Two-step process for synthesis of a single phase Na-A zeolite from coal fly ash by dialysis

Using the amorphous aluminosilicate in coal fly ash (FA), a single phase Na-A zeolite was synthesized from FA by dialysis. The FA and NaOH solution added into the tube made by semipermeable membrane were pretreated in the same NaOH solution at 85 degrees C for 24 h. After the pretreatment, the tube was removed and NaOH-NaAlO2 solution was added into the residual solution to control SiO2/Al2O3 molar ratio of the solutions from 0.9 to 4.3. The precipitates thus formed were aged for 24 h at 85 degrees C. The amorphous aluminosilicate in FA was dissolved during the pretreatment. When the NaOH-NaAlO2 solution was added into the solution after the pretreatment and then aged, white precipitates were yielded over the whole SiO2/Al2O3 range. At SiO2/Al2O3 = 0.9, the material formed was identified as a single phase Na-A zeolite. The Na-X zeolite was slightly produced at SiO2/Al2O3 >= 1.7. (C) 2006 Elsevier Ltd. All rights reserved.