The Silicate/non-silicate distribution of metals in fly ash and its effect on solubility

In a study at DOEʹs National Energy Technology Laboratory, 32 Class F fly ash samples from pulverized coal (PC) power plants were dissolved in concentrated nitric acid and in hydrofluoric acid to estimate the distribution of metals in non-silicate and silicate matrices. Nineteen cations occurred to some extent in both phases. Using a column leaching method, the release of the metals was determined with four leachant solutions; the pH of the leachants ranged between 1.2 and 12. Although the amount of an element extracted from the fly ash was low, solubility in alkaline leachants was correlated with elements in non-silicate compounds. Solubility in acid solutions was correlated more strongly with silicate phase concentration.