Comparison of Leaching Results for Three High Mercury Fly Ash Samples

Researchers at the National Energy Technology Laboratory (NETL) studied the release of mercury (Hg) from fly ash. FA51 (1.614 ppm Hg) was produced in a commercial utility burning a high Hg coal. FA52 (89.3 ppm Hg) was generated in a full scale test of activated carbon injection (ACI). FA53 (1.091 ppm Hg) was from an ACI test in a NETL combustion pilot plant. One-kg samples of each fly ash were leached in columns with five lixiviants which varied from acidic to alkaline. The concentration of Hg in the leachates of all three samples was less than 80 ng/L. FA52 produced approximately 2 L of leachate. The other two ash samples were leached with 12 to 64 L of lixiviant, and the concentration of Hg in the leachates fell below the detection limit by the end of most tests. In the acetic acid leach of FA51, Hg concentrations remained between 20 and 50 ng/L for nearly a year; and the cumulative leached amount was 0.10% of the Hg in the sample. The total Hg leached from FA52 and FA53 was less than 0.01% of the Hg in the ash. Acetic acid leached 5 to 100 times more Hg than the other solutions.