Calcined Kaolin Research Articles

Visible‐light‐driven photocatalytic activity of kaolinite: Sensitized by in situ growth of Cu‐TiO2

AbstractSensitized kaolinite with improved visible‐light catalytic activity was prepared via a facile in‐situ growth of nanosized Cu‐TiO2 on the surface of the sulfated kaolinite impregnated in Cu‐TiO2 sol. The as‐prepared photocatalysts were characterized in terms of various techniques. The transmission electron microscope and energy dispersive spectrometer results revealed that Cu‐TiO2 could grow on the surface of the pretreated kaolinite and the aggregation of Cu‐TiO2 was successfully inhibited. The X‐ray photoelectron spectrum confirmed the formation of AlOTi bonds between Cu‐TiO2 and sulfated kaolinite in the sensitized kaolinite composite. The sensitized kaolinite composite exhibited significantly improved performance in the degradation of Rhodamine B (RhB), leading to about 87% of RhB degradation in 180 min, which is superior to that of the kaolinite, calcined kaolin, and sulfated calcined kaolin under visible‐light irradiation. The superior photodegradation activity of the sensitized kaolinite composite was primarily attributed to the synergetic effect of Cu‐TiO2 sensitization and sulfation, resulting from the efficient transfer and separation of the photo‐induced charge carriers between Cu‐TiO2 and kaolinite.

Microstructural, mechanical and pozzolanic characteristics of metakaolin-based geopolymer

The use of cement contributes to global CO2 emission and this leads to the depletion of ozone layer,causing global warming. The quest to reduce or eliminate this problem has resulted in the discovery of metakaolin-based geopolymer as an alternative to the use of cement in construction work. In this study, metakaolin obtainedas a result of kaolin calcination from some deposits in Nigeria; Ogun (Imeko), Edo (Okpela), Ondo (Ifon)and Ekiti (Isan-Ekiti) were characterized and used to determine the compressive and flexural strength of metakaolin-based geopolymer concrete (Mk-GPC). Cubes of 150 × 150 × 150 mm were used for the compressive strengthtest and reinforced concrete beams of size 150 × 250 × 2160 mm were produced to test for flexural strength. A water-absorption test was also carried out on Mk-GPC and the effect of ball-milling was assessed on the strengthproperties. The results from the various tests showed that 800°C for 1 hour of calcination of kaolin gives bestcombination of performance properties due to the presence of amorphous silica in metakaolin. Mk-GPC gavehigher compressive strength and at an early age than ordinary Portland cement (OPC) concrete. The water absorptioncapacities of Mk-GPC were higher than the control samples. In the flexural strength test, the reinforcedbeams failed in flexural-shear mode and the shear capacities at 28-, 56- and 90-day curing age of the beams werebetween 0.656 and 0.938 MPa for Mk-GPC beams and between 0.563 and 0.844 MPa for the control beams. Themoment capacities for the beams were between 19.25 and 33.25 (×10³ kgm²/s²) for Mk-GPC beams and were between22.75 and 28.0 (×10³ kgm²/s²) for the control beams. The study has revealed that metakaolin-based geopolymercan serve as an alternative to cement for sustainable construction in the Nigerian construction industry.

Effect of high temperature on the performance of self-compacting mortars produced with calcined kaolin and metakaolin

The effects of high temperature up to 900 °C on the mechanical characteristics of self-compacting mortars (SCMs) containing different proportions of calcined kaolin (CK) and metakaolin (MK) were investigated in this study. The percentages of CK and MK that replace cement in this work were 0%, 5%, 10%, 15% and 20% by weight. The mechanical performance was assessed from compressive strength and flexural strength on the specimens of 40x40x160 mm size exposed 3, 28 and 90 day- water curing at ambient temperature and on the 28 day-specimens at high temperature while the durability of 28 day-SCMs samples was assessed from porosity, water absorption, sorptivity and density tests on water cured specimens of 50x50x50 mm size. The fresh properties of mortars were researched by slump and V-funnel tests. The rheological properties of fresh mortars were investigated by conducting the viscosity test. The outcomes of the study reveal that workability of mixtures was decreased with increasing proportion of MK replacement. The results also revealed that at 28 and 90 days of curing ages, the specimens of SCMs with MK15 gained the highest strength of 65.40 MPa and 79.01 MPa for about 10.13% and 15.46% more than the control specimens at the respective ages. Results illustrated that while the temperature rises, the compressive strength reduction of CK blended SCMs samples decreases with increasing replacement ratio of CK. A remarkable reduction in the total water absorption and porosity values of MK blended SCMs samples was observed. The highest density values at all SCMs mixes were observed for MK5 blended samples about 8.44% increase. 15% replacement level of MK gives the lowest sorptivity values.

