Crystal Structure Of Kaolinite Research Articles

Influence of coal-measure kaolinite with different types on the preparation of kaolinite nanotube

Coal-measure kaolinite with different types were selected to explore the influence of raw mineral on the preparation of intercalation compounds and kaolinite nanotubes. Types of coal-measure kaolinite were feldspar-pseudomorph kaolinite (HSS), worm-like kaolinite (XY), brain striatum kaolinite (CBM), mica-pseudomorph kaolinite (CBM) and crypto crystalline kaolinite (HW and HY), respectively. And the average crystal size of coal-measure kaolinite after grinding of HSS, XY, CBM, HW and HY were 2.60 μm, 6.81 μm, 3.28 μm, 0.52 μm and 0.32 μm, respectively. Characterization methods of XRD, FTIR and SEM were utilized to reveal the change in the crystal structure of kaolinite before and after intercalation reactions, the vibrational pattern of the chemical bond and the surface morphology characteristics of raw minerals and kaolinite nanotubes. Results showed that intercalation effects were significantly different among the selected coal-measure kaolinite, and the intercalation rates of intercalation compound of HSS-KD, XY-KD, CBM-KD, HW-KD and HY-KD were 80.71%, 83.33%, 82.99%, 55.13% and 65.23%, respectively. That is to say, Intercalation rates of feldspar-pseudomorph kaolinite, worm-like kaolinite, brain striatum kaolinite and mica-pseudomorph kaolinite were significantly higher than those of crypto crystalline coal-measure kaolinite which were reflected from intercalation compound of coal-measure kaolinite/dimethyl sulfoxide. Furthermore, the intercalation rates of the precursor intercalation compounds affect the intercalation effect of macromolecular intercalation agents and the yield of kaolinite nanotubes. According to the SEM patterns of kaolinite nanotubes, yield of kaolinite nanotube of HSS, XY, CBM, HW and HY were 80%, 88%, 72%, 28% and 35%, respectively. It could be concluded that yield of kaolinite nanotube of coarse crystalline coal-measure kaolinite was higher than that of crypto crystalline coal-measure kaolinite.

Study on the crystal structure using the powder method for XRD refinement and the hydration state of halloysite

Halloysite is an intelligent nano-mineral material available in abundance and at a low price. However, due to the poor crystallization performance, the current data on the crystal structure of halloysite are insufficient. This paper will compare and analyze the crystal structure of halloysite and kaolinite in the kaolin subgroup. Using the x-ray powder diffraction data, the crystal structure of halloysite is refined by Rietveld’s least square full spectrum fitting method. Compared with the crystal structure of kaolinite, the crystal structure of halloysite contains a small amount of interlayer water molecules. Through structural refinement verification, each unit cell contains 0.121 interlayer water molecules, and the water molecules are at the center of the interlayer area corresponding to the hexagonal ring of the tetrahedron layer.

Rare earth ion-adsorption clays in the presence of iron at basic pH: Adsorption mechanism and extraction method

The uptake mechanism and influence of iron (Fe) co-adsorption on the binding of rare-earth elements (REEs) on kaolinite have been investigated. REEs and varying concentrations of Fe were co-adsorbed onto kaolinite at pH 10.5. Inductively coupled plasma mass spectrometry (ICP-MS), powder X-ray diffraction (PXRD), and X-ray photoelectron spectroscopy (XPS) were used to characterize how Fe co-adsorption influenced the uptake mechanism of REEs on kaolinite. Elemental analysis by ICP-MS revealed that the REE concentrations on kaolinite were unaffected by the presence of Fe. Crystal structure of kaolinite, determined by PXRD, was not altered after REE and Fe co-adsorption. XPS suggests that the adsorbed Fe is in the form of FeOOH, while the greatly attenuated REE XPS signals upon Fe co-adsorption implies that REEs are encapsulated by Fe species. Based on these results, we conclude that FeOOH layers were formed on top of REEs on the surface of kaolinite. Synthesized REE-Fe-kaolinite samples respond poorly to ion-exchange leaching, indicating that Fe is detrimental to the REE ion-exchange efficiency. The inhibition of ion-exchange REE extraction appears to be due to the passivating FeOOH layers. In contrast to ion-exchange methods, reductive leaching was found to dissolve the FeOOH passivating layers and liberate REEs such that they became available for ion-exchange leaching.

