New Insight into Atmospheric Mercury Emissions from Zinc Smelters Using Mass Flow Analysis

Abstract

1The mercury (Hg) flow paths from three zinc (Zn) smelters indicated that a large quantity of 2Hg, approximately 38.0 -57.0% of the total Hg input, was stored as acid slag in the landfill sites. 3Approximately 15.0 -27.1% of the Hg input was emitted into water or stored as open-dumped 4 slags, and 3.3 -14.5% of the Hg input ended in the sulfuric acid. Atmospheric Hg emissions, 5 accounting for 1.4 -9.6% of the total Hg input, were from both the Zn production and waste 6 disposal processes. Atmospheric Hg emissions from the waste disposal processes accounted for 7 40.6%, 89.6% and 94.6% of the total atmospheric Hg emissions of the three studied smelters, 8 respectively. Zn production process mainly contributed to oxidized Hg (Hg 2+ ) emissions, 9whereas waste disposal process generated mostly elemental Hg (Hg 0 ) emissions. When 10 considering the emissions from these two processes together, the emission proportion of the Hg 2+ 11 mass was 51%, 46%, and 29% in smelters A, B and C, respectively. These results indicated that 12 approximately 10.8 ± 5.8 t of atmospheric Hg emissions from the waste disposal process was 13 ignored in recent inventories. Therefore, the total atmospheric Hg emissions from China's Zn 14 industry should be approximately 50 t. 15

Mercury transformation and speciation in flue gases from anthropogenic emission sources: a critical review

“…Usually, mercury is released from concentrates to flue gases during the pyrometallurgical processes of non-ferrous metals. A typical pyrometallurgical process requires four stages, including dehydration, smelting and/or roasting, extraction, and refining (Wang et al, 2010b;Zhang et al, 2012b;Wu et al, 2015). Approximately 1 % of mercury in concentrates is released to flue gas in the dehydration kiln, where the temperature varies from 150 to 700 • C (Song, 2010).…”

“…Almost all mercury compounds are thermally dissociated into Hg 0 considering the thermodynamic stability of Hg 0 at this temperature (Wang, 2011). Mercury release rates during these stages are generally over 98 % (Song, 2010;Li et al, 2010;Wu et al, 2015). The case in the industrial gold smelting process is an exception.…”

“…To minimize heavy metal emissions, the roasting and/or smelting flue gas could also require additional mercury removal after the purification system (UNECE, 2013). Since the roasting and/or smelting stage releases the most mercury, previous studies focus on mercury transformation and removal inside APCDs for the roasting/smelting flue gas (Zhang et al, 2012b;Wu et al, 2015). Figure 3 shows the mercury speciation after APCDs for non-ferrous metal smelters.…”

“…Hg p proportion after dust collectors is less than 5 % (Zhang et al, 2012b;Wu et al, 2015). Hg 0 can be homogeneously or heterogeneously oxidized in the flue gas, while the charging anode in the ESP can reduce Hg 2+ to Hg 0 .…”

“…Therefore, the resulting mercury speciation profile after the dust collectors depends on the competition between Hg 2+ reduction and Hg 0 oxidation. The proportion of Hg 2+ after dust collectors varies a lot (4-85 %) among different tested smelters (Zhang et al, 2012b;Wu et al, 2015). The total mercury removal efficiency of dust collectors is usually less than 20 %.…”