Porous Silica Gel by Acid Leaching of Metakaolin

Solids, mainly composed of silica gel, were prepared by acid leaching of metakaolins. The metakaolins were prepared by calcination of a natural kaolin at different temperatures (600, 700, 800 and 900°C). The metakaolins thus prepared were treated with 6

M

aqueous HCl at room temperature and at 90°C, varying the duration of the treatments. All metakaolins prepared by calcination at 600, 700 or 800°C showed a very similar reactivity, while that prepared by calcination at 900°C showed lower reactivity, due to a beginning of sintering. Treatments at room temperature did not alter either the structure or the properties of the metakaolins. Treatment under reflux conditions led to the leaching of most of the octahedral Al

3+

cations. Silica-based solids were thus obtained reaching, under optimal activation conditions, high BET surface areas up to 219 m

2

/g and total pore volumes up to 0.065 cm

3

g

−1

. Harsher treatments conditions (for longer periods of time) resulted in a drastic amorphisation of the final products. The solids obtained are promising adsorbents or catalyst supports.