The comprehensive utilization of oxide scale: being used in producing reduced iron powder and so on


Oxide scale which is generated on the rolled piece surface in the rolling process of the rolling mill has high content of iron. As China’s steel industry waste a large amount of oxide scale every year, it will be a very significant energy saving work to implement the comprehensive utilization of these oxide scales. According to the current research, the comprehensive utilization of oxide scale can be carried out in the following ways.

a. Oxide scale can be used to produce sponge iron or reduced iron powder

Sponge iron can be used as the supplement of the shortage steel crap. With the increasing amount of electric steelmaking, sponge iron is becoming more and more important. Due to the large equipment investment and complex process, currently it is still difficult to achieve rapid development in producing sponge iron with mineral powder. By applying appropriate technological process, coal dust can be used to reduce the oxide scale and produce the sponge iron that has high content of w(Fe), low content of impurities and stable composition, which is more suitable for being used as the high quality steel scrap than the sponge iron produced by ores (which often contains gangue impurity).

Oxide scale can be also used to produce the reduced iron powder, in which the production process can be generally divided as rough reduction and fine reduction. In the rough reduction process, the oxide scale is reduced into the sponge iron that has the content of w(Fe) more than 95 percents and w(C) less than 0.5 percent at about less than 1100 degrees Celsius; soon afterwards, smash the obtained sponge iron piece and conduct fine reduction under the ammonia decomposition atmosphere or pure hydrogen atmosphere in the range of 800 degrees Celsius-1000 degrees Celsius. Finally, smashing, screening, adjusting the particle size and making it into iron powders.

Oxide scale can produce reduced iron powder that used in the raw material of powder metallurgy. It can be reduced into the sponge iron that contains more than 98 percents of w(Fe) and generate qualified reduced iron powder before scarfing cinder, crushing, screening magnetic separation and fine reduction. Afterwards, the reduced iron powder is finely grinded in the ball mill and generates high purity iron powders that have different particle size by classifying screen. Among them , iron powder that has fine particle size can be used to produce key components of equipments, which can be fast stamped into mould and generate high strength, wear resistance and corrosion resistance components that used in the national defense industry, aviation manufacturing, communication and transportation, oil exploration and other important industries. In addition, the iron powder that has coarse particle size can be used to produce welding rods.

b. Oxide scale can be used as the sintering auxiliary ferrous raw material as well as the steelmaking flux and slagging melting agent

As FeO content of oxide scale is up to more than 50 percents, it is a kind of good performance sintering auxiliary ferrous raw material. The theoretical calculation results show that 1kg of FeO can release 1973J heat when oxidized into Fe2O3. After adding oxide scale into the sintering mixtures, the sintering productivity rate will be improved and the solid fuel combustion will be reduced due to the high temperature and sufficient sintering process. Practical production shows that 8 percent of oxide scale can increase yield by about 2 percents. Bao Steel uses oxide scale as the auxiliary material and adds it in the bedded ores, which will not only improve the permeability of sinter bed due to the big particle size of oxide scale, but also reduce the solid fuel consumption as the oxide scale will release heat in the sintering process.

In addition, oxide scale can be used as the flux of ores, which is used in the converter steelmaking. Oxide scale, being used as the flux and slagging melting agent, is a kind of high efficiency smelting flux material, which can improve the efficiency of steelmaking, reduce the consumption of coke and coal and prolong the service life of converter furnace.

c. Oxide scale can replace steel cuttings in smelting ferrosilicon or replace steel scrap in electric steelmaking

Steel cutting is an important raw material in smelting ferrosilicon. In china, about 2 million tons of steel cuttings are used in smelting the ferrosilicon every year, while the wasted oxide scale in the steel industry is about 10 million tons every year. New technology that uses oxide scale in smelting ferrosilicon instead of steel scrap has been developed now, which has achieved good economic benefits.

Scrap steel is used as the raw material in the electric steelmaking which has strict requirement on   the scrap steel material. However, as this kind of scrap steel has little quantity and high price, it is undersupply. In addition, it will bring significant economic benefits by using oxide scale, steel slag and other waste that have low price and wide source as the main raw materials instead of using the scrap steel that has little quantity and high price.