Synthesis Of Kaolinite Research Articles

Extraction of Lithium and Synthesis of Kaolinite from α‐Spodumene via Alkali Calcination

AbstractExtracting lithium from spodumene by sulfuric acid roasting is the largest commercialized way at present, which not only consumes a large amount of energy but also produces massive waste residue that will cause environmental problems. In this work, a new process for extracting lithium by directly decomposing α‐spodumene through alkali calcination is designed. The reaction of α‐spodumene with Na2CO3 at 750 °C for 2 h can decompose it and form nepheline and lithium silicate/sodium silicate. The nepheline and soluble lithium silicate/sodium silicate are separated by water leaching, and 93.9 % of lithium can be leached under optimal conditions. In addition, the synthesis of nano‐kaolinite is investigated with nitric acid solutions. Conversions of 98.7 % were obtained with 0.4 M nitric acid at 250 °C and an L/S ratio of 17.5 L/kg. The water leachate can precipitate Li2CO3 with a purity of 99.0 % by CO2 after desilicated by CaO. The final yields of Li2CO3 and kaolinite relative to the Li and Si content of the starting minerals are 91.4 % and 48.5 %, respectively. This new method achieves the full utilization of spodumene with lower energy consumption and demonstrates great potential for industrial applications.

Hydrothermal synthesis of nano-kaolinite from K-feldspar

Development of sustainable routes for the synthesis of kaolinite in nano-scale (nano-kaolinite) is very significant for producing high quality kaolinite of paper-coating grade in kaolin industry. Duplicating chemical weathering processes in nature, two routes were developed and compared for the synthesis of nano-kaolinite from K-feldspar. Kaolinite of uniform plate-like morphology with thickness of around 14 nm was obtained in this study. Both synthesis routes may lead to the comprehensive utilization of K-feldspar for the synthesis of pure kaolinite for not only high quality paper-coatings but also medical and other uses.

Oxygen Isotopic Fractionation in the Kaolinite-Water System during the Synthetic Process

Oxygen isotope fractionation is studied during the synthesis of kaolinite under controlled conditions of temperature and time. Equilibrium conditions have been established and its relationship with temperature has been studied. Kaolinite was hydrothermally precipitated starting from non-crystalline aluminosilicate gels. The amount of kaolinite obtained increases up to a limited constant value and in all cases coexists with the amorphous starting gels. It can be seen that the data obtained at 48 hours of synthesis can be considered as quasi-equilibrium, since the total isotopic equilibrium has not been reached, only the sample obtained at 24 hours should be discarded for studies in equilibrium. This would allow us, with the samples obtained at 720 hours, to try to establish a relationship between isotopic fractionation and temperature, provided that we know the water in equilibrium with the synthesized kaolinite. Two equations have been obtained that show correlation coefficients with a high statistical significance.

From Platy Kaolinite to Nanorolls

Kaolinite is one of the most important industrial clay minerals, with a worldwide consumption in the millions of tons per year and applications in a wide range of industrial areas. Traditionally, its most important use has been in the paper and ceramic industries. New, innovative techniques are being developed that are based on intercalation and grafting of kaolinite's unique dipolar layer structure. Such techniques are leading the way to the synthesis of kaolinite–polymer nanocomposites, including bionanocomposites that might have value-added properties benefiting industry and the health sciences.

Synthesis of kaolinite with dickite seed: A study by the experimental design method.:A STUDY BY THE EXPERIMENTAL DESIGN METHOD

Synthesis of kaolinite with dickite seed: A study by the experimental design method.:A STUDY BY THE EXPERIMENTAL DESIGN METHOD

