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1.
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.  相似文献   

2.
The crystal structure of two kaolinites with a different degree of planar disorder and their high temperature (HT) decomposition products have been investigated by means of symmetrical transmission powder X-ray diffractometry and the subsequent calculation of the radial distribution function (RDF). An ordered and a disordered kaolinite (international standard Kga-1 and Kga-2) were selected along with their HT reaction products at 600°C (metakaolinite) and at 900°C (mullite precursor). The calcinations and quenches have been carried out “ex-situ” prior to the data collection. The procedure for collection and reduction of the data and their interpretation is outlined. The structural characterization of the HT phase transformations is obtained by qualitative analysis of the RDF curves and is related to the extent of planar disorder in the original material. A model for the structure of metakaolinite is proposed on the basis of the present experiments, and of a review of literature data. According to this model, the structure of metakaolinite displays an almost uncollapsed structure with a short-range order in which Al is mainly in four-fold coordination. An “ab initio” modelling of the RDF curves provides a quantitative evaluation of the proposed structural model. Differences in the HT products from different kaolinites are directly correlated with the density of stacking faults in the starting kaolinites. Moreover the structure of the precursor of mullite is described and discussed with respect to the literature data. The nature and role of γ-alumina is discussed as well. Finally the DTA exothermic peak of kaolinite is interpreted in the light of the proposed general model. Received: 18 March 1997 / Revised, accepted: 26 October 1997  相似文献   

3.
 The kinetics and mechanism of hydrothermal formation of zeolite A from natural kaolinites have been studied using as starting materials two international kaolinite standards (KGa-1 and KGa-2 from Georgia, USA) exhibiting a different degree of stacking disorder. Precursors utilized for the synthesis were prepared by heating the kaolinites at 800 °C. Metakaolinite was also prepared from KGa-1 by thermal activation at 600 °C. The hydrothermal syntheses were accomplished by heating the samples in NaOH solutions at temperatures between 70 and 110 °C. The kinetic experiments were performed by time-resolved synchrotron powder diffraction in isothermal mode using a transmission geometry and an Image Plate detector. The results of the kinetic analysis are interpreted in the light of the structural state of the starting kaolinite, and of the temperature of activation of the precursor material. For kaolinite activated at high temperature the nucleation and crystallization of zeolite A is essentially independent of the defect density of the original kaolinite, and the thermal history of the precursor seems to be the main controlling parameter. The formation process of zeolite A from metakaolinite materials obtained at lower activation temperatures shows significantly faster reaction rates and lower apparent activation energies. This is again interpreted in the light of the short range inhomogeneities present in metakaolinite. As the reaction proceeds metastable zeolite A transforms into hydroxy-sodalite. Received April 18, 1996 / Revised, accepted September 27, 1996  相似文献   

4.
Summary The hydrothermal synthesis of kaolinite from various alumina and silica starting materials reacted at 200°C in aqueous solutions of oxalic acid and H2SO4 with the corresponding saturated water vapour pressure, in periods of time from 10 to 25 days, has been followed by X-ray diffraction measurements, scanning electron microscopy, and energy dispersive analysis of the products. The temperature and time periods of reactions were chosen on the basis of previously collected data on the effects of H4EDTA, a complex-forming agent, and of H2SO4, an inorganic acid, on the rate of formation of kaolinite. Aluminium-complexing acids increase the rate of formation or decrease the temperature of formation of kaolinite as shown by evidence from X-ray diffraction patterns. The influence of the starting materials as sources of aluminum, amorphous aluminum hydroxides, pseudoboehmite, allophane or gibbsite, has also been examined by X-ray diffraction, scanning electron microscopy, and by energy dispersive analysis. Scanning electron micrographs indicated that silica is a more mobile phase than alumina, based on the progressive formation of a thin coating on gibbsite during early reaction, then by growth of clusters of platy crystals of kaolin, and finally by production of pellets of stacked crystal flakes. Where gibbsite was used in the reaction mixture, boehmite was commonly observed as an intermediate phase.With 16 Figures  相似文献   

