Transformation Of Kaolinite Research Articles

Exploring microwave activation as a novel method for activating coal gangue: Focus on microwave activation mechanisms and hydration characteristics of cementitious supplementary materials

To support the decarbonization of the cement industry, coal gangue (CG) has potential as a supplementary cementitious material. The calcination process significantly impacts the phase transformation of clay minerals and the pozzolanic activity of CG. This study involved calcination of CG at 600 ℃ and 800 ℃ using both microwave and thermal activation methods. Employ XRD, XPS, FTIR, TG, and SEM to examine the impact of calcination mechanism on the crystal structure, element binding energy, chemical bonds, microstructure, and mineral composition of CG. The results indicate that the transformation of kaolinite in CG to metakaolin is completed around 600 °C. Microwave activation increased the reactive aluminate content in CG, enhancing pozzolanic activity and promoting secondary hydration with cement. This process generated additional C-(A)-S-H gels and AFm phases, which filled matrix pores, increased system density, and improved mechanical properties. The optimal activation method for CG was identified as microwave activation at 600 °C.

Diagenetic controls on the quality of shallow marine sandstones: An example from the Cambro-Ordovician Saq Formation, central Saudi Arabia

The Saq Formation is the most important Paleozoic aquifer in central and northern Saudi Arabia. However, owing to the continued depletion of the aquifers and the great depths to which the aquifers are buried in undrilled/underexplored regions, the aquifers porosity and permeability are increasingly becoming an issue of concern. Here, we employed thin-section petrography, petrophysical measurements, X-ray diffraction and scanning electron microscopic analyses, and fluid inclusion microthermometry to investigate the composition and diagenetic evolution of the Saq sandstones. The results of this study indicate that the sandstones are mainly quartz arenite in composition, mostly well sorted, and ranged in grain size from silt to coarse-grained sandstones. We observed three diagenetic stages (early, middle, and late) that impacted the porosity evolution of the Saq sandstones. Mechanical compaction, formation of authigenic kaolinite, and infiltration of smectitic clays occurred during early shallow burial diagenesis. The middle (deep-burial) diagenesis was dominated by mechanical and chemical compaction, formation of authigenic quartz overgrowths, transformation of kaolinite and smectite into illite, and precipitation of late calcite. The late (uplift-related) diagenesis resulted in the formation of authigenic kaolinite, dissolution of the late calcite, and the formation of predominantly pore-filling Fe-oxide (goethite) cement. Fluid inclusion results of this study show that quartz cement mostly formed at temperatures ranging between 151 °C and 175 °C and reached up to 272 °C, with, at least, two phases of overgrowth development. The overall high amounts of rigid grain contents (>65 %), low detrital matrix (<10 %), and coarser grain size have maintained the Saq sandstone quality (average permeability = 2100 mD) despite having been buried to great depths. The findings of this study provide useful insights into the diagenetic evolution of the Saq Formation, which has provided important input data for forward diagenetic modelling of their subsurface equivalent in Saudi Arabia and sandstones of similar depositional settings elsewhere.

Variation in the structural order of kaolinite in regolith as an effective indicator of REE mineralization

Abstract Regolith-hosted rare earth element (REE) deposits hosted by the granitic regolith in South China provide &gt;90% of the world’s heavy REEs. Kaolinite is one of the major carriers of REE ions in regolith. The formation and transformation of kaolinite can be affected by chemical weathering and hydrodynamic conditions, but the contribution of each factor has not been evaluated. This study systematically investigated the variation in abundance of phyllosilicate minerals and structural order of kaolinite in the Renju regolith-hosted REE deposit. The total abundance of 1:1 phyllosilicate minerals increased upwards along the profile from Section I to Section III. However, semi-quantitative analyses indicated that Section III-1 (depth at 10–16 m) featured an evident decrease in both abundance and structural order of kaolinite upward along the profile. The morphological feature and abundance of kaolinite revealed intensive kaolinite-to-halloysite transformation and kaolinite dissolution in Section III-1. This suggests that the alternating wetting and drying zone in Section III-1 provided a favorable kinetic environment for the entry of water molecules into the kaolinite interlayer and the kaolinite-to-halloysite transformation, resulting in both lower structural order and abundance of kaolinite in Section III-1. Moreover, REE ions started to be enriched from the alternating wetting and drying zone and formed high-grade ores at the lower part of the water table, due to a significant increase in pore water and decrease in the seepage velocity. Therefore, the abundance and structural order of secondary kaolinite can serve as important indicators of hydrodynamic changes in regolith, as well as the mineralization of regolith-hosted REEs.

