Kaolin Layer Research Articles

Kaolin polytypes revisited ab initio

The well known 36 distinguishable transformations between adjacent kaolin layers are split into 20 energetically distinguishable transformations (EDT) and 16 enantiomorphic transformations, hereafter denoted EDT*. For infinitesimal energy contribution of interactions between non-adjacent layers, the lowest-energy models must result from either (a) repeated application of an EDT or (b) alternate application of an EDT and its EDT*. All modeling, quantum input preparation and interpretation was performed with Materials Toolkit, and quantum optimizations with VASP. Kaolinite and dickite are the lowest-energy models at zero temperature and pressure, whereas nacrite and HP-dickite are the lowest-enthalpy models under moderate pressures based on a rough enthalpy/pressure graph built from numbers given in the supplementary tables. Minor temperature dependence of this calculated 0 K graph would explain the bulk of the current observations regarding synthesis, diagenesis and transformation of kaolin minerals. Other stackings that we list have energies so competitive that they might crystallize at ambient pressure. A homometric pair of energetically distinguishable ideal models, one of them for nacrite, is exposed. The printed experimental structure of nacrite correctly corresponds to the stable member of the pair. In our opinion, all recent literature measurements of the free energy of bulk kaolinite are too negative by approximately 15 kJ mol(-1) for some unknown reason.

Mining, processing and applications of the Capim Basin kaolin, Brazil

AbstractHigh-quality kaolins are produced from two sites in the Capim River area in Pará State, northern Brazil. One mine is operated by Rio Capim Caulim (RCC) owned by Imerys and the other by Pará Pigmentos S.A. (PPSA) owned by Caemi (CVRD Group). The kaolin deposits are located on low-relief plateaux with a lateritic cap. The kaolin strata are in the Ipixuna Formation of Upper Cretaceous Age. There are two distinct kaolin layers, a 4–5 m thick soft kaolin which is overlain in the southern portion of the basin by a 4–5 m thick hard kaolin. The soft and hard designations refer to particle size, with the soft kaolin being relatively coarse and the hard kaolin very fine. The kaolin is mined, partially beneficiated, and pumped through pipelines to the port at Barcarena on the Guama River, a large tributary of the Amazon River. The PPSA kaolin is fully processed at the plant near the mine site and pumped to Barcarena where it is spray dried. The RCC kaolin is only partially processed at the mine site. This partially processed kaolin is pumped to Barcarena where it is beneficiated. The finished kaolin is high quality and is shipped to North and South American, European, and Asian paper-coating markets. More than 1.6M tons were shipped from Barcarena in 2005.

Electrokinetic remediation of clayey soils containing copper(II)-oxinate using humic acid as a surfactant

The utility of humic acid (HA) as a surfactant for use in the electrokinetic remediation (ER) of the clayey soils containing copper(II)-oxinate (Cu(OX) 2) was examined. A small simulator of ER was devised, which consisted of three types of artificial soils on the basis of the commercial kaolin: kaolin, kaolin + HA and kaolin + Cu(OX) 2. The layers of kaolin containing HA and Cu(OX) 2 were sandwiched between two kaolin layers. In all experiments, a constant dc voltage gradient of 2.2 V/cm was applied through the soil for 30 h, and the pH of the solution in the anodic chamber was maintained at 7.0. Generally, HA has a negative charge at a neutral pH. However, the HA was mainly transferred to the cathodic chamber. This shows that the driving force of the HA in the system used herein is predominantly due to electroosmotic flow. Moreover, the amount of Cu(OX) 2 removed from the clayey soils in the presence of HA was three times larger than those in the absence of HA. This can be attributed to the fact that the water solubility of Cu(OX) 2 is enhanced by the presence of HA. Thus, we conclude that HA has a potential for use as an amendment for the ER of hydrophobic chemicals, such as Cu(OX) 2.

