extracting gold

Heap Leaching

2010-08-18T21:24:00.000+03:00

Heap Leaching

The successful application of heap leaching to the extraction of gold from low-grade deposits has been one of the main factors in higher output since the 1970s, especially in the United States. It is a low cost process that extracts a soluble precious metal or copper compound by dissolving the metal content from the crushed ore.

Ore is heaped onto open-air leach pads with a base of asphalt or impervious plastic sheeting. A sprinkler system is then laid along the top of the ore pile through which a solution of dilute cyanide is sprayed. The cyanide percolates down through the heap for several weeks, leaching out the gold. This solution, now enriched with gold, drains off the bottom of the pad into what is known as the "pregnant pond", from which it is pumped to the recovery plant.

It should be noted that cyanide is extremely toxic and must be handled with special care.

Heap leaching of gold was pioneered in the United States in 1973 at Placer Development's Cortez open pit in Nevada and proved on a larger scale at Pegasus Gold's Zortman Landusky mine in Montana. Although it is low cost, recovery rates average only sixty to seventy per cent, significantly less than with conventional milling. But it has enabled low-grade ores, which otherwise might not be economically viable, to be processed. In the United States, where heap leaching is used most extensively, half of all production is won by this method.

Cyanide/Cyanidation

Cyanide ions have a natural affinity for gold, which reacts with the gold solid particles to make gold cyanide complexes which are soluble in water. Cyanidation has been the principal method of extracting gold from ore since the development of the MacArthur-Forrest Process in 1887, which proved crucial in the development of the South African gold mining industry.

The perfection of the cyanide process largely replaced amalgamation with mercury that had previously been the main method of extracting gold from ore. Cyanidation has also become crucial since 1970 in gold recovery from low grade deposits through heap leaching. It should be noted that cyanide is extremely toxic and must be handled with special care.

In the MacArthur Forrest Process the ore is crushed to a fine powder and circulated through tanks containing a weak solution of cyanide, which has form tetracyano gold complexes. The complexation reaction results in dissolving the gold and the remaining rock pulp is filtered off. Zinc dust added to the cyanide solution to chemically reduce the gold oxidation state from III to zero. The gold is now in the metal element state with zero charge and appears as fine specks of gold to be precipitated out and the precipitate is then refined.

Gold

2010-07-29T18:38:00.000+03:00

Gold (pronounced /ˈɡoʊld/) is a chemical element with the symbol Au (from Latin: aurum, "shining dawn", hence adjective, aureate) and an atomic number of 79. It has been a highly sought-after precious metal for coinage, jewelry, and other arts since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, in veins and in alluvial deposits. Gold is dense, soft, shiny and the most malleable and ductile pure metal known. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Gold is one of the coinage metals and has served as a symbol of wealth and a store of value throughout history. Gold standards have provided a basis for monetary policies. It also has been linked to a variety of symbolisms and ideologies.

A total of 165,000 tonnes of gold have been mined in human history, as of 2009.^[1] This is roughly equivalent to 5.3 billion troy ounces or, in terms of volume, about 8,500 cubic meters, or a 20.4m cube.
Although primarily used as a store of value, gold has many modern industrial uses including dentistry and electronics. Gold has traditionally found use because of its good resistance to oxidative corrosion and excellent quality as a conductor of electricity.
Chemically, gold is a transition metal and can form trivalent and univalent cations in solutions. Compared with other metals, pure gold is chemically least reactive, but it is attacked by aqua regia (a mixture of acids), forming chloroauric acid, but not by the individual acids, and by alkaline solutions of cyanide. Gold dissolves in mercury, forming amalgam alloys, but does not react with it. Gold is insoluble in nitric acid, which dissolves silver and base metals. This property is exploited in the gold refining technique known as "inquartation and parting". Nitric acid has long been used to confirm the presence of gold in items, and this is the origin of the colloquial term "acid test", referring to a gold standard test for genuine value.

1 Characteristics
- 1.1 Color
- 1.2 Isotopes
2 Use and applications
- 2.1 Monetary exchange
- 2.2 Investment
- 2.3 Jewelry
- 2.4 Medicine
- 2.5 Food and drink
- 2.6 Industry
- 2.7 Electronics
- 2.8 Chemistry
3 History
4 Occurrence
5 Production
6 Consumption
7 Chemistry
- 7.1 Less common oxidation states
- 7.2 Mixed valence compounds
8 Toxicity
9 Price
10 Symbolism
11 State emblem
12 See also
13 References
14 External links

Characteristics

Native gold nuggets

Gold nuggets found in Arizona

Gold is the most malleable and ductile of all metals; a single gram can be beaten into a sheet of 1 square meter, or an ounce into 300 square feet. Gold leaf can be beaten thin enough to become translucent. The transmitted light appears greenish blue, because gold strongly reflects yellow and red.^[2] Such semi-transparent sheets also strongly reflect infrared light, making them useful as infrared (radiant heat) shields in visors of heat-resistant suits, and in sun-visors for spacesuits.^[3]
Gold readily creates alloys with many other metals. These alloys can be produced to modify the hardness and other metallurgical properties, to control melting point or to create exotic colors (see below).^[4] Gold is a good conductor of heat and electricity and reflects infrared radiation strongly. Chemically, it is unaffected by air, moisture and most corrosive reagents, and is therefore well suited for use in coins and jewelry and as a protective coating on other, more reactive, metals. However, it is not chemically inert.
Common oxidation states of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds). Gold ions in solution are readily reduced and precipitated out as gold metal by adding any other metal as the reducing agent. The added metal is oxidized and dissolves allowing the gold to be displaced from solution and be recovered as a solid precipitate.
High quality pure metallic gold is tasteless and scentless; in keeping with its resistance to corrosion (it is metal ions which confer taste to metals).^[5]
In addition, gold is very dense, a cubic meter weighing 19,300 kg. By comparison, the density of lead is 11,340 kg/m³, and that of the densest element, osmium, is 22,610 kg/m³.

[edit] Color

Different colors of Ag-Au-Cu alloys

Whereas most other pure metals are gray or silvery white, gold is yellow. This color is determined by the density of loosely bound (valence) electrons; those electrons oscillate as a collective "plasma" medium described in terms of a quasiparticle called plasmon. The frequency of these oscillations lies in the ultraviolet range for most metals, but it falls into the visible range for gold due to subtle relativistic effects that affect the orbitals around gold atoms.^[6]^[7] Similar effects impart a golden hue to metallic cesium (see relativistic quantum chemistry).
Common colored gold alloys such as rose gold can be created by the addition of various amounts of copper and silver, as indicated in the triangular diagram to the left. Alloys containing palladium or nickel are also important in commercial jewelry as these produce white gold alloys. Less commonly, addition of manganese, aluminium, iron, indium and other elements can produce more unusual colors of gold for various applications.^[4]

[edit] Isotopes

Main article: Isotopes of gold

Gold has only one stable isotope, ¹⁹⁷Au, which is also its only naturally occurring isotope. Thirty six radioisotopes have been synthesized ranging in atomic mass from 169 to 205. The most stable of these is ¹⁹⁵Au with a half-life of 186.1 days. ¹⁹⁵Au is also the only gold isotope to decay by electron capture. The least stable is ¹⁷¹Au, which decays by proton emission with a half-life of 30 µs. Most of gold's radioisotopes with atomic masses below 197 decay by some combination of proton emission, α decay, and β+ decay. The exceptions are ¹⁹⁵Au, which decays by electron capture, and ¹⁹⁶Au, which has a minor β- decay path. All of gold's radioisotopes with atomic masses above 197 decay by β- decay.^[8]
At least 32 nuclear isomers have also been characterized, ranging in atomic mass from 170 to 200. Within that range, only ¹⁷⁸Au, ¹⁸⁰Au, ¹⁸¹Au, ¹⁸²Au, and ¹⁸⁸Au do not have isomers. Gold's most stable isomer is ^198 m2Au with a half-life of 2.27 days. Gold's least stable isomer is ^177 m2Au with a half-life of only 7 ns. ^184 m1Au has three decay paths: β+ decay, isomeric transition, and alpha decay. No other isomer or isotope of gold has three decay paths.^[8]

[edit] Use and applications

[edit] Monetary exchange

Gold has been widely used throughout the world as a vehicle for monetary exchange, either by issuance and recognition of gold coins or other bare metal quantities, or through gold-convertible paper instruments by establishing gold standards in which the total value of issued money is represented in a store of gold reserves.
However, the amount of gold in the world is finite and production has not grown in relation to the world's economies. Today, gold mining output is declining.^[9] With the sharp growth of economies in the 20th century, and increasing foreign exchange, the world's gold reserves and their trading market have become a small fraction of all markets and fixed exchange rates of currencies to gold were no longer sustained. At the beginning of World War I the warring nations moved to a fractional gold standard, inflating their currencies to finance the war effort. After World War II gold was replaced by a system of convertible currency following the Bretton Woods system. Gold standards and the direct convertibility of currencies to gold have been abandoned by world governments, being replaced by fiat currency in their stead. Switzerland was the last country to tie its currency to gold; it backed 40% of its value until the Swiss joined the International Monetary Fund in 1999.^[10]
Pure gold is too soft for day-to-day monetary use and is typically hardened by alloying with copper, silver or other base metals. The gold content of alloys is measured in carats (k). Pure gold is designated as 24k. Gold coins intended for circulation from 1526 into the 1930s were typically a standard 22k alloy called crown gold, for hardness.

[edit] Investment

Main article: Gold as an investment

Many holders of gold store it in form of bullion coins or bars as a hedge against inflation or other economic disruptions. However, some economists do not believe gold serves as a hedge against inflation or currency depreciation.^[11]
The ISO 4217 currency code of gold is XAU.
Modern bullion coins for investment or collector purposes do not require good mechanical wear properties; they are typically fine gold at 24k, although the American Gold Eagle, the British gold sovereign, and the South African Krugerrand continue to be minted in 22k metal in historical tradition. The special issue Canadian Gold Maple Leaf coin contains the highest purity gold of any bullion coin, at 99.999% or 0.99999, while the popular issue Canadian Gold Maple Leaf coin has a purity of 99.99%. Several other 99.99% pure gold coins are available. In 2006, the United States Mint began production of the American Buffalo gold bullion coin with a purity of 99.99%. The Australian Gold Kangaroos were first coined in 1986 as the Australian Gold Nugget but changed the reverse design in 1989. Other popular modern coins include the Austrian Vienna Philharmonic bullion coin and the Chinese Gold Panda.

[edit] Jewelry

Main article: Jewellery

Moche gold necklace depicting feline heads. Larco Museum Collection. Lima-Peru

Because of the softness of pure (24k) gold, it is usually alloyed with base metals for use in jewelry, altering its hardness and ductility, melting point, color and other properties. Alloys with lower caratage, typically 22k, 18k, 14k or 10k, contain higher percentages of copper, or other base metals or silver or palladium in the alloy. Copper is the most commonly used base metal, yielding a redder color. Eighteen-carat gold containing 25% copper is found in antique and Russian jewelry and has a distinct, though not dominant, copper cast, creating rose gold. Fourteen-carat gold-copper alloy is nearly identical in color to certain bronze alloys, and both may be used to produce police, as well as other, badges. Blue gold can be made by alloying with iron and purple gold can be made by alloying with aluminium, although rarely done except in specialized jewelry. Blue gold is more brittle and therefore more difficult to work with when making jewelry. Fourteen and eighteen carat gold alloys with silver alone appear greenish-yellow and are referred to as green gold. White gold alloys can be made with palladium or nickel. White 18-carat gold containing 17.3% nickel, 5.5% zinc and 2.2% copper is silvery in appearance. Nickel is toxic, however, and its release from nickel white gold is controlled by legislation in Europe. Alternative white gold alloys are available based on palladium, silver and other white metals,^[12] but the palladium alloys are more expensive than those using nickel. High-carat white gold alloys are far more resistant to corrosion than are either pure silver or sterling silver. The Japanese craft of Mokume-gane exploits the color contrasts between laminated colored gold alloys to produce decorative wood-grain effects.

