Reaction Of Kaolinite Research Articles

Uptake of various cations by amorphous CaAl2Si2O8 prepared by solid-state reaction of kaolinite with CaCO3

The uptake of various ions by amorphous and crystalline CaAl2Si2O8 was investigated. The CaAl2Si2O8 samples were prepared by solid-state reaction of kaolinite with CaCO3, ground for 0–24 h and fired at 600–1000 °C for 24 h. Uptake experiments were performed both at room temperature (25 °C) and 60 °C at a solid∶solution ratio of 0.002 g ml¬1 with cation concentrations ranging from 10−4–10−2 M. The cations examined were alkali ions (Na+ and K+), alkaline earth ions (Mg2+, Sr2+ and Ba2+) and transition metal ions (Ni2+, Co2+, Cu2+ and Zn2+). The uptake of transition metal ions by amorphous CaAl2Si2O8 was found to be higher than by crystalline CaAl2Si2O8. The uptake of transition metal ions by amorphous CaAl2Si2O8 was higher than the uptake of alkali and alkaline earth ions, indicating a high selectivity for transition metal ion and their uptake was further enhanced at higher solution temperatures. Uptake of the various ions showed strong pH dependence and indicated high uptake ability at neutral pH. For the heavy metal ions the uptake selectivity was found to be Cu > Zn > Ni ≥ Co, suggesting a correlation with their ion products. The effectiveness of amorphous CaAl2Si2O8 as an uptake agent for heavy metal ions was confirmed by experiments with real river water.

Thermal reactions of kaolinite with potassium carbonate

It was previously established that kaolinite reacts with K2CO3 on heating to form products of KSiAlO4 composition. In the present study we investigated the solid state reactions with K2CO3 of four kaolinites of different thermal stability. The mixtures were calcined at temperatures ranging from 400-700°C and washed before or after boiling with the remaining K2CO3. FTIR spectra indicated that the X-ray amorphous material formed after calcining the mixtures at 500-590°C had a SiAlO4 tetrahedral framework. Attempts to convert the products to zeolites gave promising results. After calcining at 700°C under atmospheric pressure synthetic kaliophilite (KSiAlO4) was obtained. These conditions are appreciably milder than previously reported for kaliophilite syntheses. Conversion to kalsilite increased with decreasing thermal stability of the original kaolinite. In similar reactions with KCl much less K was incorporated into the amorphous phase and kaliophilite was not obtained. The reactions of the four kaolinites with K2CO3 or with KCl were similar in trend, but differed in detail.

I-S precipitation in pore space as the cause of geopressuring in Mesozoic mudstones, Egersund Basin, Norwegian continental shelf

The role of clay diagenesis in pressure-ramp (overpressure) development is evaluated from Mesozoic mudstone well cuttings in the Egersund Basin, Norwegian Continental Shelf. Major changes in the mineral assemblage over the range of increasing geopressure include -50% decrease in detrital kaolinite in bulk material, and increases in the proportions of illite, I-S, and percent of nonexpandable illite-like layers in I-S. SEM and TEM observations confirm that pore space is defined primarily by intersecting clay-mineral packets at the scale of tens or hundreds of nanometers (0.01-0.1 μm). TEM data document the reactions of kaolinite and detrital mica to form I-S. The principal reaction that occurred over the geopressure ramp was dissolution of kaolinite and precipitation of neoformed I-S in pore space of these mudstones. These changes also correspond to changes in <0.1 μm particle populations, as determined by Pt/C shadowed TEM measurements, as well as high-resolution TEM lattice-fringe observations. The neoformed I-S has dimensions similar to those of the pore space in the mudstones. The results support a mineralogical model of precipitation of diagenetic clay, resulting in severe permeability reduction, which can be related to the observed pressure ramp. These observations and results provide an integrated petrologic framework for modeling pressure-ramp development, which had been difficult to achieve using conventional basin models of porosity and permeability evolution based on mechanical compaction.

