鉛

外観

褐灰黒色〜灰黒色, 粉末

溶解性

水に不溶。硫酸に不溶。硝酸, 熱濃硫酸に可溶。硝酸に溶け、塩酸及び硫酸に溶けにくく、水にほとんど溶けない。

解説

鉛，なまり，元素記号はPb。原子番号82，原子量207.2，融点327.5℃，沸点1750℃。古くから知られた金属元素の一つで，前1500年ころにも製錬の記録があり，化合物としても顔料，医薬品などに使用された。帯青白のやわらかい金属。硬度1.5。空気中では酸化被膜のため安定。希酸には一般に侵され難い。金属，化合物とも有毒（鉛中毒）。主鉱石は方鉛鉱。鉱石を焙焼(ばいしょう)ののち溶鉱炉で溶錬して粗鉛を得る焙焼還元法が代表的な製錬法で，粗鉛は電解精製や乾式法で純度を上げる。用途は蓄電池の電極，化学装置の耐食性内張り，はんだ，活字，軸受合金，鉛管，放射線遮蔽(しゃへい)用材など。

主な性質

1. 鉛は元来、ろう白の光沢をもつが、酸化しやすいため、空気中で酸化されて〔鉛色〕を呈する
2. 鉛は低融点であり、これを利用した用途も多い
3. 鉄に比べて比重が1.4倍も大きく、X線やレントゲン線をよく吸収する
4. 鉛は柔らかく、延展性に富み、極めて薄い板に加工できる
5. 塩化鉛（ＰｂＯ）はガラスの中で光の屈折率を大きくし、放射線を遮蔽する特性がある
6. 硫酸に対する耐食性は非常に大きい。中性付近ではほとんど溶解しない（有機酸やアルカリに対してはあまり強くない）
7. 最近は環境負荷軽減のため、使用は減少する傾向にある

用途

成形材料。

用途

金属材料としては融点が低く軟らかいので加工しやすい。また摩擦係数が小さく、大気、地中、海水などの自然環境に対する耐食性が強いこと、硫酸にも侵されにくいなど化学的性質が優れており、化学反応容器の内ばり、ケーブル被覆剤、鉛蓄電池の電極材料、建築材料に使われる。また軸受合金、活字合金、易融合金の成分として広く用いられている。X線やγ(ガンマ)線、その他の放射線を吸収する力が強いので、放射線遮蔽(しゃへい)材に用いられる。すなわち原子核産業では、鉛板あるいは鉛ガラスとして放射線防護用に用いられる。ある周波数の音波を吸収するので防音材にも使用される。しかし、目的によっては軟らかすぎるので、強度を増し、鉛の性質をなくさないような合金（アンチモン添加）がよく使われる。ケーブル被覆に約1％、蓄電池グリッド用には5～9％、また、ある種の鋳物用には10～15％加えることもある。スズとの合金は軸受合金、はんだなどにも用いられる。鉛の化合物（鉛白、酸化鉛(Ⅱ)、鉛丹、テトラエチル鉛など）も金属鉛を原料としてつくられる。

主な用途

1. 鉛蓄電池（自動車用、産業用、民生用）
2. 電子電気機器（プリント基板用はんだ、電子部品、パソコン、携帯電話）
3. 鉛管、鉛板（上下水道、ガス管）
4. 無機薬品（ガラス製品、塩ビ安定材、ＴＶ．ＯＡの管球ガラス）
5. 電線（地下ケーブル被覆材）
6. その他（活字合金、遮音板、制振シート、放射能遮蔽材、軸受け）

存在

方鉛鉱PbS、白鉛鉱PbCO3、硫酸鉛鉱PbSO4、紅鉛(べにえん／こうえん)鉱PbCrO4などの鉱物として、また亜鉛、金、銀、銅などとともに複雑な鉱物として産出する。世界の埋蔵量は1.5億トン程度で、日本のそれはきわめて少ない。天然の放射性崩壊系列の終点の安定核種は鉛の同位体である。ウラン・ラジウム系列では鉛206、トリウム系列で鉛208、アクチニウム系列では鉛207であるから、放射性鉱物中の鉛の原子量から、その起源や年代を推定することができる。

毒性

金属鉛はもちろん、可溶性鉛塩など体内で溶けて鉛イオンを生じるものすべてが有毒である。リン酸鉛として骨に蓄積され慢性障害を引き起こす。おもな症状として貧血、腹痛、伸筋麻痺(まひ)、不眠、視力障害などがみられる。

説明

Lead was one of the earliest metals used by humans, with possible use extending as far back as the seventh millennium BC, and reaching its preindustrial peak usage during the reign of the Roman Empire, around the beginning of the Common Era.