COBERTURA BAUXÍTICA E ORIGEM DO CAULIM DO MORRO DO FELIPE, BAIXO RIO JARI, ESTADO DO AMAPÁ

The Morro do Felipe kaolin deposit, occurring on the left margin of the Jari river (Northern Brazil), constitutes the lower part of an ancient weathering profile which is bounded to a planation surface about 170 m high. The kaolin layer, up to 35 m thick, consists mainly of poorly ordered kaolinite with deferrification features and thin sand intercalations. In the lower part of the deposit, the kaolin is only slightly porous and disintegrates easily in water whereas in the upper part, it is more porous, firm, displays conchoidal fracture and resists disintegration in water. In both cases, the kaolin (mineral) is very similar to fire-clay type kaolinite. The kaolin deposit grades down into altered sandstones and mudstones, with conglomerate intercalations, of the Alter do Chao Formation and is overlain by an iron crust, lower nodular bauxite, upper nodular bauxite and a clayey overburden (Belterra Clay). The evolution of this alteration profile likely involved the following steps: 1) formation of an iron crust by podzolization or ground-water lateritization of Alter do Chao deposits; 2) regional bauxitization; 3) degradation of the bauxite horizon and formation of colluvial deposits; 4) deposition of the clayey overburden upon the colluvial deposits or directly on Alter do Chao sediments; 5) lowering of the base level and reactivation of weathering giving rise to the transformation of the overburden into a latosol (Belterra Clay) and the thickening and deferrification of the saprolite horizon which resulted in the present day kaolin deposit. As shows the evolution of the alteration profile, the Morro do Felipe kaolin represents a product of deep weathering which affected the Amazon region since the Lower Tertiary. The kaolinization, related firstly to bauxitization (Lower Tertiary) and triggered, at a later stage, by reactivation of tropical weathering (Upper Tertiary/Quaternary) and epirogenetic movements, resulted from the decomposition of clay minerals and possibly some feldspar, partial dissolution of quartz, neoformation of poorly ordered kaolinite and intense deferrification. It seems very likely that the process of kaolinization continues even today.

Entrifuge modelling of the transport of a pulse of two contaminants through a clay layer

This note presents some results of a theoretical and experimental study of the rates of simultaneous migration and dispersion of an aqueous organic contaminant and an aqueous inorganic contaminant. For one-dimensional vertical contaminant transport, accompanied by linear sorption in a uniform soil under a constant hydraulic gradient, the variation of concentration c with time t and depth z is governed by the advection-dispersion equation, which is a second-order linear partial differential equation. Tests were conducted using a Mark II Minidrum Centrifuge with a twin concentric shaft. The one-dimensional leaching of two contaminants simultaneously through an E-grade kaolin layer was successfully modelled. Post-test sampling showed a clear separation between the inorganic contaminant (sodium chloride) and organic contaminant (food dye) plumes. The two tests showed that this type of centrifuge testing provides good prospects for the experimental study and measurement of contaminant transport processes in fine-grained soils. However, a discrepancy between theory and observation, needing further investigation, was found in one of the tests.

Naturally Weathered Plagioclase Grains from the Idaho Batholith: Observations Using Scanning Electron Microscopy

Rates of primary silicate mineral weathering are important to understanding proton buffering and biogeochemical cycling of Si, Al, alkali metals, and alkaline earth metals in natural watersheds. The objectives of this study were to characterize the surface morphology and secondary coatings of naturally weathered oligoclase grains sampled from the Silver Creek Experimental Watersheds in the southwestern Idaho batholith. Oligoclase grains (0.5–1.0 mm) were sampled from soil, sediment, and rocks of various weathering classes within the watershed, and were characterized using scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDXRA). Oligoclase grains from unweathered bedrock (Class 1 rock) and very weakly weathered rock (Class 2) showed little evidence of weathering features such as etch pits and secondary coatings on the mineral surface. As the weathering intensity increased to Class 5, Class 6, R horizon, and C horizon oligoclase samples, the presence of etch pits and secondary coatings increased. Grains from Class 6 rock and the R horizon were characterized by numerous etch pits and secondary coatings, which covered the majority of the grain surface. The EDXRA analyses showed that the secondary coatings had Al/Si ratios approximately two times and Ca/Si ratios approximately 0.2 times that of Class 1 and Class 2 rock, indicating significant Al enrichment and Ca depletion in the weathering products. X-ray diffraction was used to positively identify a kaolin layer silicate (presumably kaolinite) as a major component of the secondary phases found on the feldsdpar surface. Observations of naturally weathered feldspar grains suggest significant differences in weathering environment or intensity between many laboratory studies and actual watersheds. Environmental conditions that may be responsible for differences in weathering intensities between natural watersheds and laboratory studies include physical factors such as solid/solution ratios, water residence times, wetting and drying cycles, and chemical factors such as the presence of secondary coatings on the mineral surface and the reactive surface area of weathered grains. Contribution no. J-2823 from the Montana Agric. Exp. Stn.

