on the Amazon coast. The chondrite- and upper continental crust-normalized patterns, along with Al/Ti and La/Th ratios, clearly indicate that muds were derived from the CMF-AB. The strong positive correlation of most of the trace elements and rare earth elements (REEs) with Al and Ti indicates their control by aluminous clay phases and a similar transport process. Overbank flows of the Vermelho River resulted in the deposition and vertical accretion of sands from the fluvial channel over the floodplain, forming discontinuous marginal levees after 4520–4710 cal yr BP. The accreted sands with the predominance of Si, Zr, and Hf and the depletion of most of the major and trace elements are likely associated with quartz enrichment and a strong sorting of heavy minerals, which is also supported by Al2O3/SiO2 vs Fe2O3/SiO2. The tributaries of the lower Vermelho River were active until 3890–4095 cal yr BP, and subsequently, the channel was abandoned as a result of the filling process. At approximately 3440–3560 cal yr BP, the floodplain was influenced by prolonged and severe droughts that fully exposed the muddy deposits and caused the enrichment of Fe-Mnoxyoxide phases. The affinity of most of the potentially toxic elements with Al signifies that these floodplain deposits are a natural record for geochemical background studies.

Contribution of the Paragenetic Sequence of Clay Minerals to Re-Examination of the Alteration Zoning in the Krafla Geothermal System

This paper revisits the clay mineralogy of the “smectite” alteration zone in the Krafla geo-thermal field via the study of an exploratory well in which temperatures range from 40 °C to 215 °C. The clay alteration consists of several mineral assemblages superimposed in time and space, resulting from different stages of water-rock interaction. Trioctahedral clay minerals (chlorite, corrensite and smectite) are observed throughout the studied section. These minerals can form in nearly closed systems as replacements of groundmass minerals/glass after interactions with resident and nearly stagnant fluids not far from chemical equilibrium (neutral to basic pH conditions) or from direct precipitation from geothermal fluids. They are locally superimposed by Al clay phases (smectite, illite/smectite and kaolinite), which result from intense leaching of the host rocks due to their interaction with low pH fluids under strong W/R ratios. The absence of mineralogical zoning is explained by the fact that hydrothermal alteration is strongly dependent on very recent hydrodynamics. The current fluid circulation generates trioctahedral clays at depth that cannot be distinguished from pervasive earlier alteration. The only easily detectable signature of current activity and the most relevant signature for geothermal exploration is the presence of Al dioctahedral phases since it indicates leaching and intense hydrothermal activity.

Preparation of functionalized halloysite reinforced polyimide composite aerogels with excellent thermal insulation properties

Excellent thermal insulating aerogels have broad application prospects in pipeline transportation, aerospace, construction and other fields. However, defects in thermal stability and mechanical are the main factors limiting their use to special environments. In this work, a novel polyimide composite aerogel is successfully synthesized through 3-Aminopropyltriethoxysilane (APTES) functionalized clay halloysite nanotubes (FHal) as inorganic enhancement phase and uniformly embedded in polyimide (PI) aerogels. Functionalization can increase the interfacial compatibility between clay inorganic phase and polyimide acid. The results indicated that FHal with high aspect ratio interacts with PI to form a three-dimensional network structure. The FHal/PI composite aerogels had low shrinkage (21.9%–30.79%), low bulk densities (65.285–71.464 mg/cm3), low thermal conductivities (39.18–42.57 mW/(m·K)), high thermal stability (onset of decomposition above 520 °C) and excellent mechanical property (1.14 MPa, 2.62 times of pure PI aerogel). Therefore, FHal/PI composite aerogels can be used as a promising thermal management material for practical and complex insulation applications.

