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Lignite, often referred to as brown coal, is a soft, brown,
combustible A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...
,
sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
formed from naturally compressed
peat Peat (), also known as turf (), is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. The peatland ecosystem covers and ...
. It has a
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
content around 25–35%, and is considered the lowest rank of
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...
due to its relatively low heat content. When removed from the ground, it contains a very high amount of moisture which partially explains its low carbon content. Lignite is mined all around the world and is used almost exclusively as a fuel for steam-electric power generation. The combustion of lignite produces less heat for the amount of carbon dioxide and sulfur released than other ranks of coal. As a result, environmental advocates have characterized lignite as the most harmful coal to human health. Depending on the source, various
toxic heavy metal A toxic heavy metal is any relatively dense metal or metalloid that is noted for its potential toxicity, especially in environmental contexts. The term has particular application to cadmium, mercury and lead, all of which appear in the World ...
s, including naturally occurring radioactive materials may be present in lignite which are left over in the
coal fly ash Fly ash, flue ash, coal ash, or pulverised fuel ash (in the UK) plurale tantum: coal combustion residuals (CCRs)is a coal combustion product that is composed of the particulates (fine particles of burned fuel) that are driven out of coal-fired b ...
produced from its combustion, further increasing health risks.


Characteristics

Lignite is brownish-black in color and has a carbon content of 60–70 percent on a dry ash-free basis. However, its inherent moisture content is sometimes as high as 75 percentKopp, Otto C
"Lignite"
in ''Encyclopædia Britannica''
and its
ash Ash or ashes are the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non-gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash ...
content ranges from 6–19 percent, compared with 6–12 percent for
bituminous coal Bituminous coal, or black coal, is a type of coal containing a tar-like substance called bitumen or asphalt. Its coloration can be black or sometimes dark brown; often there are well-defined bands of bright and dull material within the seams. It ...
. As a result, its carbon content on the as-received basis (i.e., containing both inherent moisture and mineral matter) is typically just 25-35 percent. The energy content of lignite ranges from 10 to 20 MJ/kg (9–17 million BTU per
short ton The short ton (symbol tn) is a measurement unit equal to . It is commonly used in the United States, where it is known simply as a ton, although the term is ambiguous, the single word being variously used for short, long, and metric ton. The var ...
) on a moist, mineral-matter-free basis. The energy content of lignite consumed in the United States averages (13 million BTU/ton), on the as-received basis. The energy content of lignite consumed in Victoria, Australia, averages (8.2 million BTU/ton) on a net wet basis. Lignite has a high content of volatile matter which makes it easier to convert into gas and liquid petroleum products than higher-ranking coals. Unfortunately, its high moisture content and susceptibility to
spontaneous combustion Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self heating which rapidly accelerates to high te ...
can cause problems in transportation and storage. Processes which remove water from brown coal reduce the risk of spontaneous combustion to the same level as black coal, increase the calorific value of brown coal to a black coal equivalent fuel, and significantly reduce the emissions profile of 'densified' brown coal to a level similar to or better than most black coals. However, removing the moisture increases the cost of the final lignite fuel. Lignite rapidly degrades when exposed to air. This process is called ''slacking'' or ''slackening''.


Uses

Most lignite is used to generate electricity. However, small amounts are used in agriculture, in industry, and even, as ''jet'', in jewelry. Its historical use as fuel for home heating has continuously declined and is now of lower importance than its use to generate electricity.


