Gold is a chemical element with the symbol Au (from Latin: aurum ) and the atomic number 79, making it one of the higher element of the atomic number that occurs naturally. In its purest form, it is a yellow, reddish, solid, soft, soft, and soft metal. Chemically, gold is a transition metal and a group element 11. It is one of the least reactive and solid chemical elements under standard conditions. Gold often occurs in the form of free (original) elements, such as nuggets or grains, in rocks, in blood vessels, and in alluvial deposits. It occurs in a solid solution circuit with the original elemental silver (as an electrum) and is also naturally mixed with copper and palladium. Less commonly, it occurs in minerals as a gold compound, often with telluride (gold telluride).
Gold is resistant to most acids, although dissolving in aqua regia, a mixture of nitric acid and hydrochloric acid, which forms dissolved tetrachloroatic anions. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to purify gold and to confirm the existence of gold in metallic objects, giving rise to the term acid test . Gold is also soluble in alkali cyanide solution, which is used in mining and electroplating. Gold dissolves in mercury, forming an amalgam alloy, but this is not a chemical reaction.
A relatively rare element, gold is a precious metal that has been used for coins, jewelry, and other arts throughout recorded history. In the past, the gold standard was often implemented as a monetary policy, but gold coins stopped being printed as the currency in circulation in the 1930s, and the world gold standard was abandoned for the fiat currency system after 1971.
A total of 186,700 tons of gold is on the ground, by 2015. The new gold-world consumption generated is about 50% in jewelry, 40% in investment, and 10% in industry. High flexibility, tenacity, corrosion resistance and most other chemical reactions, and electrical conductivity have led to their continued use in corrosion-resistant electrical connectors in all types of computer devices (the main industrial use). Gold is also used in infrared shields, colored glass production, gold leaf, and dental restorations. Certain gold salts are still used as anti-inflammatories in medicine. In 2016, the largest gold producer in the world so far is China with 450 tons per year.
Video Gold
Characteristics
Gold is the most easily formed of all metals; one gram can be beaten into a sheet of 1 square meter, and an avoirdupois to 300 square feet. Gold leaf can be beaten thin enough to be semi-transparent. The transmitted light looks turquoise blue, because gold is very reflective in yellow and red. Such semi-transparent sheets also strongly reflect infrared rays, making them useful as infrared shields (heat radiation) in a heat resistant protective clothing, and on sun visors for space clothing. Gold is a good conductor of heat and electricity.
Gold has a density of 19.3 g/cm 3 , almost identical to tungsten at 19.25 g/cm 3 ; thereby, tungsten has been used in counterfeiting of gold bars, such as by tungsten rods with gold, or taking existing gold bars, drilling holes, and replacing removed gold with tungsten rods. For comparison, the lead density is 11.34 g/cm 3 , and that of the densest element, osmium, is 22,588 Â ± 0.015 g/cm 3 .
Color
While most of the metal is gray or silvery white, gold is slightly reddish-yellow. This color is determined by the frequency of plasma oscillations among the valence electrons of the metal, in the ultraviolet range for most of the metal but in the visible range for gold because of the relativistic effect affecting the orbital around the gold atoms. A similar effect gives the gold color to the metallic cesium.
Common colored gold alloys include eighteen-carat gold roses made by the addition of copper. Alloys containing palladium or nickel are also important in commercial jewelry because they produce white gold alloys. The fourteen-carat gold-copper alloy is almost identical in color to a particular bronze alloy, and both can be used to produce police and other badges. White gold alloys can be made with palladium or nickel. Fourteen and eighteen carat gold alloys with silver alone look yellow-green and are referred to as green gold. Blue gold can be made with alloys with iron, and purple gold can be made with alloys with aluminum. Less commonly, the addition of manganese, aluminum, indium and other elements can produce more unusual gold colors for various applications.
Colloidal gold, used by electrons-microscopists, is red if the particles are small; bigger colloidal gold particles are blue.
Isotope
Gold has only one stable isotope, 197
Au , which is also the only natural isotope, so gold is a mononuclear element and monoisotop. Thirty-six radioisotopes have been synthesized starting in atomic masses from 169 to 205. The most stable is the 195 Au with a half-life of 186.1 days. The most stable is the 171 Au , which decays by proton emissions with a half-life of 30 Ã,Âμs. Most of the gold radioisotopes with atomic mass under 197 decays by some combination of proton emissions ,? decay, and decay . The exceptions are 195 Au , which decays by capturing the electrons, and 196
Au , which decays most often by electron capture (93%) with minor soup paths - (7%). All of the gold radioisotopes with atomic mass above 197 decompose with decay - .
At least 32 nuclear isomers have also been characterized, ranging in atomic mass from 170 to 200. In that range, only 178
, 180 181 Au , 182 >
Au , and 188 The Au does not have an isomer. The most stable isomers of Gold are 198m2 Au with a half-life of 2.27 days. The most stable gold isomer is 177m2 /span> with half-life of only 7 seconds. Synthesis
The production of gold from more general elements, such as lead, has long been the subject of human investigation, and ancient and medieval alchemical disciplines often focus on it; However, the transmutation of chemical elements did not become possible until the understanding of nuclear physics in the 20th century. The first synthesis of gold was performed by Japanese physicist Hantaro Nagaoka, who synthesized gold from mercury in 1924 with neutron bombing. An American team, working without prior knowledge of Nagaoka's previous studies, conducted the same experiment in 1941, achieved similar results and showed that the gold isotopes generated by it are all radioactive.
The current gold can be produced in nuclear reactors with irradiation either from platinum or mercury.
Only mercury isotopes 196 Hg, occurring with a frequency of 0.15% in natural mercury, can be converted to gold by neutron capture, and after the electron-decay capture to 197 Au by slow neutrons. Other mercury isotopes are converted when irradiated with slow neutrons into one another, or forming mercury isotopes of beta decay into thallium.
