Aluminosilicate Minerals Research Articles

Design and Fabrication of Dryer for Zeolite Synthesis: Engineering Solution for Enhanced Material Processing

The design and fabrication of the electric dryer from locally sourced materials represent a cutting-edge advancement in drying technology, harnessing the unique properties of Zeolite materials to enhance energy efficiency and performance. Zeolites are microporous, aluminosilicate minerals known for their high adsorption capacity and thermal stability. Drying is one operation required in Zeolite synthesis and as a developing Nation, there is need to invest in design and fabrication of dryers instead of relying on the traditional method of drying where the Zeolite are allowed to dry natural in open air. The Electric dryer is engineered to provide precise temperature and speed control, uniform heat distribution and efficient air circulation thereby enhancing drying efficiency, reducing operational costs and promoting local technology. The dryer consists of a mild steel chamber, heating element, fan, thermocouple, temperature and speed control system. The fabrication process involved machining, welding and assembly of the various components. The dryer performance was evaluated by drying Kaolin (a precursor for Zeolite synthesis) samples under a certain temperature and fan speed to obtain percentage reduction in moisture content to 20% from 60%. The temperature range of the dryer is 28 to 300 degrees Celsius, dimensions of the designed and fabricated dryer are Width of 0.2286m, Height of 0.3048m and Breadth/depth of 0.3048m, Volume of dryer is 0.0 , Insulation thickness is 0.04m. while area of dryer door is 0.110 . For panel dimension: Height is 0.254m, Width is 0.152m and area of panel is 0.0386 , Tray Dimension is 0.241m by 0.330m and area of tray 0.0795 . Standard Operating Procedure and maintenance of the electric dryer was also captured in this work. The regulation of the fan speed is a novel approach to our design. This innovation represents a significant leap in the development of energy-efficient dryer, promising enhanced performance and reduced environmental impact.

Study on the Inhibition Effect of Fly Ash on Alkali–SilicaReaction and Its Influence on Building Energy Performance

Abstract: Cracks and other defects in concrete will affect its durability, thermal insulation effect, and energy consumption. ASR is one of the common causes of concrete cracks. In this study, mortar specimens modified with fly ash were prepared using the mortar bar rapid method, and the inhibition effect of ASR in two alkali environments and the building energy efficiency characteristics were comparatively analyzed. SEM, EDS, and XRD were used to analyze the microstructure, elemental distribution, and products in the specimens’ interfacial transition zone comparatively. The results show that a replacement amount of 20–30% fly ash can restrain ASR expansion and maintain high mechanical strength. In both alkaline environments, K and Al are enriched in the interface transition zone and combine with SiO2 and Al2O3 to form a stable framework aluminosilicate mineral. In addition to the inhibition effect of fly ash on ASR, the external wall heat dissipation flux decreased from 132.6 W/m2 to 117.6 W/m2, a decrease of 11.3%, and the overall envelope heat dissipation flux decreased by 9.2%, significantly reducing building energy consumption. This study provides a new perspective for the development of building energy-saving materials and helps green buildings and sustainable development.

Photochromic Sodalites: From Natural Minerals to Advanced Applied Materials.

ConspectusWhile photochromic natural sodalites, an aluminosilicate mineral, were originally considered as curiosities, articles published in the past ten years have radically changed this perspective. It has been proven that their artificial synthesis was easy and allowed compositional tuning. Combined with simulations, it has been shown that a wide range of photochromic properties were achievable for synthetic sodalites (color, activation energy, reversibility, etc.), making them interesting as alternatives to organic photochromes but with the stability offered only by inorganic materials.The photochromism in this mineral originates from a photoinduced electron transfer from a sulfur based impurity toward a chlorine vacancy generating a trapped electron called an F-center. This F-center gives the color of the mineral. To investigate further the mechanism of the coloration and design artificial forms of these minerals, we built a multidisciplinary international consortium (Finland, Norway, United Kingdom, Belgium, and France). By combining experimental and computational characterizations, specifically designed for these minerals, we discovered that the stability of the F-center is due to the motion of a single sodium atom, able to move by more than 1 Å inside the structure to stabilize the trapped electron.Our international consortium, combining expertise in geology, material science, spectroscopy, and computational chemistry, has leveraged this understanding to design artificial sodalites for targeted applications. By adjusting their chemical composition, we can now fine-tune their photochromic properties (activation energy, color, thermal stability, etc.). As a result, photochromic sodalites have emerged as a highly promising platform for inorganic photonics, inspiring exciting new research directions. Notably, we have already demonstrated proof-of-concept applications as detectors and sensors for UV, X-ray, and α-, β-, or γ-irradiation. The first tests to use them as photosensitive films toward visible light and X-rays have also been performed to open the way of new imaging technologies.Beyond the development of technological applications for synthetic sodalites, their investigation was a driving force in the design of new experimental and computational techniques to study photochromism in the solid state. For instance, the "thermotenebrescence" technique was formulated to extract the stabilization energy of the F-center, and a methodology to compute excited states by quantum chemistry based on a multilayer electrostatic embedding was conceived for these systems. The latter has already been applied to understand other optical properties in other minerals, such as the photochromism in scapolite and tugtupite, the polychromism of cordierite and alexandrite, or the persistent luminescence in sodalites.This Account highlights the strength of a multidisciplinary approach to tackle the investigation of complex phenomena.

