Raw Kaolin Research Articles

Facile Hydrothermal Synthesis of Zeolitic ANA Membrane from Raw Kaolin

The present paper reported a preparation of zeolitic ANA (analcime) membrane on porous ceramic support by in situ synthesis method using raw kaolin as SiO 2 and Al 2 O 3 source with the molar composition of Al 2 O 3 ∙ 2.3SiO 2 ∙ 3.6Na 2 O ∙ 140.4H 2 O at hydrothermal temperature 200 oC. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the ANA membrane. The effects of aging time and hydrothermal time on the synthesis were investigated. The porous ceramic supports were prepared by adding 10.0 wt% of cristobalite and varying an amount of pore formers (activated carbon and calcite) by sintering at 1400 oC. This resulted in the high crystallinity of ANA observed on the support which was prepared from mixing of 2.5 wt% of activated carbon and 2.5 wt% of calcite. In addition to aging, it was observable that small crystals seemed to spread completely on the support within 3 days of aging. It seems that the longer the hydrothermal time is, the more obvious the crystals tightly bound with the support becomes.

Treatment of a Nigerian Kaolin ore for Improved Industrial Application

A study was carried out on leaching of Nigerian kaolin ore by Oxalic acid (C 2 H 2 O 4 .2H 2 O). The raw kaolin ore from Share, North central Nigeria was characterised by EDXRF (X-ray fluorescence) and major constituents were SiO 2 , Al 2 O 3 , and minor amounts of K 2 O, Na 2 O, CaO, TiO 2 , along with colour-imparting Fe 2 O 3 and MnO that need to be remove to upgrade the kaolin suitability for industrial usages. The effects of parameters such as C 2 H 2 O 4 concentration, temperature, and particle size were investigated. Under the standard leaching conditions of −75+63 μm particle size, 75 °C and 0.15 mol/L C 2 H 2 O 4, about 78.5% of kaolin ore was reacted within 120 minutes. Comparison of the EDX analysis of the raw and leached kaolin showed removal efficiency of 97.1% for the iron at optimal leaching conditions. Energy of activation of 17.65 kJ/mol was obtained in the study supports the proposed diffusion control mechanism for the dissolution process.

Synthesis of zeolite A using kaolin from Ethiopia and its application in detergents

Zeolite A synthesized from Ethiopian raw kaolin via alkali fusion with 91% crystallinity and CEC of >310 mg CaCO3 per g.

Synthesis of ZSM-5 from impure and beneficiated Grahamstown kaolin: Effect of kaolinite content, crystallisation temperatures and time

Raw kaolin obtained from Grahamstown, South Africa was beneficiated using wet sieving and filtration before use in the synthesis of ZSM-5 zeolite via hydrothermal treatment at various temperatures (120–190°C) and times (24–96h) under autogenous pressure. The impacts of kaolinite content and crystallisation parameters (i.e. temperature and time) on ZSM-5 formation were investigated. The mineralogical phases, morphology, surface area and porosity characteristics of the synthesised materials were investigated using XRF, XRD, FT-IR, HRSEM-EDS and N2 physisorption (BET) analyses. Catalytic tests were carried out in a fixed bed reactor, WHSV of 8h−1 and a temperature of 350°C at atmospheric pressure using 1-hexene as a feed. Beneficiation decreased the impurity content in the clay and increased kaolinite content which resulted in the formation of pure ZSM-5 zeolite. XRD and HR-SEM revealed that ZSM-5 synthesised from raw kaolin contained quartz and formed a ZSM-5/quartz coated composite. Temperature and time were critical in controlling phase purity and crystallinity of ZSM-5. At a synthesis temperature of 190°C ZSM-5 transformed into a more thermodynamically stable quartz phase. The optimum condition for synthesising pure ZSM-5 from this clay was found to be 150°C for 48h. Morphology, surface area and porosity of ZSM-5 changed with an increase in crystallisation time. ZSM-5 with a high external surface area and presence of mesopores were observed in products synthesised at 150°C for 24h. Microporosity further developed as time increased and the ZSM-5 became more crystalline. The catalyst performance studies indicated that the ZSM-5 synthesised from raw and beneficiated kaolin at crystallisation conditions 150°C and 48h had good 1-hexene transformation activity and high selectivity to gasoline range hydrocarbons. The presence of quartz in the catalyst enhanced catalyst stability and selectivity to C10+ hydrocarbons.