Occurrence and transformation behaviour of silicon-bearing minerals during high silicon coal combustion from Yunnan Province, China

To understand the mineralogical characteristics and transformation behaviours of silicon-bearing minerals during coal combustion, seven typical high silicon (high-Si) coals and two high-Si fly ashes generated from high-Si coal-fired power plants were chosen. The coals were first treated by a method of low temperature ashing and the float-sink test for heavy minerals separation. Subsequently, low temperature ashes (LTA), light mineral fractions (LM), heavy mineral fractions (HM), and fly ashes from coal-fired power plants were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) combined with energy spectrum analysis (EDX), X-ray fluorescence spectrometry (XRF), and simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC).The results show that The mineral compositions in the LTA and LM are almost the same and majorly composed of quartz, kaolinite, calcite, dolomite, daphnite, chlorite-serpentine, pyrite, and anatase. The mineral compositions identified in the HM are clearly different from those in the LTA and LM. Pyrite, fluorapatite, anatase, siderite, dolomite and a plenty of silicate minerals including quartz, clinochlore, daphnite, chlorite, and chamosite are found in the HM. Chlorite is a quite common mineral in the HM with different shapes, including schistose, long tetragonal prism, cylindrical, block-shaped, and near-spherical, can be identified. The minerals identified in the fly ashes from the high-Si coal-fired power plants include quartz, mullite, and hematite. The mullite in the fly ashes is derived from the transformations of quartz, kaolinite, and chlorite in the coals. The quartz in the fly ash is mainly derived from the unchanged quartz in coal and a secondary origin from the SiO2-Al2O3 phase transformation. The high-Si fly ash with the size fraction of 38.5–74 μm contains the highest SiO2 content.

High-pressure Raman scattering and X-ray diffraction study of kaolinite, Al2Si2O5(OH)4

Kaolinite is formed by weathering of continental crustal rocks and is also found in marine sediments in the tropical region. Kaolinite and other layered hydrous silicate minerals are likely to play a vital role in transporting water into the Earth's interior via subducting slabs. Recent studies have experimentally documented the expansion of the interlayer region by intercalation of water molecules at high pressures i.e., pressure-induced hydration. This is counter-intuitive since the interlayer region in the layered silicates is quite compressible, so it is important to understand the underlying mechanism that causes intercalation and expansion of the interlayer region.To address this, we explore the high-pressure behavior of natural kaolinite from Keokuk, Iowa. This sample is free of anatase impurities and thus helps to examine both low-energy (0–1200 cm−1) and high-energy hydroxyl (3000–4000 cm−1) regions using Raman spectroscopy and synchrotron-based powder X-ray diffraction.Our results show that the pressure dependence of the hydroxyl modes exhibits discontinuities at ∼3 GPa and ∼ 6.5 GPa. This is related to the polytypic transformation of Kaolinite from K-1 to K-II and K-II to K-III phase. Several low-energy Raman modes' pressure dependence also exhibits similar discontinuous behavior. The synchrotron-based powder X-ray diffraction results also indicate discontinuous behavior in the pressure dependence of the unit-cell volume and lattice parameters. The analysis of the bulk and the linear compressibility reveals that kaolinite is extremely anisotropic and is likely to aid its geophysical detectability in subduction zone settings. The K-I to K-II polytypic transition is marked by the snapping of hydrogen bonds, thus at conditions relevant to the Earth's interior, water molecules intercalate in the interlayer region and stabilize the crystal structure and help form the super-hydrated kaolinite which can transport significantly more water into the Earth's interior.

