Metallurgy from earth and rock into metals

Mining is the first step in turning minerals into things we can use. 

The metal must first be released from chemical captivity in its host rock or mineral. Add to reddish, earthy bauxite searing heat, reactive chemicals, and electricity - and you get aluminium. Metallurgy is the art and science of turning dull earth and rock into shiny metals.

Learn about different types of metals here.

“Of metallic affairs”

The German scholar and alchemist, Georgius Agricola (1494-1555), was the leading Renaissance figure in the field of “metallurgy” - the extraction of metals from ores, the making of alloys and other metallic materials, and metalworking.

Agricola’s contribution was to be systematic – to move from magic towards science. His treatise, “De re metallica”, became the standard mining and metallurgy text in Europe for more than 200 years. It was superseded with the rise of the science of chemistry – and the decline of alchemy - and better methods for mining and processing of mineral ores. The first translation into English from Latin was made in 1912 by mining engineer Herbert Hoover, later President of the US, and his wife, Lou Henry Hoover.

As an example of his work, Agricola described the crushing of ore into a concentrate, which was then heated or smelted in a furnace with molten lead to separate out silver from gold. Alternatively, these two metals could be separated from each other using acids.

Arabic science

“Alchemy” is derived from an Arabic term, al-kimiya, in turn derived from a Greek word meaning the smelting of metals. The leading exponent was Jabir Ibn Hayyan (721-815) who was active in Kufa, Iraq. His patron was the Caliph, Haroun ar-Rashid, who made frequent appearances in The Arabian Nights. Geber, as Ibn Hayyan was known in the West, invented many techniques in chemistry, in parallel with investigations in magic and superstition, with which alchemy is today associated.

Geber (and later imitators) was a prolific writer on many topics, which to later readers was largely obscure or incomprehensible, hence “gibberish”. For all that, the original Geber is credited with advances in: crystallisation, distillation, evaporation, and other methods of separating out chemical substances. He invented sulphuric acid, nitric acid, and hydrochloric acid. He used a mixture of the last two (aqua regia) to dissolve gold – as part of the alchemist’s search for the Philosopher’s Stone.

Practical applications of Medieval Arabic chemistry included the colouring of glass and ceramics, soap manufacture, tanning of leather, and the making of paper, inks, glues, perfumes and pharmaceuticals. Alcohol, alkali, and amalgam are among terms of Arabic origin from this period.

Jim Al-Khalili. 2010. Pathfinders: The Golden Age of Arabic Science

Goblins in the mines

In the 1600s copper miners in Germany were puzzled by a reddish ore, believed to contain copper, but from which no copper could be extracted. In frustration, they called this material “kupfernickel” – the goblin’s copper – assigning the mineral’s lack of co-operation to folk superstition. This ore turned out to be nickel arsenide, and the metal was isolated much later, in the 1750s. Nickel (Ni) was already long known in its pure form from meteorites, along with native iron.

Preceding nickel in the Periodic Table is cobalt (Co), from German “kobald”, also meaning goblin. Here too, was a metal that refused to be separated from its ore, until 1735.   

Hidden metals

Cadmium (Cd) went long undetected as a metal because its ore, cadmium carbonate, had the same properties as the carbonate of the metal sitting above it in the Periodic Table, zinc (Zn from German: zinke, a sharp edge, from the spiky crystals). But when the carbonates of both were heated to form the metal oxide, the result is white in the case of ZnO, and yellow for CdO. The distinction is vital. Zinc oxide was used in skin treatment in Germany in the early 1800s, while the cadmium equivalent is highly toxic.

The discovery of hidden metals went in the other direction too. For example, magnesium (Mg) was long thought to be calcium (Ca), which is the heavier alkaline earth metal. The famed British chemist, Sir Humphrey Davy, used electric currents in mineral salt solutions to precipitate reactive metals onto an electrode. In this way magnesium was isolated in 1808. The same method was used to isolate this metal’s heavier cousins – calcium, strontium (Sr) and barium (Ba).   

Mystery of mercury

“Hydro argyros” – liquid or water silver - was the name the philosopher Aristotle used for this unusual heavy metal, known since antiquity in Egypt, China and India. Mercury was the name the Mediaeval alchemists gave to it, in consideration of its speed of movement, hence also “quicksilver”. The planetary name has stuck, with the chemical symbol (Hg), a nod to the past.

Making mercury out of its most common ore, cinnabar or mercury sulphide (HgS), was and is straightforward. Crush the ore, heat it, and the mercury evaporates, and is then condensed using standard distillation equipment. The mercury vapour goes into a downward sloping tube, cools back into a liquid on the sides of the equipment and flows under gravity into a receiving container. 