Carbothermal Reactions of Quartz and Kaolinite with Coal Char

Reactions of quartz and kaolinite separately with coal char were examined at temperatures up to 1600 °C in argon and nitrogen atmospheres, by using thermogravimetric analysis combined with off-gas analysis. X-ray diffraction analysis was utilized to identify the reaction products. The carbothermal reactions of quartz and kaolinite began, respectively, at temperatures as low as 1200 and 1150 °C, with the evolution of CO. The formation of reaction products was quite dependent on heating conditions. Under Ar, the main product(s) were β-SiC for quartz, and β-SiC and α-Al2O3 for kaolinite. Above 1550 °C, Al2O3 gradually formed Al4C3. Under N2, the carbothermic nitridation occurred for both quartz and kaolinite in company with the formation of SiC. For quartz, the products were SiC and hexagonal β-Si3N4 at 1600 °C; however, no crystalline nitrides were distinctly observed at 1400 °C. For the case of kaolinite, β-Si3N4 was appreciably formed at 1400 °C and it disappeared at 1600 °C; above 1500 °C, AlN was formed from Al2O3. Similar changes of crystalline mineral phases were examined on heating three coals in the same manner. Silicon carbide (SiC) and aluminum nitride (AlN) were the major products in the coals treated under nitrogen at 1600 °C for 10 min. The formation of these compounds could be attributed primarily to the carbothermal reactions of kaolinite and quartz inherent in coal.

Characterization of the State of Ni2+ in Ni-Exchanged KAlSiO4 by XPS, XRF, XRD, EXAFS and NMR.

Imperfectly ordered KAlSiO4 shows a greatly increased uptake of Ni2+ from solution which motivated this study of the state of Ni2+ in Ni-exchanged KAlSiO4 using X-ray photo-electron spectroscopy (XPS), X-ray fluorescence (XRF), powder X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) and solid state nuclear magnetic resonance spectroscopy (NMR). The imperfectly ordered KAlSiO4 was synthesized by solid-state reaction of kaolinite with K2CO3 at 550°C for 24h. The Ni-exchanged KAlSiO4 samples were obtained by treatment in a solution containing 10-3-10-1M NiCl2 buffered with 0.5M NaCl at 60°C. Comparison of the surface and bulk chemical compositions analyzed by XPS and XRF indicated that the Ni2+ sorbed on the KAlSiO4 is largely concentrated at the surface. The XRD pattern of the Ni-exchanged KAlSiO4 showed weak broad peaks corresponding to a phase with a layered structure and a change in the halo pattern of the KAlSiO4. EXAFS analysis confirmed the presence of a Ni-containing layered double hydroxide (LDH; Ni1-yAly(OH)2Xy⋅nH2O) as indicated by the interatomic Ni-Ni distance and Ni coordination number. The 29Si MAS NMR showed shift and peak splitting corresponding to an increase in the degree of polymerization of the SiO4 tetrahedra forming the framework of the tridymite-type structure and the 27Al MAS NMR showed an increase of six coordinated Al in the Ni-exchanged KAlSiO4. It is concluded, from all these results, that the Ni2+ in Ni-exchanged KAlSiO4 forms a Ni-Al LDH-like phase on the surface of the KAlSiO4. This is considered to be the main reason for the higher Ni2+ uptake compared with various other cations adsorbed on imperfectly ordered KAlSiO4.

Uptake of Various Cations by Imperfectly Ordered KASiO4 Prepared by Solid-State Reaction of Kaolinite with K2CO3.

