80 Hg 200.59

Hg - Mercury

See metal norms for Mercury

Chemical Element Mercury Melting Point °C -39
Chemical Symbol Hg Boiling Point °C 357
Atomic Number 80 Density g/cm3 13.5
Atomic Weight 200.59 Oxide HgO

Properties

Mercury, along with bromine, is one of only two elements that are liquid at room temperature and pressure. It is an extremely heavy, silvery metal belonging to Group 12 of the Periodic Table, and is the 68th most abundant element within the Earth’s crust. Mercury is a fairly good conductor of electricity, but unlike most metals, is a poor conductor of heat. It is stable in air and with water, and is unreactive towards acids, except concentrated HNO3, and alkalis. Mercury freezes at -38.9°C and boils at 357°C, meaning that it is liquid over a very important range of temperature, giving it useful applications in homes and in scientific laboratories. Mercury, when touched, is toxic and is therefore slowly being replaced wherever appropriate.

History

Production peaked at about 7000 mt per year in 1987, since when many mines have closed, resulting in primary production falling in the early 2000’s to only approx 1500 mt per year.  Consumption also fell, but only to around 3,500 mt per year, with the shortfall being obtained from the recovery of secondary mercury from many of its uses and from stockpiles. Mercury can come from waste recycling (e.g. fluorescent lamps, batteries), natural gas cleaning or the industrial treatment of non-ferrous metals.

Uses

Mercury is highly toxic, its use in products and particularly from the burning of fossil fuels, is harmful to the environment.  The UN, with strong support from the EU and USA, are working towards curbing mercury emissions, with the result that new mining is continuing to reduce and, as substitutes for its many uses are developed, existing supplies of mostly secondary mercury will be securely land filled back into the earth’s crust.

The export of mercury and mercury compounds from the EU was prohibited with effect from 15 March 2011. In addition to metallic mercury, the export ban also covers other mercury compounds, as for example cinnabar ore, mercury chloride and mercury oxide. Compounds for research and development, medical or analytical analysis purposes are not covered by the prohibition.
The regulation introduces the obligation to store mercury waste either in salt mines, in deep, underground, hard rock formations, or in above-ground facilities “in a way that is safe for human health and the environment” before eventually being disposed of.

It is used above all in the chlor-alkali industry, which has undertaken to convert to techniques that are less dangerous to health and the environment; the old methods produce large quantities of highly toxic calomel (mercurous chloride).

Mercury is highly toxic to humans, especially when transformed into methylmercury. It is also bio-accumulative, meaning that it concentrates in the food chain. Numerous scientific studies blame it for cardiovascular and immune-system ailments. It can affect the brain development of unborn children, even in minimal doses.

Mercury use is declining both in the EU and globally.  Across the world, the main uses of mercury are in small-scale gold mining, the chlor-alkali industry and production of vinyl-chloride monomer, the basis of PVC plastic. In the EU only the chlor-alkali industry remains a significant user, and it is progressively phasing out the use of mercury-containing cells in its production of chlorine.

References
  • Emsley, John. Nature’s Building Blocks, An A-Z Guide to the Elements, New Edition, Oxford University Press, 2011
  • Gray, Theodore. The Elements, A Visual Exploration of Every Known Atom in the Universe, Black Dog & Leventhal Publishers, Inc, NY, 2009
  • Stwertka, Albert. A Guide to the Elements, 3rd Edition, Oxford University Press, 2012

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