Study on modes of occurrence and enhanced leaching of critical metals (lithium, niobium, and rare earth elements) in coal gangue

This paper first studied the occurrence modes of critical metals (lithium: Li, niobium: Nb, and rare earth elements: REY) in coal gangue (CG) by sequential chemical extraction, and the distribution and enrichment degree of critical metals in different density and size fractions were also studied, and then CG was pretreated with intercalation and calcination to strengthen the extraction of critical metals. The results of sequential chemical extraction showed that the residual fraction was the dominant occurrence mode of critical metals. The enrichment ratios of different density fractions were 0.57–1.23 for Li, 0.03–1.34 for Nb, 0.69–1.36 for REY, and different size fractions were 0.89–1.23 for Li, 0.46–2.21 for Nb, 0.63–1.17 for REY. Density separation and particle size classification can be used to enrich critical metals. Direct leaching of 3 M hydrochloric acid resulted in 5.76% Li and 0.74% Nb recovery. Further, the leaching efficiency of Li was improved to 17.83% using pretreatment of intercalation, and the crystal structure of kaolinite was retained in the leaching residue. In comparison, calcination pretreatment led to 92.74% Li recovery, while the leaching efficiencies of Al and Fe were correspondingly improved. This paper can provide a theoretical foundation and technological support for the extraction of critical metals from CG.

Adsorption of different valence metal cations on kaolinite: Results from experiments and molecular dynamics simulations

The hydration and ion adsorption of kaolinite, which is the most common clay mineral, play crucial roles in engineering geology and environmental applications. To investigate the effects of different valence metal cation solutions on the hydration of kaolinite, we used microcalorimetry, quartz crystal microbalance with dissipation monitoring (QCM-D) and molecular dynamics (MD) simulations to measure the hydration heat and adsorption behaviors between kaolinite and different concentrations of NaCl, MgCl2, and AlCl3 solutions. Based on the results obtained from microcalorimetry, the heat generated by the mixing of kaolinite with different ionic solutions increases with increasing metal cation valence and ion concentration. The QCM-D shows that the increase in the ion concentration leads to an increase in the adsorption volume of metal ions on the kaolinite surface. The adsorption priority of the metal ions on the kaolinite surface can be ranked as Al3+ > Mg2+ > Na+. The results of MD simulations show that the ability of hydrated ions to destroy the hydrated films on the kaolinite surface increases with the increase of the metal cation valence, while a new thicker and more dilute ion hydration structure can be easily formed. The adsorption of ions on the kaolinite surface is controlled by the crystal structure of kaolinite.

Characterization of structure of kaolinite in tectonically deformed coal: evidence of mechanochemistry

ABSTRACT Coal and gas outbursts are one of the most serious disasters in coal mines and are closely related to the distribution of tectonically deformed coal. To explore the environment of formation and the mechanochemical genetics of tectonically deformed coal and investigate the influence of tectonic stress on the crystal structure parameters of kaolinite in coal, this paper identifies whether the occurrence of the advanced evolutionary phenomenon of tectonically deformed coal is dominated by thermal metamorphic temperatures or mechanochemical stress. Three pairs of unaltered coal and tectonically deformed coal samples were collected from three different coal seams at the No. 8 coal mine in Ping Dingshan Henan Province in China. After low-temperature ashing treatment, SEM, XRD and FTIR were used to characterize the kaolinite crystal morphology, crystallinity parameter (Hinckley index, HI), structural defects, and other characteristics. The results show that compared with the unaltered coal, the crystal morphology of kaolinite in tectonically deformed coal is more disordered, the crystal plane spacings, d(020), d(1–10), and d(11–1), increase, the crystallinity parameter HI decrease from 1.018, 1.104, 1.001 (more than 1, ordered) to 0.882, 0.784, 0.978 (less than 1, disordered), and the strength of the characteristic absorption band decreases, the differences in morphology and structural defects are mainly caused by the destruction of bonds, such as -OH, Al-O-Si, Al-O-Al, and Si-O-Si. Tectonic stress promotes the mechanochemical evolution of kaolinite in coal, resulting in lattice dislocations, an increase in crystal plane spacing, an increase in crystal defects and a decrease in the ordering degree. The experimental phenomenon of kaolinite converting to montmorillonite (microcrystalline kaolinite) and the mechanochemical evolution result of the crystallinity parameter decrease reflect that the crystal structure of kaolinite in tectonically deformed coal has not evolved to be ordered with the aid of temperature, which confirms that stress plays a dominant role in the evolution of advanced phenomenon of tectonically deformed coal structures.

