トリウム 化学特性,用途語,生産方法
歴史
その発見は比較的早く、1828年スウェーデンのベルツェリウスがノルウェー産鉱石中の新元素をスカンジナビア神話の雷神トールThorにちなんで命名した。1898年に至り、ドイツのシュミットG. C. N. Schmidt（1865―1949）とフランスのM・キュリー（ポーランド生まれ）が独立に放射性元素であることをみいだした。［岩本振武］
性質
銀白色の立方晶系．密度11.780 g cm－3(20 ℃)．融点1750 ℃，沸点4790 ℃(α形)．1386 ℃ で体心立方晶．密度11.724 g cm－3(20 ℃)(β形)に転移する．水，アルカリには侵されないが，塩酸に易溶，過塩素酸，硫酸に徐々に溶け，硝酸では不動態となる．トリウムの酸化数2～4，通常の酸化数4で，無色の安定な化合物をつくる．標準電極電位 Th4＋/Th－1.83 V．第一イオン化エネルギー586.5 kJ mol－1(6.08 eV)，ThⅣ(六配位)のイオン半径0.108 nm．ハロゲン，窒素とは高温で反応する．塩化物，臭化物，ヨウ化物，塩素酸塩，臭素酸塩，硫酸塩などは水に可溶，水酸化物，フッ化物，ヨウ素酸塩，リン酸塩，シュウ酸塩などは水に不溶．塩類はチタンやジルコニウムの塩ほど加水分解しやすくはないが，水溶液を温めると容易に加水分解する．多種類の酸イオンと錯化合物をつくりやすく，たとえば，[Th(NO3)6]2－，[Th(SO4)4]2－ などがある．溶接用電極棒，高輝度放電(HID)ランプ電極, 船底塗料などに利用されている．健康衣料·寝具，家庭用温泉器(入浴剤)，医療用枕などに含まれていることがある．トリウムは原子力基本法のいう「核燃料物質·核原料物質」で「核原料物質，核燃料物質及び原子炉の規制に関する法律施行令」により，900 g を超える場合は使用許可を要する．
存在と製法
地殻岩石圏に広く分布し、主要鉱物にはトリアン石ThO2、トール石Th(SiO4)があるが、工業資源としてはモナズ石（主成分CePO4）が重要である。原鉱には他の元素が多く含まれているため、粉砕後、濃硫酸溶解、リン酸塩、シュウ酸塩、硝酸塩などとしての分別沈殿を重ね、溶媒抽出法で精製し、電解法あるいは還元法で金属トリウムを得る。
解説
Th．原子番号90の元素．電子配置[Rn]6d27s2の周期表3族遷移金属元素．アクチノイド元素の一つ．天然放射性元素である．原子量232.0381(1)．天然放射性核種として量的にはほとんどすべて 232Th(α線放出，半減期1.40×1010 y)であるが，微量の 234Th，230Th(ウラン系列)，228Th(トリウム系列)，231Th，227Th(アクチニウム系列)が含まれる．そのほか，質量数209～238の人工放射性核種が知られている．1829年，スウェーデンのJ.J. Berzelius(ベルセリウス)によってトール石のなかから発見された．トールは北欧神話の雷神Thorで，Berzeliusはほかの鉱石に誤ってこの名称をつけていたが，新元素の発見により元素名とともに命名しなおした．宇田川榕菴は天保8年(1837年) に出版した「舎密開宗」で，これを音訳して多𠌃母(トリュウム)としている．天然にはトール石，ホウトリウム鉱などの鉱物が知られているが，資源的にはモナズ石が利用される．地殻中の存在度3.5 ppm．埋蔵量はオーストラリア，インド，アメリカ，ノルウェイで世界の80％ を占める．ThO2をアルゴン中または真空中でカルシウム還元するか，ハロゲン化物の融解塩電解または熱分解などにより金属を得る．森北出版「化学辞典（第2版）
性質と用途
銀白色のもろい金属で、フッ化水素酸以外の希酸に溶けにくいが、塩酸、王水に溶ける。硝酸には不動態（不働態）となって溶けない。金属粉末は燃えやすい。高温ではハロゲン、窒素、水素と直接反応する。
天然には質量数223から234までの同位体が存在するが、232のものが事実上100％の存在比を示し、トリウムの原子量はこの同位体の質量によって定められている。トリウム232はトリウム系列の出発核種であり、中性子照射によって原子炉燃料となるウラン233を製造する原料となる。
ウラン・ラジウム系列中で生ずるトリウム234はウランX1、同230はイオニウム、アクチニウム系列中の同231はウランY、同227はラジオアクチニウムとよばれることもある。
加熱によって熱電子を放出しやすいので、光電管、放電管、熱陰極材料となるほか、合金材料にも使われる。化合物は酸化数＋Ⅳとなるのが普通である。
説明
Discovered in 1828 by Berzelius, thorium is a naturally occurring
radioactive metal with no stable isotopes, which is named for the
Norse god Thor. It is about as abundant as lead. Soil commonly
contains an average of about six parts of thorium per million
parts (ppm) of soil. Thorium occurs in the minerals thorite,
thorianite, orangite, and yttrocrasite, and in monazite sand.
