CHARACTERIZATION OF MICROPOROUS SILICA PREPARED BY SELECTIVE LEACHING OF CALCINED KAOLINITE: EFFECT OF CALCINING TEMPERATURE

Microporous silica was prepared by selective leaching of the Al2O3 component from calcined kaolinite. The kaolinite was calcined at various temperatures from 400 to 1000°C for 24 h. It was then chemically treated with a 20 mass% H2SO4 solution at 90°C for 2 h and the effect of the calcining temperature was studied. The chemical composition of the acid leached product changed largely by elevating the calcining temperatures from 425 to 475°C owing to selective leaching of Al2O3 from metakaolinite and became almost SiO2 composition above this calcining temperatures. With decreasing of Al2O3 content in the products, the specific surface area increased and became higher than 300m2g-1. It further increased gradually with higher calcining temperature up to 700°C because of the increase of efficiency of selective leaching. The pore size distribution was calculated by the Horvath-Kawazoe method based on Ar gas isotherms and the slit-shaped pore size was about 0.6nm in width for all the products with irrespective to the calcining temperatures. Since the particle shape was preserved after the leaching treatment, those pores are considered to be formed in the interlayers of the SiO4 tetrahedral layers largely preserving the original metakaolinite structure.