PROCESS FOR PROCESSING SILICON-DIOXIDE-CONTAINING AIR-BORNE WASTE FINES TO PRECIPITATE SILICAS AND SILICATES

摘要

The present invention provides a process for processing to silicas and silicates silicon-dioxide-containing air-borne waste fines obtained from the production of silicon metal and silicon alloys which comprises the following steps: I. dissolving the air-borne waste fines to form alkali metal silicate solutions having a high molar ratio (SiO2:Me 1/2 O), (Me being alkali metal) at temperatures ranging from 60 to 110.degree.C, II. purifying the alkali metal silicate solutions from organic constituents by treatment with at least one of active carbon and oxidizing agents and separating the non-decomposed residue from the solution, and III. reacting the alkali metal silicate solution with at least one of inorganic or organic acids and salts of aluminium, magnesium and calcium at temperatures ranging from approximately 60 to 110.degree.C in the pH range from approximately 1 to 12, subsequently filtering, washing and drying the filter-cake dough and comminuting the filter cake granulate to obtain finely divided, amorphous pure silicas and silicates having a whiteness degree according to Degen ranging from 90 to 95% and specific surface-area values according to BET in the range from 30 to 800 sq m per gram.