Framework for Monitoring and Control of the Production of Calcined Kaolin

In response to the growing demand for sustainable products and services, the kaolin calcination industry is developing practices that optimise the use of resources. The main challenges include more efficient use of raw materials and a reduction in the energy consumed by the calcination furnace. An opportunity to achieve this lies in the optimisation of the calcination process. This can be done by giving real-time feedback on the quality parameters of the generated calcined kaolin. This study proposes the use of infrared spectroscopy as a monitoring technique to determine the chemical properties of the calcined kaolin product. The basis of the monitoring system is the measurement of the kaolin soluble alumina content as one of the most important quality parameters; this property is an indicator of the over- or under-use of raw materials and energy during the calcination process and can advise the operations regarding the optimisation of the working conditions of the furnace. The implementation of an infrared-based monitoring system would lead to increased efficiency in the production of calcined kaolin.

Alkaline Activation of Kaolin Group Minerals

Zeolites can be obtained in the process of the alkali-activation of aluminosilicate precursors. Such zeolite–geopolymer hybrid bulk materials merge the advantageous properties of both zeolites and geopolymers. In the present study, the effect of the type and concentration of an activator on the structure and properties of alkali-activated metakaolin, and metahalloysite was assessed. These two different kaolinite clays were obtained by the calcination of kaolin and halloysite, and then activated with sodium hydroxide and water glass. The phase compositions were assessed by X-ray diffraction, the microstructure was observed via scanning electron microscope, and the structural studies were conducted on the basis of the infrared spectra. The structure and properties of the obtained alkali-activated materials depend on both the type of a precursor and the type of an activator. The formation of zeolite phases was observed when the activation was carried out with sodium hydroxide alone, or with a small addition of water glass, regardless of the starting material used. The higher proportion of silicon in the activator solution does not give crystalline phases, but only an amorphous phase. Geopolymers based on metahalloysite have better compressive strength as the result of the better reactivity of metahalloysite compared to metakaolin.

Improvement in the Synthesis Conditions and Studying the Physicochemical Properties of the Zeolite Li-A(BW) Obtained from a Kaolinitic Rock

Crystallization of zeolite Li-A(BW) from kaolinite (Standard Porcelain by the IMERYS Minerals Ltd) through a conventional hydrothermal treatment is here achieved for the first time with no additives as reported in the literature. Moreover lower kaolin calcination temperatures and lower synthesis temperatures are tested and verified in this work. The synthesis process is rather simple as the reaction of kaolinite with alkali occurs very readily after calcination of at 650 °C. Metakaolin is mixed with calculated amount of aluminum hydroxide and lithium hydroxide and the experiment is performed at ambient pressure and 180 ± 0.1 °C. Li-A(BW) is characterized by powder X-ray diffraction, high temperature X-ray diffraction, scanning electron microscopy, inductively coupled plasma optical emission spectrometry, thermal analysis and infrared spectroscopy. Calculation of cell parameters (through Rietveld Refinement) and density, specific surface and pore size are also achieved. The amount of amorphous phase in the synthesis powders is estimated with quantitative phase analysis using the combined Rietveld and reference intensity ratio methods. The results become notably attractive in view of a possible industrial transfer of the synthesis protocol.

