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Gold

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  • 1. GOLD Presented to, Sir Inam ul Haq Submitted by, Syeda Mehvish Dildar University of Education Lahore
  • 2. ProjectProject Jauharabad campus July 12, 2007 1.INTRODUCTION Gold, symbol Au (from Latin aurum, “gold”), soft, dense, bright yellow metallic element. Gold is one of the transition elements of the periodic table (see Periodic Law); its atomic number is 79. 2.PROPERTIES Pure gold is the most malleable and ductile of all the metals. It can easily be beaten or hammered to a thickness of 0.000013 cm (0.000005 in), and 29 g (1.02 oz) could be drawn into a wire 100 km (62 mi) long. It is one of the softest metals (hardness, 2.5 to 3) and is a good conductor of heat and electricity. Gold is bright yellow and has a high luster. Finely divided gold, like other metallic powders, is Mehvish , COM UE JauharabadMehvish , COM UE Jauharabad 22
  • 3. ProjectProject black; colloid ally suspended gold ranges in color from ruby red to purple (see Colloid). Gold is extremely inactive. It is unaffected by air, heat, moisture, and most solvents. It will, however, dissolve in aqueous mixtures containing various halogens such as chlorides, bromides, or some iodides. It will also dissolve in some oxidizing mixtures, such as cyanide ion with oxygen, and in aqua regia, a mixture of hydrochloric and nitric acids. The chlorides and cyanides are important compounds of gold. Gold melts at about 1064°C (about 1947°F), boils at about 2856°C (about 5173°F), and has a specific gravity of 19.3; its atomic weight is 196.97. 3.OCCURRENC E Gold is found in nature in quartz veins and secondary alluvial deposits as a free metal or in a combined state. It is widely distributed although it is rare, being 75th in order of abundance of the elements in the crust of the Earth. It is almost always associated with varying amounts of silver; the naturally occurring gold-silver alloy is called electrum. Gold occurs, in chemical combination with tellurium, in the minerals calaverite and sylvanite along with silver, and in the mineral nagyagite along with lead, antimony, and sulfur. It Occurs with mercury as gold amalgam. It is generally present to a small extent in iron pyrites; galena, the lead sulfide ore that usually contains silver, sometimes also contains appreciable amounts of gold. Gold also occurs in seawater to the extent of 5 to 250 parts by weight to 100 million parts of water. Although the quantity of gold present in seawater is more than 9 billion metric tons, the cost of recovering the gold would be far greater than the value of the gold that could thus be recovered. 4.USE S Mehvish , COM UE JauharabadMehvish , COM UE Jauharabad 33
  • 4. ProjectProject The metal has been known and highly valued from earliest times, not only because of its beauty and resistance to corrosion, but also because gold is easier to work than all other metals. In addition, gold was easier to obtain in pure form than the other metals. Because of its relative rarity, gold became used as currency and as a basis for international monetary transactions (see Dollar; Gold Standard). The unit used in weighing gold is the troy ounce; 1 troy ounce is equivalent to 31.1 grams. The major portion of the gold produced is used in coinage and jewelry (see Metalwork). For these purposes it is alloyed with other metals to give it the necessary hardness. The gold content in alloys is expressed in carats (see Carat). Coinage gold is alloyed with copper or silver. Green gold used in jewelry contains copper and silver; white gold contains zinc and nickel, or platinum metals. GoldGold isis alsoalso usedused ii nn the form of goldthe form of gold leaf in the arts ofleaf in the arts of gilding andgilding and lettering. Purple oflettering. Purple of Cassius, aCassius, a Mehvish , COM UE JauharabadMehvish , COM UE Jauharabad 44
  • 5. ProjectProject precipitate ofprecipitate of finely divided goldfinely divided gold and stannicand stannic hydroxide formedhydroxide formed by the interactionby the interaction of auric chlorideof auric chloride and stannousand stannous chloride, is usedchloride, is used in coloring rubyin coloring ruby glass. Chlorauricglass. Chlorauric acid is used inacid is used in Mehvish , COM UE JauharabadMehvish , COM UE Jauharabad 55
  • 6. ProjectProject photography forphotography for toning silvertoning silver images.images. Potassium goldPotassium gold cyanide is used incyanide is used in electro gildingelectro gilding.. Gold is also usedGold is also used in dentistry.in dentistry. Radioisotopes ofRadioisotopes of gold are used ingold are used in biologicalbiological Mehvish , COM UE JauharabadMehvish , COM UE Jauharabad 66