Valorising cassava pomace biosolid in fired clay bricks production: Physical, mechanical and thermal evaluation

In this study, the practicability of recovering cassava pomace biosolids (CPB) for use as pore forming materials in fired clay bricks was examined. The raw materials were characterized for their chemical, mineral and thermal properties and found suitable for fired clay brick production. Modelled test brick samples containing up to 15% CPB were fabricated and fired at 900 and 1000 °C. Apparent porosity increased from 31.2% to 48.6% at 900 °C. Bulk density reduced from 1.97 g/cm3 to 1.58 g/cm3 at 1000 °C during firing with the progressive introduction of CPB in the brick bodies. Water absorption values of bricks fired at 1000 °C ranged between 10.80% and 28.82%. Compressive strengths of bricks declined from 20.01 MPa to 6.3 MPa at 900 °C firing. However, this decline was compensated with an over 30% improvement in thermal insulation as thermal conductivities reduced from 0.84 W/mK to 0.54 W/mK. Phase analysis evidenced kaolinite transformation into metakaoline and mullite, geothite dehydroxylation into hematite and the formation of wollastonites in the fired brick samples. Morphological analysis of CB-15 brick series showed significant differentials in terms of the nature of pores developed and clay vitrification due to changes in firing temperatures. Overall, CB-10 brick series was considered suitable for load supporting structural construction whereas CB-15 were most apt for thermal insulation walling construction. Consequently, by adjusting the CPB content within 2.5–15 wt% in the bricks’ bodies, the produced bricks could be applicable to a wide spectrum of construction applications.

Mitigation of efflorescence, drying shrinkage and water demand of calcined clay-based geopolymers with biological waste ashes as activator and hardener

Uncertainties associated with durability and sustainability of geopolymer due to formation of efflorescence, shrinkage and activator cost are setbacks for its real-life applications. Therefore, the aim of this study was to produce geopolymers with improved durability and sustainability using local kaolin clay as precursor, cocoa-pods-ash (CPA) as alternative alkali hydroxide activator, periwinkle-shells-ash (PSA) as hardener and quarry-dust (QD) as filler. Local kaolin clay calcined at 700 °C (M7C), was replaced with some fractions of CPA and activated with only Na2SiO3 to produce binders (CPAG). The PSA was added to the best fit of M7C/CPA as fast-setting-agent, while QD was added to the best fit of M7C/CPA/PSA to produce mortars. 100% kaolin clay activated with 8MNaOH/Na2SiO3 was used as reference geopolymer. The geopolymers were cured at R.T for 7 and 28 days and characterised for physical, mechanical and durability properties. Clay, CPA, PSA, QD and geopolymers were characterised using XRF, ATR-FTIR and XRD. Reactivity was studied using isothermal conduction calorimetry. The ATR-FTIR and XRD results indicated transformation of kaolinite to metakaolinite in the clay, presence of K-C-O bond in CPA and O-C-O bond in PSA. Reference geopolymers set at 4 h while CPAG ranged from 14 to 19 h. With the addition of PSA, setting time reduced to values between 4 and 11 h. The compressive strength of reference geopolymer was 18.1 ± 0.3 MPa at 28 days, while CPAGs values ranged from 23.5 ± 0.3 to 35.6 ± 0.3 MPa. Best compressive strength was achieved with 2% PSA addition. No shrinkage in CPA-containing geopolymers while reference geopolymer had value of 0.03%. Efflorescence tendencies of the CPA-containing geopolymers reduced by 25–75% when compared with reference. Application of CPA as alternative activator improved the mechanical property, durability and sustainability of geopolymers.

Diagenetic signatures in the deltaic and fluvial-estuarine Messinian sandstone reservoirs in the Nile Delta as a tool for high-resolution stratigraphic correlations

The current study utilizes a range of diagenetic fingerprints to differentiate between sandstone facies deposited in the Nile Delta before and during the Messinian salinity crisis (MSC), which is normally a challenging task considering the complex bio- and lithostratigraphic subdivisions of Messinian rock units. Subaerial exposure of the pre-MSC (Qawasim deltaic sandstone), during drawdown of the Mediterranean Sea at the time of the MSC, triggered pervasive dissolution of unstable rock fragments, kaolinization of feldspar, and meteoric dolomitization of carbonate. This was followed by mesogenetic calcite cementation and kaolinite transformation into dickite in deeply buried Qawasim sandstone. Comparatively, the Abu Madi estuarine facies, deposited during transgression after drawdown related to the MSC, is characterized by eogenetic iron (Fe)-calcite, glauconite, and pyrite (averages of 14.5%, 6%, and 2%, respectively). This facies transition is marked by abundance of mature glauconite (with potassium oxide (K2O) at about 8%) whose content abates upward from the transgression surface. Moreover, the compositional variability of the Abu Madi sandstone gave rise to multiple diagenetic trajectories that resulted in chlorite formation presumably following smectite and kaolinite. Listed diagenetic variations in the studied Messinian sandstone resulted from a complex interplay between rocks’ compositional, depositional, and burial attributes, ultimately serving as a basis for high-resolution stratigraphic correlation in continental and marginal marine settings with poor biostratigraphic controls.