As fuel

Lignite is often found in thick beds located near the surface, making it inexpensive to mine. However, because of its low
energy density In physics, energy density is the amount of energy stored in a given system or region of space per unit volume. It is sometimes confused with energy per unit mass which is properly called specific energy or . Often only the ''useful'' or extrac ...
, tendency to crumble, and typically high moisture content, brown coal is inefficient to transport and is not traded extensively on the world market compared with higher coal grades. It is often burned in power stations near the mines, such as in Australia's
Latrobe Valley The Latrobe Valley is an inland geographical district and urban area of the Gippsland region in the state of Victoria, Australia. The traditional owners are the Brayakaulung of the Gunai nation. The district lies east of Melbourne and nes ...
and Luminant's Monticello plant in Texas. Primarily because of latent high moisture content and low energy density of brown coal,
carbon dioxide emissions Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China an ...
from traditional brown-coal-fired plants are generally much higher per
megawatt-hour A kilowatt-hour (unit symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy: one kilowatt of power for one hour. In terms of SI derived units with special names, it equals 3.6 megajoules (MJ). Kilowatt-hours are a common b ...
generated than for comparable black-coal plants, with the world's highest-emitting plant being Australia's
Hazelwood Power Station The Hazelwood Power Station is a decommissioned brown coal-fuelled thermal power station located in the Latrobe Valley of Victoria, Australia. Built between 1964 and 1971, the 1,600-megawatt-capacity power station was made up of eight 200MW uni ...
until its closure in March 2017. The operation of traditional brown-coal plants, particularly in combination with strip mining, is politically contentious due to environmental concerns. The
German Democratic Republic German(s) may refer to: * Germany (of or related to) ** Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **G ...
relied extensively on lignite to become energy self-sufficient, and eventually obtained 70% of its energy requirements from lignite. Lignite was also an important chemical industry feedstock via
Bergius process The Bergius process is a method of production of liquid hydrocarbons for use as synthetic fuel by hydrogenation of high-volatile bituminous coal at high temperature and pressure. It was first developed by Friedrich Bergius in 1913. In 1931 Bergius ...
or Fischer-Tropsch synthesis in lieu of petroleum, which had to be imported for hard currency following a change in policy by the
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...
in the 1970s, which had previously delivered petroleum at below market rates. East German scientists even converted lignite into coke suitable for metallurgical uses (
high temperature lignite coke High temperature lignite coke (BHT coke) is a carbon-rich fuel that is produced from lignite by exposure to heat in the absence of oxygen ('' pyrolysis''). History Because East German industry urgently needed coke after the Second World War ...
) and much of the railway network was dependent on lignite either through steam trains or electrified lines mostly fed with lignite derived power. As per the table below, East Germany was the largest producer of lignite for much of its existence as an independent state. In 2014, about 12 percent of Germany's energy and, specifically, 27 percent of Germany's electricity came from lignite power plants, while in 2014 in
Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders wi ...
, lignite provided about 50 percent of its power needs. Germany has announced plans to phase out lignite by 2038 at the latest. Greece has confirmed that the last coal plant will be shut in 2025 after receiving pressure from the
European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are located primarily in Europe, Europe. The union has a total area of ...
and plans to heavily invest in
renewable energy Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
.


Home heating

Lignite was and is used as a replacement for or in combination with
firewood Firewood is any wooden material that is gathered and used for fuel. Generally, firewood is not highly processed and is in some sort of recognizable log or branch form, compared to other forms of wood fuel like pellets or chips. Firewood ca ...
for home heating. It is usually pressed into briquettes for that use. Due to the smell it gives off when burned, lignite was often seen as a fuel for poor people compared to higher value hard coals. In Germany briquettes are still readily available to end consumers in home improvement stores like Obi,
Bauhaus The Staatliches Bauhaus (), commonly known as the Bauhaus (), was a German art school operational from 1919 to 1933 that combined crafts and the fine arts.Oxford Dictionary of Art and Artists (Oxford: Oxford University Press, 4th edn., 20 ...
, or Hornbach but also at supermarkets like Rewe.


In agriculture

An environmentally beneficial use of lignite is in agriculture. Lignite may have value as an environmentally benign
soil amendment A soil conditioner is a product which is added to soil to improve the soil’s physical qualities, usually its fertility (ability to provide nutrition for plants) and sometimes its mechanics. In general usage, the term "soil conditioner" is often ...
, improving cation exchange and phosphorus availability in soils while reducing availability of heavy metals, and may be superior to commercial K humates. Lignite fly ash produced by combustion of lignite in power plants may also be valuable as a soil amendment and fertilizer. However, rigorous studies of the long-term benefits of lignite products in agriculture are lacking. Lignite may also be used for the cultivation and distribution of
biological control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also i ...
microbes that suppress plant pests. The carbon increases the organic matter in the soil while the biological control microbes provide an alternative to chemical pesticides. '' Leonardite'' is a soil conditioner rich in
humic acid Humic substances (HS) are organic compounds that are important components of humus, the major organic fraction of soil, peat, and coal (and also a constituent of many upland streams, dystrophic lakes, and ocean water). For a long era in the 19th an ...
s that is formed by natural oxidation of lignite near the surface of the Earth.


In drilling mud

Reaction with quaternary amine forms a product called amine-treated lignite (ATL), which is used in
drilling mud In geotechnical engineering, drilling fluid, also called drilling mud, is used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are als ...
to reduce fluid loss during drilling.


As an industrial adsorbent

Lignite may have potential uses as an industrial adsorbent. Experiments show that its adsorption of
methylene blue Methylthioninium chloride, commonly called methylene blue, is a salt used as a dye and as a medication. Methylene blue is a thiazine dye. As a medication, it is mainly used to treat methemoglobinemia by converting the ferric iron in hemoglobin ...
falls within the range of
activated carbon Activated carbon, also called activated charcoal, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed (activated) to have small, low-volume pores that increase the surface area availa ...
s currently used by industry.


