Effects of pH, ORP, and Conductivity on Leaching of Trace Metals from Fly Ash

摘要

Leaching of metals from coal utilization by-products (CUB) is being studied to assess thernpotential for environmental damage. Samples contained in fixed-bed columns were leachedrnwith five lixiviants. The lixiviants simulated environmental liquids and varied from acidic tornalkaline (pH 1 to pH 11). The leachates were analyzed for major and trace metals. Tracernmetals that formed cations were leached by acidic lixiviants although, in most cases, the totalrnamount leached was small. The concentrations of metals were low initially, increased rapidlyrnafter the alkalinity of the CUB was depleted, then dropped rapidly after a maximum wasrnreached. For normal Class F fly ash samples, the maximum concentrations of acid solublerntrace metals in the leachate were typically less than 10 mg/L. A Class F fly ash producedrnduring an SCR test produced leachates with much higher concentrations of metals. ORPrnappeared to be as good an indicator of leaching progress as pH for this SCR material whilernconductivity was a less indicative but possibly adequate monitor.