Size Distribution of Inorganic Elements in Bottom Ashes from Seven Types of Bio-Fuels across Beijing-Tianjin-Hebei Region, China

摘要

A total of fifty-six bottom ash (BA) samples from the indoor burning of seven bio-fuels (BFs) using a zaotai stove were collected from eight sampling sites across the Beijing-TianjinHebei (BTH) region from April till December in 2016. Each one was divided into six parts as PM+148, PM93–148, PM67–93, PM53–67, PM40–53 and PM–40 using a vibrating screen. The three parts containing the smallest particles, consisting of PM53–67, PM40–53 and PM–40, were selected for analysis of 39 inorganic elements (IEs) using ICP-MS and ICP-OES. The firewood–walnut (WAL) sample had the lowest ash yield as 34.3 ± 3.55 g kg–1; the corresponding values for the 6 crop straws were millet (MIL) sorghum (SOR) sesame (SES) corn (COR) cotton (COT) soybean (SOY). The ash yields, in general, positively correlated with the particle sizes of the BAs for all seven BFs. The top eight elements (TEs), namely Si, Ca, Mg, K, P, Al, Na and Ti, dominated in all BAs regardless of their fluctuation among the BFs, and ?8TEs were well correlated with ?39IEs (R2 = 0.99, p 0.001). The ?39IEs were not correlated with the particle size of the BA due to the significant fluctuation of these TEs. The trace elements, namely Sc, Li, P, V, Cr, Co, Ni, Sb, As, Y, Cs, Bi, Tl, Th, Sn, Cd, La, Ce, Sm, W and U, were negatively well correlated with the particle sizes of the BAs, while the TEs, except for Al, did not display this trend. The heavy metal (HM) profiles were similar between any two sizes of BA for all BFs based on lower values of the coefficient of divergence (CD); with higher CD values, 6 out of 21 pairs of BFs had different HM profiles. All 7 BFs produced higher levels of Zn, Cu, Pb, V, Cr and Ni than other HMs. The content of V in BAs from COR was beyond the limit designated by European countries for BAs used as soil conditioner. The enrichment factors (EFs) of 12 HMs were not correlated with the particle sizes of the BAs, due to the fluctuation of Al, which was used as a reference element among differently sized BAs. The HMs Cu, Zn, Cd and Sn had higher EFs (more than 10), indicating that they were significantly influenced by human activities.