Elemental fingerprints in natural nanomaterials determined using SP-ICP-TOF-MS and clustering analysis

Detection and quantification of engineered nanomaterials in environmental systems require precise knowledge of the elemental composition, association, and ratios in homologous natural nanomaterials (NNMs). Here, we characterized soil NNMs at the single particle level using single particle-inductively coupled plasma-time of flight-mass spectrometer (SP-ICP-TOF-MS) in order to identify the elemental purity, composition, associations, and ratios within NNMs. Elements naturally present as a major constituent in NNMs such as Ti, and Fe occurred predominantly as pure/single metals, whereas elements naturally present at trace levels in NNMs occurred predominantly as impure/multi-metal NNMs such as V, Nb, Pr, Nd, Sm, Eu, Gd, Tb, Er, Dy, Yb, Lu, Hf, Ta, Pb, Th, and U. Other elements occurred as a mixture of single metal and multi-metal NNMs such as Al, Si, Cr, Mn, Ni, Cu, Zn, Ba, La, Ce, W, and Bi. Thus, elemental purity can be used to differentiate ENMs vs. NNMs only for those elements that occur at trace level in NNMs. We also classified multi-metal NNM into clusters of similar elemental composition and determined their mean elemental composition. Six major clusters accounted for more than 95% of the detected multi-metal NNMs including Al-, Fe-, Ti-, Si-, Ce-, and Zr-rich particles' clusters. The elemental composition of these multi-metal NNM clusters is consistent with naturally occurring minerals. Titanium occurred as a major element (>70% of the total metal mass in NNMs) in Ti-rich cluster and as a minor (<25% of the total metal mass in NNMs) element in likely clay, titanomagnetite, and aluminum oxide phases. Two rare earth element (REE) clusters were identified, characteristic of light REEs and heavy REEs. The findings of this study provide a methodology and baseline information on the elemental composition, associations, and ratios of NNMs, which can be used to differentiate NNMs vs. ENMs in environmental systems.

Transformation of bentonite used in green sand molds during metal casting process and its relevance in sand reclamation

Green sand molds in foundry use bentonite as a binder. During the casting process, the heat transferred to the surrounding sand in the mold leads to the degradation of bentonite structure, thereby forming new types of deposits on the surface of sand grain. This results in deactivation of binder and unsuitability of sand for its reuse. In the present work, useful insights are provided into this transformation that may help in developing technology to reclaim the sand for its reuse in foundry. The green sand and bentonite were subjected to high temperatures over the range 500 °C–1100 °C, for varying periods (10–120 min) and analyzed. It was found that the binder in the used sand existed in four different forms. These were active clay, loosely bound dead clay, strongly bound sintered clay and high-temperature phases; the latter three forms need to be removed in the reclamation process. While a simple mechanical attrition method can remove the loosely bound dead clay, it fails in removing the other two forms, that are referred as oolitic deposits of sintered clay and high-temperature phases. More aggressive attrition or chemical treatment may be necessary to facilitate their removal. Analytical methods such as FTIR, DSC, SEM, and X-ray diffraction were used to show the differences between clay binder and oolitic deposits and how the transformation takes place from one form to the other as a function of temperature. Furthermore, the kinetics of oolitic formation was examined and the results showed that the formation of oolitic deposits follows temperature-dependent first-order kinetics.

Predicting zeolites’ stability during the corrosion of nuclear waste immobilization glasses: Comparison with glass corrosion experiments

During the long-term corrosion of nuclear waste glasses under nuclear waste disposal conditions, the precipitation of zeolitic phases has been linked to a delayed acceleration in glass corrosion (known as “Stage III”). Hence, predicting the thermodynamic propensity for zeolites to form upon the dissolution of nuclear waste glasses is key to ensure their long-term performance. Here, we compile a unified, internally-consistent thermodynamic database “clay20” to estimate the stability of clay and feldspar phases relevant to nuclear waste immobilization glasses, including beidellite(Mg, Ca, Na, K), kaolinite, montmorillonite(Mg, Ca, Na, K), nontronite(Mg, Ca, Na, K), saponite(Ca, Na, K), and albite. Based on this, we report a geochemical modeling method allowing us to predict the stability of secondary phases (including zeolites, calcium–silicate–hydrate gels, and clays) upon the dissolution of nuclear waste immobilization glasses. We show that this approach offers a realistic description of the stability of the secondary phases forming during the dissolution of two archetypical model nuclear glasses (namely, the International Simple Glass, ISG, and WVUTh-203) under conditions relevant to nuclear waste disposal (T = 90 °C, p = 1 bar) as a function of pH. We find that the formation of silica and clay secondary phases is thermodynamically favored at low pH (pH < 10), whereas, in contrast, zeolite (analcime) and calcium–silicate–hydrate phases are favored at high pH (pH > 10.5). This suggests that thermodynamics (i.e., not solely kinetics) might play a key role in determining the range of solution pH wherein stage III corrosion may occur, i.e., when zeolite formation is favored.

