Mercury (Hg) is a unique heavy metal, famously known as quicksilver for its distinct silvery appearance and liquid state at room temperature. This unusual characteristic made it a subject of fascination for alchemists and gave it widespread application in industry, medicine, and mining for millennia. The quest for this element drove significant global trade and the establishment of vast mining centers across continents. Understanding where mercury has been sourced is essential to tracing its profound impact on human history and the environment.
Extracting Mercury from Cinnabar
The geological source of nearly all historically mined mercury is the bright red mineral cinnabar, a form of mercuric sulfide (HgS). Cinnabar is the most common mercury ore, typically found in areas with recent volcanic activity or hot springs. The process to isolate the pure, liquid metal from this ore is straightforward and was known to ancient civilizations.
The primary method for extraction involves roasting, where the cinnabar ore is heated in furnaces in the presence of air. This thermal treatment causes an oxidation reaction, converting the mercuric sulfide into elemental mercury vapor and sulfur dioxide (SO₂) gas. The chemical reaction is represented as HgS + O₂ → Hg + SO₂.
Because mercury has a relatively low boiling point of 357°C, it easily vaporizes during the roasting process. The resulting hot vapor is channeled into a cooling system, where it condenses back into its liquid, metallic form. This simple thermal reduction allowed for efficient, large-scale mercury production for centuries.
Major Historical Global Mining Sites
For much of world history, the global supply of mercury was dominated by a few major mining complexes. The mine at Almadén, Spain, holds the record as the largest known mercury deposit on Earth, with continuous operation dating back to the Roman period. Almadén is estimated to have supplied approximately one-third of all mercury consumed throughout human history, ceasing its mining operations in 2001.
Another major European source was the mine in Idrija, Slovenia, where cinnabar was first discovered in 1490. Idrija became the world’s second-largest mercury mine, providing about one-eighth of the total historical supply until its closure in 1995. Both Almadén and Idrija formed an axis of European supply.
The third major historical site was the Santa Bárbara mine in Huancavelica, Peru, which became the largest source of mercury in the Western Hemisphere. Discovered in 1564, the mine was essential to the Spanish colonial economy, supplying the quicksilver needed for the amalgamation process to extract silver from the vast deposits at Potosí, in modern-day Bolivia.
Current Global Sources and Regulatory Shifts
The landscape of mercury sourcing has changed dramatically due to international environmental agreements designed to reduce the element’s circulation. The most significant factor is the Minamata Convention on Mercury, a global treaty adopted in 2013. This convention aims to protect human health and the environment from anthropogenic mercury releases and explicitly requires parties to phase out primary mercury mining.
As a result, the dominant sources of new mercury are no longer dedicated mines. Instead, the global supply has shifted primarily toward recycling and byproduct recovery from other industrial processes. Mercury is now reclaimed from various end-of-life products, including industrial waste, fluorescent light bulbs, batteries, and dental amalgam.
A significant portion of the current supply is byproduct mercury, which is recovered during the mining and smelting of other non-ferrous metals, such as zinc, copper, or gold. This byproduct recovery extracts mercury that is naturally present in the primary ore, particularly in countries like China and Mexico.
Despite the decline in primary mining, the global demand and circulation of mercury are still heavily influenced by Artisanal and Small-Scale Gold Mining (ASGM). This sector employs amalgamation to separate fine gold particles from ore and is the largest consumer of mercury globally. The mercury used in ASGM is often sourced from stockpiles or the regulated market, and its subsequent release is a major driver of global mercury pollution.