Microstructural and mechanical properties of poly(sialate-siloxo) networks obtained using metakaolins from kaolin and halloysite as aluminosilicate sources: A comparative study

This work focuses on the comparison between the mechanical and microstructural properties of poly(sialate-siloxo) networks based on metakaolins from halloysite and kaolin. Poly(sialate-siloxo) networks were prepared using three metakaolins as aluminosilicate sources. Sodium waterglass from rice husk ash and commercial sodium waterglass were used as chemical reagents. The obtained results showed that metakaolins from kaolins have plate shapes with coarse particle sizes whereas the one from halloysite has a spherical morphology and smaller particle sizes. The IR spectra of poly(sialate-siloxo) networks from calcined halloysite indicate the higher value of the wavenumber of the main band. The XRD patterns of all poly(sialate-siloxo) networks show the broad hump structure with higher intensity between 18 and 40°(2θ). The XRD patterns of poly(sialate-siloxo) networks show the band of the unreacted metakaolin at about 20.45°(2θ). This band is more pronounced on the XRD patterns of geopolymer cements from calcined halloysite. The obtained poly(sialate-siloxo) networks based on metakaolins from halloysite and kaolin have a compact, homogenous and denser microstructures. The compressive strength values of the poly(sialate-siloxo) networks using calcined kaolin are ranging from 58.43 to 66.52 MPa whereas those using calcined halloysite are between 72.29 and 88.50 MPa. The compressive strength values of poly(sialate-siloxo) networks using calcined halloysite are higher compared to those from calcined kaolin. The higher compressive strength values of the geopolymer cements from calcined halloysite could be attributed to the fine and spherical particle sizes of calcined halloysite. This implies that the shape and the fine particle sizes of the raw materials influence the properties of the poly(sialate-siloxo) networks. Metakaolin from halloysite can be used as an aluminosilicate source for producing poly(sialate-siloxo) network with higher mechanical properties.

Enhancement of the Mechanical Properties of Kaolin Geopolymer Using Sodium Hydroxide and Calcium Oxide

This article presents the effect of adding sodium hydroxide and calcium oxide on the mechanical properties of a kaolin-based geopolymer binder cured at room temperature. A geopolymer binder was first prepared using calcined kaolin as an aluminosilicate precursor and sodium silicate as alkaline activator. The calcium and sodium hydroxide were then added at dosages of 0, 5, 10, 15, and 20% by weight of kaolin, and the compressive strength was measured for specimens cured at room temperature. The results showed that the addition of either 5 wt.% sodium hydroxide or 10 wt.% calcium oxide dramatically increased the room-temperature compressive strength of kaolin geopolymer by 90% and 105%, respectively. The addition of either 5 wt.% sodium hydroxide, or 10 wt.% calcium oxide has also enhanced the water stability of the kaolin geopolymer by about 120%. X-ray diffraction (XRD)and scanning electron microscopy (SEM) test techniques were performed to get insight the binder microstructural phases and its chemical characteristics.

Effect of thermochemical activation of clay raw materials on phase formation, microstructure and properties of aluminosilicate proppants

In this study, the complex influence of the preliminary calcination temperature of refractory clay raw materials and mineralizing oxide additives on phase formation, microstructure and properties of aluminosilicate proppants was researched. The morphology structure and phase composition of specimens were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the effectiveness on the addition of 3d-transition element oxides (Fe2O3 and MnO2) and alkaline and alkaline earth oxides (Na2O, MgO, CaO) and B2O3 to the sintering process of samples based on kaolin depends on the temperature of preliminary kaolin calcination (900–1100 °C) and temperature sample sintering (1350–1450°C). Based on the effectiveness of the influence on aluminosilicate ceramic sintering at the temperature range of 1400–1450°C, the recommended additives can be sequentially arranged as follows: Fe2O3 > MgO > MnO2 > Na2O > B2O3 > CaO. The thermal activity scheme for each group of mineralizer additives depending on the temperature conditions of the consolidation process has been proposed in this study. The use of mineralizing additives with kaolin calcined at a temperature range of 980–1100 °C produces lightweight aluminosilicate proppants with bulk density of up to 1.50 g/cm3 at sintering calcination of 1400–1450 °C, which can endure destructive pressures up to 52 MPa.

