Ferroalloys Processing
Ferroalloys are master alloys made of iron and one or more non-ferrous metals. They are classified into two main groups:
1. Bulk ferroalloys – produced in large quantities in electric arc furnaces (e.g., ferrochrome, ferrosilicon, ferromanganese, silicomanganese, ferronickel). These are mainly used in steelmaking and foundries.
2. Special ferroalloys – produced in smaller quantities but with diverse applications.
Approximately 90% of ferroalloys are used in the steel industry.
Production Methods:
Ferroalloys can be produced in submerged electric arc furnaces, metallothermic (exothermic) furnaces, or electrolytic cells. The most common is the submerged electric arc furnace, a reduction-smelting process. Metallic ores (ferrous, silicon, manganese, or chrome oxides) react with a carbon-based reducing agent (coke, charcoal, high/low volatility coal, or wood chips). Limestone may be added as a flux.
The raw materials are first crushed, screened to size, and, when necessary, dried before being transferred to the mix house for weighing and blending. From there, the prepared material is transported to furnace hoppers using conveyors, bucket elevators, skip hoists, or rail cars. The furnace charge is then fed by gravity through a chute, either continuously or in batches, depending on process requirements.
Inside the high-temperature reaction zone, the carbon source reacts with metal oxides to generate carbon monoxide, which serves as the reducing agent to convert the ores into base metals. An example reaction for ferrosilicon production is shown below:
Fe2O3 + 2SiO2 + 7C → 2FeSi7CO
Smelting in an electric arc furnace is achieved by converting electrical energy into heat. An alternating current applied to the electrodes generates an arc, causing current to pass through the furnace charge between the electrode tips. This creates a high-temperature reaction zone, reaching up to 2000 °C (3632 °F). Typically, three carbon electrodes, arranged in a triangular configuration, extend through the furnace cover into the shell.
The molten alloy and slag that collect on the furnace hearth are tapped at intervals of 1 to 5 hours through a tap hole. During tapping, and/or in the reaction ladle, slag is skimmed from the molten metal surface. The slag may be disposed of in landfills, sold as road ballast, or recycled as a raw material in a furnace or ladle to produce related ferroalloys.
Once cooled and solidified, the large ferroalloy castings are broken into smaller pieces using drop weights or hammers. These fragments are subsequently crushed, screened (sized), and stored in bins before shipment. In some cases, alloys are kept in lump form in storage inventories prior to final sizing for delivery.