[edit] Medicine

In medieval times, gold was often seen as beneficial for the health, in the belief that something that rare and beautiful could not be anything but healthy. Even some modern esotericists and forms of alternative medicine assign metallic gold a healing power.^[13] Some gold salts do have anti-inflammatory properties and are used as pharmaceuticals in the treatment of arthritis and other similar conditions.^[14] However, only salts and radioisotopes of gold are of pharmacological value, as elemental (metallic) gold is inert to all chemicals it encounters inside the body. In modern times, injectable gold has been proven to help to reduce the pain and swelling of rheumatoid arthritis and tuberculosis.^[14]^[15]
Gold alloys are used in restorative dentistry, especially in tooth restorations, such as crowns and permanent bridges. The gold alloys' slight malleability facilitates the creation of a superior molar mating surface 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 more prominent teeth such as incisors is favored in some cultures and discouraged in others.
Colloidal gold preparations (suspensions of gold nanoparticles) in water are intensely red-colored, and can be made with tightly controlled particle sizes up to a few tens of nanometers across by reduction of gold chloride with citrate or ascorbate ions. Colloidal gold is used in research applications in medicine, biology and materials science. The technique of immunogold labeling exploits the ability of the gold particles to adsorb protein molecules onto their surfaces. Colloidal gold particles coated with specific antibodies can be used as probes for the presence and position of antigens on the surfaces of cells.^[16] In ultrathin sections of tissues viewed by electron microscopy, the immunogold labels appear as extremely dense round spots at the position of the antigen.^[17] Colloidal gold is also the form of gold used as gold paint on ceramics prior to firing.
Gold, or alloys of gold and palladium, are applied as conductive coating to biological specimens and other non-conducting materials such as plastics and glass to be viewed in a scanning electron microscope. The coating, which is usually applied by sputtering with an argon plasma, has a triple role in this application. Gold's very high electrical conductivity drains electrical charge to earth, and its very high density provides stopping power for electrons in the electron beam, helping to limit the depth to which the electron beam penetrates the specimen. This improves definition of the position and topography of the specimen surface and increases the spatial resolution of the image. Gold also produces a high output of secondary electrons when irradiated by an electron beam, and these low-energy electrons are the most commonly used signal source used in the scanning electron microscope.^[18]
The isotope gold-198, (half-life 2.7 days) is used in some cancer treatments and for treating other diseases.^[19]

[edit] Food and drink

Gold can be used in food and has the E number 175.^[20]
Gold leaf, flake or dust is used on and in some gourmet foods, notably sweets and drinks as decorative ingredient.^[21] Gold flake was used by the nobility in Medieval Europe as a decoration in food and drinks, in the form of leaf, flakes or dust, either to demonstrate the host's wealth or in the belief that something that valuable and rare must be beneficial for one's health. Gold foil along with silver is sometimes used in South Asian sweets such as barfi.^[22]
Danziger Goldwasser (German: Gold water of Danzig) or Goldwasser (English: Goldwater) is a traditional German herbal liqueur^[23] produced in what is today Gdańsk, Poland, and Schwabach, Germany, and contains flakes of gold leaf. There are also some expensive (~$1000) cocktails which contain flakes of gold leaf.^[24] However, since metallic gold is inert to all body chemistry, it adds no taste nor has it any other nutritional effect and leaves the body unaltered.^[25]

[edit] Industry

The 220 kg gold brick displayed in Chinkuashi Gold Museum, Taiwan, Republic of China

The world's largest gold bar weighs 250 kg. Toi museum, Japan.

A gold nugget of 5 mm in diameter (bottom) can be expanded through hammering into a gold foil of about 0.5 square meter. Toi museum, Japan.

Gold solder is used for joining the components of gold jewelry by high-temperature hard soldering or brazing. If the work is to be of hallmarking quality, gold solder must match the carat weight of the work, and alloy formulas are manufactured in most industry-standard carat weights to color match yellow and white gold. Gold solder is usually made in at least three melting-point ranges referred to as Easy, Medium and Hard. By using the hard, high-melting point solder first, followed by solders with progressively lower melting points, goldsmiths can assemble complex items with several separate soldered joints.
Gold can be made into thread and used in embroidery.
Gold is ductile and malleable, meaning it can be drawn into very thin wire and can be beaten into very thin sheets known as gold leaf.
Gold produces a deep, intense red color when used as a coloring agent in cranberry glass.
In photography, gold toners are used to shift the color of silver bromide black and white prints towards brown or blue tones, or to increase their stability. Used on sepia-toned prints, gold toners produce red tones. Kodak published formulas for several types of gold toners, which use gold as the chloride.^[26]
As gold is a good reflector of electromagnetic radiation such as infrared and visible light as well as radio waves, it is used for the protective coatings on many artificial satellites, in infrared protective faceplates in thermal protection suits and astronauts' helmets and in electronic warfare planes like the EA-6B Prowler.
Gold is used as the reflective layer on some high-end CDs.
Automobiles may use gold for heat dissipation. McLaren uses gold foil in the engine compartment of its F1 model.^[27]
Gold can be manufactured so thin that it appears transparent. It is used in some aircraft cockpit windows for de-icing or anti-icing by passing electricity through it. The heat produced by the resistance of the gold is enough to deter ice from forming.^[28]

[edit] Electronics

The concentration of free electrons in gold metal is 5.90×10²² cm⁻³. Gold is highly conductive to electricity, and has been used for electrical wiring in some high-energy applications (silver is even more conductive per volume, but gold has the advantage of corrosion resistance). For example, gold electrical wires were used during some of the Manhattan Project's atomic experiments, but large high current silver wires were used in the calutron isotope separator magnets in the project.
Though gold is attacked by free chlorine, its good conductivity and general resistance to oxidation and corrosion in other environments (including resistance to non-chlorinated acids) has led to its widespread industrial use in the electronic era as a thin layer coating electrical connectors of all kinds, thereby ensuring good connection. For example, gold is used in the connectors of the more expensive electronics cables, such as audio, video and USB cables. The benefit of using gold over other connector metals such as tin in these applications is highly debated. Gold connectors are often criticized by audio-visual experts as unnecessary for most consumers and seen as simply a marketing ploy. However, the use of gold in other applications in electronic sliding contacts in highly humid or corrosive atmospheres, and in use for contacts with a very high failure cost (certain computers, communications equipment, spacecraft, jet aircraft engines) remains very common.^[29]
Besides sliding electrical contacts, gold is also used in electrical contacts because of its resistance to corrosion, electrical conductivity, ductility and lack of toxicity.^[30] Switch contacts are generally subjected to more intense corrosion stress than are sliding contacts. Fine gold wires are used to connect semiconductor devices to their packages through a process known as wire bonding.

[edit] Chemistry

Gold is attacked by and dissolves in alkaline solutions of potassium or sodium cyanide, and gold cyanide is the electrolyte used in commercial electroplating of gold onto base metals and electroforming. Gold chloride (chloroauric acid) solutions are used to make colloidal gold by reduction with citrate or ascorbate ions. Gold chloride and gold oxide are used to make highly valued cranberry or red-colored glass, which, like colloidal gold suspensions, contains evenly sized spherical gold nanoparticles.^[31]

[edit] History

The Turin Papyrus Map

Funerary mask of Tutankhamun

Jason returns with the golden fleece on an Apulian red-figure calyx krater, ca. 340–330 BC.

Gold has been known and used by artisans since the Chalcolithic. Gold artifacts in the Balkans appear from the 4th millennium BC, such as that found in the Varna Necropolis. Gold artifacts such as the golden hats and the Nebra disk appeared in Central Europe from the 2nd millennium BC Bronze Age.
Egyptian hieroglyphs from as early as 2600 BC describe gold, which king Tushratta of the Mitanni claimed was "more plentiful than dirt" in Egypt.^[32] Egypt and especially Nubia had the resources to make them major gold-producing areas for much of history. The earliest known map is known as the Turin Papyrus Map and shows the plan of a gold mine in Nubia together with indications of the local geology. The primitive working methods are described by Strabo and included fire-setting. Large mines also were present across the Red Sea in what is now Saudi Arabia.
The legend of the golden fleece may refer to the use of fleeces to trap gold dust from placer deposits in the ancient world. Gold is mentioned frequently in the Old Testament, starting with Genesis 2:11 (at Havilah) and is included with the gifts of the magi in the first chapters of Matthew New Testament. The Book of Revelation 21:21 describes the city of New Jerusalem as having streets "made of pure gold, clear as crystal". The south-east corner of the Black Sea was famed for its gold. Exploitation is said to date from the time of Midas, and this gold was important in the establishment of what is probably the world's earliest coinage in Lydia around 610 BC.^[33] From the 6th or 5th century BC, the Chu (state) circulated the Ying Yuan, one kind of square gold coin.
In Roman metallurgy, new methods for extracting gold on a large scale were developed by introducing hydraulic mining methods, especially in Hispania from 25 BC onwards and in Dacia from 150 AD onwards. One of their largest mines was at Las Medulas in León (Spain), where seven long aqueducts enabled them to sluice most of a large alluvial deposit. The mines at Roşia Montană in Transylvania were also very large, and until very recently, still mined by opencast methods. They also exploited smaller deposits in Britain, such as placer and hard-rock deposits at Dolaucothi. The various methods they used are well described by Pliny the Elder in his encyclopedia Naturalis Historia written towards the end of the first century AD.
The Mali Empire in Africa was famed throughout the old world for its large amounts of gold. Mansa Musa, ruler of the empire (1312–1337) became famous throughout the old world for his great hajj to Mecca in 1324. When he passed through Cairo in July 1324, he was reportedly accompanied by a camel train that included thousands of people and nearly a hundred camels. He gave away so much gold that it depressed the price in Egypt for over a decade.^[34] A contemporary Arab historian remarked:

“	Gold was at a high price in Egypt until they came in that year. The mithqal did not go below 25 dirhams and was generally above, but from that time its value fell and it cheapened in price and has remained cheap till now. The mithqal does not exceed 22 dirhams or less. This has been the state of affairs for about twelve years until this day by reason of the large amount of gold which they brought into Egypt and spent there [...]	”
—Chihab Al-Umari^[35]