Using fast neutrons, the mercury isotope 198 Hg, which makes up 9.97% of natural mercury, can be converted by separating the neutrons and into 197 Hg, which then breaks down into stable gold. This reaction, however, has a smaller activation cross-section and can only be done with unmoderated reactors.
It is also possible to expel some very high energy neutrons to other mercury isotopes to form 197 Hg. However, such high-energy neutrons can only be produced by particle accelerators.
Maps Gold
Chemistry
Although gold is the noblest of precious metals, it still forms many diverse compounds. The oxidation state of gold in its compounds ranges from -1 to 5, but Au (I) and Au (III) dominate chemistry. Au (I), referred to as aurous ions, is the most common oxidizing state with soft ligands such as thioether, thiolate, and tertiary phosphine. Au (I) compounds are usually linear. A good example is Au (CN) 2 - , which is the golden soluble form encountered in mining. Binary halide gold, like AuCl, forms a zigzag polymer chain, again showing linear coordination in Au. Most of the drugs based on gold are Au (I) derivatives.
Au (III) (auric) is a general oxidation state, and illustrated by gold (III) chloride, Au 2 Cl 6 . The center of gold atoms in the Au (III) complex, like other d 8 compounds, is usually rectangular, with chemical bonds that have both covalent and ionic characters.
Gold does not react with oxygen at any temperature and, up to 100 ° C, is resistant to attack from ozone.
Some halogens are free to react with gold. Gold is heavily stricken by fluorine in red-red heat to form gold (III) fluoride. The gold powder reacts with chlorine at 180 ° C to form AuCl 3 . Gold reacts with bromine at 140 ° C to form gold (III) bromide, but only reacts very slowly with iodine to form monoiodide.
Gold does not react with sulfur directly, but gold (III) sulphide can be prepared by passing hydrogen sulfide through a dilute solution of gold (III) chloride or chlorauric acid.
Gold is readily soluble in mercury at room temperature to form amalgam, and forms alloys with many other metals at higher temperatures. These alloys can be produced to modify hardness and other metallurgical properties, to control melting point or to create exotic colors.
Gold reacts with potassium, rubidium, cesium, or tetramethylammonium, to form auride salts respectively, containing Au - ions. Cesium auride is probably the most famous.
Gold is not affected by most acids. It does not react with hydrofluoric, hydrochloric, hydrobromic, hydriodic, sulfuric, or nitric acid. It reacts with selenic acid, and is dissolved by aqua regia, a mixture of 1: 3 nitric acid and hydrochloric acid. Nitric acid oxidizes metals into 3 ions, but only in small amounts, usually undetectable in pure acids because of the chemical equilibrium of the reaction. However, the ions are removed from equilibrium by hydrochloric acid, forming AuCl 4 - ion, or chloroauric acid, thus allowing further oxidation.
Gold is also unaffected by most bases. It does not react with dilute sodium or potassium hydroxide, solid, or liquid. However, it reacts with sodium or potassium cyanide under alkaline conditions when oxygen is present to form a soluble complex.
Common oxidation states of gold include 1 (gold (I) or aurous compounds) and 3 (gold (III) or aurat compounds). The gold ions in the solution are easily reduced and precipitated as metals by adding other metals as reducing agents. The added metal is oxidized and dissolved, allowing gold to be removed from the solution and recovered as a solid precipitate.
Rare oxidation conditions
Less common gold oxidation states include -1, 2, and 5.
The oxidation state -1 occurs in compounds containing an Au - anion, called aurides. Cesium auride (CsAu), for example, crystallizes in the cesium chloride motif. Other aurics include from Rb , K , and tetramethylammonium (CH 3 ) 4 N . Gold has the highest Pauling electronegativity of any metal, with a value of 2.54, making auride anuride relatively stable.
Gold (II) compounds are usually diamagnetic with Au-Au bonds such as [Au (CH 2 ) 2 P (C 6 H 5 ) 2 ] 2 Cl 2 . Evaporation solution Au (OH)
3 concentrated H
2 SO < In line: vertical-align: baseline "> 4 produces red gold crystal (II) sulfate, Au 2 (SO 4 ) 2 . Originally considered a valence-blending compound, it has been shown to contain Au 4
< sub-type cater, analogous to better-known mercury (I) ions, in-line, Hg 2
2 . A complex (II), tetraxenonogold (II) cation, containing xenon as ligand, occurs in [AuXe 4 ] (Sb 2 F 11 ) 2 .
Pentafluoride gold, along with its derived anions, AuF - 6 , and the diffluorine complex, gold heptafluoride, is the only gold example (V) , the highest verified oxidation state.
Some gold compounds show
Cluster compounds are very much defined. In such a case, gold has a fractional oxidation state. Representative examples are octahedral species {} (< 5 ) 3 )} 6 2 . The golden Chalcogenides, such as gold sulphide, display the same Au (I) and Au (III) amounts.
Medical use
The gold and complex medical applications have a long history for thousands of years. Some gold complexes have been used to treat rheumatoid arthritis, the most commonly used are: aurothiomalate, aurothioglucose, and auranofin. Both gold (I) and gold (III) compounds have been investigated for possible anti-cancer drugs. For complex gold (III), the reduction to gold (0/I) under physiological conditions should be considered. Stable complexes can be produced by using different types of high bi-, tri-, and tetradentate ligand systems that have been demonstrated in vitro and in vivo.
Origins
The theory of celestial origin
Gold is thought to have been produced in the nucleosynthesis of supernovae, and from the collision of neutron stars, and has been present in the dust from which the Solar System was formed. Since the Earth has melted when it is formed, almost all the gold that is on the early Earth may sink to the planet's core. Therefore, most of the gold that is in the earth's crust and mantle is thought to have been sent to Earth later, by asteroid impact during the Late Weight bombardment, some 4 billion years ago.
