Behavior of kaolinite and illite-based clays as landfill barriers

The technical requirements for the landfill of municipal wastes in the European Union (EU) are given in the Council Directive 1999/31/EC. A geological barrier of at least 1 m thickness with a hydraulic conductivity (HC) of 1 · 10^− 9 m/s is required. Where the geological barrier does not naturally meet the above conditions, a geological barrier of at least 0.5 m thick must be artificially established. We studied at controlled conditions, the ability of some clays (kaolinite or illite based) to act as landfill barriers. Several Spanish ceramic clays were compacted in columns (0.5 m length) and characterized for mineralogical, physical–chemical and heavy metal ions adsorption properties after 10 months leaching experiments. Zn, Cd, Pb and Cr salts were dosed in the synthetic leachates in order to test their in-depth retention. The specific surface area decreased in the material located near the clay–leachate interface region (< 6 cm) due to biofilm formation around clay particles, but bulk mineralogical properties were not affected. Although all the clays fulfilled the HC requirements, the diffusion of anions (chloride) reached more than 30 cm in kaolinite–illite or pure illite clays. The presence of significant traces of smectite (< 5%) was critical in anion transport retardation. Heavy metal ions were generally retained in the first 10 cm but in high surface-area illitic clays, the anions and heavy metal ions transport was stopped at < 6 cm. The clay mineralogy and the presence of carbonates and soluble salts greatly influenced the behavior of the barrier materials. Carbonate dissolution and precipitation affected < 6 cm depth. Divalent cations of carbonates selectively occupied the exchangeable positions and inhibited the retention of Na⁺, NH₄⁺ and K⁺, in the leachates. Sulphate was reduced at a depth of 20–30 cm. This biogeochemical process contributed to cadmium retention, presumably precipitated as sulphide.     

Clay content of argillites: Influence on cement based mortars

The pozzolanic activity of four heated powders containing different clays has been tested. Mineral transformations during calcination from 20 to 900 °C have been followed by X-ray diffraction (XRD) and Differential Scanning Calorimetry (DSC). Compressive strength tests were performed at 1, 7 and 28 days on cement–clay mortars using 30% of pozzolanic material as a replacement by mass for cement. Calcination temperatures corresponded to the stages of potentially high reactivity identified by XRD. Results indicated that there exists incompatibility between clay minerals which can not be activated at the same temperatures. Products of recrystallisation of the earlier activated clay were already formed when the second clay type was activated. Concerning the type and the abundance of clay minerals in the raw material, this study evidences that the compressive strength is, at first approximation, correlated with the percentage of activated clay and less with the nature of the clay assemblage.     

Biodesulfurization of two Colombian coals with native microorganisms

A biodesulfurization process was carried out for two coals from the southwest of Colombia using a consortium of native microorganisms Acidithiobacillus ferrooxidans-like and Acidithiobacillus thiooxidans-like. Characterization techniques as X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM/EDX) and chemical analysis were used in order to establish the mineralogy of the process. The sulfur content in coals varies from 2.6% to 5.7%, and pyrite is the main sulphide present in the inorganic phase. Other minerals in the substrates include kaolinite, calcite, dolomite and quartz. An 85–95% reduction of pyritic sulfur and 31–51% of total sulfur in a period of 30 days were achieved, for a particle size of − 74 µm, 10% w/v pulp density and 30 °C.     

Characterization of ceramic tiles prepared from two clays from Sergipe — Brazil

We report an investigation of stain formation after use of clay–ceramic floor tiles produced by an industry from Sergipe, Brazil. Two types of raw materials have been used (C1 and C2) and test specimens were prepared at firing temperatures of 1000, 1120 and 1140 °C, being afterwards immersed in muriatic acid, evidencing stain formation for C1 tiles. After ICP chemical analysis, the original clays and tiles were characterized by powder X-ray diffraction (XRD) and TGA measurements, evidencing that C1 contained a higher carbonate percent than C2. Tile specimens were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), flexural strength, apparent density, linear shrinkage, and water absorption. In contrast to tiles prepared from C2, those prepared from C1 presented higher interparticle porosity and both linear shrinkages and water absorption variations with temperature were very incipient, suggesting that the high porosity and the low sintering caused the low staining resistance.     

