Tunisian Clay Research Articles

Ceramic tiles based on central Tunisian clays (Sidi Khalif formation)

AbstractThis study aims to find alternatives to some overexploited deposits in the north of Tunisia. The clays of the Sidi Khalif formation, of Uppermost Jurassic to Lower Cretaceous age, seem suitable to support this strategy, due to their abundance. In terms of mineralogy, they can be divided into two distinct groups, related to their palaeogeographic and eustatic contexts. The clays of the Sidi Khalif formation from Jebel Houareb (JH) and Jebel Meloussi (JM) are richer in clay minerals, while those of Jebel Rhouis (JR) and Jebel Boudinar (JB) zones are dolomite-rich. The compositional differences between the two groups influenced their technological behaviour in production of ceramic tiles. Upon firing, forsterite and gehlenite crystallized in the carbonate-rich JR and JB clays, whereas mullite formed in the JH and JM clays. Concerning their ceramic properties, the tiles made from JR or JB clays showed low bending strength and high water absorption. For JH and JM, the tiles had slightly greater mechanical resistance, but exhibited considerable linear shrinkage. These defects were partially corrected by introducing new formulations based on the same clays and by altering the firing cycles (HM1, HM2, RB1 and RB2). With these modifications, “Porcelanico” and “Monoporosa” technologically conforming tiles were obtained from HM2 and RB2 formulations, respectively.

Removal of phosphate ions from aqueous solution using Tunisian clays minerals and synthetic zeolite

AbstractPhosphate ions are usually considered to be responsible for the algal bloom in receiving water bodies and aesthetic problems in water. From the environmental point of view, the management of such contaminant and valuable resource is very important. The present work deals with the removal of phosphate ions from aqueous solutions using kaolinitic and smectic clay minerals and synthetic zeolite as adsorbent. The pH effect and adsorption kinetic were studied. It was found that phosphate could be efficiently removed at acidic pH (between 4 and 6) and the second order model of kinetics is more adopted for all samples. The isotherms of adsorption of phosphate ions by the two clays and the zeolite samples show that the zeolite has the highest rate of uptake (52.9 mg P/g). Equilibrium data were well fitted with Langmuir and Freundlich isotherm.

Difference in pozzolanic behaviour of Tunisian clays with lime and cement

Two local clays, one from the region of Tabarka and the other from Medenine, were tested as pozzolanic materials. The characterisation of the raw and the calcined clays included X-ray diffraction (XRD), differential thermal analysis, thermogravimetry and infra-red spectroscopy. The pozzolanic activity was evaluated by mechanical tests, performed on calcined clay–lime and on calcined clay–cement mini-cylinders, and by physical method (dosage of calcium hydroxide (Ca(OH)2) by differential scanning calorimetry). The identification of the hydrated phases was done by XRD, differential scanning calorimetry and scanning electron microscopy. Kaolinitic clay from Tabarka was found to have the highest pozzolanic activity, compared with the illito-kaolinitic clay from Medenine containing some haematite. It was demonstrated that the haematite contained in the last clay did not contribute to the pozzolanic reaction in the presence of calcium hydroxide while in the presence of cement, the pozzolanic reactivity is improved. The haematite contained in Medenine clay contributes to the reaction with cement to form iron substituted ettringite and iron-substituted C–S–H. Furthermore, a new hydrated ferritic phase (Ca3Fe2(OH)12) is formed. The major hydraulic products such as C–S–H, C2ASH8 and C4AH13 were identified.

Purification of industrial effluent by microfiltration and ultrafiltration ceramic membranes: comparative study between commercial and elaborated Tunisian clay membranes

Abstract Industrial effluents treatment was investigated using ceramic Microfiltration (MF) and Ultrafitration (UF) tubular membranes. The comparison of performances between commercial ceramic membranes based on alumina material and elaborated ones based on Tunisian clay material was studied. MF and UF tests applied to cuttlefish effluent treatment were carried out respectively with 0.2 μm and 5 nm commercial membranes and 0.18 μm and 15 nm prepared membranes. The results show that for the two processes, the performances in term of permeate flux and quality of the treated wastewater using clay membranes was a little better than that obtained with commercial one.