Synthesis of Kaolinite from Powdered Volcanic Glass by Hydrothermal Reaction

Synthesis of Kaolinite from Powdered Volcanic Glass by Hydrothermal Reaction

Synthesis of Kaolinite

Synthesis of Kaolinite

Hydrothermal Synthesis of Kaolinite

Hydrothermal Synthesis of Kaolinite

Mechanochemically enhanced synthesis of isomorphously substituted kaolinites

A mechanochemical method for the rapid, bulk synthesis of kaolinite has been developed. Metal hydroxides and silicic acid are mechanically ground and hydrothermally treated for as little as a day at 250 °C to produce X-ray pure crystalline materials. This approach has been expanded to allow the synthesis of kaolinites with a portion of the aluminum sites isomorphously substituted with other trivalent metals. The synthetic parameters, such as length of mechanical and hydrothermal treatment, were studied. Products were analyzed by powder X-ray diffraction, attenuated total reflectance infrared spectrometry, scanning electron microscopy, and transmission electron microscopy. The samples exhibited strong order along the c axis and less order along the a and b axes. Trivalent transition and rare earth metals were used to replace aluminum in the structure. These metals included Cr, La, Ce, Pr, Nd, Eu, Gd, Ho, and Er. Cerium (III) substituted kaolinite was successfully synthesized utilizing air-free conditions. This approach allows bulk quantities of substituted kaolinites to be prepared in a relatively short amount of time and offers a new route to synthesize pure and substituted kaolinites that may have novel catalytic properties.

Hydrothermal Synthesis of Kaolinite and its Formation Mechanism

AbstractIn spite of many studies of kaolinite synthesis, questions remain as to the transformation of gel into kaolinite, the kinetics of the reaction, and the influence of solution chemistry. The purpose of the present study was to perform a hydrothermal synthesis in order to understand better the transformation from boehmite to kaolinite. Kaolinite was synthesized from amorphous SiO2 and Al(OH)3·xH2O at fixed temperature (250°C) and pressure (30 bar). The initial pH of the solution was 2. The reaction time for the synthesis was varied from 2 to 36 h. The physical properties of synthesized kaolinite were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), nuclear magnetic resonance (NMR) spectroscopy, field-emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy dispersive spectrometry (EDS).The early stage of kaolinite synthesis followed activation of amorphous Al(OH)3·xH2O to initiate the reactions, i.e. ionization and subsequent crystallization of boehmite. The boehmite reacted continuously with Si4+ dissolved in solution and gradually transformed to disordered, lath-shaped boehmite. In XRD and IR patterns, the typical peaks of boehmite were weakened or disappeared following the reaction.Structural transformation from boehmite to kaolinite occurred when the Al/Si ratio of the aluminosilicate was 1.0. The kaolinite formed was in the form of curved flakes and its crystallinity increased with reaction time. In the final stage of reaction the morphology of kaolinite changed from flaky to polygonal. The hexagonal, platy kaolinite was therefore developed to allow the gradual variation of the chemical composition, crystal structure, and morphology.

Synthesis of kaolinite from micas and K-depleted micas

AbstractThe weathering stages of K-depleted biotite, K-depleted phlogopite, and natural biotite were investigated using hydrothermal treatment with A1C13 solution at 200°C for 12 to 72 h. Although there were some differences in the degree of weathering of the two K-depleted micas, both first transformed to hydroxy-Al interlayered vermiculite (HIV), which then altered to kaolinite. In case of the natural biotite, the biotite first transformed to a K-depleted mica-like phase, which then altered to kaolinite. The natural biotite had resisted weathering to kaolinite more than did the K-depleted biotite, as expected. The K-depleted phlogopite had less resistance in weathering to kaolinite than the K-depleted biotite. The transformation process changed the color of the micas. The K-depleted biotite changed from greenish-black through yellow to pale gray whereas the natural biotite changed from greenish-black through beige to yellow. However, in the case of K-depleted phlogopite, there was no significant color change during the transformation process. The presence of the interlayer K+ ions and the structural Fe2+ ions in mica appear to have contributed to the differences in the degree of weathering to kaolinite among the micas investigated.