The uptake of various cations by imperfectly ordered KAlSiO4 was investigated. The KAlSiO4 was prepared by solid-state reaction of kaolinite with K2CO3 at 550°C for 24h. Uptake experiments were performed at 60°C using 0.5g of the KAlSiO4 and 50ml of solution containing 10-3-10-1M of each cation, with and without 0.5M NaCl buffer. The cations were alkali (Li+ and Na+), alkaline earth (Mg2+, Ca2+, Sr2+ and Ba2+) and transition metal cations (Ni2+, Co2+, Cu2+ and Zn2+). From the comparison of uptakes of various cations by KAlSiO4 and zeolite Na-A, it was found that the ratio of uptake by both exchange materials increased with decreasing ionic radius of the exchanging cations, the KAlSiO4 showing higher uptake of Ni2+ than zeolite Na-A. This trend became more distinct for the uptake of Ni2+ in simulated acid waste solution and groundwater because of the suppressing effects by co-existing alkali and alkaline earth cations especially for zeolite Na-A.

Thermal analysis of topaz synthesis from kaolinite

The present work represents a thermal analysis study of topaz synthesis from kaolinite by its sintering with aluminium fluoride using a derivatograph. Also, it includes the study of the influence of aluminium fluoride on the thermal behaviour of kaolinite. The products of sintering were identified microscopically and by using a Siemens Crystalloflex diffractometer. The DTA and X-ray powder diffraction data show the beginning of the appearance of both topaz and mullite at 600°C and indicate that the reaction of kaolinite and aluminium fluoride of different amounts takes place in two distinct steps. The first is marked by a medium endothermic peak at 750–790°C, representing the intensive formation of topaz, and the second by a large and sharp or wide endothermic peak at 930–950°C, representing its subsequent dissociation with the formation of either mullite or (corundum and mullite) or corundum, depending on the amount of aluminium fluoride. This process is accompanied by a sharp decrease in weight, (TG curve), due to the volatilization of silicon tetrafluoride, water vapour and other gases. The synthesized topaz is colourless in thin sections and crystallizes in orthorhombic system in the form of elongated prismatic crystals, with perfect basal (0 0 1) cleavage; it is optically positive.

A kaolinite-NMF-methanol intercalation compound as a versatile intermediate for further intercalation reaction of kaolinite

A kaolinite-organic intercalation compound containing methanol was proved to be a versatile host for further displacement reaction with alkylamines. Kaolinite-organic intercalation compounds with polar molecules, such as N-methylformamide (NMF) and formamide, were used as the starting materials. After stirring the kaolinite-NMF intercalation compound with methanol, the basal spacing increased to 1.11 nm. The 13C MAS NMR result of the product indicated that methanol was intercalated into kaolinite by partial displacement with NMF. By use of the methanol-treated kaolinite intercalation compound as the intermediate, alkylamines were intercalated into the interlayer space of kaolinite by displacing with methanol.

Nitrogen Isotopic Composition of Ammonium-rich Illite in Anthracites and Organic-rich Shales from Eastern Pennsylvania

Previous studies (Daniels and Altaner 1990; Sucha et al, 1994) have shown that ammonium-bearing illite/ muscovite can be formed, at temperature above 200~ by reaction of kaolinite with ammonia, derived from the thermal degradation of organic nitrogen. In the part icular case of Eastern Pennsylvania, the present work reports, for the first time, the isotopic composition of nitrogen in ammonium rich illite from low grade metamorphic rocks associated with anthracites ranking above Rmax: 4%.

Hydrothermal Reaction of Kaolinite with Calcium Hydroxide and Dissolution of Reaction Products in Hydrochloric Acid

Hydrothermal reaction between kaolinite and Ca(OH)2 with starting CaO/kaolinite ratios from 0.2 to 1.2 g/g was carried out at 150−300 °C for up to 5 h. The effect of digestion conditions on the conversion of kaolinite was investigated. Kaolinite was completely converted to calcium-bearing compounds after Ca(OH)2 digestion at 300 °C for 2 h. Reaction products were identified by X-ray diffraction, thermogravimetric, and differential thermal analyses. Different digestion conditions resulted in varying reaction products, including hibschites, omisteinbergite, tobermorite or poorly-crystalline tobermorite, and jaffeite. The dependence of reaction sequence on digestion conditions has been proposed from the results obtained. After digestion, the dissolution of reaction products in dilute HCl solution was investigated. Leaching with 6% HCl at room temperature under stirring could entirely extract the aluminum, silicon, and calcium from digested samples so long as kaolinite was completely converted.

