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

Three sepiolites with differences in composition and structural ordering were treated with 0.2N HCl and 0.2N HNO3 solutions assisted with microwave radiation. This treatment caused in the firsts 16min 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 48h with conventional heating methods. The influence of mineralogical impurities, “crystallinity” and chemical composition on the reactivity of sepiolite were also studied. •Heating treatment by microwaves is an effective method in sepiolite acid activation.•Microwave-assisted acid treatment of sepiolite provokes important structural and compositional changes.•Sepiolite “crystallinity” (order–disorder) is an important factor in the microwave-assisted acid activation.•Microwave-assisted acid activation is more effective in the presence of HNO3.