Obtaining High Temperature Stable Sepiolite via Optimization of Acid Treatment Conditions

Abstract

Acid treatment of sepiolite under different molarity of HCl at various times was studied to find the best acid treatment conditions for obtaining anhydrous sepiolite without structural folding and with fully open and empty channels. It was found that high molarity (e.g., 3 M) acid treatment causes severe acid attack and heterogeneous magnesium dissolution from sepiolite particles. In contrast, the low molarity (e.g., 0.5 M) acid treatment dissolves magnesium homogeneously through the particles. This, in turn, affects the behavior of sepiolite upon calcination at 450ºC in that homogeneous magnesium dissolution gives better structural stability and consequently higher amount of open channels with the least amount of magnesium removal (25%). This is verified by rehydration behavior and specific surface area measurements after the calcination, where over 90% of the surface area could be preserved after the calcination of the low molarity acid-treated samples. No change in the morphology of sepiolite fibers was observed after acid treatment.