セレン

外観

灰赤色～黒色, 粉末

溶解性

硝酸及び熱硫酸に溶け、水にほとんど溶けない。

反応

セレンの化合物は、一般に酸化数-2、+2、+4および+6で存在します。セレンは、酸素と反応して二酸化セレンを生成 (Se₈+8O₂→8SeO₂)し、硝酸で酸化することで、亜セレン酸を直接作ることができます (3Se+4HNO₃+H₂O→3H₂SeO₃+4NO)。さらに、セレンはフッ素と反応して六フッ化セレンを生成 (Se₈+24F₂→8SeF₆) し、シアン化物と反応するとセレノシアネートを生成します (Se₈+8KCN→8KSeCN)。

解説

セレン,原子番号34の元素．電子配置[Ar]3d104s24p4の周期表16族非金属元素．原子量78.96(3)．質量数74(0.89(4)％)，76(9.372(9)％)，77(7.63(16)％)，78(23.77(28)％)，80(49.61(41)％)，82(8.73(22)％)の6種の安定同位体と，質量数64～94の放射性同位体が知られている．地球上に広く分布しているが，その量は硫黄よりずっと少ない．少量は遊離の形で産出するが，おもに銅，銀，鉛，鉄の硫化鉱中に含まれて産出する．地殻中の存在度0.05 ppm．銅電解精錬でできる陽極スライムから，貴金属回収の際に副産物として得られる．

主な性質

1. 単体セレンには多くの同素体があるが、最も安定なものは長らせん構造の「灰色セレン」（金属セレン）で、半導体性質、光伝導体性質を持つ
2. 金属セレンは暗所で殆んど電気を導かず、光を当てると固体内の電子が励起して電気が通じる（光伝導性）。セレンは光の中では特にオレンジや赤い光に敏感
3. セレン化カドミウムを主成分とする赤色顔料のカドミウムレッドは光電池にも利用されている

用途

ケルダール法全窒素分析の分解助剤、ガラス脱色剤、合金材料、赤外線偏光子、顔料製造原料、触媒。

製法

単体で産出することはほとんどなく、金属のセレン化物として硫化物に伴って産出することが多く、これら金属製錬の副産物として得られる。たとえば、銅の電解精錬のときの陽極泥をソーダ灰とともに焼いて亜セレン酸ナトリウムとして分離し、二酸化硫黄(いおう)で還元しセレンを得る。粗セレンは水素中で熱してセレン化水素とし、これを1000℃に強熱して分解すると純セレンが得られる。さらに純度の高いものは帯域融解法で得られる。市販のガラス状セレンを加熱してからゆっくりと冷却すると灰黒色の金属セレンが得られ、二硫化炭素溶液から結晶させると赤色の結晶セレンが得られる。

応用

灰色セレンはH2Oと160 ℃ で徐々に酸化される．F2，Cl2，Br2，Sと直接反応する．希塩酸，希硫酸に不溶，酸化性の濃硝酸，濃硫酸に可溶．ガラスに，鉄分による緑色を打ち消すためと熱線遮断の目的で添加される量が多い．そのほか，青色顔料，赤色顔料の原料，ゴム添加剤，ガラス・陶磁器の着色剤として使用されている．光の強度に応じて導電率が変化するため，光電池や光電管にも利用されている．新しい用途として，アモルファス・セレン利用のX線のデジタル検出装置などがある．乾式コピー機の感光体としての用途はほぼ消滅した．

主な用途

1. 電子?情報機器（乾式複写機感光体、光ディスク、太陽電池）
2. 整流器部品（電流制御装置）
3. 着色剤（ガラス）
4. 顔料（塗料）
5. 化学薬品（試薬他）

説明

Selenium was discovered in 1817 by J?ns Jacob Berzelius. Especially noted was the similarity of the new element to the previously known tellurium. Selenium is an essential trace element atw0.1 ppm in diets. Selenium is a biologically active part of a number of important proteins, particularly enzymes involved in antioxidant defense mechanisms, thyroid hormone metabolism, and redox control of intracellular reactions. In humans and animals, selenium plays a role in protecting tissues from oxidative damage as a component of glutathione peroxidase.