Technological features of Renaissance pottery from Deruta (Umbria, Italy): An experimental study

This work is focused on the assessment of the basic technological features of the pottery production in Deruta in the Renaissance period. For this purpose, clay samples and two kinds of ceramic products (tiles and wares) dating back to the XVIth century were characterized using different analytical techniques: optical, cathodoluminescence and electron microscopy on thin sections, X-ray fluorescence and X-ray diffraction on the bulk powdered samples. Then two clays best representing the chemical composition of the ceramic products underwent laboratory experimental firing tests at different conditions following the procedure of firing applied in the XVIth century as reported in the ancient historical documents. The firing products underwent textural, chemical and mineralogical characterization by the same analytical techniques in order to be compared with the clays and the shards. Archaeometric investigation of the ceramic bodies led to the identification of two different clay raw materials, both of local provenance, for the tile and the ware production. Archaeometric investigation of the glazes showed some differences between the wares from different workshops. In this respect the typology and the quality of the glaze resulted to be much more effective than the texture and composition of the ceramic body in characterizing the wares from different coeval workshops. Results of the experimental tests evidenced the firing products result from a complex mix of physical and chemical variables strictly correlated to one another. Above all, the heating rate and the amount of calcite in the clay raw material are crucial driving forces of the kinetics of firing. Comparison between the original and the experimental ceramic products indicated ranges of biscuit firing temperature of 850–1050 °C and of 950–1050 °C for the tiles and the wares, respectively, and a low heating rate in both cases.     

Clay minerals and iron oxides-oxyhydroxides as fingerprints of firing effects in a limestone monument

Different Portuguese limestones-Encarnadão, Amarelo de Negrais, Lioz and Gresoso-have been widely used as building materials and ornamental stones in the architecture of Lisbon (Portugal) area.The aim of the study of those materials was focused on fire-induced stone damage, mainly on identifying the thermal transformations of clay minerals and iron oxides-oxyhydroxides. Taking into account an applied component to the cultural heritage, a special attention was given to one of the most ancient Portuguese monuments — Lisbon Cathedral, specifically its cloister that was severely damaged by a fire that occurred right after the 1755 earthquake.A set of samples collected from outcrops were studied and subjected to artificial heating. The results were compared with those obtained from samples collected in the monument. XRD, SEM-EDS and ⁵⁷Fe Mössbauer spectroscopy were used. The < 2 µm fraction varies significantly between unheated (outcrop samples) and artificially heated samples, particularly in relation to iron oxides-oxyhydroxides. Kaolinite is the dominant clay mineral, followed by illite and smectite. Goethite is the iron oxyhydroxide characteristic of all studied lithotypes both in unheated samples and samples artificially heated to 250 °C. Encarnadão is the exception presenting hematite in those conditions. As firing temperature increases (300 °C–600 °C) disordered hematite appears at the expense of goethite, and smectite is no longer detected. Mössbauer spectra further reveal that Fe²⁺ in silicate minerals is fully oxidized at 600 °C but remains in the carbonate structure up to this temperature. The SEM-EDS analyses show that 2:1 clay minerals have Si and Al as main cations and minor amounts of K and Fe. It also shows that all the clay minerals and Fe-rich particles are always associated to the limestone porosity.. The present results show that the clay minerals, namely illite–smectite mixed-layer and smectite, can be used as indicators of stone provenance used in Lisbon Cathedral Cloister as well as fingerprints of the temperature achieved during the fire of Lisbon Cathedral that most likely was not higher than 350 °C.     

Physicochemical properties of talc ore from three deposits of Lamal Pougue area (Yaounde Pan-African Belt, Cameroon), in relation to industrial uses

