Limestone As a Flux in Steel Making

Limestone Identification

• Limestone is the solid rock form of calcium carbonate. In nature, limestone is typically formed in the Earth's oceans. Shell and skeletal remains of sea creatures accumulate at the ocean's bottom, creating sediment. Over time, limestone hardens from the accumulated sediment. In addition, limestone's calcium carbonate composition can precipitate, or form, from the surrounding marine water for creating small limestone deposits.

Steel Manufacturing

• Steel creation begins with iron ore within a blast furnace. However, the iron ore must be heated significantly for the limestone to efficiently react and work properly. Heated air and coke -- solid carbon fuel -- combust to generate high heat within the blast furnace. Workers add limestone to the iron ore during its melting process.

Limestone Flux

• Crushed limestone is added to a molten iron ore solution. The heat within the mixture causes a chemical reaction within the limestone. As a result of the chemical reaction, the molten iron's impurities travel and adhere to the limestone flux, effectively purifying the iron's configuration. Typical impurities are sulfur and phosphorus. The resulting steel has a higher quality for strong structural integrity.

Removal

• Limestone does not normally remain in the steel mixture for hardening. The limestone and impurity combination rises to the top of a molten steel mixture during the heating period. Workers can easily skim the crushed limestone out of the mixture, effectively removing the impurities at the same time. The impurities are considered acidic in nature, causing steel deterioration and weakness if they remain in the final steel mixture.

Environmental Impact

• Limestone removes harmful sulfur from the steel, which effectively removes it from the environment. Sulfur contributes to air pollution when emitted into the atmosphere from industrial processes, such as steel manufacturing. Large amounts of steel manufactured each day would contribute a significant amount of sulfur into the environment without the limestone's natural flux processes.