TEs enrichment characteristic in different size particulate from coal-fired flue gas: Part 2. Mechanism and correlation analysis

The correlation analysis between TEs enrichment and fly ash physiochemical properties was carried out to explore the TEs formation mechanism in different size fly ashes. The fly ash samples collected from circulating fluidized bed (CFB) and pulverized coal (PC) boilers were separated into PM100, PM50, PM10, and PM2.5 by aerodynamic cutting method, the TEs enrichment contents in different size particles were measured by ICP-MS, the porous structure and chemical components of different size particles were detected by BET and XRF characterization, the unburnt carbon contents in different size particles were analyzed by the improved two-atmosphere thermogravimetry. The porous structure correlation results show that the specific surface area of fly ash is positively related to TEs enrichment, and the high volatility As, Pb, and Cd have bigger specific surface area correlation coefficients. The fly ash pore size is found to have a negative relationship with TEs enrichment. An equilibrium adsorption model deriving from the Lennard-Jones 12-6 function was developed to reveal this negative correlation. It's found that Cr, As, and Pb have higher pore size correlation coefficients because they have higher adsorption equilibrium constants. The unburnt carbon has a negative correlation with TEs because the unburnt carbon content decreases with particle size decrement meanwhile the TEs enrichment content increases with particle size abatement. The fly ash chemical components alumina, iron oxide, and calcium oxide have a positive correlation with TEs enrichment because they can absorb TEs by chemical effect. Based on the DFT calculation of gaseous lead and cadmium adsorption, it confirms that the highest TEs enrichment correlation of alumina is due to the strongest chemical adsorption effect.