5.
Degradation of coke in the blast furnace is influenced by its inherent mineral matter, the formation of which is itself dependent upon the nature of the coal mineral matter. To date few studies have been made of coke mineralogy and its relationship to the mineralogy of the parent coal. In this study the effect of carbonisation on coal mineral matter has been investigated by a detailed quantitative mineralogical examination of nine cokes and their parent coals. The quantitative analysis was performed on X-ray diffraction patterns of the mineral matter of cokes and coals, using SIROQUANT™. Coke mineralogy and its composition varied strongly between cokes, more strongly than variations in elemental composition of the ash. The mineral matter in the studied cokes consisted of crystalline mineral phases and also significant levels of amorphous phase (ranging between 44 and 75%). Decomposition of clays such as kaolinite, montmorillonite, illite and chamosite produced the amorphous phase and some of the crystalline mineral phases such as mullite, γ-alumina, spinel, cristobalite and leucite. The type of association of mineral matter in coals had an important role in how the clays decomposed. For example, association of kaolinite with silica-bearing minerals in intimate intermixture favoured formation of mullite over γ-alumina. Akermanite and diopside result from reaction of kaolinite with associated calcium bearing minerals (calcite, dolomite or ankerite). Quartz, fluorapatite and the three polymorphs of TiO2 (anatase, brookite and rutile) were the coal minerals that were least affected during carbonisation, as they were also found in the cokes, yet even they were affected in some cases.  相似文献   

6.
高岭石形成赛隆过程相变初探   总被引：5，自引：0，他引：5  
本文对比了高岭石热分解及经碳热还原氮化作用制备赛隆过程中的相变情况，我们发现高岭石在这两种过程中发生的相变并不尽相同，加热高岭石最终形成莫来石和方石英过程中的相变，在其经碳热还原氮化作用制备赛隆的过程中是否出现，取决于温度、时间、Ｃ／Ｓｉ原子比、Ｎ２流量等实验条件，后者因受众多实验因素的影响，其相变过程远较前者复杂。因此，笔者认为这两种过程中相变是相同的观点有进一步探讨的必要。  相似文献   

7.
 The kinetics of the dehydroxylation of chrysotile was followed in situ at high temperature using real-time conventional and synchrotron powder diffraction (XRPD). This is the first time kinetics parameters have been calculated for the dehydroxylation of chrysotile. The value of the order of the reaction mechanism calculated using the Avrami model indicates that the rate-limiting step of the reaction is a one-dimensional diffusion with an instantaneous nucleation or a deceleratory rate of nucleation of the reaction product. Hence, the rate-limiting step is the one-dimensional diffusion of the water molecules formed in the interlayer region by direct condensation of two hydrogen atoms and an oxygen atom. The calculated apparent activation energy of the reaction in the temperature range 620–750 °C is 184 kJ mol−1. The diffusion path is along the axis of the fibrils forming the fibers. The amorphous or short-range ordered dehydroxylate of chrysotile is extremely unstable because forsterite readily nucleates in the Mg-rich regions. Moreover, it is less stable than the dehydroxylate of kaolinite, the so-called metakaolinite, which forms mullite at about 950 °C. This difference is interpreted in terms of the different nature of the two ions Mg2+ and Al3+ and their function as glass modifier and glass-forming ion, respectively. Received: 10 April 2002 / Accepted: 7 January 2003 Acknowledgements This work is part of a COFIN project (04 Scienze della Terra, NR 17, 2000) supported by MURST. Dr Dapiaggi is kindly acknowledged for help during the data collection at the Dipartimento di Scienze della Terra, University of Milan.  相似文献   

8.
运用NETZSCH STA 409PC同步热分析仪针对新疆克拉玛依油田红浅扩大试验区中的稠油样品在氧化过程中高岭石的影响,分析测试。研究结果表明,高岭石的加入影响了稠油的低温及高温氧化反应,使稠油的低温氧化DTA峰值温度从437.6℃增加为455.4℃;高温氧化DTA峰面积显著减小,峰值从607.8℃减小为597.8℃;高岭石含量的增加,有利于降低稠油的低温,高温氧化的DTA峰值温度。随着升温速率的增加,混合样品中稠油的低温,高温氧化及高岭石脱羟基反应呈现为动力学过程。研究结果有助于深入认识原油的氧化过程,对提高采收率和推动稠油油藏的有效开发具有重要的意义。  相似文献   