Use of clay-mineral alteration patterns to define syntectonic permeability of joints (cleat) in Pennsylvania anthracite coal

Joints (cleat) in Pennsylvania anthracite contain two distinct clay-mineral assemblages, both of which formed by alteration of preexisting kaolinite at peak metamorphic conditions during the Alleghanian orogeny. The first assemblage, NH 4-illite or pyrophyllite ± quartz, formed by reaction of kaolinite with methane-rich fluids derived from within the coal. The second assemblage, sudoite ± tosudite ± rectorite ± berthierine, formed by the reaction of kaolinite with ferromagnesian-bearing hydrothermal fluids which must have come from outside the coal. In an earlier paper, we suggested that the first assemblage indicated clay diagenesis in low-permeability environments, and that the second assemblage indicated clay diagenesis in high-permeability environments. If this premise is correct, then the distribution of clay-mineral alteration assemblages serves to define syntectonic permeability variations in coal cleat. The first assemblage dominates in the coal matrix itself, in isolated cleat, in cleat that parallel the regional trend of Alleghanian folds, and in the mirror portions of cleat oriented perpendicular to the fold trends, suggesting that these regions are low-permeability environments. The second assemblage dominates in the hackle fringe of interconnected cleat that trend perpendicular to the strike of the Appalachian orogen, suggesting that these regions are high-permeability environments. Our results emphasize that syntectonic cleat permeability is a function of cleat orientation, macroscopic cleat interconnectivity and orientation, as well as microscopic cleat-surface morphology.

水を媒体とした粘土鉱物の生成と変化

Formation and transformation of clay minerals occur ubiquitously at the interface between mineral and water in the upper part of the Earth crust. The solution-mediated reactions pertaining to clay minerals are characterized by a consecutive transformation from metastable phases toward final stable phases based on the Ostwald's step rule and by the phase transformations via dissolution and recrystallization processes. Two examples have been introduced in this communication: one is the allophane→halloysite→kaolinite reaction series in weathering and the other is the smectite→illite/smectite interstratified minerals→illite reaction series in diagenesis. Understanding of the kinetics of these reactions in natural open systems are only qualitative at present; it is necessary in future to accumulate more data in terms of the rates and mechanisms of dissolution and growth of these minerals in order to understand quantitatively the dynamics of the solution-mediated geochemical reactions.

Kinetic study of the kaolinite-mullite reaction sequence. Part II: Mullite formation

The present work is a follow-up of the investigation on the decomposition reaction of kaolinite as a function of the defectivity of the starting material and the temperature of reaction. In the present work we study the high temperature reaction of mullite synthesis from kaolinite, from the starting point of the results obtained in the first part. Time resolved energy-dispersive powder diffraction patterns have been measured using synchrotron radiation in isothermal conditions. The apparent activation energy for mullite nucleation and growth is found to be related to the defective structure of the starting kaolinite, which thus must have an influence on the chemical homogeneity of the amorphous intermediate phase. The analysis of the kinetic data indicate that the initial reaction mechanism is controlled by mullite nucleation, while as the reaction proceeds it shifts towards a grain growth-limited process which is intermediate between phase boundary and diffusion controlled. The order of the reaction obtained from standard analysis of the isothermal kinetic data is lower in the case of the ordered kaolinite KGa-1, in agreement with a rate limiting process more strongly limited by diffusion. For each sample there is a small but significant decrease in the order of the reaction at higher temperature: we interpret the change as related to the variation of the diffusion process in the amorphous phase due to the growing grains of mullite and cristobalite. The values of the activation energies and induction times are comparable neither to a model of mullite formation from a monophasic gel, nor mullite formation from a diphasic gel, being intermediate between the two. We can infer that the amorphous precursors from natural kaolinites can be considered pseudo-monophasic gel-like phases, approaching the monophasic gel-like behaviour as the defectivity of the initial kaolinite increases.

