STABILITY AND POROSITY OF ALUMINA-PILLARED CLAY IN ACID AND BASIC SOLUTIONS

Alumina-pillared montmorillonite was treated during two days at room temperature with solutions of NaOH and HCl at concentrations ranging from 0.005 to 0.100 M. In order to investigate the stability and porosity of the clay during and after the treatment, X-ray diffraction (XRD), direct current plasma (DCP) atomic emission spectrometry (EAS), nitrogen adsorption isotherms and discrete micropore size distributions were used. No structural collapse occurred during these treatments, however, some Al3+ was leached out from the structure: from 0.09 mmol Al3+ per g clay at pH 2.44 to 1.43 mmol/g at pH 1.75 for the acid treatment and from 0.03 mmol/g at pH 10.73 to 0.62 mmol/g at pH 11.85 for the base treatment. Moreover, the NaOH modification resulted in a small decrease in surface area, micropore volume and interlayer distance. On the other hand, the acid modification showed an increase in micropore volume (more than 30% compared to the initial value of 0.11 ml/g) and a considerable increase in surface area (from 341 m2/g for the untreated pillared clay up to 462 m2/g for the one treated with 0.100 M HCl). A model is proposed to explain these trends in porosity for this type of pillared clay which is treated in an acid or basic solution.