Résumé:
Algerian halloysite was heated at 600 °C and treated with HCl 5N. The materials were characterized by
chemical analysis, TEM, and FT-IR spectroscopy, and used in the elimination of Congo red (CR) from aqueous
solution. The effects of contact time and temperature were investigated. The thermal treatment at 600 °C results in
the formation of dehydroxylated structure. Acid attack involves an increase in SiO2 content, due to the leaching of
Al ions from octahedral sheet. Thermo-chemical treatment also diminishes the percentage of impurities and
maintains the tubular morphology. Kinetic data follow the pseudo-second order model, whilst thermodynamic
parameters lead to a not spontaneous and endothermic process. Significant changes occur in the vibrational spectrum
of H600-5N (halloysite treated at 600 °C and with HCl 5N), after adsorption of Congo red, with the involvement of
amino and sulfoxide groups. The mechanism highlights an outer-sphere surface complexation of SiOH....H2O
species, i.e., SiOH linked to H2O via H-bonds.
