Dehydroxylation Of Clay Minerals Research Articles

Research on the Harmless Treatment of Weak Muddy Intercalation in Red-Bedded Soft Rock via Microwave Energy

The WMI (weak muddy intercalation) is a typical weak structural surface in the red-bedded rock mass; ensuring slope stability by increasing the strength of the WMIs helps reduce project costs and carbon emissions. With the advantages of energy saving, high efficiency, and green, microwave technology has attracted scholars’ attention to geotechnical material property improvement. However, the mineral composition of the WMIs is complex and variable, and the applicability of microwave technology needs further evaluation. In this paper, the effects of microwave temperature and clay mineral types and content on the physical and mechanical properties of the WMIs were evaluated. The results show that microwave heating can substantially improve the uniaxial compressive strength of the WMIs, regardless of the types and content of clay minerals. Dehydration, dehydroxylation of clay minerals, and local melting of albite occurring in the specimens under microwave heating enhanced the strength of the soil particles and the interparticle joints. The strength increase ratios of the WMI specimens increased with the temperature increase. With the increase in clay mineral content, the strength increase ratio of kaolinite WMIs and illite WMIs decreased, while the strength increase ratios of montmorillonite WMIs increased. The present multiple regression analysis methods are used to establish the strength prediction models of the WMI microwave-reinforced specimens, which can guide the engineering application.

Structural transformation and dehydroxylation of clay minerals in lithium-bearing clay

Structural transformation and dehydroxylation of clay minerals in lithium-bearing clay

Calcination of Clay Raw Materials in a Fluidized Bed.

Clay raw materials are diverse in terms of their mineral composition, as well as the content of colouring oxides and their physical properties. Determining the suitability of raw materials for various purposes requires comprehensive studies on their properties, as well as their appropriate correction, which is possible through the use of appropriate modification techniques. One of the most commonly used technologies for the enrichment of clay raw materials is to subject them to high temperatures, which, depending on the temperature regime used in the technological process, may cause the decomposition and removal of some addditional components (e.g., carbonates), as well as the removal of water and dehydroxylation of clay minerals, reversible structural changes, and the complete and permanent reconstruction of the mineral phases. This paper presents a new application for fluidization technology in the calcination of clay raw materials. The results of the experiment show that the fluidization method is competitive compared to the technologies that have been used so far, as a result of, inter alia, the much shorter time period required to carry out the calcination process and, consequently, the much lower energy expenditure, the high efficiency of burning coal, and the lower CO2 emissions resulting from the mixing taking place in the reactor.

Effect of Calcium Hydroxide Content on Pozzolanic Reaction of Calcined Clays: Their Mechanical Properties and Microstructures

The research aimed to investigate the effect of calcium hydroxide content on pozzolanic reaction of calcined clays. Pozzolanic reaction of calcined clay was determined in terms of its mechanical properties, phase development and microstructures. Three clay minerals (two kaolinitic clays and kaolinite-montmorillonite clay) were chosen to produce pozzolanic materials via calcination at temperature of 700 °C to allow dehydroxylation of clay minerals. Ratios of calcium hydroxide to calcined clays were varied from 0.1 to 0.5. Mixing water contents or liquid to solid ratios (0.62, 0.75 and 0.80) and curing times (7 and 28 days) were also studied. It was found that calcium aluminosilicate hydrate (stratlingite) could be formed after pozzolanic reactions of all clay minerals. The development of stratlingite agreed with the strength development showing the highest compressive strength at 26 MPa (28 days) when kaolinite-montmorillonite clay was used as pozzolanic material and the ratio of calcium hydroxide to calcined clay was 0.5.

