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Lignite (derived from Latin lignum meaning 'wood') often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal 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 for lignite produces less heat for the amount of carbon dioxide and sulfur released than other ranks of coal. As a result lignite is the most harmful coal to human health. Depending on the source, various toxic heavy metals, including naturally occurring radioactive materials, may be present in lignite which are left over in the coal fly ash produced from its combustion, further increasing health risks. 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 percent and its ash content ranges from 6–19 percent, compared with 6–12 percent for bituminous coal. 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) on a moist, mineral-matter-free basis. The energy content of lignite consumed in the United States averages 15 MJ/kg (13 million BTU/ton), on the as-received basis. The energy content of lignite consumed in Victoria, Australia, averages 8.6 MJ/kg (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 can cause problems in transportation and storage.

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Lignite

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 is typically hard but friable. Its quality is ranked higher than lignite and sub-bituminous coal, but lesser than anthracite. It is the most abundant rank of coal, with deposits found around the world, often in rocks of Carboniferous age.

Greenhouse gas emissions

Greenhouse gas emissions (abbreviated as GHG emissions) from human activities strengthen the greenhouse effect, contributing to climate change. Carbon dioxide (), from burning fossil fuels such as coal, oil, and natural gas, is one of the most important factors in causing climate change. The largest emitters are China followed by the US, although the United States has higher emissions per capita. The main producers fueling the emissions globally are large oil and gas companies.

Utilisation de composés carbonés afin de diminuer la concentration de cadmium dans des végétaux comestibles de Nouvelle-Zélande

Guilhem Chanson

Cadmium (Cd) is a non‐essential trace element which is toxic at high concentrations. Cd is added to New Zealand soils through superphosphate fertilizer. The Cd is then absorbed by vegetables and may exceed the limit of 0.1 mg/kg value, thus leading to economic and health risks. Previous studies have shown that lignite can significantly reduce the absorption of Cd by pasture, and that this effect is dependent on soil type. In addition, other studies have shown that compost can reduce the absorption of some metals. The effects of these amendments were tested on Cd uptake by vegetables, as they are more sensitive to the toxic effects of Cd than pasture grass. We studied the absorption of Cd in vegetables grown in two New Zealand soils with and without Cd spiking. We also studied the effect of an amendment with compost and two amendments with lignite. The results show that the amendment with compost reduced the absorption of Cd in all plants studied. The decrease of the absorbed concentration was up to 60% in some cases. Amendments with lignite showed significant decreases and one significant increase in the concentration of Cd in vegetables. The decreases of Cd observed in the various amendments were not typically related to the extractable Cd concentration or to the soil pH. Finally, we observed no clear pattern concerning the absorption of other elements. Because of the highly variable composition of compost, a comprehensive study with different types of compost is recommended to better understand the effects of compost on Cd uptake by vegetables. In addition, a study on the persistence of compost into the soil should also be performed.

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