The European exploration of the Americas was fueled in no small part by reports of the gold ornaments displayed in great profusion by Native American peoples, especially in Central America, Peru, Ecuador and Colombia. The Aztecs regarded gold as literally the product of the gods, calling it "god excrement" (teocuitlatl in Nahuatl).^[36]
Although the price of some platinum group metals can be much higher, gold has long been considered the most desirable of precious metals, and its value has been used as the standard for many currencies (known as the gold standard) in history. Gold has been used as a symbol for purity, value, royalty, and particularly roles that combine these properties. Gold as a sign of wealth and prestige was made fun of by Thomas More in his treatise Utopia. On that imaginary island, gold is so abundant that it is used to make chains for slaves, tableware and lavatory-seats. When ambassadors from other countries arrive, dressed in ostentatious gold jewels and badges, the Utopians mistake them for menial servants, paying homage instead to the most modestly dressed of their party.
There is an age-old tradition of biting gold to test its authenticity. Although this is certainly not a professional way of examining gold, the bite test should score the gold because gold is a soft metal, as indicated by its score on the Mohs' scale of mineral hardness. The purer the gold the easier it should be to mark it. Painted lead can cheat this test because lead is softer than gold (and may invite a small risk of lead poisoning if sufficient lead is absorbed by the biting).
Gold in antiquity was relatively easy to obtain geologically; however, 75% of all gold ever produced has been extracted since 1910.^[37] It has been estimated that all gold ever refined would form a single cube 20 m (66 ft) on a side (equivalent to 8000 m³).^[37]
One main goal of the alchemists was to produce gold from other substances, such as lead — presumably by the interaction with a mythical substance called the philosopher's stone. Although they never succeeded in this attempt, the alchemists promoted an interest in what can be done with substances, and this laid a foundation for today's chemistry. Their symbol for gold was the circle with a point at its center (☉), which was also the astrological symbol and the ancient Chinese character for the Sun. For modern creation of artificial gold by neutron capture, see gold synthesis.
During the 19th century, gold rushes occurred whenever large gold deposits were discovered. The first documented discovery of gold in the United States was at the Reed Gold Mine near Georgeville, North Carolina in 1803.^[38] The first major gold strike in the United States occurred in a small north Georgia town called Dahlonega.^[39] Further gold rushes occurred in California, Colorado, the Black Hills, Otago, Australia, Witwatersrand, and the Klondike.
Because of its historically high value, much of the gold mined throughout history is still in circulation in one form or another.

[edit] Occurrence

This 156-ounce (4.85 kg) nugget was found by an individual prospector in the Southern California Desert using a metal detector.

Gold's atomic number of 79 makes it one of the higher atomic number elements which occur naturally. Like all elements with atomic numbers larger than iron, gold is thought to have been formed from a supernova nucleosynthesis process. Their explosions scattered metal-containing dusts (including heavy elements like gold) into the region of space in which they later condensed into our solar system and the Earth.^[40]
On Earth, whenever elemental gold occurs, it appears most often as a metal solid solution of gold with silver, i.e. a gold silver alloy. Such alloys usually have a silver content of 8–10%. Electrum is elemental gold with more than 20% silver. Electrum's color runs from golden-silvery to silvery, dependent upon the silver content. The more silver, the lower the specific gravity.

Relative sizes of an 860 kg block of gold ore, and the 30 g of gold that can be extracted from it. Toi gold mine, Japan.

Gold left behind after a pyrite cube was oxidized to hematite. Note cubic shape of cavity.

Gold is found in ores made up of rock with very small or microscopic particles of gold. This gold ore is often found together with quartz or sulfide minerals such as Fool's Gold, which is a pyrite.^[41] These are called "lode" deposits. Native gold is also found in the form of free flakes, grains or larger nuggets that have been eroded from rocks and end up in alluvial deposits (called placer deposits). Such free gold is always richer at the surface of gold-bearing veins owing to the oxidation of accompanying minerals followed by weathering, and washing of the dust into streams and rivers, where it collects and can be welded by water action to form nuggets.
Gold sometimes occurs combined with tellurium as the minerals calaverite, krennerite, nagyagite, petzite and sylvanite, and as the rare bismuthide maldonite (Au₂Bi) and antimonide aurostibite (AuSb₂). Gold also occurs in rare alloys with copper, lead, and mercury: the minerals auricupride (Cu₃Au), novodneprite (AuPb₃) and weishanite ((Au, Ag)₃Hg₂).
Recent research suggests that microbes can sometimes play an important role in forming gold deposits, transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits.^[42]
The world's oceans contain gold. Measured concentrations of gold in the Atlantic and Northeast Pacific are 50–150 fmol/L or 10-30 parts per quadrillion. In general, Au concentrations for Atlantic and Pacific samples are the same (~50 fmol/L) but less certain. Mediterranean deep waters contain higher concentrations of Au (100–150 fmol/L) attributed to wind-blown dust and/or rivers. At 10 parts per quadrillion the Earth's oceans would hold 15,000 tons of gold^[43]. These figures are three orders of magnitude less than reported in the literature prior to 1988, indicating contamination problems with the earlier data.
A number of people have claimed to be able to economically recover gold from sea water, but so far they have all been either mistaken or crooks. A so-called reverend, Prescott Jernegan ran a gold-from-seawater swindle in the United States in the 1890s. A British fraudster ran the same scam in England in the early 1900s.^[44] Fritz Haber (the German inventor of the Haber process) did research on the extraction of gold from sea water in an effort to help pay Germany's reparations following World War I.^[45] Based on the published values of 2 to 64 ppb of gold in seawater a commercially successful extraction seemed possible. After analysis of 4000 water samples yielding an average of 0.004 ppb it became clear that the extraction would not be possible and he stopped the project.^[46] No commercially viable mechanism for performing gold extraction from sea water has yet been identified. Gold synthesis is not economically viable and is unlikely to become so in the foreseeable future

Specimens of native gold
Gold-257476.jpg "Rope gold" from Lena River, Sakha Republic, Russia. Size: 2.5×1.2×0.7 cm.	Crystalline gold from Mina Zapata, Santa Elena de Uairen, Venezuela. Size: 3.7×1.1×0.4 cm.	Gold leaf from Harvard Mine, Jamestown, California, USA. Size 9.3×3.2× >0.1 cm.

[edit] Production

Main articles: Gold prospecting, Gold mining, and Gold extraction

World gold production trend

Gold output in 2005

The entrance to an underground gold mine in Victoria, Australia

Pure gold precipitate produced by the aqua regia refining process

Gold extraction is most economical in large, easily mined deposits. Ore grades as little as 0.5 mg/kg (0.5 parts per million, ppm) can be economical. Typical ore grades in open-pit mines are 1–5 mg/kg (1–5 ppm); ore grades in underground or hard rock mines are usually at least 3 mg/kg (3 ppm). Because ore grades of 30 mg/kg (30 ppm) are usually needed before gold is visible to the naked eye, in most gold mines the gold is invisible.
Since the 1880s, South Africa has been the source for a large proportion of the world's gold supply, with about 50% of all gold ever produced having come from South Africa. Production in 1970 accounted for 79% of the world supply, producing about 1,480 tonnes. 2008 production was 2,260 tonnes. In 2007 China (with 276 tonnes) overtook South Africa as the world's largest gold producer, the first time since 1905 that South Africa has not been the largest.^[47]
The city of Johannesburg located in South Africa was founded as a result of the Witwatersrand Gold Rush which resulted in the discovery of some of the largest gold deposits the world has ever seen. Gold fields located within the basin in the Free State and Gauteng provinces are extensive in strike and dip requiring some of the world's deepest mines, with the Savuka and TauTona mines being currently the world's deepest gold mine at 3,777 m. The Second Boer War of 1899–1901 between the British Empire and the Afrikaner Boers was at least partly over the rights of miners and possession of the gold wealth in South Africa.
Other major producers are the United States, Australia, Russia and Peru. Mines in South Dakota and Nevada supply two-thirds of gold used in the United States. In South America, the controversial project Pascua Lama aims at exploitation of rich fields in the high mountains of Atacama Desert, at the border between Chile and Argentina. Today about one-quarter of the world gold output is estimated to originate from artisanal or small scale mining.^[48]
After initial production, gold is often subsequently refined industrially by the Wohlwill process which is based on electrolysis or by the Miller process, that is chlorination in the melt. The Wohlwill process results in higher purity, but is more complex and is only applied in small-scale installations.^[49]^[50] Other methods of assaying and purifying smaller amounts of gold include parting and inquartation as well as cupellation, or refining methods based on the dissolution of gold in aqua regia.^[51]
At the end of 2009, it was estimated that all the gold ever mined totaled 165,000 tonnes^[52] This can be represented by a cube with an edge length of about 20.28 meters. The value of this is very limited; at $1200 per ounce, 165,000 tons of gold would have a value of only 6.6 trillion dollars.
The average gold mining and extraction costs were about US$317/oz in 2007, but these can vary widely depending on mining type and ore quality; global mine production amounted to 2,471.1 tonnes.^[53]
Gold is so stable and so valuable that it is always recovered and recycled. There is no true consumption of gold in the economic sense; the stock of gold remains essentially constant while ownership shifts from one party to another.^[54]

[edit] Consumption

India is the world's largest consumer of gold, as Indians buy about 25% of the world's gold,^[55] purchasing approximately 800 tonnes of gold every year. India is also the largest importer of the yellow metal; in 2008, India imported around 400 tonnes of gold.^[56]

[edit] Chemistry

Although gold is a noble metal, it forms many and diverse compounds. The oxidation state of gold in its compounds ranges from −1 to +5, but Au(I) and Au(III) dominate its chemistry. Au(I), referred to as the aurous ion, is the most common oxidation state with soft ligands such as thioethers, thiolates, and tertiary phosphines. Au(I) compounds are typically linear. A good example is Au(CN)₂⁻, which is the soluble form of gold encountered in mining. Curiously, aurous complexes of water are rare. The binary gold halides, such as AuCl, form zigzag polymeric chains, again featuring linear coordination at Au. Most drugs based on gold are Au(I) derivatives.^[57]
Au(III) (auric) is a common oxidation state and is illustrated by gold(III) chloride, AuCl₃. Au(III) complexes, like other d⁸ compounds, are typically square planar.
Aqua regia, a 1:3 mixture of nitric acid and hydrochloric acid, dissolves gold. Nitric acid oxidizes the metal to +3 ions, but only in minute amounts, typically undetectable in the pure acid because of the chemical equilibrium of the reaction. However, the ions are removed from the equilibrium by hydrochloric acid, forming AuCl₄⁻ ions, or chloroauric acid, thereby enabling further oxidation.
Some free halogens react with gold.^[58] Gold also reacts in alkaline solutions of potassium cyanide. With mercury, it forms an amalgam.

[edit] Less common oxidation states

Less common oxidation states of gold include −1, +2, and +5.
The −1 oxidation state occurs in compounds containing the Au⁻ anion, called aurides. Caesium auride (CsAu), for example, crystallizes in the caesium chloride motif.^[59] Other aurides include those of Rb⁺, K⁺, and tetramethylammonium (CH₃)₄N⁺.^[60]
Gold(II) compounds are usually diamagnetic with Au–Au bonds such as [Au(CH₂)₂P(C₆H₅)₂]₂Cl₂. The evaporation of a solution of Au(OH)₃ in concentrated H₂SO₄ produces red crystals of gold(II) sulfate, AuSO₄. Originally thought to be a mixed-valence compound, it has been shown to contain Au4+2 cations.^[61]^[62] A noteworthy, legitimate gold(II) complex is the tetraxenonogold(II) cation, which contains xenon as a ligand, found in [AuXe₄](Sb₂F₁₁)₂.^[63]
Gold pentafluoride and its derivative anion, AuF−6, is the sole example of gold(V), the highest verified oxidation state.^[64]
Some gold compounds exhibit aurophilic bonding, which describes the tendency of gold ions to interact at distances that are too long to be a conventional Au–Au bond but shorter that van der Waals bonding. The interaction is estimated to be comparable in strength to that of a hydrogen bond.