Three talc deposits were discovered at Ngoung, Lamal Pougue and Bibodi Lamal (Cameroon). They derived from ultramafic rocks and are enclosed in a Pan-African garnet and muscovite-bearing mica schist of the Yaoundé series. The physico-chemical properties of these talc deposits have been investigated by different techniques including Scanning Electron and Transmission Microscopy (SEM and TEM), chemical analyses, X-ray diffraction (XRD), infrared spectroscopy, particle size analysis by laser diffraction and low temperature gas absorption–desorption. The mineralogical composition deduced from XRD is wide (talc + chlorite + tremolite ± anthophyllite ± chromite ±serpentine ± brucite ± magnesite ± dolomite), but due to the high talc contents (≈ 90%) the samples are close to monomineralic. SEM studies reveal that all talc deposits comprise bundles of platy talc and a few prismatic crystals of amphiboles and other contaminating minerals. Laser diffraction confirms the coarse particle size of the talc crystals. Mode values are as high as 105–170 μm (except two samples displaying 76 and 42 μm) and d50 ranges from 107 to 25 μm. The values of specific surface area measured by BET and t-plot methods range from 1 to 6 m²/g and are correlated with external specific surface area measured by laser diffraction. Discrepancies from the trend are due to the semi-crystalline texture of the samples and mostly to intra-crystalline structural defects revealed by TEM observations. In infrared spectra, specific absorption bands are distinguished for talc, chlorite, tremolite, carbonates, serpentine, brucite and water. Occasional substitutions in minerals led to a shift in some absorption bands. The chemical composition criteria important for most of the industrial applications such as ceramics and pharmaceutics are closely complied with in untreated samples from these deposits. In summary, high talc proportions, chemical compositions, platy morphology and coarse grain size of its crystals lead to the conclusion that the studied deposits are economically attractive. The data set of the present work is an important tool for choosing the beneficiation methods for specific applications.     

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.     

Iron role on mechanical properties of ceramics with clays from Ivory Coast

Three clays from Gounioubé deposits were used for the manufacture of floor tiles. The strength distributions by the Weibull statistical model are interpreted in relation to clay chemical and mineralogical compositions and particularly to the iron role by Mössbauer spectroscopy. With clays without additions, results of mechanical strength of sintered materials show that clays alone are not really suitable for the manufacture of ceramics. But clay calcite mixes (10 wt% of CaCO₃) favor a significant increase of mechanical resistance, which are similar to used standards. This behavior is due to the formation of a three-dimensional network of anorthite crystals within the silico-aluminate materials. Beside the anorthite role, the iron oxide content of the clays influences the mechanical strength. With Gounioubé clays, it is shown that the increase of iron content in clays causes a decrease of the ceramic strength. This behavior is related to the clay compositions, which contain iron in the form of goethite. During the thermal transformations, part of the iron is involved in both the structural transformations and the densification phenomenon of the silico-aluminate phase. But the most part of iron readily transforms into hematite crystallites, which are embedded within the silico-aluminate. They accentuate the heterogeneous nature of the material and favor the decrease of the mechanical strength.     

Saudi Arabian clays for lead removal in wastewater

Three types of local clays–Tabuk, Baha, and Khaiber–were tested for their abilities to adsorb lead ions from wastewater. The effect of pH on the adsorption of lead ions was also investigated. The clays were treated with hydrochloric acid to activate adsorption sites within clay particles. Untreated Tabuk clay had the largest adsorption capacity, about 30 mg lead/g clay, in comparison with those of Baha and Khaiber clays. The smallest adsorption was observed with Khaiber clay, about 10 mg lead/g clay; this may be attributed to the prior existence of lead within the clay. The adsorption of the acid-activated clays was not enhanced compared to those of untreated clays. The Langmuir model described the experimental data for all untreated clays, while the Freundlich model described the experimental data of untreated Khaiber clay and treated Baha clay. The local clays tested in this study, especially Tabuk clay, may be utilized as cost-effective and efficient adsorbent materials for removing heavy metals from wastewater in Saudi Arabia.     

Effects of sand addition on production of lightweight aggregates from Tunisian smectite-rich clayey rocks

Smectite-rich claystone–marlstone samples from 12 outcrops located in the Southern Atlas domain of Tunisia were investigated with regard to manufacture of lightweight aggregates (LWAs). The clayey materials mainly consist of smectite, kaolinite and illite, together with quartz, calcite, dolomite and feldspars as accessory components. 10–12 mm pellets were prepared from wet paste and initially heated to 600 °C, 700 °C or 800 °C (depending on the raw material) for at least 2 h in order to avoid any explosion of the aggregate. The pellets were then subjected to a quick firing process at 1180 °C. The addition of 15% of quartz sand (< 250 μm grain size) to the raw materials was found to improve some required pre-treatments and give better expansion properties to some of the aggregates. The addition of 1% used automobile oil to the clay and quartz sand mixtures caused the formation of more gas and a drop in bloating temperature. The obtained LWAs were characterized by physical properties such as apparent density, mechanical resistance, water absorption and expansion. The laboratory results were comparable to those of two commercial LWAs from France (Argidécor®) and Portugal (LECA®) and provide new openings for the utilization of Tunisian claystone in civil engineering work or in agricultural applications.     

