Kaolin Minerals Research Articles

Interfacial premelting of ice in nano composite materials.

The interfacial premelting in ice/clay nano composites was studied by high energy X-ray diffraction. Below the melting point of bulk water, the formation of liquid water was observed for the ice/vermiculite and ice/kaolin systems. The liquid fraction is gradually increasing with temperature. For both minerals, similar effective premelting layer thicknesses of 2-3 nm are reached 3 K below the bulk melting point. For the quantitative description of the molten water fraction in wet clay minerals we developed a continuum model for short range interactions and arbitrary pore size distributions. This model quantitatively describes the experimental data over the entire temperature range. Model parameters were obtained by fitting using a maximum entropy (MaxEnt) approach. Pronounced differences in the deviation from Antonow's rule relating interfacial free energy between ice, water, and clay are observed for the charged vermiculite and uncharged kaolin minerals. The resultant parameters are discussed in terms of their ice nucleation efficiency. Using well defined and characterized ice/clay nano composite samples, this work bridges the gap between studies on single crystalline ice/solid model interfaces and naturally occurring soils and permafrost.

The nature, origin and significance of luminescent layers in the Bazhenov Shale Formation of West Siberia, Russia

Abstract Argillites that strongly luminesce under UV radiation were detected in the Bazhenov Shale Formation (BSF) of the West Siberian Basin during routine core examination and found to be persistent over a wide lateral area. The mineralogy and fabric of these luminescent layers were characterized by optical and fluorescence microscopy, SEM, TEM, XRD and IR methods. Optical and fluorescence microscopy showed that the luminescent layers were to a large extent derived from volcanic ash falls and could be described as meta-tuffites, although normal detrital sedimentation continued at the same time. The layers have a thickness of several mm to a maximum of 3–4 cm and can be defined as a clay-rich regional horizons extending for over 500 km. XRD showed that two principal clay minerals were predominant, namely a kaolinite group minerals, (kaolinite-rich) and a mixed-layer illite-smectite (I/S) similar to that found in K-bentonite. Total organic matter in the luminescent layers is much lower than that in the enclosing BSF clayey-silty siliceous sediments above and below as shown by pyrolytic analyses. Evidence is presented that the luminescent characteristic of the argillites is related to their clay mineralogy, specifically to their content of kaolin minerals, although a contribution from nitrogenous organic matter cannot be entirely discounted. In some ways the luminescent argillites can be compared with bentonites associated with ash transformations or with tonsteins in coal beds, which are also derived from volcanic ash falls and contain highly crystalline kaolinite. However, tonsteins originate at or near land surface whereas the argillites were apparently formed in the deep ocean. But just as tonsteins can be used for detailed stratigraphic studies and are valuable in the context of coal exploration, so may the luminescent argillites prove to be significant both stratigraphically and in the search for economic hydrocarbon deposits, bearing in mind that their clay mineralogy may be sensitive to temperature and depth of burial and related to their placement in the oil and gas window.

Surface‐treated kaolin minerals as a complement or substitute to glass fibers in thermoplastics

Glass fiber (GF)‐related mold abrasion and tool wear make it undesirable for certain thermoplastics applications. Furthermore, fiber attrition during processing and orientation sensitivity raise concerns over compromised performance. In this study, kaolin minerals with varying properties and surface‐treatments are tested to potentially replace GFs in nylon composites. Composites are melt‐compounded and injection molded using lab‐scale and industrial‐scale equipment. Mechanical properties (tensile, flex, impact), heat distortion temperature, and thermal decomposition using thermogravimetric analysis (TGA) are used to comparatively characterize kaolin composite formulations against 30% weight GF composites. Kaolin minerals with high aspect ratio and good interfacial contact are found to show strength and modulus improvements up to 80% that of GF. Additionally, low aspect ratio kaolin composites were found to surpass GF composites in impact strength. A synergistic effect is found between high and low aspect ratio kaolin that can potentially lead to further enhancement in properties with the added possibility of blending minerals to customize composite performance. Such findings suggest that kaolin minerals can be used to customize the properties of composites in manners previously unattainable through GF usage alone. Scale up trials show potential for kaolin to replace GFs at industrial levels. POLYM. ENG. SCI., 59:E330–E338, 2019. © 2018 Society of Plastics Engineers

