Mineralogy and physico-chemical properties of alluvial clays from Sanaga valley (Center,Cameroon): Suitability for ceramic application

Alluvial clays from four localities along the Sanaga River (Center Cameroon) were studied by physico-chemical, mineralogical and technological characterization in order to assess their suitability as ceramic raw materials. The chemical compositions indicated that SiO₂ (65–70%) and Al₂O₃ (12–15%) are major elements while Fe₂O₃ is less (4–7%). Kaolinite, quartz and feldspar are the main minerals. Particle size distribution and chemical composition are indicative of “plastic red clays” belonging to heavy sandy clays group. Their medium to high plasticity is suitable for fired earth and fine ceramics products. Pressed samples were fired at temperatures ranging between 900 and 1100 °C for coarse ceramic products. Linear shrinkage, flexural strength and water absorption indicated that the clays from one site (Mbandjock) are good for brick making. Clays from the three other localities present poor technological properties (higher shrinkage and cracks), they need degreasers before use as ceramic raw materials. Although water absorption and flexural strength parameters are good for all the studied samples, firing shrinkage needs to be improved.     

Study of mixtures using simplex design for the addition of chamotte in clay bricks

The red clay ceramic industry is associated with several environmental damages, from the extraction of natural resources as raw materials to the generation of high amounts of waste. This study proposed the incorporation of the ceramic bricks waste (chamotte) in ceramic mixtures for the production of clay bricks. In order to define the greater content of chamotte, which can be added maintaining the technical qualities required for the product, the experimental design of mixtures was used, with the production of bricks containing the chamotte and two other clayey materials. The compositions were subjected to firing at 850, 950, and 1050°C. The properties of firing linear shrinkage, apparent specific mass, water absorption, apparent porosity, and axial compressive strength were evaluated. It was observed that chamotte (C) contributed to the improvement of some of these properties, such as linear shrinkage. Overlapping the response surfaces obtained in the statistical analysis, the optimal chamotte (C) content was determined for each firing temperature. It was concluded that the incorporation of up to 30% chamotte (C) is technically feasible considering the evaluated temperature range. In this way, there is a product that adds both sustainability and technical performance to the ceramic industry.     

Composition and ceramic properties of ball clays for porcelain stoneware tiles manufacture in Poland

The paper presents the results of investigations of mineralogical, grain and chemical composition, and ceramic properties of 18 white-firing ball clays from five producing regions in eastern and central Europe. Relationships between the bending strength of the clay after drying and its grain size and mineralogical composition were studied. High contents of illite and illite/smectite minerals in the clay, and low crystallinity of kaolinite and illite, strongly influenced plasticity but also improved sinterability, as appropriate phase transitions of clay minerals began at lower temperatures. The clays were also highly reactive towards other components of the ceramic batches for porcelain stoneware tile production. The ball clays from the Donetsk region in Eastern Ukraine are recommended for the porcelain stoneware tile production in Poland, while the Polish, German and Czech clays may be used only as supplementary components.     

Sintering studies on plastic clays

Plastic clays are essential ingredients for ceramic body manufacture as binding agents for imparting plasticity, workability and green strength to raw materials. Seven clay samples which are mainly kaolinitic were chosen for the present studies. The mineralogy and crystallinity of the raw materials and the phase changes taking place during their sintering under different conditions were examined. The properties of the fired samples, such as water absorption, linear shrinkage and MOR were determined and a correlation of the strength of the sintered material with the microstructure was attempted. The observed variation in the properties was explained as a function of mineralogy, crystallinity and the amount and nature of the impurities present in the clays. The effect of the blending of an aluminosilicate gel and other mineral constituents with clays on their properties after sintering was also studied.     