Chemical Transformations of 2D Kaolinic Clay Mineral Surfaces from Sulfuric Acid Exposure.

A combined experimental and computational approach is used to investigate the chemical transformations of kaolinite and metakaolin surfaces when exposed to sulfuric acid. These clay minerals are hydrated ternary metal oxides and are shown to be susceptible to degradation by loss of Al as the water-soluble salt Al2(SO4)3, due to interactions between H2SO4 and aluminum cations. This degradation process results in a silica-rich interfacial layer on the surfaces of the aluminosilicates, most prominently observed in metakaolin exposed to pH environments of less than 4. Our observations are supported by XPS, ATR-FTIR, and XRD experiments. Concurrently, DFT methodologies are used to probe the interactions between the clay mineral surfaces and H2SO4 as well as other sulfur-containing adsorbates. An analysis performed using a DFT + thermodynamics model shows that the surface transformation processes that lead to the loss of Al and SO4 from metakaolin are favorable at pH below 4; however, such transformations are not favorable for kaolinite, a result that agrees with our experimental efforts. The data obtained from both experimental techniques and computational studies support that the dehydrated surface of metakaolin interacts more strongly with sulfuric acid and provide atomistic insight into the acid-induced transformations of these mineral surfaces.

Specifying the structural formula of kaolinite from the Orenburg Region by means of spectroscopic methods

Kaolinite certification is necessary when using it as a raw material in the ceramic industry. The kaolin clay deposit discovered in the Orenburg Region in 2018 is presumably the largest in the country. Within the Koskolskaya area, 5 mineral deposits have been described. Three of them are particularly promising deposits of high-quality kaolin clay. Previously, studies of the technological and physical characteristics of clay from this deposit were carried out. The purpose of our study was to derive and specify the structural formula of kaolinite contained in the clays. After elutriation and grinding in a ball mill, natural clay was sifted through a sieve with meshes of 40 μm. The conducted IR, Raman, and EPR spectroscopy, as well as DTA allowed us to monitor the process of metakaolinisation, which occurs as a result of dehydration of kaolinite (i.e. the process of transformation of kaolinite into metakaolinite). Spectroscopic methods made it possible to analyse the parameters of the fine structure, in particular, the degree of crystallinity of kaolinite particles and the occurrence of iron and magnesium ions in hydroxyl sheets. Conducting a series of experiments, we managed to specify the structural formula of the kaolinite of the Koskolsky deposit of the Orenburg region: K,Na,Ca,Ba Al Fe ,Fe Mg Mn,Cr 0.16 3.62 3+ 2+0.11 0.27 0.01 Si Ti O OH 3.86 0.14 10 8. The square brackets indicate the cationic compositions of the hydroxyl and siloxane sheets that formed the surface charge of the mineral particles. Compensator ions remain outside the square brackets. Thus, in our study we assessed the substance used as a raw material in the ceramic industry and determined the role of elutriation and mechanical treatment of kaolin clay.

Impact of magmatic intrusion on diagenesis of shallow marine sandstones: An example from Qasim Formation, Northwest Saudi Arabia