化学的特性

Jewelers most frequently encounter selenium in the form of brass-black and gun-bluing compounds. Selenium print toner used by photographers is sometimes used by jewelers as a metal-coloring solution. These coloring mixtures usually contain selenic acid. Selenic acid can release hydrogen selenide gas that can cause illness, and used daily, it might enlarge the liver and spleen. Tellurium is sometimes used in association with selenium.

物理的性質

Selenium is a soft metalloid or semimetal that is similar to tellurium, located just belowit in the oxygen group, and sulfur, which is just above it in the same group. Selenium hasseveral allotropic forms that range from a gray metallic appearance to a red glassy appearance.These allotropic forms also have different properties of heat, conductivity, and density. In itsamorphous state, it is a red powder that turns black and becomes crystalline when heated.Crystalline selenium has a melting point of 220°C, a boiling point of 685°C, and a densityof 4.809 g/cm³.

同位体

There are a total of 35 isotopes of selenium. Five of these are stable, anda sixth isotope has such a long half-life that it is also considered stable: Se-82 =0.83×10⁺²⁰ years. This sixth isotope constitutes 8.73% of selenium’s abundance in theEarth’s crust, and the other five stable isotopes make up the rest of selenium’s abundanceon Earth.

名前の由来

Named for the Greek word selene, meaning “moon.” Jons Jacob Berzelius (1779–1848) discovered selenium and named it after the mineral called “eucairite,” which in Greek means “just in time.”

天然物の起源

Selenium is the 67th most abundant element in Earth’s crust. It is widely spread over theEarth, but does not exist in large quantities. As a free element it is often found with the elementsulfur.
There is only one mineral ore that contains selenium: eucairite (CuAgSe). Although rich inselenium, it is too scarce to be of commercial use. Almost all selenium is recovered from theprocessing of copper and the manufacturing of sulfuric acid as a leftover sludge by-product.This makes selenium’s recovery profitable. Recovering it from eucairite is not profitable.
Selenium is found in Mexico, Bosnia, Japan, and Canada. It can be found in recoverablequantities in some soils in many countries.

特性

Crystalline selenium is a p-type semiconductor. It acts as a rectifier that can change electriccurrent from alternating current (AC) to direct current (to DC). It has photovoltaic proper ties, meaning it is able to convert light (radiant) energy that strikes it into electrical energy.Selenium’s resistance to the flow of electricity is influenced by the amount of light shining onit. The brighter the light, the better the electrical conductivity.
Selenium burns with a blue flame that produces selenium dioxide (SeO₂). Selenium willreact with most metals as well as with nonmetals, including the elements in the halogen group17.

使用

selenium is a trace mineral used for years in topical preparations for its anti-fungal properties. Selenium has been shown to have other protective effects such as repairing DnA, reducing the DnA-binding of carcinogens, and suppressing gene mutations. In laboratory studies, skin lotions containing selenium compounds have been shown to decrease uV-induced skin damage such as inflammation, blistering, and pigmentation.

定義

selenium: Symbol Se. A metalloidelement belonging to group 16 (formerlyVIB) of the periodic table; a.n.34; r.a.m. 78.96; r.d. 4.81 (grey); m.p.217°C (grey); b.p. 684.9°C. There are anumber of allotropic forms, includinggrey, red, and black selenium. Itoccurs in sulphide ores of other metalsand is obtained as a by-product(e.g. from the anode sludge in electrolyticrefining). The element is asemiconductor; the grey allotrope islight-sensitive and is used in photocells,xerography, and similar applications.Chemically, it resemblessulphur, and forms compounds withselenium in the +2, +4, and +6 oxidation states. Selenium was discoveredin 1817 by J?ns Berzelius.

調製方法

Selenium (Se), a nonmetallic element of the sulfur group, is widely distributed in nature. It is obtained along with tellurium as a by-product of metal ore refining, chiefly from copper deposits. About 16 ton is mined a year globally. The global refinery production of selenium, excluding the U.S. production, increased from about 1,400 metric ton in 2000 to about 1510 metric ton in 2008 and 1500 in 2009.
Because selenium is present in fossil fuels, up to 90% of the selenium content in ambient air is emitted during their combustion. Air pollution concentrations averaged from 0.38 ng/m³ in remote areas to 13 ng/m³ in urban areas. The mass medium particle diameter was 0.92 mm. The worldwide emissions of 10,000 tons/year from natural sources exceed the atmospheric emissions from anthropogenic sources (5100 ton). However, 41,000 tons is emitted into the aquatic ecosystems. The largest contributors are electric power generating plants that produce 18,000 ton; manufacturing processes account for 12,000 ton.
Most of the world’s selenium today is provided by recovery from anode muds of electrolytic copper refineries. Selenium is recovered by roasting these muds with soda or sulfuric acid or by melting them with a soda and niter.