Traditionally, gold is thought to have been formed by a r-process (fast neutron capture) in supernova nucleosynthesis, but it has recently been suggested that gold and other elements heavier than iron can also be produced in quantity by the r-process in a collision neutron star. In both cases, the satellite spectrometer only indirectly detects the resulting gold: "we have no spectroscopic evidence that the [elements] have actually been produced," wrote author Stephan Rosswog. However, in August 2017, heavy elemental signs, including gold, were observed by gravitational wave detectors and other electromagnetic observatories in the event of a GW170817 neutron star merger. The current astrophysical model shows that the incident of merging a single neutron star generated between 3 and 13 Earth gold masses.
The asteroid that formed the Vredefort crater 2.020 billion years ago is often credited with the Witwatersrand basin hatchery in South Africa with the richest gold deposits in the world. However, Witwatersrand's gold-bearing rocks were laid between 700 and 950 million years before the impact of Vredefort. This golden rock has been covered by a thick layer of Ventersdorp lava and Supergroup Transvaal rocks before the meteor struck. What the impact Vredefort achieved, however, was to distort the Witwatersrand basin in such a way that the gold bearing rocks were brought to the surface of the current erosion in Johannesburg, at Witwatersrand, just inside the crater edge of the original 300 km diameter caused by the meteor strike. The discovery of the deposit in 1886 launched the Witwatersrand Gold Rush. About 22% of all gold that is currently available on Earth has been extracted from this Witwatersrand rock.
Earth origin
In 2017, a group of international scientists, including JosÃÆ'Â © Ã © MarÃÆ'a GonzÃÆ'¡lez JimÃÆ'Â © nez and RamÃÆ'³n y Cajalan, in collaboration with the University of Granada and other universities, while researching the origins of gold, have historically established that "come to the Earth's surface from the deepest regions of our planet, "evidenced by their findings at Massif Deseado in Patagonia Argentina.
Genesis
On Earth, gold is found in the ore in the rock formed from the time of Precambrian onward. This most often occurs as an original metal, usually in a solid solution of metal with silver (ie as a gold silver alloy). Such alloys usually have an 8-10% silver content. Electrum is a gold element with over 20% silver. Electrum colors run from gold-silver to silver, depending on the silver content. The more silver, the lower the specific gravity.
Original gold occurs because it is very small for microscopic particles embedded in rocks, often together with quartz or sulphide minerals such as "Fool's Gold", which is pyrite. This is called a lode deposit. The metal in the original state is also found in the form of free flakes, seeds or larger nuggets that have been eroded from the rock and ends in alluvial deposits called placer deposits. Such free gold is always richer on the surface of the golden bearing veins because of accompanying mineral oxidation followed by weathering, and the washing of dust into rivers and streams, where it collects and can be welded by the action of water to form nuggets.
Gold sometimes occurs in combination with tellurium as mineral calaverite, krennerite, nagyagite, petzite and sylvanite (see telluride minerals), and as a rare bismuthide malidite (Au 2 Bi) and antimonide aurostibite (AuSb 2 ). Gold also occurs in rare mixtures with copper, lead, and mercury: mineral auricupride (Cu 3 Au), novodneprite (AuPb 3 ) and weishanite ((Au, Ag) sub> 3 Hg 2 ).
Recent research has shown that microbes can sometimes play an important role in forming gold deposits, transporting and depositing gold to form grains and nuggets that collect in alluvial deposits.
Another recent study claimed water in a volatile error during an earthquake, saving gold. When an earthquake strikes, it moves along the fracture. Water often lubricates faults, fills and jogs. About 6 miles (10 kilometers) below the surface, under extraordinary temperatures and pressures, water carries a high concentration of carbon dioxide, silica, and gold. During an earthquake, jogging errors suddenly open wide. The water in the vacuum instantly evaporates, flickers into vapor and forces silica, which forms mineral quartz, and gold comes out of the liquid and to the nearest surface.
Sea Water
The world's oceans contain gold. The measured gold concentrations in the Atlantic and the Northeast Pacific are 50-150 femtomol/L or 10-30 parts per quadrillion (about 10-30 g/km 3 ). In general, gold concentrations for the south Atlantic and middle Pacific samples are the same (~ 50 femtomol/L) but less certain. The deep Mediterranean waters contain slightly higher gold concentrations (100-150 femtomol/L) associated with dust and/or wind-blown streams. At 10 parts per quadrillion the Earth's oceans will have 15,000 tons of gold. These figures are three orders of magnitude smaller than those reported in the literature before 1988, suggesting contamination problems with previous data.
Some people claim to be able to recover gold economically from seawater, but they are wrong or act in deliberate deception. Prescott Jernegan run a gold-of-the-sea con artist in the United States in the 1890s, as did a British con artist in the early 1900s. Fritz Haber undertook research on the extraction of gold from seawater in an effort to help pay for German reparations after World War I. Based on the published value of 2 to 64 ppb of gold in seawater, commercially successful extraction is likely to be possible. After analysis of 4,000 water samples yielding an average of 0.004 ppb it became clear that extraction would not be possible and he stopped the project.
History
The golden artifacts found in the Nahal Kana cave cemetery dated during the 1980s show this originated in the Chalcolithic, and is considered the earliest discovery of the Levant. Gold artifacts in the Balkans also emerged from the 4th millennium BC, as found in the Varna Necropolis near Lake Varna in Bulgaria, considered by one source (La Niece 2009) to be the earliest and "ancient" golden discovery. Gold artifacts such as gold hats and Nebra discs appeared in Central Europe from the 2nd century BC Bronze Age.
The oldest map of the gold mine was taken in 19 Ancient Egyptian Dynasties (1320-1200 BC), while the first written reference to gold was recorded in the 12th Dynasty around 1900 BC. Egyptian hieroglyphs from as early as 2600 BC illustrate gold, which is claimed by King Tushratta of Mitanni is "more than dung" in Egypt. Egypt and especially Nubia have the resources to make them the main gold producing region for much of history. One of the earliest known maps, known as the Turin Papyrus Map, shows a gold mine plan in Nubia along with local geological indications. The primitive method of work is described by Strabo and Diodorus Siculus, and includes the setting of fire. Large mines are also present in the Red Sea in what is now Saudi Arabia.