Rocks in some underground mines may also contain thorium in
a more concentrated form. After these rocks are mined, thorium
is usually concentrated and changed into thorium dioxide or
other chemical forms. Thorium-bearing rock that has had most
of the thoriumremoved from it is called ‘depleted’ ore or tailings.
化学的特性
Thorium is a silvery-white, soft, ductile metal which is a natural radioactive element.
物理的性質
Thorium is a radioactive, silvery-white metal when freshly cut. It takes a month or morefor it to tarnish in air, at which point it forms a coating of black oxide. Although it is heavy,it is also a soft and malleable actinide metal. The metal has a rather low melting point, but itsoxide has a very high melting point of about 3,300°C. Thorium reacts slowly with water butreacts more vigorously with hydrochloric acid (HCl).
Thorium’s melting point is 1,750°C, its boiling point is 4,788°C, and its density is 11.79g/cm
3.
同位体
There are 30 radioisotopes of thorium. One isotope in particular, thorium-232,although a weak source of radiation, has such a long half-life (1.405×10
+10 years, orabout 14 billion years) that it still exists in nature and is considered stable.
名前の由来
Thorium was named for Thor, the Scandinavian (Norse) god of “thunder.”
天然物の起源
Thorium is the 37th most abundant element found on Earth, and it makes up about0.0007% of the Earth’s crust. It is mostly found in the ores of thorite, thorianite (the oxide ofthorium), and monazite sand. It is about as abundant as lead in the Earth’s crust. As a potentialfuel for nuclear reactors, thorium has more energy potential than the entire Earth’s supply ofuranium, coal, and gas combined.
特性
Thorium is chemically similar to hafnium (
72Hf ) and zirconium (
40Zr), located just above itin group 4 (IVB). Thorium-232 is found in nature in rather large quantities and goes througha complicated decay process called the thorium decay series. This series involves both alphaand beta emissions, as follows: Th-232 →Ra-228→Ac-228→Th-228→Ra-224→Rn-220→Po-216→Po-212→Pb-212→Bi-212→Ti-208→Pb-208. Thorium-232 can also be convertedinto thorium-233 or uranium-233 by bombarding it with neutrons. This results in Th-232adding a neutron to its nucleus, thus increasing its atomic weight. It then decays into uranium-233. This makes it potentially useful as an experimental new type of fissionable materialfor use in nuclear reactors designed to produce electricity.
使用
Thorium has several commercial uses. For example, thorium oxide (ThO
2) has several uses,including in the Welsbach lantern mantle that glows with a bright flame when heated by agas burner. Because of the oxide’s high melting point, it is used to make high-temperaturecrucibles, as well as glass with a high index of refraction in optical instruments. It is alsoused as a catalyst in the production of sulfuric acid (H
2SO
4), in the cracking procedures inthe petroleum industry, and in the conversion of ammonia (NH
3) into nitric acid (HNO
3).Thorium is used as a “jacket” around the core of nuclear reactors, where it becomes fissionableuranium-233 that is then used for the nuclear reaction to produce energy. Additionally,it is used in photoelectric cells and X-ray tubes and as a coating on the tungsten used to makefilaments for light bulbs. It has great potential to supplant all other nonrenewable energysources (i.e., coal, gas, and atomic energy). Thorium-232 can be converted into uranium-233,a fissionable fuel available in much greater quantities than other forms of fissionable materialsused in nuclear reactors.
定義
A toxic
radioactive element of the actinoid series
that is a soft ductile silvery metal. It has
several long-lived radioisotopes found in a
variety of minerals including monazite.
Thorium is used in magnesium alloys, incandescent
gas mantles, and nuclear fuel
elements.
Symbol: Th; m.p. 1780°C; b.p. 4790°C
(approx.); r.d. 11.72 (20°C); p.n. 90;
r.a.m. 232.0381.
調製方法
Thorium is extracted from monazite sand concentrates for
metallurgical and other purposes by digestion with either hot,
fuming sulfuric acid or caustic soda. The resultant mass is
diluted with water that dissolves thorium, uranium, and rare
earth metals, leaving unreacted monazite, silica, rutile
(TiO2), and zircon (ZrSiO4). Neutralization of the liquor
precipitates thorium phosphate, leaving behind uranium and
most of the rare earth metals.