Production of geopolymer composites enhanced by nano-kaolin material

Nowadays kaolin raw material is usually used to produce nano-kaolin for geopolymer enhancement by using firing method. In the present study, kaolin used was taken from the Naqus Formation (Cambro-Ordovician age), west of Gabal El Gunna, Sinai, Egypt. Nano-kaolin material is an ultrafine material and was prepared from the taken kaolin by the firing process at 800 for 2 ℃ h with a heating rate of 5 /min. Six mixes were prepared and their laboratory specimens were made ℃ and cured up to 90 days. Water cooled slag was used as starting material, and sodium hydroxide and sodium silicate were used in the study as activators for the used kaolin. The formed geopolymer mixes with different ratios (1%, 1.5%, 3%, 5%, and 7%) of nano-kaolin as a partial replacement for the raw kaolin were investigated. Gelenium Ace super plasticizer was added in the ratio of 4% from the dry weight to ensure good dispersing of the used nano clay. Results showed that increasing the percentage of nano-kaolin up to 3% results in an enhancement in the mechanical properties as compared with the control mix up to 90 days of curing, while higher ratios are not preferable where they lead to agglomeration of the added nano materials and matrix dilution.

Equilibrium Study of Heavy Metals Adsorption on Kaolin

The adsorption of Cu(II), Cd(II), and Zn(II) from one- and two-component systems, on the raw and Na-form of kaolin, was investigated under batch conditions. The transformation of the raw kaolin into its Na-form causes surface-to-surface arrangement of crystals, which led to quantitatively similar but certainly different metal ion isotherm curves. Subsequently, the identified homogeneous Langmuirian adsorption on raw kaolin changed after sodium saturation into a heterogonous one. The Langmuir constants obtained from one-component systems were used to test the applicability of the new isotherm equation for modeling of the two-component equilibrium on raw kaolin. This model yielded quantification of the relative amounts of binding sites on the kaolin, showing partial specificity of the adsorbent to the individual metal ions. The validity of the model was confirmed by the alignment between the modeled equilibrium surface and 225 experimental points obtained for two different experimental sets.

Comparative studies on physico-mechanical properties of composite materials of low density polyethylene and raw/calcined kaolin

The paper describes the preparation of the composite materials of low density polyethylene (LDPE) as the base mixed separately with raw kaolin and the same calcined at 800 °C under the same variation in weight percentage using single-screw extruder and a mixing machine operated at a temperature between 190 and 200 °C. Some of the mechanical and physical properties such as Young's modulus, elongation at break, shore hardness and water absorption were determined at different weight fractions of filler (0, 2, 7, 10 and 15%). It was found that the addition of filler increases the mechanical properties. Absorption test was done in water at different immersion times for different composites. The degree of water absorption of composite materials was found to decrease with increasing wt% of kaolin filler (0–15%) according to Fick's law. Calcined kaolin produces better mechanical properties than raw kaolin.

Synthesis of zeolite A from Ethiopian kaolin

Zeolite A is synthesized using natural kaolin from Ethiopia. Raw kaolin and mechanically purified kaolin from Ansho, southern part of Ethiopia, have been surveyed. The starting kaolin and the final zeolite A samples were characterized by X- Ray Diffraction (XRD), elemental analysis (ICP), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA) and Cation Exchange Capacity (CEC). Metakaolinization was achieved by calcining the kaolin in air at 600 °C within 3 h, much lower than the temperatures previously reported in the literature. The optimization of the hydrothermal synthesis includes various NaOH concentrations at 100 °C, for different reaction time. Zeolite A with molar ratio SiO2/Al2O3 = 2.04 and Na2O/SiO2 = 0.44 was obtained with 90% crystallinity using solid/liquid (1.25 g/25 ml) and reaction time of 3 h which is significantly lower than the literature value that can reach up to 24 h. In this study, cubic crystal with rounded edge of zeolite A having cation exchange capacity of 295 mg CaCO3/g (4.6 meq Ca2+/g) of anhydrous zeolite is obtained that can be a good candidate for detergent formulation.