Challenges to access and safeguard mineral resources for society: A case study of kaolin in Portugal

Present and future demands of minerals require enlightened land use policies and practices that consider geological resources as a whole, anticipating potential conflicts and proposing/monitoring solutions to ensure the access to mineral resources and their responsible use. The use of a multi-criteria methodology able to balance the geological knowledge (grounding the identification of mineral resources) with the economic, environmental and social dimensions implicated in their current or foreseen exploitation may provide the way needed to conciliate the foremost goals of any mining planning and land-use planning exercises. The safeguarding of kaolin resources was the selected case study because: (i) the current and future access to these resources are confronted with different types of conflicts with other land uses; (ii) the exploitation and transformation of kaolin are increasingly important to the regional and national economy, generating as well numerous jobs all over the added value chain and attracting foreign investment; and (iii) the historical environmental liabilities related to old exploitations that still grounds strong apprehensions by the public in general. In this study, the Portuguese kaolin resources were represented by 136 specific tracts, 110 being classified as of “public importance” after considering criteria supporting the geological knowledge dimension. Preceded by a structured point densification scheme, an interpolation process was performed, within the kriging formalism. The resulting map delimited a total area of ≈342 km2 (0.4% of Portugal mainland) whose intrinsic value should support a safeguarding decision on the current and future access to kaolin resources in Portugal mainland. The 29 active and productive mines were further classified based on the economic, environmental and social dimensions and distributed within the three levels of priority for safeguarding, as proposed by the methodology. The results achieved are underestimated mostly due to several limitations of the available databases. Nevertheless, this remains a powerful potential tool to be applied for kaolin mineral resources safeguarding in two distinct and coexisting ways: (1) for future access, ensuring the supply of forthcoming generations and avoiding the sterilisation of tracts of “public importance”; and (2) for the short-medium term access, assigning specific areas to exploitation activities, regularly supplying the industry and markets. This methodology has been successfully applied to other minerals (e.g. Mateus et al., 2017), but additional efforts must be made to extend the assessment to other raw materials.

Formation of new low field signals in the EPR spectra of kaolin minerals

Formation of new low field signals in the EPR spectra of kaolin minerals

Stability of kaolin dispersion in the presence of lignin-acrylamide polymer

Abstract Dispersion of kaolin in aqueous systems is important in many industries including ceramics, chemicals, pharmaceuticals and paints. In this work, kraft lignin-acrylamide (KAM) polymers were produced via polymerizing kraft lignin and acrylamide (AM) monomer with different molar masses and charge densities, and they were used for stabilizing kaolin dispersion at varied pHs. The surface tension and contact angle studies demonstrated that KAM improved the surface hydrophilicity of kaolin mineral particles. Among KAM polymers (KAM-1, KAM-2 and KAM-3), KAM-3 with the highest molar mass (Mw) of 97,000 g/mol and charge density of −2.1 meq/g had the highest adsorption of 2.16 mg/g onto kaolin mineral particles. It was also found that KAM adsorption on kaolin mineral particles was pH dependent with KAM adsorption decreasing with increasing pH from 4 to 10. Generally, increasing ionic strength enhanced the adsorption of KAM on kaolin mineral particles. Salt reduced electrostatic repulsion between the anionic KAM polymers and the negatively charged kaolin mineral particles and facilitated the adsorption. Relationship between zeta potential and relative turbidity of kaolin dispersion was developed at different levels of KAM adsorption. KAM (especially KAM-3) increased the volume fraction of kaolin mineral particles in the dispersion. It also improved the stability of kaolin dispersion, and the impact was more noticeable at pH 10. Treating the dispersion with KAM was more effective than mechanical stirring in stabilizing kaolin mineral particles.