Bauxite ‘red mud’ in the ceramic industry. Part 2: production of clay-based ceramics

Some potential uses of red mud as a raw component in clay mixtures for ceramic bodies production are presented. The influence of increasing amounts of red mud on the forming procedure, sintering and final properties was analyzed. Samples were produced by uniaxial pressing and slip casting. Two different clays are used as basic materials, the former being currently employed for the production of bricks by extrusion, the second — almost pure Kaolin — for high quality ceramic manufacturing. In both cases the addition of red mud led to more deflocculated solid–water systems and an increase of the critical moisture content. Mixtures prepared with the first clay and red mud loads up to 50% were fired at 850°C. The red mud content did not influence the sample porosity while determining a strength decrease attributed to the inertness of red mud at the working temperature. Samples produced using the second clay and red mud (0 – 20%) were fired at 950 and 1050°C. The addition of red mud determined increases of density and flexural strength which can be accounted for by the formation of a larger amount of glassy phase at higher red mud contents. The results of this work indicate excellent perspectives for using ‘red mud’ as raw material in mixtures with clay for the production of ceramic bodies.     

The influence of shaping and firing technology on ceramic properties of calcareous and non-calcareous illitic–chloritic clays

Two very different illitic–chloritic clays (calcareous and non-calcareous), both currently used in the Italian brickmaking industry, were used. Technological testing consisted in a simulation of the industrial processing performed at a laboratory scale. The pieces were obtained by three shaping techniques, pressing, extrusion and moulding, and fired at 1000 and 1100 °C, in fast and slow heating cycles. In each case their technological properties were studied. The microstructure and technological parameters of the ceramic pieces vary greatly, depending on the clay composition and the processing techniques. Pressing always produces pieces made from non-calcareous clay with the lowest drying and firing shrinkage, open porosity and water absorption. As it regards the calcareous clay, the lowest values of drying and firing shrinkage and water absorption are obtained by extrusion and moulding, respectively. The mechanical resistance, pore size distribution and critical pore diameter do not reflect clearly the influence of shaping techniques. Independently from the shaping technique adopted, all non-calcareous bodies show higher Maage's indexes than the calcareous ones. In any case, the Maage's durability factor is higher in extruded samples.     

Firing behavior of argillites from northern Tunisia as raw materials for ceramic applications

This study reports the firing properties of clayey materials from northern Tunisia to evaluate their possible use as raw material in ceramic. Physical, chemical, and mineralogical characterization and thermal behavior were carried out by inductively coupled plasma atomic emission, X-ray diffraction, Fourier transform infrared spectroscopy, differential thermal analysis, particle size distribution, and Atterberg limits tests. Firing properties were evaluated by color, firing shrinkage, water absorption, bulk density, apparent porosity, and flexural strength. Studied clayey materials are made up mainly by kaolinite and illite and are rich in iron. The main transformations after thermal analysis were identified from 500°C to 1000°C subsequent to the dehydroxylation of clay minerals, calcite decomposition, and the recrystallization process. Fired samples up to 1100°C showed better physical and mechanical properties related with a great densification resulting in a significant increase in linear shrinkage, bulk density, and flexural strength and a decrease in apparent porosity and water absorption up to 1100°C. This behavior is due to a crystalline and liquid phases formed at low firing temperature associated with a high content of fluxing agents. The fired ceramic materials exhibited low water absorption up to 2.26% and high flexural strength up to 32.6 MPa, which makes their potential use for some earthenware and stoneware products.     

DIFFERENTIAL THERMAL ANALYSES OF SOME MISSOURI FIRE CLAYS*

Differential thermal analyses were made of a large number of fire clays representative of Missouri production. Flint clays gave typical kaolinite curves. The curves of plastic and semiplastic clays were similar to that of kaolinite. Staining with aniline dyes, petrographic determination, and ceramic behavior indicate that clay minerals other than kaolinite are present in Missouri semiplastic clays but these (other clay minerals) were not revealed by the differential thermal method. High-alumina hurley clays showed variously endothermic peaks of diaspore, boehmite, and kaolinite, but no exothermic peak which is characteristic of kaolinite.     

Optimization of wastes content in ceramic tiles using statistical design of mixture experiments

Mineral extraction and processing industries have been cited as sources of environmental contamination and pollution. The inclusion of wastes into productive cycles represents an alternative form of restoration, which is interesting from both environmental and economic standpoints. In this work, the development of ceramic tile formulations containing kaolin processing and granite sawing wastes was investigated using the statistical design of mixture experiments methodology. Ten formulations using the raw materials, red clay, kaolin processing and granite sawing wastes, were selected and used in the mixture design. Test specimens were fired and characterized to determine their water absorption, linear firing shrinkage and modulus of rupture. Regression models were calculated, correlating the properties with the composition. The significance and validity of the models were confirmed by statistical analysis and verification experiments. The regression models were used to optimize the waste content in ceramic compositions. The results showed that formulations containing up to 62% of waste could be used in the production of ceramic tiles.     

