Gold: The Element

Gold is represented by the symbol 'Au'. The source of the symbol is a Latin word, aurum. Ancient Greeks, fascinated by the yellowness of gold, named it aurum, meaning 'light of dawn'. The element gold 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. The atomic mass of gold is 196.96655 amu. Its melting point is 1064 degrees C; while its boiling point is 2807 degrees C. Crystals of gold are cubic in nature.

Gold is heavy and dense. Its density or specific gravity, when measured at 293 degrees Kelvin, 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 referred to as gold is Au-197, a stable isotope. Gold is inert in nature. It is neither corroded by air nor affected by most of the reagents.

Gold is found in free form as well as 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. Harvesting sea to obtain gold is not economically viable, yet. The effort costs more than the value of the gold obtained.

Gold is one of the precious metals coveted by man. With a few exceptions, almost all men and most women dream of possessing gold. In one or another form, it has attracted admirers through all ages and civilizations. Malleable and ductile, gold can be shaped, bent or drawn out. It can be pulled and stretched to make a thin wire. It can be hammered into a sheet, called gold leaf, many times thinner than human hair. The thickness of a gold leaf could be as small as 0.000127 millimeter. Gold is used in abundance to make jewelry.

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. Carat tells you of the quantity of gold present in the alloy.

Color
Yellow, Rose & Pink: Copper added to gold results in an alloy that is of yellow color. If more copper is added, the color changes from pink to shades of rose.
Green: When silver is added to gold, we get alloys with greenish shades.
White: Alloy of gold and nickel is white or gray in color; while, gold when alloyed with palladium is white (pure) in color.

Sources
The two main sources of gold are placer deposits and load deposits.
Load Deposits: Gold is found to be held captive by rock. These load deposits alias vein deposits are mined to get gold.
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 set the gold loose. Gold is carried away by the current. Ultimately, with the lessening current, heavy gold sinks to 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. in the silt. While washing, gold settles to the bottom of the pan. The gold nuggets and gold particles called gold dust are then scooped out of the pan.
Sluicing: A sluice box is used to increase the scale and speed of the gold-prospecting activity. A man-made channel is fed with silt and washed with a large quantity of water to get the gold.
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: When gold is found in the form of load deposits, it needs to be mined. The mining of gold is done in open-pit or underground gold mines. In the open-pit form, mining work is done above the surface of the earth. It is also called open-cast or strip mining. Gold ore is obtained by removing the surface soil. The pit is dug deeper and 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, Val d'Or in Canada are few of the gold-producing mines.

Extraction
Many methods are used to extract gold from ores. Here are a few of them.
Cyanide Mill: Processing starts by crushing and grinding the ore to make it fine. Water is added to make pulp. This process continues, till the fine particles of gold are set free. And at the appropriate time, weak cyanide is added to the solution. Gold dissolves in cyanide. This is termed as 'cyanidation'. The pulp is aerated. Gold particles remain in a dissolved and suspended state in the solution. The gold 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 for gold. In case of modern mills, more than 95 percent of gold extraction is possible.
Heap Leaching: Ore is placed on a plastic sheet. Cyanide solution is spread on it. Gold dissolves in the cyanide. Heaps are laid to facilitate draining of the solution which is collected. Gold leaden solution is then precipitated for gold. Heap leaching can extract 65 to 85 percent of gold.

Uses
Coins: Gold is used to make coins. However, the only people interested in gold coins nowadays are coin collectors. In the past, gold coins were used as currency. And, there are still areas and fields of business that accept gold as the only medium of payment.
Currency: 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. When compared with gold, they are at an 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 gold is used in high-end electronic instruments, printed circuit boards. Especially, when performance and dependability of the equipment takes precedence over the cost. Gold is also used for satellite construction.
Reflector: Gold can be used as a shield to protect sensitive instruments from infrared radiations. It reflects infrared radiation effectively and is therefore used in spacecrafts 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 nano-particle form 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. Complete teeth are also made with gold.

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