Abstract: Na Silicate and H₂SO₄ are reacted to produce acidic silicic acid hydro-gel. If the hydrogel is washed with acidifying tap water at pH 3, the product is typical fine-pored silica gel with av. pore radius (r)7.5～8.2Å, specific surface area (S)637-690m²/g and pore volume (V) 0.26mL/g. After the impregnation of acidic hydrogel with H₂SO₄ solutions of various concentrations for 24 h (and then dried at once), the specific surface area and apparent density decreased with increasing the concentration of the acid used, but the pore volume, av. pore radius and av. particle diameter increased with increasing the concentration of the acid used. When the concentration is sufficiently high (3-l8mol/L), the pore structure and adsorption properties of the resulting silica gel are similar, all of these products are extremely coarse-pored silica gels (r= 292-300Å, S-98m²/g, V= 1.43-1.47ml/g). On the other hand, if the same hydrogel is impregnated with HC1 solutions of various concentrations, the relationship between pore structure of silica gel and concetration of the acid used is roughly similar to that as mentioned above.In the concentration range of 3-16mol/L, the properties of the resulting silica gel are almost consistent, but they are not typical coarse-pored silica gels (r=53Å, S = 270m²/g, V = 0.71-0.72mL/g).

Key words: Silica gels, Acid-treatment, Structure, Adsorption properties