Mercury emission into atmosphere

Mercury emission from electric utilities is the largest uncontrolled source of mercury release into the atmosphere, and globally it accounts for up to 59% of the total annual atmospheric loading of mercury from both natural and anthropogenic sources. Coal-fired power plants are now considered the greatest source of environmental mercury in the U.S., and the only significant source that continues... 

The mercury burden of the environment derives predominantly from natural sources [3]. Input into the atmosphere occurs by degassing of the earth s crust and emissions from volcanoes and by soil erosion into the surface waters. Mining is not the only anthropogenic source for mercury. The ubiquitous occurrence of traces of mercury in the whole earth s crust leads via the combustion of fossil fuel, the smelting of iron and other metals, as well as the production of cement to the release of large quantities of mercury vapor into the atmosphere and in this way increases the total amount of mercury in the ecosphere [4,5]. 

Hazardous waste burning incinerators, cement kilns, and LWAKs do not follow a tiered approach to regulate the release of toxic metals into the atmosphere. The MACT rule finalized numerical emission standards for three categories of metals mercury, low-volatile metals (arsenic, beryllium, and chromium), and semivolatile metals (lead and cadmium). Units must meet emission standards for the amount of metals emitted. For example, a new cement kiln must meet an emission limit of 120pg/m3 of mercury, 54pg/m3 of low-volatile metals, and 180 pg/m3 of semivolatile metals. 

Cadmium (Cd) anode cells are at present manufactured based on nickel-cadmium, silver-cadmium, and mercury-cadmium couples. Thus wastewater streams from cadmium-based battery industries carry toxic metals cadmium, nickel, silver, and mercury, of which Cd is regarded the most hazardous. It is estimated that globally, manufacturing activities add about 3-10 times more Cd to the atmosphere than from natural resources such as forest fire and volcanic emissions. As a matter of fact, some studies have shown that NiCd batteries contribute almost 80% of cadmium to the environment,4,23 while the atmosphere is contaminated when cadmium is smelted and released as vapor into the atmosphere4 Consequently, terrestrial, aquatic, and atmospheric environments become contaminated with cadmium and remain reservoirs for human cadmium poisoning. 

Of all the metals in the periodic table, mercury, Hg (atomic number 80), is the only one to exist as a liquid at ambient temperatures. Mercury is also volatile, which means that uncontained mercury atoms evaporate into the atmosphere. Today, the atmosphere carries a load of about 5000 tons of mercury. Of this amount, about 2900 tons are from current human activities, such as the burning of coal, and 2100 tons appear to be from natural sources, such as outgassing from Earth s crust and oceans. Since the mid-igth century, however, humans have emitted an estimated 200,000 tons of mercury into the atmosphere, most of which has since subsided onto the land and sea. It is probable, therefore, that a large portion of the mercury emitted from "natural" sources is actually the re-emission of mercury originally put there by humans over the last 150 years. 

The natural global bio-geochemical cycling of mercury is characterized by degassing of the element from soils and surface waters, followed by atmospheric transport, deposition of mercury back to land and surface waters, and sorption of the compound to soil or sediment particulates. Mercury deposited on land and open water is in part revolatilized back into the atmosphere. This emission, deposition, and revolatilization creates difficulties in tracing the movement of mercury to its sources (WHO 1990). Particulate-bound mercury can be converted to insoluble mercury sulfide and precipitated or bioconverted into more volatile or soluble forms that re-enter the atmosphere or are bioaccumulated in aquatic and terrestrial food chains (EPA 1984b). 

Waste disposal and mining activities are characteristic point sources for environmental pollutants in air, vater, and soil (Table 9.3). Waste incineration typically releases more volatile metals such as mercury, cadmium and lead into the atmosphere emission control, therefore, is not only crucial for smelting activities, but also the decisive prerequisite for all technologies involving higher temperature and vaste materials. Landfill leachates are enriched... 

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