Bismuth is a chemical element with the symbol Bi and atomic number 83. It is a brittle metal that exhibits a silvery-white color when freshly produced, though it often develops a characteristic rosy or iridescent pink cast due to surface oxidation. Historically, Bismuth was recognized as the heaviest element that was considered non-radioactive, though for all practical purposes it is treated as stable. The metal is relatively scarce in the Earth’s crust, possessing an abundance comparable to that of silver.
Global Sources and Primary Production
Bismuth production is highly concentrated geographically and is largely dependent on the mining of other metals. China dominates the global supply chain, consistently accounting for the vast majority of the world’s mined and refined Bismuth. China’s production figures have recently represented over 80% of the worldwide output, with a significant amount coming from its lead and copper mining operations.
Global production numbers for Bismuth are often difficult to track because the metal is overwhelmingly recovered as a co-product, not a primary resource. After China, other nations contribute significant amounts to the global supply, including Mexico, Peru, and Bolivia. Bolivia is a notable exception in the global market, as it has historically hosted one of the few mines where Bismuth was the primary target. The supply of Bismuth is closely linked to the economic activity and output of the base metal industries, particularly lead and copper.
Geological Context and Extraction
Bismuth is rarely found in commercially viable concentrations to be mined as a standalone product. The metal’s occurrence is typically associated with polymetallic deposits, meaning it is embedded within the ores of more abundant metals. This strong association means that Bismuth is overwhelmingly recovered as a byproduct during the initial processing of those primary ores.
The most common host ores for Bismuth are those containing lead, copper, tin, tungsten, and silver. For example, Bismuth often substitutes for lead within the mineral galena, the primary ore of lead, making lead smelting a major source of Bismuth supply. These deposits typically form in hydrothermal veins, which are mineral deposits created by hot, mineral-rich fluids circulating through rock formations.
Initial extraction involves conventional mining techniques, such as underground or open-pit methods, to remove the primary ore from the earth. Once the ore is brought to the surface, it undergoes crushing and grinding, followed by mineral concentration processes like flotation. This initial concentration step separates the Bismuth-bearing minerals, such as bismuthinite or bismite, from the waste rock before the complex metallurgical process begins.
Refining and Purification
The concentrated material, which is still a mix of Bismuth and the primary metal, then enters the metallurgical processes required for separation. Since Bismuth often travels with lead, a common method for its recovery is the Betterton-Kroll process, which separates impurities from the molten lead bullion. The Bismuth is removed from the lead at the final stages of the refining operation.
In copper refining, Bismuth can be found in the anode sludge and is recovered through hydrometallurgical techniques, which involve leaching solutions. After initial separation, the resulting crude Bismuth metal still contains other elements, most notably lead. To achieve the high purity levels of 99.999% required for specific electronic or pharmaceutical applications, further purification is necessary.
These final purification stages often involve pyrometallurgical methods, such as reacting the molten metal with chlorine gas to convert impurities like lead into chlorides while the Bismuth remains unchanged. Alternatively, zone refining is employed, a process where a narrow molten zone is passed down a solid ingot, pushing impurities to the ends to yield high-purity Bismuth. Electrolysis in a sodium alkali melt can also be used as a purification step, especially for removing trace radioactive contaminants like polonium.
Essential Applications of Bismuth
The demand for Bismuth is driven by its unique properties, particularly its low toxicity compared to other heavy metals. A significant portion of the global supply goes into the pharmaceutical sector, where Bismuth subsalicylate is the active ingredient in common over-the-counter stomach remedies. This compound is used for treating intestinal disorders and in therapies to eradicate the bacterium Helicobacter pylori.
Bismuth is used in metallurgy to create low-melting point alloys, which often serve as replacements for toxic lead. These fusible alloys melt below the boiling point of water and are used in safety devices like fire sprinkler heads and electrical fuses. Its ability to expand slightly upon solidification also makes it useful in precision casting.
As environmental regulations restrict the use of lead, Bismuth has become an important non-toxic substitute in various applications. It is used in lead-free solders for electronics, plumbing fittings, and in ammunition such as lead-free shot and bullets. Bismuth oxychloride is also valued for its pearlescent quality and is used as a pigment in cosmetics like eyeshadow and nail polish.