Reactive laser ablation in liquid synthesis of aluminosilicate nanominerals.

Nanoscale aluminosilicate minerals have wide ranging applications in areas including catalysis, environmental remediation, and medicine. This work reports a reactive laser ablation in liquid (RLAL) synthetic route to aluminosilicate nanominerals that enables facile tuning of their elemental composition, crystallinity, and morphology. Both the precursor solution pH and the choice of base used to adjust the pH were found to determine the properties of the nanominerals produced by laser ablation of a silicon target in aqueous solution of aluminum nitrate. Addition of ammonia produced amorphous phases with fiber- or tube-like morphologies and high aluminum content under alkaline conditions. In contrast, the addition of potassium hydroxide produced highly crystalline quasi-spherical particles, with numerous aluminum silicate and potassium aluminum silicate phases. These results show that manipulation of the precursor solution chemistry for RLAL can produce aluminosilicate nanominerals with a wide range of properties, demonstrating the flexibility of RLAL for synthesis of tailored nanominerals for specific applications.

Review on Gallium in Coal and Coal Waste Materials: Exploring Strategies for Hydrometallurgical Metal Recovery.

Gallium, a critical and strategic material for advanced technologies, is anomalously enriched in certain coal deposits and coal by-products. Recovering gallium from solid residues generated during coal production and utilization can yield economic benefits and positive environmental gains through more efficient waste processing. This systematic literature review focuses on gallium concentrations in coal and its combustion or gasification by-products, modes of occurrence, gallium-hosting phases, and hydrometallurgical recovery methods, including pretreatment procedures that facilitate metal release from inert aluminosilicate minerals. Coal gangue, and especially fly ashes from coal combustion and gasification, are particularly promising due to their higher gallium content and recovery rates, which can exceed 90% under optimal conditions. However, the low concentrations of gallium and the high levels of impurities in the leachates require innovative and selective separation techniques, primarily involving ion exchange and adsorption. The scientific literature review revealed that coal, bottom ash, and coarse slag have not yet been evaluated for gallium recovery, even though the wastes can contain higher gallium levels than the original material.

Utilization of Copper Flotation Tailings in Geopolymer Materials Based on Zeolite and Fly Ash.

Copper flotation tailings (FTs), resulting from the separation and beneficiation processes of ores, are a significant source of environmental pollution (acid mine drainage, toxic elements leaching, and dust generation). The most common disposal method for this industrial waste is dumping. However, due to their favorable physical and chemical properties-the high content of aluminosilicate minerals (60-90%)-flotation tailings can be effectively treated and reused through geopolymerization technology, thereby adding value to this waste. The objective of this study was to evaluate the potential of utilizing the geopolymerization of FTs to produce sustainable materials. Geopolymers based on natural zeolite (NZ), sodium-modified natural zeolite (NaZ), and fly ash (FA) were prepared using 20%, 35%, and 50% of FTs, activated with a 10 M NaOH solution. The study investigated the influence of Ca/Si, Si/Al, and Na/Al molar ratios on the structural, thermal, and mechanical properties (XRD, TG/DTG and unconfined compressive strength, UCS), and contaminant immobilization (TCLP method) of geopolymers. Geochemical modeling via the PHREEQC program was employed to interpret the results. The findings indicated that the UCS value decreased in zeolite-based geopolymers as the content of FT increased due to the inertness of the tailings and the low calcium content in the system (Ca/Si ≤ 0.3), in contrast to the FA-based geopolymer. The highest UCS of 44.3 MPa was recorded in an FA-based geopolymer containing 50% flotation tailings, with optimal molar ratios of 0.4 for Ca/Si, 3.0 for Si/Al, and 1.1 for Na/Al. In conclusion, the geopolymerization process has been determined to be a suitable technological approach for the sustainable treatment and reuse of FTs.