[edit] Mixed valence compounds

Well-defined cluster compounds are numerous.^[60] In such cases, gold has a fractional oxidation state. A representative example is the octahedral species {Au(P(C₆H₅)₃)}₆²⁺. Gold chalcogenides, such as gold sulfide, feature equal amounts of Au(I) and Au(III).

[edit] Toxicity

Pure metallic (elemental) gold is non-toxic and non-irritating when ingested^[65] and is sometimes used as a food decoration in the form of gold leaf. Metallic gold is also a component of the alcoholic drinks Goldschläger, Gold Strike, and Goldwasser. Metallic gold is approved as a food additive in the EU (E175 in the Codex Alimentarius). Although gold ion is toxic, the acceptance of metallic gold as a food additive is due to its relative chemical inertness, and resistance to being corroded or transformed into soluble salts (gold compounds) by any known chemical process which would be encountered in the human body.
Soluble compounds (gold salts) such as gold chloride are toxic to the liver and kidneys. Common cyanide salts of gold such as potassium gold cyanide, used in gold electroplating, are toxic both by virtue of their cyanide and gold content. There are rare cases of lethal gold poisoning from potassium gold cyanide.^[66]^[67] Gold toxicity can be ameliorated with chelation therapy with an agent such as Dimercaprol.
Gold metal was voted Allergen of the Year in 2001 by the American Contact Dermatitis Society. Gold contact allergies affect mostly women.^[68] Despite this, gold is a relatively non-potent contact allergen, in comparison with metals like nickel.^[69]

[edit] Price

Gold price per troy ounce in USD since 1960, in nominal US$ and inflation adjusted in 2008 US$.

Like other precious metals, gold is measured by troy weight and by grams. When it is alloyed with other metals the term carat or karat is used to indicate the amount of gold present, with 24 carats being pure gold and lower ratings proportionally less. The purity of a gold bar or coin can also be expressed as a decimal figure ranging from 0 to 1, known as the millesimal fineness, such as 0.995 being very pure.
The price of gold is determined through trading in the gold and derivatives markets, but a procedure known as the Gold Fixing in London, originating in September 1919, provides a daily benchmark price to the industry. The afternoon fixing was introduced in 1968 to provide a price when US markets are open.
Historically gold coinage was widely used as currency; when paper money was introduced, it typically was a receipt redeemable for gold coin or bullion. In an economic system known as the gold standard, a certain weight of gold was given the name of a unit of currency. For a long period, the United States government set the value of the US dollar so that one troy ounce was equal to $20.67 ($664.56/kg), but in 1934 the dollar was devalued to $35.00 per troy ounce ($1125.27/kg). By 1961, it was becoming hard to maintain this price, and a pool of US and European banks agreed to manipulate the market to prevent further currency devaluation against increased gold demand.

Swiss-cast 1 kg gold bar

On March 17, 1968, economic circumstances caused the collapse of the gold pool, and a two-tiered pricing scheme was established whereby gold was still used to settle international accounts at the old $35.00 per troy ounce ($1.13/g) but the price of gold on the private market was allowed to fluctuate; this two-tiered pricing system was abandoned in 1975 when the price of gold was left to find its free-market level. Central banks still hold historical gold reserves as a store of value although the level has generally been declining. The largest gold depository in the world is that of the U.S. Federal Reserve Bank in New York, which holds about 3%^{[citation needed]} of the gold ever mined, as does the similarly laden U.S. Bullion Depository at Fort Knox.
In 2005 the World Gold Council estimated total global gold supply to be 3,859 tonnes and demand to be 3,754 tonnes, giving a surplus of 105 tonnes.^[70]
Since 1968 the price of gold has ranged widely, from a high of $850/oz ($27,300/kg) on January 21, 1980, to a low of $252.90/oz ($8,131/kg) on June 21, 1999 (London Gold Fixing).^[71] The period from 1999 to 2001 marked the "Brown Bottom" after a 20-year bear market.^[72] Prices increased rapidly from 1991, but the 1980 high was not exceeded until January 3, 2008 when a new maximum of $865.35 per troy ounce was set (a.m. London Gold Fixing).^[73] Another record price was set on March 17, 2008 at $1023.50/oz ($32,900/kg)(am. London Gold Fixing).^[73] In the fall of 2009, gold markets experience renewed momentum upwards due to increased demand and a weakening US dollar. On December 2, 2009, Gold passed the important barrier of US$1200 per ounce to close at $1215.^[74] Gold further rallied hitting new highs in May of 2010 after the European Union debt crisis prompted further purchase of gold as a safe asset.^[75]^[76]
Since April 2001 the gold price has more than tripled in value against the US dollar,^[77] prompting speculation that this long secular bear market has ended and a bull market has returned.^[78]

[edit] Symbolism

Gold bars at the Emperor Casino in Macau

Gold has been highly valued in many societies throughout the ages. In keeping with this it has often had a strongly positive symbolic meaning closely connected to the values held in the highest esteem in the society in question. Gold may symbolize power, strength, wealth, warmth, happiness, love, hope, optimism, intelligence, justice, balance, perfection, summer, harvest and the sun.
Great human achievements are frequently rewarded with gold, in the form of gold medals, golden trophies and other decorations. Winners of athletic events and other graded competitions are usually awarded a gold medal (e.g., the Olympic Games). Many awards such as the Nobel Prize are made from gold as well. Other award statues and prizes are depicted in gold or are gold plated (such as the Academy Awards, the Golden Globe Awards, the Emmy Awards, the Palme d'Or, and the British Academy Film Awards).
Aristotle in his ethics used gold symbolism when referring to what is now commonly known as the "golden mean". Similarly, gold is associated with perfect or divine principles, such as in the case of Phi, which is sometimes called the "golden ratio".
Gold represents great value. Respected people are treated with the most valued rule, the "golden rule". A company may give its most valued customers "gold cards" or make them "gold members". We value moments of peace and therefore we say: "silence is golden". In Greek mythology there was the "golden fleece".
Gold is further associated with the wisdom of aging and fruition. The fiftieth wedding anniversary is golden. Our precious latter years are sometimes considered "golden years". The height of a civilization is referred to as a "golden age".
In Christianity gold has sometimes been associated with the extremities of utmost evil and the greatest sanctity. In the Book of Exodus, the Golden Calf is a symbol of idolatry. In the Book of Genesis, Abraham was said to be rich in gold and silver, and Moses was instructed to cover the Mercy Seat of the Ark of the Covenant with pure gold. In Christian art the halos of Christ, Mary and the Christian saints are golden.
Medieval kings were inaugurated under the signs of sacred oil and a golden crown, the latter symbolizing the eternal shining light of heaven and thus a Christian king's divinely inspired authority. Wedding rings have long been made of gold. It is long lasting and unaffected by the passage of time and may aid in the ring symbolism of eternal vows before god and/or the sun and moon and the perfection the marriage signifies. In Orthodox Christianity, the wedded couple is adorned with a golden crown during the ceremony, an amalgamation of symbolic rites.
In popular culture gold holds many connotations but is most generally connected to terms such as good or great, such as in the phrases: "has a heart of gold", "that's golden!", "golden moment", "then you're golden!" and "golden boy". Gold also still holds its place as a symbol of wealth and through that, in many societies, success.

Extracting gold from rock

2010-07-29T18:33:00.000+03:00

The Challenge
Unlike alluvial gold, which is found as very small flakes on river banks, gold-bearing rocks have to be dug out of the ground. We want pure gold, but gold-bearing rocks include lots of other materials such as quartz, calcite and the sulfides of other metals. We need to separate the gold from everything else in the rock so the rock needs to be treated in some way.
In New Zealand we chiselled some rocks from an outcrop near a small creek. We were pretty sure our rocks contained some gold as there were disused gold mines dating back from the 1870s close by.
Crushing the rock Crushing the gold bearing rock is not as simple as it sounds. We can't just hit it with a hammer because pieces will fly everywhere and we may lose some of our gold. What we need is a very strong container and bash plate. That way, we can crush the rock without losing any of the precious gold particles.

We also need a special kind of hammer, which fits into the container without leaving too much room for the rock to escape. Rather than use a conventional hammer, we used pulleys and a rope to raise and drop a heavy weight. Pulleys increase the length of rope that needs to be pulled in order to raise the heavy weight but at the same time they reduce resistance. If we use a two-pulley system we will have to pull the rope twice as far as if we had one pulley or no pulleys at all, but we will be able to lift twice as much weight. This would be useful because, for the same effort, we can use twice the weight to crush our rocks.

Powdering the rock
The next step was to take the crushed pieces of rock and make them even smaller. We used a heavy metal rod (a broken half shaft from a four wheel drive) and smashed the small bits of rock in a saucepan. The rock needed to be powdered for us to get to all the gold within the rock. This is a time-consuming job because we needed a very fine powder - far finer than even sand. We wore out several pairs of gloves in the process.
Mercury
We used mercury to get the gold out of the powdered rock. Gold, like most minerals, can be 'dissolved' in mercury to form what's called an amalgam. An amalgam is a physical mixture, a type of alloy. This is a comparatively straightforward way of separating the gold from the rock, as the rock remains untouched by the mercury.
However, the use of mercury is very hazardous and mercury pollution in South American rivers following recent gold rushes has poisoned many indigenous inhabitants of the Amazon rainforest as well as the environment.
But how could we get our hands on some mercury?
Where could we find mercury?
The most common ore of mercury is called cinnabar. Its scientific name is mercury sulfide (HgS). In its pure man-made form it's called vermillion, a pigment much valued by painters. Luckily, we were given a huge chunk of cinnabar for this challenge - even though there are large deposits of cinnabar in New Zealand, there were none where we were based. Unfortunately, the cinnabar we were given was of a pretty low grade. But needs must and we had to use it. In some cinnabar ores, where the mercury sulfide concentration is high, you can actually see small beads of metallic mercury in the ore. It certainly wasn't the case with our cinnabar, unfortunately.
It theory at least all we needed to do was grind the cinnabar to a fine powder, and heat it gently, whereupon the mercury sulfide readily decomposes, producing mercury vapour (and sulfur). The mercury vapour can be condensed on the walls of a cold test tube as metallic beads, making them quite easy to collect.
The amalgamation
So how do you use mercury to extract the gold from gold-bearing rock? When you mix the finely powdered gold-bearing rock with some mercury, the gold within the rock dissolves, to form what's called a gold amalgam.
The next step in the process is to separate the gold amalgam from any 'unreacted' mercury. We did this by squeezing the crude amalgam through a small piece of chamois leather. Shiny metallic beads of mercury oozed through the leather, leaving the gold amalgam behind.
Baked potatoes
We now had some gold amalgam, but the challenge was to obtain gold, not some weird alloy. So how do you recover the gold from the amalgam?
Believe it or not, that's where a potato comes in handy. Mercury has a melting temperature well below that of gold, and, when gold amalgam is heated gently, it decomposes to give mercury vapour and purified gold. The flesh of the potato absorbs the mercury vapour, preventing its escape into the atmosphere.
It sounds absurd, but our resident alchemist, Mikey B got it to work. The gold that we got this way looked a bit black and bitty, but it was definitely gold. I don't know how efficient the process was, but we probably got a couple of grams of gold from several large sacks of our gold-bearing rock. And all it took was a lot of crushing and a bit of chemistry wizardry.

