- Cobalt (Co) is a hard, lustrous, silver-gray transition metal with atomic number 27, positioned in Group 9 of the periodic table.
- It has nine valence electrons—two in the 4s subshell and seven in the 3d subshell—and commonly exhibits oxidation states of +2 and +3, although other states from −1 to +5 occur in specific compounds. Its atomic structure consists of twenty-seven protons, typically thirty-two neutrons, and twenty-seven electrons arranged in four shells.
- Naturally occurring cobalt is composed almost entirely of the stable isotope cobalt-59 (⁵⁹Co), though the radioactive isotope cobalt-60 (⁶⁰Co) is produced artificially and has important applications in medicine and industry.
- Cobalt is relatively rare in Earth’s crust, occurring at about 25 parts per million. It is found in various minerals, often associated with nickel, copper, and iron ores, such as cobaltite (CoAsS), erythrite (Co₃(AsO₄)₂·8H₂O), and skutterudite ((Co,Ni)As₃). Significant cobalt deposits occur in the Democratic Republic of the Congo (DRC), which supplies the majority of the world’s cobalt, as well as in Russia, Australia, and Canada.
- The element has been used since ancient times in the form of cobalt compounds, particularly for producing blue pigments in glass, ceramics, and glazes. However, cobalt as a distinct metal was first isolated in 1735 by Swedish chemist Georg Brandt, who demonstrated that the blue color in glass was due to a new element rather than to bismuth. The name “cobalt” comes from the German Kobold, meaning “goblin” or “evil spirit,” a reflection of the difficulties miners faced when smelting ores that emitted toxic arsenic fumes.
- In modern industry, cobalt is valued for its high strength, corrosion resistance, and ability to retain magnetic properties at high temperatures. It is a key component in superalloys used for jet engine turbines, gas turbines, and other high-performance applications. Cobalt-based alloys such as stellite are used for cutting tools and wear-resistant surfaces. Cobalt is also used to produce strong permanent magnets, notably samarium–cobalt magnets, which are essential in aerospace, electronics, and renewable energy technologies.
- Cobalt compounds have diverse applications. Cobalt(II) salts are used as catalysts in the petroleum and chemical industries, in drying agents for paints and inks, and in electroplating for wear-resistant coatings. Cobalt-60, a radioactive isotope, is used in cancer radiotherapy, sterilization of medical equipment, and radiographic imaging, as well as in industrial radiography for inspecting metal parts and welds.
- Biologically, cobalt is an essential trace element in the form of vitamin B₁₂ (cobalamin), which is required for red blood cell formation, DNA synthesis, and neurological function. Cobalt deficiency in grazing animals can lead to anemia and poor growth due to insufficient vitamin B₁₂ synthesis by gut microbes. However, excessive cobalt exposure can cause lung and heart problems, and cobalt-60 poses significant radiological hazards.
- Environmentally, cobalt mining—particularly in the DRC—has raised concerns over ecological damage, toxic waste, and human rights issues, including unsafe working conditions and child labor. Recycling cobalt from spent batteries and industrial waste is becoming increasingly important to reduce environmental and ethical impacts.