Intervalence charge transfer in aluminum oxide and aluminosilicate minerals at elevated temperatures

Abstract Single-crystal optical spectra of corundum (Al2O3) and the Al2SiO5 polymorphs andalusite, kyanite, and sillimanite, containing both Fe2+-Fe3+ and Fe2+-Ti4+ intervalence charge transfer (IVCT) absorption bands were measured at temperatures up to 1000 °C. Upon heating, thermally equilibrated IVCT bands significantly decreased in intensity and recovered fully on cooling. These trends contrast with the behavior of crystal field bands at temperature for Fe, Cr, and V in corundum, kyanite, and spinel. The effects of cation diffusion and aggregation, as well as the redistribution of band intensity at temperature, are also discussed. The loss of absorption intensity in the visible and near-infrared regions of the spectrum of these phases may point to a more general behavior of IVCT in minerals at temperatures within the Earth with implications for radiative conductivity within the Earth.

Association of tungsten with aluminosilicate mineral colloids and silicotungstates in soil porewaters: Insights into the unexpectedly high tungsten mobility in soil

Association of tungsten with aluminosilicate mineral colloids and silicotungstates in soil porewaters: Insights into the unexpectedly high tungsten mobility in soil

Shrinkage behavior of alkali-activated materials using ground bottom ashes, calcined clays, volcanic ashes, and fluidized bed combustion ashes as precursors

The global decline in the availability of fly ash and slag, the most common precursors for alkali-activated materials (AAMs), necessitates the exploration of alternative materials. Alkali activation technology presents an opportunity to utilize a wide range of naturally occurring and industrial byproducts rich in aluminosilicate minerals as precursors, offering a low-carbon alternative to traditional cement. This study investigates the volumetric deformations in AAMs produced from four groups of nontraditional and natural pozzolan-based (NNP) materials: low-purity calcined clays (CC), volcanic ashes (VA), ground bottom ashes (GBA), and fluidized bed combustion ash (FBC). Volumetric deformations—including chemical, autogenous, and drying shrinkage—were characterized using ASTM standards for portland cement. Chemical and autogenous deformations were minimal across most materials, while excessive drying shrinkage was observed in all but the calcined clays. The application of shrinkage-reducing admixtures and internal curing effectively mitigated this shrinkage. Further analyses of total heat release during activation, bound water content, pore solution surface tension, and porosity provided insights into the shrinkage and expansion mechanisms. With effective drying shrinkage control measures, alkali-activated NNPs show promise as viable low-carbon binders.

Bioleaching of lithium from jadarite, spodumene, and lepidolite using Acidiothiobacillus ferrooxidans.

Lithium (Li) is becoming increasingly important due to its use in clean technologies that are required for the transition to net zero. Although acidophilic bioleaching has been used to recover metals from a wide range of deposits, its potential to recover Li has not yet been fully explored. In this study, we used a model Fe(II)- and S-oxidising bacterium, Acidiothiobacillus ferrooxidans (At. Ferrooxidans), to extract Li from three different minerals and kinetic modelling to predict the dominant reaction pathways for Li release. Bioleaching of Li from the aluminosilicate minerals lepidolite (K(Li,Al)3(Al,Si,Rb)4O10(F,OH)2) and spodumene (LiAl(Si2O6)) was slow, with only up to 14% (approximately 12 mg/L) of Li released over 30 days. By contrast, At. ferrooxidans accelerated Li leaching from a Li-bearing borosilicate clay (jadarite, LiNaB3SiO7OH) by over 50% (over 120 mg/L) in 21 days of leaching, and consistently enhanced Li release throughout the experiment compared to the uninoculated control. Biofilm formation and flocculation of sediment occurred exclusively in the experiments with At. ferrooxidans and jadarite. Fe(II) present in the jadarite-bearing clay acted as an electron donor. Chemical leaching of Li from jadarite using H2SO4 was most effective, releasing approximately 75% (180 mg/L) of Li, but required more acid than bioleaching for pH control. Kinetic modelling was unable to replicate the data for jadarite bioleaching after primary abiotic leaching stages, suggesting additional processes beyond chemical leaching were responsible for the release of Li. A new crystalline phase, tentatively identified as boric acid, was observed to form after acid leaching of jadarite. Overall, the results demonstrate the potential for acidophilic bioleaching to recover Li from jadarite, with relevance for other Li-bearing deposits.