Rheological and casting properties of two Egyptian clays

Slips from Kalabsha and Malkatta clays, widely used in the Egyptian ceramics industry, were prepared with the aid of an appropriate deflocculant at a constant specific gravity of 1·80—which lies within the practical working range for the slip casting technique. The rheological and casting properties, including plasticity of clay pastes, apparent viscosity and thixotropy of the clay slips, as well as casting rate, water retention, porosity and mechanical strength of their casts, were studied.The two clays behave in a quite different manner, reflecting the marked variation in their nature. Kalabsha clay slip has the minimum apparent viscosity with moderate thixotropy in the presence of 0·8% deflocculant addition, while Malkatta clay slip needs twice as much deflocculant to attain maximum fluidity, which is accompanied by a little higher thixotropic structure. Kalabsha clay slip casts faster and leads to cast having lower water retention, shrinkage, modulus of rupture and bulk density and of higher apparent porosity than that of Malkatta slip. In formulating ceramic bodies processed by the slip casting method, a blend of the two clays must be utilized in order to get a mixture having the proper flow properties and the best casting qualities. For thin-walled articles, the content of Kalabsha clay should be kept lower than that of Malkatta clay; the reverse holds for heavy-section casts.     

Environmental and technical aspects of the utilisation of tannery sludge as a raw material for clay products

This paper is a report on the results of a feasibility study on the immobilisation of tannery sludge by producing a ceramic product. The main purpose of this work was to test the clays used in the manufacture of a ceramic that could incorporate tannery sludge. The raw materials, tannery sludge and clay, were mixed together in different proportions. The ceramic specimens were characterised with respect to water absorption, porosity, linear shrinkage and transverse rupture strength. Leaching tests, in accord with the Brazilian and German regulations, were done on ceramic bodies made with different additions of sludge. In order to evaluate the possibility of air contamination during the firing process, preliminary studies of air emissions were carried out The mechanical properties of the samples evaluated were similar to those specified for ceramic bricks. All the leaching tests have shown that the main sludge contaminant i.e. chromium, could be immobilised within a finished ceramic product. The studies of air emissions have shown that zinc and chlorine are mainly collected from gas emissions and hence are not immobilised by the ceramic system. The study shows that the properties of the ceramic materials produced are acceptable for applications such as bricks for the building industry.     

Reformulation of roofing tiles body with addition of granite waste from sawing operations

A ceramic body traditionally used to produce roofing tiles was reformulated by the addition of granite waste from sawing operations. The objective was to obtain a ceramic product with better technological properties. The main tool for the reformulation was the definition of the appropriate particle size of the raw materials as given by the Winkler diagram. The raw materials were characterized with respect to their mineralogical composition by X-ray diffraction, particle size distribution as well as chemical composition and plasticity. Specimens were made by extrusion and fired at temperatures from 850 to 1100 °C. The technological properties determined were: dry bulk density, linear shrinkage, water absorption and mechanical strength. Microstructural analysis of the fired samples was carried out by X-ray diffraction. The results showed that the granite waste contributes to reduce the plasticity and the linear shrinkage of the ceramic bodies. One reformulated ceramic body exhibited better values of water absorption and mechanical strength than the industrially used.     

