What is mercury used for?
Mercury is used as a metal and compound for numerous industrial and household-related applications, such as the following (for liquid mercury): electrodes in chlorine-alkali equipment; electrical switches; thermometers; barometers; manometers. Liquid mercury is also used in fluorescent light bulbs (elemental mercury adsorbed at the fluorescent powder) and amalgam, nearly half of which is composed of mercury.
In many countries, elemental mercury is used for small scale gold mining operations. Mercury compounds are used for applications such as the following: chemical-industry catalysts; button cells; paint pigments; seed dressers; medical-product preservatives. These applications occasion a correspondingly large variety of waste.
Many industrial processes such as coal combustion, natural-gas scrubbing, and metallurgy generate mercury that needs to be discharged and disposed of.
Waste containing mercury
Depending on its origin, waste containing mercury falls into various European Waste List classification and is in all cases classified as hazardous waste.
The following main factors need to be taken into account when it comes to disposing of waste containing mercury:
• The volatility of elemental mercury and certain compounds thereof
• Amalgam formation in conjunction with numerous metals
• The low solubility of most mercury compounds
• The possibility of microbial formation in methyl mercury.
The technical guidelines for the environmentally sound management of wastes consisting of elemental mercury and wastes containing or contaminated with mercury, which were adopted by the Tenth Meeting of the Conference of the Parties to the Basel Convention, set forth the environmentally sound disposal methods for waste containing mercury. The following non-preliminary methods are mentioned in this document:
• R4 Recycling/reclamation of metals and metal compounds
• R5 Recovery of other inorganic substances
• R8 Recovery of components from catalysts
• D5 Specially engineered landfill
• D9 Physicochemical treatment
• D12 Permanent storage (e.g. emplacement of containers in a mine and so on)
Disposal of waste containing mercury
Waste containing mercury needs to be permanently removed from the biosphere in a suitable manner and stored in suitable containers. In Germany, the optimal conditions for such storage are found in underground facilities. Only small amounts of waste containing mercury may be stored above ground, insofar as such waste complies with the limit values set forth in Annex 3 of the Landfill Oridiance (Deponieverordnung) regulation. The limit values for mercury, which vary according to parameters such as storage facility class, are derived from standardized batch extraction tests of mercury dissolved in water.
It is oftentimes useful to apply a treatment method involving thermally extracting mercury from other wastes. The metallic mercury thus captured is then used for an authorized application or is disposed of separately.
A UBA study titled "Behaviour of mercury compounds at the underground disposal in salt formations and their portential mobilisation by saline solutions" investigated long term underground storage of metallic mercury and of metallic mercury chemically converted to mercury sulfide. Stabilizing mercury as mercury sulfide is now a viable method in Germany for large scale use. In weighing the pros and cons of permanently storing liquid metallic mercury versus storing it as a solid (mercury sulfide), integrated criteria need to be applied.