Nanotechnology and Cancer

2010-07-29T18:31:00.002+03:00

Nanotechnology is one of the most popular areas of scientific research, especially with regard to medical applications. We've already discussed some of the new detection methods that should bring about cheaper, faster and less invasive cancer diagnoses. But once the diagnosis occurs, there's still the prospect of surgery, chemotherapy or radiation treatment to destroy the cancer. Unfortunately, these treatments can carry serious side effects. Chemotherapy can cause a variety of ailments, including hair loss, digestive problems, nausea, lack of energy and mouth ulcers.

But nanotechnologists think they have an answer for treatment as well, and it comes in the form of targeted drug therapies. If scientists can load their cancer-detecting gold nanoparticles with anticancer drugs, they could attack the cancer exactly where it lives. Such a treatment means fewer side effects and less medication used. Nanoparticles also carry the potential for targeted and time-release drugs. A potent dose of drugs could be delivered to a specific area but engineered to release over a planned period to ensure maximum effectiveness and the patient's safety.
These treatments aim to take advantage of the power of nanotechnology and the voracious tendencies of cancer cells, which feast on everything in sight, including drug-laden nanoparticles. One experiment of this type used modified bacteria cells that were 20 percent the size of normal cells. These cells were equipped with antibodies that latched onto cancer cells before releasing the anticancer drugs they contained.
Another used nanoparticles as a companion to other treatments. These particles were sucked up by cancer cells and the cells were then heated with a magnetic field to weaken them. The weakened cancer cells were then much more susceptible to chemotherapy.
It may sound odd, but the dye in your blue jeans or your ballpoint pen has also been paired with gold nanoparticles to fight cancer. This dye, known as phthalocyanine, reacts with light. The nanoparticles take the dye directly to cancer cells while normal cells reject the dye. Once the particles are inside, scientists "activate" them with light to destroy the cancer. Similar therapies have existed to treat skin cancers with light-activated dye, but scientists are now working to use nanoparticles and dye to treat tumors deep in the body.
From manufacturing to medicine to many types of scientific research, nanoparticles are now rather common, but some scientists have voiced concerns about their negative health effects. Nanoparticles' small size allows them to infiltrate almost anywhere. That's great for cancer treatment but potentially harmful to healthy cells and DNA. There are also questions about how to dispose of nanoparticles used in manufacturing or other processes. Special disposal techniques are needed to prevent harmful particles from ending up in the water supply or in the general environment, where they'd be impossible to track.
Gold nanoparticles are a popular choice for medical research, diagnostic testing and cancer treatment, but there are numerous types of nanoparticles in use and in development. Bill Hammack, a professor of chemical engineering at the University of Illinois, warned that nanoparticles are "technologically sweet" [Source: Marketplace]. In other words, scientists are so wrapped up in what they can do, they're not asking if they should do it. The Food and Drug Administration has a task force on nanotechnology, but as of yet, the government has exerted little oversight or regulation.
For more information on nanoparticles, medical research and other related topics, please check out the links on the next page.

How could gold save my life?

2010-07-29T18:29:00.000+03:00

In a study published in the July 2007 issue of Analytical Chemistry, scientists from Purdue University detailed their use of gold nanoparticles to detect breast cancer. Their work, along with similar studies at other universities, has the potential to radically change breast cancer detection.
The procedure works by identifying the proteins found on the exteriors of cancer cells. Different types of cancer have different proteins on their surfaces that serve as unique markers. Nanorods, gold nanoparticles shaped like rods, use specialized antibodies to latch onto the protein markers for breast cancer, or for another cancer type. After the nanorods bind to proteins in a blood sample, scientists examine how they scatter light. Each protein-nanorod combination scatters light in a unique way, allowing for precise diagnoses.
The use of gold nanoparticles is not new to this study. These tiny particles -- it would take 500 of them to span the width of a human hair -- are particularly suited to detect toxins, pathogens and cancers and are a subject of much experimentation [Source: BBC News]. The scientists at Purdue used nanorods capable of attaching to three types of breast cancer markers, with two of the markers identifying how invasive the cancer is. The lead researcher on the study, Joseph Irudayaraji, said that these nanorods could one day form part of a much more thorough test, binding to up to 15 unique markers [Source: Physorg].

Using nanorods cuts the price of the diagnosis by two-thirds compared to the similar method of flow cytometry, in which fluorescent markers bind to cancer cells. Flow cytometry requires a bigger sample size with thousands of times more cells than is needed for nanorods, meaning that nanorods are capable of helping to determine earlier diagnoses. Nanorods prove much less invasive than some other methods because they use blood samples and don't require a biopsy. Part of the cost savings comes from scientists being able to use a conventional microscope and light source to view the samples, unlike other methods that employ expensive microscopes or lasers.
In a different study, Dr. Irudayaraj showed that gold nanorods could be used to detect cancer stem cells. The discovery is particularly valuable because cancer stem cells cause the out-of-control growth that makes malignant tumors so deadly.
Dr. Irudayaraji said that gold nanoparticles could be widely available for cancer diagnoses sometime in 2011.
Besides being part of exhaustive tests that can detect cancers early on, nanoparticles may also form the basis of future cancer treatments. Lasers that react with gold nanoparticles could be used to destroy cancer cells. Or, nanoparticles could be used as targeted drug-delivery systems.
On the next page, we'll examine these efforts to use nanotechnology to fight cancer and some of the dangers involved.

The Future of Gold

2010-07-29T18:25:00.002+03:00

If gold is relatively rare and most of it has already been mined, does it have much of a future? One thing to remember is that a significant portion of the world's supply of gold is held in reserve by central banks or by individuals who keep gold as an investment. By some estimates, so-called "bar hoarding" accounts for nearly 236 tons (214 metric tons) of gold [source: National Geographic]. Recycling also plays an important role. Approximately 85 percent of all the gold ever found is still being used today, which means that the gold in your favorite jewelry could have once glittered from the headdress of an Incan or Aztec king [source: Temescu].

Some scientists are looking to the heavens to find more gold. In 1998, the Near Earth Asteroid Rendezvous (NEAR) spacecraft passed close to the asteroid Eros and sent back data indicating that the potato-shaped space rock was a vast warehouse of metals. If Eros is typical of stony meteorites that crash to Earth, then it contains about 3 percent metal. Given the dimensions of the asteroid, NASA scientists estimate that Eros may house 20 billion tons (18.1 billion metric tons) of gold and similar amounts of other metals, such as aluminum and platinum [source: BBC News].
Back on Earth, prospectors continue to search for new gold deposits using new, highly sensitive methods of detection. These new methods greatly increase the odds that once-overlooked gold will be discovered. For example, a gold mine near Carlin, Nev., is producing gold from a large low-grade deposit that was opened in 1965 after intensive scientific and technical work had been completed. Other such deposits most certainly exist.
Wherever new mines are established, mining companies will need to focus more on the environmental impact of their operations. Extracting a single ounce of gold requires the removal of 250 tons (227 metric tons) of rock and ore [source: National Geographic]. Then there's the effluent -- the cyanide-laced liquid from the extraction and refining processes -- that's most often dumped offshore. "No Dirty Gold," a campaign run by the nonprofit Earthworks, seeks to raise the environmental standards of the global mining industry. The campaign has enlisted the support of 30 of the world's leading jewelry companies, persuading them to stop selling gold from mines with questionable practices.
Such a campaign is unlikely to stop the global demand for gold. But perhaps it will make us realize that the gold rings on our fingers have a life and a history far beyond our own.

Gold and Money

2010-07-29T18:24:00.000+03:00

One big use we didn't talk about last section was gold's role as a form of currency. You can read much more in How Currency Works, but it's worth mentioning here because gold and money are practically synonymous. Gold coins have been around for centuries, probably since King Croesus, the ruler of ancient Lydia, issued pure gold coins on a large scale in 640 B.C. As we mentioned, the Greeks and Romans also minted gold coins, like the widespread Roman aureus coins. It would be many years before another coin would be so popular. That coin was the ducat, introduced in Venice in 1284. Great Britain issued its first major gold coin, the florin, the same year. Ephraim Brasher, a goldsmith, struck the first U.S. gold coin in 1784.

In addition to making coins out of gold, governments also hold gold in reserve in case they need to make payments for international debts. In fact, the world's central banks hold about 20 percent of the aboveground supply of gold [source: World Gold Council]. The U.S. government stores its reserves in two locations -- the Federal Reserve Bank in New York City and the United States Bullion Depository at Fort Knox, Ky. Walk into either facility, and you would see bricklike bars, known as ingots, stacked like firewood. Each bar is 7 inches by 3.625 inches by 1.75 inches and weighs 400 ounces, or 27.5 pounds. In metrics, that comes out to a bar roughly 18 centimeters by 9 centimeters by 4 centimeters weighing a little more than 11 kilograms. Fort Knox currently holds 147.3 million ounces of gold (4.2 million kilograms). With a book value of $42.22 per ounce, that makes the Fort Knox holding worth $6.2 billion [source: United States Mint]!

The demise of the gold standard has led to the rebalancing of those reserve portfolios. You can read more about the gold standard in this HowStuffWorks article on the New Deal, but here are a few basics. Countries on the gold standard will exchange paper currency for gold and will buy and sell gold at a fixed price. In 1900, with the passage of the Gold Standard Act, the United States formally adopted the gold standard, only to abandon it in 1971.

Uses for Gold: Jewelry, Health Care and Technology

2010-07-29T18:22:00.000+03:00

Throughout history, jewelers and goldsmiths have selected gold as their precious metal of choice because of its unique properties. Gold is naturally beautiful and resists corrosion and tarnishing. It is also soft and malleable, which allows artists to shape the metal into almost any design. Most jewelry is still made that way -- by individuals using craft skills and simple tools that have been around for centuries. Factory production of gold jewelry, however, is becoming more common.

Electronics manufacturers also use gold extensively to take advantage of its high conductivity. Gold conducts electricity better than all other metals except silver and copper. And it doesn't corrode easily. This makes the metal an ideal choice for plating contacts, terminals, printed circuits and semiconductors. A typical computer, for example, uses gold in both the display and the circuit board. Each computer holds only a small amount -- less than 0.1 kilograms (3.5 ounces) of a 27-kilogram (60-pound) machine [source: SWICO Recycling] -- but the numbers add up. According to the U.S. Geological Survey, one metric ton (1.1 tons) of circuit boards can contain 40 to 800 times the amount of gold contained in gold ore mined in the U.S. [source: Grossman].
Other industries that rely on computers and microelectronics, such as aerospace, use large amounts of gold. According to the World Gold Council, NASA used more than 40.8 kilograms (90 pounds) of gold in the construction of the Columbia space shuttle. Much of it found its way into electrical contacts and circuit boards, but a large amount was used in thin-film applications. Sheets of gold 0.15 millimeters (0.006 inches) thick are highly reflective and make effective radiation shields. Similar gold films are now being used to coat the windows of large office buildings, deflecting the sun's rays and controlling passive heating.
Other industries have founds ways to put gold to work, too.

Health care: Dentists use gold for crowns, and certain medicines, such as sodium aurichloride for rheumatoid arthritis, also contain gold.
Food and beverage: Small amounts of gold sometimes brighten foods such as jelly or liqueurs, like Goldschläger.
Chemicals: Gold can catalyze, or speed up, certain chemical reactions more efficiently than other toxic catalysts.
Environment: Gold can play a role in reducing pollution. For example, scientists have recently discovered that gold particles energized by the sun can destroy volatile organic chemicals.

