Influence of the free silica generated during acid activation of a sepiolite on the adsorbent and textural properties of the resulting solids

Abstract

A sepiolite from Vallecas (Spain) has been treated with 1.25 and 2.5 wt.% HCl aqueous solutions, at 25 °C for 2, 6, 24 and 48 h. The resulting solids were characterized using XRD, FTIR, TEM and nitrogen adsorption–desorption isotherms at 77 K and the free silica formed during the acid attack was digested and determined in all samples. The solids obtained after free silica digestion were also characterized and compared with the same solids before digestion. The influence of the unattacked sepiolite and of the free silica generated during acid activation is thus proved. Free silica has little influence on the properties of the solids obtained when acid treatment of sepiolite has been mild, because these solids are mainly formed by unattacked sepiolite. This influence becomes very important when solids obtained after more intense acid treatments are considered.