Dorfner to sell hydrous & calcined kaolin from 20 Microns Ltd

Dorfner to sell hydrous & calcined kaolin from 20 Microns Ltd

The effect of calcination temperature on metakaolin structure for the synthesis of zeolites

ABSTRACTThe aim of this research was to determine the temperature of kaolin calcination in order to obtain an intermediate product (metakaolin) for the synthesis of geopolymers with potential application as self-supporting zeolitic membranes. The products obtained were analysed with X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The structural analysis of the metakaolins obtained suggested that the optimal temperature for the proposed application is 700°C. After alkali activation of metakaolin, it is possible to obtain zeolite A and hydroxysodalite. The factors analysed, determining the type and quantity of crystalline phases, were activation temperature and concentration of sodium hydroxide solution (activator). The largest amounts of zeolites were obtained by alkali activation with 9 mol/dm3 NaOH solution at 70°C.

Control strategy for a multiple hearth furnace in kaolin production

In the face of strong competition, the kaolin calcination industry is aiming at higher profitability through increased productivity and reduction of costs. Specifically, the industry is facing market demands to maintain product quality with the depletion of high-quality ore. Therefore, considerable research is being conducted to enhance existing processes and their operation and control. In this paper, the concept of a mineralogy-driven control strategy for multiple hearth furnaces for kaolin production is presented and discussed. The aim of the advanced control concept is to increase capacity and to reduce energy consumption while maintaining the desired product quality. The control is based on two main soft sensors: the spinel phase reaction rate indicator for energy use reduction and the mullite content indicator for capacity improvement. In this simulation study, the control strategy is tested and compared with an industrial controller based on a proportional–integral scheme as a benchmark. The results show that the capacity of the process is considerably improved and energy use is remarkably reduced.

Toward an on-line characterization of kaolin calcination process using short-wave infrared spectroscopy

ABSTRACTIn the production of calcined kaolin, the on-line monitoring of the calcination reaction is becoming more relevant for the generation of optimal products. In this context, this study aimed to assess the suitability of using infrared (IR) spectroscopy as a potential technique for the on-line characterization of the calcination of kaolin. The transformation of kaolin samples calcined at different temperatures were characterized in the short-wave (SWIR) spectra using the kaolinite crystallinity (Kx) index and the depth of the water spectral feature (1900D). A high correlation between the standard operational procedure for the quality control of calcined kaolin and the Kx index was observed (r = -0.89), as well as with the 1900D parameter (r = -0.96). This study offers a new conceptual approach to the use of SWIR spectroscopy for the characterization the calcination of kaolin, withdrawing the need of using extensive laboratory techniques.

Al-MCM-41 Synthesized from Kaolin via Hydrothermal Route: Structural Characterization and Use as an Efficient Adsorbent of Methylene Blue

The mesoporous material Al-Mobil Composition of Matter No. 41 (Al-MCM-41) was successfully obtained from kaolin, a low cost raw material, by means of hydrothermal route. The process of synthesis of Al-MCM-41 was based on calcination of kaolin, dealumination by acid treatment, hydrothermal synthesis in alkaline medium and surfactant extraction. The characterization of the obtained mesoporous material was carried out by techniques such as: X-ray diffraction, infrared vibrational spectroscopy, 29Si and 27Al solid state nuclear magnetic resonance, scanning electron microscopy, transmission electron microscopy and N2 adsorption-desorption. The X-ray diffraction at low angles allowed the determination of the cell parameter, which was 4.02 nm. The analyses of scanning and transmission electron microscopy revealed important morphological properties of the synthesized material. N2 adsorption/desorption showed a Brunauer-Emmett-Teller (BET) specific surface area of 1,303 m2 g-1, pore volume of 1.23 cm3 g-1 and average diameter of 2.45 nm. The mesoporous material presented a maximum adsorption capacity of 316 mg g-1 for the cationic dye methylene blue (MB) in a concentration typical of industrial effluents, which makes it a potential adsorbent for MB removal from wastewaters.