Gold is mentioned in the letter Amarna numbered 19 and 26 from around the 14th century BC.
The golden feather legend may refer to the use of sweaters to trap gold dust from placer deposits in the ancient world. Gold is often mentioned in the Old Testament, beginning with Genesis 2:11 (in Havilah), the story of the Golden Cow and many parts of the temple including the Menorah and the gold altar. In the New Testament, it includes the gift of the wise men in the first chapter of Matthew. The book of Revelation 21:21 describes the city of New Jerusalem as the streets "made of pure gold, clear as crystal". The exploitation of gold in the southeast corner of the Black Sea is said to date from the Midas period, and gold is important in the formation of what was probably the world's earliest currency in Lydia around 610 BC. From the 6th or 5th century BC, Chu (the state) circulated Ying Yuan, a type of square gold coin.
In Roman metallurgy, new methods for extracting large-scale gold were developed by introducing hydraulic mining methods, especially in Hispania from 25 BC onwards and in Dacia from 106 AD. One of their largest mines is at Las Medulas in LeÃÆ'³n, where seven long waterways allow them to drain most of the large alluvial deposits. Mine on Ro? Is it Montan? in Transylvania is also very large, and until now, still mined by opencast method. They also exploit smaller deposits in the UK, such as placers and hard-rock deposits in Dolaucothi. The various methods they used were well explained by Pliny the Elder in his encyclopedia Naturalist Historia written towards the end of the first century AD.
During Mansa Musa (ruler of the Mali Empire from 1312 to 1337) pilgrimage to Mecca in 1324, he passed through Cairo in July 1324, and was reportedly accompanied by camel trains covering thousands of people and nearly a hundred camels in which he gave so much oppressive gold prices in Egypt for more than a decade, causing high inflation. A contemporary Arab historian commented:
Gold was at high prices in Egypt until they came in that year. The mithqal does not go under 25 dirhams and is generally above, but since then the value is down and its price is cheap and it remains cheap until now. Mithqal does not exceed 22 dirham or less. It has been a problem for about twelve years to this day on the basis of the amount of gold they bring to Egypt and spend it there [...].
European explorations in America are encouraged not least by reports of gold ornaments that are displayed very much by Native Americans, especially in Mesoamerica, Peru, Ecuador, and Colombia. The Aztecs regarded gold as the product of the gods, calling it a "goddish" ( teocuitlatl in Nahuatl), and after Moctezuma II was killed, much of this gold was sent to Spain. However, for North American natives, gold is considered useless and they see much greater value in other minerals directly related to its usefulness, such as obsidian, flint, and slate. Rumors of cities are filled with El Dorado gold legend.
Gold plays a role in western culture, as a cause of desire and corruption, as told in the fairy tales of children like Rumpelstiltskin - where Rumpelstiltskin turns straw into gold for the farmer's daughter in return for her child when she becomes a princess - and the theft of the spawning chickens gold in Jack and the Beanstalk.
The main prize at the Olympics and many other sports competitions is the gold medal.
75% of the current gold has been extracted since 1910. It is estimated that the amount of gold currently known internationally will form a single cube of 20 m (66 ft) on the side (equivalent to 8,000 m 3 ).
One of the primary goals of alchemists is to produce gold from other substances, such as lead - perhaps by interaction with mythical substances called philosopher stones. Although they have never succeeded in this effort, the alchemists are indeed interested in systematically figuring out what can be done with substances, and this lays the groundwork for today's chemistry. Their symbol for gold is a circle with a dot in the middle (?), Which is also a symbol of astrology and ancient Chinese characters for the Sun.
Gold treasures have been rumored to be found in various locations, following tragedies such as the treasure of a Jewish temple in the Vatican, after the destruction of the temple in 70 AD, the gold deposit in the Titanic, the Nazi golden carriage after World War II.
The Dome of the Rock is covered with a very thin gold glaze. The Sikh Emas Temple, Harmandir Sahib, is a building covered by gold. Similarly the emerald Wat Phra Kaew Buddha temple in Thailand has statues and gold ornamental roofs. Some of the European kings and queen crowns are made of gold, and gold is used for the bride's crown since antiquity. An ancient Talmudic text of about 100 AD describes Rachel, the wife of Rabbi Akiva, receiving "Jerusalem of Gold" (diadem). A Greek cemetery crown made of gold was found in a cemetery around 370 BC.
Etymology
"Gold" is a word of a word with similar words in many Germanic languages, derived through Proto-Germanic * gulÃÆ'¾? from Proto-Indo-European * ?? elh? - ("to shine, shine, to yellow or green").
The Au symbol is from Latin: aurum , the Latin word for "gold". The Proto-Indo-European ancestor of aurum is * h? ÃÆ' Â © -h? Us-o - , which means "shine". This word comes from the same root (Proto-Indo-European * h? U? Es - "up to dawn") as * h? ÃÆ' Â © u? S? S , the ancestor of the Latin word Aurora, "dawn". This etymological relationship may be behind the frequent claim in scholarly publications that aurum means "shining dawn".
Culture
Great human accomplishments are often rewarded with gold, in the form of gold medals, gold trophies and other decorations. Winners of athletic events and other storied competitions are usually awarded gold medals. Many awards such as the Nobel Prize are made of gold as well. Sculptures and other award prizes are depicted in gold or gold-plated (such as Academy Awards, Golden Globe Awards, Emmy Awards, Palme d'Or, and British Academy Film Awards).
Aristotle in ethics uses gold symbolism when referring to what is now known as the gold mean. Likewise, gold is associated with perfect or divine principles, as in terms of gold ratio and golden rule.
Gold is further linked to the wisdom of aging and yield. The fiftieth wedding anniversary is gold. The most precious or most successful last years are sometimes considered "golden years". The height of civilization is called the golden age.
