Steel slag specifically refers to the slag discharged during the steelmaking process, mainly refers to the oxides formed after the elements in the metal charge are oxidized during the blowing process, the eroded furnace lining and repair materials, and impurities brought in by the metal charge And slagging materials specially added to adjust the properties of steel slag, such as limestone, dolomite, iron ore, silica, etc.

(1) Main components of steel slag
Steel slag is mainly composed of oxides of calcium, iron, silicon, magnesium and a small amount of aluminum, manganese, phosphorus, etc. The main mineral phases are solid solutions formed by tricalcium silicate, dicalcium silicate, calcium magnesium olivine, calcium magnesium rhodoxene, calcium aluminate ferrite, and oxides of silicon, magnesium, iron, manganese, and phosphorus. Contains a small amount of free calcium oxide, metallic iron, fluoroapatite, etc. In some areas, because the ore contains titanium and vanadium, steel slag also slightly contains these components.

(2) Types of steel slag
According to different smelting processes, the steel slag produced can be mainly divided into converter slag, electric furnace slag, casting slag and stainless steel slag. Converter slag is the waste slag produced during converter steelmaking. It mainly comes from the impurities brought in by the metal charge, the oxides formed after the oxidation of elements contained in scrap steel and molten iron, and slagging agents such as desulfurization products, oxidants, silica, and limestone are added. And eroded lining materials, etc.; electric furnace slag is the slag produced in the process of electric furnace steelmaking, which mainly comes from impurities brought in during charging, adding silica, limestone and other slagging materials, iron, sulfur, phosphorus, The oxides formed after the oxidation reaction of silicon, aluminum and other elements and the eroded furnace lining materials, etc.; the casting slag is the mixture of slag and molten steel left after the molten steel in the ladle passes through ingot casting or continuous casting; , The waste slag produced in the 400 series stainless steel process has a higher mineral composition than converter slag, and the content of inconel is higher.

(3) Treatment and application of steel slag
With the diversified development of domestic and foreign steelmaking processes, technologies, physical and chemical properties of steel slag, and slag-making systems, steel slag treatment processes are increasingly diversified, mainly including air quenching, water quenching, hot pouring, hot stuffing, Roller method, air-cooled spray method, etc. When selecting a steel slag treatment process, usually proceed from investment, environment and energy saving, comprehensive utilization of steel slag, etc., on the basis of ensuring the smooth development of the steelmaking process, comprehensively consider the fluidity and viscosity of steel slag, and select the best treatment process , fully separate slag and iron, and ensure the activity of steel slag as much as possible, and minimize the instability of steel slag.
Steel slag production is generally 15% to 20% of crude steel production. According to the conversion of crude steel production, the world will discharge about 282-376 million tons of steel slag in 2020, and my country will discharge about 149 million tons of steel slag in 2019, and the amount of steel slag will increase to about 160 million tons in 2020, and there is still a large amount of steel slag that has not been processed.

The ways to use steel slag are mainly concentrated in the following aspects: as road materials, backfill materials, sinter raw materials, steel slag cement, steel slag powder used in concrete, floor tiles and building wall materials.
(1) Used as raw materials for sintering ore and ingredients for ironmaking and steelmaking
There are more than 50% calcium oxide in steel slag, which can partially replace lime as sinter flux. Adding an appropriate amount of steel slag to the sintered ore can improve the quality of the sintered ore, promote the improvement of the drum index and sintering rate, reduce the weathering rate, increase the yield of finished products, and at the same time, it is beneficial to the improvement of sintering pelletization and sintering speed, and the production cost is also reduced. It can be reduced; as flux for ironmaking and steelmaking, steel slag is returned to blast furnace for use, mainly by using calcium oxide in slag to replace limestone. It can also recover and utilize beneficial components in steel slag, reduce flux consumption, improve the fluidity of blast furnace slag, and increase the output of ironmaking and steelmaking. However, it cannot be used in large quantities, because the strong alkaline substances in steel slag have an impact on the service life of the blast furnace. There are nearly 25% metallic iron in steel slag, and 10% to 15% steel scrap. Through manual and magnetic separation, scrap iron and steel of various sizes can be extracted and recovered, and a large part of the slag with high iron grade can be used for refining Steel and iron-making raw materials can reduce environmental pollution and improve economic benefits.
(2) Road materials
The most important thing to use steel slag as road material is to solve the problem of poor stability of steel slag, which can be done from the following two aspects: first, pretreatment of steel slag, so that free calcium oxide can be decomposed into Ca(OH)2 as soon as possible. For example, the use of water spray heat stuffy, waste heat self-decomposition and other processes. Then, active materials such as lime are mixed into the steel slag. The addition of active materials such as lime reacts chemically with steel slag, which can accelerate the digestion of f-CaO in steel slag and hydrate it to generate Ca(OH)2. It has a very good improvement effect, and its strength is high, and it also has a very good effect on improving the bearing capacity of the roadbed.
(3) Backfill material
Steel slag has certain characteristics such as hydraulicity and gelatinization. Taking advantage of these characteristics, using steel slag as backfill material can improve the quality of trench backfill. However, in order to ensure the quality of backfill engineering, it is necessary to formulate material technical performance standards and mixing processing technology. . Hot powdered steel slag is used as trench backfill material, which can meet the requirements of backfill strength, stimulate the potential activity of steel slag, and develop its engineering application characteristics. Civilized construction environment and many other aspects have economic, social and environmental benefits.
(4) Floor tiles and building wall materials
Finely ground steel slag and adding appropriate amount of additives can reduce the instability of f-CaO, and can be used as floor tiles and building wall materials. The material has stable performance, good frost resistance, and the strength continues to increase in the later stage, so it can be used as a load-bearing wall material in industrial and civil buildings.
(5) Steel slag cement and steel slag admixtures used in concrete
Steel slag contains tricalcium silicate, dicalcium silicate and other gelling substances, which have certain hydraulic gelling properties. In addition, the content of Fe2O3 in steel slag is also high, which is very suitable for the production of cement admixture to replace iron ore powder. The particle size of steel slag is generally not greater than 12mm before it can be used as cement mixture, and the amount of steel slag should not exceed 10%. The addition of steel slag powder is beneficial to improve the density, impermeability and wear resistance of concrete, and at the same time protect the steel bars. The liquid phase alkalinity of steel slag powder is above 14.0, adding a certain amount of steel slag powder in concrete can also change the liquid phase alkalinity of concrete and improve the performance of concrete.