Élaboration d’adsorbants de métaux à base de matériaux aluminosilicatés poreux fonctionnalisés et leur application à la potabilisation des eaux

Abstract

In this study we used the thermally exfoliated vermiculite to remove manganese in aqueous solution. The adsorption mechanism of manganese nitrate on this clay was studied by analysis of the isotherms of the cations exchanged from the vermiculite (K+ and Ca2+) and the ions (NO3- and Mn2+) adsorbed on the vermiculite. The kinetic of adsorption of the Mn2+ ions on vermiculite was found of pseudo-second-order type with a constant rate of 0,170 g.mg-1.min-1. The adsorption temperature dependence between 25 °C and 45 °C has demonstrated an endothermic and spontaneous adsorption. The amount of exchanged Mn2+ ions in equivalent per gram represents only 17% of the total adsorbed uptake. 83% of the Mn2+ and NO3- ions have been adsorbed at the edges of the layers. The milling of the vermiculite has involved a decrease in the grains size and thus an increase in the edge layer adsorption site content allowing an increase of 19 % of the maximum adsorption uptake compared to raw vermiculite. The milled vermiculite was more grinded by sonication at 20 kHz. Increasing of sonication time, presence of H2O2, and the increase of the vermiculite concentration have caused an accentuation of sonication effect, this resulted the decreasing of the size to 8 µm. Moreover, a 2% fraction of submicron-sized particles was appeared. The pH of the vermiculite suspensions was increased. The number of the -OH sites was determined by acid-base titration using Gran method was also increased. The infrared spectra of the raw and sonicated vermiculites in H2O or containing H2O2 were very similar. XRD spectra showed that the sonication did not affect the vermiculite structure. The sonication leads to increase the maximum uptake by 31 %. The linear variation of the Mn2+ adsorption capacity with respect to the sum of the estimated geometric perimeter of the sonicated particles (assuming square shaped particles) confirms an adsorption process at the edge of layers. The sonicated sample during 5 h in H2O2 has been grafted with butylimidazolium. This was realized in two steps. In the first step, we grafted 3- chloropropyltrimethoxysilane instead of the –OH sites. In the second step, we conducted a nucleophilic substitution of chlorine with methyl-imidazole. Infrared spectroscopy shows that grafting was real and XRD that this was not an intercalation