In some forms of Christianity and Judaism, gold has been associated with holiness and evil. In the Book of Exodus, the Golden Calf is a symbol of idolatry, while in the Book of Genesis, Abraham is said to be rich in gold and silver, and Moses was commanded to cover the Blessing Chair of the Ark of the Covenant with pure gold. In Byzantium's iconography, the circle of light of Christ, Mary, and Christian saints are often gold.
According to Christopher Columbus, those who have something gold have something of great value on Earth and the substance to even help the soul to heaven.
The wedding rings are made of gold. It lasts long and is unaffected by the passing of time and can help in the symbolism of eternal oaths in the presence of God and the perfection of marriage. In the Orthodox Christian marriage ceremony, a pair of couples decorated with gold crowns (though some choose the wreath, on the contrary) during the ceremony, an amalgamation of the symbolic ceremony.
Production
The World Gold Council states that by the end of 2017, "there are 187,200 tons of stocks on the ground". It can be represented by a cube with an edge length of about 21 meters. At $ 1,349 per troy ounce, 187,200 metric tons of gold will have a value of $ 8.9 trillion.
In 2017, the largest gold producer in the world so far is China with 455 tons. The second largest producer, Australia, mined 270 tons in the same year, followed by Russia with 250 tons.
Mine and search for leads
Since the 1880s, South Africa has been the source of most of the world's gold supply, and about 50% of the gold currently recorded comes from South Africa. Production in 1970 accounted for 79% of the world's supply, about 1,480 tons. In 2007 China (with 276 tons) took over South Africa as the world's largest gold producer, the first time since 1905 that South Africa has not yet become the largest.
In 2014, China is a leading gold mining country in the world, followed by Australia, Russia, the United States, Canada, and Peru. South Africa, which has dominated world gold production for much of the 20th century, has declined to sixth place. Other major producers are Ghana, Burkina Faso, Mali, Indonesia, and Uzbekistan.
In South America, the Pascua Lama controversial project aims to exploit rich fields in the high mountains of the Atacama Desert, on the border between Chile and Argentina.
Currently about one quarter of the world's gold output is estimated to come from small-scale or artisanal mining.
The city of Johannesburg, located in South Africa, was established as a result of the Witwatersrand Gold Rush which resulted in the discovery of some of the largest natural gold deposits recorded in history. The gold fields are limited to the north and northwest sides of the Witwatersrand basin, which is a 5-7 km thick layer located, in many places, far below Free State, Gauteng and surrounding provinces. These Witwatersrand rocks are exposed on the surface at Witwatersrand, in and around Johannesburg, but also in remote patches in southeast and southwest Johannesburg, as well as bows around the Vredefort Dome located near the center of the Witwatersrand basin. From this surface exposure the dips basin is extensive, requiring some mining to occur in depths of nearly 4000 m, making them, especially the Savuka mine and TauTona to the southwest of Johannesburg, the deepest mine on earth. Gold is found only in six areas where arcade rivers from the north and north-west form the widely-flooded delta of the river before it is flowed to the "Witwatersrand sea" where the remaining deposits of Witwatersrand are deposited.
The Second Boer War of 1899-1901 between the British Empire and the Afrikaner Boers was at least partly on the rights of miners and possession of gold in South Africa.
During the 19th century, gold rush occurred whenever large gold deposits were discovered. The first documented discovery of gold in the United States was at Reed Gold Mine near Georgeville, North Carolina in 1803. The first major gold strike in the United States occurred in a small town in northern Georgia called Dahlonega. Further Gold rush takes place in California, Colorado, Black Hills, Otago in New Zealand, Australia, Witwatersrand in South Africa, and Klondike in Canada.
Extraction and Purification
The most economical gold extraction in large deposits, easily mined. The value of ore as small as 0.5 parts per million (ppm) can be economical. The typical ore grades in the open pit are 1-5Ã, Â £ ppm; ore content in underground or hard rock mines is usually at least 3 ppm. Since 30 ppm ore content is usually required before gold is seen with the naked eye, in most gold mines, gold is not visible.
The average gold mining and extraction costs were approximately $ 317 per troy ounce in 2007, but this can vary greatly depending on the type of mining and ore quality; global mining production amounted to 2,471.1 tons.
After initial production, gold is often then refined industrially by the Wohlwill process based on electrolysis or the Miller process, ie chlorination in the melt. The Wohlwill process results in higher purity, but is more complex and is only applied in small-scale installations. Other methods to test and refine smaller amounts of gold include separation and inquartation and cupellation, or purification methods based on gold dissolution in aqua regia.
Consumption
The consumption of gold produced in the world is about 50% in jewelry, 40% in investment, and 10% in industry.
According to the World Gold Council, China is the world's largest gold consumer in 2013 and toppled India for the first time with China's consumption up 32 percent annually, while India only rose 13 percent and world consumption rose 21 percent. Unlike India where gold is mainly used for jewelry, China uses gold for manufacturing and retailing.
Pollution
Gold production is associated with a contribution to harmful pollution.
Low grade gold ores may contain less than one ppm of gold metal; Such ore is milled and mixed with sodium cyanide to dissolve gold. Cyanide is a highly toxic chemical, which can kill living things when exposed in small amounts. Many of the cyanide spills from gold mines have occurred in developed and developing countries that kill aquatic life in a vast river. Environmentalists consider this event to be a major environmental disaster. Thirty tons of ore used are disposed of as waste to produce one troy ounce of gold. Gold ore deposits are the source of many heavy elements such as cadmium, lead, zinc, copper, arsenic, selenium and mercury. When the sulphide-bearing minerals in the ore disposal are exposed to air and water, the sulfides turn into sulfuric acid which in turn dissolves these heavy metals facilitating their travel to surface water and ground water. This process is called mine acid drainage. This gold ore jetty is a very dangerous long-term waste, which only occupies a nuclear waste dump.
It used to be a common use of mercury to regain gold from ores, but now the use of mercury is largely confined to small-scale individual miners. Small amounts of mercury compounds can reach the body of water, causing heavy metal contamination. Mercury can then enter the human food chain in the form of methylmercury. Mercury poisoning in humans causes impaired brain function and severe retardation.
