Abstract
The alkaline waste solutions produced after synthesizing the pure-form zeolite from coal fly ash (FA) were recycled for preparation of zeolite. The FA was pretreated in NaOH solution at 85°C. After pretreatment, the remaining FA was removed and the molar ratio SiO2 / Al2O3 of the residual solution was adjusted at 2.0 by adding a mixture of NaOH and NaAlO2 solutions. After aging the solution at 85°C, white precipitates composed of a single phase Na-A zeolite were formed. Using the waste solution after synthesizing the zeolite, the FA was again pretreated and synthesis of zeolite was done under the same aforementioned condition. The pretreatment of FA and aging processes were repeated up to six cycles. For all cycles, the FA particles were dissolved during pretreatment to elute Si4+ and Al3+ in the solution, and the white precipitates mainly composed of Na-X zeolite were generated without changing the yield of the zeolites.