In 1974, U.S. domestic use of thorium was about 80 tons,
about one-half of which was employed to produce nuclear
fuels and for nuclear research. Principal nonenergy applications applications
were in the production of Welsbach incandescent
gaslight mantles, as a hardener in Th–Mg alloys, in thoriated
tungsten electrodes, and for chemical catalytic uses.
Overall, the consumption of thorium in the United States
has decreased significantly over the past several decades as
nonradioactive substances have replaced thorium in many
applications.
一般的な説明
Silver to grayish radioactive metal. Twice as dense as lead. Radioactive materials emit ionizing radiation, detectable only using special instruments. Exposure to intense levels of radiation or prolonged exposure to low levels can be harmful. Film is also damaged by radiation.
空気と水の反応
Pyrophoric material, spontaneously ignites in air.
反応プロフィール
THORIUM when heated with chlorine (or sulfur), reacts vigorously with incandescence [Mellor 7:208 1946-47]. When thorium is heated with phosphorus, they unite with incandescence [Svenska Akad. 1829 p.1].
危険性
Flammable and explosive in powder form.
Dusts of thorium have very low ignition points and
may ignite at room temperature. Radioactive decay
isotopes are dangerous when ingested.
健康ハザード
Radiation presents minimal risk to transport workers, emergency response personnel and the public during transportation accidents. Packaging durability increases as potential hazard of radioactive content increases. Undamaged packages are safe. Contents of damaged packages may cause higher external radiation exposure, or both external and internal radiation exposure if contents are released. Low radiation hazard when material is inside container. If material is released from package or bulk container, hazard will vary from low to moderate. Level of hazard will depend on the type and amount of radioactivity, the kind of material it is in, and/or the surfaces it is on. Some material may be released from packages during accidents of moderate severity but risks to people are not great. Released radioactive materials or contaminated objects usually will be visible if packaging fails. Some exclusive use shipments of bulk and packaged materials will not have "RADIOACTIVE" labels. Placards, markings and shipping papers provide identification. Some packages may have a "RADIOACTIVE" label and a second hazard label. The second hazard is usually greater than the radiation hazard; so follow this GUIDE as well as the response GUIDE for the second hazard class label. Some radioactive materials cannot be detected by commonly available instruments. Runoff from control of cargo fire may cause low-level pollution.
安全性プロファイル
Suspected carcinogen.
Taken internally as Th02, it has proven to
be carcinogenic due to its radioactivity. On
an acute basis it has caused dermatitis.
Flammable in the form of dust when
exposed to heat or flame, or by chemical
reaction with oxidizers. The powder may
ignite spontaneously in air. Potentially
hazardous reactions with chlorine, fluorine,
bromine, oxygen, phosphorus, silver, sulfur,
air, nitryl fluoride, peroxyformic acid.
職業ばく露
Metallic thorium is used in nuclear reactors to produce nuclear fuel; in the manufacture of incandescent mantles; as an alloying material, especially with some of the lighter metals, for example, magnesium as a reducing agent in metallurgy; for filament coatings in incandescent lamps and vacuum tubes; as a catalyst in organic synthesis; in ceramics; and in welding electrodes. Exposure may occur during production and use of thorium-containing materials, in the casting and machining of alloy parts; and from the fume produced during welding with thorium electrodes. Thorium nitrate is an oxidizer. Contact with combustibles, and reducing agents will cause violent combustion or ignition.
環境運命予測
Thorium’s usage may result in release of thorium compounds
to the environment through various waste streams. As noted
above, thorium is also found naturally, particularly in monazite
sand. Thorium compounds are expected to exist in the
particulate phase if released to the atmosphere based on their
low vapor pressures and may be removed from the air by wet
and dry depositions. Th and ThO2 have low mobility in soils.
In aquatic releases, adsorption is expected to be the primary
means of removal from the system.
輸送方法
UN2975 Thorium metal, pyrophoric, Hazard class: 7; Labels: 7-Radioactive material, 4.2-Spontaneously combustible material. Note: UN/NA 2975 doesn’t appear in the 49 CFR Hazmat Table.
不和合性
The powder may ignite spontaneously in air. Heating may cause violent combustion or explosion. May explosively decompose from shock, friction, or concussion. Incompatible with strong oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause violent fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides, nitryl fluoride; peroxyformic acid; silver, sulfur.
廃棄物の処理
Recovery and recycling is in the preferred route.
トリウム 上流と下流の製品情報
原材料
準備製品