Synthesis of Kaolinite with a High Level of Fe3+ for Al Substitution

AbstractFe-rich kaolinites were synthesized at 225°C in distilled water from gels with different Fe/Al ratios (0.15, 0.25, 0.35) and with Si/(Al + Fe) = 2. X-ray diffraction patterns of the reaction products showed that kaolinite was the only long-range crystalline phase synthesized. Analytical electron microscopy analyses of individual particles and Fourier transform infrared spectra indicated that Fe3+ was isomorphously incorporated into the kaolinite octahedral sheet and that tetrahedral substitution did not occur. The Fe content hosted in the synthetic kaolinites was similar to that incorporated into its corresponding starting gel. The highest Fe content in the particles reached 30 mol.% of the octahedral occupancy. Increases in the b parameter are proportional to increases in Fe for Al substitution. The extent of isomorphic substitution of Al by Fe is the highest ever reported for both natural and synthetic samples. At the nano-scale, there is no evidence of discontinuity in the solid-solution between the Si2Al2O7 and Si2Al1.4Fe0.6O7 end-members, such as short-range disorder or clustering of Fe and Al in domains.

In situ transformation of amorphous gels into spherical aggregates of kaolinite: A HRTEM study

AbstractInitial stages of the gel-to-kaolinite transformation were studied using HRTEM. Spherical aggregates of kaolinite crystals were produced during the synthesis of kaolinite by hydrothermal treatment of Si-Al amorphous gels. Prior to sphere formation, gels transform into pseudospherical domains that have a Si/Al ratio of one and display no SAED pattern. The spherical particles consist of radially arranged sectors of stacks of planar crystallites. Crystals display nonbasal spacings of 4.5, 4.2 and 3.8 Å and a basal spacing of 7.1 Å , the c* axis following the radius of the sphere.Interpretation of the 3D nanostructure of the spheres is difficult. The c* axis exhibits a radial disposition, but the relative orientation of the a* and b* axes in neighbouring crystallites may produce bent layers or incoherent contacts. In addition, curved layers with a d spacing of 7.4 Å may be attributed to halloysite layers collapsed under microscopy conditions. The disappearance of the spheres during the hydrothermal treatment is probably due to preferential dissolution of either highstress areas near bent layers or non-crystalline material filling crystal boundaries. Dissolution leads to sphere disaggregation and allows the component columnar crystals to continue to grow. Observations of the gel matrix suggest that under our experimental conditions kaolinite crystallizes via an in situ transformation of the gel.

Effects of oxalic acid addition on the hydrothermal synthesis of kaolinite

Kaolinite was hydrothermally synthesized from alumina gel and silicate by dissolving alumina gel in oxalic acid before it was mixed with silicate, effects of the amount of addition on the species of synthetic products were discussed. The reaction product was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that analcite is the only phase of the reaction solution without oxalic acid, the proportion of kaolinite in product increases with the amount of addition, and kaolinite is the main species when the molar ratio of oxalic acid to alumina reaches 0.6:1.0. This is because oxalic acid addition is beneficial to the formation of kaolinite through changing the coordination number of aluminium from four to six, while the mixture of alumina gel, before it was dissolved in oxalic acid with silicate interfered with the crystallization of kaolinite.

Synthesis of kaolinite under saturated steam at 220°C

Synthesis of kaolinite under saturated steam at 220°C

Effects of Temperature and pH on the Kaolinite Crystallinity

Kaolinite is common in weathering area. Crystallochemical characteristics of these natural occurring minerals have been widely studied by all current characterization methods and specially by X-ray diffraction and infrared spectrometry (e.g. Brindley et al., 1986; Ambrosi and Nahon, 1986). However, our knowledge of the actual influence of the different conditions of kaolinite formation on its characteristics is only partial. In order to estimate these effects we realized an experimental study. Particularly, we determined the influence of synthesis temperature and pH on the crystallinity of kaolinite. Considering the kinetic slowness of kaolinite synthesis at low temperature (Espiau and Pedro, 1984), we used hydrothermal conditions to optimize the rate formation of kaolinite. Moreover, it appeared interesting to use as starting material a synthesized product including already a noticeable amount of synthesized kaolinite with a medium crystallinity to show up the possible transformation of this initial kaolinite.