Gold extraction is also a very energy intensive industry, extracting ore from deep mines and grinding large quantities of ore for further chemical extraction requires nearly 25 kW/h of electricity per gram of gold produced.
Monetary use
Gold has been widely used throughout the world as money, for efficient indirect exchange (versus barter), and for storing wealth in hoards. For the purpose of exchange, candy produces standard gold bullion bars, bars and fixed weight units and other purity.
The first coins known to contain gold were beaten in Lydia, Asia Minor, around 600 BC. The gold aptitude coin used during the period of Greek history both before and during Homer's lifetime was weighed between 8.42 and 8.75 grams. From previous preference in using silver, the European economy re-established gold as a coin during the thirteenth and fourteenth centuries.
Bills (which are due to be gold coins) and gold certificates (can be converted into gold coins in issuing banks) are added to the gold standard money supply in most of the nineteenth-century industrialized countries. In preparation for World War I the warring countries moved into fractional gold standards, inflated their currency to finance the war effort. After the war, the winning countries, especially the British, gradually restored the convertibility of gold, but the international flow of gold through the exchange bill remained embargoed; international shipments are made exclusively for bilateral trade or to pay for war reparations.
After World War II, gold was replaced by a nominally convertible currency system linked to a fixed exchange rate following the Bretton Woods system. The gold standard and the convertibility of direct currency into gold have been abandoned by the world government, led in 1971 by the United States's refusal to redeem dollars in gold. Fiat currency now fills most of the monetary role. Switzerland is the last country to bind its currency with gold; it supported 40% of its value until Switzerland joined the International Monetary Fund in 1999.
Central banks continue to keep some of their liquid reserves as gold in some form, and metal exchanges such as the London Bullion Market Association are still clear transactions in gold, including future delivery contracts. Currently, gold mining output is declining. With sharp economic growth in the 20th century, and an increase in foreign exchange, the world's gold reserves and their trading markets have become small fractions of all markets and the exchange rate of fixed currency into gold has been replaced by floating prices for gold and gold. future contracts. Although gold stocks only grow 1 or 2% per year, very little metal is consumed irreversibly. The above ground inventory will satisfy many decades of industrial use and even craftsmen at current prices.
The proportion of gold (grain) of alloy is measured by rust (k). Pure gold (commercially called fines gold) is designated as 24 carats, abbreviated to 24k. The British gold coins intended for circulation from 1526 to the 1930s are usually a standard 22k alloy called the golden crown, for hardness (American gold coins for circulation after 1837 containing 0.900 pure gold alloys, or 21.6 kt).
Although the price of some platinum group metals could be much higher, gold has long been regarded as the most desirable precious metal, and its value has been used as the standard for many currencies. Gold has been used as a symbol for purity, value, royalty, and especially the role that incorporates these qualities. Gold as a sign of wealth and prestige was ridiculed by Thomas More in his treatise Utopia . On the imaginary island, gold is so abundant that it is used to make chains for slaves, cutlery, and latrines. When the ambassadors from other countries arrive, wearing fine gold jewelry and badges, Utopian people think of them as rude servants, paying homage to their simplest party dress.
The golden code of ISO 4217 is XAU. Many gold holders keep it in the form of coins or bullion bars as a hedge against inflation or other economic disruptions. Modern bar coins for investment or collector purposes do not require good mechanical wear properties; they are usually pure gold at 24k, although American Gold Eagle and British gold sovereignty continue to be printed in 22k metal (0.92) in historical tradition, and Krugerrand South Africa, which was first released in 1967, also 22k (0.92).
The special issue The Canadian Gold Maple Leaf coin contains gold with the highest purity of bar coins, with 99.999% or 0.99999, while the popular issue Maple Gold Leaf Canada coins has a purity of 99 , 99%. In 2006, the United States Mint started producing Buffalo American bullion coins with a purity of 99.99%. Gold Kangaroos Australia was first created in 1986 as the Australian Gold Nugget but changed the reverse design in 1989. Other modern coins include the Vienna Viennese Philharmonic bullion coin and the Chinese Golden Panda.
Price
In September 2017, gold is worth about $ 42 per gram ($ 1,300 per troy ounce).
Like other precious metals, gold is measured by weight and by grams. The proportion of gold in alloys was measured by carat (k), with 24 carats (24k) to pure gold, and less proportionately lower rust numbers. The purity of gold bars or coins can also be expressed as decimal numbers ranging from 0 to 1, known as royal smoothness, such as almost pure 0.995.
The price of gold was determined through trade in the gold and derivatives markets, but the procedure known as Gold Fixing in London, originating in September 1919, provided daily benchmark prices to the industry. The afternoon improvements were introduced in 1968 to provide a price when the US market is opened.
History
Historically gold coins are widely used as currency; when paper money is introduced, it is usually a receipt that can be exchanged for gold coin or gold bullion. In a monetary system known as the gold standard, certain gold weights are given the name of the unit of currency. For the long term, the United States government set the value of the US dollar so a troy ounce was equal to $ 20.67 ($ 0.665 per gram), but in 1934 the dollar was devalued to $ 35.00 per troy ounce ($ 0.889/g). In 1961, it became difficult to maintain this price, and a group of US and European banks agreed to manipulate the market to prevent further currency devaluation of an increase in gold demand.
On March 17, 1968, economic conditions led to the collapse of the gold pool, and a two-tiered pricing scheme was established in which gold is still used to complete international accounts at $ 35.00 per troy ounce ($ 1.13/g) but the price of gold in the private market allowed to fluctuate; this two-tier pricing system was abandoned in 1975 when gold prices were allowed to find its free-market level. Central banks still hold historical gold reserves as a store of value even though their level has generally declined. The world's largest gold deposit is owned by the US Federal Reserve Bank in New York, which holds about 3% of the known gold is present and recorded for today, just as the US Bullion Storage is equally burdened at Fort Knox. In 2005, the World Gold Council estimated total global gold supply to be 3,859 tonnes and demand to 3,754 tonnes, delivering a 105 ton surplus.