Ceramic behaviour of five Chilean clays which can be used in the manufacture of ceramic tile bodies

This study is focussed on the behaviour of ceramic clays from Chile which has an important local ceramic industry. Five deposits of clays with industrial application have been studied. The clays come from San Vicente de Tagua-Tagua (SVTT), Litueche (L), Las Compañías – Río Elqui (LC), La Herradura – Coquimbo (LH) and Monte Patria – Coquimbo (MP). The chemical and mineralogical compositions of clays were determined by X-ray fluorescence (XRD) and X-ray diffraction (XRD), respectively. Also, the plasticity index (PI) was measured for each sample. The chemical and mineralogical compositions of samples differ considerably. Test samples have been prepared by pressing and firing in the range of 800–1150 °C. Linear contraction (LC), water absorption capacity (WAC) and thermodilatometric analysis (TDA) were done in order to characterize clays after firing. A considerable decrease in the WAC coinciding with the beginning of vitrification, is observed between 1050 and 1100 °C. At 1150 °C the porosity of the tile bodies decreases significantly and the tile bodies became earthenware. All studied clays seem to be easily adaptable to a correct dry pressing ceramic process. In particular, illite–kaolinite-rich samples show the best behaviour. Samples SVTT are suitable for the production of fast firing vitreous pieces. L samples present the highest refractory behaviour.     

Healing clays: Mineralogical and geochemical constraints on the preparation of clay–water suspension (“argillic water”)

Clays have been long taken internally due to their sorption effects and the mechanical shielding developed by sheet morphologies. The purpose of this paper is the modelling of the mentioned traditional application in terms of chemical and mineralogical budget towards the body.Four polymineralic clays potentially suitable for therapeutic use were analysed for their mineralogical and geochemical composition. Quartz is always present, as well as feldspars, whereas carbonates are more variable (from trace levels, to about 40%). The clay mineralogy is characterised by mixed layers illite–smectite, kaolinite and illite. Most chemical elements show little anomalies compared to average shale [Turekian, K.K., Wedephol, K.H., 1961. Distribution of the elements in some major units of the earth's crust. Geological Society of America Bulletin, 72, 175–192], excluding Ca that is enriched according to the carbonate occurrence. Another geochemical feature is the depletion of more electronegative elements, among which very hazardous elements may be found.For the preparation of “argillic water”, the clays were dispersed in water and three suspensions were prepared to test the effect of settling time (5 min, 1 h, and 24 h). After the settling, the supernatant was centrifuged to analyse the solution and the particulate. The grinding of clays (a common practice for industrial uses) sensibly reduce the mineralogical selectivity of settling, nevertheless, quartz and feldspars are depleted during settling and phyllosilicates are enriched or fluctuate when the starting value is high; the carbonate content increases or decrease within a narrow interval. The grinding procedure minimises the different behaviour of clay minerals dispersed in water because the clay assemblage of suspended particulate does not show significant trends; only illite shows a slightly decrease.The solute composition is dominated by Na > Si > Ca > K > Mg. The comparison of the 4 clays indicates that the sample richest in mixed layers shows the highest content of many trace elements in solution. The variations of solution chemistry indicate that the less soluble elements decrease with the time of settling (e.g. Fe, Al, Mn): the elements hosted in organic matter or sulphides and soluble in oxidative media, increase with time (V, Mo, Sb, As). Many other elements are rather constant or at very low concentrations. The occurrence of sorptive minerals tends to hide these trends mainly during the first hour of settling.The chemical input to the body was calculated adding the amount of element in solution to the extractable amount from the digestion of particulates. The latter is based on the simulated digestion of clays taken from the literature. A critical point is the definition of a threshold that discriminates between useful and excessive ingestion of chemical elements. Since no reference models are available, the limit for drinking water was used. Considering that adults drink 2 l of water, the maximum daily dose for water was transformed into the amount of each chemical element considered by the law and compared with the amount available from the preparation of “argillic water”. Based on these results, the settling of clays can be tuned in order to emphasise the desired composition or to minimise side effects.     