Effects of Acidity on the Hydrothermal Synthesis of Kaolinite from Silica-Gel and Gibbsite

AbstractA comparative study is reported in which kaolinite has been hydrothermally synthesized at several pH conditions. The syntheses were carried out at 220 °C for 3 to 10 d with distilled water or acidic solutions using a mixture of silica-gel derived from alkoxide and gibbsite with a Si/Al ratio of 1:1 as the starting material. Use of acidic solution for the synthesis promotes the dissolution of the starting materials and leads to kaolinitization at an earlier stage of the reaction. However, the rate of kaolinitization is found to be rather slow, in comparison to the reaction with distilled water. The synthetic kaolinite was characterized by X-ray powder diffraction pattern. Kaolinite synthesized with distilled water was poorly grown for direction of the stacking. For example, crystallite size along the c*-axis = 155 Å, whereas kaolinite synthesized with acidic solution gave a higher crystallite size along the c*-axis, such as 253 Å in the case of the synthesis with 0.1 N HCl. Hinckley index of the synthetic kaolinite was varied from 0.35 to 0.80 by the acidity of the reaction. Different kaolinitization processes are implied by differences observed in the rate of kaolinitization, which has an influence on the nature of the stacking faults of the kaolinite.

Effect of grinding of the starting material on hydrothermal synthesis of kaolinite.

It has been found that initial grinding of starting materials is effective in promoting reactivity in the synthesis of kaolinite. A mixture of amorphous silica and aluminum hydroxide with a Si/Al atomic ratio of 1.0 was ground and then used as the starting material for hydrothermal synthesis. The starting material was placed in a Teflon reaction vessel together with distilled water, and kept at 220°C. The characterization of the starting materials and products was carried out with XRD, IR, DTA-TG, 29 Si- and 27 Al-MAS/NMR, and TEM. The starting material which had been ground for 200h was an amorphous aluminosilicate with four- and six-coordinated Al. Kaolinite could be obtained from this well-ground starting material in a relatively short reaction time in comparison to mixtures not subjected to the pre-grinding process. In the latter case, bayerite was changed into bohmite, and was then converted to well crystallized kaolinite with euhedral morphology of the hexagonal plate. The differences in the local structures of the starting material around the Si, Al atoms, and OH groups, which had been brought about by the mechanochemical reaction during the grinding, are likely to have an influence on formation of kaolinite.

Hydrothermal Synthesis of Kaolinite from Water Quenched Blast Furnace Slag

Hydrothermal Synthesis of Kaolinite from Water Quenched Blast Furnace Slag

Effects of the Structure of Silica-Alumina Gel on the Hydrothermal Synthesis of Kaolinite

AbstractKaolinite was hydrothermally synthesized from two kinds of silica-alumina gels to examine the effect of the structure of the starting material. Two kinds of gels were prepared by precipitation at different pH conditions (pH = 9.6 and 4.2) from solutions containing water glass and aluminum sulfate. Na ions in the gels were removed with a resin before the hydrothermal treatment, but a slight amount of sulfate ions was still present in the gels. The nuclear magnetic resonance spectra of the starting gels suggested that the gel prepared at pH 9.6 consists of networks with alternating SiO4- and A1O4-tetrahedra (partially AlO6-octahedra), whereas the gel prepared at pH 4.2 consists of a sheet structure related to allophane. After the hydrothermal treatment at 220°C for 9 days, kaolinite particles with spherical shape were obtained from the former gel, and platy kaolinite was crystallized from the latter one. The difference in morphology of synthetic kaolinite was attributable to the structures of the starting gels, and the pH values in the hydrothermal reactions were not very significant to the morphology.