WEATHERING OF FLY ASH: ENVIRONMENTAL IMPLICATIONS AND GEOCHEMICAL CHANGES DURING SHORT AND LONG TERM STORAGE

Fly ash is the particulate product of coal combustion captured by coal-fired power plant filtration systems. Studies have shown that coal combustion products (CCPs), and subsequently the effluent from their holding ponds, can have high concentrations of many trace elements such as As, B, Sr, Ba, and Se, which can have harmful effects on wildlife. Fly ash can be used as a mineral filler in concrete and cement, or is stored indefinitely in holding ponds. We have systematically investigated the short and long term changes in reactivity, mineralogy, and morphology of fly ash during the weathering process in holding ponds. In this study, fresh dry fly ash was collected from several hoppers within a coal-fired power plant with the intent of performing short and long term leaching experiments to simulate ash in a holding pond. Seven samples were rotated end over end for 1 hour, 1 day, 1 week, 1 month, 2 months, 6 months, and 1 year at 10:1 liquid to solid ratio with deionized water. The 6 month and 1 year samples were allowed to settle without rotation after 90 days. Additional experiments were simulated at 1:1, 2:1, and 5:1 liquid to solid ratios with deionized water. The final experiment followed the EPA’s Synthetic Precipitation Leaching Procedure (SPLP - EPA Method 1312). Anions and cations in the leachate were analyzed by IC, and trace elements by ICPMS. Mineralogy of the fresh and weathered fly ash was analyzed by XRD, and morphology by SEM. Results from the experiments indicate that SO₄ was the prevalent anion across all samples (1,491 mg/kg in the 1 day samples to 224 mg/kg in the 1 month samples). The 1 month samples released the highest concentration of trace elements with concentrations of Li (3.68 mg/kg), Cr (3.67 mg/kg), and Ba (12.87 mg/kg). However, most Li was detected in the 1 day samples (6.71 mg/kg). The results from the weathering of the fresh ash were compared with the same experiments performed on ash that had been weathered in a holding pond. These results indicate that the reactivity of fly ash can vary based upon the amount of time weathered and the solid to liquid ratio, which can have implications for disposal and effluent.