Purification of industrial effluent by microfiltration and ultrafiltration ceramic membranes: comparative study between commercial and elaborated Tunisian clay membranes

Purification of industrial effluent by microfiltration and ultrafiltration ceramic membranes: comparative study between commercial and elaborated Tunisian clay membranes

Microstructural and Mechanical Properties in Traditional Ceramics as a Function of Quartzofeldspathic Sand Incorporation

We intend to study the influence of addition of quartzo-feldspathic sand on the mechanical properties and the microstructure of Tunisian illite-kaolinite clay ceramics. The fired characteristics of the clay and quartzo-feldspathic sand mixtures have been studied separately at soaking temperatures reaching respectively 850°, 950° and 1050°C during a firing profile of ∼7–8 h. Investigation of phase transformations of the mixed samples shows that albeit the proportion of the quartz has been increased, its peak intensity remains constant. Such stability may be explained by quartz dissolution in the glassy phase. The mechanical strength of the mixed samples has been examined in terms of flexural strength. In the studied case, the latter increases from 13.5 to 23.3 N.mm−2 as the sample becomes denser in the mixture M2. It may also be noticed that an overdose of quartz reduces the mechanical strength. Hence, a moderate addition of well-sorted fine quartzofeldspathic sand ameliorates the mechanical properties and the microstructure. The latter is analysed by scanning electron microscope (SEM).

Modification of Tunisian clay membrane surface by silane grafting: Application for desalination with Air Gap Membrane Distillation process

New ceramic hydrophobic porous membranes were proposed for application in membranes distillation. Two kinds of hydrophobic membranes were prepared by grafting 1H,1H,2H,2H-perfluorodecyltriethoxysilane (C8 compound) on the Tunisian clay ceramic membranes with pore diameters of 0.18 μm and 15 nm. Air Gap Membrane Distillation (AGMD) experiments were performed for seawater and aqueous solutions of sodium chloride as feed. The effect of the mean temperature, pore diameter of the membrane and salt concentration were studied. The water vapor permeability of the proposed membranes was determined. The new membranes seem to be promising in the field of membrane distillation. High salt rejection rates higher than 99% were obtained for both modified MF and UF ceramic clay membranes.

Mechanical modelling of materials coated with nanocomposite

The purpose of this study was to establish a mathematical equation that links the creep and relaxation forces to the clay percentage of nanocoated material based on a Zener analogical model. For this reason, a theoretical equation of the tensile resistance of a fabric coated with nanocomposites is presented. The samples whose properties are analysed by such equations were constructed from commercial resins, which are actually used in the textile field to enhance properties such as comfort, elasticity or impermeability of the fabric materials and the Tunisian natural clay. Relaxation deformations and creep forces were determined by using a dynamometer measuring the necessary force to maintain a constant elongation, and the calculated deformation when the fabric is stretched by a constant force equal to 80% of its rupture force. The mathematical equations obtained by modelling the coated fabric’s mechanical behaviour help in analysing and explaining the measured rupture forces that have been presented in a previous work. It was found that Young’s modulus increases by increasing the clay quantity and the calculated values show that the values of mechanical resistance are in good agreement with the measured values of the tensile tests. Also, it was found that when nanocomposites are used in coating a fabric, the fabric becomes more elastic and more resistant, and this can be proved by Young’s modulus and the viscosity (η computing).

Treatment of Industrial Effluents by MF and UF Ceramic Membranes:Comparative Study using Commercial and Elaborated Tunisian Clay Membranes

Industrial effluents treatment was investigated using ceramic Microfiltration (MF) and Ultrafiltration (UF) tubular membranes. The comparison of performances between commercial ceramic membranes based on alumina material and elaborated ones based on Tunisian clay material was studied. MF and UF tests applied to cuttlefish effluent treatment were carried out respectively with 0.2 μm and 5 nm commercial membranes and 0.18 μm and 15 nm prepared membranes. The results show that for the two processes, the performances in term of permeate flux and quality of the treated wastewater using clay membranes was a little better than that obtained with commercial one.

Study of mechanical behavior of lightweight aggregates concrete of Tunisian clay

In this study, we treated the mechanical behavior of lightweight concrete with Tunisian clay aggregates, shaped and expanded in the laboratory. A method of manufacturing aggregate was followed. The choice of materials was packed and a physical, chemical, mineralogical and thermal (DTA / TGA) characterization of clay and aggregates was performed. For current cement content, we determined the compressive strength at 3, 28 and 90 days for a fixed water-cement ratio E/C. The Young's modulus was determined with empirical formulae. Thus, by SEM observations, we studied the aggregates and the interfacial transition zone (ITZ) between the cement paste and the aggregates at different ages. The obtained constitutes concrete is hence a structure concrete according to the AFNOR norms and the ACI Guide.