Preparation and Fracture Characteristic of Laminated Alumina/Mullite Composite

Alumina/kaolin laminated composites have been fabricated at 1650°C by firing multilayers of 1mm thick alumina sheets and 50 or 100μm thick kaolin tapes. During firing, the kaolin layers changed to mixed phases of mullite and SiO2-rich glass. The bending strength of these composites dose not depend on the numbers of laminated kaolin tapes, but depends on the thickness. It was camparable with that of monolithic alumina sheets. The fracture behavior of laminated composites varied with the thickness of kaolin tapes. The composites with pillar-like mullite crystals grown perpendicular to the kaolin layers of 50μm showed a linear relation in the load/deflection curve. On the other hand, the composites prepared with 100μm-kaolin tapes contained two types of mullite crystals: pillar-like mullite crystals grown at the interface between alumina sheet and kaolin tape and needle-like mullite crystals formed in the center area of the kaolin tape. These composites with thicker kaolin tapes showed a non-linear relation in the load/deflection curve.

Coat of Alumina Sheet with Needle-like Mullite

A new alumina substrate coated with porous mullite layer consisting of needle-like crystals was developed for improving the physicochemical properties of the substrate surface. Calcined porous alumina substrates with a 40% porosity and an average pore diameter of 0.1μm were dipped into aqueous suspensions of New Zealand kaolin with particle sizes of below 1μm for 5-20sec to form a kaolin layer 10-40μm thick. The porous alumina substrates coated with kaolin were fired at 1500° to 1650°C to enhance the growth of thick needle-like mullite crystals with lengths of 1-10μm and diameters of about 1μm over the surface of dense alumina substrates. The glassy phase coexisting with mullite crystals over the substrate surface was dissolved in a hydrofluoric acid solution. Pillar-like mullite crystals with diameters of about 3μm were formed at the interface between alumina substrate and mullite layer fired at 1650°C. The pillar-like mullite crystals contained a larger amount of Al2O3 than needle-like mullite crystals with the chemical composition of 3Al2O3⋅2SiO2. No cracks were observed at the interface between the alumina substrate and porous mullite layer after thermal shock test with a temperature difference of 400°-450°C.

Quantification Curves for the X-Ray Powder Diffraction Analysis of Mixed-Layer Kaolinite/Smectite

AbstractX-ray powder diffraction patterns for many interstratified kaolinite/glycolated smectites were calculated by changing combinations of probabilities and transition probabilities of two component layers. Reichweite = 0 and Reichweite = 1 structures were investigated. The calculated d-values were plotted, with PKS (the probability that a smectite layer succeeds a kaolin layer given that the first layer is a kaolinite layer) and PSK as the axes of coordinates. These d-values were then linked into equal d-value curves on a graph. Four equal d-value diagrams for mixed reflections ranging from 34.0 to 17.1 Å, from 8.5 to 7.2 Å, from 6.13 to 5.68 Å, and from 3.540 to 3.401 Å were constructed. Two examples of identifying natural kaolinite/smectite minerals using these diagrams are presented.