Study on the Strength Development of Cemented Backfill Body from Lead‐Zinc Mine Tailings with Sulphide

The unconfined compressive strength (UCS) development of cemented backfill materials for lead‐zinc mine tailings with sulphide was studied. The results showed that the UCS of the cemented backfill body with ordinary Portland cement (OPC) as binder decreased in the later curing days, regardless of particle size. Under the same conditions, the higher the OPC content, the higher the UCS of the cemented backfill body, and the UCS of the cemented backfill body began to decrease at the longer curing days. Under the same conditions, the finer the tailings, the lower the UCS of the cemented backfill body at each age, and the UCS of the cemented backfill body began to decrease at the earlier curing age. X‐ray diffraction analysis (XRD) showed that the reduction of the UCS of the cemented backfill body was related to the formation of an expansive substance (expansive gypsum) in the cemented backfill body, which led to the cracking of the test sample. In the cemented backfill materials of coarse tailings of lead‐zinc mine, the composite binder formed by OPC and calcined kaolin (CK) containing metakaolin was used; the amount of calcium hydroxide, the hydration product of cement, was reduced or eliminated due to the pozzolanic reaction of metakaolin; and the amount of expansive gypsum was reduced or eliminated, so the UCS of the cemented backfill body increased within 360 days of curing.

Hydroxyapatite from Golden Apple Snail Shell with Calcined Kaolin for Biomaterial Applications

Biomaterials containing calcium phosphate ceramics have been used as bone substitute materials. In this study, the compressive strength and in vitro bioactivity tests of hydroxyapatite (HAp) from golden apple snail shell mixed with calcined kaolin (CK) were investigated for used as bone substitute materials. Mixed paste samples were cured at 23°C and 60°C for 2 days and curing continued at 23°C for 7 days. The effects of HAp:CK weight ratio on compressive strength and apatite formation in simulated body fluid (SBF) were investigated. The good compressive strength was 32.93 MPa at 25 % hydroxyapatite with 75% calcined kaolin at curing temperature of 60°C. Apatite formation was observed on sample surfaces after soaking in SBF for 28 days using SEM, EDS and XRD analyses. It was found that apatite formation took place on the surface of samples, consisting of HAp, after immersion in SBF.

SYNTHESIS OF ZEOLITE AND COMPOSITE OF ZEOLITE/TiO2 FROM KAOLIN AND ITS APLICATION TO ADSORPTION-PHOTODEGRADATION OF METHILEN BLUE

<p>In this study, zeolite was synthesized from kaolin which was founded from Bangka Belitung as the starting material. Meanwhile, sodium silicate was used as silica source. Zeolite is material with many benefits, such as become an adsorbent. Kaolin has been used as starting material due to high content of silica and alumina, i.e 35 - 50 %. Zeolite was prepared by hydrothermal synthesis process, by mixing the metakaolin which was produced by calcination of kaolin at 700 °C for 6 hours, with sodium silicate and NaOH. The NaOH was used to activate the major components of Si and Al in the kaolin.The hydrothermal process was conducted at 100 °C for 24 hours with various concentrations of NaOH, i.e 1.5 N and 2.5 N. The NaOH concentration might determine the type of zeolite obtained. To improve the nature as adsorbent, zeolites modified into zeolit/TiO<sub>2</sub>. The addition of TiO<sub>2</sub>into the prepared zeolit aimed to produce a material with capability as adsorbent-photocatalyst. The result of research found that the addition of NaOH 1.5 N produced zeolite NaP1. Meanwhile, the addition of NaOH 2.5 N produced the NaP1 zeolite, zeolite X, and faujasite. The composite of zeolit/TiO<sub>2</sub>has ability on adsorption-photocatalytic as it was proven by methylene blue degradation under ultraviolet light.</p>

SYNTHESIS OF ZEOLITE AND COMPOSITE OF ZEOLITE/TiO2 FROM KAOLIN AND ITS APLICATION TO ADSORPTION-PHOTODEGRADATION OF METHILEN BLUE