Mercury is the only metal that is liquid at normal temperatures and pressures. Familiar to most of us as the moving part to a thermometer, it has had a range of uses, some of them dangerous historically – the making of hats, for example.

Miners in search of gold in rivers have seized on an unusual chemical property of mercury, the 80th element in the Periodic Table, one heavier than gold (79). Placed in contact, gold flakes in an ore concentrate will be absorbed as an amalgam into the mercury. That becomes a sticky, grey lump that is then heated – in a closed apparatus – to evaporate the mercury, which is condensed and recycled for reuse, leaving the gold.

Gold when alloyed to its other near neighbour in the Periodic Table, platinum (78), will be familiar to wearers of jewellery as “white gold”.        

The rocky road to discovery

When the Industrial Revolution started in the 1750s the majority of the elements in the Periodic Table were as yet undiscovered, and their properties unknown. These new metals have allowed the development of aeroplanes and spacecraft, nuclear energy, other renewable energy technologies, electronics and ICT, satellite navigational systems (GPS), advances in medicine, and more.     

Platinum (Pt) is one of few metals discovered outside of Europe. It was known to indigenous peoples in Latin America where granules were beaten together (sintering) into jewellery and artefacts, often as an alloy with gold. With its very high melting point, European colonisers of Meso-America in the 1500s found platinum impossible to smelt or forge. It took until 1783 to solve that problem. The French chemist Francois Chabaneau produced batches of impure platinum metal having inconsistent physical and chemical properties, because it contained small quantities of other as yet unknown “platinum group metals”, including iridium.    

Iridium (Ir) is the most corrosion-resistant metal on Earth. It was discovered in 1803, with osmium (Os), as a residue left when impure platinum - was dissolved in a mixture of hydrochloric and nitric acid (aqua regia). These three are among the platinum group metals, along with rhodium (Rh) and palladium (Pd), and are often found together in ore deposits. While New Zealand is prospective for platinum group metals, a mineable resource is yet to be found.

Unusually high levels of iridium are found all over the world in the rock layer that marks the extinction of the dinosaurs, the boundary between the geological time periods of Earth history called the Cretaceous and Tertiary. Possibly, the Cretaceous extinction was caused by an Ir-rich comet striking the Earth 65 million years ago, filling the atmosphere with dust and cooling global temperatures.

Tungsten (W) has the highest melting point of any element. The road to discovery of this tough, heavy metal travelled from Ireland (1779), to Sweden (1781), and Spain (1783). It started with the deduction that wolframite, a mineral containing iron and manganese tungstate (WO4), contained a metal unknown to science. Carl Scheele made an oxide from calcium tungstate (scheelite), and called the hidden metal “tung sten”- heavy stone. The Elhuyar brothers in Spain – later sent to Latin America to help in the mines – produced the metal by adding acid to wolframite, and then charcoal. Interest in scheelite has come and gone in New Zealand; nonetheless, W remains a metal of interest to explorers and miners.

Vanadium (V) is used in steel alloys that are light, tough, strong, and heat resistant. It is commonly used in motor parts, including jet engines. The road to its discovery started in 1801 with a brown lead ore found in Mexico, which produced a range of colours in the salts produced from it. Andres del Rio called the unknown element “panchromium” – Greek for all colours. In 1830 a Swedish chemist found an unknown element in an iron ore, which he named after the Scandinavian goddess of beauty, Vanadis, and the name stuck. The metal was then isolated from its chloride salt in 1867 in Manchester. Vanadium is a potential by-product of offshore ironsands deposits in New Zealand.              

Titanium (Ti) is light, very strong, and very resistant to corrosion. Like vanadium, Ti is a space-age metal. Its uses are varied and include: ship propellers, joints in hip replacements, drill bits, watches and gold clubs. Titanium dioxide produces a strong, white pigment used in dyes and paints, which accounts for most Ti production globally.

In 1791 Reverend William Gregor identified a reddish brown oxide in some ironsands. This turned yellow when dissolved in sulphuric acid, and purple when reduced in the presence of iron, revealing an unknown metal oxide. This he called “manaccanite”, after the parish in Cornwall, England, where he lived and worked. Four years later German chemist Martin Klaproth deduced a new metal from the mineral, rutile, which he named after the Titans, the sons of the Earth goddess of Greek mythology. He later determined that this was the same metal that Gregor had discovered but the new name stuck. It took until 1910 to produce the pure metal by heating titanium chloride under pressure. Commercial production began in 1936 using a new process of heating TiCl4 with magnesium, which scavenges the chloride and releases Ti. In New Zealand, titanium occurs in titanomagnetite ironsands along the western seaboard of the North Island, and in ilmenite ironsands along the western South Island.