Refining Gold

2010-07-29T18:21:00.000+03:00

The final stage of gold production -- refining -- involves removing impurities that remain after the smelting process. Refining companies receive doré bars, as well as scrap gold, and reliquefy the metal in a furnace. Workers add borax and soda ash to the molten metal, which separates the pure gold from other precious and less precious metals. A sample is then taken to a lab for tests, or assays, that measure the gold content. In most cases, the gold is 99.9 percent pure. Workers cast the gold produced during refining into bars.
What happens next depends on how the gold will be used. Pure gold is generally too soft for most practical applications, so other metals are nearly always added to it. When gold is combined in this way, it forms an alloy. Scientists and goldsmiths often use colors to designate the various gold alloys that are possible. For example, white gold is made by combining gold with nickel, silver or palladium. Red or pink gold is an alloy of gold and copper. And blue gold is the result of mixing gold with iron.
Karatage refers to how much gold is present in an object versus another alloy. A higher karatage indicates a higher proportion of gold in the sample. So, 24-karat gold is 100 percent gold, while 12-karat gold has exactly half as much. The common karatages are shown in the accompanying sidebar.

Interestingly, different cultures prefer different karatages. For example, the people of India are partial to 22-karat gold, while Europeans prefer 18-karat gold. In the United States, 14-karat gold, which offers a balance between gold content, hardness and affordability, is by far the most popular [source: World Gold Council: Jewelry Inspirations].
Most people are familiar with karatage as it applies to jewelry, and jewelry accounts for nearly two-thirds of the global demand for gold [source: Gerlach]. In the next section, we'll examine the other uses of gold.

How Pure Is Your Gold?

24 karats = 100 percent gold
22 karats = 91.75 percent gold
21 karats = 87.5 percent gold
18 karats = 75 percent gold
14 karats = 58.5 percent gold
12 karats = 50.25 percent gold
10 karats = 42 percent gold
9 karats = 37.8 percent gold
8 karats = 33.75 percent gold

Extracting Gold

2010-07-29T18:19:00.002+03:00

Removing the gold-bearing rock from the ground is just the first step. To isolate pure gold, mining companies use a complex extraction process. The first step in this process is breaking down large chunks of rock into smaller pieces. At a mill, large machines known as crushers reduce the ore to pieces no larger than road gravel. The gravel-like material then enters rotating drums filled with steel balls. In these drums, the ore is ground to a fine slurry or powder.
Next, mill operators thicken the slurry with water to form pulp and run the pulp through a series of leaching tanks. Leaching dissolves the gold out of the ore using a chemical solvent. The most common solvent is cyanide, which must be combined with oxygen in a process known as carbon-in-pulp. As the cyanide and oxygen react chemically, gold in the pulp dissolves. When workers introduce small carbon grains to the tank, the gold adheres to the carbon. Filtering the pulp through screens separates the gold-bearing carbon.
The carbon moves to a stripping vessel where a hot caustic solution separates the gold from the carbon. Another set of screens filters out the carbon grains, which can be recycled for future processing. Finally, the gold-bearing solution is ready for electrowinning, which recovers the gold from the leaching chemicals. In electrowinning, operators pour the gold-bearing solution into a special container known as a cell. Positive and negative terminals in the cell deliver a strong electric current to the solution. This causes gold to collect on the negative terminals.

Smelting, which results in nearly pure gold, involves melting the negative terminals in a furnace at about 2,100 degrees F (1,149 degrees C). When workers add a chemical mixture known as flux to the molten material, the gold separates from the metal used to make the terminals. Workers pour off the flux and then the gold. Molds are used to transform the liquid gold into solid bars called doré bars. These low-purity bars are then sent to refineries all over the world for further processing.

Prospecting and Mining Gold

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More than 90 percent of the world's gold has been produced following the rushes of the mid- to late 1800s [source: World Gold Council]. The entire process of gold mining can be broken down roughly into four steps: prospecting, mining, extracting and refining.
Early discoveries of gold relied on the blind luck of someone spotting a yellow glint in a stream or in a crack between rocks. But the search today is more systematic and precise. First, geologists know more about how gold forms. They know, for example, that the metal is present in almost all rocks and soil, but the grains are so small that they're invisible. Only in a few areas is the gold concentrated enough to be mined profitably. Scientists, known as prospectors or explorationists, search for these deposits. This is known as prospecting. Sometimes, these deposits contain pure gold. In most deposits, however, gold is combined with silver or another metal. After finding indications of gold, scientists drill to obtain samples from below the surface, which they analyze for their gold content. If there's enough gold in the deposit, the mining company may set up a large-scale mining operation.

How gold is mined depends on the deposits. Lode deposits are concentrations of gold found in solid rock. If the gold-bearing rock is located at the earth's surface, the mining company will use open-pit techniques. First, miners drill a pattern of holes, which they then fill with explosives. Next, they detonate the explosives to break up the ground so it can be loaded into haul trucks.
If the lode deposit is located beneath the Earth's surface, underground mining is necessary. In this case, miners drill a shaft, or an adit, into the ground to access the lode. Then they dig long vertical tunnels, known as stopes, that extend from the top of the ore block to the bottom. After they drill and load explosives into the ore block, the miners detonate the explosives, causing broken ore to fall to the bottom of the stope. There, ore is loaded into trucks and taken to the surface.
Placer deposits -- accumulations of loose gold in the sediments of a streambed or a beach -- are mined differently. Miners scoop up sand, gravel and rock, and mix it with generous amounts of water. The gold, because of its greater density, sinks faster than the other materials and collects at the bottom. Many miners use a metal or plastic pan to separate the gold from sediments, a process known as panning.

History of Gold: The Middle Ages and the Mad Rushes

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Marco Polo, the Venetian explorer who traveled to China in 1271 and served on the court of Kublai Khan, did much to inspire Europe's notion that vast gold treasures could be found in distant lands. His book, "The Travels of Marco Polo," told of great palaces with walls covered in gold and silver. Christopher Columbus most certainly read Polo's book and hypothesized that one might reach the trade-rich Orient by sailing west across the Atlantic.

Columbus' successful voyage to the Caribbean in 1492-93 touched off an unprecedented wave of exploration. Although spreading Christianity was a major objective of Spain, obtaining gold and silver were high priorities, too. In 1511, King Ferdinand, who financed Columbus on his fateful journey to the New World, spoke unequivocally when he said, "Get gold, humanely if you can, but at all hazards, get gold." Throughout the 16th century, the Spanish concentrated on conquering Central and South America, all the while searching for El Dorado, a city in which gold was supposed to be as common as sand.

Every time explorers discovered a major source of gold, they reported that they had found the mythical city and started a gold rush. One of the first rushes occurred in Brazil's Minas Gerais region in 1700. Gold mining in this area became the main economic activity, making Brazil the largest gold producer by 1720. Slaves, brought in from Africa, used primitive technologies, such as panning, to do the mining.

Panning became iconic of the California Gold Rush, as well, although the first U.S. gold rush occurred 3,000 miles (4,828 kilometers) away and 45 years earlier -- in North Carolina. Until the 1830s, North Carolina supplied all of the domestic gold coined for currency by the U.S. Mint in Philadelphia. Then, on Jan. 24, 1848, New Jersey-born contractor and builder John Marshall found flakes of gold while overseeing construction of a sawmill near Sacramento, Calif. By the end of the year, an estimated 5,000 people were mining in California. That number exploded to 40,000 by the end of 1849 [source: PBS].

Similar rushes gripped other nations in the 19th century. A gold rush in Australia began in 1850 when Edward Hammond Hargraves found gold in New South Wales. And in 1868, George Harrison uncovered gold in South Africa while digging up stones to build a house.

History of Gold: Flashy Coffins and Ancient Egypt

2010-07-29T18:16:00.000+03:00

When most people think of prehistoric humans transitioning from the Stone Age to the Bronze Age, they picture a movement from stone tools to tools made from copper or copper combined with tin. But in some regions of the world, early humans may have worked gold before other metals. For example, in Bulgaria, archaeologists have found decorative gold objects dating to about 4000 B.C. Most civilizations in North Africa, Asia and Europe transitioned out of the Stone Age between 6000 B.C. and 2500 B.C., so gold was certainly embraced by humans early in their development.
There's no doubt that ancient Egyptians had a voracious appetite for gold. Descriptions of the metal appeared in hieroglyphs as early as 2600 B.C. By 1500 B.C., gold had become the recognized medium of exchange for international trade.

The source of this gold was Nubia, or Kush, a sub-Saharan empire located on the Nile south of Egypt. Pharaohs sent expeditions to Nubia to mine the quartz lodes for gold, which Egyptian goldsmiths transformed into vessels, furniture, funerary equipment and sophisticated jewelry.By 550 B.C., the Greeks had started mining the Mediterranean and Middle East for gold. The Romans continued the practice, introducing sophisticated techniques, such as hydraulic mining, or hushing, which involved using large volumes of water to dislodge rock and remove debris. They also minted coins on a scale never before seen, producing millions of gold aureus coins, each stamped with the emperor's head, between A.D. 200 and 400.
At about the same time, South American civilizations were making great headway with gold metalworking. People of the Middle Sicán era (A.D. 900 to 1100), living in present-day Peru, produced enormous quantities of precious metal artifacts. Their goldsmiths specialized in using sheet metal created by hammering gold ingots with stone hammers on stone anvils. The result was a startling array of gold ornaments, masks, headdresses and other objects.
These are the kinds of treasures Europeans were hungry to find when they began to explore the world to their west. Up next, we'll see how lust for gold helped to shape the fortune of empires and ordinary men.

How Gold Works

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Introduction to How Gold Works

Nothing has captured the imagination of humans like gold. Egyptians considered the bright yellow metal to be divine and indestructible, a physical manifestation of the sun itself.
The Egyptian word for gold is nub, which survives in the name Nubia, an ancient region in northeast Africa that became a major supplier of the precious metal. Aztecs used the word teocuitlatl -- "excrement of the gods" -- to describe gold. And on the periodic table, gold is represented by the symbol Au, from the Latin aurum, which means "shining dawn." By any name, gold has always been associated with wealth and power.

Greed for gold fueled Spanish colonization of the Americas. And the gold rushes of the 19th century, both in California and Australia, triggered a hunger for gold that has hardly been satiated today.
You might think that the constant searching, digging and panning would have yielded enough gold to line every road in Oz, but you'd be wrong. In all of history, only 161,000 tons (146,057 metric tons) of gold have been mined [source: National Geographic]. Compare that to the 5.6 million tons (5.1 million metric tons) of aluminum produced by the United States -- in a single year [source: International Aluminum Institute].
The rarity of gold, however, is just one reason why people value the metal. Its unique physical and chemical properties also make it useful. A one-ounce piece of gold can be hammered into a sheet five-millionths of an inch thick or drawn out into 50 miles (80 kilometers) of wire [source: Temescu]. And it's chemically inert, which means it won't react easily with other chemicals.
Of course, as Shakespeare once said, "All that glitters is not gold." The shiny wedding band on a bride's finger has its dark underbelly. Gold mining is bad for the environment, producing more waste per ounce than any other metal. More troubling, it's dangerous for the low-wage workers employed around the world to pry the metal from the Earth. Hundreds of miners are killed each year by rockfalls and explosions. Hundreds more are buried alive underground.
Understanding all of these issues is critical to understanding how gold works. On the next few pages, we'll study element number 79 on the periodic table and try to to understand the power it holds over our imaginations. Let's start by considering gold's long history, a journey that will take us from the dawn of civilization to the great gold rushes of the late 19th century.