Igneous intrusions are common in sedimentary basins, and their occurrence can significantly affect the diagenesis and reservoir quality evolution of sandstones, thereby strongly impacting their hydrocarbons-, geothermal-, and CO2-storage potentials. The Qasim sandstones in the Tabuk region (NW Saudi Arabia) experienced shallow burial diagenesis (&amp;lt;2 km) when the Tertiary magma intruded to form basaltic sills (0.4–4 m thick). The sedimentology, tectono-stratigraphic framework, provenance, and chemostratigraphy of the Qasim Formation have been extensively covered in the literature. However, the impact of the magmatic intrusion on diagenesis and reservoir quality evolution of the sandstones remains enigmatic. This study employed thin-section petrography, QEMSCAN, XRD, SEM, and energy-dispersive spectrometer analyses to investigate the role of magmatic intrusion on diagenesis and reservoir quality of the Qasim sandstones. The results of the study indicate that reservoir porosity is principally influenced by primary depositional characteristics (grain size and sorting), diagenetic alterations, and magmatic intrusions. Sandstones with coarser grain size and better sorting have the best intergranular porosity and vice versa. The “normal” diagenetic processes that have significantly affected the reservoir porosity of the sandstones occurred during both shallow burial (eodiagenesis) and uplift (telodiagenesis). The eogenetic alterations include mechanical compaction, early diagenetic cementation by calcite, pyrite, and kaolinite, whereas the telogenetic alterations include the formation of kaolinite, goethite, hematite. Overall, mechanical compaction is the main driver for porosity loss in the sandstones. The intrusion-related diagenetic processes include the dissolution of quartz grains, rounded quartz overgrowths, and calcite cement, and the transformation of kaolinite into dickite and chlorite. Detrital quartz and rounded quartz overgrowths have undergone dissolution due to acidic pore fluids from magma and high temperature. The transformation of kaolinite into dickite occurred in a dissolution-recrystallization fashion, and the amounts of kaolinite and dickite increase in fine-grained sediments away from sill contact due to hydrodynamic processes that deposited muscovite (which form kaolinite) in low energy environments. The chloritization of kaolinite was localized, and the magma-induced dissolution of goethite likely supplied the requisite high Fe content. Additionally, the intrusion has resulted in the dissolution of the early calcite and increase in porosity towards the sill contact. However, values for compactional porosity loss have relatively remained similar both at and away from the sill contact, as the sill is too thin to exert significant vertical loading. This study has relevance to understanding hydrocarbon exploration and exploitation in sediment-lava sequences, and to understanding the development of sediment-lava systems.

Study of Structural Transformation and Chemical Reactivity of Kaolinite-Based High Ash Slime during Calcination

The transformation of kaolinite into metakaolinite by thermal activation to obtain highly active aluminosilicate is commonly known. In addition to kaolin, the high content of kaolinite in coal mining waste is another potential source for obtaining an aluminosilicate precursor, thereby protecting the environment and adding value to industrial wastes. In this paper, the kaolinite-based high ash slime (KAS) was calcined at temperatures ranging from 400 °C to 1000 °C under air, N2, and CO2 atmospheres, respectively. The thermal behaviors and structural evolution of each component in KAS were analyzed by thermal analysis (TG-DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Moreover, the chemical reactivity of Al2O3 and SiO2 in calcined KAS was evaluated by HCl and NaOH leaching methods. The results show that the applied KAS in this study primarily consisted of kaolinite and carbon, while the minor mineral phases included quartz, calcite, and pyrite. Additionally, the structural transformation of kaolinite during calcination included dehydroxylation, sintering, and the formation of mullite. Crystalline kaolinite completely decomposed into semicrystalline metakaolinite at 600–800 °C, accounting for the increase in chemical reactivity. The interlayer sintering of metakaolinite and the recrystallization of amorphous components led to the decrease in chemical reactivity after 800 °C. Furthermore, the thermal behaviors of carbon in KAS are greatly affected by the calcination atmosphere. The presence of carbon reduced the chemical reactivity of calcined KAS.

Clay mineralogy and provenance modeling of the Paleoproterozoic Kaladgi shales, Dharwar Craton, Southern India: Implications on paleoweathering and source rock compositions