化学的特性

Lead is a lustrous silvery metal that tarnishes in the presence of air and becomes a dull bluish gray. The chemical symbol, Pb, is derived from plumbum, the Latin word for waterworks, because of lead’s extensive use in ancient water pipes. Lead has four electrons in its valence shell, but only two ionize readily. The usual oxidation state of lead in inorganic compounds is therefore +2 rather than +4. Lead generally forms stable compounds; the most important ones are lead oxide (PbO) and lead carbonate (PbCO₃)₂. Four stable lead isotopes exist in nature (²⁰⁸Pb , ²⁰⁶Pb , ²⁰⁷Pb, and ²⁰⁴Pb , in order of abundance). Lead mined from deposits of different geologic eras has entered the environment, so that today there are wide variations and extensive mixture of isotopic ratios of lead in commerce and in the environment. These differences in isotopic ratios may sometimes be used as nonradioactive tracers in environmental and metabolism studies.

性質

軟らかい青白色の金属。熱伝導率、電導率ともに銀の約8％にあたる。容易に切ったり曲げたり延ばしたりできる。新しい切り口は金属光沢をもつが、空気中では表面が酸化され鈍い色となる。このさびは表面を覆い、内部にまで及ばないので、腐食しにくい。空気中で熱すれば酸化鉛(Ⅱ)PbOとなる。酸化鉛(Ⅱ)を450℃付近で長く熱すると四酸化三鉛Pb3O4となるが、550℃以上でふたたび酸化鉛(Ⅱ)となる。ハロゲンとは直接反応してハロゲン化物を生じ、硫黄(いおう)と熱すると硫化物となる。希硫酸には溶けないが、熱濃硫酸や硝酸には鉛(Ⅱ)塩を生じて溶ける。酸素があれば酢酸のような弱酸にも溶ける。冷アルカリ溶液に徐々に溶け、熱アルカリには速やかに溶けて亜鉛(あなまり)酸塩M₂PbO₂となる。二酸化炭素を溶かした水中では表面に緻密(ちみつ)な鉛白（塩基性炭酸鉛）の皮膜を生じて内部が保護される。
6Pb＋3O2＋2H2O＋4CO2―→2[2PbCO3・Pb(OH)2]
鉛が有毒であるにもかかわらず水道の鉛管に使用されたのはこのためである。酸化数Ⅱの化合物のほかに、酸化鉛(Ⅳ)PbO2、酢酸鉛(Ⅳ)Pb(CH3CO2)4などの化合物がある。これら酸化数Ⅳの化合物は、二価化合物を塩素を含む酸化剤で処理したり、電解酸化することによってつくられる。ほかに、テトラエチル鉛Pb(C2H5)4のような有機鉛化合物が知られる。

物理的性質

Lead is a bluish-white, heavy metallic element with properties that are more metal-like thanthe properties of metalloids or nonmetals. Lead can be found in its native state, meaning thatelemental metallic lead can be found in deposits in the Earth’s crust. However, most lead isfirst mined as galena ore (lead sulfide, PbS). The galena is mixed with lead sulfate, lead sulfide,and lead oxide and is then roasted at a high temperature. The air supply is reduced, followedby an increase in heat and the vaporization of the sulfates and oxides of lead, which are drawnoff as gases. The molten lead is then recovered.
Lead is only slightly soluble in water. However, it is also toxic. This is the reason lead isno longer used to pipe fresh water into homes. It does not react well with acids, with theexception of nitric acid. Lead’s melting point is 327.46°C, its boiling point is 1,740°C, andits density is 11.342 g/cm³.

同位体

There are 47 isotopes of lead, four of which are stable. One of these four is Pb-204, which makes up 1.4% of the natural abundance of lead found on Earth. In reality thisisotope is not stable but has a half-life that is so long (1.4×10⁺¹⁷ years), with some of theancient deposits still existing, that it is considered stable. The other three stable isotopes oflead and their proportion to the total natural abundance are as follows: Pb-206 = 24.1%,Pb-207 = 22.1%, and Pb-208 = 52.4%. All the other isotopes are radioactive.