In jewelry

Jet is a form of lignite that has been used as a gemstone. The earliest jet artifacts date to 10,000 BCE and jet was used extensively in necklaces and other ornamentation in Britain from the
Neolithic The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several pa ...
until the end of
Roman Britain Roman Britain was the period in classical antiquity when large parts of the island of Great Britain were under occupation by the Roman Empire. The occupation lasted from AD 43 to AD 410. During that time, the territory conquered wa ...
. Jet experienced a brief revival in Victorian Britain.


Geology

Lignite begins as an accumulation of partially decayed plant material, or peat. Peat accumulates most readily in areas where there is ample moisture, slow subsidence of the land surface, and lack of disturbance by rivers or oceans. Peat swamps are otherwise found in a wide variety of climates and geographical settings. Under these conditions, the area remains saturated with water, which covers dead plant material and protects it from degradation by atmospheric oxygen. Anaerobic bacteria may continue to degrade the peat, but this process is slow, particularly in acid water. Once the peat is buried by other sediments, biological degradation essentially comes to a halt, and further changes are a result of increased temperature and pressure from burial. Lignite forms from peat that has not experienced deep burial and heating. It forms at temperatures below , primarily by biochemical degradation. This includes humification, in which microorganisms extract hydrocarbons from the peat and humic acids are formed. The humic acids make the environment more acidic, which slows the rate of further bacterial decay. Humification is still incomplete in lignite, coming to completion only when the coal reaches sub-bituminous rank. The most characteristic chemical change in the organic material during formation of lignite is the sharp reduction in the number of C=O and C-O-R functional groups. Lignite deposits are typically younger than higher-ranked coals, with the majority of them having formed during the
Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...
period.


Extraction

Lignite is often found in thick beds located near the surface. These are inexpensive to extract using various forms of
surface mining Surface mining, including strip mining, open-pit mining and mountaintop removal mining, is a broad category of mining in which soil and rock overlying the mineral deposit (the overburden) are removed, in contrast to underground mining, in whic ...
, though this can result in serious environmental damage. Regulations in the United States and other countries require that land that is surface mined must be restored to its original productivity once mining is complete. Strip mining of lignite in the United States begins with
drilling Drilling is a cutting process where a drill bit is spun to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary cutting tool, often multi-point. The bit is pressed against the work-piece and rotated at ...
to establish the extent of the subsurface beds.
Topsoil Topsoil is the upper layer of soil. It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs. Description Topsoil is composed of mineral particles and organic matt ...
and
subsoil Subsoil is the layer of soil under the topsoil on the surface of the ground. Like topsoil, it is composed of a variable mixture of small particles such as sand, silt and clay, but with a much lower percentage of organic matter and humus, and ...
must be properly removed and either used to reclaim previously mined-out areas or stored for future reclamation.
Excavator Excavators are heavy construction equipment consisting of a boom, dipper (or stick), bucket and cab on a rotating platform known as the "house". The house sits atop an undercarriage with tracks or wheels. They are a natural progression fr ...
and truck
overburden In mining, overburden (also called waste or spoil) is the material that lies above an area that lends itself to economical exploitation, such as the rock, soil, and ecosystem that lies above a coal seam or ore body. Overburden is distinct from tai ...
removal prepares the area for
dragline A dragline excavator is a piece of heavy equipment used in civil engineering and surface mining. Draglines fall into two broad categories: those that are based on standard, lifting cranes, and the heavy units which have to be built on-site. ...
overburden removal to expose the lignite beds. These are broken up using specially equipped tractors (''coal ripping'') and then loaded into bottom dump trucks using front loaders. Once the lignite is removed, restoration involves grading the mine spoil to as close an approximation as practical of the original ground surface (Approximate Original Contour or AOC). Subsoil and topsoil are restored and the land reseeded with various grasses. In
North Dakota North Dakota () is a U.S. state in the Upper Midwest, named after the indigenous Dakota Sioux. North Dakota is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north and by the U.S. states of Minnesota to the east, ...
, a
performance bond A performance bond, also known as a contract bond, is a surety bond issued by an insurance company or a bank to guarantee satisfactory completion of a project by a contractor. The term is also used to denote a collateral deposit of good faith mo ...
is held against the mining company for at least ten years after the end of mining operations to guarantee that the land has been restored to full productivity. A bond (not necessary in this form) for mine reclamation is required in the US by the Surface Mining Control and Reclamation Act of 1977.