Gold extraction

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Gold extraction or recovery from its ores may require a combination of comminution, mineral processing, hydrometallurgical, and pyrometallurgical processes to be performed on the ore.

Gold mining from alluvium ores was once achieved by techniques associated with placer mining such as simple gold panning and sluicing, resulting in direct recovery of small gold nuggets and flakes. Placer mining techniques since the mid to late 20th century have generally only been the practice of artisan miners. Hydraulic mining was used widely in the Californian gold rush, and involved breaking down alluvial deposits with high-pressure jets of water. Hard rock ores have formed the basis of the majority of commercial gold recovery operations since the middle of the 20th century where open pit and or sub-surface mining techniques are used.
Once the ore is mined it can be treated as a whole ore using a dump leaching or heap leaching processes. This is typical of low-grade, oxide deposits. Normally, the ore is crushed and agglomerated prior to heap leaching. High grade ores and ores resistant to cyanide leaching at coarse particle sizes, require further processing in order to recover the gold values. The processing techniques can include grinding, concentration, roasting, and pressure oxidation prior to cyanidation.

Gold miners excavate an eroded bluff with jets of water at a placer mine in Dutch Flat, California sometime between 1857 and 1870.

1 Types of ore
2 Concentration
3 Leaching
4 Refractory gold processes
5 Gold smelting
- 5.1 Mercury removal
- 5.2 Iron removal
6 Gold from electronics and other scrap
7 Gold Refining and Parting
8 See also
9 References

High-grade gold ore from a quartz vein near Alma, Colorado. The appearance is typical of very good gold-quartz ore.

Types of ore

Gold Nuggets found in Arizona

Gold occurs principally as a native metal, usually alloyed to a greater or lesser extent with silver (as electrum), or sometimes with mercury (as an amalgam). Native gold can occur as sizeable nuggets, as fine grains or flakes in alluvial deposits, or as grains or microscopic particles embedded in other rocks.
Ores in which gold occurs in chemical composition with other elements are comparatively rare. They include calaverite, sylvanite, nagyagite, petzite and krennerite.

[edit] Concentration

Gravity concentration has been historically the most important way of extracting the native metal using pans or washing tables. However, froth flotation processes may also be used to concentrate the gold. In some cases, particularly when the gold is present in the ore as discrete coarse particles, a gravity concentrate can be directly smelted to form gold bars. In other cases, particularly when the gold is present in the ore as fine particles or is not sufficiently liberated from the host rock, the concentrates are treated with cyanide salts, a process known as cyanidation leaching, followed by recovery from the leach solution. Recovery from solution typically involves adsorption on activated carbon followed by solution concentration or stripping and or electrowinning.
Froth flotation is usually applied when the gold present in an ore is closely associated with sulfide minerals such as pyrite or arsenopyrite, and when such sulfides are present in large quantities in the ore. In this case, concentration of the sulfides results in concentration of gold values. Generally, recovery of the gold from the sulfide concentrates requires further processing, usually by roasting or wet pressure oxidation. These pyrometallurgical or hydrometallurgical treatments are themselves usually followed by cyanidation and carbon adsorption techniques for final recovery of the gold.
Sometimes gold is present as a minor constituent in a base metal (e.g. copper) concentrate, and is recovered as a by-product during production of the base metal. For example, it can be recovered in the anode slime during the electrorefining process.

[edit] Leaching

If the gold can not be concentrated for smelting, then it is leached by an aqueous solution:

The cyanide process is the industry standard.
Thiosulfate leaching has been proven to be effective on ores with high soluble copper values or ores which experience pregrobbing by carbonaceous components.

[edit] Refractory gold processes

A "refractory" gold ore is an ore that is naturally resistant to recovery by standard cyanidation and carbon adsorption processes. These refractory ores require pre-treatment in order for cyanidation to be effective in recovery of the gold. A refractory ore generally contains sulfide minerals, organic carbon, or both. Sulfide minerals often trap or occlude gold particles, making it difficult for the leach solution to complex with the gold. Organic carbon present in gold ore may adsorb dissolved gold-cyanide complexes in much the same way as activated carbon. This so-called "preg-robbing" carbon is washed away because it is significantly finer than the carbon recovery screens typically used to recover activated carbon.
Pre-treatment options for refractory ores include:

Roasting
Bio-oxidation
Pressure oxidation
Ultrafine grinding

The refractory ore treatment processes may be preceded by concentration (usually sulfide flotation). Roasting is used to oxidize both the sulfur and organic carbon at high temperatures using air and/or oxygen. Bio-oxidation involves the use of bacteria that promote oxidation reactions in an aqueous environment. Pressure oxidation is an aqueous process for sulfur removal carried out in a continuous autoclave, operating at high pressures and somewhat elevated temperatures. Ultrafine grinding may be used when liberation of gold particles from the surrounding mineral matrix is the primary refractory characteristic of the ore.

[edit] Gold smelting

[edit] Mercury removal

Mercury is a health hazard, especially when in gas form. To remove this hazard, before smelting, gold precipitates from electrowinning or Merrill-Crowe processes are usually heated in a retort to recover any mercury present, that would otherwise cause health and environmental problems due to its release (volatilization) during smelting. The mercury present is not usually from the mercury amalgamation process that is no longer used by formal gold mining companies, but from mercury in the ore that has followed gold through the leaching and precipitation processes.
In the event that there are high levels of copper or silver present, leaching of the precipitate using nitric or sulfuric acids may be required.

[edit] Iron removal

Nitric acid or forced air oven oxidation can also be used to dissolve iron from the electrowinning cathodes before smelting. Gravity concentrates can often contain high grinding steel contents, and so their removal using shaking tables or magnets is used before smelting. During smelting iron can be oxidized using nitre. Excessive use of nitre will corrode the smelting pot, increasing both maintenance costs and the risk of catastrophic leaks (known as run-aways, or holes in the pot through which the molten charge is lost).

[edit] Gold from electronics and other scrap

Electronic gold

Gold can be extracted from electronics scrap, scrap jewelry, and dental scrap. The gold in these items is still valuable, but must first be extracted from the scrap in order to be returned into circulation in its purified form.
The greatest concentrations of gold in scrap electronics are in CPUs, card edge connectors and component interconnects. The gold on these items is typically plated in very thin layers, so to extract a worthwhile quantity requires a large amount of outdated or defective electronics and computer equipment. Additional sources include manufacturers' scrap and surplus discrete electronic components.
Gold Scrap Recovering has become a more popular hobby lately. Electronics are outdated so quickly, and peoples houses are filling up faster and faster with this "useless" stuff, it is becoming easier for people to find free old electronics to recover scrap gold, silver and platinum from. A lot of people hang onto this stuff for years simply because they do not know how to properly dispose of electronics, because of this, it is easy to find free old electronics rich in rare scrap metals for free at garage sales or websites like Craigslist. ^[2]

[edit] Gold Refining and Parting

Main article: Gold parting

Gold Parting is primarily the removing of silver from gold and therefore increasing the purity of gold. The parting of gold from silver has been done since ancient times starting in Lydia in the 6th century BC. Various techniques have been practised; salt cementation from ancient times, parting using distilled mineral acids from medieval times, and in modern times using chlorination using the Miller process and electrolysis using the Wohlwill process.

Winter Prospecting for Gold in Arizona

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arizona gold prospecting video

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Gold prospecting

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Gold Prospecting Cache Creek, Colorado -- Digging In The Dry Gulch

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Gold Prospecting Cache Creek, Colorado -- Sluicing For Gold

2010-03-19T16:35:00.001+03:00

Gold Prospecting Advertures

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There are so abounding belief of the gold blitz days. Both online and in books, magazines etc. We do charge them and we charge to be appreciative of them. There is no bigger abecedary than the past. If we apprentice from it and accumulate history animate in what anytime we are accomplishing we will apprentice more. Accumulate the accomplished present.

2010-03-19T16:30:00.000+03:00

The Gold Pan as a Production Tool 1

The capital affair to bethink about the use of a gold pan is that while it is actual able as a gold-catching device, it can alone action a bound aggregate of streambed material. For this reason, the gold pan is frequently not acclimated as a assembly apparatus in bartering use, added than in the a lot of limited locations breadth it would be actual difficult to booty ample pieces of equipment, and breadth there is alone a baby bulk of streambed actual present -- which is paying able-bodied abundant to achieve the animadversion worthwhile.

The gold pan is a lot of frequently acclimated to locate a richer paying breadth by sampling, so that beyond assembly accessories can be brought into that area to plan the arena to balance added gold.

There are belief in the old mining annal about the arena getting so affluent during the 1849 gold blitz that as abundant as 96 ounces of gold were recovered from a individual pan. That is $50,000 at today’s amount of exchange, and accept to accept been some actual affluent arena indeed!

Stories like that are attenuate and pay-dirt like that is not run beyond actual often. However, it is not too aberrant to apprehend of prospectors today who are able to consistently aftermath bigger than an ounce of gold per anniversary with a gold pan in the top country, and accept the gold to appearance for it. Some do better, but these prospectors accept usually been at it for awhile and accept amid hot spots. I alone apperceive of two guys who abutment themselves with a gold pan, and one of them lives appealing well. As mentioned earlier, the gold pan gives you absolute accessibility, and these prospectors attending about to acquisition the pockets in the apparent basement forth the edges of the creek-beds in their areas, acrimonious up a few pieces here, a few there, and a little abridged of gold already in awhile. It adds up, and to them it is bigger than punching a time clock.

There is still affluence of affluent arena to be begin in gold country if you are accommodating to do the plan complex in award it.

Gold Animadversion Procedure

Panning gold is basically simple, already you apprehend that you are accomplishing the aforementioned affair that the river does if it causes gold to apply and drop during flood storms.

The action basically consists of agreement the actual that you wish to action into your pan and afraid it in a larboard to appropriate motion underwater to could cause the gold, which is heavy, to plan its way down against the basal of your pan. At the aforementioned time, the lighter materials, which are worthless, are formed up to the apparent of the gold pan breadth they can be swept away. The action of afraid and across-the-board is again until alone the heaviest of abstracts are left-namely the gold and heaviest atramentous sand.

Once you are out in the field, you will apprehension that no two humans pan gold absolutely alike. After you accept been at it awhile, you will advance your own little twists and all-overs to achieve the able result.

Here follows a basal gold animadversion action to alpha off with which works able-bodied and is simple to learn:

STEP 1: Already you accept amid some alluvium that you wish to sample, abode it in your gold pan-filling it about 3/4 of the way to the top. After you accept been at it awhile, you can ample your pan to the top after accident any gold. While agreement actual in your pan, aces out the larger-sized rocks, so that you can get added of the abate actual and gold into the pan.

STEP 2: Choose a atom to do your panning. It is best to aces a area area the baptize is at atomic six inches abysmal and finer abounding just abundant to ambit abroad any silty baptize that may be done from your pan. This way, you can see what you are accomplishing better. You do not wish the baptize affective so apace that it will agitated your animadversion actions. A balmy accepted will do, if available.

It is consistently best to acquisition a atom area there’s a bedrock or log or stream-bank or something that you can sit down aloft while panning. You can pan finer while squatting, admiration or angle over, but it does get tiresome. If you are planning to action added than just one or two pans, sitting down will accomplish the action abundant added pleasant.

STEP 3: Carry the pan over to your bent atom and deluge it underwater.