Kinetic study of the kaolinite-mullite reaction sequence. Part I: Kaolinite dehydroxylation

The decomposition reaction of kaolinite has been investigated as a function of the defectivity of the starting material and the temperature of reaction. Time resolved energy-dispersive powder diffraction patterns have been measured using synchrotron radiation, both under a constant heating rate (heating rates from 10 to 100° C/min) and in isothermal conditions (in the temperature range 500 to 700° C). The apparent activation energy of the dehydroxylation process is different for kaolinites exhibiting a different degree of stacking fault density. The results of the analysis of the kinetic data indicate that the starting reaction mechanism is controlled by diffusion in the kaolinite particle. The diffusion process is dependent on the defective nature of both kaolinite and metakaolinite. At high temperatures, and at higher heating rates, the reaction mechanism changes and the resistance in the boundary layer outside the crystallites becomes the rate-limiting factor, and nucleation begins within the reacting particle. During the final stage of the dehydroxylation process the reaction is limited by heat or mass transfer, and this might be interpreted by the limited diffusion between the unreacted kaolinite domains and the metakaolinite matrix.

Experimental studies of silicate-carbonate reactions—I. Applications to diagenesis

The formation of clays and CO 2 from silicate-carbonate reactions and the effect of these products on reservoir quality and fluid chemistry have been well recognized in the study of sediment diagenesis. The phase relationships for the reaction of kaolinite + dolomite + quartz to calcite + chlorite-smectite + CO 2 reactions were chemographically examined and experimentally evaluated. The phase boundary of this reaction on a T− X CO 2 diagram was interpolated between high temperature experimental data and low temperature field data. The results can be applied to predict the amounts, type and timing of clay and CO 2 formation during sediment diagenesis. The variation of pore fluid composition (e.g. Ca 2+ and Mg 2+) caused by these reactions was also evaluated using a geochemical modeling program. The major conclusions and implications are the following: (1) the concentration of CO 2 in the reaction fluid controls the reaction temperature as well as the clay type (chlorite vs smectite) formed. The equilibrium boundary provides a guideline for estimating the CO 2 contents, the sealing integrity and temperatures of a diagenetic system based on the observed mineral assemblages; (2) the silicate-carbonate reactions can occur in diagenetic environments that are open to CO 2, and can therefore, be an important inorganic source of CO 2 which can lead to the formation of CO 2-rich gas fields and secondary porosity. The diagenetic reactions, however, are significantly suppressed in a closed system (e.g. overpressure zone) and therefore cannot significantly contribute to overpressure formation nore generate enough pressure to create fractures; and (3) the formation of smectite of chlorite which can serve as a sink for Mg 2+ and to a lesser extent, for Ca 2+. The pore fluid released from these reactions during shale diagenesis, in general, contains much less Mg 2+ than Ca 2+. The reactions in shales are likely sources of Ca 2+ for carbonate cements but not of Mg 2+ for dolomitization.

Chemographic analysis of assemblages involving pyrophyllite, chloritoid, chlorite, kaolinite, kyanite, quartz: application to metapelites in the Witwatersrand goldfields, South Africa