Thermal activation and alkali dissolution of silicon from illite

TGA, DTA, FTIR, XRD and 29Si MAS NMR were used to investigate the thermal activation of illite. Illite experiences a series of thermal solid-state phase transformations. Dehydroxylation at 400700 °C forms dehydrated illite, which remains the layered framework of illite. From 700 °C to 1093 °C, Si–O tetrahedral framework remains unchanged. When heated above 1093 °C, the layered structure is destroyed and an amorphous silica-rich glass phase is formed. The mullitization occurs when the temperature exceeds 1100 °C.XRD and FTIR studies show that the silica in silica-rich glass phase dissolves in soda liquor, which indicates that silicon can be removed from illite after thermochemical activation (TCA) followed by alkali leaching. The formation of sodium aluminosilicates of Na₉₆Al₉₆Si₉₆O₃₈₄ and 0.95Na₂O · Al₂O₃ · 3.25SiO₂ · 4.79H₂O during alkali leaching may reduce the desilication to a great extent.Desilication tests after TCA show that the suitable activation conditions for illite are 11001150°C and 9060 min. A desilication of 45% was obtained under the conditions for an ore sample bearing about 85% illite, 9% quartz and 5% muscovite.     

Isomerization of 1-butene catalyzed by ion-exchanged,pillared and ion-exchanged/pillared clays

A natural smectite clay (STx-1, USA) was ion-exchanged with Al, Fe or pillared with polyoxocations of the same metals. Samples were also prepared by combining these two treatments. The prepared solids were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), thermogravimetric analysis (TGA), TPD of ammonia and N₂ adsorption. The catalytic activity was evaluated by using the isomerization of 1-butene at 300 °C. XRF results showed an increase in the content of Al or Fe thus giving evidence that these metals were effectively exchanged or deposited over the starting material. Al- and Fe-pillared clays showed a significant increase of the surface area. Ion-exchanged clays showed similar surface areas to that of the starting clay. From XRD patterns only the Al-pillared clay gave an increase of the d-spacing. The synthesized pillared clays were superior catalysts for the isomerization of 1-butene than the ion-exchanged clays; the ion-exchanged/pillared clays showed a similar catalytic behavior as that of the parent pillared clays. The Al-pillared clay was the best catalyst for the reaction and its efficiency was related to the high acidity and high surface area.     

Thermal analysis of montmorillonites modified with quaternary phosphonium and ammonium surfactants

The thermal stability of seven organically modified montmorillonites (‘organoclays’) has been investigated using differential thermal analysis, differential scanning calorimetry, and thermogravimetry in conjunction with X-ray diffractometry. Six organoclays were synthesised by replacing the interlayer inorganic cations, initially present, with quaternary phosphonium and ammonium surfactant cations. The samples modified with tetrabutylphosphonium (TBP), and butyltriphenylphosphonium (BTPP) ions have an appreciably higher thermal stability than the octadecyltrimethylammonium (ODTMA)-modified clays. Thus, in the case of TBP- and BTPP-modified montmorillonites, the onset temperature of decomposition is close to 300 °C. Samples modified with hexadecyltributylphosphonium (HDTBP) ions have a lower onset temperature of decomposition of 225 °C. In comparison, the onset temperature for ODTMA-montmorillonites (obtained at different concentrations of ODTMA-bromide) ranges from 158 to 222 °C, being highest where the concentration of intercalated surfactant is lowest. The onset temperature for a commercial alkylsilane-treated quaternary ammonium-modified organoclay (S-BEN N-400FP) is 207 °C. The basal spacing of the TBP- and BTPP-modified clays is 1.7–1.8 nm, indicating a monolayer arrangement of quaternary phosphonium ions in the interlayer space, while the value of 2.5 nm for HDTBP-montmorillonite indicates a more open structure. The ODTMA-modified samples have basal spacings ranging from 1.9 to 2.1 nm, indicative of a bilayer to pseudo-trilayer arrangement. The exceptionally high basal spacing of 3.4 nm for the S-BEN N-400FP organoclay might be due to interlayer penetration of organosilane hydrolysis products during synthesis. The thermal properties of organoclays are apparently related to the nature of the surfactants and their arrangement in the interlayer space of montmorillonite.     