Preparation and thermal properties of commercial vermiculite bonded with potassium silicate

Expanded vermiculite bonded with potassium silicate finds use as high-temperature insulation boards. The thermal properties of the vermiculite boards are critical for their applications and expected lifetime. This work reports on the processing and thermal properties of vermiculite boards (400–600 kg m−3) prepared from three different commercial vermiculite sources. Commercial vermiculite is first expanded through flash-heating, then mixed with potassium silicate and then finally pressed to boards. The untreated- and expanded vermiculite and the boards are studied with X-ray diffraction, differential scanning calorimetry, thermogravimetry, heating microscope and electron microscope. The expansion process affects the ability of the expanded vermiculite to reabsorb moisture and the ability is dependent on vermiculite source. The vermiculite boards undergoes several physical-chemical transitions at elevated temperatures. Water from both clay minerals and binder is lost at <250 °C. At 800–1200 °C, the dehydroxylation of clay minerals first occurs, then the boards shrink, and forsterite (Mg2SiO4) and leucite (KAlSi2O6) crystallise subsequently. At 1200–1420 °C, the leucite melts and the boards shrink again. The crystallisation- and melting temperatures depend on the vermiculite source. These findings provide practical guidelines for processing vermiculite into lightweight boards.

Marl as a supplementary material to alkali-activated blended cements

The increasing need of raw materials is one of the drivers for further development of inorganic binders, including alkali-activated cements. This research focuses on the study of the potential suitability of raw and calcined marl with a high calcite/aluminosilicates ratio as a supplementary material for alkali-activated blended systems using alkali-activated salg cement as an example. Marl calcined at 800 °C was found to be a more promising supplementary material for alkali-activated blended cements compared to raw marl. The thermal treatment at 800 °C results in the partial amorphization; formation of reactive Si, Al, and Ca due to the dehydroxylation of clay minerals and decarbonation of calcite. These provide the marl with the capability to form aluminosilicate hydrate gels and contribute to the mechanical characteristics of hardened activated mixed pastes. The hardened blended ground granulated blast furnace slag/calcined marl systems activated by hydrous sodium silicate and cured at room temperature had 28-day compressive strength of 27.5–40 MPa depending on the ratio of the slag/calcined marl. XRD, TG/DSC, FTIR, optical microscopy, and SEM were used to investigate the reaction products, as well as the microstructure of the activated blended pastes.

Non-Isothermal Kinetic Evaluation of Pyrophyllite Dehydroxylation

Dehydroxylation of clay minerals is an important process with several applications. Despite the industrial use of several well defined clay minerals, only the dehydroxylation kinetics of kaolinite has been reported. Still, the kinetics of these solid state reactions is yet to be understood using unambiguous model. In the present work, we have performed detailed kinetic analysis of dehydroxylation of pyrophyllite clay using non-isothermal kinetics by thermogravimetry (TG) at different heating rates. The TG data has been analysed initially with model-free methods (ASTM E 698, ASTM 1641, Friedman analysis and Ozawa-Flynn-Wall method). Interestingly, both the model-free methods of analysis have unequivocally indicated that activation energy (Eact) changes very marginally with progress of reaction and a single activation energy barrier is present. This surmises that the dehydroxylation process is a single stage process. A multivariate non-linear regression on the dynamic thermal data at different heating rates has been performed to determine the most probable kinetic model based on statistical fit. It has been found that, TG data provides best fit with regression coefficient (r2) value of 0.994, when a single stage Avrami type diffusion reaction model is assumed, and an activation energy of 159 kJ.mol−1.

Volcanic edifice weakening via devolatilization reactions

SUMMARY Edifice instability, that can result in catastrophic flank collapse, is a fundamental volcanic hazard. The subvolcanic basement can encourage such instability, especially if it is susceptible to mechanical weakening by devolatilization reactions near magmatic temperatures. For this reason, understanding how the physical and chemical properties of representative lithologies deteriorate at high temperatures is potentially highly relevant for volcanic hazard mitigation. This is particularly true for sedimentary rock, commonly found underlying volcanic edifices worldwide, that undergo rapid deterioration even under modest temperatures. Therefore, here we present the first experimental study of devolatilization reactions, induced by magmatic temperatures, on sedimentary rock comprising a subvolcanic basement. Our results show that, for a marly limestone representative of the basement at Mt Etna, devolatilization reactions, namely the dehydroxylation of clay minerals and the decarbonation of calcium carbonate, result in a dramatic reduction of mechanical strength and seismic velocities. These temperature-driven reactions can promote volcanic instability at stresses much lower than previously estimated.