Proterozoic clastic sediments reveal vast information regarding provenance, depositional conditions, and environmental evolutions. Peninsular India comprising Archean cratons, also have numerous intracratonic Proterozoic sedimentary basins along their margins. The Archean Dharwar craton in southern India has many Proterozoic successions, namely Cuddapah, Kurnool towards the East, and Kaladgi, Badami, and Bhima towards the northern margin. The Paleoproterozoic Kaladgi Basin (∼1.85 Ga) consists of siliciclastic sedimentary rocks with stromatolitic carbonate formations. XRD analysis of shale layers of the Lower Lokapur and Upper Simikere Subgroups have been carried out to understand the primary clay mineral assemblages, weathering history, and provenance. The Lower and Upper shale layers of Lokapur and Simikere Subgroups show a dominance of montmorillonite and kaolinite, respectively. The geochemical affinities and the clay mineral assemblages indicate a more mafic source to the lower shales (Manoli and Hebbal Formations) and increased felsic contribution to the upper shales (Govindakoppa and Daddanhatti Formations). Illite is ubiquitous in all the shales of the Kaladgi Supergroup possibly representing the diagenetic transformation of montmorillonite and kaolinite to illite. Geochemical modeling of provenance has been carried out using (Eu/Eu*)N, (La/Yb)N, (Gd/Yb)N, and (La/Sm)N of all the plausible source rocks and the average compositions of lower and upper shales. The modeling results suggest that the lower shales are derived from a source of mafic rocks – 45 %, K-rich granite – 35 %, and TTG – 20 %. While the upper shales are derived from source characterized by K-rich granites – 61 % and intermediate volcanic rocks – 39 %. These results signify the classical unroofing of TTG-greenstone belts exposing K-rich granites with the progression of sedimentation. Further, a good correlation between K-enrichment (a measure of % difference between CIA and pre-metasomatic CIA) and ƩLREE is attributed to the abundance of kaolinites that fractionate more LREE.

Reservoir heterogeneity of an Eocene mixed siliciclastic-carbonate succession, northern Pannonian Basin

The quality of any reservoir is strongly controlled by diagenetic processes, especially of those that are comprised of mixed siliciclastic-carbonate sequences. An Eocene mixed siliciclastic-carbonate sequence forms reservoirs with diverse reservoir quality in the Hungarian Palaeogene Basin, which is found within the Pannonian Basin. Late Eocene transgression established extensive shallow-marine depositional environments strongly controlling the early diagenetic processes. Drill cores and cuttings were selected from several boreholes, representing a wide range of lithofacies to reveal the cause for reservoir heterogeneity. Petrographic, stable isotope and fluid inclusion analyses were performed to identify the diagenetic processes that controlled the porosity evolution of the reservoir, The early diagenetic calcite neomorphism caused lateral homogeneity, whereas the early meteoric water incursion enhanced reservoir properties via the development of dissolution pores, which in turn resulted in vertical reservoir heterogeneity. The deterioration of porosity started in the eogenetic realm by kaolinite formation and continued during mesodiagenesis as burial calcite, quartz, dolomite and minor illite cement precipitated in remaining pore spaces. Petrographic evidence, such as kaolinite transformation into dickite and fluid inclusion homogenisation temperatures highlight the role of temperature increase with burial, the effect of changing fluid chemistry during the evolution of the basin is documented by the chemical zonation of dolomite, the variation in salinities of the fluids enclosed fluid inclusions, as well as recurrent and prolonged periods of cementation with calcite, quartz and dolomite. Mesogenetic processes were accompanied by hydrocarbon emplacement and the formation of late-stage pyrite. The propagation and cementation of faults first contributed to increase and later to reduce fluid flow, respectively. These steps collectively resulted in a heterogeneous reservoir, characteristic of the Eocene sequence in the Hungarian Palaeogene Basin.

Weathering stage and topographic control on rare earth element (REE) behavior: New constraints from a deeply weathered granite hill