<p>In this study, zeolite was synthesized from kaolin which was founded from Bangka Belitung as the starting material. Meanwhile, sodium silicate was used as silica source. Zeolite is material with many benefits, such as become an adsorbent. Kaolin has been used as starting material due to high content of silica and alumina, i.e 35 - 50 %. Zeolite was prepared by hydrothermal synthesis process, by mixing the metakaolin which was produced by calcination of kaolin at 700 °C for 6 hours, with sodium silicate and NaOH. The NaOH was used to activate the major components of Si and Al in the kaolin.The hydrothermal process was conducted at 100 °C for 24 hours with various concentrations of NaOH, i.e 1.5 N and 2.5 N. The NaOH concentration might determine the type of zeolite obtained. To improve the nature as adsorbent, zeolites modified into zeolit/TiO<sub>2</sub>. The addition of TiO<sub>2</sub>into the prepared zeolit aimed to produce a material with capability as adsorbent-photocatalyst. The result of research found that the addition of NaOH 1.5 N produced zeolite NaP1. Meanwhile, the addition of NaOH 2.5 N produced the NaP1 zeolite, zeolite X, and faujasite. The composite of zeolit/TiO<sub>2</sub>has ability on adsorption-photocatalytic as it was proven by methylene blue degradation under ultraviolet light.</p>

Defluorination of drinking water using surfactant modified zeolites

The prevalence of high concentrations of fluoride (i.e. > 1.5 mg/l) in groundwater in the Northernpart of Ghana especially around the Bongo communities has been an issue of concern.Owingto the arid nature of these localities, the inhabitants (who are mainly peasant farmers), relymore on groundwater sources for their drinking water. With the strenuous nature of their joband the warm weather conditions, the farmers generally consume more water, thus becomingmore vulnerable to dental and skeletal fluorosis. This study focused on the removal of fluoridefrom groundwater by employing surfactant modified zeolites (SMZ) synthesized using locallyavailable kaolin material as precursor. The zeolite synthesis involved calcination of kaolin, alkaline fusion and hydrothermal treatment. The final product was modified with 5g/L Hexadecyltrimethylammonium bromide (HDTMABr). The zeolite was characterised by Xray Diffraction(XRD), Energy Dispersive Xray (EDX) and Scanning Electron Microscopy (SEM) and the modified form employed in batch fluoride removal studies. The fluoride adsorption kinetics was studiedusing model water with varying initial fluoride concentration. From the EDX analysis, the synthesized zeolite NaLSX was found to comprise predominantly Oxygen (60%), Silicon (15%), and Aluminium (13%). The SEM showed the zeolite NaLSX crystals to be octahedrally shaped. The unmodified zeolite NaLSX was incapable of adsorbing fluoride ions but the surfactant modified zeolite adsorbed fluoride. The fluoride adsorption capacity of the modified zeolite was pH dependent and peaked at pH 6.0 – 7.0. Keywords : characterization, defluoridation, groundwater, surfactant, zeolites

Effect of highly processed calcined kaolin residues on apple water use efficiency

Processed calcined kaolin particle films (PKPF) have been shown to repel some insects and reduce various environmental stresses often resulting in improved yield and quality of horticultural crops. PKPF studies in the literature have various water use efficiency (WUE) responses. The purpose of this study was to evaluate 2 application rates of PKPF (3% and 12%) on the whole tree water use efficiency and compare gas exchange values with carbon isotopic discrimination and seasonal water use efficiency in order to determine if there are consistent effects on WUE in apple and infer the mechanisms of action. Fruit yield and total biomass influence WUE whether WUE is measured directly in whole plant chambers, estimated by biomass/unit evapotranspiration, or Δ13C. Δ13C analysis of WUE generally found that the untreated control had lower values and therefore higher WUE than PKPF treatments. Whole plant gas exchange analysis of WUE generally lacked the sensitivity to identify the treatment differences observed using Δ13C analysis and those treatment differences identified were contrary to Δ13C analysis. A lysimeter study supported the reduced WUE of PKPF treated plants by demonstrating increased E with a range of PKPF residue amounts. The lysimeter results suggest that for well-watered and presumably non-stressed conditions, gas exchange is limited by leaf temperature and the concomitant leaf-air vapor pressure deficit that influence stomatal conductance. When leaf temperature is reduced by PKPF, the response results in increased stomatal conductance and gas exchange, as measured by increased E. The reduction in WUE by PKPF treatment is balanced by an increase in overall gas exchange and increased yield and quality.