ABSTRACTThe Witwatersrand goldfields contain abundant assemblages that include pyrophyllite, chloritoid, chlorite, kaolinite and/or kyanite, with quartz. A chemographic analysis of the system Fe(Mg)‐Al‐Si‐O‐H involving these minerals yields 22 potential phase diagrams. Using orientation criteria and thermodynamic calculations as further constraints, this list has been reduced to three possible diagrams. New thermodynamic data favour one of these in particular.This chemographic analysis demonstrates that formation of chloritoid is not restricted to the breakdown reaction of kaolinite plus chlorite in the F(M)ASH system, as stated by previous studies, but could be from pyrophyllite + chlorite → chloritoid + quartz + H2O.The metamorphic temperature variation between Witwatersrand goldfields exceeded 65d̀ C, based on chlorite and chloritoid compositions. The lower and upper pressure limits are constrained by the andalusite to kyanite, and the sudoite/chlorite to carpholite boundaries, i.e. 1.5–2.8, and 7 kbar, respectively. The widespread pyrophyllite, chlorite and Fe‐chloritoid in all the Witwatersrand goldfields, and the local occurrence of sudoite indicate a consistent low‐pressure environment in which Mg‐chloritoid would not be stable.

Time‐Temperature‐Transformation Curves for Kaolinite‐α‐Alumina

The C‐shaped time‐temperature‐transformation curves (T‐T‐T curves) of cristobalite formation and the L‐shaped T‐T‐T curves of α‐alumina reaction were established for a high‐purity kaolinite‐α‐alumina mixture during heating. The results revealed that cristobalite formation in kaolinite was retarded by the presence of α‐alumina between 1250° and 1350°C and was totally prohibited above 1380°C due to the reaction of kaolinite with α‐alumina to form secondary mullite. The reaction of α‐alumina with kaolinite was initiated at about 1250°C. It became quite extensive above 1380°C and was extremely fast at 1600°C and above, indicating the strong effect of the eutectic liquid formation at ∼1587°C in silica‐alumina. The effectiveness of the established T‐T‐T curves was demonstrated and discussed.

Hydrothermal reaction of kaolinite in presence offluoride ions at pH < 10

Silica-rich zeolites were obtained by the reaction of kaolinite and metakaolinite in fluoride-containing medium at elevated temperature. These products have been compared to the corresponding products obtained in alkaline medium. Kaolinite gave zeolite P directly without any intermediate metastable phase, whereas zeolite NaX was the stable intermediate when metakaolinite was used as the starting material. The intermediates and products of the reactions were studied by using XRD, i.r., n.m.r., and SEM techniques. The crystals formed in fluoride medium were found to be quite large in size. However, seeding was essential and the degree of crystallization attained was low in the formation of zeolite NaX. A chabazite-type zeolite phase appeared in both systems after longer reaction times.

Flash calcination of kaolinite studied by DSC, TG and MAS NMR

The structural changes occurring during the dehydroxylation of kaolinite have been followed using flash calcination to produce kinetically frozen calcines. The percentage of dehydroxylation was varied by changing the furnace residence time or temperature and/or heating speed. These calcination conditions affected the reaction kinetics, but the products depended only on the extent of dehydroxylation.Changes in the position and enthalpy of the endothermic transformation to metakaolinite and the high temperature exothermic reaction of metakaolinite have been followed using Differential Scanning Calorimetry of the flash calcines and related to Thermogravimetry. 27Al magic-angle-spinning NMR spectra, at high magnetic fields and spin rates, enabled the reaction of kaolinite to be monitored and provides new information on the nature of the species formed in the course of dehydration.

Formation of Mullite from Sol‐Gel Mixtures and Kaolinite

Critical analyses of published reaction studies on kaolinite, and sol‐gel and powder mixtures equivalent to 3Al2O3·2SiO2 mullite, were made. Supplementary experiments on reactions of kaolinite at different rates of heating were analyzed. Complete atomic homogeneity of precursors results in formation of tetragonal mullite. Colloidal precursors initially form spinel which reacts with the remaining silica by a diffusion‐nucleation mechanism to form orthorhombic mullite. Precursors with intermediate atomic homogeneity follow both reaction paths. Kaolinite with a layer lattice structure has two‐dimensional atomic homogeneity. Both reaction routes are followed and their degree of interaction is dependent on the crystallinity and impurities of the kaolinite.