Lead was mentioned in the Book of Exodus In alchemy, lead was thought to be the oldest metal and was associated with the planet Saturn. Lead pipes that bear the insignia of Roman emperors are still in service and many Roman "pigs" ingots of lead figure in Derbyshire lead mining history and in the history of the industry in other English centres.
Lead's symbol Pb is an abbreviation of its Latin name plumbum for soft metals; originally it was plumbum nigrum , where plumbum candidum was tin. The English word "plumbing" also derives from this Latin root. Lead also refers collectively to the organic and inorganic compounds of lead, which are toxic. Lead poisoning was documented in ancient Rome, Greece, and China. In the 20th century, the use of lead in paint pigments was sharply reduced because of the danger of lead poisoning, especially to children.
Much of this shift was a result of the U. Lead may still be found in harmful quantities in stoneware, vinyl such as that used for tubing and the insulation of electrical cords , and brass manufactured in China. Around , many children's toys made in China had been recalled due to lead in paint used to color the product. Metallic lead does occur in nature, but it is rare. Lead is usually found in ore with zinc , silver and most abundantly copper , and is extracted together with these metals.
The main lead mineral is galena PbS , which contains Lead ore galena is found commonly in north-east Wales. The North-east Wales Orefield was by far the most important source of lead and zinc in Wales and second in national importance only to the North Pennine Orefield.
Lead mining dates back to at least Roman times and continued until well into the 20th century. Galena is present in steeply dipping fissure veins and in pipes and is in Mississippi Valley-type lead-zinc-fluorite and copper-dolomite associations. The mineralisation occurs in the upper parts of the Loggerheads and Cefn Mawr Formations of the Carboniferous Limestone.
Sulfide ores are roasted, producing primarily lead oxide and a mixture of sulfates and silicates of lead and other metals contained in the ore. Lead oxide from the roasting process is reduced in a coke-fired blast furnace. Three additional layers separate in the process and float to the top of the metallic lead. These are slag silicates containing 1.
These wastes contain concentrations of copper, zinc, cadmium, and bismuth that can be recovered economically, as can their content of unreduced lead. Metallic lead that results from the roasting and blast furnace processes still contains significant contaminants of arsenic, antimony, bismuth, zinc, copper, silver, and gold.
The melt is treated in a reverberatory furnace with air, steam, and sulfur, which oxidizes the contaminants except silver, gold, and bismuth. The oxidized contaminants are removed by drossing, where they float to the top and are skimmed off. Most lead ores contain significant concentrations of silver, resulting in the smelted metal also containing silver as a contaminant.
Metallic silver as well as gold is removed and recovered economically by means of the Parkes process. Desilvered lead is freed of bismuth according to the Betterton-Kroll process by treating it with metallic calcium and magnesium, which forms a bismuth dross that can be skimmed off. Very pure lead can be obtained by processing smelted lead electolytically by means of the Betts process. The process uses anodes of impure lead and cathodes of pure lead in an electrolyte of silica fluoride.
Worldwide production and consumption of lead is increasing. Total annual production is about 8 million tonnes; about half is produced from recycled scrap. The main countries are Australia, China and the US, which account for more than half of primary production. The most common lead ore is galena or lead sulfide. At current use rates, the supply of lead is estimated to run out in 42 years.
Lead is a poisonous metal that can damage nervous connections especially in young children and cause blood and brain disorders. Long term exposure to lead or its salts especially soluble salts or the strong oxidant PbO 2 can cause nephropathy, and colic-like abdominal pains.
The concern about lead's role in cognitive deficits in children has brought about widespread reduction in its use lead exposure has been linked to schizophrenia.
Most cases of adult elevate blood lead levels are workplace-related. Older houses may still contain substantial amounts of lead paint. White lead paint has been withdrawn from sale in industrialized countries, but the yellow lead chromate is still in use; for example, Holland Colours Holcolan Yellow.
