HEAVY METAL LEACHING FROM DIFFERENT FLY ASHES USES DIFFERENT LEACHING METHODS

Abstract

The coal fly ash samples (Lignite coal fly ash, bituminous coal fly ash and treated bituminous coal fly ash) were collected from different power plants. The fly ash characterizations in this research were analyzed by X-Ray Fluorescence (XRF) for ash chemical composition. Scanning Electron Microscope (SEM) was used for microstructure and particle size analysis. Initial pH of fly ash samples was measured. The fly ash samples were determined the leaching behaviors of As, Cr, Pb and Zn by Toxicity Characteristic Leaching Procedure (TCLP) test using acetic acid as leachant. For pseudo-total concentration of elements in fly ash, the microwave-assisted digestion was used in this experiment according to USEPA. According to microwave digestion method, the heavy metals (As, Pb and Zn) were richer in LCFA except Cr. The results of TCLP showed that the leachability of heavy metals is highest in LCFA and lowest in T-BCFA. The concentrations of heavy metals in TCLP test were below the regulatory level of contaminant except As from LCFA. Jar leaching test was used to determine the leaching trends of heavy metals by using DI water as leachant. Column leaching test was conducted using DI water and synthetic acid rain (SAR). The results from jar leaching test showed that the leaching concentration (LCs) trends of heavy metals were separated to four different trends (1) LCs increased with increasing contact time, (2) LCs decreased with increasing contact time, (3) LCs were stable over time and (4) LCs were unstable and fluctuated. Leaching concentrations from different leachants (DI and SAR) were not different, and the leaching trends using DI water and SAR were similar from column leaching test.