Chemical and Physical Comparative Study of the Effect of Wet and Dry Beneficiation of Kankara Kaolin

Chemical and physical comparative effect of wet and dry beneficiation processes for purification of kaolin was studied. X-ray flourescence XRF and particle size analysis of kaolin clay before and after beneficiation were carried out. The Si/Al ratio of the raw kaolin which was 1.90 decreased by 1.6 and 17.9% after the wet and dry beneficiation processes respectively. The clay content of the raw clay which was 48 wt% was improved to 73 wt% after the dry beneficiation while the impurity content was reduced from 52 to 27wt%. http://dx.doi.org/10.4314/njt.v34i2.13

Hydrothermal synthesis of high purity zeolite A from natural kaolin without calcination

Zeolite A is a commercially and environmentally important microporous material, which is commonly synthesized from calcined kaolin. One major drawback inherent to this approach is that the properties (i.e., purity, particle size, morphology, and cation-exchange capacity) of the final product depend largely on the quality of the raw kaolin ores. Herein we report on a new hydrothermal route for the synthesis of high purity zeolite A with controllable particle size and morphology, from natural kaolin without conventional high temperature calcination. This route starts with hydrothermal reaction of natural kaolin with NaOH to form hydrous sodium aluminosilicates (i.e. hydroxycancrinite and nepheline hydrate), which are then dissolved in dilute HCl. The resulting acid solution, after filtration to remove unreacted impurity minerals such as quartz and muscovite, is then adjusted to pH=7 to form an amorphous Si and Al gel, which is used for the hydrothermal synthesis of zeolite A. A comparative study of zeolite A samples synthesized from this new route and those from the conventional calcination method reveals that the former have more controllable size and morphology than the latter, giving rise to higher brightness and enhanced cation-exchange capacity. Another major advantage of this new method is that the common impurity minerals such as quartz, muscovite and feldspars in natural kaolin can be removed, giving rise to high purity zeolite A and possibly expanding this technique to the use of low-grade kaolin.

The rare earth element potential of kaolin deposits in the Bohemian Massif (Czech Republic, Austria)

Four kaolin deposits in the Bohemian Massif were studied in order to assess the potential for the recovery of rare earth elements (REE) as by-products from the residue after extraction and refining of the raw kaolin. The behaviour of REE + Y during kaolinitization was found to be largely a function of pre-alteration mineralogy. In the examples studied, i.e. granite-derived deposits of Kriechbaum (Austria) and Božicany, and arkose-derived deposits of Kaznějov and Podbořany (all Czech Republic), the REE + Y are predominantly hosted by monazite which has remained unaffected by kaolinitization. The overall REE + Y content of the variably kaolinitized rocks is strongly dependent on their genesis. While ion adsorption plays only a minor role in the concentration of REE + Y in the studied kaolinitized rocks, the processing and refining of the raw kaolin leads to residues that are enriched in REE + Y by a factor of up to 40. The use of a magnetic separator and a hydrocyclone in the processing of the raw material can yield REE + Y contents of as much as 0.77 wt%. Although this value compares well with the REE + Y concentration in some potentially economic REE + Y projects elsewhere, the overall tonnage of the (REE + Y)-enriched residue is by far not sufficient to consider economic extraction of REE + Y as by-product. Our results are most probably applicable also to other kaolin deposits derived from the weathering of Hercynian basement granites elsewhere (e.g. in Saxonia and Bavaria, Germany). Overall, the potential for REE + Y production as by-product from kaolin mining has to be regarded as minimal.

Effect of Metakaolin Sand on Properties of Cement Composites

The Slovak natural raw material kaolin sand containing 36 wt.% of kaolinite from Vyšný Petrovec deposit was thermally transformed at 650 °C for 1 hour to the metakaolin sand with relevant content of metakaolinite. Behaviour of cement composites having replacement of Portland cement with metakaolin sand including 0; 5; 10 and 15 wt.% of metakaolinite and water to solids ratio of 0.5 cured in water for 28 days and 90 days was studied by thermal analysis, X-ray diffraction analysis and mercury intrusion porosimetry analysis. The study concerned calciumsilica hydrate and calcium aluminate hydrate formation, portlandite dehydroxylation and calcite decarbonation. The influence of curing time and metakaolinite content were estimated. The replacement of Portland cement by metakaolin sand led to positive effect on relevant compressive strengths. The changes in microstructure involved especially reduction in portlandite content and pore structure refinement.