Zeolites – tabletting ibuprofen with and without zeolites as an excipient

Abstract Introduction Drug delivery via the oral route is a patient and industry-preferred approach. However, maintaining plasma concentrations of the active pharmaceutical ingredient (API) within the therapeutic window can be challenging with immediate-release (IR) tablets. To avoid the plasma peaks and troughs associated with IR tablets, sustained release (SR) formulations have been investigated. Zeolites are microporous aluminosilicate minerals that represent a novel tabletting material with the potential for modifying drug release due to their unique adsorption and ion exchange properties1. Aim This study will investigate the potential for inclusion of zeolites within orally disintegrating tablets (ODTs) and assessment of their ability to modify API release. Methods In-house, 50%w/w ibuprofen (IBU)-loaded ODTs (IHODTs) were prepared from Pearlitol® Flash, magnesium (Mg) stearate and 2 different zeolites (CP814C and CP814E), incorporated at 5%w/w each, using a manual tablet press. Formulations were prepared and mixed for 10 minutes in a cube mixer prior to direct compression (DC) into tablets. Physical characteristics of the tablets were assessed by hardness and friability measurements. Tablet quality was assessed by disintegration and dissolution analysis to British Pharmacopeia (BP) standards2. Release profiles were assessed against various models to determine the effect of zeolites on the release of IBU. Formulations were further examined and characterised using scanning electron microscopy (SEM) and energy-dispersive x-ray (EDX) spectroscopy. An ethics evaluation was completed, and the study was identified as not having any ethical considerations by the University of South Wales. Results The mean weight of blank ODTs was found to be 225.3mg, with a mean thickness of 3.65mm, diameter of 8.10mm, hardness of 43.9±9.2N (mean±SD, n=5) and friability of 0.2±0.2% (mean±SD, n=3). The hardness of IHODTs was found to be 59.98±1.6N, reducing to 54.9±4.3N and 43.4±0.7N (mean±SD, n=3) with the inclusion of CP814C and CP814E, respectively. The friability of IHODTs containing zeolites was 1.76±0.4% and 1.91±0.9N (mean±SD, n=3), for CP814C and CP814E, respectively; conforming to BP specification2. The disintegration time for all in-house tablets, both with and without a zeolite included, was found to be an order of magnitude greater than commercial ODTs (CT) controls, but all remained within the BP specification2. The release of IBU from IHODTs and CTs showed good correlation to the first-order release model (R2 = 0.96 and 0.98, respectively), indicating IR behaviour. Similarly, the release of IBU from IHODTs containing zeolites was shown to correlate best with the first-order release model, R2 = 0.91 for CP814C and R2 = 0.90 for CP814E, respectively. SEM analysis suggested a homogeneous blend of components within IHODTs, whilst EDX analysis indicated the presence of silicon and aluminium from zeolites, and Mg and carbon from Mg stearate and IBU, respectively. Discussion / Conclusion This study investigated the effect of zeolite inclusion on the release properties of ODTs containing IBU. Although the quality of ODTs containing zeolites was not compromised, this study suggests that inclusion of a zeolite by DC only, does not significantly modify the release profile. Future studies are required to ascertain whether zeolites can achieve SR from ODTs using alternative API loading approaches, such as solvent loading1.

Performance and life cycle of Portland limestone cement mixes admixed with gypsum

In this study, the life cycle and performance of normal concrete containing 35% limestone and 2% gypsum made in different ratios of water to binder (w/b) were examined. Its cost and CO2 emissions were found to be 13% and 35% lower compared to the control concrete. However, because of the greater replacement of cement with limestone filler, there is a reduction in its workability, the development of heat and strength, and the penetration resistance of water and chloride ions, especially in the early ages. The addition of gypsum marginally improved these concrete properties, but its quantity should be limited to 2% by weight of the binder. The use of gypsum beyond this limit led to a significant decrease in the properties of concrete. Anorthite, a calcium aluminosilicate mineral, was found in this concrete, and its fractured morphology was found to be more occupied with unreacted angular limestone particles. This low-carbon concrete showed an improvement in compressive strength with decreasing w/b ratios. The limestone reserve in India is abundant and spread evenly across its length and depth, and its use as the main replacement for cement in normal strength mixes would greatly reduce the impact of CO2 on the environment.