名前の由来

From the Latin word alumen, or aluminis, meaning “alum,” which is a bitter tasting form of aluminum sulfate or aluminum potassium sulfate.

天然物の起源

Lead is the 35th most abundant element on Earth. Although it has been found in its freeelemental metal state, it is usually obtained from a combination of the following ores: galena(PbS), anglesite (PbSO₄), cerussite (PbCO₃), and minum (Pb₃O₄). Lead ores are locatedin Europe (Germany, Rumania, and France), Africa, Australia, Mexico, Peru, Bolivia, andCanada. The largest deposits of lead in the United States are in the states of Missouri, Kansas,Oklahoma, Colorado, and Montana.
One of the most famous mining towns is the high-altitude western city of Leadville,Colorado. The boom started with the gold rush of the 1860s, followed by silver mining in the1870s and 1880s. Today, this city is the site of mining operations not only for lead, but alsofor zinc and molybdenum. At the height of its fame, Leadville had a population of almost50,000 people. Today the population is about 2,500.
Lead is commonly obtained by roasting galena (PbS) with carbon in an oxygen-rich environmentto convert sulfide ores to oxides and by then reducing the oxide to metallic lead.Sulfur dioxide gas is produced as a waste product. Large amounts of lead are also recoveredby recycling lead products, such as automobile lead-acid electric storage batteries. About onethirdof all lead used in the United States has been recycled.

特性

Although lead can be found as a metal in the Earth’s crust, it is usually mined and refinedfrom minerals and ores. Lead is one of the most common and familiar metallic elementsknown. Although it is somewhat scarce, found at proportions of 13 ppm, it is still more prevalentthan many other metals. Lead is noncombustible. and it resists corrosion.
When lead, which is very soft, is freshly cut, it has shiny blue-white sheen, which soonoxidizes into its familiar gray color. Lead is extremely malleable and ductile and can be workedinto a variety of shapes. It can be formed into sheets, pipes, buckshot, wires, and powder.Although lead is a poor conductor of electricity, its high density makes it an excellent shieldfor protection from radiation, including X-rays and gamma rays.

使用

Construction material for tank linings, piping, and other equipment handling corrosive gases and liqs used in the manufacture of sulfuric acid, petroleum refining, halogenation, sulfonation, extraction, condensation; for x-ray and atomic radiation protection; manufacture of tetraethyllead, pigments for paints, and other organic and inorganic lead Compounds; bearing metal and alloys; storage batteries; in ceramics, plastics, and electronic devices; in building construction; in solder and other lead alloys; in the metallurgy of steel and other metals.

定義

lead: Symbol Pb. A heavy dull greysoft ductile metallic element belongingto group 14 (formerly IVB) ofthe periodic table; a.n. 82; r.a.m.207.19; r.d. 11.35; m.p. 327.5°C; b.p.1740°C. The main ore is the sulphidegalena (PbS); other minor sources includeanglesite (PbSO₄), cerussite (PbCO₃), and litharge (PbO). Themetal is extracted by roasting the oreto give the oxide, followed by reductionwith carbon. Silver is also recoveredfrom the ores. Lead has a varietyof uses including building construction,lead-plate accumulators, bullets,and shot, and is a constituent of suchalloys as solder, pewter, bearing metals,type metals, and fusible alloys.Chemically, it forms compoundswith the +2 and +4 oxidation states,the lead(II) state being the more stable.

調製方法

The geometric mean soil lead level is 38 mg/kg. Lead rarely occurs in the elemental state, but exists widely throughout the world in a number of ores, the most common of which is the sulfide, galena. The other minerals of commercial importance are the oxides, carbonate (cerussite), and the sulfate (anglesite), which are much less common.
Lead also occurs in various uranium and thorium minerals, arising directly from radioactive decay. Because certain isotopes are concentrated in lead derivatives from such sources, both the atomic weight and the density of the samples vary significantly from normal lead. Lead ores generally occur in nature in association with silver and zinc. Other metals commonly occurring with lead ores are copper, arsenic, antimony, and bismuth. Most of the world production of arsenic, antimony, and bismuth is a result of their separation from lead ores. Commercial lead ores may contain as little as 3% lead, but a lead content of 10% is most common. The ores are concentrated to ≥ 40% lead content before smelting. A variety of mechanical separation processes may be employed for the concentration of lead ores, but the sulfide ores are generally concentrated by flotation processes.

