Almadén, cradle of European chemistry

Everything is chemistry. We are made of atoms and molecules, practically invisible substances that make us fall in love, excite us, excite us. Chemicals make us human. Now we know that all matter in the universe is made up of 118 elements , from hydrogen, which fills the stars and outer space, to oganeson, a synthetic element manufactured on the banks of the Volga, in Dubna (Russia). However, in ancient times, we only knew a few elements, especially metals. Our ancestors made lead pipes, copper mirrors, and gold jewelry. Also part of this small family was a special metal, a liquid metal: mercury.

Mercury has fascinated us since prehistoric times. It is the only metal that is liquid at room temperature, and it is also extremely dense. A liter of mercury weighs almost 13 times more than a liter of water. Cinnabar, a salt of mercury, decorates caves, burial sites and murals with its characteristic vermilion color — a very deep blood red. Near the Hermitage of the Virgen del Castillo, in Ciudad Real, there are some cave paintings with cinnabar red as the main color. This mineral abounds in those parts. Years later, when the Romans conquered the Iberian Peninsula, they excavated in the same area to extract cinnabar and transform it into mercury. Over time, this mine would give its name to a town: Almadén, in Arabic “the mine.”

The importance of Almadén (Ciudad Real) In the history of chemistry it is incalculable

The importance of Almadén (Ciudad Real) in the history of chemistry is incalculable. So much so that the European Chemical Society (EuChemS) has decided to give this town a distinction as a landmark historical site, a recognition that has only received one other European site — the Swedish Ytterby mine, where eight chemical elements have been discovered. Last day Several personalities gathered in Almadén to celebrate this event and to remember the importance and repercussion of this mercury mine. UNESCO also recognizes the geological value of the territory, a mineral deposit from which the vast majority of the mercury extracted during the last twenty centuries comes. In addition, Almadén has been a World Heritage Site since 2012. If you have played with the content of a mercury thermometer – pushing the metal droplets, noticing their heaviness, observing that, surprisingly, this liquid does not wet – it probably came from Almadén.

More Beyond paint and thermometers, we have found other applications for mercury over time. The Romans mined cinnabar to decorate their colorful mosaics, but they also learned to separate its two components (mercury and sulfur) by applying heat. Then, they used the liquid metal to obtain other more valuable metals, such as gold and silver. Mercury forms mixtures —amalgams— that make it possible to extract precious substances from ores. Some CSIC studies suggest that Roman miners in Astorga (León) used mercury to purify gold and obtain more concentrated and valuable samples. During the Middle Ages, alchemists used mercury in numerous transformations, hoping to transmute elements and obtain valuable products. Although these alchemical recipes often lead to great confusion, because alchemy did not use the name of liquid metal to describe the element, but rather mysterious concepts, such as the ‘principle of fluidity’ and the ‘soul’ of substances. When the first Spanish explorers traveled to America, they recovered the Roman mercury amalgams. Much of the gold, silver and platinum extracted from the mines of the new continent were isolated thanks to the mercury of Almadén. The looted wealth allowed the development of the La Mancha mine and the creation in 1930 of the first Academy of Mines in the country, which would train thousands of engineers. Among these students, Andrés Manuel del Río, scientist and naturalist who discovered vanadium, one of the three elements of the periodic table discovered by Spaniards, stood out. The academy was also directed by Fausto Delhúyar from Logroño, discoverer – along with his brother Juan José – of tungsten, the metal in the filament of light bulbs.

Almadén became an unparalleled supplier of mercury

Almadén became an unparalleled supplier of mercury. In the middle of the 19th century, the chemical and pharmaceutical industry began to develop in Germany, France and the United Kingdom, where mercury was a fundamental raw material. Among other uses, its role in the Castner – Kellner process for electrolysis of common salt stands out. Using electricity, chemists separate sodium chloride into chlorine and caustic soda (sodium hydroxide). Both compounds are key substances for the chemical industry. Chlorine made purification and disinfection processes possible, because it is a strong oxidant that destroys pathogens such as viruses and batteries. Caustic soda, on the other hand, is necessary for the manufacture of soap, and has applications in the manufacture of paper, the oil refinery and the extraction of aluminum, among others. Disinfectants and soap, without these products it would have been difficult to overcome the COVID pandemic – 33.

Unfortunately, mercury also has a dark side. It is an extremely toxic substance, both in metallic form and combined in the form of salts and organic compounds. In addition to being a liquid, mercury easily evaporates and enters the blood through the respiratory system. The effects are so evident that they have generated sayings and cultural references: the talkative hatter from Alice in Wonderland reflects the English tradition. Being ‘mad as a hat’ is a popular expression — these artisans used mercury to tan and treat hides. The famous Isaac Newton is also believed to have suffered from chronic mercury poisoning from his alchemical hobbies. Despite having transcended as one of the fathers of modern physics, Newton practiced alchemy, the predecessor of chemistry. He must have done it in poorly ventilated and hidden rooms, inadvertently inhaling toxic fumes of mercury, sulfur, and other substances. In 1777, workers at a factory in Norwich that used mercury as a disinfectant developed a disorder known as Hunter-Russell syndrome, a type of mercury poisoning. Years later, in the decade of 1950, several factories in the Japanese bay of Minamata mercury was poured into different rivers, causing a brutal disaster — more than died people, and some 3000 developed a severe neurological syndrome with symptoms such as altered touch, impaired eyesight, incoordination and paralysis. Certainly, much of this mercury bioaccumulated in animal species, generating long-term effects that are still incalculable. Mercury contamination increases as we move up the food chain, reaching worrying levels in large fish such as tuna and swordfish.

Visita al Baritel de San Andrés, una estancia dentro de las minas de Almadén.
Visit to the Baritel de San Andrés, a stay within the Almadén mines. Antonio M. Rodríguez García

Last Wednesday, in Almadén, a festive event took place with different scientific conferences and the discovery of a commemorative plaque by Floris Rutjes, President of EuChemS. Several personalities from Spanish chemistry also attended the event, such as Pilar Goya Laza (who between 2018 and 2021 was the first female president of EuChemS), Sonsoles Martín de Santamaría and Antonio Echavarren (Secretary General and President of the Royal Spanish Society of Chemistry, RSEQ); as well as representatives of the University of Castilla-La Mancha, the managers of the Almadén mines and numerous municipal and regional authorities in the region.

De izquierda a derecha, Antonio M. Rodríguez, María Antonia Herrero (UCLM), Sonsoles Martín de Santamaría, Antonio Echavarren (RSEQ) y Pilar Goya, Nineta Hrastelj (EuChemS), bajo la placa conmemorativa de Almadén.
From left to right, Antonio M. Rodríguez, María Antonia Herrero (UCLM), Sonsoles Martín de Santamaría, Antonio Echavarren (RSEQ) and Pilar Goya, Nineta Hrastelj (EuChemS), under the commemorative plaque of Almadén.

The Scientific and historical value of the Almadén mines is undeniable. Although they have been closed since 2003, their legacy is eternal. Quoting the president of EuChemS: “We are confident that this recognition will present the city as a tourist destination where science and history are combined, highlighting how chemistry is rooted in Europe’s cultural heritage. ” Thanks to initiatives like this, Almadén is still alive.

The recording of the event is available for free on YouTube thanks to the collaboration of the Royal Spanish Society of Chemistry.

Fernando Gomollón Bel is a chemist and science communicator.

Antonio M. Rodríguez García is a postdoctoral researcher at UCLM

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