TEs enrichment characteristic in different size particulate from coal-fired flue gas: Part 1. Enrichment and leachability

The trace elements (TEs) and particulate matter (PM) emissions from coal-fired power plants have received much concern in recent years due to their harm to human health and the environment, however, the TEs enrichment characteristic in PM and their migration and transformation mechanisms with PM are not clear yet, especially in fine particles. In this work, the enrichment contents of seven TEs Cd, Pb, Mo, As, Ni, Mn, Cr in coal combustion byproducts collected from circulating fluidized bed (CFB) and pulverized coal (PC) boiler were studied to investigate the influence of boiler type on TEs enrichment behavior. The aerodynamic cutting method was used to separate the fine particles PM10 and PM2.5 from bulk fly ash to study the impact of particle size on TEs enrichment behavior. In addition, the modified BCR sequent extraction method was applied to study TEs occurrence forms in different size particles to evaluate their environment contamination risk. The results show that except low volatility Mn, all the TEs are mainly enriched in fly ash rather than bottom slag and gypsum. The coal combustion in PC boiler is more complete so bottom slag in PC boiler commonly has less TEs enrichment content than that in CFB boiler. The volatile TEs including Cr, Ni, As, Cd, Pb are most enriched in PM2.5, while the enrichment contents based on fly ash volume fraction of seven TEs are most in PM50 (for CFB boiler) and PM10 (for PC boiler), since PC boiler has more PM10 volume fraction. Even though the TEs occurrence forms in different size particles are various due to the complexity of TEs combination mechanism with fly ash, the soluble F1 fraction overall exhibits size-dependence and is highest in PM2.5. RAC result indicates that As, Cd, Mn, Ni, Cr have medium environment risks, especially when they occur in PM2.5.