PROCESSO PARA A PREPARACAO DE POEIRAS RESIDUAIS CONTENDO DIOXIDO DE SILICIO PARA DAR ACIDO SILICICO DE PRECIPITACAO E SILICATOS

There is provided a process for treating air-borne dust containing silicon dioxide in order to form a silicic acid or a silicate. The air-borne dust is dissolved in an alkali metal hydroxide solution to form an alkali metal silicate solution. The alkali metal silicate solution is purified by treating it with activated charcoal and/or oxidation agents. Non-decomposable substances remaining after the purification step are removed from the alkali metal silicate solution. The alkali metal silicate solution is then reacted with acids and/or salts of aluminum, magnesium and calcium. The resulting product is then filtered, washed and dried, and then comminuted to form a finely divided, amorphous, substantially pure, precipitated, silicic acid or silicate having a whiteness according to Berger at a wave length of 460 m mu of about 90 to about 95% and a specific surface area of about 30 to about 800 m2/g BET. The resulting products are useful as reinforcing fillers in the rubber and plastics industries, as well as additives in the paint, varnish, lacquer, paper, cosmetic, pharmaceutical, feed and pesticide industries.