Gold - (Au)
Gold is metallic, with a yellow colour when in a mass, but when finely divided it may be black, ruby, or purple. It is the most malleable and ductile metal; 1 ounce (28 g) of gold can be beaten out to 300 square feet. It is a soft metal and is usually alloyed to give it more strength. It is a good conductor of heat and electricity, and is unaffected by air and most reagents.
Gold is usually alloyed in jewellery to give it more strength, and the term carat describes the amount of gold present (24 carats is pure gold). It is estimated that all the gold in the world, so far refined, could be placed in a single cube 60 ft. on a side.
The most common gold compounds are auric chloride (AuCl3) and chlorauric acid (HAuCl4). A mixture of one part nitric acid with three of hydrochloric acid is called aqua regia (because it dissolved gold, the King of Metals). It is unaffected by air and most reagents.
Gold in the environment
Most gold is mined and comes from gravels and quarts veins or is associated with pyrites deposits. Two thirds of the world's supply comes from South Africa, and 2/3 of USA production is from South Dakota and Nevada. Other main mining areas are Canada and Russia. Gold is found in sea water, but no effective economic process has been designed (yet) to extract it from this source. World production is around 2500 tonnes per year, but reserves are estimated to be ten of thousand of tonnes.
Effects of exposure: Inhalation: May cause irritation if exposure is prolonged or excessive. Ingestion: No adverse effects expected. Skin: May cause irritation and allergic reaction. Eye: May cause irritation.
Gold is used to cure rheumatoid arthritis, under a treatment called Chrysoteraphy. It is prescribed when treatment with non-steroid antu-infiammatory drugs is failing to give relief.
Gold has not been evaluated for its ecotoxicity. However, the biodegradation of gold under aerobic conditions is expected to be very poor and there is no evidence to suggest it creates ecological problems when released into the environment. Since gold is insoluble, it is believed to have minimal bioaccumulation and bioavailability characteristics.
Back to periodic Table