Impact of thermal treatment on halloysite nanotubes: A combined experimental-computational approach

Halloysite nanotubes (HNTs) are naturally occurring aluminosilicate minerals, known for their unique tubular structure, which have garnered significant interest for a wide range of applications. This study explores the morphological changes of HNTs when subjected to thermal treatment ranging from 25 °C to 1100 °C using a combination of experimental characterization techniques and molecular dynamics simulations. Techniques such as solid-state NMR (SSNMR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area measurements, and Fourier Transform Infrared Spectroscopy (FT-IR) were employed to analyse the structural evolution. The results reveal two major transitions: the first occurring between 400 and 500 °C, corresponding to the release of intercalated water and partial distortion of the HNT structure, and the second occurring between 900 and 1000 °C, marked by the collapse of the tubular structure and the exposure of alumina on the surface. These findings provide significant insights into the thermal stability of HNTs, informing future applications, especially in high-temperature environments.

Protective role of reactive aluminum phases to stabilize soil organic matter against long-term cultivation in the humid tropics under volcanic influence

ABSTRACT Cultivation can cause rapid depletion of soil organic matter (SOM), particularly in the humid tropics. Understanding the factors controlling SOM storage is a key step toward effective soil management for sustainable crop production. While clay + silt content is known to be an important factor for soil organic carbon (SOC) storage, recent studies have shown greater importance of oxalate-extracted Al (Alo; roughly corresponds to short-range-order aluminosilicate minerals and organo-Al complexes) and Fe (Feo). However, the extent to which these mineralogical factors control the response of SOM pool to land-use changes remains unclear, especially in the tropics. This study aimed to clarify the factors regulating SOM content in croplands compared to secondary forests or home gardens in Negros Occidental, Philippines. Along two line transects having a wide range of Alo contents, soil samples were collected at a depth of 0 − 10 cm from sugarcane sites (n = 33; long-term continuous cultivation of >70 years) that were paired with either secondary forests (n = 10) or home gardens (n = 20). Sugarcane sites had significantly lower SOC and total nitrogen (N) contents than secondary forest and home garden sites, whereas there was no clear difference between the latter two land uses. Both SOC and total N contents showed significant positive correlations with Alo content and, to a much less extent, with Feo content, but not with clay + silt content. The slope of the regression line between SOC and Alo was indifferent between sugarcane and the other two land uses, while the intercept was significantly lower in the sugarcane sites. These results suggest the protective role of Alo phases in both agricultural and forest soils and the presence of unprotected SOM (e.g. plant litter) in the latter sites. Furthermore, δ13C analysis suggested that the proportion of forest (C3 plant) derived carbon remaining in the sugarcane soils ranged between 10% and 50% and increased with Alo content. Together, our study showed indirect evidence of Alo-induced stabilization of SOM against long-term cultivation under the humid tropical environment.

Mineralogy and geochemical controls on the distribution of REY-Ga-Se-Nb enrichment in the No. 6 Coal Seam, Soutpansberg Coalfield, South Africa

