| 摘要 |
Silicon dioxide containing waste flue dust from the production of silicon metal and silicon alloys is converted to crystalline zeolite molecular sieves of type A by (1) dissolving the flue dust in alkali metal hydroxide solution with the formation of alkali metal silicate solution having a module (SiO2:Me2IO) in the range of 2.0:1 to 3.5:1 at a temperature of 60 DEG -100 DEG C.; (2) purifying the thus obtained alkali metal silicate solution from organic constituents by treatment with activated carbon and/or an oxidizing agent and separating the non-decomposable residue from the solution; and, (3) reacting alkali metal aluminate solution present at room temperature with the diluted, purified alkali metal silicate solution with a module (SiO2:Na2O) of 2.0:1 to 3.5:1 obtained by steps (1) and (2) and subsequently crystallizing the reaction mixture ((2.0-4.4)Na2O:Al2O3; (1.3-1.8)SiO2:(90-120)H2O) at a temperature of 90 DEG -95 DEG C. for a period of 6-12 hours, subsequently filtering, washing to pH of about 10-11 and drying to recover a crystalline, zeolitic molecular sieve of type A having a degree of whiteness according to Berger (A. Berger, Die Farbe 8 Nr. 4/6 (1959) pages 187-202) at 460 mu in the range of 90-95%. |
