The uses and application fields of mercury

The use of mercury in vapor lamps can be traced back to over 3,000 years ago. The bright red color of cinnabar (natural mercuric sulfide) was used by ancient people as decoration and paint. Cinnabar was regarded as a longevity and health-preserving elixir. Additionally, mercury was also used to extract metals such as gold and silver. With the development of technology, metallic mercury and its compounds have been widely applied in fields such as chemistry, medicine, metallurgy, electrical instruments, military, and other advanced and high-tech sectors. Mercury is mainly used to manufacture scientific measuring instruments (such as barometers, thermometers, etc.), electronic and electrical products, chemical drugs, catalysts, mercury vapor lamps, electrodes, and mercury fulminate. Among the total mercury usage, metallic mercury accounts for approximately 30%, while mercury in compound form accounts for about 70%.

Mercury metal is mainly used as a catalyst in China, accounting for 70% of its total applications. It is followed by scientific measuring instruments at 9%, drugs at 8%, vapor lamps at 5%, electrodes at 3%, mercury fulminate at 2%, and gold panning at 3%. The main application fields and proportions of mercury metal in China are shown in the following figure:

In the chemical industry, mercury is used as an electrode in electrolysis of table salt to produce chlorine gas and soda ash; mercury compounds can be used as catalysts, preservatives, etc.

In the electrical and instrument industries, mercury is used to manufacture mercury salt dry batteries, mercury lamps, barometers, diffusion pumps, mercury switches and many other physical instruments; mercury is also used in thermometers, especially in those measuring high temperatures.
Note: In China (excluding Hong Kong, Macao and Taiwan regions), thermometers still use mercury. China plans to gradually ban the use of mercury thermometers by 2015. Now, alcohol has gradually replaced mercury to make general thermometers.

Mercury used in medicine is employed in the pharmaceutical field as alloys and compounds for dental fillings and disinfectant drugs. Due to its disinfectant, diuretic and analgesic effects, it can also be used as raw materials for treating ulcers and scabies. However, as mercury is a toxic metal, the usage of mercury and its compounds in the pharmaceutical industry has significantly decreased in recent years. Only a few countries still use them.

In the military industry, mercuric fulminate [Hg(ONC)2] is an important initiating agent. Mercuric fulminate is also known as fulminate of mercury and is one of the earliest discovered and utilized initiating explosives. Depending on the method of production, there are two types of crystalline forms: white and gray. Pure mercuric fulminate is a white crystal, but in most cases it appears brownish-yellow and has a density of 4.42 g/cm³. It has low hygroscopicity and is relatively stable at room temperature. It decomposes after heating at 50°C for two hours. It reacts vigorously with metals such as aluminum and magnesium when in the presence of water, and has a slow reaction with zinc and lead. Mercuric fulminate should be avoided from coming into contact with metals such as aluminum, manganese, zinc, and copper. Mercuric fulminate is toxic and its toxicity is similar to that of mercury. It was first used as a fuse cap in 1815 and as a detonator in 1865. The emergence of mercuric fulminate has led to a rapid expansion of the field of explosives. Some substances that were previously unknown to have explosive properties have continued to be discovered and included in the system of explosives. Mercuric fulminate was the first substance used as a specialized initiating agent in firearms and was used in percussion gun barrels in the middle of the 19th century. Due to its unstable nature, it was later replaced by other chemical substances.

In the metallurgical industry, amalgamation method is used to extract gold and thallium is extracted from the smoke dust of lead smelting; mercury amalgamation method (mercury can dissolve other metals to form amalgam) is commonly used in the metallurgical industry to extract metals such as gold, silver and thallium (except iron).

The application of mercury in precision and high-tech fields is constantly emerging, such as in the mold for precision castings, coolant for plutonium atomic reactors, cadmium-based bearing alloys, etc. 

Cosmetics contain mercury-based pesticides and preservatives; gaseous mercury is used in mercury vapor lamps, and gaseous mercury is also used in the manufacture of fluorescent lamps (due to the random disposal of discarded energy-saving lamps causing environmental pollution and subsequently affecting human health, it has gradually been phased out); it is used in the manufacture of liquid mirror telescopes; inorganic mercury compounds can be used as pigments, coatings, etc., and are applied in painting, cosmetics and printing industries, etc.

Note: Thiomersal is widely used in the manufacture of eyebrow tinting creams. In 2008, Minnesota, USA became the first state in the United States to ban the addition of mercury to cosmetics.