Resources and Reserves


List of countries by lignite reserves


Australia

The
Latrobe Valley The Latrobe Valley is an inland geographical district and urban area of the Gippsland region in the state of Victoria, Australia. The traditional owners are the Brayakaulung of the Gunai nation. The district lies east of Melbourne and nes ...
in Victoria,
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
, contains estimated reserves of some 65 billion tonnes of brown coal.Department of Primary Industries, Victorian Government, Australia, ‘Victoria Australia: A Principle Brown Coal Province’ (Fact Sheet, Department of Primary Industries, July 2010). The deposit is equivalent to 25 percent of known world reserves. The coal seams are up to 98 metres thick, with multiple coal seams often giving virtually continuous brown coal thickness of up to 230 metres. Seams are covered by very little
overburden In mining, overburden (also called waste or spoil) is the material that lies above an area that lends itself to economical exploitation, such as the rock, soil, and ecosystem that lies above a coal seam or ore body. Overburden is distinct from tai ...
(10 to 20 metres). A partnership led by
Kawasaki Heavy Industries (or simply Kawasaki) is a Japanese Public company, public multinational corporation manufacturer of motorcycles, engines, Heavy equipment (construction), heavy equipment, aerospace and Military, defense equipment, rolling stock and ships, headq ...
and backed by the governments of Japan and Australia has begun extracting hydrogen from brown coal. The liquefied hydrogen will be shipped via the transporter ''
Suiso Frontier The is the world's first liquid hydrogen carrier ship. Design and construction The ''Suiso Frontier'' was built by Kawasaki Heavy Industries, following support by the governments of Japan and Australia. The ship carries liquid hydrogen, the ...
'' to Japan.


North America

The largest lignite deposits in North America are the
Gulf Coast The Gulf Coast of the United States, also known as the Gulf South, is the coast, coastline along the Southern United States where they meet the Gulf of Mexico. The list of U.S. states and territories by coastline, coastal states that have a shor ...
lignites and the Fort Union lignite field. The Gulf Coast lignites are located in a band running from
Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
to
Alabama (We dare defend our rights) , anthem = " Alabama" , image_map = Alabama in United States.svg , seat = Montgomery , LargestCity = Huntsville , LargestCounty = Baldwin County , LargestMetro = Greater Birmingham , area_total_km2 = 135,7 ...
roughly parallel to the Gulf Coast. The Fort Union lignite field stretches from
North Dakota North Dakota () is a U.S. state in the Upper Midwest, named after the indigenous Dakota Sioux. North Dakota is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north and by the U.S. states of Minnesota to the east, ...
to
Saskatchewan Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...
. Both are important commercial sources of lignite.


Types

Lignite can be separated into two types. The first is xyloid lignite or fossil wood and the second form is the compact lignite or perfect lignite. Although xyloid lignite may sometimes have the tenacity and the appearance of ordinary wood, it can be seen that the combustible woody tissue has experienced a great modification. It is reducible to a fine powder by
trituration Trituration (Latin, ''grinding'') is the name of several different methods used to process materials. In one sense, it is a form of comminution (reducing the particle size of a substance). In another sense, it is the production of a homogeneous pow ...
, and if submitted to the action of a weak solution of
potash Potash () includes various mined and manufactured salts that contain potassium in water- soluble form.
, it yields a considerable quantity of
humic acid Humic substances (HS) are organic compounds that are important components of humus, the major organic fraction of soil, peat, and coal (and also a constituent of many upland streams, dystrophic lakes, and ocean water). For a long era in the 19th an ...
. Leonardite is an oxidized form of lignite, which also contains high levels of humic acid. Jet is a hardened, gem-like form of lignite used in various types of jewelry.


Production

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwee ...
is the largest producer of lignite, followed by
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
,
Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...
, and
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
. Lignite accounted for 8% of all U.S. coal production in 2019.


Gallery

File:Braunkohletagebau Schleenhain.jpg, Open-pit
United Schleenhain coal mine The United Schleenhain Coal Mine is a coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, o ...
in
Saxony, Germany Saxony (german: Sachsen ; Upper Saxon: ''Saggsn''; hsb, Sakska), officially the Free State of Saxony (german: Freistaat Sachsen, links=no ; Upper Saxon: ''Freischdaad Saggsn''; hsb, Swobodny stat Sakska, links=no), is a landlocked state of ...


See also

*
Rheinisches Braunkohlerevier The Rheinisches Braunkohlerevier, often called the Rhenish mining area, is a lignite mining area or district in the Cologne Bay, on the northwestern edge of the Rhenish Slate Mountains. The mining of lignite using the Open-pit mining, open pit me ...
*
NLC India Limited NLC India Limited (NLC) (formerly Neyveli Lignite Corporation Limited) is a central public sector undertaking under the administrative control of the Ministry of Coal, Government of India. It annually produces about 30 million tonnes of Lig ...
* * * * * * * *


References


External links

*
Geography in action – an Irish case study
{{Authority control Coal Organic minerals