Bleaching of kaolins and clays by chlorination of iron and titanium

The quality of the clays and over all kaolin is measured in function of iron content, since this element gives an undesirable reddish color to this type of minerals. The use of chlorination for iron and titanium removal from different clay and kaolin minerals, used in Argentinian ceramic industry, has been investigated to establish reaction mechanisms, precautions and optimal conditions to bleach the clays. The method consists of the calcinations of the pellets in a flow of chlorine gas at temperatures between 700 and 950 °C, to remove the iron and the titanium by volatilization of the respective chlorides. Isothermal and non-isothermal chlorination assays were made and the effects of the temperature, reaction time, and carbon content in the sample over the bleach of the minerals and the phase transformations suffered by these minerals during the chlorination step were investigated. The removed amounts of iron and titanium were determined by X-ray fluorescence, the phase transformations were followed by X-ray diffraction and the samples' bleaching was established making an analysis of the space of the color by the spectrophofotometric method CIELAB. Also, a thermodynamic analysis of the system using HSC Chemistry for Windows software was made. The experimental results show that for red clay with high colloidal iron content, the optimum working temperature for the iron quantitative removal, without aluminium loss, is close to 850 °C, in controlled atmosphere free of O₂ and H₂O; lower temperatures require long reaction times. The extraction of titanium is not quantitatively achieved, as that of iron, even for long reaction times, because this element is present in different structures, with the consequent variation of its reactivity. The content of carbon and organic matter in the clays, in the case of the San Luis red clay, is enough for extraction improvement. However, the optimum concentration of carbon can vary depending on the type of clay and the amount of Fe₂O₃ in the mineral. The formation of phases such as α-Al₂O₃, a product of chlorination, increases the piece hardness. The methodology used in this work allows for obtaining a great improvement in the color of the final product of the firing, achieving ceramic materials with notable whiteness, even with red clays.     

Analysis of temperature effect on ceramic brick production from alluvial deposits, Tamilnadu, India

This study focuses on the thermal behaviour of alluvial clays in the production of ceramic brick industries, which are largely found on the bank of the Cauvery river, Tamilnadu, India. Clay bars were prepared which consisted of quartz, kaolinite, illite, chlorite, feldspars and iron oxides. The test samples were fired in the range of 700–1100 °C and were examined with chemical analysis, thermogravimetric–differential thermal analysis (TG–DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). An increase in firing temperature resulted in dehydroxylation of clay minerals, persistence of quartz and formation of Ca-anaesthetic plagioclase. SEM images visualized the vitrification of the fired bricks, which increased the compressive strength of the fired bars. The bricks made with alluvial clays displayed less water absorption and higher compressive strength, indicating that they could be used in the brick industry. The results of this work assisted the industries to select more appropriate natural clay composition and firing dynamics for making the bricks.     

Recycling and Utilization of some Waste Clays for Production of Sintered Ceramic Bodies

The recycling of industrial waste clays for production of an interesting ceramic product is the main goal of the present research work. Ceramic bodies were prepared using Feeders or Cyclons waste clays, sand and feldspar. 0.0, 15, 20, and 25 wt.% of sand were added at the expanse of kaolin (75-50 wt.%). Constant mass percent (25 wt.%) of feldspar was added for all ceramic compositions. The designed batches were sintered at 1200–1400 °C. Physical properties were determined by water displacement method. Phase composition and microstructure were investigated by x-ray diffraction and scanning electron microscope, respectively. The compressive strength was also determined. The results indicated that the ceramic bodies prepared from Cyclons’ waste clay exhibited higher physical and mechanical properties than that prepared from Feeders’ clay after sintering at 1400 °C. The addition of sand enhances the porosity, water absorption, bulk density and mechanical strength after sintering at 1400 °C due to the formation of mullite network and glassy phases.

     

Study of clay's mineralogy effect on mechanical properties of ceramic body using an experimental design

Three clays minerals namely illite (I), montmorillonite (M), and kaolin (K) were chosen as references to study the effect of mixture composition of clays on the mechanical properties and the shrinkage of the fired ceramic. The study was accomplished using the experimental design methodology. More specifically, a mixture design was carried out in order to establish relationships between mechanical strength and shrinkage of finished products and the proportions of the three clay mineral references in the mixture. The statistical study shows that the fitted models were adequate to describe these properties of fired ceramic bodies. The results demonstrate that the mechanical resistance was mainly governed by the amount of montmorillonite mineral. In fact, the mixture design performed in this study shows clearly that montmorillonite can be incorporated in industrial ceramic products up to 45 wt% with high mechanical resistance. On the other hand, the shrinkage decreases strongly with the amount of kaolin in the mixture and increases with the amount of illite while montmorillonite exhibits moderate effect on this property. The higher strength was shown in mixture in which mullite and anorthite appear together due to the presence of kaolinite and illite and give, as a consequence, a synergic power.     