Comparison Thermal and Hardness of CaO-MgO-Al2O3-SiO2-B2O5 Glass from Different Sources of Kaolin Minerals as Main Raw Mineral

Comparison Thermal and Hardness of CaO-MgO-Al2O3-SiO2-B2O5 Glass from Different Sources of Kaolin Minerals as Main Raw Mineral

Characterization and Fabrication of Metakaolin using Pulau Bangka Kaolin

Geopolymer material is an advanced material that is now being looked for its use as a refractory material, additive for building material, as well as other applications. Geopolymer is produced by polymerizing the precursor used in the process. One of the common precursors being used as geopolymer is metakaolin. The metakaolin was produced by thermal treatment (calcination) of kaolin minerals, which will convert its mineral structure from crystaline into amorphous and make it more reactive. This paper presents the fabrication and characterization of metakaolin using kaolin from Bangka island. The main structure of kaolin used in this study are kaolinite and muscovite according to XRD results obtained. Metakaolin was produced by thermal treatment using three different calcination temperatures ranged from 600 to 700°C and calcined for 4 hours. Prior to calcination, some specimens will be mechanically milled using planetary ball mill for 15 minutes with the milling speed of 20.00 rad/s and will also be calcined with the same parameter. As a comparison, commercial metakaolin MetaStar also be used to compare it to all metakaolin produced. All metakaolin produced are characterized by XRD and SEM, and STA test will be performed to kaolin to examine its thermal behavior. The STA test performed to both milled and non-milled sample shows that dehydroxylation and reconstruction process occurs at temperature range of 460-520°C and 520-640°C for kaolin sample, and at temperature of 426-537°C and 537-618°C for milled kaolin sample. XRD pattern obtained shows that almost all metakaolin produced have the relatively similar pattern to each other as well as to MetaStar, with the main peak of quartz (SiO2) at 2= 26.60° to 26.65°. The SEM results shows the characteristic layered-laminate plate-like structure of kaolin. Compared to another SEM results obtained, it can be concluded that there are no changes to the visible structure of metakaolin produced with the same kaolin used after calcination.

Statistical Treatment of Bleaching Kaolin by Iron Removal

In the present study, oxalic acid was used as a leaching reagent to remove iron from a kaolin mineral. Statistical analysis was conducted to determine the most influential factors in the dissolution of iron from the kaolin mineral. Our goal was ferric iron solubilization and its reduction to ferrous iron to improve the iron removal in the acid medium. Leaching experiments were conducted at atmospheric pressure. A two-level factorial design of the type 24 was utilized. The dependent variable was the percentage of dissolved iron, and the dependent variables in this study were acid concentration (0.35 and 0.50 M), temperature (75 °C and 100 °C), leaching time (2 and 4 h), and pH (1.5 and 2.5). An analysis of variance revealed that the effects of the factors temperature (b), pH (d), and the combined effects of temperature and time (bc) resulted in the maximum dissolution of iron of 88% at 100 °C, giving a kaolin mineral with a whiteness index 93.50%.

Response surface approach for optimization of Hg(II) adsorption by 3-mercaptopropyl trimethoxysilane-modified kaolin minerals from aqueous solution

The optimization of Hg(II) adsorption conditions from aqueous solutions with 3-mercaptopropyl trimethoxysilane-modified kaolin (MMK) used as a new adsorbent was analyzed by response surface methodology (RSM) approach. The MMK adsorbent was characterized by means of energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). According to the quadratic model obtained from central composite design (CCD) in RSM, the optimal conditions for adsorption were found to be 30.83 mg/L, 0.1 g, 7.44 and 31.41 °C for C o , adsorbent dosage, initial pH, and T (°C), respectively. With the obtained model, the maximum amount of adsorbed Hg(II) and %Hg(II) removed was calculated to be 30.10 mg/g and 98.01%, respectively. Langmuir and Dubinin-Radushkevich isotherms fitted well the experimental results. Thermodynamic studies revealed that the adsorption was physical, exothermic, spontaneous. The results indicate that MMK a new adsorbent has great potential for the removal of Hg(II) from aqueous media.