Study by Differential Scanning Calorimetry of Water-in-Oil Emulsions Stabilized by Clays and CTAB

In this work, we have tested various formulations in order to get emulsions containing pure water, Tunisian olive oil, Tunisian clays, and an ammonium salt. Two different types of clays: smectite and kaolinite and the cethyltrimethylamonium bromide (CTAB) were tested. CTAB is used as surfactant and a compound modifying the clays properties. The amount of CTAB being fixed at 0.66 w/w, the proportions of clays were varied from 0 to 9% for each of the following proportions of water: 10, 20, 30%. To the aqueous phase obtained by mixing two separate aqueous phases: water + CTAB and water + clay, the oil was added drop by drop, the agitation being maintained at 5000 rpm. The obtained mixtures were analyzed by Differential Scanning Calorimetry (DSC), optical microscopy and bottle tests. An optimized formulation containing water (30%), smectite clay (5.3%) and CTAB (0.66%) was found to give W/O emulsions which kinetic stability is greater than 75 days regarding coalescence and greater than 700 hours regarding sedimentation.

Efficiency of natural and acid-activated clays in the removal of Pb(II) from aqueous solutions

The adsorption of Pb(2+) ions onto Tunisian clay in aqueous solution was studied in a batch system. Four samples of clay (RGC, RRC, AGC, and ARC) were used. The raw RGC and RRC clays were sampled in jebel Tejera-Esghira in Medenine area (Southeast of Tunisia). AGC and ARC corresponds respectively to RGC and RRC activated by 6M sulphuric acid. The adsorbents employed were characterized by X-Ray Diffraction, chemical analysis, and the specific surface area was also estimated. The ability of clay samples to remove Pb(2+) ions from aqueous solutions has been studied at different operating conditions: temperature and pH. The optimum pH for lead ions retention was found 7.0 for the four clay samples. The effect of temperature on adsorption phenomenon was also investigated. The results indicated that adsorption is an exothermic process for lead ions removal. The equilibrium adsorption data were analysed using the Langmuir and Freundlich isotherms. The adsorption capacities (X(m)) for RRC, RGC, ARC and AGC were found 17.84, 25.44, 27.15 and 40.75 mg g(-1), respectively. The performance of the red clay after activation was compared to that of silica gel, which has maximum adsorption of 20 mg g(-1). On the other hand, although the performance of activated carbon (88.3 mg g(-1)) is by far higher than that of the green clay after activation, the latter seems to have better performance than that of the silica gel.

Elaboration and characterisation of low cost ceramic support membrane

A porous tubular ceramic membrane was prepared from low cost Tunisian clay. The characterisation of the raw material and the effect of the sintering temperature on the morphology, pores size distribution and the mechanical properties of the ceramic membrane were studied. A ceramic membrane fired at 1000°C for 1 h presented a mean pore diameter of ∼1·04 μm. The porosity was equal to 38 vol.-%. The filtration of a 0·5 g L−1 bovine serum albumin solution indicated that the limiting flux of permeate was 245 L h−1 m−2 bar−1, which corresponded to a retention rate of about 13%.

Physico-chemical characterization of acid-activated clay: Its industrial application in the clarification of vegetable oils

The physico-chemical characterization of Tunisian bentonitic clays is based on the determination of the mineralogical composition (X-ray diffractions and infrared spectroscopy), chemical analysis, cation exchange capacities and the total surface area. The result given by these techniques show that these samples were smectic clay of beidellitic character. In the other hand, the activation of these clays by hydrochloric acid shows an increase of the specific surface area and favorite the clarification of vegetable oils.

Technological behaviour of some Tunisian clays prepared by dry ceramic processing

AbstractLower Cretaceous (AJO and AJR) and Oligocene clays (AS) from northern Tunisia were analysed to evaluate their possible use in the production of earthenware tiles by dry processing and fast double-firing. The Cretaceous clays are carbonate-rich (AJO = 20%, AJR = 12%) while the Oligocene ones are carbonate-free. This led to noticeable differences in firing behaviour (shrinkage, sintering rate and loss on ignition) and consequently in functional properties (water absorption, mechanical strength, porosity). The AJO firing shrinkage is very small, which makes this clay suitable for rapid firing. The clays are illite-kaolinite-rich but the AS sample is mostly smectitic (44%) and so is used (10 wt.% maximum) only to adjust the consistency of the powder during pressing. The average agglomerate size ranges from 100 to 350 μm and the distribution is suitable for easy pressing of powders without any special need for further adjustments. Characterization of fired products confirms the high potential of these clays since all properties fall within the ceramic International Standards (ISO). For both technical and economic reasons dry processing is recommended for production of earthenware tiles, in particular for countries in sunnier climates, where solar energy can be exploited for clay drying.