Coal is being explored as a potential alternative source for rare earth elements (REY + Sc), which are critical for advancing modern technology. Previous research has mainly focused on assessing the concentration and distribution of REY + Sc in coals from South Africa. However, the modes occurrence of these elements in coal is yet to be investigated. This study offers new insights on the mineralogy and inorganic geochemistry of the No. 6 Seam coal from the Soutpansberg Coalfield (South Africa). The objective is to investigate the distribution, enrichment, and modes of occurrence of critical elements such as Ga, Se, Nb, and REY + Sc within this coal. The No. 6 Seam is a medium rank-B, moderate vitrinite (avg. 41.5 vol%) coal, and contains major minerals such as kaolinite, quartz, and minor minerals including muscovite, siderite, dolomite, pyrite, and calcite. The total REY + Sc concentrations in the coal samples range from 79.9 to 332.1 mg/kg (avg. 213.2 mg/kg; whole-coal/rock basis), higher than global averages for hard coal. The upper continental crust (UCC) normalized concentration coefficients (CC) of the coal shows enrichment of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Yb, and Y. Distinct REY + Sc enrichment patterns are observed across different coal horizons, divided into two categories: light-REY (LREY) and medium-REY (MREY) in the bottom horizon coal [bottom-upper (BU) and bottom-lower (BL)], whereas the middle horizon coal [middle-upper (MU) and middle-lower (ML)] are enriched in medium-REY (MREY) and heavy-REY (HREY). The BU and BL samples show greater REY + Sc enrichment relative to the MU and ML samples. The samples also contain elevated concentrations of Ga (max. 106.1 mg/kg), Se (max. 50.9 mg/kg), and Nb (max. 14.8 mg/kg), exceeding the average values reported for Chinese coals.When considering the correlations between REY + Sc and major oxide elements, minerals, and organic petrographic assemblages, REY + Sc appears to be more closely associated with inorganic fraction, particularly aluminosilicate (such as kaolinite) and carbonate minerals (like dolomite), rather than with the organic fraction. The kaolinite and dolomite represent mostly detrital input and epigenesis, respectively. Gallium in the coal is primarily associated with aluminium oxide-hydroxide, Nb with minerals such as clay, rutile/anatase, and zircon; and Se with pyrite. Redox-sensitive elemental ratios of Al2O3/TiO2 andTiO2/Zr suggest that the detrital components of the No. 6 Seam coals were predominantly derived from a source consisting of felsic-intermediate rocks. These materials likely represent the weathering products of magmatic rocks from the passive-continental margin tectonic framework of the Limpopo Mobile Belt. Paleoclimatic conditions are inferred to be warm-humid to hot, with the peat deposited under suboxic-to-oxic environments. High values of critical REY percentage (REYdef,rel%: 29.85 to 39.75 %) and an outlook coefficient ≥ 0.7 suggest these Soutpansberg coal samples to be promising for REY + Sc recovery along with Ga.

Mesoscale Reorganization of the Depolymerized Aluminosilicate into Single-Crystalline Hierarchical Zeolite.

Controllable synthesis of hierarchical zeolites from natural aluminosilicate minerals is considered an efficient and eco-friendly approach for the production of high-performance zeolites, but its synthesis mechanism is still obscure. Herein, we take the synthesis of a single-crystalline hierarchical NaA zeolite using submolten salt depolymerized kaolin (SMS-K) as the sole source of silicon and aluminum via a mesoscale reorganization strategy as an example to elucidate the reorganization process. Comprehensive morphological and structural analyses reveal that sodium-rich voids in SMS-K facilitate concurrent assembly both within the interior and at the interface of the amorphous gel, leading to the formation of numerous nanoparticles with short-range order which assemble into single-crystal nanocube NaA zeolites with intracrystalline mesopores. By harnessing confinement effects, SMS-K modulates the growth of nanoparticle sizes and enhances the intimate interconnection of nanocubes, thereby yielding NaA zeolite aggregates that exhibit hierarchical porosity, encompassing micro-, meso-, and macropores. This study offers the potential for designing and precisely controlling the fabrication of hierarchical zeolites derived from natural minerals.

Microstructural characteristics of aluminosilicate minerals in cement clinker prepared from coal gangue, carbide slag, and desulfurization gypsum

Utilizing solid waste to prepare cement clinker with low-calcium minerals is crucial for the low-carbon evolution of cementitious materials. In this study, a belite-ye’elimite-ternesite cement clinker was prepared using coal gangue, carbide slag, and desulfurization gypsum instead of non-renewable resources. The evolution law of the silica-alumina mineral phase in cement clinker under different calcining temperatures was tested and analysed. The results show that the predominant mineral phases in cement clinker consist of belite, ye’elimite, and ternesite at 1200 °C to 1250 °C. The composition of cement clinker transforms into belite and ye’elimite as the calcination temperature increases to 1300–1400 °C. At 1400 ℃, the content of belite in cement clinker reaches a remarkable 85 %. The results of XPS and NMR spectra showed that the chemical binding energy and chemical shift of Al in the cement clinker changed after calcination, representing the transformation of the aluminate in kaolinite, with [AlO6], to ye’elimite, with [AlO4]. The peak fitting results of 29Si NMR spectra semi-quantitatively describe the transition process of the silicate mineral phase from kaolinite to ternesite and then to belite. Morphologically, the increase in calcination temperature leads to a significant enlargement of the grain size of belite in cement clinker. This study can provide a basis for research on the phase regulation of cement clinker composed mainly of low-calcium minerals.

Dissolution of Volcanic Ash in Alkaline Environment for Cold Consolidation of Inorganic Binders.