A study of rare earth ion-adsorption clays: The speciation of rare earth elements on kaolinite at basic pH

Synthesized rare earth ion-adsorption clays (La, Ce, Nd, Dy and Y, ~ 400 ppm each) were prepared from kaolinite at various basic pH in open-air conditions. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICP-MS) were used to characterize the effect of pH on the adsorption mechanism of rare earth elements (REEs) on kaolinite. The crystal structure of kaolinite by XRD analysis is not altered after REE adsorption, suggesting that REEs are bound to the surface of kaolinite. Elemental analysis by XPS and ICP-MS show that the surface concentration of REEs on kaolinite is pH dependent, and a local maximum of the surface concentration is achieved at pH 10. Three characteristics of the La 3d5/2 XPS photoemission feature were measured and compared to those of standard La compounds to probe the speciation of REEs, and electrostatically bound hydroxides such as REE(OH)2+ are identified as the primary species on the surface of kaolinite. Compared to the typical ion-adsorption clays with intrinsic acidic pH, clays synthesized at basic pH exhibit similarly high rare earth ion-exchange efficiency with ammonium sulfate (AS), suggesting that rare earth ion-adsorption clays can exist in both acidic and basic environments.

Ti-bearing minerals in sedimentary kaolin deposits of Egypt

Titanium (Ti) is a major impurity in the economic Carboniferous and Cretaceous sedimentary kaolin deposits in Egypt. The current study clarifies the distribution of Ti and its modes of occurrence in these deposits through petrographic, mineralogical, and geochemical investigations. It is found that Ti is present as an independent mineral phase rather than in the crystal structure of kaolinite. Ti occurs mainly as uniform very fine-grained and rounded anatase crystals in pockets within the kaolin mass of all deposits. Traces of rutile, leucoxene and ilmenite are present in the sand fractions. Average anatase content ranges between 1.4% and 3%. Cretaceous kaolin deposits show a homogeneous distribution of anatase regardless of the location (1.8 and 2.8%), while Carboniferous deposits are heterogeneous with the highest anatase content in the Abu Natash deposit (3%) and the lowest (1.4%) in the Khaboba deposit. The positive correlations between TiO2 and some trace elements such Cr, Nb and Zr in the clay fractions, where anatase is the only Ti-bearing mineral, suggest the occurrence of most of such elements in the anatase structure.The occurrence of anatase as uniform very fine-grained crystals as pockets within the kaolin mass, together with the presence of ilmenite and/or leucoxene in the sand fractions of the studied kaolin samples suggests an authigenic origin for the anatase as a result of post-depositional alteration of ilmenite precursor to leucoxene. The positive correlations between TiO2 and trace element contents probably support this assumption. The higher trace element contents in the anatase from different deposits compared to the associated leucoxene and ilmenite are considered to result from relative enrichment of the immobile trace elements during the alteration of ilmenite and leucoxene to anatase.

First-principles studies on the elastic constants of a 1:1 layered kaolinite mineral

The mechanical behavior of minerals under high pressure has attracted considerable interest in recent years. Clay minerals, including kaolinite, are common minerals found in sedimentary environments and their behavior under pressure is an important factor in understanding seismogenic zones. Kaolinite is a ubiquitous member of the kaolin group of 1:1 phyllosilicates that have recently been found to undergo a structural phase transition between 2.0 and 2.5 GPa. In this study, the bulk modulus and elastic constants of kaolinite have been calculated from first principles within density functional theory (DFT) for the first time. The bulk modulus is predicted to be 23 GPa for kaolinite. The calculated elastic constant tensors indicate that the a direction is slightly more flexible than the b direction. The calculated elastic constant tensor along c is much lower than the constants calculated along a and b consistent with the crystal structure of kaolinite. Elastic wave velocities for P- and S-waves were calculated to be 7.34 and 3.50 km/s, respectively. Since an agreement between the theoretical and experimental values is satisfactory, we conclude that the theoretical calculations presented here are useful in seismic research for predicting the mechanical properties of minerals that are difficult to obtain experimentally because of their small particle size (typically <2 micrometers).

