cobalt

cobalt. It is a hard, lustrous, silver-gray transition metal found naturally only in chemically combined form. The free element, produced by reductive smelting, is a crucial component in numerous high-performance alloys and rechargeable batteries. Its compounds have been used for centuries to impart a distinctive deep blue color to glass, glazes, and pigments.

Properties

Cobalt is a ferromagnetic metal with a high Curie temperature of approximately 1121 degrees Celsius, maintaining its magnetic properties up to very high temperatures. It is harder than iron and nickel and exhibits significant strength and wear resistance, particularly when alloyed. The most common oxidation states are +2 and +3, with cobalt(II) salts yielding pink to red hues in solution and forming numerous coordination complexes. The element has one stable isotope, cobalt-59, while the radioactive cobalt-60 is an important gamma-ray source produced in nuclear reactors like the NRX and used in industrial radiography and medical therapies such as the Gamma Knife.

History

The use of cobalt compounds for blue coloring dates to ancient civilizations, including the Bronze Age cultures of the Aegean Sea and the Tang dynasty in China. The name derives from the German *Kobold*, meaning "goblin," coined by miners in the Erzgebirge mountains who found its ores troublesome and believed malicious spirits had contaminated the valuable silver ore. Swedish chemist Georg Brandt is credited with isolating the metal around 1735 and demonstrating it was the source of the blue color, not bismuth as previously thought. Its strategic importance surged during the 20th century, with developments like the Stellite alloys during World War I and the discovery of Alnico magnets.

Occurrence and production

Cobalt is rarely found as a native metal and primarily occurs in minerals such as cobaltite, erythrite, and skutterudite, often associated with ores of copper, nickel, and iron. Major deposits are found in the Democratic Republic of the Congo within the Central African Copperbelt, as well as in Canada's Sudbury Basin, Australia, and Russia. Production is predominantly a byproduct of nickel and copper mining, involving complex processes of flotation, smelting in facilities like those in Norilsk, and final refining through hydrometallurgy or electrolysis. Significant refining capacity also exists in Finland at the Kokkola refinery and in China.

Applications

The primary use of cobalt is in rechargeable battery chemistries, including lithium cobalt oxide cathodes for li-ion batteries powering devices from Apple Inc. products to Tesla, Inc. electric vehicles. Its high-temperature strength makes it essential in superalloys for jet engine turbine blades and gas turbine components used by companies like General Electric and Rolls-Royce Holdings. Cobalt-based alloys such as Vitallium are used in orthopedic implants, while Stellite is used for cutting tools and wear-resistant parts. Cobalt blue pigments remain vital for coloring porcelain, glass, and paint, and cobalt-60 is a critical source for food irradiation and cancer treatment in devices like the Gamma Knife.

Biological role and health issues

Cobalt is a key component of cobalamin, or vitamin B12, essential for DNA synthesis and neurological function in humans; a deficiency can lead to pernicious anemia. However, excessive exposure, particularly in industrial settings like hard metal production or mining in the Katanga Province, can cause adverse health effects. Inhalation of cobalt dust can lead to respiratory issues such as asthma and interstitial lung disease, known as "hard metal lung disease." The International Agency for Research on Cancer classifies cobalt metal with tungsten carbide as possibly carcinogenic. Environmental release, often from mining activities near Lubumbashi, can impact aquatic ecosystems.

Category:Chemical elements Category:Transition metals Category:Dietary minerals