Interfacial electrochemical properties of natural Moroccan Ghassoul (stevensite) clay in aqueous suspension.

A raw Moroccan clay locally named "Ghassoul" (Gh) was characterized using several techniques such as Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Brunauer, Emmett and Teller method (BET), Scanning Electron Microscopy (SEM) and simultaneous Thermo-Gravimetric and Differential Thermal Analysis (TGA/DTA). These techniques indicate that the Gh consists essentially of steveniste, calcite, dolomite and quartz. The study of the interfacial electrochemical properties of Gh in different solutions of electrolyte salts (NaCl, CsCl, NaF, NaBr and LiCl) was carried out using the potentiometric and conductometric titrations It was shown that the Gh particles were stable in aqueous phase within the pH range (3-12) and the point of zero charge (PZC) was located at pH = 10.7. The adsorption sequence, carried out at various ionic strengths, showed that the adsorption mechanism onto the Gh particles is both electrostatic and specific at pH below the pH, while at a pH range greater than the pH the mechanism is electrostatic in nature. The total number of surface sites, determined using the graphical extrapolation method, was 11OH/nm. Ionization constants ( and ) in the presence of various electrolytes have also been determined and their values are 10.08 and 12.38, respectively.