Materials science 3: Gold

The shiny treasure unburied from the earth

Gold has always been of major significance to humans. This comes as no surprise as the metal is hard to beat when it comes to drawing attention thanks to its distinctive and shiny yellow color. In nature, it is therefore still found predominantly in its native metallic form, which means as a pure chemical element. From as early as the Copper Age until today. Initially, the classic gold washing was used to extract gold from sediments. Our ancestors applied this method on river banks where they flooded sand containing gold with water and then let the mixture circulate in a pan. Since gold is heavier than sand, it settled on the bottom and could then be processed further. In addition, gold was and still is extracted from placer deposits. In geology, this term refers to secondary mineral enrichments in sediments such as sand and gravel, in which mineral-containing grains have become sorted, concentrated and deposited independently by mechanical flows and due to their weight. Ancient documents such as the Turin Papyrus, one of the most important topographic maps from around 1160 BC, already contains a site plan of an ancient Egyptian gold mine. The early methods were later complemented by the methods of amalgamation and cupellation or by a combination of both. The former takes advantage of a property of mercury that lets this element absorb gold in the form of an alloy. Which means: During amalgamation, stone dust is blended with mercury, which produces a shiny alloy, the so-called amalgam. This amalgam is heated until the mercury evaporates, leaving behind pure raw gold. By contrast, the latter of the above methods involved the separation of gold from alloys with less precious metals.

Modern gold production

Today, a distinction is made between primary gold, i.e. "mountain gold" from mines and mining plants, as well as secondary gold, i.e. "wash gold" or "nuggets". Especially the production, also called mining, of primary gold is extremely complex. This complexity has given rise to a variety of methods, designed to extract underground gold particles from the rock. While these still include amalgamation, cyanide leaching has become the most common. In the first step, golden soil is ground into fine sand. A sodium cyanide solution then dissolves the precious metal from this dust. With the help of zinc dust, the gold can finally be filtered out of the lye solution and then washed and dried. Gold can also be extracted using the anode sludge method. This method involves the application of electrochemical principles: Electrolysis causes gold to accumulate as sludge under the anode, which must then be separated from other precious metals also contained in the rock. The borax method is another environmentally friendly variant for gold extraction. Borax lowers the melting point of the ore mass, which lowers the heat required for the extraction. During the melting process, gold then settles down in the crucible, while other metals rise upwards. It can then be easily extracted. Recycling, i.e. the processing of dental and jewelry processing waste as well as e-waste, is also playing an increasingly important role.

For ritual objects or used as legal tender

The seductive shine, rarity and the seeming perpetuity of gold enticed people as early as thousands of years ago to utilize gold primarily for creating unique ritual objects. For example, golden burial items found at a burial ground in Bulgaria are among the oldest gold artifacts of mankind. Researchers have dated these items between 4600 and 4300 BC. Some ancient earrings, hair clips, gold hats or works of art have now also been recovered across the globe. Sadly, the discovery and processing of the precious metal is also accompanied by darker chapters in history. For instance, the thirst for land, but also for gold, is considered one of the essential reasons for wars and conquests in modern times. In particular, the discovery of America in 1492 - and thus the exploitation of indigenous peoples - is linked closely to this voracity. Historically, gold was also often used as currency. Which means: One monetary unit corresponded to a certain amount of gold. Gradually, however, all the world's currencies were detached from gold, as the gold standard limited the money supply issued as well as the amount of public debt.