Usually, there are two smelting types of iron ore:
1. Acid sinter
It mainly consists of iron concentrates and rich iron powder mixing with agents of fusion. The iron ore contained are mainly magnetite and hematite, and main binding minerals are fayalite (2FeO•SiO2) and kirschsteinite (CaO•FeO•SiO2).
The sintered acid iron ore does not pulverize naturally during the cooling process. It has high mechanical strength, and contains much ferric oxide (FeO), resulting in poor reducibility and bad temperature resistance.
A large amount of limestone is required to smelting this kind of iron ore and concentrates.
2. Iron ore concentrates
Poor iron ore can be ground and separated to obtain an iron powder with high grade. Iron ore concentrates is the raw material to produce artificial rich iron ore.
Iron ore concentrate can be divided into magnetic concentrate, hematite concentrate, and limonite concentrate according to different iron ore components. It can also be divided into weakly magnetic concentrate, strongly magnetic concentrate, flotation concentrate, and gravity concentrate.
In general, magnetite concentrate is obtained from magnetic ores by the method of magnetic separation.
Hematite concentrate is obtained by gravity separation, flotation separation, high-intensity magnetic separation, and magnetizing
calcination – magnetic separation or a combined separation process.
Limonite concentrate is obtained by gravity separation, high-intensity magnetic separation, or magnetizing calcination – magnetic separation.
There are 4 details of iron concentrates required by smelting plant:
1 High iron content
The iron content of magnetite concentrate should be more than 65%, iron in hematite concentrate should be more than 60％ and in limonite concentrate should be more than 50%. The fluctuation of iron content should be in the range of 0.5%.
2 Low water content
The humidity contained in the concentrate has large effects on storage, transportation, mixture, and briquette. Commonly, the humidity of magnetite concentrate should be no more than 10%, and no more than 12% in limonite concentrate and hematite concentrate.
3 Uniform size
The iron concentrate used for producing pellets should be uniform. There should be more than 70% of particles under the size of 0.074 mm, and the specific surface area should be better to be in the range of 1200 to 2000 cm2/g.
4 Low impurities
The fewer impurities (such as sulfur, phosphorus, lead, arsenic, zinc and copper), the better iron concentrates. It is usually required:
|Lead||No more than 0.1%|
9 elements in iron ore badly effected on its smelting
The minerals badly effected on the iron ore smelting are usually sulfur, phosphorus, potassium, sodium, lead, arsenic, zinc, titanium and copper. Generally, they have the following bad effects on smelting:
Elements that bad for iron ore smelting
1 Sulfur (S): it is the most harmful element to iron ore smelting. It will make the steel with hot brittleness. More sulfur contained in iron ore, more cost in the following blast furnace desulfurization will spend.
2 Phosphorus (P): it is also the common harmful element for steel material. It will bring the steel with cold brittleness. Phosphorus in iron ore will be sintered into the cast iron during the smelting process.
And during the following steelmaking process, the dephosphorization will be getting more complex and the cost will be increased.
3 Alkali metals (K & Na): alkali metals mainly include potassium and sodium.
The effect of potassium and sodium on the blast furnace is not proportional, and the blast furnace itself has a certain capacity of discharging alkali, and the alkali metal has little influence on the blast furnace within the control range.
However, if there is too much alkali metals remained in the iron ore, exceeding the alkali discharge capacity of the blast furnace, the alkali metals will be concentrated, causing the alkali metal content of the charge in the middle and upper part of the blast furnace to exceed the original level of the charge greatly.
More alkali metals contained in iron ore are inclined to reduce the softening temperature and move up the soft melt zone, which is not conducive to the development of indirect reduction.
4 Lead (Pb): almost all lead is reduced in the blast furnace. As the density of lead is as high as 11.34 t/m3, which is easy to destroy and burn though the brick joints of the furnace bottom.
5 Zinc (Zn): zinc is easy to gasify, and the vaporized zinc vapor easily enters the brick joint. The zinc will become zinc oxide after oxidation, and its volume will expand, thereby destroying the refractory brick lining on the upper body of the furnace, and harming the smelting effect.
6 Arsenic (As): arsenic is also one of the harmful elements for steel, which makes the steel cold brittleness and poor welding performance.
In addition, arsenic volatilizes in the sintering process, which has a great impact on the environment.
7 Copper (Cu): copper will bring the steel with hot brittleness, which will make steel hard to roll and welding. However, a small amount of copper can improve the corrosion resistance of steel.
In blast furnace smelting, all the copper is reduced into cast iron.
8 Titanium (Ti): it can improve the wear resistance and corrosion resistance of steel.
However, during the smelting of the blast furnace, the slag will deteriorate, and about 90% of the titanium will enter into the slag.
The low content of titanium has little effect on the slags and smelting process. But when the content is high, it will thicken slag and cause poor fluidity, which has a great influence on the smelting process and is easy to form furnace nodules.
For the smelting of iron ore, better control of the above harmful elements in the content of iron ore, not only can control the smelting effect, but also can improve the performance of the product, achieving good iron ore utilization rate, and bringing more profits for the enterprise.