After Nixon's surprise on August 15, 1971, prices began to greatly increase, and between 1968 and 2000 the price of gold ranged widely, from a high of $ 850 per troy ounce ($ 27.33/g) on ​​21 January 1980, to the lowest point. $ 252.90 per troy ounce ($ 8.13/g) on ​​June 21, 1999 (London Gold Fixing). Prices increased rapidly from 2001, but high 1980s were not exceeded until January 3, 2008, when a new maximum of $ 865.35 per troy ounce was set. Another record price set on March 17, 2008, at $ 1023.50 per troy ounce ($ 32.91/g).
At the end of 2009, the gold market experienced a new upward momentum due to rising demand and weakening US dollar. On December 2, 2009, gold hit a new high close at $ 1,217.23. Gold further rallied to a new high in May 2010 after the EU debt crisis prompted further gold purchases as a safe asset. On March 1, 2011, gold hit an all-time high of $ 1432.57, based on investor concerns about the ongoing unrest in North Africa and the Middle East.
From April 2001 to August 2011, spot gold prices more than fivefold in value against the US dollar, reaching a new all-time high of $ 1,913.50 on Aug. 23, 2011, fueling speculation that the long bear market has ended and the bull market has been restored. However, prices then start a slow decline towards $ 1200 per troy ounce by the end of 2014 and 2015.
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Jewelry
Due to the softness of pure gold (24k), it is usually alloyed with base metals for use in jewelry, altering its hardness and ductility, melting points, colors and other properties. Alloys with a lower rust rating, typically 22k, 18k, 14k or 10k, contain a higher percentage of copper or other base metals or silver or palladium in the alloy. The toxic nickel, and its release of nickel white gold are controlled by law in Europe. Palladium-gold alloys are more expensive than nickel ones. High white carat alloys are more resistant to corrosion than pure silver or sterling silver. Japanese crafts Mokume-gane exploits the contrasting colors between laminated colored gold alloys to produce a decorative wood-grain effect.
In 2014, the gold jewelry industry continues to increase despite a drop in gold prices. Demand in the first quarter of 2014 boosted turnover to $ 23.7 billion according to a World Gold Council report.
Gold solder is used to combine gold jewelry components with solder or high-temperature hardener. If the work is to be qualified, the gold soldering alloy must be in accordance with the smoothness (purity) of the work, and the alloy formula is made for the colors of yellow and white gold. Gold solder is usually made in at least three ranges of melting point called as Easy, Medium and Hard. By using a hard solder point, the first high melting point, followed by a solder with an increasingly low melting point, a goldsmith can assemble complex objects with several separate solder joints. Gold can also be made into yarn and used in embroidery.
Electronics
Only 10% of the world's new gold consumption is produced for the industry, but by far the industry's most important use for new gold is in the manufacture of free corrosion-free electrical connectors in computers and other electrical devices. For example, according to the World Gold Council, typical cell phones may contain 50 mg of gold, worth about 50 cents. But as nearly one billion phones are produced each year, the 50 cents gold value on each phone adds $ 500 million of gold just from this app.
Although gold is attacked by free chlorine, good conductivity and general resistance to oxidation and corrosion in other environments (including resistance to non-chlorinated acids) has led to widespread industrial use in the electronic age as a thin layer of coating on electrical connectors, thus ensuring connections the good one. For example, gold is used in more expensive electronic cable connectors, such as audio, video, and USB cables. The benefits of using gold over other connective metals such as tin in this application have been debated; gold connectors are often criticized by audio-visual experts because it is unnecessary for most consumers and seen only as a marketing tactic. However, the use of gold in other applications in electronic sliding contacts in very humid or corrosive atmospheres, and used for contact with extremely high failure costs (certain computers, communications equipment, spacecraft, jet engines) remains very common.
In addition to shifting electrical contacts, gold is also used in electrical contacts due to its resistance to corrosion, electrical conductivity, toughness and lack of toxicity. Switching contacts generally experience more intense corrosion stress than the shear contact. The fine gold wire is used to connect semiconductor devices to their packets through a process known as wire binding.
The concentration of free electrons in gold metal is 5,91ÃÆ'â € "10 22 cm -3 . Gold is highly conductive for electricity, and has been used for power cables in some high energy applications (only silver and copper are more conductive per volume, but gold has the advantage of corrosion resistance). For example, gold electric cables were used during some of the Manhattan Project atomic experiments, but high-current silver wires were used on the calutron isotope separating magnets in the project.
It is estimated that 16% of the world's gold and 22% of the world's silver is contained in electronic technology in Japan.
Medicine
Metal and gold compounds have long been used for medicinal purposes. Gold, usually as a metal, is probably the most ancient medicine given (apparently by shamanic practitioners) and is known by Dioscorides. In medieval times, gold is often considered beneficial to health, in the belief that something so rare and beautiful can not be anything but healthy. Even some modern esoteric experts and alternative forms of medicine give metallic gold a healing power.
In the 19th century, gold had a reputation as a "nerve", a therapy for neurological disorders. Depression, epilepsy, migraines, and gland problems such as amenorrhea and impotence are treated, and especially alcoholism (Keeley, 1897).
The apparent paradox of true toxicology of the substance shows the possibility of a serious gap in the understanding of gold action in physiology. Only salts and gold radioisotopes have pharmacological value, because the element (metal) of gold is inert for all the chemicals it finds in the body (ie, digested gold can not be attacked by stomach acid). Some gold salts do have anti-inflammatory properties and currently two are still used as drugs in the treatment of arthritis and other similar conditions in the US (sodium aurothiomalate and auranofin). These drugs have been explored as a means to help reduce the pain and swelling of rheumatoid arthritis, and also (historically) against tuberculosis and some parasites.