9.
In this paper, an experimental study was conducted in order to test the feasibility of sintering mullite directly from the high-alumina fly ash, without adding any extra material. The results show that the mullite contents in most sintered samples are over 70%. The samples sintered from the beneficiated fly ash have a higher content of mullite than those from the as-received fly ash under the same synthetic conditions. To obtain an equal amount of mullite, a higher sintering temperature is needed for the beneficiated fly ash than for the as-received fly ash. Considering the physical properties of sintered mullite, the favorable sintering temperature is 1400℃ for the as-received fly ash and 1500℃ for the beneficiated fly ash. A higher sintering temperature and a shorter holding time are profitable to sintering mullite. The orthogonal test confirmed that the dominant factor affecting mullite synthesis is sintering temperature, and that the most profitable matching conditions are 200 MPa-1500℃-3 h for the as-received fly ash and 200 MPa-1500 ℃-4 h for the beneficiated fly ash.  相似文献   

10.
高岭石与碱剂作用后反应液中硅铝元素变化规律研究   总被引：1，自引：2，他引：1  
陈忠  沈明道 《矿物岩石》1997,17(3):53-58
本文系统地研究了高岭石与碱剂间的作用对反应后的液相参数进行全面测定，以查清温度，反应时间，碱性驱替剂的种类浓度等因素与液相参数和固相参数的关系。提出高岭石的非一致性溶蚀趋势，并探讨高岭石与碱性驱替剂的作用机理，丰富了化学驱油过程中化学剂与矿物作用方面的基础理论。  相似文献   

11.
27Al,29Si MAS NMR studies of kaolinite and its thermal transformation products show that in the kaolinite-mullite reaction series there is an extensive segregation of Al2O3 and SiO2 and the reaction of Al2O3 with SiO2 to form mullite is the main path of mullite formation. At about 850° C, the peak intensity of A1(V) reaches its maximum and with the further rise of temperature the A1(V) signal completely disappears. At about 950°C, γ-Al2O3 accounts for about 71% of the material phases containing Al atoms. In the series there is no obvious presence of Al-Si spinel. The27Al and29Si MAS NMR spectra show that there is an obvious difference between the temperature points for Al-O2(OH)4 octahedral sheet collapsing and Si-O4 tetrahedral sheet breaking down.  相似文献   

12.
Experimental investigation was made on hydrothermal alteration of sericite in acid solution. It is found that the sericite is changed to pyrophyllite through kaolinite at 270° C and 260° C, and the alteration is considered to be a consecutive reaction involving two steps, from sericite to kaolinite and from kaolinite to pyrophyllite. On the other hand, pyrophyllite is not formed at 190° C and the sericite is altered to kaolinite. The rate of reaction in each step of this hydrothermal alteration is dependent on reaction temperature and chemical composition of the solution. From the results of the quantitative analyses of the experimental products, kinetic constants and related parameters were obtained.By using these numerical values, an alteration process can be followed in a given model. Computed results for some cases of an alteration of sericite in acid solution are presented. Geological phenomena such as rock alteration or weathering are thought to progress in a disequilibrium state and in an open system. An attempt described in this paper is a physicochemical approach to treat an alteration process accompanied with material transfer occurring in an open system from a kientic viewpoint.  相似文献   

13.
A mass transfer model of bauxite formation   总被引：1，自引：0，他引：1  
The formation of bauxite due to weathering of a granitic protolith has been simulated by means of a one-dimensional flow and reaction model based on the mass transfer principle. The model couples mineral dissolution and precipitation reactions, speciation in solution, and advective solute transport in a porous medium. A very important aspect of the modeling study is the use of mineral reaction rates determined experimentally in the laboratory. The important effects of solution saturation state and pH have been incorporated into the kinetic rate laws governing the heterogeneous reactions. The values of these parameters have been obtained from the scientific literature to guarantee that realistic reaction rates are used in the simulations. Albite and quartz are the minerals that make up the parent rock in the model. Gibbsite, kaolinite, and a Na-mica (as a surrogate for smectite) are the secondary minerals that have been taken into account. Long-term simulations (>1 Ma) have been run, and the formation of a bauxitic profile, with an upper gibbsite-rich and a lower kaolinite-rich zone, is predicted. In early stages of the process (up to a few hundreds of thousands of years), both gibbsite and kaolinite precipitate directly from solution as a consequence of albite dissolution. In later stages, the bulk of gibbsite precipitation derives from the incongruent dissolution of kaolinite, while kaolinite precipitation is still caused by the dissolution of albite. This is also reflected by the formation of two reaction fronts in the profile. These results are compared with weathering sequences from the Los Pijiguaos bauxite deposit, Venezuela. The overlap between the gibbsite and kaolinite zones and the replacement of kaolinite by gibbsite are consistent with model calculations. Mechanical denudation has to be called upon to explain the limited thicknesses of the weathering profiles in the field. The role of mechanical erosion is supported by the presence of microsedimentary structures in the bauxite and the balance between dissolved and suspended loads in the streams draining the area.  相似文献   