A systematic study on the dissolution in concentrated alkali of two volcanic ashes from Cameroon, denoted as DAR and VN, is presented here. One volcanic ash, DAR, was 2 wt% richer in Fe and Ca and 4 wt% lower in Si than the other, designated as VN. Such natural raw materials are complex mixtures of aluminosilicate minerals (kaersutite, plagioclase, magnetite, diopside, thenardite, forsterite, hematite, and goethite) with a good proportion of amorphous phase (52 and 74 wt% for DAR and VN, respectively), which is more reactive than the crystalline phase in alkaline environments. Dissolution in NaOH + sodium silicate solution is the first step in the geopolymerisation process, which, after hardening at room temperature, results in solid and resistant building blocks. According to XRD, the VN finer ash powders showed a higher reactivity of Al-bearing soluble amorphous phases, releasing Al cations in NaOH, as indicated by IPC-MS. In general, dissolution in a strong alkaline environment did not seem to be affected by the NaOH concentration, provided that it was kept higher than 8 M, or by the powder size, remaining below 75 µm, while it was affected by time. However, in the time range studied, 1-120 min, the maximum element release was reached at about 100 min, when an equilibrium was reached. The hardened alkali activated materials show a good reticulation, as indicated by the low weight loss in water (10 wt%) when a hardening temperature of 25 °C was assumed. The same advantage was found for of the room-temperature consolidated specimens' mechanical performance in terms of resistance to compression (4-6 MPa). The study of the alkaline dissolution of volcanic ash is, therefore, an interesting way of predicting and optimising the reactivity of the phases of which it is composed, especially the amorphous ones.

Facile Synthesis of Zeolite NaX from Natural Attapulgite Clay for Pb2+ Adsorption

The synthesis of zeolites from natural aluminosilicate minerals has drawn extensive attention due to its significant utility in greening the zeolite manufacturing process. In this study, pure-phase NaX zeolite was synthesized via a low-temperature hydrothermal method, utilizing natural, low-quality attapulgite clay as the raw material. Acidified clay was fully activated through alkali fusion at 200 °C, and the impact of alkali fusion temperature, H2O/Na2O ratio, aging temperature, and crystallization time on the resulting crystalline NaX zeolite was investigated. The optimal conditions for obtaining pure NaX zeolite were determined to be alkali melting at 200 °C for 4 h, an H2O/Na2O ratio of 50, aging at 40 °C, and a crystallization period of 11 h at 90 °C. With a large BET surface area of 328.43 m2/g, the obtained NaX zeolite was used to adsorb Pb2+ from wastewater with a removal rate of 95%. This research provides a valuable method for the extensive and efficient utilization of low-grade natural attapulgite clay. Moreover, this is the first report on the synthesis of pure-phase NaX zeolite using only low-quality natural attapulgite clay as raw material through an atmospheric pressure water bath method.

Hydrochemical Characteristics and Formation Mechanism of Geothermal Fluids in Zuogong County, Southeastern Tibet

Zuogong County is located in the southeast of Tibet, which is rich in hot spring geothermal resources, but its development and utilization degree are low, and the genetic mechanism of the geothermal system is not clear. Hydrogeochemical characteristics of geothermal water are of great significance in elucidating the genesis and evolution of geothermal systems, as well as the sustainable development and utilization of geothermal resources. The hydrogeochemical characteristics and genesis of the geothermal water in Zuogong County were investigated using hydrogeochemical analysis, a stable isotope (δD, δ18O) approach, and an inverse simulation model for water–rock reactions using the PHREEQC. The results indicated that the Zuogong geothermal system is a deep circulation heating type without a magmatic heat source. The chemical types present in the geothermal water from the Zuogong area are HCO3 and HCO3·SO4, and the main cations are Na+ and Ca2+. The groundwater is replenished by atmospheric precipitation and glacier meltwater. The salt content of geothermal water mainly comes from the interaction between water and surrounding rocks during the deep circulation process. The reservoir temperature of geothermal water in Zuogong is 120–176 °C before mixing with non-geothermal water and drops to 62–98 °C after mixing with 58 to 79% of non-geothermal water. According to the proposed conceptual model, geothermal water mainly produces water–rock interaction with aluminosilicate minerals in the deep formation, while in shallow areas it interacts mainly with sulfate minerals. These findings contribute to a better understanding of the geothermal system in Zuogong County, Tibet.