Gold: Information About the Sources and Uses of the Element

Gold is a highly valuable element, which has been known to the mankind for more than 5,500 years. The following article provides information about the various sources, extraction processes, and uses of this element.
Gold is represented by the symbol 'Au'. The source of the symbol is a Latin word, aurum. Ancient Greeks, fascinated by its yellowness, named it aurum, meaning 'light of dawn'. The element with atomic number 79, sits between platinum and mercury in the periodic table of elements. Gold belongs to period 6 and group 11 in the periodic table. Its atomic mass is 196.96655 amu. Its melting point is 1064 °C; while its boiling point is 2807 °C.

Gold is heavy and dense. Its density or specific gravity, when measured at 293 K, is 19.32 g/cm. There are 21 isotopes of gold. Half-life of Au-194 is 1.6 days. Half-life is the time required for half of the atoms of radio isotopes to undergo decay. What we refer to as gold is Au-197, a stable isotope. It is inert in nature. It is neither corroded by air nor affected by most of the reagents.

It is found in free form as well as in compound form with silver, quartz, lead, tellurium, copper, zinc, and calcite. It is found with copper as tetra-auricupride (AuCu) and auricupride or cuproauride (AuCu3). It can also be found in sea water, however, it can't be extracted from the sea water as it is not economically viable.

The element is malleable and ductile, i.e. it can be made into sheets and drawn in thin wires, respectively. Its thickness could be as small as 0.000127 millimeter, which makes it useful in jewelry making.

In its pure form, gold is soft. It needs to be hardened by adding other metals to it, before it is used to make jewelry. Troy ounces is the measure of pure gold, and carat tells you of the quantity of gold present in the alloy.

Color
Red, Rose, & Pink: Red gold is obtained by mixing gold and copper in 3:1 ratio. Rose gold is made by mixing gold, copper, and silver. Pink gold is also obtained my mixing gold, copper, and silver, but in different proportion.
Green: When silver is added to gold, we get alloys with greenish yellow shades.
White: It is an alloy of gold, nickel, and palladium.

Sources
The two main sources of gold are placer deposits and lode deposits.
Load Deposits: It is found to be held captive by rock. The load deposits alias vein deposits are present in the cracks and veins of the rocks.
Placer Deposits: Gold gets accumulated in the form of placer deposits due to the action of water. Rivers, springs gnaw at the load deposits and sets it loose. It is carried away by the current, and when the river slows down, the gold falls at the bottom.

Mining
Gold mining is accomplished in different ways. Let's take a look at them.
Panning: In streams and rivers, gold can be found in free form. The silt is collected from the bottom in a pan, and is washed many times to get rid of the soil, etc. While washing, it settles to the bottom of the pan. The nuggets and particles called gold dust are then scooped out of the pan.
Sluicing: A sluice box is used to increase the scale and speed of prospecting. A man-made channel is fed with silt and washed with a large quantity of water. This separates the gold by flushing.
Dredging: A sluice box is made to float on the surface of the prospective water body. Using a suction hose, the silt at the bottom is carried to the sluice box where it is washed. Heavy gold particles are allowed to settle, and are scooped out.
Hard Rock Mining: The mining is done in open-pits or underground mines. In the open-pit form, mining is done above the surface of the earth. It is also called open-cast or strip mining. The ore is obtained by removing the surface soil. The pit is dug deeper to excavate gold. The underground mining technique is used to remove the gold which is out of reach of a surface mine. Tunnels and shafts are dug into the bowels of the earth. The rock containing gold is transported to the surface and processed. Kalgoorlie in Western Australia, Tati in northeast Botswana, and Val d'Or in Canada are few of the gold-producing mines.

Extraction
The extraction depends on the type of ore from which the element is extracted. This element is extracted by the process of leaching, smelting, etc.

Cyanide Mill: Processing starts by crushing and grinding the ore to make it fine. Then, water is added to make pulp from this powder. This process continues, till the fine particles of gold are separate from the ore particles. At appropriate time, weak cyanide is added to the solution. Cyanide dissolves the gold, and this is termed as 'cyanidation'. The pulp is then aerated. Gold particles remain in a dissolved and suspended state in the solution. The pulp is then moved to large and shallow tanks. Solution-bearing gold flows over the brim of the tanks and is collected. Heavy materials such as soil, rock particles, etc. sink to the bottom of the tanks. The material is further filtered. In case of modern mills, more than 95 percent of gold extraction is possible.

Uses
The usefulness of this element is attributed to the diversity in the physical properties of this element. It is good conductor of electricity, doesn't tarnish, is malleable and ductile, and has a good luster.
Coins: Gold is used to make coins, and has long been used as a medium of exchange of money. Though, they are no longer used for financial transaction, in the past, these coins were used as currency. There are still areas and fields of business which accept gold as the only medium of payment. Many countries have reserves of gold bullion to maintain the credibility of their currency. This bullion is nothing but bars of solid gold. They are used for the purpose of adding value to the paper money.
Jewelry: Diamonds are precious and sought after by man, but when compared with gold they have insurmountable disadvantage. Diamonds have a fixed shape, especially after they are cut and polished. On the other hand, gold can be given any shape, however delicate and intricate. Therefore, jewelers find it an easy material to work with.
Electronics: Because of high electrical conductivity and inertness, the element is used in high-end electronic instruments, printed circuit boards, cell phones, calculators, etc. It is also used for construction of units of global positioning system. It can be used as a shield to protect sensitive instruments from infrared radiations. It reflects infrared radiation effectively and is therefore used in spacecraft and telescopes.
Alternative Medicine: Currently, gold is being used as an alternative medicine in the treatment of arthritis. Au-198, which is radioactive, is used in the treatment of cancer. It is hoped that in certain diseases like cancer, gold in the form of nano-particles could deliver drugs to the affected parts of the body.
Dentistry: Caps for teeth are made using gold. Gold caps can stand the pressure of chewing better than porcelain caps. This element is used for fillings, crowns, bridges, and orthodontic appliances.

Man uses many metals; but, gold is a special one for him. Its uses encompass many aspects of human life from jewelry to religion.