Microwave assisted acid treatment of sepiolite: The role of composition and “crystallinity”

Three sepiolites with differences in composition and structural ordering were treated with 0.2 N HCl and 0.2 N HNO3 solutions assisted with microwave radiation. This treatment caused in the firsts 16 min the progressive Mg2 + depletion of the octahedral sheet, the gradual degradation of the sepiolite structure and the formation of an amorphous silica phase which contributes to a noticeable increase of the BET specific surface area. The assistance of microwaves during the acid treatment allows us to get specific surface areas equivalent to those obtained after 48 h with conventional heating methods. The influence of mineralogical impurities, “crystallinity” and chemical composition on the reactivity of sepiolite were also studied.