Ferrous Metals: Properties, Production, and Environmental Impact
Ferrous metals are those containing iron as a base. Types of iron minerals include magnetite, hematite, limonite, and siderite. These minerals have the advantage of being abundant and contain a high proportion of pure iron.
Steel Production
The steel gathering process occurs through blast furnaces (using iron ore) and electric ovens (using scrap metal).
Raw Materials
Iron ore: Before being introduced into the furnace, iron ore should be subject to a series of treatments. These treatments consist of crushing and grinding the ore to separate the useful material from the unusable.
Coke: Created from coal, coke’s mission is to produce the heat needed to smelt the ore and to generate the chemical reactions necessary for iron oxide reduction. It also supports the weight of the raw material introduced, preventing crushing, allowing burning at the bottom, and letting gases rise to the top of the furnace.
Flux: Composed of lime, its mission is to:
- React chemically with the unusable material in the mineral, dragging it towards the top of the liquid mass to form slag.
- Lower the melting point of the unusable material so that the slag is liquid.
Steel Transformation from Cast Iron
This involves the removal of impurities from pig iron in refining ovens. The most commonly used process in steel refining is the converter or a process called LD.
Feedstock Used in Electric Furnaces
Scrap metal (not containing other non-ferrous metals like copper, aluminum, or lead), flux (limestone), and alloys (Ni, Cr, Mo, etc.) are used.
Steel Casting
Conventional: Liquid steel is poured into molds to achieve the desired shape. It is then allowed to cool, and the piece is removed.
Continuous: A more economical method where liquid steel is poured onto a bottomless mold or lid-shaped cross-section curve to get the geometric shape of the product.
On Molds: If product demand is low, the material is strained inside molds and cooled. The ingots are then stored until demand increases.
Rolling Mills
This involves passing the solidified steel between two rollers that rotate at the same speed but in opposite directions. This increases the length and reduces the cross-sectional area. There are two types:
- Hot rolling: Occurs at approximately 1000°C.
- Cold rolling: Occurs at ambient temperature.
Classification of Ferrous Products
Iron: Ferrous products where the percentage of carbon is between 0.01% and 0.03%. These are very soft and difficult to obtain, therefore having few industrial applications.
Steels: Iron-carbon alloys that can contain other chemical elements. Carbon content ranges from 0.03% to 1.76%.
Cast Irons: Iron-carbon alloys that can have other chemical elements. Carbon content ranges from 1.76% to 6.67%.
Graphite: Obtained when the carbon percentage is greater than 6.67%. In practice, these have limited applications as they are very fragile.
Types of Steel
Unalloyed: When the percentage of the chemical elements involved in the alloy is below the maximum indicated (0.6-0.7%).
Alloy or Special: Besides iron and carbon, these contain other elements provided above the specified limits.
Commercial Presentations of Steel
Sheet metal: Rolled plates measuring from 1×2 meters to 3×3 meters.
Bars: Pieces much longer than wide, massive, and with variable sections.
Profiles: Hollow pieces of variable sections whose length can vary between 5 and 12 meters.
Environmental Impact of Ferrous Products
Raw Materials: Iron ore mines are often open pit, causing acoustic and scenic impact, as well as destruction of habitats. Coke production emits CO, CO2, and ammonia fumes.
Mineral Processing to Commercial Product: Emissions released during blast furnace refining and lamination include:
- Heavy metals (mercury, cadmium, etc.) that pollute air, water, and land.
- Waste gases and dust from blast furnaces and electric furnaces (CO, CO2, NOx, SOx, etc.).
Other types of pollution: Mud from gas purification, wastewater contaminated with acid oils, and noise.
Measures used to counteract these effects: Isolation of areas with noisy machinery, filtering of heavy metal particles and gases, and separation of industrial areas from urban centers.
Disposal or Recycling of Used Ferrous Products: These impacts are much smaller than those caused by manufacturing the product from iron ore.