Toxin Leachability from Coal Fly Ash Utilized in Synthetic Lightweight Aggregates

Synthetic lightweight aggregates — produced by commingling coal fly ash and waste mixed plastics — represent an alternative lightweight aggregate for use in construction. Although the presence of trace contaminants in fly ash is an obstacle to its use, previous studies have shown that encapsulation of fly ash in plastic can mitigate toxin leaching. This paper presents a study on the reduction in leachable arsenic, lead, and selenium from coal fly ash incorporated into these aggregates. For the arsenic leaching study, two fly ashes were tested: a high-carbon Raw ash and low-carbon Processed ash. Aggregates were created with ash-to-plastic ratios of 0:100, 20:80, 50:50, and 80:20. The ashes and aggregates were subjected to leaching at various pHs. Arsenic levels were measured using graphite furnace atomic absorption. For the lead and selenium leaching study, Processed ash was utilized in the creation of 80:20 aggregates. Lead and selenium levels in the leachate were measured using an inductively coupled plasma spectrometer. Results demonstrated a reduction in leaching for all three compounds. The observed reductions were significant, with up to 96.69% reduction achieved for arsenic, 96.94% for selenium, and 80.58% for lead. It can be concluded that utilization of fly ash in SLAs provides a beneficial ash reuse strategy.