Gold alloys are used in restorative dentistry, especially in dental restorations, such as crowns and permanent bridges. The sheer flexibility of gold alloys facilitates the creation of superior molar surfaces with other teeth and produces results that are generally more satisfactory than those produced by the creation of porcelain crowns. The use of gold crowns in teeth more prominent as the incisors is favored in some cultures and discouraged in others.
The colloidal gold preparation (suspension of gold nanoparticles) in water is very red, and can be made with tightly controlled particle size up to several tens of nanometers with a reduction of gold chloride with citrate or ascorbic ion. Colloidal gold is used in research applications in medical science, biology and materials. Immunogold labeling techniques exploit the ability of gold particles to adsorb protein molecules to their surfaces. Colloidal gold particles coated with specific antibodies can be used as probes for the presence and position of antigens on the cell surface. In the ultrathin tissue seen with an electron microscope, the immunogold label appears as a very solid dot on the antigen position.
Gold, or gold and palladium alloys, are applied as conductive coatings for biological specimens and other non-conductor materials such as plastics and glass for viewing in scanning electron microscopes. The coating, which is normally used by sputtering with argon plasma, has a triple role in this application. The very high electrical conductivity of gold transmits an electrical charge to the earth, and its very high density provides power to the electrons in the electron beam, helping to limit the depth at which the electron beam penetrates the specimen. This improves the definition of the position and topography of the specimen surface and increases the spatial resolution of the image. Gold also produces high outputs of secondary electrons when irradiated by electron beams, and these low-energy electrons are the most commonly used signal sources used in scanning electron microscopes.
Golden isotopes-198 (part-time 2.7 days) are used, in nuclear medicine, in some cancer treatments and to treat other diseases.
Cuisine
- Gold can be used in food and has the number E 175. By 2016, the European Food Safety Authority publishes an opinion on gold re-evaluation as a food additive. Concerns include the possible number of minutes of gold nanoparticles in food additives, and that gold nanoparticles have been shown to be genotoxic in mammalian cells in vitro.
- Gold leaf, debris or dust is used on and in some gourmet foods, especially sweets and drinks as decorative ingredients. Gold flakes are used by the nobility in medieval Europe as decorations in food and drink, in the form of leaves, flakes or dust, either to show the wealth of the host or in the belief that something valuable and rare must be beneficial to one's health..
- Danziger Goldwasser (German: Water Gold from Danzig) or Goldwasser (English: Goldwater ) is a traditional German herbal drink produced in Gda? sk, Poland, and Schwabach, Germany, and contains gold leaf splinters. There are also some expensive cocktails (c $ 1000) containing golden flakes. However, because metallic gold is inert for all body chemistry, it has no taste, does not provide nutrients, and leaves the body unchanged.
- Vark is a foil made of pure gold that is sometimes gold, and is used to cultivate sweets in South Asian cuisine.
Miscellanea
- Gold produces deep red when used as a dye on cranberry glass.
- In photography, gold toner is used to shift the silver color of black-and-white bromide molds to a brown or blue tone, or to enhance their stability. Used in sepia-ton prints, gold toner produces red tones. Kodak published a formula for several types of gold toner, which uses gold as chloride.
- Gold is a good reflector of electromagnetic radiation like infrared light and visible light, as well as radio waves. It is used for protective coatings on many artificial satellites, in infrared proteplates in thermal protection suits and astronaut helmets, and in electronic warfare aircraft such as EA-6B Prowler.
- Gold is used as a reflective layer on some high-end CDs.
- Cars can use gold to protect heat. McLaren uses gold foil in his F1 model engine compartment.
- Gold can be produced so thin that it looks semi-transparent. This is used in some aircraft cockpit windows for de-icing or anti-icing by passing the electricity through it. The heat generated by gold resistance is sufficient to prevent ice formation.
- Gold is attacked by and dissolves in potassium or sodium cyanide alkali solutions, to form cyanide gold salts - a technique that has been used in extracting metallic gold from ores in cyanide processes. Gold cyanide is an electrolyte used in commercial gold electroplating to basic metals and electroforming.
- A solution of gold chloride (chloroauric acid) is used to make colloidal gold by reduction with citrate ions or ascorbate. Gold chloride and gold oxide are used to make cranberry or red glass, which, like a colloidal gold suspension, contain the same spherical gold nanoparticles.
- Gold, when dispersed in nanoparticles, can act as a heterogeneous chemical reaction catalyst.
Toxicity
Pure gold (element) of gold is non-toxic and does not cause irritation when ingested and is sometimes used as a food decoration in the form of gold leaf. Metallic gold is also a component of alcoholic beverages GoldschlÃÆ'¤ger, Gold Strike, and Goldwasser. Metallic gold is approved as a food additive in the EU (E175 in Codex Alimentarius). Although the gold ion is toxic, the acceptance of metallic gold as a food additive is due to the relatively chemical inertia, and the resistance becomes corroded or turned into a soluble salt (a gold compound) by known chemical processes that will be encountered in humans. body.
Soluble compounds (gold salts) such as gold chloride are toxic to the liver and kidneys. Common cyanide salts of gold such as potassium cyanide gold, used in gold electroplating, are toxic because of their cyanide and gold content. There is a rare case of deadly gold poisoning of potassium gold cyanide. The toxicity of gold can be improved by chelation therapy with agents such as dimercaprol.
Metal gold was selected as Allergen of the Year in 2001 by the American Contact Dermatitis Society, gold contact allergies affecting most women. Nonetheless, gold is a relatively unrelated contact allergen, compared to metals such as nickel.
Samples of the Aspergillus niger fungus are found to grow from gold mining solutions; and was found to contain a cyan metal complex; such as gold, silver, copper and zinc. The fungus also plays a role in the dissolution of heavy metal sulfides.
See also
References
External links
- Hart, Matthew, GoldÃ,: the most lucrative metal race in the world ", New York: Simon & Schuster, 2013. ISBNÃ, 9781451650020
- Ã, "Gold". EncyclopÃÆ'Â|dia Britannica . 11 (issue 11). 1911. Source of the article : Wikipedia
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