Intergradient Vermiculite-Kaolin Mineral in a Korean Ultisol

AbstractA 14-Å mineral coexisting with kaolin minerals, mica, and gibbsite in a Korean Ultisol and showing X-ray powder diffraction features of “chloritized” vermiculite was studied by a combination of methods. The 14-Å mineral collapsed on saturation with K+ after extraction with hot 1/3 M sodium citrate, but the Si/Al ratio of the extracted material was close to 1.0 and kaolin minerals dissolved, as indicated by difference infrared spectroscopy. The 14-Å mineral was also collapsed by heating at or above 350°C. The difference infrared spectra and the X-ray powder diffraction patterns indicated that two forms of kaolin mineral are present that differ in thermal stability; one decomposed by heating at or below 375°C and the other by heating above 375°C. The former kaolin mineral is probably associated with vermiculite and the latter is present as a discrete form. The 14-Å mineral was inferred to be an intergradient vermiculite-kaolin mineral, in which most vermiculite layers each partially transform into double kaolin layers, and to represent an intermediate phase during the transformation of 2:1 to 1:1 layer silicates in acid soils.

MINERALOGY, GENESIS AND CLASSIFICATION OF FERRUGINOUS SOILS OF THE EASTERN MYSORE PLATEAU, INDIA

SummaryThe relationship of geomorphic and climatic history and formation of the ferruginous soils, formed on the acidic Peninsular Gneiss, of the Mysore Plateau, India, is discussed. The profiles studied are found on two different land systems. The soils of the older, fairly smooth landscape are composed of colluvium over truncated laterite profiles, with a gravel layer and a prominent kaolin layer over the weathered rock. These soils show an accumulation of pedogenic haematite grains in the sand fraction and have considerable kaolinite and amorphous ferri‐aluminosilicate minerals in the clays.The soils of the younger, rugged landscape have similar clay mineralogy, but do not have a gravel layer, or haematite grains. The influence of the coarse‐grained parent rock is seen in the large amounts of quartz gravel. The absence of granulation is attributed to lack of accumulation of iron.The soils have been formed in an earlier, more humid climate than prevails today. The original laterite profiles were formed on a plane surface, and subsequent change in climate has led to change in the land forms and dissection. Truncation of the profiles was followed by deposition of red colluvium over the resistant ferruginous layer.These ancient soils do not fit the criteria for Oxisols in the U.S. classification, but fit well in the French system as ‘Sols Ferrallitiques’, subclass ‘fiablement désatures en (B)’. The soil from a low lying area, formed from colluvium under hydromorphic conditions. is classified as‘Vertisols et Paravertisols'.

The Relationship Between the Hydrated and Dehydrated States of an Halloysite

AbstractA study of the mineralogical changes taking place during the loss of interlayer water in an halloysite has been carried out in order to clarify the relationship between the most hydrated and least hydrated states of the mineral. A number of samples of halloysite which together exhibit a variety of average interlayer water capacities were obtained by the conditioning of a largely hydrated sample with different atmospheres of known relative humidities. Profiles were obtained of X-ray peaks which characterize the interlayer water capacities of halloysite samples. An attempt has been made to analyse these profiles into a sum of peaks attributable to the fully hydrated and dehydrated states of the mineral. Such an analysis does not satisfactorily explain the profile shapes. A mechanism of interstratification of hydrated and dehydrated kaolin layers in which there is a tendency towards the segregation of these layer types gives a more satisfactory explanation of these profile shapes. It is concluded that dehydration takes place through an interstratification in which there is a partial segregation of the two basic layer types. This conclusion implies that halloysites with all average interlayer water contents between 0 and 2 molecules per unit cell may exist and that fully hydrated halloysite and dehydrated halloysite are the end members of a continuous series of hydration states.

Light scattering in microporous materials using a photon diffusion model

The experimental values of the scattering cross sections of cellulose membrane filters and kaolin layers are determined as a function of wavelength, pore size and void volume, by using a photon diffusion model. The pore sizes and void volumes are determined experimentally by mercury penetration porosimetry. It is found that the rate of change of the scattering cross section with wavelength as a function of pore dimension enables pore sizes to be determined nondestructively from reflectance measurements.

