L. Nibou

MINERALOGICAL AND PHYSICOCHEMICAL INVESTIGATION OF Mg-SMECTITE FROM JBEL GHASSOUL, MOROCCO

Abstract‘Ghassoul’ clay is a Mg-rich clay from Morocco which is of great industrial use and interest, but its characterization is still incomplete. The purpose of this study was to provide further details regarding the structure and characteristics of this important commercial clay mineral. Mineralogical and physicochemical characterizations of the raw form of ‘Ghassoul’ clay from Jbel Ghassoul in Morocco, and of its <2 µm size fraction, purified and Na+-saturated, were carried out using X-ray diffraction (XRD), X-ray fluorescence (XRF), infrared spectroscopy (IR), and differential and thermogravimetric analysis (DTA/TG). The XRD data revealed that the raw Ghassoul clay consists mainly of a Mg-rich trioctahedral smectite, stevensite, together with quartz and dolomite. The IR spectra consisted of vibrations typical of trioctahedral smectites. The DTA/TG curves were also similar to those of trioctahedral smectites. Chemical analysis confirms that this Mg-rich trioctahedral smectite is a stevensite characterized by a limited isomorphic substitution of Si4+ by Al3+. The thermal transformations examined by in situ XRD as a function of the firing temperature from 100 to 1200°C indicated that stevensite was transformed to enstatite (MgSiO3) at temperatures >800°C and that quartz was transformed to cristobalite when the temperature exceeded 1100°C. These transformations were irreversible. The specific surface area and cation exchange capacity (CEC) of the ‘Ghassoul’ clay are 133 m2/g and 75 meq/100 g, respectively. The main exchangeable cation is Mg2+ (53 meq/100 g).

Synthesis and characterization of pillared stevensites: application to chromate adsorption

The purpose of this work was to study the synthesis of pillared interlayered clays from Moroccan stevensite called locally ‘Ghassoul’. This clay has been intercalated with cetyltrimethylammonium surfactant (CTA‐Stv) and aluminium hydroxypolycation (Al13‐Stv). Characterization studies were performed using XRF, XRD, FTIR and DTA/TG analysis. Basal spacing values of Al13‐Stv and CTA‐Stv increased respectively from 13.5 Å for natural stevensite to 17.5 and 17.6 Å with increasing Al13 7+/clay and CTA+/clay ratios. The DTA/TG results showed that Al13‐Stv has a relatively high thermal stability compared with CTA‐Stv. A quasi‐irreversible intercalation by exchanging the interlayer inorganic cations with voluminous pillars Al13 7+ or CTA+ was observed. Batch adsorption of chromate anions from aqueous solutions was investigated and the results showed that both pillared clays had great affinity for the chromate compared with untreated stevensite. The Dubinin–Kaganer–Radushkevich (DKR) model was selected to describe the adsorption isotherms. The maximum adsorption capacities for natural stevensite, Al13‐Stv and CTA‐Stv are 13.7, 75.4 and 195.6 mmol/kg, respectively.

Effects of Phenol Addition on Oil Extraction from Moroccan Oil Shale by Supercritical Toluene

In the present work, the effect of phenol on the supercritical extraction of the organic matter from Tarfayas oil shale with toluene was evaluated. The experimental results showed clearly that phenol had a significant effect on the yield and the composition of the oils obtained. Moreover, it was shown that phenol was a very efficient modifier for oil shale, giving a good yield of recovery and a suitable maturation of the organic matter. The pitches prepared by mixing phenol and toluene contain more aromatics and have a high char yield at 950 °C compared to those obtained by extraction with supercritical toluene alone.