Modification of kaolinite surfaces through mechanochemical treatment—a mid-IR and near-IR spectroscopic study

The modification of kaolinite surfaces through mechanochemical treatment has been studied using a combination of mid-IR and near-IR spectroscopy. Kaolinite hydroxyls were lost after 10 h of grinding as evidenced by the decrease in intensity of the OH stretching vibrations at 3695 and 3619 cm −1 and the deformation modes at 937 and 915 cm −1. Concomitantly an increase in the hydroxyl-stretching vibrations of water is observed. The mechanochemical activation (dry grinding) causes destruction in the crystal structure of kaolinite by the rupture of the OH, AlOH, AlOSi and SiO bonds. Evidence of this destruction may be followed using near-IR spectroscopy. Two intense bands are observed in the spectral region of the first overtone of the hydroxyl-stretching vibration at 7065 and 7163 cm −1. These two bands decrease in intensity with mechanochemical treatment and two new bands are observed at 6842 and 6978 cm −1 assigned to the first overtone of the hydroxyl-stretching band of water. Concomitantly the water combination bands observed at 5238 and 5161 cm −1 increase in intensity with mechanochemical treatment. The destruction of the kaolinite surface may be also followed by the loss of intensity of the two hydroxyl combination bands at 4526 and 4623 cm −1. Infrared spectroscopy shows that the kaolinite surface has been modified by the removal of the kaolinite hydroxyls and their replacement with water adsorbed on the kaolinite surface. NIR spectroscopy enables the determination of the optimum time for grinding of the kaolinite. Further NIR allows the possibility of continual on-line analysis of the mechanochemical treatment of kaolinite.

The Effect of Quartz Content on the Mechanochemical Activation of Kaolinite

The mechanochemical activation (dry grinding) causes destruction in the crystal structure of kaolinite by the rupture of the O–H, Al–OH, Al–O–Si, and Si–O bonds. The major mineral constituents of natural kaolins are kaolinite and quartz. In this study, the attention was mainly directed to the role of quartz content (4, 25, 50, and 75 wt%) in the mechanochemical amorphization of kaolinite. Grinding experiments were carried out for 1, 2, 3, and 4 h in a planetary mill. The rate of destruction of the kaolinite structure was followed by X-ray diffraction, thermal analysis, and Fourier transform infrared (DRIFT) spectrometry. The distortion and rupture of the kaolinite structure induced by grinding was reflected in line broadening, increases in mean lattice strain, and reduction of peak areas (intensities). The increased quartz content resulted in acceleration of the mechanically induced amorphization of the kaolinite structure. The crystalline order of kaolinite was completely destroyed after grinding the sample containing 75 wt% quartz for 4 h. On the other hand, 4 h of grinding was sufficient only to cause some increase in the defect density of kaolinite in the case of samples with lower quartz contents (25 and 4 wt%). The results indicate that quartz grains act as grinding bodies during the intensive dry grinding of kaolinite.

The Effect of Mechanical Treatment on the Crystal Structure and Thermal Behavior of Kaolinite

AbstractThe destruction of the crystal structure of kaolinite caused by mechanical forces was investigated by X-ray diffraction, thermal analysis, infrared spectroscopy, and specific surface area determination. Attention was also directed to the change of thermal reactions of milled kaolinite. Grinding experiments for 5 min, 10 min, and 1, 2, 4, 6, and 10 h were carried out in an AGO I planetary mill. After 1 h of grinding, the crystalline order of kaolin is destroyed; but the amorphization continues in the course of prolonged grinding. Grinding for 1 h produces a favorable state for forming mullite-type crystals after heating even at 1000°C.

Verification of the Triclinic Crystal Structure of Kaolinite

AbstractOn the basis of neutron diffraction studies, the two inner-hydroxyl ions in highly ordered kaolinite were recently shown to be differently oriented. One of the inner-hydroxyl ions points generally toward a hole in the octahedral sheet and the other toward a hole in the tetrahedral sheet. These orientations and the locations of the other atoms in the primitive triclinic unit cell have now been determined for a sample of Keokuk kaolinite with improved precision compared with that reported earlier. Rietveld structure refinement was carried out for the entire crystal structure simultaneously (99 atom positional and 17 other parameters) with each of two newly collected sets of high-resolution neutron powder diffraction data. The different orientations of the inner-hydroxyl ions are the most marked evidence that the unit cell is not C centered. The positions of the inner-surface hydrogen atoms provide further evidence in that all differ from a C-centered relationship by six to eight estimated standard deviations in their y coordinates. The cell is, therefore, not centered. The space group is P1.

