Method for producing foamed ceramics

A method for the manufacture of foamed ceramics comprising 60 - 75% silica from a starting composition capable of forming, when heated, a viscous, sintered and porous mass, said starting composition comprising

• a. at least one silica-containing material selected from the group consisting of:
• fly ash obtained from waste-heat boilers,
• dust removed from waste gases emanating from
• electrometallurgical processes, and
• dust trapped in stone crushing plants, and
• sand
• and
• b. a product containing both ferrous compounds and readily carboniferous substances,
• said compounds and substances being capable of impairing pore formation,
• which method comprises mixing with the starting composition
• I. silicon carbide, and
• Ii. a strongly oxidizing agent selected from the group consisting of MnO.sub.2,NaNO.sub.3 and KMnO.sub.4 capable of oxidizing the ferrous compounds into ferric compounds and the carbon of the readily oxidizable carboniferous compounds and the carbon of the SiC into gaseous compounds under the heating process, gaseous compounds from the SiC being formed after the composition has begun to melt, thereby to cause the pore formation to take place.