Refinement of the Crystal Structure of Nacrite

AbstractThe crystal structure of nacrite from Pike’s Peak district, Colorado, has been refined by least squares and electron density difference maps utilizing ten levels of data. Complete refinement was inhibited by thick domains involving a/3 interlayer shifts in the “wrong direction”. The ideal structure is based on a 6R stacking sequence of kaolin layers, in which each successive layer is shifted relative to the layer below by −1/3 of the 8·9 Å lateral repeat. This direction is X in nacrite, contrary to the usual convention for layer silicates, because of the positioning of the (010) symmetry planes normal to the 5·1 Å repeat direction. Alternate layers are also rotated by 180°. The pattern of vacant octahedral sites reduces the symmetry to Cc and permits description of the structure as a 2-layer form with an inclined Z axis.Adjacent tetrahedra are twisted by 7·3° in opposite directions so that the basal oxygens approach more closely both the Al cations in the same layer and the surface hydroxyls of the layer below. Interlocking corrugations in the oxygen and hydroxyl surfaces of adjacent layers run alternately parallel to the [110] and [11̄0] zones in successive layers. The upper and lower anion triads in each Al-octahedron are rotated by 5·4° and 7·0° in opposite directions as a result of shared edge shortening. Nacrite has a greater interlayer separation and smaller lateral dimensions than dickite and kaolinite, and the observed β angle deviates by 1½° from the ideal value. These features, as well as its overall lesser stability, are believed due to the less favorable positioning in nacrite of the basal oxygens relative to the directed interlayer hydrogen bonds.

A refinement of the dickite structure and some remarks on polymorphism in kaolin minerals

SummaryThe crystal structure of the clay mineral dickite (Al2Si2H4O9) has been refined to a greater accuracy than that reported in an earlier analysis. Improved lattiçe parameters are: a 5·15±0·001, b 8·940±0·001, c 14·424 ± 0·002Å., β 96° 44′± 1′. The dickite structure shows several significant distortions from the geometry of the idealized kaolin layer, including deformation and rotation of the silica tetra-hedra. The most striking features of the octahedral layer are the extremely short shared edges of 2·37 Å. Although the analysis was not sufficiently accurate to position the hydrogen atoms with certainty, a model consistent with the infrared absorption spectra is proposed. The stacking sequences of kaolin-layer minerals have been considered with reference to the structural features observed in dickite. There are thirty-six ways of superposing two kaolin layers commensurate with the OH-O bonds found in kaolinite, dickite, and nacrite. The twelve sequences showing the least amount of cation-cation superposition between consecutive kaolin layers can be used to construct two one-layer cells, kaolinite and its mirror image, and twelve two-layer cells, including dickite and nacrite. The distortions of the kaolin layer introduce secondary variations in the interlayer bonding that suggest that dickite and nacrite are the most stable of the kaolin layer structures, since they possess the shortest oxygen-hydroxyl contacts.

Wet Grinding on Kaolin Minerals

Abstract The effects of wet grinding on kaolin minerals were examined by X-ray diffraction method, differential thermal analysis, electron microscopy and density measurement. The effects of wet grinding of kaolin minerals are different from those of dry grinding, particularly at the early stage of grinding. It has been considered that the force of dry grinding acts as fracturing and cleaving forces, while the force of wet grinding acts as a weak cleaving force for kaolinite and as a weak fracturing force for halloysite in the early stage of grinding. It has been revealed that the effects of wet grinding depend on the shape of crystal in the original kaolin mineral in the early stage of grinding, and beyond a certain stage of grinding, they depend on the structural per-fectness of the kaolin layer, that is, the internal degree of crystallinity of the original kaolin mineral.

X-ray studies of halloysite and metahalloysite

The experiments described below on the dehydration of halloysite were largely carried out in the laboratoire Central des Services Chimiques de l'État, Paris, where we enjoyed not only the excellent facilities of the laboratory but also the advice of Monsieur J. Méring and Mile R. Glaser who had made similar studies of montmorillonite. The use of a Guinier-type focusing camera with strictly monochromatic radiation was especially useful. These experiments were undertaken because little was known about the dehydration process beyond the recognition that it occurs very readily in dry atmospheres and at low temperatures. The main experimental difficulty lies in differentiating between water adsorbed oil external surfaces of the clay particles (adsorbed water) and water internally absorbed between the kaolin layers (interlayer water).