  • 7. ProjectProject research and inresearch and in the treatment ofthe treatment of cancer (seecancer (see Isotopic Tracer).Isotopic Tracer). 5.GOLD MINING The simplest process used for mining gold is panning, using a circular dish often with a small pocket at the bottom. The prospector fills the dish with gold-bearing sand or gravel, holds it under a gentle stream of water, and swirls it. The lighter parts of the gravel are gradually washed off and the gold particles are left near the center of the pan or in the pocket. As gold mining developed, more elaborate methods were introduced and hydraulic mining was invented. The hydraulic method consists of directing a powerful stream of water against the gold-bearing gravel or sand. This operation breaks down the material and washes it away through specially constructed sluices in which the gold settles, while the lighter gravel is floated off. For mining on rivers, elevator dredges are generally used. The elevator dredge is a flat-bottomed boat that uses an endless chain of small buckets to scoop up the material from the river bottom and empty it on the dredge into a trommel (a container built of screening). The material is rotated in the trommel as water is played on it. The gold-bearing sand sinks through perforations in the trommel and drops onto shaking tables, Mehvish , COM UE JauharabadMehvish , COM UE Jauharabad 77
  • 8. ProjectProject on which it is further concentrated. Dredging can also be used in dry beds of ancient rivers if ample water is within a reasonable distance. A pit is dug, and the dredge is moved in and floated on water pumped from the adjacent source. Extensive underground deposits of gold-bearing rocks are often discovered by a small outcrop on the surface. Shafts are sunk, as in coal mining, and the ore is brought to the surface. It is then crushed in special machines. Gold is extracted from gravel or from crushed rock by dissolving it either in mercury (the amalgam process) or in cyanide solutions (the cyanide process). Some ores, especially those in which the gold is chemically combined with tellurium, must be roasted before extraction. The gold is recovered from the solution and melted into ingots. Gold- bearing rock with as little as 1 part of gold to 300,000 parts of worthless material can be worked at a profit. The rarest form of gold is a nugget. The largest known nugget, the Welcome Stranger, weighing 2,284 troy oz (equivalent to 59.0 kg/130.1 pounds), was turned up accidentally, just below the surface of the ground, by a wagon wheel in Victoria, Australia, in 1869. 6.GOLD PRODUCTION Gold production dates from the Etruscan, Minoan, Assyrian, and Egyptian civilizations, when placer gold was derived from alluvial sands and gravels by simple processes of washing or panning. Gold was produced in this manner at an early period in India, central Asia, the southern Ural Mountains and in the regions bordering the eastern Mediterranean. With progress in mining technique, primary auriferous (gold-bearing) veins were exploited; this type of gold mining attained some importance before the Christian era. During the middle Ages little progress was made in gold production and mining. At the time of the discovery of the Americas the value of the total gold stock of Europe was probably less than $225 Mehvish , COM UE JauharabadMehvish , COM UE Jauharabad 88
  • 9. ProjectProject million. During the succeeding 350 years, from the end of the 15th century to about 1850, the world gold output totaled about 4,665,000 kg (about 150 million troy oz). South America and Mexico became large producers of gold during this period. Spain's domination in South America resulted, in the 16th century, in a large increase in gold produced in the New World; some resulted from simple seizure of gold from the Native Americans, who had long mined the metal. In the same century Mexico contributed about 9 percent of the total world production. Gold was discovered in Australia in February 1851, and rich fields were found there. By the middle of the 19th century the United States produced a considerable percentage of the world gold production. In the United States gold has been produced in two regions: the eastern region along the Appalachian Mountains, and the western region along the Rocky Mountains and the Sierra Nevada, Coast, and Cascade ranges. Gold has been found in numerous places on the eastern slope of the Appalachians from Newfoundland and Labrador, Canada, to Alabama, although workable deposits occur only in Nova Scotia and in the southern United States. In the South the auriferous belt, ranging up to 120 km (75 mi) in width, extends from Virginia through North Carolina, South Carolina, and Georgia into Alabama. Both veins and surface deposits have been worked; some pockets of ore were exceptionally rich. The first gold shipped to the United States Mint for coinage from the southern states was from North Carolina in 1804. For the next 20 years the value of the annual output of North Carolina amounted to less than $2,500. In 1829 Virginia and South Carolina, in 1830 Georgia, in 1831 Alabama and Tennessee, and in 1868 Maryland shipped gold to the mint for coinage. The western gold fields extend in the Cordilleran region from Alaska to Mexico. Gold was discovered first in this region in California on January 24, 1848, during excavation for a sawmill on land settled by the American pioneer John Sutter. During the next five years gold valued at more than $285 million, an amount 21 times greater than the value of the total previous production of the entire country, was produced in California. The gold rush took place at this Mehvish , COM UE JauharabadMehvish , COM UE Jauharabad 99
