Process for converting silicon dioxide containing waste flue dust to crystalline zeolitic molecular sieves of type Y with a Faujasite structure

A process for the preparation of crystalline zeolite molecular sieves of Type Y from waste flue dust containing silicon dioxide obtained from the production of silicon metal or a silicon alloy or is a mixture of flue dusts from the production of silicon metal and silicon alloy comprising (1) dissolving the flue dust in alkali metal hydroxide solution with the formation of alkali metal silicate solution having the mole ratio SiO.sub.2 :Me.sup.I.sub.2 O in the range of 4.0:1 to 5.0:1 at a temperature of 60.degree.-110.degree. C.;

• (2) purifying the thus obtained alkali metal silicate solution from organic constituents by treatment with activated carbon or an oxidizing agent or a mixture of activated carbon and oxidizing agent and separating the non-decomposable residue from the solution;
• and, (3) reacting alkali metal aluminate solution present at room temperature with the purified alkali metal silicate solution with a mole ratio SiO.sub.2 :Me.sup.I.sub.2 O of 4.0:1 to 5.0:1 obtained by steps (1) and (2) and subsequently crystallizing the reaction mixture (SiO.sub.2 :Al.sub.2 O.sub.3 =4-7:1, Me.sup.I.sub.2 O:SiO.sub.2 =0.4-0.7, H.sub.2 O:Me.sup.I.sub.2 O=30-50:1) at a temperaure of 75.degree.-100.degree. C. with stirring for a period of 8-48 hours, subsequently filtering to remove the product from the mother liquor, washing and drying to recover a zeolite molecular sieve of Type Y with a Faujasite structure having a degree of whiteness according to BERGER at 460.mu. in the range of 90-95%.