Crystallochemical aspect of clay and clayish matter minerals luminescence

X-ray luminescence (XRL) spectra in optical range of wave-lengths and thermoluminescence (TL) curves of several clay and clayish matter minerals were recorded for the first time. Mineral composition of all the samples was determined on the base of X-ray diffraction results. It was stated that XRL of clay minerals is related to their crystallochemical characteristics (type and degree of regularity of structure and isomorphism occurrence in particular). In the opinion of the authors, differences between luminescent characteristics of halloysite and kaolin minerals are related to syngony (triclinic or monoclinic) and possibility of Si4+ substitution with Al3+ in tetrahedral coordination that lead to uncompensated charges appearing and formation of luminescence centres based on silicon and aluminium tetroxides.

Accumulation of Free Electret Charges in Small-Sized Electrically Active Systems

The paper focuses on the study of structural features and electret properties of the fine-sized mineral kaolin. Special attention is paid to the mechanism of interphase interaction at the interface of electrically active heterogeneous media that leads to the emergence of internal self-electric field capable of ensuring the current circulation in such systems. The authors consider the possibility of regulating the processes of local change in the polar water structure under the impact of the self-electric field.

A Quasi-Solid-Phase Approach to Activate Natural Minerals for Zeolite Synthesis

Synthesis of zeolites or zeolite/clay composites from natural aluminosilicate minerals has received extensive attention because of its great usefulness in greening the zeolite manufacturing process, in which effective activation of natural aluminosilicate minerals is crucially important. Herein, we present an energy saving and green approach, the quasi-solid-phase activation method, to efficiently destruct the natural minerals under the conditions of a temperature as low as 100 °C and an activation time as short as 30 min. Our strategy consists of the following three steps: (1) preparation of a mixture of a natural kaolin mineral, NaOH, and water by kneading, (2) extruding of the mixture into sticks, and (3) low-temperature calcination of the stick, featured by the combined use of mechanochemical actions. The results showed that 84.7% Si species and 69.0% Al species in the kaolin mineral underwent a large degree of depolymerization in the kneading and extruding steps, and following calcination at 100 °C r...

Dissolution kinetics of kaolin mineral in acidic media for predicting optimal condition for alum production

The dissolution kinetics and mechanisms of reaction of Batagbon Kaolin in sulphuric and fluosilicic acids were studied. Leaching temperature, acid concentration, particle size, solid-to-liquid ratio, and stirring speed were selected as process parameters. It is observed that the dissolution rate increases with decreasing particle size and solid-to-liquid ratio, and increases with stirring speed, acid concentration, and leaching temperature. The experimental results indicate that the dissolution rate is of mixed control via hydrogen ion [H+] action, with reaction order of 0.813 and the reaction kinetics can be expressed as K m t=[1-(1-x)1/3+y/6[(1-x)1/3+ 1-2(1-x)2/3]. The activation energy of the process is determined to be 21.6 kJ/mol. The level of the product quality is also evaluated.

EPR spectra of a new radiation-induced paramagnetic centre in kaolins

AbstractThe EPR spectrum of a previously unreported paramagnetic centre formed in kaolin minerals by exposure to γ radiation is described. This centre, which is referred to here as the ‘C-centre’, was seen initially during an investigation of the radiation dose response of the EPR signal in the natural Lampang kaolin from northern Thailand, and its EPR properties are now presented for a purified sample from this material. They suggest a paramagnetic centre with rhombic symmetry based on O− associated with a single 27Al atom. Computer simulations suggest spin Hamiltonian parameters of g1 = 1.976, g3 = 2.0417 and A(27Al) = 2.10 mT, with g2 ≈ 2.01. This C-centre was also seen as a minor radiationinduced component in both crude and purified Ranong kaolin samples, along with a stronger signal from the B-centre radical. It seems to be associated with the kaolinite component, but was lost on annealing to 300°C after which only the signal from the A-centre was visible.