Economy analysis of the implementation of extruded tiles fabrication in a ceramic industry containing ornamental rock waste

As a result of the economic crisis faced in Brazil, industries in the red ceramic sector have economic problems. The objective of this work was to evaluate, technologically and economically, through analysis of economy, the implementation of the production of ceramic tiles, a material with higher added value than bricks and ceramic blocks, in a ceramic industry located in the state of Rio de Janeiro, Brazil. The ceramic tiles were produced containing the incorporation of ornamental rock waste (ORW). The state has a region that has a red ceramic pole, but produces only products with lower added value. For this, specimens were produced with four different ceramic masses burned at temperatures in the range of 800 to 1050°C. Three masses were produced with different clays from the region (ceramic mass 1, 2 and 3) and a ceramic mass 4 was evaluated containing the clay that presented the best results and with the inclusion of sand and ORW, aiming at the analysis of economy. It was found that the masses containing only clays showed satisfactory parameters of resistance, but showed deficiencies in water absorption. The fourth mass, however, presented acceptable values in all the evaluated properties and was chosen to carry out a full-scale industrial test, which enabled the development of economic analysis and an economic analysis using the theory of real options. The results obtained in this last stage were also positive, providing an internal rate of return of 16.82%, above the minimum practiced rate of 15%, proving the efficiency of the economy applied to the manufacture of extruded tiles in the industries of the study region.     

Effect of physicochemical characteristics on the use of clays from Kindia (Guinea) in ceramic compositions

To evaluate their potential uses in ceramic compositions, two different types of abundant clays from Kindia (Guinea Conakry), denoted ABD and ARD, were characterized with the chemical and mineralogical compositions, the specific surface area, the plasticity index, the particle size distribution, and the thermal behavior. Kaolinite and muscovite are the main clay minerals that are identified. Besides, non-plastic minerals are large amount of quartz with a small particles size, goethite, hematite, anatase, and a small quantity of gibbsite. The two clays have a high plasticity index that is consistent with the small particle size and the broad size distribution. During heating, the fluxing behavior of the two clays induces a significant densification that is favored by the muscovite mineral combined with the reactive fine quartz. Besides, the firing shrinkage is limited to values of 4.5% and 3.5% for ABD and ARD respectively. In the objective of manufacturing ceramics, the two clays present the required properties. They present a sufficient plastic index in the green state, and after firing they lead to dense ceramics with an interesting bright color. The limited firing shrinkage is favorable to maintain the dimensional stability of vitrified ceramics as porcelain.     

The role of a coal gasification fly ash as clay additive in building ceramic

The clean coal integrated gasification in combined cycle (IGCC) technology of electrical power generation is different than conventional process in combustible treatment which generates inorganic wastes in the form of glassy slag and fly ash with singular properties. We have studied the fly ash coming from ELCOGAS IGCC power plant as additive to clays for building ceramic fabrication.

The addition of this new kind of fly ash to a clay of medium plasticity to elaborate pressed specimens, that were baked at 900 °C, improves the sintering of the paste and consequently an improvement of absorption, saturation and mechanical properties of the fired bodies, with no negative effects on shrinkage, colour alteration or efflorescence. In contrast, this fly ash does not mend the excessive firing shrinkage when added to a clay of a high plasticity index.     

Influence of mineralogical composition of applied ball clays on properties of porcelain tiles

Relations between quality of ball clays applied in raw materials batches for manufacture of porcelain tiles, and physical properties and microstructure of obtained tiles, were investigated. Studied clays constituted 35% of the batch, while the other components were unchangeable. Stoch index, new IR 3620/3700 index and XRIR index (Stoch index multiplied by IR 3620/3700 index), were proposed to take into account crystallinity of kaolinite and contents of illite and smectites in studied clays. Relationship between XRIR index value of clay, and water absorption and abrasion resistance of the obtained ceramic material, was found. Water absorption of the tile is also correlated with grain size distribution and bending strength of used clay. Optimal ball clay for porcelain tile production should exhibit: Stoch index - min. 4.3; IR 3620/3700 index - min. 1.2; XRIR index - min. 4.8; grain size median - max. 0.27 μm; bending strength after drying - min. 8.0 MPa.