一般的な説明

Selenium is a reddish colored powder that may become black upon exposure to air. Selenium is toxic by ingestion. Selenium is used to manufacture electronic components and rubber.

空気と水の反応

Insoluble in water.

反応プロフィール

SELENIUM, silicon, or sulfur ignites in fluorine gas at ordinary temperatures [Mellor 2:11-13 1946-47]. A mixture of barium carbide and selenium heated to 150° C becomes incandescence [Mellor 5:862 1946-47]. Calcium carbide and selenium vapor react with incandescence [Mellor 5:862 1946-47]. A moist mixture of selenium and chlorates, except the alkali chlorates, becomes incandescent. Selenium reacts violently with chromium trioxide [Mellor 11:233 1946-47]. Reaction of selenium and silver bromate (also potassium bromate) is violently explosive [Mellor 2, Supp1:763 1956]. Freshly reduced selenium reacts vigorously with nitric acid. Trace amounts of organic matter probably influenced the reaction [J. Chem. Soc. 1938 p.391]. The reaction between zinc and selenium or tellurium is accompanied by incandescence [Mellor 4:476-480 1946-47].

危険性

The fumes and gases of most selenium compounds are very toxic when inhaled. SeO2 andSeS₂ are toxic if ingested and very irritating to the skin. They are also carcinogenic.
Although some compounds of selenium are poisonous, as an element it is essential in traceamounts for humans. It is recommended that 1.1 to 5 milligrams of selenium be included inthe daily diet. This amount can be maintained by eating seafood, egg yokes, chicken, milk,and whole grain cereals. Selenium assists vitamin E in preventing the breakdown of cells andsome chemicals in the human body.

火災危険

Combustible material: may burn but does not ignite readily. Containers may explode when heated. Runoff may pollute waterways. Substance may be transported in a molten form.

取扱いおよび保管上の注意

取扱い及び保管上の注意は、下記の通りです。

• 容器を密栓し、乾燥した冷暗所に保管する。
• 屋外や換気の良い区域のみで使用する。
• 激しく反応するため、強酸との接触は避ける。
• 火災や爆発のおそれがあるため、硝酸や強酸化剤との接触は避ける。
• 使用時は保護手袋、保護衣、保護眼鏡、保護面を着用する。
• 取扱い後はよく手を洗浄する。
• 皮膚に付着した場合は、速やかに水で洗い流す。
• 眼に入った場合は、水で数分間注意深く洗う。

参考文献

法規情報

セレンは、毒物及び劇物取締法で「毒物」、労働安全衛生法で「名称等を表示すべき危険物及び有害物」「名称等を通知すべき危険物及び有害物」、化学物質排出把握管理促進法 (PRTR法) で「第1種指定化学物質」に指定されており、使用の際には注意が必要です。さらに、消防法では「消防活動阻害物質」に、労働基準法では「疾病化学物質」に該当します。

セレンの使用用途

セレンの使用用途として、半導体性、光伝導性などの特性を利用して、セレン整流器、乾式複写機の感光ドラム、太陽光電池に使用されています。その他には、着色剤やゴムの添加剤としても使用されています。
現在では、毒性があるため使用が制限され多くの用途で代替品が使用されています。

食品においては、セレンは生体内で必須元素であることからサプリメントとして使用されています。毒性の強い元素であるため、必要量と中毒量の差が小さく、サプリメントとしての摂取には注意が必要です。

セレンの性質

セレンは、温度変化の速度によって相互変換する同素体が複数存在し、融点が170～217℃、沸点が685℃、密度は4.2～4.8です。化学反応で調製された場合、セレンは通常、アモルファスの赤レンガ色の粉末ですが、急速に溶融すると、黒色のガラス質形態を形成し、通常はビーズとして市販されています。赤色のα、β、およびγ型のセレンは、二硫化炭素などの溶媒の蒸発速度を変えることによって、黒色セレンの溶液から製造されます。