Rare earth elements (REE) are sensitive tracers of rock-water interactions and soil formation processes. In this study, we investigated the REE concentration and distribution patterns for both bulk samples and acid leachable phase for a series of regolith and soil profiles developed on a deeply weathered granite hillslope in a subtropical climate. The exogenous input had little impact on the REE distributions on the studied hillslope. The REE distribution in the profiles was controlled by changes in the physical and chemical environmental parameters and mineral transformation during weathering. However, the specific mechanisms differed among the different weathering stages and profiles located at different positions along the slope. Among the environmental parameters, the profile redox state and acidity were the dominant factors controlling the REE behavior, with organic materials as the main regulators. A strong positive relationship between chemical index of alteration (CIA) and La/Yb was observed for the regolith samples, but the La/Yb ratio decreased upward from a depth of 120 cm (the bottom depth of the soil horizon) as the CIA value increased, suggesting a preference for light REE (LREE) fixation in kaolinite formed during the dissolution of feldspar; however, a conversion occurred during the subsequent pedogenesis period. The hilltop soil profile was characterized by the strongest LREE depletion and the highest positive Ce anomaly (~7.31–14.28), compared with other profiles down the hillslope (~0.84–2.78). The strongest LREE depletion on the hilltop profile JLN-S4 suggested a preference for LREE release resulting from the transformation of kaolinite to gibbsite, and the highest Ce anomaly indicates that Ce was fixed in a more oxidized environment within a well-drained profile. The hill foot profile JLN-S1 had the highest LREE leaching rate, but also the lowest heavy REE (HREE) leaching rate, which was ascribed to its lowest erosion rate, lowest pH value, and reductive conditions in a more hydromorphic zone down the hill. The releasing rates of REE calculated by a mass balance model at different positions along the catena ranged from 1395 to 14,379 μg m−2y−1. All the observed REE fractionation regimes and weathering rate variations along the hillslope illustrated that topography-regulated hydrologic condition played a critical role in the release and migration of REE during granite weathering.

Role of diagenetic alterations on porosity evolution in the cretaceous (Albian-Aptian) Bima Sandstone, a case study from the Northern Benue Trough, NE Nigeria

The Cretaceous Bima Sandstone is a potential hydrocarbon reservoir that is currently being explored in the Northern Benue Trough, NE Nigeria. The sedimentological characteristics and tectonic evolution of the formation have been extensively studied by previous researchers. However, the impact of diagenetic alterations on porosity evolution of the sandstone is poorly understood. This study employed a multi-technique approach, including thin-section petrography, SEM, XRD, and cathodoluminescence analyses to investigate the role of framework composition, primary depositional characteristics, and diagenetic alterations on porosity evolution of the sandstones. The results of the study indicate that the Bima Sandstone has a present-day intergranular porosity ranging from 0 to 25.9%, averaging 5.8%. Diagenetic alterations, including mechanical and chemical compaction and quartz cementation, have significantly modified the porosity of the sandstones more than the primary depositional features (grain size and sorting). Porosity reduction was mainly due to mechanical compaction (av. 32.1%) than cementation (av. 7.4%). Quartz overgrowths (up to 15%) are the most abundant cement in the sandstones, formed primarily due to lack of grain-coating clays. The main eogenetic alterations related to shallow burial include dissolution and kaolinitization of feldspars and, to some extent, mechanical infiltration of smectitic clays, which formed largely discontinuous clay coatings and pore-filling clays. Mesogenetic alterations related to deep-burial include the formation of quartz overgrowths, transformation of kaolinite and smectite into illite, and pervasive albitization of both plagioclase and K-feldspar, which is exclusively associated with the deepest, Lower Bima Sandstone Member, and has significantly reduced the secondary porosity in the sandstones. Telogenetic alterations related to uplift, mainly include dissolution and kaolinitization of unstable feldspars, which has significantly increased the present-day, secondary porosity of the sandstones to up to 15%. Pore-filling clays (chlorite, illite, and kaolinite) have had a small impact on the intergranular porosity of the sandstones, mainly because of their low volume. The study provides insights into how diagenesis can significantly affect the reservoir porosity of the sandstones and could also assist in reducing the risk of exploration of the fluvial reservoir in the basin and elsewhere.

Study on Pyrolysis-Mechanics-Seepage Behavior of Oil Shale in a Closed System Subject to Real-Time Temperature Variations.

In situ mining is a practical and feasible technology for extracting oil shale. However, the extracted oil shale is subject to formation stress. This study systematically investigates the pyrolysis–mechanics–seepage problems of oil shale exploitation, which are subject to thermomechanical coupling using a thermal simulation experimental device representing a closed system, high-temperature rock mechanics testing system, and high-temperature triaxial permeability testing device. The results reveal the following. (i) The yield of gaseous hydrocarbon in the closed system increases throughout the pyrolysis reaction. Due to secondary cracking, the production of light and heavy hydrocarbon components first increases, and then decreases during the pyrolysis reaction. The parallel first-order reaction kinetic model shows a good fit with the pyrolysis and hydrocarbon generation processes of oil shale. With increasing temperature, the hydrocarbon generation conversion rate gradually increases, and the uniaxial compressive strength of oil shale was found to initially decrease and then increase. The compressive strength was the lowest at 400 °C, and the conversion rate of hydrocarbon formation gradually increased. The transformation of kaolinite into metakaolinite at high temperatures is the primary reason for the increase in compressive strength of oil shale at 400–600 °C. (ii) When the temperature is between 20 and 400 °C, the magnitude of oil shale permeability under stress is small (~10−2 md). When the temperature exceeds 400 °C, the permeability of the oil shale is large, and it decreases approximately linearly with increasing pore pressure, which is attributed to the joint action of the gas slippage effect, adsorption effect, and effective stress. The results of this research provide a basis for high efficiency in situ exploitation of oil shale.