Analysis of temperature effect on ceramic brick production from alluvial deposits, Tamilnadu, India

This study focuses on the thermal behaviour of alluvial clays in the production of ceramic brick industries, which are largely found on the bank of the Cauvery river, Tamilnadu, India. Clay bars were prepared which consisted of quartz, kaolinite, illite, chlorite, feldspars and iron oxides. The test samples were fired in the range of 700–1100 °C and were examined with chemical analysis, thermogravimetric–differential thermal analysis (TG–DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). An increase in firing temperature resulted in dehydroxylation of clay minerals, persistence of quartz and formation of Ca-anaesthetic plagioclase. SEM images visualized the vitrification of the fired bricks, which increased the compressive strength of the fired bars. The bricks made with alluvial clays displayed less water absorption and higher compressive strength, indicating that they could be used in the brick industry. The results of this work assisted the industries to select more appropriate natural clay composition and firing dynamics for making the bricks.

Bromine volatilization during firing of calcareous and non-calcareous clays: Archaeometric implications

The influence of carbonates in the temperature of Br volatilization during firing of clays and its implications in archaeometric studies are investigated. The main goal is to determine the circumstances in which Br content of fired products (“pottery”) can be considered inherited from raw material or added to ceramic pastes after production. Seven samples representing different types of clays (non-calcareous clays, calcite-rich clays and dolomite-rich clays) from Algarve region (South Portugal) were studied before and after firing at temperatures ranging from 300 °C to 1100 °C by steps of 100 °C. Original clays were characterized by major element geochemistry, obtained by X-ray fluorescence, and by mineralogy of bulk rock and < 2 μm fraction, using X-ray diffraction. The chemical composition of the test pieces (unfired and fired at various temperatures) of each clay was determined by instrumental neutron activation analysis, as it enables obtaining Br concentration with high precision and accuracy. Thermogravimetric analysis was done to better characterize mass changes after firing. The results confirm the influence of clays composition, especially the presence of carbonates rather than the clay minerals associations, on temperature of Br volatilization: i) in non-calcareous clays Br volatilized more intensely up to 600 °C, suggesting its association with combustion of organic matter and dehydroxylation of clay minerals; ii) in calcareous clays Br volatilized more strongly after 800―900 °C, suggesting that at least part of the process is associated with decarbonation reactions. As a result, this study contributes to elucidate that not all Br existing in pottery can be interpreted as a contamination product. Instead, Br can be inherited from raw material and its presence in pottery, particularly in carbonate-rich pastes, may simply indicate that the temperature attained in the kiln was not enough for its complete volatilization. Extending the Algarve study to other clay materials used in ancient ceramics, the conclusions of this study may assist broad archaeometric studies.

TEM study of mineral transformations in fired carbonated clays: relevance to brick making

AbstractThis study uses transmission electron microscopy (TEM) and analytical electron microscopy (AEM) supported by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to investigate the mineralogical and textural changes produced in carbonated clays by firing. Sample bars were prepared using raw clays composed of quartz, illite and carbonates with minor amounts of smectite, chlorite, feldspars and Fe oxides. The raw samples were then fired at temperatures of between 800 and 1050°C. The XRD data show that increases in firing temperature result in dehydroxylation of clay minerals, carbonate decomposition and the formation of Ca-bearing silicates (e.g. gehlenite, wollastonite, pyroxenes and anorthite). The sizes of the Ca-silicate crystals make the use of the SEM inappropriate since they lie below the resolution threshold. However, TEM/AEM do provide the required textural and compositional characterization, revealing that there is a broad range of pyroxene compositions, some of which resemble fassaite, and that Ca/Mg ratios increase with temperature. The TEM also shows significant dehydroxylation and vitrification of the clay-rich matrix at T of ~800°C. Observed mineralogical and textural changes probably occurred in a system with a local disequilibrium much like small-scale, high-temperature metamorphic reactions (i.e. pyrometamorphism). The importance of these results is that they enable the selection of more appropriate raw clay composition and firing dynamics (temperature, firing duration and cooling rate) for both the brickmaking industry and brick conservation in the field of cultural heritage.