STEP 4: Use your fingers to aerate the capacity of the pan to breach it up absolutely and could cause all of the actual to become saturated with water. This is the time to plan afar all the clay, dirt, roots, moss and such with your fingers to ensure that all the abstracts are absolutely torn up and in a aqueous accompaniment of abeyance whithin the pan.

The pan should be underwater while accomplishing this. Mud and alluvium will float up and out. Do not affair yourself about accident any gold if this happens. Remember: gold is abundant and will bore added in your pan while these lighter abstracts are amphibian out and away.

STEP 5: After the absolute capacity of the pan accept been thoroughly torn up, yield the pan in your easily (with bilker riffles on the far ancillary of the pan) and agitate it, application a active larboard and appropriate motion just beneath the apparent of the water. This activity will advice to breach up the capacity of the pan even added and will aswell alpha to plan the added abstracts downwards in the pan while the lighter abstracts will alpha to surface.

Be accurate not to get so active in your larboard and appropriate afraid that you consume actual out of the pan during this step. Depending aloft the bendability of the actual that you are working, it may be all-important to alternating accomplishing accomplish four and 5 over afresh a few times to get all of the pan’s capacity into a aqueous accompaniment of suspension. It is this aforementioned aqueous accompaniment of abeyance that allows the added abstracts to bore in the pan while the lighter abstracts appear to the surface.

STEP 6: As the afraid activity causes rocks to acceleration up to the surface, ambit them out of the pan application your fingers or the ancillary of your hand. Just ambit off the top band of rocks which accept formed their way up to the pan’s surface.

Don’t anguish about accident gold while accomplishing this, because the aforementioned activity which has brought the lighter rocks to the apparent will accept formed the gold added down against the basal of the pan.

When acrimonious the beyond rocks out of the pan, accomplish abiding that they are apple-pie of adobe and added particles afore you bung them out. Adobe sometimes contains pieces of gold and aswell has a addiction to grab assimilate the gold in your pan.

Note: Working the raw actual through a allocation awning into the gold pan during Step 1 or Step 3 will annihilate the charge to ambit out beyond rocks in Step 6. This will aswell acquiesce you to pan a beyond sample of the finer-sized material(which contains all the gold you will acquisition in a pan sample).

STEP 7: Continue to do accomplish 5 and six, afraid the pan and across-the-board out the rocks and pebbles(if present), until a lot of of the medium-sized actual is out of your pan.

STEP 8: Angle the advanced bend of your pan bottomward hardly to accompany the forward-bottom bend of the pan to a lower position. With the pan agee forward, agitate it aback and alternating application the aforementioned larboard and appropriate motion. Be accurate not to angle the pan advanced so abundant that any actual is agitated over the forward-edge while shaking.

This agee afraid activity causes the gold to alpha alive its way down to the pan's forward-bottom edge, and continues to plan the lighter abstracts to the apparent area they will be added calmly swept off.

STEP 9: Carefully, by application a advanced and astern movement, or a slight annular motion just beneath the apparent of the water, acquiesce the baptize to ambit the top band of worthless, lighter abstracts out of the pan. Only acquiesce the baptize to ambit out a little at a time, while watching carefully for the added abstracts to be baldheaded as the lighter abstracts are swept out. It takes some acumen in this footfall to actuate just how abundant actual to ambit off afore accepting to agitate afresh so that no gold is lost. It will just yield a little convenance in animadversion gold afore you will activate to see the aberration amid the lighter abstracts and the added abstracts in your pan. You will advance a feel for alive how abundant actual can be cautiously swept out afore re-shaking is necessary. If you are aboriginal starting, it is best to re-shake as generally as you feel that it is bare to anticipate accident any gold. If in doubt, shake! There are a few factors which can be acicular out to advice you with this. Added abstracts are usually darker in blush than the lighter materials. You will apprehension while afraid the pan that it is the lighter-colored abstracts that are cavernous on the surface. You will aswell apprehension that as the lighter abstracts are swept out of the pan, the darker-colored abstracts are uncovered.

Materials tend to get darker (and heavier) as you plan your way down against the basal of the pan, area the darkest and heaviest abstracts will be found, they getting the amethyst and atramentous sands, which are usually minerals of the adamant family. The barring to this is gold, which is heaviest of all. Gold usually is of a ablaze and agleam brownish blush and shows out able-bodied in adverse to the added added abstracts at the basal of the gold pan.

One added agency to accumulate in apperception is that the lighter abstracts ambit out of your pan added calmly than do the added materials. As the added abstracts are uncovered, they are added added aggressive to getting swept out of the pan, and will accord you an adumbration of if it is time to re-shake.

As you plan your way down through your pan, sometimes gold particles will appearance themselves as you get down to the added materials. If you see gold, you apperceive it is time to re-shake your pan.

There is addition accepted adjustment of across-the-board the lighter abstracts out of the top of your pan which you ability adopt to use. It is done by dipping your pan beneath the baptize and appropriation it up, while acceptance the baptize to run off the advanced bend of the pan, demography the top band of actual forth with it.

STEP 10: Once the top band of lighter actual is done out of your pan, re-shake to accompany added lighter abstracts to the top. By "lighter materials," I beggarly in allegory to the added materials. If you abide to agitate the lighter abstracts to the top and ambit them off, eventually you will be larboard with the heaviest actual of all, which is the gold. It does not yield abundant afraid to accompany a new band of lighter actual to the surface. Maybe 5 or 6 abnormal of afraid will do it, maybe less. It all depends aloft the bendability of the actual and how abundant gold is present.

Continue to backbone out the larger-sized rocks and dust as they appearance themselves during the process.

STEP 11: Every few cycles of across-the-board and re-shaking, angle your pan aback to the akin position and re-shake. This keeps any gold from getting accustomed to plan its way up the forward-edge of your pan.

STEP 12:Continue the aloft accomplish of across-the-board and re-shaking until you are down to the heaviest abstracts in your pan. These usually abide of old pieces of advance and added metal, coins, BB's, old bullets, buckshot, nails, garnets, baby amethyst and atramentous adamant rocks, and the abundant atramentous beach concentrates. Atramentous bank abide mainly or in allotment of the following: magnetite (magnetic atramentous sands), hematite (non-magnetic atramentous sands), titanium, zircon, rhodolite, monazite, tungsten materials, and sometimes pyrites (fool's gold), additional any added items which ability be present in that area which accept a top specific gravity-like gold and platinum.

Mine Gold in the World

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Mining of Warcraft - is this way, you can see that now the world's major occupation. Since the release of expansion pack is the kind of occupation of the burning crusade, was known throughout the game. To demand higher during the mining of minerals can earn your jewelry. Until now, the jewels are mined for their many players. The auction house you, and you can find the metal, through it, your job level goes up. People who rock the auction house said, "buy" to determine whether the sign will be sold through.

World of Warcraft one of the main mining area is Uproar. Wow this place is filled with so much copper and tin, mining is the most visited places. This place time is faster because ripsaw can think back to me.

The following is a barren place to go. In this section, tin mining, many find a good spot. This part is quick and ripsaw, we do not expect much to please me back. Cases, if you continue to explore the place, back to my tin Razor Scorpio is a great place bristles.

That was the tin and copper must be sold immediately. If you are in the auction, please make sure to verify the bronze availability and price all together. Costs are also sold separately from the sales of copper and other frequently. It is necessary to control the market needs to know everything.

predictions gold for 2010

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History of gold mining

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Romans used hydraulic mining methods on a large scale to extract gold from extensive alluvial deposits, such as those at Las Medulas. Mining was under the control of the state but the mines may have been leased to civilian contractors some time later. The gold helped finance the growth of the empire, and was an important motive in the Roman invasion of Britain by Claudius in the first century AD, although there is only one known Roman gold mine at Dolaucothi in west Wales. Gold was a prime motivation for the campaign in Dacia when the Romans invaded Transylvania in what is now modern Romania in the second century AD. The legions were led by the emperor Trajan, and their exploits are shown on the grand column in City Hall. The discovery of gold in the Witwatersrand led to the Second Boer War and ultimately the founding of South Africa.

Electronic gold

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The greatest concentrations of gold in scrap electronics are in CPUs, card edge connectors and component interconnects. The gold on these items is typically plated in very thin layers, so to extract a worthwhile quantity requires a large amount of outdated or defective electronics and computer equipment. Additional sources include manufacturers' scrap and surplus discrete electronic components

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When the region in search of gold, natural features to be noted is the nature of the underlying topography, including fractures and joint systems, cash flows at the speed of the streams and other features visible under water, as large stones or any other obstacles that could act as a trap for gold. One where the physical characteristics cause some changes in the volume of water flow resulting in a sharp drop in flow rate, these favorable conditions for the deposition of gold. The inside of the bends of the river and the downstream area, behind rocks and rock cliffs are common places for the recovery of gold deposits. Narrow and deep fissures cracked especially those that occur in situations of high diving cliff in a strike or a tendency to be perpendicular to the flow of current is particularly favorable for the appearance of gold.

A series of parallel narrow and deep cracks or fissures at right angles to the direction of flow is very good, because it is natural riffles. These traps are more likely to be found in shale, schist, gneiss and other rocks very articulate. Gold is concentrated almost always at or near the bottom of the pitfalls that can occur as a natural by rounded granules or flakes and nuggets ranging from microscopic to several inches long, thick gold is usually depths.Any more deep and narrow crevices which are under coverage should be cleaned thoroughly at the deepest level, here is where most of the gold is.

GOLD VS DOLLAR

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hunting for gold nuggets

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finding a 4.5oz gold nugget

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One of the devices used for prospecting for gold nuggets

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Some innovative ways to explore for gold

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How to Find Gold

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Make Yer Own GOLD At Home

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extracting gold

Heap Leaching

Gold

Contents

Characteristics

[edit] Color

[edit] Isotopes

[edit] Use and applications

[edit] Monetary exchange

[edit] Investment

[edit] Jewelry

[edit] Medicine

[edit] Food and drink

[edit] Industry

[edit] Electronics

[edit] Chemistry

[edit] History

[edit] Occurrence

[edit] Production

[edit] Consumption

[edit] Chemistry

[edit] Less common oxidation states

[edit] Mixed valence compounds

[edit] Toxicity

[edit] Price

[edit] Symbolism

Extracting gold from rock

Nanotechnology and Cancer

How could gold save my life?

The Future of Gold

Gold and Money

Uses for Gold: Jewelry, Health Care and Technology

Refining Gold

Extracting Gold

Prospecting and Mining Gold

History of Gold: The Middle Ages and the Mad Rushes

History of Gold: Flashy Coffins and Ancient Egypt

How Gold Works

Gold extraction

Contents

Types of ore

[edit] Concentration

[edit] Leaching

[edit] Refractory gold processes

[edit] Gold smelting

[edit] Mercury removal

[edit] Iron removal

[edit] Gold from electronics and other scrap

[edit] Gold Refining and Parting

Winter Prospecting for Gold in Arizona

arizona gold prospecting video

Gold prospecting

Gold Prospecting Cache Creek, Colorado -- Digging In The Dry Gulch

Gold Prospecting Cache Creek, Colorado -- Sluicing For Gold

Gold Prospecting Advertures

Mine Gold in the World

predictions gold for 2010

History of gold mining

Electronic gold

GOLD VS DOLLAR

hunting for gold nuggets

finding a 4.5oz gold nugget

One of the devices used for prospecting for gold nuggets

Some innovative ways to explore for gold

How to Find Gold

Make Yer Own GOLD At Home