Natural gamma-ray spectroscopy (NGS) as a proxy for the distribution of clay minerals and bitumen in the Cretaceous McMurray Formation, Alberta, Canada

Detailed examination of the mineralogy of the Cretaceous McMurray Formation within a facies framework is used to assess the use of natural gamma-ray spectroscopy (NGS) and a pulsed neutron generator (PNG) tool in delineating variation in clay mineral and bitumen contents. Characterization of the mixed-layer (interstratified) clay phases in the McMurray Formation provides an improved understanding of clay interaction in bitumen processing and tailings settling behavior, important for mine planning and tailings remediation schemes. Mineral diversity in the McMurray Formation was determined on facies attributed samples using whole rock X-ray diffraction (XRD), cation exchange capacity (CEC) measurements, elemental analysis (XRF), clay size fraction (<2 µm) XRD analysis, reflected light microscopy, and cryogenic-scanning electron microscopy (cryo-SEM). Kaolinite was ubiquitous in the entire McMurray Formation with lower and middle McMurray Formation sediments also containing mixed-layered illite–smectite (I-S) with a low expandability≈ 20–30%. Upper McMurray Formation sediments by contrast had higher expandability (≈ 60–70%). In floodplain sediments of the lower McMurray Formation an additional clay mineral was quantified as a kaolinite-expandable mixed-layer (clay) mineral. The associated CEC values of this mineral are 10 times the baseline for the McMurray Formation. NGS spectra from cores showed that yields of potassium (K), uranium (U), and thorium (Th) had distinct facies associations, correlated with a clay mineral signature. The resultant indicator is capable of highlighting zones within an oil sands ore body that are empirically known, by industry, to process poorly through extraction plants. A bitumen indicator from the carbon yield derived from a PNG logging tool assesses bitumen content. NGS and PNG allow a full assessment of clay mineral (fines) and bitumen profiles, with the future prospect that these techniques could be used to assess ore and tailings behavior in near-real time.

Potential for calcination of a palygorskite-bearing argillaceous carbonate

The intensive use of cement as a building material causes significant pollution. The majority of CO2 emissions come from the manufacturing process and not from the product itself. Indeed, the decarbonation of limestone and the use of fuels during clinkerisation are very polluting. One of the main solutions to reduce the environmental footprint of the cement industry is the use of Supplementary Cementitious Materials (SCMs) in substitution of clinker. Among them are glass powders, fly ashes, blast-furnace slags or calcined clays. This article focuses on the thermal reactivity of an argillaceous‑carbonate sample containing palygorskite, smectite and dolomite. The sample was calcined at different temperatures and investigated using Solid State Nuclear Magnetic Resonance (NMR), X-ray diffraction (XRD), and Scanning Electron Microscope (SEM). The increase in calcination temperature leads to an amorphisation of the clay fraction of the sample, resulting in a change in the coordination of the octahedral aluminium atoms. The progressive transformation of 6-fold aluminium atoms to 5-fold and 4-fold was quantified as a function of the calcination temperature. Furthermore, calcium issued from the decarbonation of dolomite reacts with silicon from the amorphisation of clay phases to form poorly-crystallized belite (C2S). This dual system (pozzolanic and hydraulic) makes this sample a promising candidate as SCM in blended cements. The multi-technique analysis applied in this study allows to highlight a direct correlation between the calcination temperature and the induced structural modification.