Measurements, factor analysis and modeling of element leaching from incineration bottom ashes for quantitative component effects

Abstract

Long-term incineration bottom ash (IBA) samples from two wastes-to-energy incineration plants (plant S and plant T) were subject to batch leaching tests and pH-static leaching tests. Log-transformed leaching concentrations of trace metals were statistically significantly correlated (S: p < 1.8 × 10−122, R2 = 0.55; T: p < 1 × 10−77, R2 = 0.47) with their log-transformed total contents as a whole in batch leaching tests. Statistical analysis of the leaching results was further performed to quantitatively determine the key components in affecting element leaching behaviors under various conditions. Firstly, principle components composed of pH, cationic strength (CS), pH × CS (integrated effects), Na, K, Ca, Fe, Al, inorganic carbon (IC) and dissolved organic carbon (DOC), underwent multivariate factor analysis, accounting for 98.3% and 97.8% variability among IBA samples for pH-static leaching tests from S and T, while accounting for 94.1% and 89.4% variability among IBA samples for batch leaching tests from S and T, respectively. Given the high variabilities (89.4–98.3%) obtained from selected components, they were testified as good geochemical indicators to suggest element leaching potential. Backward stepwise multiple regression model was then constructed with the components, to monitor 12 trace metals (Ag, As, Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sr and Zn) and 11 major elements (Ca, Na, K, Fe, Al, Mg, Mn, Si, Cl−, SO42−, F−). Based on the model, pH-driven geochemistry dominated the leaching behavior in pH-static leaching tests, explaining 36.6–99.2% from S and 51.1–98.8% from T variation amongst all elements investigated. Contrastively, mineral dissolution (by CS, Na and K) (Index = 1.11–1.72) and DOC (Index = 0.83–1.72) demonstrated more influences in batch leaching tests whereas pH (Index = 0–0.83) played a secondary role. On the other end carbonation (based on Ca and IC) was one of the least factors (Index = 0.46–0.69 and 0.56–0.69 among IBA samples for pH-static leaching and batch leaching, respectively) on element leaching from both tests. Based on the study, control of certain components which may highly impact the metal leaching e.g. pH, CS, Na, K, DOC, etc., are crucial during IBA upgrading processes for reduced IBA leaching and thus cleaner production of IBA-based aggregates for environmental-friendly applications.