Dolomitic Lime in Steelmaking

Dolomitic Lime in Steelmaking

Steel is one of the world’s most important construction materials. Steel is used in almost all aspects of modern life, including buildings, bridges, cargo ships, automobiles, appliances, medical instruments, and many other applications.

In 2024, the United States produced 81 million tons of raw steel with Indiana, Ohio, Texas, and Pennsylvania producing most of the nation’s steel. Roughly 13% of America’s steel consumption is from imported sources. In June 2025, U.S. steel tariffs rose to 50%. As of August 2025, U.S. steel production is up 1.2% year over year.

Steel is an alloy of iron and carbon, and contains smaller amounts of manganese, silicon, phosphorus, sulfur, and oxygen. Carbon steel is typically over 98% iron. Stainless steel, engineered for corrosion resistance, contains significant amounts of chromium and nickel. 304 stainless steel, for example, is also known as 18/8, which is 18% chromium and 8% nickel. Iron is the major component in all types of steel.

Iron ore consists of iron oxides, the primary forms being magnetite (Fe3O4) and hematite (Fe2O3). In the United States, iron ore is mined in Michigan, Minnesota, and Utah. When heated in the presence of a reductant, such as carbon monoxide, metallic iron is obtained.

The extraction of iron from iron ore dates to about 2,000 BC. Furnaces called bloomeries were used to create blooms of hot metallic iron, which were then hammered and shaped into the desired objects. This was referred to as wrought iron. Cast iron is an iron product which contains a higher oxygen content and is harder to shape.

The blast furnace appeared in Europe in the 14th century. The modern blast furnace uses coke, iron ore and limestone to produce “pig iron”. Pig iron is an intermediate iron product which contains relatively high amounts of oxygen. Pig iron is then sent to a basic oxygen furnace which is used to make steel. In the United States, basic oxygen furnaces account for 28% of steel production. The balance, 72%, is almost entirely produced from electric arc furnaces.

A major advantage of steel is that it can be recycled indefinitely. Electric arc furnaces are commonly used today and use electrical current to melt recycled steel. Graphite electrodes bore into the scraps of steel until melting occurs, and heating may be supplemented using chemical energy.

Lime is a critical ingredient in the production of steel. Lime serves as a flux to remove impurities such as silica, phosphorus, and sulfur. In an electric arc furnace, the lime flux consists of quicklime (CaO) with a blend of up to 50% dolomitic lime (CaO·MgO). The total flux is about 50-120 pounds per ton of steel. In a basic oxygen furnace, the flux is about 30-50% dolomitic lime.

Dolomitic lime is a naturally occurring mineral which is calcined in a lime kiln to remove the carbonate group. Dolomitic lime is much higher in magnesium than quicklime. The magnesium oxide component of dolomitic lime is typically about 40.5% by weight.

The primary advantage of dolomitic lime versus quicklime is that it extends the life of refractory bricks in the furnace. Basic refractories contain magnesia, dolomite, and chrome. Magnesia brick is made from periclase, a dead-burned form of magnesium oxide. The magnesium content provided by dolomitic lime in the molten steel will slow the dissolution of magnesium-based refractory bricks.

Martin Marietta Magnesia Specialties manufactures high-purity dolomitic lime in Woodville, OH, serviced by rail and truck transportation for flexible logistics.