The effect of alkalinity of Class F PC fly ash on metal release

Thirty-five samples of Class F fly ash from pulverized coal (PC) combustion boilers were leached with deionized water, acetic acid, and sulfuric acid. The release of metal ions from fly ash was related to the pH of the leachant solution and to the alkalinity of the ash. The maximum soluble concentration of the metallic elements was measured when the pH of the leachate was less than 5. Twenty-three of the samples were strongly alkaline and buffered the leachate until the ash was neutralized. The leachate from the other 13 samples became acidic with the addition of less than 1 L of 0.1 N acid. The alkalinity of the ash and the volume of acid required to neutralize it were a function of the Ca concentration.