NEUTRALIZATION AND RELEASE OF METALS PROPERTIES OF FLY ASH

Abstract

The neutralization property and the release of metals for three types of coal combustion ash were evaluated. Fly ash (FA), fluidized bed ash (FBA), and hydrated fly ash (HFA) were assessed for their variation in physical, chemical and mineralogical properties. Acidic solutions of different pH were used to equilibrate the ash in conservative and nonconservative systems. Release studies were conducted for the following metals: iron, manganese, zinc, magnesium, aluminum, calcium, cadmium, sodium, chromium, copper, and nickel. Data indicated that pH was a very significant factor for the release of metals from the fly ash surface. At high pH iron was the least released cation from fly ash, whereas calcium was the most desorbed cation. Comparison of the three ashes indicated that FA and FBA were excellent buffering materials. However in the case of FBA, there seemed to be a critical pH at which a drop in the proton titration curve was apparent, and large amounts of metals were released into solution. On the other hand, HFA showed lower buffering intensity compared to the other two fly ashes. Changes in pH with time were also studied since time had an impact on the titration curve at the equivalence point. Although pHmore » was increasing with time, it had no impact on the titration curve after neutralization had occurred. Comparison of fly ash with limestone for neutralization properties revealed that fly ash had less buffer intensity than limestone, but it gave solutions a higher initial pH.« less