Mullite production: phase transformations of kaolinite, thermodynamics of the process

The growing demand for mullite raw materials, which meet industrial requirements originates the search for new and alternative sources, as well as efficient technologies for obtaining the target products (nanocomposites). The article suggests a method for obtaining mullite from kaolinite experimentally (Vezhayu-Vorykvinsky deposit, Russia). Structural kaolinite transformations (Al-Si-O-Me system), mineral phases transformations, and thermodynamics of the process have been studied. Based on the estimation of the thermodynamics of the reactions, the preferable reaction of mullite formation was determined. The article shows, that formation of the target product, mullite nanocomposite, has several intermediate phases (metakaolinite, pseudomullite). The transformations of the initial kaolinite structure include the removal of structural water and separation of the silica-oxygen tetrahedral and alumina-oxygen octahedral layers, the decomposition into free oxides, breaking of bonds between the silica-oxygen tetrahedrons and the partial increase in the coordination number of aluminium ions, the formation of mullite and cristobalite from free oxides. The proposed approach controls the ratio of Al2O3 and SiO2 phases at certain stages, which will further improve the mechanical and other properties of the matrix of the obtained raw materials for the target prototypes of industrial products.

Thermal activation and structural transformation mechanism of kaolinitic coal gangue from Jungar coalfield, Inner Mongolia, China

The benefits of industrial solid waste as a supplementary cementitious material in the manufacture of eco-efficient cement are evident in the context of sustainable and green development. Coal gangue from the Jungar coalfield, Inner Mongolia, China, was characterized and activated thermally at 500 °C–1000 °C. This study investigated the effects of thermal activation conditions on the phase and structural changes of the minerals in coal gangue. The pozzolanic activity of the thermally activated coal gangue was evaluated using both direct and indirect methods. The experimental results show that the coal gangue had a silicoaluminous nature mainly comprising of kaolinite. The pozzolanic activity of coal gangue depends on the phase and structural transformation of kaolinite during calcination. Highest pozzolanic activity is reached when calcined at 800 °C for 2 h, with lime consumption and strength activity index up to 1039 mg g−1 and 1.1, respectively. The high pozzolanic activity of metakaolinite was attributed mainly to the formation of a five-coordinated Al sheet and the less polymerized Si sheet after dehydroxylation under calcination.

Effects of kaolinite and its thermal transformation on oxidation of heavy oil

Kaolinite is a common 1:1 layered clay mineral in oil reservoirs and also a natural solid acid catalyst. Some studies have shown that kaolinite has a catalytic effect on the oxidation of heavy oil. Its catalytic effect depends on the type and amount of acid sites and is closely related to its thermal transformation, particularly the dehydroxylation process. The effects of kaolinite and its thermal transformation on the oxidation of heavy oil were investigated with thermal analysis and the Ozawa-Flynn-Wall isoconversional method. The results revealed that kaolinite had significant effects on the High-temperature oxidation (HTO) and Fuel deposition (FD) stages of heavy oil oxidation, but its effect on the Low-temperature oxidation (LTO) stage was small. In the HTO stage, the temperature at which the CO2 release rate peaked decreased dramatically, whereas the temperature at which the H2O release rate peaked increased remarkably. With the increase in the content of added kaolinite, the maximum activation energy in the FD stage of the oxidation reaction of heavy oil and the average activation energy in the HTO stage gradually decreased. It was noteworthy that the transformation of kaolinite upon thermal treatment, especially the dehydroxylation process above 400 °C, resulted in a progressive decline in the peak temperature in the HTO stage of heavy oil, but had little influence on that in the LTO stage of heavy oil oxidation.