The role of magnesium on the stability of crystalline sepiolite structure

Sepiolite is a hydrate magnesium silicate special clay mineral. Some of the specific properties of this silicate are its large specific surface (about 320 m2/g) together with a very reduced ion exchange capacity. Additionally, it is possible to leach the magnesium cations at the octahedral layer by acid attack, increasing the specific surface area up to the limit of the collapse of the structure. In the present investigation, we have found that the crystalline framework collapses when the fraction of leached Mg2+ is greater than or equal to 0.33. Before the collapse it is possible to obtain sepiolite with different substituted metallic cations into the octahedral sites. As an example, the optimal composition of Ni–sepiolite was obtained after the lixiviation by acid attack at pH 0 for 1 h without the collapse of structure.