Manganese: It Turns Iron into Steel (and Does So Much More)

What is steel made of? Iron, most people would say — and they would be right. Far fewer know it is also made of manganese. Only a little goes into each ton, but it is as essential as the iron: you can't make steel without manganese.

The United States uses about 500,000 metric tons of manganese a year, mostly for steel, and imports all of it. Manganese (chemical symbol Mn) is a common ferrous metal making up roughly 0.1 percent of the Earth's crust — the 12th most abundant element. Early uses were mostly pigments and oxidants in chemistry, but its importance exploded with modern steelmaking in the 1860s. Because it is essential, irreplaceable in steel, and mined by only a few nations, it is counted among the most critical mineral commodities for the United States.

How it is used

Steel accounts for as much as 90 percent of manganese use, in the United States and worldwide.

• In turning iron ore — iron combined with oxygen — into iron, manganese removes oxygen and sulfur.
• It is an essential alloying metal that turns iron into steel, making it stronger and less brittle.
• Each ton of steel uses 6 to 9 kilograms: about 30 percent in refining the ore and the other 70 percent as alloy in the finished steel.

It is also alloyed with aluminium — adding corrosion resistance; most beverage cans are about 1.5 percent manganese — and with copper. Non-metallurgical uses include battery cathodes, soft ferrites in electronics, micronutrients in fertiliser and animal feed, water-treatment chemicals, and colourants for car undercoat paint, bricks, frits, glass, textiles and tiles. "Manganese violet" colours plastics, powder coatings, artists' glazes and cosmetics.

Ancient Egyptians and Romans used pyrolusite, a manganese dioxide mineral, to control the colour of glass: a little removed the greenish-yellow tint from iron impurities, more turned glass pink, purple or black. Manganese dioxide is still used as a colourant. Photo by Scott Jackson, USGS.

In ancient Greece, manganese naturally present in the iron ore the Spartans used may explain why their steel weapons outclassed their enemies'.

Where it comes from

Manganese combines readily with oxygen, carbon and silicon, forming many minerals. Ores usually hold 25 to 45 percent manganese, mostly as oxides (or hydroxides) and carbonates. They are widespread, but most of the world's supply comes from a few mining districts.

Most ores are thick layers of manganese-rich sedimentary rock laid down in ancient oceans under special conditions: changes in seawater chemistry first built up dissolved manganese, then precipitated manganese minerals on the seabed. These layers now lie in the bedrock of the continents. Some are rich enough to be ore as they are (primary ore); in others, later geologic processes enriched the original sediment (secondary ore). Nearly all ore is upgraded near the mine, and most is smelted into the alloys ferromanganese and silicomanganese, which — rather than the ore itself — are what most metallurgy uses.

Ferromanganese nodules carpeting the seabed off Johnston Island, in the U.S. Exclusive Economic Zone near Hawaii (field of view about 4 square metres); inset, individual nodules about 3 centimetres across from the equatorial Pacific. Photos by James Hein, USGS.

A vast potential source lies on the deep seabed of many oceans: potato-sized ferromanganese nodules. Thirteen organisations were exploring and researching them, mostly in the equatorial Pacific. If mining them proves technically, economically and legally viable, they could supply the world with manganese for a very long time.

World supply and demand

In 2011, 70 percent of the world's manganese ore came from four countries — in order, South Africa, Australia, China and Gabon. Those four plus Brazil and Ukraine hold 90 percent of proven reserves. The United States, like many industrial countries, especially in Europe, has no manganese reserves.

The country has two manganese ferroalloy producers and three manganese chemical producers, but still imports large amounts of alloys, chemicals and metal. Demand has always tracked steel production, which has typically grown 1 to 2 percent a year in the United States, and is expected to keep doing so.

Securing future supplies

World reserves are enough for foreseeable demand, but total dependence on imported ore has long worried the United States, given the risk of political or military disruption. The country has large resources of manganese-enriched rock, mostly in Maine and Minnesota, but they are far lower grade than ores available elsewhere and uneconomic to mine.

There is no global shortage. On land, South Africa's great Kalahari manganese district holds roughly 70 percent of the world's known manganese resources, so South Africa will likely stay dominant for a long time.

The Mamatwan manganese mine in South Africa's Kalahari district. A thick layer of manganese ore is mined from the open pit, whose benches follow the layering of the ore body. Photo by William Cannon, USGS.

If deep-sea mining becomes economic, supply could shift from land to ocean. Estimated nodule resources dwarf those on land and could greatly diversify supply for the United States and others — and besides the largely international deep seabed, substantial manganese resources might be developed within the U.S. Exclusive Economic Zone, entirely under U.S. jurisdiction.

The USGS Mineral Resources Program, the principal federal source of research and information on manganese and other non-fuel minerals, publishes production and consumption data.

Sources

• Cannon, W.F., 2014, Manganese—It turns iron into steel (and does so much more): U.S. Geological Survey Fact Sheet 2014–3087. https://pubs.usgs.gov/publication/fs20143087 — the USGS photographs come from its PDF; a steel photograph from Wikimedia Commons is left out.
• Rewritten in hubnx's own words.