Filtration properties of two Tunisian clays suspensions: effect of the nature of clay

The knowledge of the filtration properties are very important and can ascertain if a clay is suitable or not for use as a lining material for waste disposal. The general objective of our work is to determine a relation between structure and microtexture of two Tunisian clays (C1 and C2) and macroscopic properties of cakes formed by filtration. The result of permeability by water and waste solution (pH = 3) shows that the clay C2 is more impermeable than C1. In addition, the cake obtained after filtration test by filter-press for both clays present many interesting observations. However, for a ratio of (40%) of clay–water, the thickness of cake (e) in the case of C2 is more important (e = 10mm) than for C1 (e = 7mm). Similarly, the water retention (WR) is of order 34% for C2 and 26% for C1. This is due to the mineralogical composition of sample C2 which is essentially the smectite (swelling clay). Although, (WR) and (e) are slightly changed using the waste solution, it exist a lowering of plasticity of clay filter cake. This is illustrated by the SEM images that showed an interconnected micro-crack for the cake of sample C2, due to the degradation by acidic attack.

Filtration and standardized properties of Jebel Om El Khecheb clay (Tunisia) and Wyoming bentonite

AbstractThe rheological and filtration properties of a Tunisian clay are presented and compared with those of Wyoming bentonite. The study was part of an evauation of Tunisian mining resources in general, and of the bentonitic deposits in particular. Qualitatively, the two clays exhibit the same rheological and filtration behaviour but quantitatively the properties of purified Wyoming bentonite are distinctly better at the same concentration. The difference can be related to the mineralogical structure and the presence of 13% illite in the Tunisian clay. Standard tests show that the rheological behaviour of the purified Tunisian clay is close to that of the raw Wyoming bentonite and conform to the American Petroluem Institute (A.P.I.) standards for medium-depth drilling formulations.

Influence of mineralogy of Tunisian clays on pozzolanic activity—assessment by different methods

Five local clays were characterised by several physicochemical methods to predict their pozzolanic reactivity. The studied samples were treated thermally at 600, 700 and 800°C. The heat-treated samples were characterised by X-ray diffraction. The pozzolanic activity was assessed by chemical (Chappelle test), mechanical (compressive strength at 28 days) and physical (differential thermal analysis/thermogravimetry) methods. It was found that under the chosen conditions, the kaolinitic clay fraction was transformed to an amorphous phase that was reactive with lime, whereas the illitic phase remained in a crystalline form and was consequently unable to produce pozzolans. The montmorillonitic fraction started to gain pozzolanic activity above a calcination temperature of 700°C. It was also demonstrated that the pozzolanic activity of the clays calcined at 700°C was directly related to the percentage of kaolinite in the crude samples. The hydration products were C–S–H and C4AH13, and C3AH6 and C2ASH8 were also detected in samples that were rich in alumina.

Removal of fluoride from acidic wastewater by clay mineral: Effect of solid–liquid ratios

The ability of three Tunisian clays (H, MK and ZB) to remove fluoride from acidic waste solution has been investigated. The studies were carried out as functions of solid–liquid percentage (10, 20 and 30%), contact time, pH and effect of concentrations of other ions. The kinetic study shows that the percentage of fluoride removed increased with the agitation time. The equilibrium was achieved within 48 h minimum and the highest adsorption was reached for MK clay for clay–lixiviat suspension of 10%. Moreover, for all samples, the fluoride adsorption obeyed the Langmuir isotherm model. On the other hand, the influence of other ions on fluoride removal depends of the relative affinity of the ions by the type of clays and the relative concentrations of these ions.

Alteration of Chemical Composition and the Oxidative Stability of Bleached Pomace−Olive Oil on Activated Clays

This work is a contribution to the study of the bleaching process, which is a very important stage in the refining process of vegetable oils and used to reduce or convert undesired constituents to harmless ones from fats and oils. The virgin olive oil, taken as reference, and the pomace-olive oil were bleached in the optimal conditions using Tunisian bleaching earths (South of Tunisia) which were activated in our laboratory and compared with commercial clays. It was shown that activated Tunisian clays are characterized by a very important adsorptive capacity, comparable to that of commercial clays. Also, the physicochemical stability of bleached oils was studied. The fatty acid composition (GC), the triacylglycerol composition (HPLC), and the oxidative stability (UV spectrometry) allowed us to conclude that oils, bleached with the Tunisian activated clays, do not undergo considerable physicochemical alterations and remain corresponding to the international standards for refined oils for human consumption.