Leaching Characteristics of Trace Elements from Municipal Solid Waste Incineration Fly Ash

Beneficial reuse of municipal solid waste incineration (MSWI) fly ash depends on demonstrating that this material presents acceptable environmental risk. Leaching characteristics of trace elements from municipal solid waste incineration (MSWI) fly ash samples were investigated by laboratory leach tests. Concentrations of arsenic (As) and barium (Ba) from water leach tests (WLTs), synthetic precipitation leaching procedure (SPLP), and column leach tests (CLTs) were observed to exceed the Maximum Contaminant Level (MCL) according to US EPA drinking water standards. Concentrations of As from CLTs decreased steadily with increasing cumulative liquid-to-solid ratio (L/S), but still exceeded the MCL at L/S ratio of 10. pH dependent leaching of Ba was observed from batch and column leach tests. Leaching of Ba in one ash sample was 2-3 times higher than another sample in both WLTs and SPLP, with a higher leachate pH of 11.3. Lower concentrations of Ba (30 to 300 mu g/L) were observed in CLTs with lower leachate pH. Concentrations of As decreased significantly below pH= 4, then showed a steady release with concentrations of 2-10 mu g/L for 4 < pH < 12. Leaching concentrations of boron (B) and Ba were independent of pH until pH= 9. Leaching behavior of copper (Cu) followed the cationic pattern in which the concentration of elements steadily decreased with pH.