Quantitative determination of pyrite in, ceramic clay raw materials by DTA

Abstract The thermal oxidative decomposition in air of 0–1.5 wt% of pyrite added to two traditional powdered clays was investigated by non-isothermal DTA. It emerged that the first step of the exothermic oxidation of pyrite, in the 350–500°C range, partly overlapped the endothermic dehydroxylation of clay minerals, centred at 590°C, and the result was dependent on the pyrite contents. Based on the values of the area of the oxidative peak and of the corresponding oxidation heat, it is possible to calculate quantitatively the amount of pyrite present in the industrial clay bodies and therefore to inform the technicians of the factories so they can avoid the negative effects of reducing reactions that could occur during firing of ceramic raw materials.

内外液化用原料炭の基礎性状 （ＩＩ） 鉱物質組成

Reaction characteristics for liquefaction of Japanese and foreign coals are being studied as part of the program of coal liquefaction at the Government Industrial Development Laboratory, Hokkaido. In this study, samples of mineral matter from various coals prepared by a low-temperature ashing technique (LTA) and by a high-temperature ashing technique (HTA) were examined by inductively-coupled plasma emission spectroscopy (ICP), X-ray fluorescence (XRF) and X-ray diffraction in order to obtain fundamental information to clarify the effects of inherent mineral matter on coal liquefaction.The contents of ashes prepared by a low-temperature ashing technique (LTA) and by a high-temperature ashing technique (HTA) range from ca.2wt% to ca.27wt%. The LTA content is higher than the HTA content in most cases due to dehydration and dehydroxylation of clay minerals, decomposition of carbonate minerals, and dehydration of sulfate minerals by high-temperature treatment.According to the results of ICP analysis, the main components of mineral matter in coal are Si, Ti, Al, Ca, Na, K, Fe and Mg, and the minor components (0.01-0.20wt%) are Mn, Zn, V, Cr, Ni, Cu, and Be. Australian Yallourn lignite is rich in Fe and Mg, and poor in Si and Al. Canadian sub-bituminous coals (Egg Lake and Wabamum) and Chinese Shori lignite and sub-bituminous coals (Koken and Karinga) are rich in Ca. American Kaiser #3 bituminous coal is rich in Fe, Mn, Cu and Be, and Colombian Titiribi bituminous coal is rich in Ca, Fe and Cu. Australian sub-bituminous coals (Wandoan and Liddell) and Japanese sub-bituminous coal (Taiheiyo) and bituminous coal (Shin-Yubari) have a comparatively similar elemental composition.According to the results of X-ray diffraction, the LTA contains quartz, kaolinite, illite, calcite, dolomite, pyrite etc. The HTA contains less identifiable components, namely, quartz, metakaolin, anhydrite, bassanite, hexahydrite etc.

Pure and impure clays and their firing products

Mossbauer spectroscopy is highly suited for the study of clays whose industrial uses depend on the iron content. Reactions that take place during clay firing can be readily monitored by Mossbauer spectroscopy. Following dehydroxylation of clay minerals, the quadrupole splitting of octahedrally coordinated iron (III) increases abruptly, but reverts to lower values upon the formation of new, better ordered phases at higher temperatures. It is also shown that iron oxides may account for a considerably higher proportion of the total iron content of many clays than is commonly recognized, and their existence must be taken into consideration for a correct interpretation of the Mossbauer spectra of clays.

The Role of Water Vapour in the Dehydroxylation of Clay Minerals

Water vapour atmospheres are known to raise the temperature of the endothermic reaction of clay minerals in differential thermal analyses. In isothermal kinetic studies of dehydroxylation, it is shown that a stationary state is attained depending on the operating temperature. The rate of dehydroxylation is a function of specimen size and shape, which suggests a controlling influence by entrapped water vapour. Even at constant reaction temperatures, the rate of dehydroxylation varies greatly between the interior and the exterior of a specimen. The bearing of these results on thermal analyses and on kinetic studies generally is discussed.