製法

鉛冶金(やきん)のおもな原料は方鉛鉱で、焙焼(ばいしょう)、焼結して酸化物の塊とし、石灰石、コークスなどと溶鉱炉で強熱して粗鉛を得る。粗鉛（98.5％）の精製には乾式法と電解法がある。この精製過程で不純物として含まれている金や銀などが副産物として回収される。乾式法は歴史が古く、イギリスの工業化学者A・パークスが1842年に原理を発見したパークス法では、融解状態で亜鉛が鉛に溶けにくいこと、また金や銀が表面に浮かぶ亜鉛層に溶けやすいことを利用する。すなわち、少量の亜鉛を加えて、粗鉛中の金・銀を亜鉛合金として分離し精鉛とする。電解法は、粗鉛を陽極とし、ヘキサフルオロケイ酸鉛PbSiF6と遊離の酸H2SiF6を含む水溶液を電解して、陰極板（純鉛）上に鉛を析出させる（ベッツ法）。電解鉛とよばれ、高純度のもの（99.999％）が得られる。鉛（地金）は世界で約1053万トン生産されたが、日本では輸入鉱物からの生産を含めても25万トン程度である。消費量は世界で約1041万トン、日本では約23万トン（2011）。

一般的な説明

Soft silver-bluish white to gray metal.

空気と水の反応

Insoluble in water.

反応プロフィール

In the presence of carbon, the combination of chlorine trifluoride with aluminum, copper, Lead, magnesium, silver, tin, or zinc results in a violent reaction [Mellor 2, Supp. 1: 1956]. A solution of sodium azide in copper pipe with Lead joints formed copper and Lead azide, both are detonating compounds [Klotz 1973]. Sodium acetylide becomes pyrophoric when mixed with metals like Lead. Mixtures of trioxane with 60% hydrogen peroxide in contact with metallic Lead when heated detonated. Lead containing rubber ignited in a nitric acid atmosphere. Lead is incompatible with strong oxidants such as: ammonium nitrate, chlorine trifluoride, hydrogen peroxide, etc.

健康ハザード

The acute toxicity of lead and inorganic lead compounds is moderate to low. Symptoms of exposure include decreased appetite, insomnia, headache, muscle and joint pain, colic, and constipation. Inorganic lead compounds are not significantly absorbed through the skin.
Chronic exposure to inorganic lead via inhalation or ingestion can result in damage to the peripheral and central nervous system, anemia, and chronic kidney disease. Lead can accumulate in the soft tissues and bones, with the highest accumulation in the liver and kidneys, and elimination is slow. Lead has shown developmental and reproductive toxicity in both male and female animals and humans. Lead is listed by IARC in Group 2B ("possible human carcinogen") and by NTP as "reasonably anticipated to be a carcinogen," but is not considered to be a "select carcinogen" under the criteria of the OSHA Laboratory Standard.

火災危険

Flash point data for Lead are not available, however, Lead is probably non-combustible.

燃焼性と爆発性

Lead powder is combustible when exposed to heat or flame.

工業用途

Not only is lead the most impervious of all common metals to x-rays and gamma radiation, it also resists attack by many corrosive chemicals, most types of soil, and marine and industrial environments. Although lead is one of the heaviest metals, only a few applications are based primarily on its high density. The main reasons for using lead often include low melting temperature, ease of casting and forming, good sound and vibration absorption, and ease of salvaging from scrap.
With its high internal damping characteristics, lead is one of the most efficient sound attenuators for industrial, commercial, and residential applications. Sheet lead, lead-loaded vinyls, lead composites, and lead-containing laminates are used to reduce machinery noise. Lead sheet with asbestos or rubber sandwich pads are commonly used in vibration control.

特性

陽子を 82 個持ち原子核の安定性が 高い
重くてやわらかい
展延性が良い

発がん性

Lead and lead compounds are reasonably anticipated to be human carcinogens based on limited evidence of carcinogenicity from studies in humans and sufficient evidence of carcinogenicity from studiesin experimental animals.

貯蔵

work with lead dust, molten lead, and lead salts capable of forming dusts should be conducted in a fume hood to prevent exposure by inhalation.

不和合性

Violent reactions of lead with sodium azide, zirconium, sodium acetylide, and chlorine trifluoride have been reported. Reactivity of lead compounds varies depending on structure.

廃棄物の処理

Excess lead and waste material containing this substance should be placed in an appropriate container, clearly labeled, and handled according to your institution's waste disposal guidelines. For more information on disposal procedures, see Chapter 7 of this volume.