Identification and Simultaneous Optimisation of Tunisian Clay Properties: Preliminary Study for the Ceramic Products

The relationship between composition and physical parameters such as specific surface area, cationic exchange capacity and plasticity is studied with the aim of developing regression models that would permit the prediction of clay properties. These models could be useful for mineralogists and industrial applications. Nineteen representative clay samples were collected from Jebel Ressas in north-eastern Tunisia. Mineralogical data show that clay samples cover a very large variety of minerals. The main clay mineral is illite (50–60 wt%), secondary minerals including quartz, calcite and minor amounts of Na-feldspar. This study reveals that the average amount of silica (SiO₂) and alumina (Al₂O₃) are 51.9 and 19.6 wt%, respectively. The contents of lime (CaO) and iron (Fe₂O₃) vary between 4 and 8 wt% whereas the amount of alkalis (Na₂O + K₂O) is on average 4.1 wt%. The grain size data indicates a significant amount of silt fraction, and the fraction <2 µm varies between 23 and 35 wt%. Values for plasticity index range from 16 to 28 wt%. The cation exchange capacity and the specific surface values are 34.1–45.7 meq/100 g of air-dried clay and 302–374 m²/g, respectively. Lastly, regression models are used to correlate the properties with the mineralogical and chemical compositions. The significance and the validity of models were confirmed by statistical analysis and verification experiments. The regression models can be used to select the clay properties (plasticity index, cation exchange capacity and specific surface) in relation with clay minerals proportions and the finer fraction amounts.     

Nitrate sorption by organosmectites

The use of organoclays as adsorbents in the remediation of polluted water has been the subject of many recent studies. In this present work, a Tunisian smectite modified by two cationic surfactants was used as a sorbent for the investigation of the adsorption kinetics, isotherms and thermodynamic parameters of nitrate ions at various contact time, initial concentrations and temperatures. Two simplified kinetic models, first-order and second-order, were used to predict the adsorption constants. It was found that the adsorption kinetics of nitrate was best described by the second-order model. Adsorption isotherms and equilibrium adsorption capacities were determined by the fittings of the experimental data to two well-known isotherm models including Langmuir and Freundlich. The results showed that Langmuir model appears to fit the adsorption better than Freundlich model. The equilibrium constants were used to calculate thermodynamic parameters, such as the change of free energy, enthalpy and entropy.     

Determination of point of zero charge of PILCS with single and mixed oxide pillars prepared from Tunisian-smectite

Different pillared interlayer clays (PILCs) with single oxide pillars of Cr and Al and mixed oxide pillars of these metals have been prepared from a Tunisian purified smectite (Hp): Several Al/metal, OH/metal and metal/clay ratios were used in order to investigate the effect on the chemical and physical properties, specifically the point of zero charge of the synthesized pillared clays. These chromium pillared clays compounds at n meq (Nitrate) and at n meq (Chlorite) are noted pillared clay and pillared clays \(Hp(20,40,60)_{NO_3 } \) and Hp(20,40,60)_Cl. The structure of the pillared materials are studied by XRD and cationic exchange capacity, the textural property are investigated by the specific surface area S_BET. The acid-base chemistry “surface acidity” of these products was analysed by using acid-base potentiometric in order to determine the PZC of each sample. The resulting materials exhibited basal spacings in the range of 13.96–21.13 Å, with high surface areas (10.58–198 m² g^?1). Pillared clays prepared from Tunisian purified smectite showed an increase of basal spacings and surface areas. A relatively strong interaction between metal and aluminium in the pillars was observed. The samples are studied by acid-base potentiometric. This experimental method is used to determine the point of zero charge (PZC). The PZC values of the edge sites are 8.2 for Tunisian purified smectite and 6.8; 5.9; 5.19; 6.84; 5.86; 5.73; 6.78; 7.56 for the differents samples respectively: \(Hp(20,40,60meq)_{NO_3 } \) Hp(20,40,60meq)_Cl; Hp-Cr/Al; Hp-Al.