A GENERAL METHOD FOR THE CONVERSION OF FLY ASH INTO ZEOLITES FOR IMMOBILIZING RADIOACTIVE WASTES

摘要

A general method that can convert various coal ashes into zeolites was studied. Fly ashes were reacted with fused sodium hydroxide at 550 deg C and ambient pressure followed by dissolution in aqueous solution and heat treatment. The faujasite type zeolite and zeolite P were precipitated from the solution of fused powders cured at 60 deg C and 90 deg C, respectively, and ambient pressure. Those zeolites converted from coal ashes were characterized by the X-ray diffraction method and Scanning Electron Microscopy. The ion exchange capacities with Cesium ion of zeolites converted from fly ashes were obtained by measuring the increase of sodium ion concentration in solution. When faujasite type zeolite converted from fly ash was heated at different temperatures, the thermal stability of faujasite was studied by XRD and nitrogen gas adsorption analysis. The result indicates that the crystal structure of faujasite was thermally stable at 540 deg C. The fusion method is critical to convert fly ashes with different chemical compositions into faujasite. With a higher concentration of the soluble aluminosilicate in the fused powders, the yield of faujasite increased.