Firing transformations of Chilean clays for the manufacture of ceramic tile bodies

This contribution is focused on the study of the mineralogical changes occurring in the ceramic body after heating ceramic clays. Chile has an important local ceramic industry. Five deposits of clays with industrial applications were studied. The clays came from San Vicente de Tagua-Tagua (SVTT), Litueche (L), Las Compañías-Río Elqui (LC), La Herradura-Coquimbo (LH) and Monte Patria-Coquimbo (MP). The samples were heated to 830, 975, 1080 and 1160 °C keeping at the maximum temperature for 35 min. The bending strength of each ceramic body was determined at 1100 °C. Mineralogical analysis of the fired samples was carried out by X-ray diffraction. The SVTT contained quartz, spinel, cristobalite, microcline, albite, anorthite, hematite and enstatite; the LC clays quartz, mullite, spinel, microcline, albite, anorthite, hematite, diopside, enstatite, illite/muscovite and talc; the LH clays quartz, cristobalite, microcline, albite, anorthite, hematite, diopside, illite and augite; the MP clays quartz, cristobalite, microcline, albite, anorthite, hematite, diopside, gehlenite, enstatite and wollastonite and the L clays quartz, microcline and mullite. The persistence of illite at at least 900 °C was observed for LC and LH. SVTT and LH showed the required specifications for earthenware. The L clays were refractory clays with very low bending strength.     

Shelf life stability of diatomites

Diatomites or diatomaceous earths are biogenic sediments mainly consisting of porous siliceous algae skeletons. Some diatomites are industrially processed and used for different applications.For some applications and sometimes for the authorization of products for new applications it is important to prove the ‘shelf life stability’ which means that the properties of the product should not change upon storage.Freshly prepared silica gel is known to alter upon aging e.g. with respect to the specific surface area and porosity, respectively. This can be relevant for diatoms as well since recent skeleton consist of XRD amorphous silica which – upon aging – crystallizes, finally forming microcrystalline silica. The age of most of the diatomites being mined is higher than 1 million years. Accordingly, one could expect that storage for some years does not alter the diatomite properties. However, it is at least conceivable that prolonged open storage (exposure to air) can lead to the adsorption of molecules from air which in turn would block reactive adsorption sites.The aim of this study is to assess the shelf-life-stability of diatomite and perlite based on long term tests. Therefore, two different diatomite samples and a perlite sample (XRD amorphous volcanic alumosilicate glass) were stored at different conditions for 1 year. All materials were investigated with respect to structural aspects as well as adsorption capacity.Using the common mineralogical methods X-ray diffraction (XRD) and infrared spectroscopy no structural changes could be observed. In contrast, the determination of the amount of soda soluble silica turned out to be a valuable tool for the identification of structural changes. Using this method a slightly higher reactivity of the perlite surface after storage at 60 °C in water was found which possibly can be explained by the beginning devitrification process. At the same conditions, the diatomite sample which mostly consists of XRD amorphous silica showed a slight decrease of the amount of soda soluble silica which was interpreted as the beginning (re)crystallization process. The diatomite sample containing swellable clay minerals lost some water adsorption capacity upon extensive drying.Systematic changes of material properties after 1 year storage could only be observed under exaggerated conditions (120 °C or storage in water at 60 °C). It is concluded that the investigated materials are stable under common storage conditions.     

Mineralogical and morphological changes of calcined paper sludge at different temperatures and retention in furnace

This work reports the project of thermal effects in mineralogy and texture of the paper sludge to employ them as pozzolanic material.For this reason, the chemistry and mineralogical composition has been studied, as well as its morphology by XRD, SEM and EDX.The initial sludge has been treated to 700, 750 and 800 °C during 2 and 5 h being observed that initial kaolinite becomes metakaolinite and that its pozzolanic activity with a paper sludge treated to 700 °C for 2 h is comparable to that of a commercial metakaolinite. The transformation of kaolinite after the dehydroxylation is to convert in amorphous metakaolinite. At the temperature mentioned above, calcite from the initial sludge is maintained active.It is concluded that the pozzolanic activity of metakaolinite is strongly related to the crystallinity of the original kaolinite. Well-ordered kaolinite is transformed into more reactive metakaolinite.     

Influence of firing temperature on the ceramic properties of clays from Campos dos Goytacazes, Brazil

The characteristics of two clays used for red ceramic production in Campos dos Goytacazes, southeast of Brazil, were investigated. Characterization was performed by X-ray diffraction, chemical analysis, as well as granulometric and plasticity measurements. Technological properties related to water absorption, linear shrinkage and flexural strength were obtained from specific tests. Samples were prepared by pressing clay bodies at 20 MPa, which were then fired at temperatures from 850 to 1200 °C. The results showed that both clays from three deposits are highly plastic due to the elevated percentage of kaolinitic clay minerals. The samples richer in clay minerals present higher linear shrinkage as well as a decrease in water absorption in comparison to the others. The effectiveness of these clays for red ceramic production has been discussed in terms of the Winkler diagram.