Clays and bodies for ceramic tiles: Reappraisal and technological classification

The ceramic tile industry is a dynamic sector whose technological innovation and market trends have drawn a complex picture of products and processes. Raw materials have been deeply involved in such an evolution: the flexibility of current manufacturing cycles enables the use of a very wide range of clays, whose chemical and mineralogical composition, particle size distribution and ceramic properties were reappraised. The classical reference schemes are no longer able to properly describe and predict the role of clays in tilemaking. In order to fill this gap, an industry-oriented, technological classification of clay raw materials is proposed on the basis of chemical (Fe2O3 content) and mineralogical parameters (amount of phyllosilicates and carbonates) together with particle size (fractions <2μm and >63μm) and plasticity (methylene blue index and Atterberg plastic index). It firstly discriminates light-firing and dark-firing clays according to an iron oxide threshold of 3%. Light-firing clays are distinguished by the amount of kaolinite group minerals and plasticity in “kaolins” (high-grade, low-grade, and raw kaolins, kaolinitic loams) and “plastic clays” (ball clays, pyrophyllitic clays, white bentonites); the distinction of three classes of ball clays with increasing plasticity is envisaged. Dark-firing clays are classified according to coarse-grained fraction and amount of carbonates in carbonate-rich types (marly and carbonatic clays), red loams and red clays; these latter are furtherly differentiated by the relative abundance of clay minerals. Such a classification is essential to draw the guidelines for body formulation and to explain the criteria followed in the industrial practice for each category of ceramic tiles. Key properties are discussed to design batches for porous tiles, vitrified and semi-vitrified red stoneware, and vitrified light-firing bodies. Both the clay classification and the guidelines to body formulation are intended to provide up-to-date tools to assess the ceramic potential and correct use in tilemaking of clay materials, but they cannot substitute a throroughful technological characterization, adequately simulating the industrial processing.

Refinement of industrial kaolin by microbial removal of iron-bearing impurities

The commercial value of kaolin raw materials is greatly affected by the presence and content of iron-bearing impurities, which can have a detrimental effect on the whiteness and refractoriness of manufactured products. Because of the high cost and environmental impact of techniques currently used to remove these impurities, some effort is now targeted toward the development of alternative methods, such as biological processes. This paper reports a series of anaerobic microcosm experiments conducted to evaluate the suitability of iron-respiring bacteria (IRB) of the Shewanella species (S. alga BrY, S. oneidensis MR-1, S. putrefaciens CN32, and S. putrefaciens CIP 8040), in bioleaching iron-bearing impurities from raw kaolin. All tested bacterial strains were able to reduce and leach ferric iron present in the kaolin, thereby substantially improving its color properties. Among the tested bacteria, S. putrefaciens CIP8040 produced the greatest improvements, with increases in ISO brightness and whiteness from 74% to 79% and from 54% to 66%, respectively, in 5days at 30°C. Neither secondary mineral nor crystal-chemical alteration of the kaolinite was observed by X-ray diffraction and infrared spectroscopy. Observations of the biotreated kaolins by scanning electron microscopy showed that the original hexagonal shape of the clay particles became less regular. Further research and development should now focus on optimising the rate and extent of the bioleaching process before its application at a larger pilot or industrial scale. In particular, further studies should evaluate the environmental and economical benefits compared to currently used approaches, such as the chemical bleaching with sodium hydrosulfite.

Surface modification with cold plasma application on kaolin and its effects on the adsorption of methylene blue

In this study, cold plasma treatment was applied for the surface modification of kaolin adsorbent to improve the removal of methylene blue (MB) from aqueous solution. To achieve the aim, the conditions for adsorption, including cold plasma application time, initial dye concentration, and pH were investigated with respect to the removal efficiency of MB. The changes of the surface property before and after cold plasma treatment were discussed. The maximum adsorption capacity of MB compared with untreated raw kaolin increased from 19.60 to 51.02mg/g (up to approximately 2, 5-fold) after modification by cold plasma. The experimental data were analyzed using pseudo first-order and second-order kinetic models. The surface properties of kaolin treated with cold plasma were investigated with scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and point of zero charge (pzc) measurements to understand the adsorption mechanism.

