Spongy iron is obtained by restoring concentrates or high-quality iron ores when exposed to relatively low temperatures - less than 1100 degrees Celsius. Such processes exclude ore smelting and sintering.
History
It has long been proven that it is possible to immediately obtain iron from ore. In the laboratory, this process is easy to implement. As a result, metallurgists were faced with the task of creating technological methods for the extraction of iron in industrial volumes directly from ore. Now such methods are found and implemented in production.
Iron, obtained directly from ore, is called sponge. And production methods are homeless or direct recovery methods.
The first experiments on producing sponge iron without using blast furnaces in the Soviet Union were undertaken in the 1950s.
The first production of this metal was introduced into the industry in the 70s. The first technological methods for producing sponge iron without the use of blast furnaces were notable for their low productivity. The resulting product contained many diverse impurities.
Natural gas gave a new impetus to this production. In the 80s of the XX century, it began to be widely used in mining and metallurgical production. Then it was found that it is ideal for direct reduction of iron from ore. Moreover, other non-natural gases began to be widely used (associated gas from oil production, gas fractions during the gasification of various coals, etc.).
The improvement of technological processes and their introduction in the 90s led to the fact that the energy intensity and capital costs for direct reduction of iron decreased significantly. A significant increase in non-blast furnace iron production began.
Direct non-routine production of spongy iron - processes when a metal is reduced from ore using gases, solid carbon. And also jointly - solid carbon and gas. It is carried out at a temperature of the order of 1000 degrees Celsius. At the same time, the natural rock is not brought to slag, impurities in it are not restored, as a result of which the metal is obtained quite clean. Specialists call this process other terms:
- direct production of spongy iron;
- coke-free metallurgy;
- homeless metallurgy;
- partial metallization of ore.
Currently, methods of mining metal by such methods on an industrial scale are practiced in Russia, China, Sweden, Germany, the UK, Norway and other countries.
All known methods are divided into two groups:
- iron is formed under the influence of a gaseous reducing agent on the ore;
- under the influence of solid reducing agent on iron ore.
Almost five hundred patented methods for producing spongy iron by the homeless method.
Iron reduction with a gaseous substance
Hydrogen and carbon monoxide are used for gaseous reduction. Usually use the method when the iron ore is ground and heated to 850 degrees, followed by firing. Then it is sent to a rotary tube furnace. There, the metal is reduced under the influence of reducing gases moving towards the ore mass. Before leaving the oven, it enters a cooling container. Then the final product is crushed using a ball mill.
Subsequently, the mass passes through a special magnetic separator. The iron sorted by the separator then goes under the press, which carries out the formation of sponge iron into briquettes.
Iron production as a solid reducing agent
If the production involves the technology of producing sponge iron by solid reduction, then this method involves the following operations:
- ore crushing and grinding;
- to achieve a high concentration of iron, not more than 3% waste rock, magnetic enrichment is carried out;
- enriched ore is mixed with fossil fuels of organic origin, which include sawdust and other similar organic structures;
- creation of the resulting mass of briquettes, followed by moving them for firing in the furnace.
The reduction of iron occurs due to the combustion of carbon, which is enclosed in briquettes.
The resulting sponge iron, both during solid and gaseous reduction, is subsequently sent for standard processing to produce steel.
Remelting is usually carried out in electric furnaces, while the necessary amount of carbon and other impurities is introduced into the metal.
Process classification
Metallurgists classify the processes of homeless iron production by the type of final product, namely:
- production of materials for a blast furnace with partial metallization (from 30 to 50 percent);
- production of sponge iron, a solid, highly metallized product (from 85 to 95 percent), for subsequent processing into steel;
- iron production of a critical, ductile metallized product;
- production of intermediate or cast iron in a liquid state, for further melting process.
Direct Recovery Products
Four types of direct reduction iron products are commonly considered:
- spongy;
- metallized charge;
- screaming;
- cast iron or carbon intermediate.
Sponge iron
It is obtained as a result of processes when the reduction of metals occurs without melting, at a temperature of less than 1000-1200 degrees Celsius. Based on what the initial raw material was, hard sponge iron - porous structures, or pellets. In certain cases, it is a metal powder. In addition, this metal is also characterized by the fact that it has a sufficiently high porosity (sponge-like shape) due to the fact that upon restoration, the bulk characteristics of the raw materials underwent insignificant changes.
The porous surface of such iron leads to a high degree of oxidation during storage and transportation, when exposed to an unfavorable environment (high humidity).
The chemical composition of this metal is due to its composition with the initial raw material (ore). Compared to scrap, sponge iron is cleaner. In it, the minimal presence of impurities of other metals.
The sponge iron obtained by direct reduction is also distinguished by the presence of gangue in it. Due to the fact that the source material is rich concentrates and ores, they are not subjected to additional purifications. As a result, iron contains all inclusions of gangue from the source ore.
Sponge iron has found its application in the production of steel, the manufacture of iron powder and copper cementation.
Metallized charge
Partially reduced iron is called a metallized charge. It is used to cool the melting process, as well as for subsequent melting in blast furnaces. The recovery rate of metallized charge is below 80%. Spongy iron is much cleaner, its recovery is more than 90%.
Screaming Iron
Critical iron produced in a homeless manner is produced in tubular rotary kilns. Its recovery temperature is in the range from 1100 to 1200 degrees Celsius. This product is a small metal particles in which slag impurities. The volume of slag in the critical iron is high, approximately 10-20 percent. This iron is characterized by significant impurities of sulfur and phosphorus.
Apply kritz for subsequent remelting in blast furnaces. Certain technologies use this product for steelmaking in electric furnaces.
Carbon Intermediate or Cast Iron
These products are obtained with solid fuel recovery technology. In their characteristics, they are similar to those smelted in blast furnaces. Moreover, carbon intermediate or cast iron is sometimes obtained with a much lower content of impurities.
Further work with these materials for steel production is carried out by traditional methods.