生物学的応用

Selenium is a component of a number of proteins. Selenium can exist as an anion at biological pH, which makes it able to both give and accept electrons. The best understood physiological functions of selenium are two enzyme functions. One of these functions is done as part of a family of proteins named glutathione peroxidase (one is found inside of cells, another is outside cells in places like the plasma).
Glutathione peroxidase is part of the body's antioxidant defense network by eliminating peroxides, including hydrogen peroxide, which can be both precursors and products of free radicals. Selenium also functions in an enzyme that is part thyroid hormone synthesis. A more recently discovered selenium enzyme is known as thioredoxin reductase, which seems to have a number of regulatory roles within cells, and seems to affect antioxidant defense by inßuencing electron ßow in some reactions. One interesting point about this enzyme is that in rats, the enzyme activities can be increased by elevating selenium intake above those normally considered adequate.

安全性プロファイル

Poison by intravenous route. When heated to decomposition it emits toxic fumes of Se. See also SELENIUM and SELENIUM COMPOUNDS

職業ばく露

Most of the selenium produced is used in the manufacture of selenium rectifiers. It is also utilized as a pigment for ruby glass, paints, and dyes; as a vulcaniz- ing agent for rubber; a decolorizing agent for green glass; a chemical catalyst in the Kjeldahl test; as an insecticide; in the manufacture of electrodes, selenium photocells, sele- nium cells, and semiconductor fusion mixtures; in photo- graphic toning bathes; and for dehydrogenation of organic compounds. It is also used in veterinary medicine and in antidandruff shampoos. Se is used in radioactive scanning for the pancreas and for photostatic and X-ray xerography. It may be alloyed with stainless steel; copper, and cast steel. Selenium is a contaminant in most sulfide ores of copper, gold, nickel, and silver; and exposure may occur while removing selenium from these ores.

輸送方法

UN3283 Selenium compound, solid, n.o.s., Hazard Class: 6.1; Labels: 6.1-Poisonous material, Technical Name Required.

純化方法

Dissolve selenium in small portions in hot conc HNO3 (2mL/g), filter and evaporate to dryness to give selenious acid which is then dissolved in conc HCl. Pass SO2 gas through the solution whereby selenium (but not tellurium) precipitates. It is filtered off and washed with conc HCl. This purification process is repeated. The selenium is then converted twice to the selenocyanate by treating with a 10% excess of 3M aqueous KCN (CARE), heated for half an hour on a sand-bath and filtered. Add an equal weight of crushed ice to the cold solution, followed by an excess of cold, conc HCl, with stirring (in an efficient fume cupboard as HCN is evolved) which precipitates selenium powder. This is washed with water until colourless, and then with MeOH and is heated in an oven at 105o. Finally it is fused for 2hours in vacuo. It is cooled, crushed and stored in a desiccator [Tideswell & McCullough J Am Chem Soc 78 3036 1956].

Structure and conformation

It takes three types of structures, metallic (grey) selenium, crystal (red) selenium, and amorphous selenium. The space lattice of metallic selenium belongs to the hexagonal system with two types, A and B. The B type is the most stable and the quasi-stable; A type changes to the B type slowly. The structure of the B type is an infinite zigzag chain containing three atoms in a unit cell with lattice constant of a=0.4355 nm, c=0.4949 nm, Se–Se=0.232 nm, and ＜Se– Se–Se=105° . The space lattice of crystal belongs to the monoclinic system with a=0.905 nm, b=0.907 nm, c=1.161 nm, Se–Se=0.234 nm, b=90841' , and ＜Se–Se–Se=105.38° ±2.3° . There may be two types for crystal selenium. Amorphous selenium changes to metallic selenium slowly at room temperature. Sometimes, selenium is classified into trigonal and amorphous types3 .

不和合性

Reacts violently with strong acids and strong oxidizers, chromium trioxide; potassium bromate;cadmium. Reacts with incandescence on gentle heating with phosphorous and metals, such as nickel, zinc, sodium, potassium, platinum. Reacts with water @ 50 ? C forming flammable hydrogen and selenious acids.

廃棄物の処理

Powdered selenium: dispose in a chemical waste landfill. When possible, recover selenium and return to suppliers

予防処置

During use and handling of selenium, occupational workers should be careful to avoid contact with the skin. Selenium compounds are considered very damaging to the liver, and hazardous.