Old paint should not be stripped by sanding, as this produces inhalable dust. Lead salts used in pottery glazes have on occasion caused poisoning, when acid drinks, such as fruit juices, have leached lead ions out of the glaze. Lead is considered to be particularly harmful for women's ability to reproduce. For that reason, many universities do not hand out lead-containing samples to women for instructional laboratory analyses. Lead as a soil contaminant is a widespread issue, since lead is present in natural deposits and may also enter soil through leaded gasoline leaks from underground storage tanks or through a wastestream of lead paint or lead grindings from certain industrial operations.
Inhibition of both these steps results in ineffective heme synthesis and subsequent microcytic hemoglobin -poor anemia. It is clear from the Pourbaix diagram below that lead is more likely to corrode in a citrate medium than it is in a non-complexing medium. Gold, for example, was associated with the Sun due to its colour and value.
Lead was the least desirable of the ancient metals due to its dull grey colour and heaviness, so it was associated with Saturn — the furthest of the known planets. Fast forward to the Middle Ages, and lead became an object of great interest to alchemists. Alchemy was a mix of chemistry and philosophy that sought to turn lead into gold. Alchemists thought that all metals were made of the same substance, but metals like lead were spiritually and physically immature forms of the higher metals.
With refinement, lead could become spiritually perfect just like gold. Even famous scientists like Sir Isaac Newton dabbled in alchemy.
It this era of modern science, the historical mix of science, philosophy and religion may appear unusual. All scientific knowledge is produced within a larger society and culture. The tentative scientific knowledge of ancient and classical civilisations was influenced by cultural aspects of the time.
As new information was discovered, the old ways of thinking were discarded. Lead is usually found as an ore — in combination with other elements such as silver.
This type of ore has a low melting point so it was relatively easy to smelt, and lead became a byproduct of the more valuable silver. Humans have been making items from lead for around 9, years. The ancient Egyptians and Greeks used lead in cosmetics, glass and enamels.
Other early civilisations used lead to make coins, as a writing material and for medicinal purposes. During the Middle Ages, lead was commonly used in roofing and piping due to its malleability and durability. In , builders used tonnes of thin lead panels to cover the roof of Notre Dame Cathedral, and later tonnes went into its spire. Rectifying properties were discovered at metal—galena point contacts by F. Braun in 3. In J. Bose detected an electromagnetic wave using galena — a key event for the development of the radio 4.
Infrared detectors based on lead chalcogenides that is, sulfides, selenides and tellurides represented a major advance in infrared technology, for example for night vision and for the spectroscopic analytical techniques that are now available to chemists.
Lead chalcogenides are also characterized by low direct-bandgaps, which change depending on the sizes of the crystallites and cover a broad spectral range — a phenomenon called the quantum confinement effect, which forms the basis for devices such as field-effect transistors, solar cells and photodetectors. The widespread production and consumption of lead continued until the twentieth century, through uses in petrol, lead-acid batteries, paint, radiation shielding and in the polyvinyl plastic industry as a stabilizer.
However, humans are susceptible to lead poisoning by either acute or, more often, chronic exposure. Lead accumulates in the body and interferes with various processes, resulting in neurotoxic effects with a variety of symptoms. Even as far back as the Roman period maladies were correlated with lead, through the use of 'lead sugar' lead acetate beverages and pipes for water supply. Yet these early warnings were not acted on until the mid-twentieth century, from which point the use of lead started being closely monitored in many countries — resulting in measures such as bans from petrol and paint.
Fortunately, lead poisoning can now be treated with chelating agents typically ethylene diamine tetraacetate , using their greater affinity to the heavy metal to form complexes that can be expelled from the body.
Sadly it is estimated that, at current use rates, the metal we've relied on for thousands of years will run out in about four decades. A more positive side of this situation is that these developments are generating renewed interest in recycling and thoughtful progress in fuel-cell technology. Mellor, J. Google Scholar.
Rochow, E. Braun, F. Rogalski, A. Download references. You can also search for this author in PubMed Google Scholar. Correspondence to Somobrata Acharya.
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