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A silica gel of improved hardness and abrasion resistance, increased adsorption power, and other valuable properties is produced by a highly economic process. A useful manufacturing system for making such silica gel and a simple apparatus for producing silica gel spheres of considerably larger diame

A silica gel of improved hardness and abrasion resistance, increased adsorption power, and other valuable properties is produced by a highly economic process. A useful manufacturing system for making such silica gel and a simple apparatus for producing silica gel spheres of considerably larger diameter than heretofore known are provided.

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In a process of producing silica gel, including the steps of precipitating a silicic acid-containing starting materials and acid reactant to first form an unstable silicic acid containing sol as an intermediate product, subsequently gelling the sol, washing the gel to remove the salts, and drying th

In a process of producing silica gel, including the steps of precipitating a silicic acid-containing starting materials and acid reactant to first form an unstable silicic acid containing sol as an intermediate product, subsequently gelling the sol, washing the gel to remove the salts, and drying the gel, the improvements which comprise carrying out the precipitation process in two steps, wherein in the first step a first silicic acid-containing starting material with a silicon dioxide content between about 20% and about 32% by weight is introduced in such a fine distribution and at such a high discharge velocity into the acid reactant, while being subjected to high speed agitation, until a pH-value of the acid reactant between about 1.5 and about 1.8 is attained, that instantaneous reaction between the acid and the silicic acid containing starting material takes place without any precipitation of silicic acid, and wherein in the second precipitation step a second silicic acid-containing starting material having a silicon dioxide content between about 8% and about 14% by weight is introduced into the acid reactant until a pH-value of between about 2.6 and about 3.5 is attained, thereby producing a sol having a silicon dixoide content of about 14% to about 18% by weight, and carrying out the washing step by washing with a washing liquiD of a pH between about 1.8 and about 12.0. silica gel having a silicon dioxide content of between about 16% and about 24%, a pore diameter of between about 20 and about 25 Angstroem, a wetting heat of between about 32 and about 35 cal./g., a bulk weight between about 720 and about 770 g./cm.3, an adsorption temperature of up to about 100°C. and a desorption temperature of between about 150°C. and about 200°C.