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 A for natural stevensite to 17.5 and 17.6 A 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.