Preparation of Porous Silica by Acid Dissociation of Thermally Activated Kaolinite

Abstract

Preparation of porous silica from thermally activated kaolinite was investigated by using acid dissociation process, and the relationship between structural transformation and acid dissociation properties of aluminium were elucidated. AlVI transfers into AlV and AlIV when kaolinite changes into metakaolinite during thermal activation. AlV is dissoluble in acid, while AlVI, AlIV are difficult to be dissolved into acid, therefore, the coordinations of aluminium affect acid dissociation of alumina markedly. Mesoporous silica is made by acid dissociation alumina of metakaolinite, and the specific surface area of porous silica is determined by acid dissociation ratio of alumina. The dissociation ratio of aluminum is up to 97% when kaolinite is activated at 900°C for 15 min. Specific surface area of the porous silica material is 357 m2/g, the pore volume is 0.43 cc/g, and BJH pore diameter is 2.18 nm. The pore is found to be in the worm-like shape by high resolution TEM analysis.

Rare earth elements (REEs) recovery and porous silica preparation from kaolinite

“…Thermal activation results in the loss of structural hydroxyl groups of kaolinite. Therefore, higher chemical reactivity and Al solubility were obtained, which are necessary for the preparation of porous silica [40,63,64].…”

“…During the leaching process, Al, Fe, Mg, and other metal ions are dissolved, while the tetrahedral SiO 4 layers of metakaolinite were preserved. The specific surface area, porous characteristics, and acidity of the porous silica prepared from metakaolinite suggested excellent adsorption capacities [37][38][39][40]. Given that both the REE extraction and porous silica preparation use acid leaching, it is technically feasible to obtain both REEs and porous silica from thermally activated kaolinite.…”

Template-free synthesis of kaolin-based mesoporous silica with improved specific surface area by a novel approach

“…Lenarda et al (2007) prepared mesoporous silica of the increased S BET up to 288 m 2 /g by acid-treating the kaolin precalcined at 850°C for 2 h. Perissinotto et al (1997) and Okada et al (1998) pretreated kaolin at 600°C and acid-etched it into nanoporous silica of increased S BET up to~330 m 2 /g. Li et al (2011) obtained a porous silica with a S BET of 357 m 2 /g by acid-dissociating the alumina of 900°C-calcined kaolin. Shu et al (2014) acid-etched 850°C-calcined kaolin and improved the S BET to 430 m 2 /g.…”

Acid leaching recovery and occurrence modes of rare earth elements (REEs) from natural kaolinites

“…The c)). This result revealed that a portion of the REEs in MO form were converted to AS species as calcination temperature increased from 600 • C to 900 • C. The reduction in solubility is likely due to the sintering of kaolinite at the higher temperature, which normally occurs as temperature exceeds 800 • C (Li et al, 2011). Compared with other REEs, Sc has a nearly equal portions of MO and AS distributions (41% versus 38%) after calcination at 600 • C (Fig.…”