14.
鄂尔多斯盆地东部太原组砂岩骨架颗粒中几乎没有碎屑长石,残余的微量长石(在岩石中的平均含量为0.4%.低于X射线衍射检测限)主要为钾长石,同时具有较低的自生高岭石含量(1.02%)、很低的自生石英含量和同期火山物质含量,以及较高的自生伊利石含量(1.22%),这表明太原组的自生伊利石主要是在相对高温的深埋藏封闭条件下,通过钾长石溶解反应:钾长石+H~++H_2O→高岭石+硅质+K~+和高岭石伊利石化反应:高岭石+K~+→伊利石+H~++H_2O或其加和反应:钾长石+高岭石→硅质+伊利石+H_2O形成,后者通过消耗钾离子而克服钾长石溶解的动力学屏障,是前者的重要驱动反应,并向流体输出氢离子,因此对次生孔隙的形成、尤其是在相对深埋藏的成岩过程中与钾长石溶解有关的次生孔隙的形成具有显著的积极作用.  相似文献   

15.
Recovery of highly viscous oil from some of the deeper oil sand deposits of northern Alberta, Canada, is made possible through injection of heat by steam or hot water flooding of the reservoirs. The rise in temperature lowers the viscosity of the bitumen allowing it to be produced. The increase in temperature accelerates the reactions between the matrix and pore minerals of the formation and can produce reaction products which can significantly alter the permeability of the reservoir. If carbonate minerals are present in the reservoir, inorganic CO2 may also be a reaction product.

The Grand Rapids reservoir consists of relatively clean quartz sand containing 7 wt.% kaolinite, 1 wt.% calcite and a trace of smectite. Core floods of this sand by a neutral NaCl brine at 265°C, 8.2-MPa overburden pressure, 6.0-MPa fluid pressure and a flow velocity of 0.4 pore volumes per hour were used to determine the potential for hydrothermal reactions between clays and carbonate minerals in a natural reservoir sand. Reaction progress was followed by continuous sampling of the production fluids. The produced water was analyzed and the phase chemistry was calculated back to the run conditions using the computer code SOLMNEQF.

Mass-balance considerations on produced total inorganic carbon (TIC) show that calcite broke down very quickly, the maximum in CO2 production occurring after only one pore volume of fluid had passed through the core. The Ca released from the breakdown of calcite was incorporated in the formation of smectite as was shown by post-run clay mineral analysis by the following unbalanced chemical reaction:

calcite+kaolinite+H4Si04Ca-smectite+H20+CO2

Silica was supplied by the dissolution of quartz. Silica concentrations analyzed in the production fluid were depressed from those predicted by previously published quartz rate equations because of the rapid rate of smectite synthesis.

These observations were used to formulate the following model for the passage of the first pore volume of NaCl brine through the core. Initially calcite is present throughout the core. As the brine enters the inlet of the core, it equilibrates with calcite. The brine remains in equilibrium with calcite throughout the core as quartz and kaolinite react to form smectite. This model was tested with the computer code PATH.UBC using CO2 production as a measure of the progress variable ξ. A best fit was achieved to the produced fluid chemistry by varying relative dissolution rates of kaolinite and quatz and varying the suppression of precipitation of certain minerals.  相似文献   


16.
粘土矿物碱耗协同效应研究   总被引：4，自引：0，他引：4  
陈忠  高晓勇 《岩石学报》2000,16(3):459-464
选择蒙脱石,高岭石,伊利石等三种在储层中最党风的储层粘土矿物,两两分别按２Ｌ：０,１：１,０：２质量配比组成复配物系列;在３０℃、５０℃温度下按１：５,１：８,１：１０（ｇ／ｍｌ）固／液比分别与１．６％的Ｎａ２ＣＯ３深液反应８ｈ,３６０ｈ;监测反应前后碱液浓度的变化;计算了各条件下各自的绝对碱耗量。结果表明三种粘土矿物中蒙脱石耗碱最大,高蛉石的耗碱量与伊利石的接近;随着固／液比减小和温度升高,矿物  相似文献   