Soil genesis and mineralogy across a volcanic lithosequence

Lithology is a principle state factor of soil formation, interacting with climate, organisms, topography and time to define pedogenesis. A lithosequence of extrusive igneous lithologies (rhyolite obsidian, dacite, andesite and basalt) was identified in the Clear Lake Volcanic Field in the Coast Range of northern California to determine the effects of lithology on pedogenesis, clay mineralogy and soil physiochemical properties. Based on regional landscape erosion rates (0.2–0.5mmyr−1), the soil residence times for the investigated pedons (~150cm deep) were of the order of 3000 to 7500years indicating that the soils developed under the relatively stable Holocene mesic/xeric climate regime. Soils from all lithologies developed to a similar Xeralf taxonomy with remarkably consistent physiochemical properties. Although total (Fet) and dithionite-citrate extractable (Fed) iron concentrations diverged across lithologies, the degree of weathering as assessed by the Fed/Fet ratio was similar across the lithosequence. In spite of large differences in silica content of the parent materials, the clay mineralogical assemblage of all lithologies was dominated by kaolin minerals (kaolinite and/or halloysite). All pedons displayed an increase in halloysite and the degree of halloysite hydration with increasing depth, except the basalt pedon, which was dominated by kaolinite with only trace halloysite. We attribute this lack of halloysite in the basalt pedon to the lower silica activities associated with this silica-poor lithology. There was a lack of nanocrystalline minerals across all lithologies as inferred from selective dissolution. The dominance of crystalline materials is a function of the xeric soil moisture regime whereby summer soil profile desiccation promotes dehydration and crystallization of metastable nanocrystalline precursors. Further, the pronounced summer dry period results in dehydration of halloysite (1.0nm) to halloysite (0.7nm; also referred to as meta halloysite in some literature), together with transformation to kaolinite, in the upper soil profile. In spite of the relatively young soil residence times of these soils (Holocene age), the effects of lithology persisted only in differences in Fe oxide concentrations (Fed), as well as a lack of significant halloysite in basalt pedons. The overwhelming effect of climate in these highly weatherable parent materials narrowed the trajectory of pedogenesis, resulting in soils from contrasting lithologies converging on kaolin mineralogy, a lack of nanocrystalline constituents, and similar soil physiochemical properties.

Ash Characterization of Four Residual Wood Fuels in a 100 kWth Circulating Fluidized Bed Reactor Including the Use of Kaolin and Halloysite Additives

Solid biomass ash related issues and adequate fuel characterization, especially for fuels with similar thermochemical properties, are still major challenges in combustion. As a consequence, the fuel switching and the valorization of unconventional available fuels are hazardous. An integrated strategy to characterize biomass fuels for ash related issues is applied to four residual woody fuels, namely, a mesquite wood mixture, rubberwood, an invader bush wood, and bamboo wood. The characterization is performed with detailed analyses including (i) ash composition, (ii) ash association forms by leaching, (iii) recently reviewed predictive correlations, (iv) thermochemical equilibrium computations to predict the ash phases formed as a function of the combustion parameters and with the use of a state-of-the-art oxide database, and (v) experimental testing in a 100 kWth circulating fluidized bed pilot reactor (CFB100). The CFB100 testing allowed investigation of the fuel ash cycle including fly ash recirculation, agglomeration and fouling tendencies, and the use of halloysite and kaolin mineral additives. Among the four fuels, bamboo evidenced the higher agglomeration trend, which increased when reducing the additive. With respect to the other fuels, rubberwood seems to have a slightly higher tendency to initiate the coating-induced agglomeration mechanism. Concerning fouling, the mesquite mixture wood is more prone to deposition, mainly because of the formation of Ca-based deposits, while for the other three fuels, ash partitioning shows that the majority of reactive alkali metals fed to the pilot is accumulated in the bottom ash and circulating material. The novel integrated strategy is successfully applied for advanced solid biomass fuel characterization for combustion.

