SYNTHESIS AND PROPERTIES OF ZEOLITES FROM COAL FLY-ASH

Previous attempts to use fly ash as a soil amendment have had limited success because of its low nutrient value, low cation exchange capacit y (CEC), and elevated levels of toxic trace elements. However, treatin g fly ash with NaOH or KOH at an elevated temperature converts the ash into zeolite minerals and solubilizes the toxic trace elements, which are removed in the base solution. The CEC of the untreated fly ash wa s < 100 mmol(c) kg(-1) but increased to over 3000 mmol(c) kg(-1) when heated for 3 days at 100 degrees C in 3 M NaOH. The dominant zeolites formed at 100 degrees C in NaOH were zeolite Na-PI and zeolite P-C, an d at temperatures of 150-250 degrees C, the mineralogy changed to zeol ite X and pectolite. In KOH at 100 degrees C, zeolite K-G (potassium c habazite) was formed. The fly ash zeolites had a high affinity for K+, Ca2+, and NH4+, although attempts to use the treated ash to remove NH 4+ and heavy metals from wastewater and electroplating wastes were onl y partially successful. Potential uses of the treated ash were limited due to the high pH that resulted from the dissolution of the zeolite minerals. At pH 4 and pH 5, the rate of fly ash zeolite dissolution wa s 1000 times faster than most aluminosilicate minerals. Attempts to pr oduce a zeolitic material with NH4OH or fluorides were not successful.