17.
The present work investigated the adsorption and mobility (desorption) of Sb(V) on kaolinite using batch experiments. The adsorption of Sb(V) on kaolinite was studied as a function of contact time, pH, ionic strength, humic acid (HA), initial Sb(V) concentration and temperature. Kinetic studies suggest that the equilibrium is achieved within 24 h. The adsorption of Sb(V) was strongly affected by changes in I at low ionic strength and unaffected at high ionic strength. The adsorption is weakly dependent on the presence of humic acid, but is strongly dependent on pH. Within the range tested, the optimal pH for Sb(V) adsorption is 3.6, and close to 75% removal can be achieved. Desorption is dependent on the original suspension pH. The addition sequence of Sb(V)/HA do not influence the adsorption of Sb(V) on kaolinite. The adsorption data fit both the Freundlich and Langmuir isotherm. The thermodynamic parameters (ΔH 0, ΔS 0 and ΔG 0) were calculated from the temperature dependence, and the results suggest the endothermic and spontaneous nature of the process.  相似文献   

18.
Thermal transformations of kaolinite of different degree of crystallinity have been monitored by 27Al and 29Si high-resolution NMR with magic-angle spinning (MAS NMR), X-ray diffraction, Fourier transform infrared, atomic absorption spectrophotometry and thermogravimetric analysis. NMR shows differences in the dehydroxylation process of kaolinites with different degree of crystallinity and reveals the presence of short-range order in metakaolinite. 29Si NMR spectra acquired with a 30 s recycle delay of poorly and highly crystalline samples heated at 480 and 500° C, respectively, contain three distinct signals; we discuss their assignment in the light of experiments involving leaching of the samples with aqueous KOH. Ca. 40% of Si sites retain their original Q 3 symmetry just above the onset of dehydroxylation and the Q 4 environment is present showing that a small amount of amorphous silica has already segregated. The spectrum of samples treated at 1000° C contains a signal at -110ppm (from Q 4 silicons) and a faint resonance, from mullite, at ca. -87 ppm. 29Si NMR also shows that cristobalite germs are already present at 950–1000° C. The 27Al MAS NMR spectra of metakaolinite reveal the presence of 4-, 5-and 6-coordinated Al. Changes in the three Al populations as a function of temperature have been monitored quantitatively. Below 800° C, 4-and 5-coordinated Al appears at the expense of 6-coordinated Al, but above 800° C the amount of 6-coordinated Al increases again. We suggest a dehydroxylation scheme which accounts for the presence of 4-and 5 coordinated Al. Above 900–950° C the latter signal is no longer present in the 27Al NMR spectra and new 4-and 6-coordinated Al species (mullite and γ-alumina) appear. We propose new ideas for the structure of metakaolinite.  相似文献   

19.
Conclusions In studying the degree of order (or disorder) in kaolinite, X-ray diffraction and DTA are commonly used, but spectroscopic method (as EPR, IR)has become a useful and additional tool now. The total iron content and the intensity of Fe3+(I) line are not always correlated negatively with order degree in natural kaolinite. But in the present case, they show direct correlations. So it appears that they cannot be used as an ideal parameter for measuring the order degree in kaolinite. The ratio of Fe3+(E)line and Fe3+(I)line intensities obtained directly from EPR spectrum of Fe3+at geff=4 appears to be a better EPR parameter for measuring the magnitude of order degree in kaolinite and for determining the intensity of some geological processes (such as weathering, hydrothermal alteration and so on) with aid of kaolinite. However, EPR data can only be used to qualitatively estimate the degree of order in kaolinite and related geological process for the present. There is still much work to be done in order to make EPR a method of quantitative estimation in the field.  相似文献   

20.
晋北罕见的“烧变高岭岩”研究   总被引：2，自引：0，他引：2  
晋北大同及浑源一带,在上石炭世太原统四号煤系中,常见有洁白色的粘土岩,外貌酷似“人工熟料”,其成因与煤层的自燃作用有关。由于原岩主要矿物为高岭石故命名这种洁白色的粘土岩为“烧变高岭岩”。  相似文献   

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