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Oil shale ((エストニア語:põlevkivi)) is a strategic energy resource that constitutes about 4% of Estonia's gross domestic product. The oil shale industry in Estonia is one of the most developed in the world.〔IEA (2013), p. 20〕 In 2012, the country's oil shale industry employed 6,500 people – about 1% of the national workforce. Of all the oil shale fired power stations in the world, the two largest are in this country.〔〔 In 2012, 70% of mined oil shale was used for electricity generation, accounting for about 85% of Estonia's total electricity production. A smaller proportion of the mined oil shale is used to produce shale oil, a type of synthetic oil extracted from shale by pyrolysis, which is sufficient to keep Estonia as the second largest shale oil producer in the world after China. In addition, oil shale and its products are used in Estonia for district heating and as a feedstock material for the cement industry. There are two kinds of oil shale in Estonia, both of which are sedimentary rocks laid down during the Ordovician geologic period.〔 〕 Graptolitic argillite is the larger resource, but, because its organic matter content is relatively low, it is not used industrially. The other one is kukersite, which has been mined for almost a hundred years and is expected to last for another 25–30 years. By the end of 2012, the total kukersite resource was 4.8 billion tonnes, of which up to 650 million tonnes was recoverable. Kukersite deposits in Estonia account for 1.1% of global oil shale deposits.〔 In the 18th and 19th centuries, Estonian oil shale was described by several scientists and used as a low-grade fuel. Its use in industry commenced in 1916. Production of shale oil began in 1921 and oil shale was first used to generate electrical power in 1924.〔Ots (2004), pp. 15–16〕 Shortly thereafter, systematic research into oil shale and its products began, and in 1938 a department of mining was established at Tallinn Technical University. After World War II, Estonian oil shale gas was used in Saint Petersburg (then called Leningrad) and in northern cities in Estonia as a substitute for natural gas. Increased need for electricity in the north-west of the Soviet Union led to the construction of large oil shale-fired power stations. Oil shale extraction peaked in 1980. Subsequently, the launch of nuclear reactors in Russia, particularly the Leningrad Nuclear Power Station, reduced demand for electricity produced from oil shale, and, along with a post-Soviet restructuring of the industry in the 1990s, led to a decrease in oil shale mining. After decreasing for two decades, oil shale mining started to increase again at the beginning of the 21st century. The industry continues to have a serious impact on the environment. In 2012, it produced about 70% of Estonia's ordinary waste, 82% of its hazardous waste, and more than 70% of its greenhouse gas emissions. Its activities lower groundwater levels, alter water circulation, and spoil water quality. Water pumped from the mines and used by oil shale-fired power stations exceeds 90% of all water used in Estonia. Leachates from waste heaps pollute surface and groundwater. Former and current oil shale mines cover about one percent of Estonia's territory. ==Resource== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Oil shale in Estonia」の詳細全文を読む スポンサード リンク
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