Yong Wei,Guijian Liu,Biao Fu,Ruwei Wang,Yuan Liu,Xuan Xue,Mei Sun
Inhalable fine particulate matter (PM), which is rich in Pb and other pollutants from coal-fired power plants, can cause air pollution and severe health problems. To facilitate the development of efficient techniques for controlling fine particulate Pb emissions, in this study, various types of size-resolved fine PM (<10.0 μm) were collected from the outlets of fabric filter units (FFs) at an industrial circulating fluidized bed (CFB) power plant to assess the distribution and partitioning behavior of Pb. The results showed that the mass particle size distribution (PSD) of the collected fine PM followed unimodal distribution, peaking at 5.8–4.7 μm, which might be caused by the fragmentation of limestone additives and new-formed CaSO 4 . However, the mass PSD of Pb for size-fractionated PM displayed different distribution pattern. Two peaks were observed in the size ranges of 5.8–4.7 μm and 1.1–0.7 μm. The mechanism of Pb enrichment in the supermicron particles was mainly controlled by the surface adsorption reaction, which could be explained by 1/d p dependence and be improved using excess active CaO produced by the injected limestone. For submicron particles, gas-film transfer or heterogenous condensation (mass transfer) might represent the deposition mechanism . Besides Pb enrichment, it was found that the submicron particles (<0.7 μm) mainly consisted of Si-rich and Si–Al phases. The emission of those fine SiO 2 -bearing particles should be limited as they can be inhaled and can damage the respiratory system.
Recent studies suggest that pelagic sediments can enrich rare-earth elements (REE) acting as a significant reservoir for the global REE budget as well as a potential resource for future exploitation. Although Ca-phosphate (e.g., bioapatite fossils) and Fe-Mn (oxyhydr)oxides (e.g., micronodule) have been considered important REE carriers in deep-sea sediments, the proportion of REE held by each mineral phase remains enigmatic. Here, we have investigated the sediments from two promising REE-rich prospective areas: the Tiki Basin in the Southeast Pacific (TKB) and the Central Indian Ocean Basin (CIOB). The mineral grains including bioapatite fossils and Fe-Mn micronodules have been inspected individually by in-situ microscale analytical methods. Correspondently, the REE bound to Ca-phosphate and Fe-Mn (oxyhydr)oxides have been sequentially extracted and quantified. The crucial role of Ca-phosphate is substantiated by sequential leaching which reveals its dominance in hosting ~69.3–89.4% of total REE. The Fe-Mn (oxyhydr)oxides carry ~8.2% to 22.0% of REE in bulk sediments, but they account for ~70.0–80.5% of Ce owing to their preferential adsorption of Ce over the other REE. Surface sediment on modern seafloor can accumulate high REE contents resulting from the REE scavenging by the host phases within the range of sediment-seawater interface. Differences between TKB and CIOB samples indicate that the REE enrichment in the deep-sea environment may be controlled by multiple factors including the productivity of overlying seawater (e.g., phosphorus flux), water depth relative to carbonate compensation depth (CCD), sedimentation rate, redox condition, and hydrothermal vent input (e.g., Fe-Mn precipitations).
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