Thermal decomposition of sepiolite and variations in pore structure with and without acid pre-treatment

Abstract

Sepiolite is a high surface area clay mineral containing channels of molecular dimensions. In industrial applications as an adsorbent or catalyst support, the mineral should have thermal stability. In this study, the effect of heat treatment on sepiolite structure was investigated. Thermal decomposition of raw sepiolite and acid pre-activated sepiolite samples were carried out with a thermogravimetric analyser. Approximately 24% weight loss was observed till 900°C. This value decreased to 14% for acid pre-treated samples. The surface area value of the original sepiolite was 148 m2g-1, and it increased to 263 m2g-1 at 100°C. Further increase in temperature caused channel plugging and crystal structure deformation, as a result the surface area values showed a decrease with temperature. On the other hand, acid pre-treatment caused a change in pore size distribution by increasing the surface area 2.5 times. Acid pre-treatment also restricted the possible crystal structure deformations during temperature changes. While the surface area of the original mineral which was heated up to 900°C was 60 m2g-1, the corresponding value of the acid pre-treated sepiolite was 360 m2g-1.