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.