Crystal Structure of Kaolinite: Dimethylsulfoxide Intercalate

AbstractThe crystal structure of the kaolinite: dimethylsulfoxide (DMSO) intercalate (P1, a = 5.187(2), b = 8.964(3), c = 11.838(4) Å, α = 91.53(1)°, β = 108.59(2), γ = 89.92(1)°) has been determined using spectroscopic and X-ray and neutron powder diffraction data. Both the X-ray and neutron powder diffraction patterns were refined. Solid-state 13C, 29Si, and 27Al nuclear magnetic resonance data and previously collected infrared spectroscopic data provided a useful starting model for structural refinement. Due to the extreme overlap of reflections of this low-symmetry unit cell, the Rietveld method proved inadequate, and quasi-single crystal methods were employed. Each DMSO molecule was found to be triply hydrogen bonded above the octahedral vacancy in the gibbsitic sheet of the kaolinite layer. One methyl group is keyed into the ditrigonal hole in the tetrahedral sheet with the other S-C bond parallel to the sheet. The DMSO molecules are accommodated by significant horizontal displacement of individual kaolinite layers to achieve almost perfect overlap of the octahedral vacancy by the adjacent ditrigonal hole.

Atom Positions in Highly Ordered Kaolinite

AbstractThe crystal structure of kaolinite(Pl, a = 5.153(1), b = 8.941 (1), c = 7.403 (1)Å, α = 91.692(3)°, β = 104.860(3)°, γ = 89.822(3)°, specimens from Keokuk geodes) has been refined in detail and that of dickite (Cc, a = 5.1460(3), b = 8.9376(5), c = 14.4244(6) Å, β = 96.761(5)°) has been re-refined, both from powder diffraction data with the Rietveld method. Except for the hydrogen atoms, the layer structures in both clays are very similar and are much as inferred or determined previously by others. The rotation in the tetrahedral sheet is 7(1)°. The two inner hydroxyl O-H bonds in kaolinite are differently oriented; one points into an octahedral vacancy and the other somewhat away from the octahedral sheet and toward the unoccupied center of an oxygen triangle formed by the two apical oxygens and shared basal oxygen of two adjacent SiO4 tetrahedra. All six of the inner surface hydrogen atoms appear to be nearly equally involved in the hydrogen bonding between kaolinite layers in kaolinite.

Role of lattice hydroxyls of kaolinite in phosphate fixation and their replacement by fluoride

This investigation was made with the purpose of studying the role that lattice hydroxyls play on phosphate fixation, and the effect of fluoride ions on the surface lattice hydroxyls of kaolinite. The results obtained by means of quantitative infrared spectroscopy show that phosphate ions do not replace surface lattice hydroxyls of kaolinite. Accordingly, titration of excess alkalinity produced when kaolinite is placed in contact with fluoride solutions and direct infrared spectroscopic analysis of hydroxyl content show that lattice hydroxyls are replaced by fluoride. In fact, in a case where the fluoride solution was 0.40 N it was found that 22% of the lattice hydroxyls were replaced by fluoride ions. X-ray powder photographs of untreated and fluorinated kaolinite show that the “ d” spacings and the intensities have remained the same, indicating that the crystal structure of kaolinite has not been altered.

NATURE AND PROPERTIES OF YAMAGATA BENTONITE

The following are the results of my study on a certain yellow species of the Yamagata bentonite.(1). A water imbibing mass at the swelling equilibrium (25.0°C) contains 0.359g of dry clay per 100g of the mass, and its calculated values of sp. volume and swelling ratio are 0.980cc and 1:73.0 respectively.(2). On adding ample water an abnormally rapid swelling is observed on the surface of a dry or partially imbibing clay mass. Let us call the swelling “surface swelling”. The surface swelling, with some quickness, takes an equilibrium which correspond to a terrace, nearer to the origin, on the time-swelling curve, and leaves a gelatineous thin film on the surface, a film completely covering the surface, insists against further penetration of water. A time interval to reach the equilibrium of the surface swelling becomes shorter both with the increase of initial distribution density of surface particle and with dryness or concentration of the mass of clay, and yet the gel film thickens with the shortened time interval just mentioned.(3). A film of bentonite, 0.1-0.05mm thick, does a directional swelling, viz., at the swelling equilibrium the ratio of swelling is 1:39.0 in the direction of thickness and 1:1.37 in that of spreading.(4). The swelling velocity of film, in both directions, may well be denoted by the following equation:di/dtk(i∞-it)Here, it is a ratio of swelling at any time interval t, and i∞ another at infinite time, k being a constant of proportionality. This equation is quite the same as that of simple chemical reaction velocity.(5). On considering a mechanism of film formation we can infer a type of bentonite micelle model. The model has a layer structure which can be exemplified by a alternative film layer of Al-hexite an Si-hexite, and it has almost the same structure as the crystal structure of kaolinite or some base-exchange type clay.

The Crystal Structure of Kaolinite

The Crystal Structure of Kaolinite