Occurrence of tosudite in the Guezouman, Tarat and Tchirezrine 2 formations, hosts of uranium deposits in Niger (Tim Mersoï basin)

AbstractTosudite, a regularly interstratified chlorite-smectite, crystallizes as an alteration mineral of several preexisting Al-bearing silicates (feldspars, kaolin minerals, chlorites) present in arkosic sandstones hosted in uranium deposits in Niger. X-ray diffraction patterns show a sharp superstructure at 29–29.6 Å for an air-dried state and a peak at 30.8–31.6 Å following ethylene glycol solvation. The 060 reflection at 1.507–1.509 Å indicates an overall dioctahedral character, and the very low coefficient of variation of the d00l reflections for the solvated mineral (0.03–0.13) permits validation of the regular interstratification justifying its identification as tosudite. Microprobe analysis allowed specification of the component layers of this mixed-layer mineral. The chlorite is a di-trioctahedral type analogous to sudoite (Si3Al4Mg2(OH)8), and the smectite component is a low-charge montmorillonite type Tosudite is characterized by large Al2O3 and MgO contents and small Fe content; its composition corresponds approximately to the formula where octahedral occupancy is ∼7. Scanning electron microscope (SEM) observations show that tosudite is closely associated with some uranium minerals: tosudite crystallization occurred during a late alteration event which post-dates burial diagenesis and during which uranium was remobilized by Mg-rich oxidizing fluids.

Cooling as the key parameter in formation of kaolinite-ammonium acetate and halloysite-ammonium acetate complexes using homogenization method

Although the one-step homogenization method has proved to be the simplest and cost-efficient way to intercalate ammonium acetate into kaolinite, the effectiveness of this method is not high enough for potential industrial applications in the area of nanocomposites. To enhance its efficiency we performed systematic experiments to analyze the influence of the intercalation parameters (kaolin mineral content, ammonium acetate to water mass ratio, type of sample holder, temperature, crystallinity and type of kaolin minerals).Instead of keeping the samples at room temperature or slightly above (60–80°C), which is generally preferred in intercalation methods, cooling below 0°C was proved to be the key parameter for direct intercalation of ammonium acetate by the homogenization method. Even after 8 weeks of aging at room temperature with optimal additional intercalation parameters, not more than 57% degree of intercalation was achieved, while only 1 week of cooling at −10 °C resulted in about 80% degree of intercalation (using the same additional parameters). The most applicable intercalation procedure was obtained by using 2.1:1. AAc to water mass ratio with 48wt% kaolin mineral content and keeping the samples at −24°C (where the influence of kaolin mineral type can become negligible) for 1 week in closed sample holder.

Characterization and predictive reaction model for cement-sand-kaolin composite for CO2 sequestration

The sustainability and sturdiness of cement based composite is increasingly coming to the forefront of infrastructural design, maintenance and as a green material that is environmentally benign. This paper seeks to develop a predictive mathematical global reaction rate model for atmospheric carbon dioxide sequestration in sandcrete composite of cement, mineral kaolin as supplementary aggregate material (SAM), sand and water. Standard experimental techniques and procedures were used. MatCad Professional (R14) software was used to simulate the developed model equation. Results obtained indicate that the overall global reaction rates for CO2 sequestration was higher in both experimental and simulated for the developed sandcrete-kaolin (S-K) composite (9.064×10−6 and 9.532×10−6mol/kgs) at 30°C compared to the reference kaolin-free sandcrete (S-S) composite (4.058×10−7 and 4.056×10−7mol/kgs) at an early stage of setting (9h). The quantity of carbon dioxide sequestered after 9h of carbonation ranges between 0.0185–0.0214kg/m3 for sandcrete-kaolin composite, while for the reference specimen it ranges from 0.0128 to 0.011kg/m3 at 30–45°C. The simulated results based on the developed overall global reaction rates compared strongly with the experimental in most of the parameters investigated. The mineralogical compositions and microstructure changes of the carbonated samples characterized using X-ray Diffractometer (XRD), X-ray Fluorescence (XRF), Scanning Electron Microscopy (SEM) and Diffraction Spectrometer (EDS) showed that addition of mineral kaolin to sandcrete enhanced the rate of CO2 sequestration.