Manganese

Manganese may be the most important industrial metal that most people have never heard of. Without it, modern steel production would be nearly impossible — manganese removes sulfur and oxygen impurities from molten steel and acts as a critical alloying element that dramatically improves hardness and toughness. It also plays essential biological roles, acting as a cofactor in enzymes that protect cells from oxidative damage and that help build the connective tissue of bones. In the deep ocean, manganese accumulates into mysterious potato-sized nodules on the seafloor, representing one of the largest untapped mineral deposits on Earth. Despite its quiet reputation, manganese is woven into both the history of chemistry and the fabric of modern civilization.

Steel and iron production consume approximately 90 percent of all manganese mined globally. Manganese is added to steel as ferromanganese or silicomanganese alloys to desulfurize the melt, increase hardenability, and improve wear resistance. High-manganese Hadfield steel, containing around 12 percent manganese, is extraordinarily tough and work-hardens under impact, making it ideal for mining equipment, rail switches, and rock crushers. Manganese dioxide is the cathode material in standard alkaline batteries and carbon-zinc dry cells. Potassium permanganate, a vivid purple compound, is used as a disinfectant, water treatment agent, and oxidizing agent in organic synthesis. Manganese sulfate and other manganese salts serve as micronutrient fertilizers. Methylcyclopentadienyl manganese tricarbonyl was used as an octane-boosting gasoline additive, though environmental concerns have reduced its use.

The mineral pyrolusite, manganese dioxide, was known to ancient glassmakers who used it to decolorize glass tinted green by iron impurities — a practice referenced by ancient Romans. In the eighteenth century, Swedish chemist Carl Wilhelm Scheele recognized pyrolusite as containing a new element, but it was Johan Gottlieb Gahn who first isolated metallic manganese in 1774 by reducing pyrolusite with carbon. The element was named after Magnesia, a region in Greece associated with several mineral discoveries. Early chemists quickly found manganese useful in bleaching and in chemistry, and the industrial revolution cemented its role in steelmaking. The discovery that manganese is an essential biological trace element came much later, in the twentieth century, when researchers identified manganese-dependent enzymes including superoxide dismutase and arginase.

Manganese is the twelfth most abundant element in Earth's crust, averaging about 950 parts per million. It is widespread in rocks, soils, and water, most commonly as oxide minerals. The largest land-based deposits are in South Africa, which holds roughly 80 percent of global reserves, along with significant deposits in Australia, China, Brazil, India, and Gabon. Pyrolusite and psilomelane are the most commercially mined ore minerals. Deep-sea manganese nodules, which litter vast swaths of the Pacific, Atlantic, and Indian Ocean floors at depths of 4,000 to 6,000 meters, represent potentially enormous resources also containing cobalt, nickel, and copper, though commercial harvesting has not yet begun at scale. Manganese is an essential micronutrient present in all living organisms, concentrated in the liver, kidneys, and bones.

Manganese forms compounds in oxidation states from +2 to +7, producing a striking variety of colors and chemical behaviors. Manganese(II) compounds, typically pale pink, are the most stable under ordinary conditions. Manganese dioxide, MnO2, is the primary ore mineral and an important industrial oxidant and battery cathode material. Potassium permanganate, KMnO4, is an intensely purple solid that releases oxygen as it decomposes, making it a powerful disinfectant and oxidizing agent used in medicine, water treatment, and synthesis. Manganese sulfate is used as a fertilizer supplement and in animal feed. Manganese chloride serves as a precursor for other manganese chemicals and as a nutritional supplement. In biology, manganese is a key component of the oxygen-evolving complex in photosystem II, the molecular machine in plants and algae that splits water molecules to release the oxygen in Earth's atmosphere.

• Ancient Roman glassmakers added manganese dioxide to their molten glass to neutralize the green tint caused by iron impurities — they called it 'glassmakers' soap' without knowing they were using a transition metal compound.
• The seafloor contains trillions of manganese nodules — potato-sized mineral concretions that grow at the astonishing rate of a few millimeters every million years, making them among the slowest-growing geological formations on Earth.
• Hadfield steel, developed in the 1880s by Robert Hadfield, contains about 12 percent manganese and actually gets harder when struck or abraded, a property called work hardening that makes it ideal for mining and railroad equipment.
• The oxygen in Earth's atmosphere owes its existence in part to manganese: the oxygen-evolving complex at the heart of photosynthesis uses a cluster of four manganese atoms to split water molecules and release O2.
• Potassium permanganate is so intensely colored that a single crystal dissolved in a bathtub of water turns the entire volume a vivid purple, demonstrating the extraordinary tinting power of manganese in its highest oxidation state.