  • 10. ProjectProject time, when people from all parts of the world rushed to the new gold district (see Forty-niners). The discovery furnished the incentive for the exploration and development of the whole far-western section of the United States. The Comstock Lode, a famous discovery made in 1859, is situated on an eastern spur of the Sierras, extending into Nevada. Placers and veins similar to those of the Sierras are found also in Oregon and Washington. The Rocky Mountains and the outlying ranges, which were first prospected in the early 1860s, include an immense area of gold-bearing territory. Rich gravels have been worked at the following locales: near Leadville, Fairplay, and in San Miguel County, Colorado; near Helena and Butte, Montana; along the Snake and Salmon rivers, Idaho; near Deadwood, South Dakota; at Santa Fe, New Mexico; and in Alaska. Placer deposits of gold were discovered on the Yukon River in Canada and Alaska in 1869. The discovery in 1896 of a rich deposit in the Bonanza Creek, a headwater of the Klondike River, which in turn is a tributary of the Yukon, led to another gold rush. In 1910 discoveries were made on Bitter Creek, near Stewart, British Columbia. In 1911 gold was also discovered in Alaska, some 30 km (some 20 mi) from the Canadian boundary at the source of the Sixty Mile River, which rises in Alaska and flows into the Yukon River. Since 1911 the production of gold in Ontario, in the Porcupine and Kirkland lake districts, has gone ahead rapidly. Important discoveries of gold mixed with copper were made in northwestern Québec. The gold production of Australia has been famous since 1851; the chief centers of production are in Western Australia and Victoria. South Africa is the world's leading supplier of gold, producing 376 metric tons in 2003; its most important gold mines are in the Witwatersrand region. Some 70 other countries produce gold in commercial quantities, but two thirds of the total worldwide production now comes from South Africa, the United States, Australia, China, Canada, and Russia. In 2003, the amount of gold produced in the United States was 277 metric tons. U.S. consumption, by major markets, included jewelry and arts, 55 percent; industry, 42 percent; Mehvish , COM UE JauharabadMehvish , COM UE Jauharabad 1010
  • 11. ProjectProject and dental, 3 percent. Most jewelry manufacturing in the United States is centered in New York City and Providence, Rhode Island. On December 31, 1974, the U.S. federal government lifted a 41-year ban on the private ownership of gold. Around that time gold was being traded on the London bullion market at record highs approaching $200 an ounce. After subsequent sharp decreases, prices rose to a high of $850 in January 1980. They then dropped considerably and in the early 1990s settled at about $370 an ounce. Summary (Gold) Gold, symbol Au (from Latin aurum, “gold”), soft, dense, bright yellow metallic element. Gold is one of the transition elements of the periodic table (see Periodic Law); its atomic number is 79. Gold is found in nature in quartz veins and secondary alluvial deposits as a free metal or in a combined state. It is widely distributed although it is rare, being 75th in order of abundance of the elements in the crust of the Earth. Pure gold is most malleable and ductile of all the metals. It can easily be beaten or hammered to a thickness of 0.000013 cm (0.000005 in), and 29 g (1.02oz) could be drawn into a wire 100 km (62mi) long. It is one of the softest metals (hardness, 2.5 to 3) and is a good conductor of heat and electricity. Gold is bright yellow and has a high luster. Finely Divided gold, like other metallic powders, is black; colloid ally suspended gold ranges in color from ruby red to purple (see colloid). The metal has been known and highly valued from earliest times, not only because of its beauty and resistance to corrosion, but also because gold is easier to work than all other metals. In addition, gold was easier to obtain in pure Mehvish , COM UE JauharabadMehvish , COM UE Jauharabad 1111
  • 12. ProjectProject form than the other metals. Because of its relative rarity, gold became used as currency and as a basis for international monetary transactions (see Dollar; Gold Standard). The unit used in weighing gold is the troy ounce; 1 troy ounce is equivalent to 31.1 grams. In fact, gold is very use full metal. July7,2007 Mehvish , COM UE JauharabadMehvish , COM UE Jauharabad 1212

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