Development of kaolinite supported ferric oxalate heterogeneous catalyst for degradation of 4-nitrophenol in photo-Fenton process

Ferric oxalate catalyst supported on phosphoric acid treated kaolin (ATKaol) was prepared and tested on the degradation of 4-nitrophenol (4-NP). The X-ray fluorescence (XRF) and Brunauer–Emmett–Teller (BET) characterization results showed drastic distortions in the raw kaolin (Kaol) crystalline structure and an increase in specific surface area (SSA) from 18.78 to 166.12m2g−1 after acid treatment. The incorporation of Fe was confirmed with Fourier transformed infra-red spectroscopy (FTIR), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) results. The degradation of 4-NP without UV was slower compared to when UV was used. There was no appreciable degradation in the absence of either catalyst or hydrogen peroxide (HP). The acid treated kaolinite catalyst (ATKaolCat) exhibits high catalytic activity without pH adjustment degrading 99% of 4-NP (100ppm) in 4min using 2.0g ATKaolCat and 20% excess HP at 40°C. The reusability study shows 9.4% decrease in efficiency after 5 rounds. The kinetic model developed showed good agreement with the experimental data. The model showed that ATKaolCat has higher selectivity for direct oxidation of 4-NP to mineralized products compared to oxidation via intermediates. These qualities make the catalyst promising in 4-NP degradation.

Synthesis and Characterization of Mesoporous Molecular Sieve Al-MCM-41 Using Kaolin as Raw Material

Ordered hexagonally mesoporous molecular sieve Al-MCM-41 with Si/Al (atom) ratio=9 was prepared by hydrothermal synthesis using raw kaolin. X-ray diffraction (XRD), Nitrogen adsorption desorption, Transmission Electron Microscope (TEM) and Energy Dispersive X-ray Detector (EDX) were employed to characterise raw kaolin, calcined kaolin, as-synthesized and calcined Al-MCM-41. The results indicated that characteristic reflections of raw kaolin disappeared after calcination, both of as-synthesized and calcined Al-MCM-41 exhibited well ordered hexagonally mesoporous molecular sieve structure.

Prospects for Using Combined Metallurgical Production Technogenic Raw Material in the Refractory Industry

Features are provided for the chemical and mineral composition of standard electrocorundum sludge and transformation of its components during oxidation firing, and also analysis of chamotte based on combined technogenic raw material and kaolin. Properties are indicated for the mullite and glass phase formed, and mullite refractoriness based on different components. An indispensable condition for obtaining high quality chamotte and mullite in poured layers is oxidation of the lower titanium compounds contained in sludge. The temperature for liquid phase appearance is 830 – 1130°C. Mineralizer admixtures reduce aluminosilicate melt viscosity.

Kaolin-based geopolymers: Effect of mechanical activation and curing process

The present work aimed to investigate the influence of mechanical activation of raw kaolin on the final compressive strength of as-obtained geopolymers regarding the curing profile. A commercial raw kaolin containing 81.5mass% of kaolin (labeled KBip) was used. Mechanical activation was performed by dry ball-milling of raw kaolin at 250rpm for 1h. The curing temperatures were 40°C, 70°C or 100°C for 24h, 48h or 72h. The compressive tests were conducted on geopolymers after the 2nd, 7th, 14th and 28th days of ageing. Mechanical activation was performed to improve mechanical properties. Results showed that without mechanical activation, the optimal curing condition was 24h at 70°C and the compressive strength was 15MPa after 28days of ageing. Under mechanical activation, improvement of the compressive strength was obtained with a curing time of 72h at 70°C (to reach 35% increase) or with a curing temperature of 100°C (for 76% improvement). The formation of alkaline aluminosilicate gels and new crystalline hydrated phases controlled the strength development of geopolymers while the occurrence of carbonated species was responsible for the degradation of mechanical properties.

Production of Refractory Lining for Diesel Fired Rotary Furnace, from Locally Sourced Kaolin and Potter’s Clay

This research was conducted to formulate a refractory lining recipe for lining diesel fired rotary furnace from locally sourced kaolin, using locally sourced potter’s clay as binder. Six samples (A-F) of kaolin clay mined locally from Apata II area, Ondo road, in Ile-Ife,Nigeria, were roasted at 1200oC held for 8 hours, mixed with different percentages of raw kaolin and appropriately made into briquettes using potter’s clay of good plasticity as binder. The samples were tested for various refractory properties. The result showed that sample mixes A (100% chamotte), B (80% chamotte, 20% rawkaolin) and C (60% chamotte, 40% raw kaolin) are considered to have good properties. However, the optimum material-mix for the refractory bricks lining, with particular reference to the highest thermal shock resistance was found to be 80% chamotte mixed with 20% raw kaolin.