The molten steel slag of the blast furnace or the iron furnace contains 10% to 30% of Fe, 40% to 60% of CaO, and about 2% of Mn. If you return it directly to the blast furnace as a flux, it will save a lot of limestone and dolomite resources. Ca, Mg and the like in the steel slag are present in the form of oxides, and do not need to undergo the decomposition process of the carbonate, thereby saving a large amount of heat energy. Since the current blast furnace utilizes high alkalinity sinter or flux sinter, substantially no limestone is added, so the amount of steel slag directly returned to the blast furnace instead of limestone will be limited. However, for ironworks with insufficient sintering capacity and high limestone in the blast furnace, the use of steel slag as a blast furnace flux is still very large.
Steel slag can also be used as a molten iron furnace to replace limestone and some fluorite. It is proved that it has no obvious influence on the temperature of molten iron, the sulfur content of molten iron, the melting rate, the alkalinity of slag and the fluidity, and is technically feasible. Steel mills that use iron furnaces and a considerable number of machinery plants that produce castings can be used.
For steelmaking return slag converter steelmaking, the use of high alkalinity return steel slag per ton of steel is about 25kg, and with the use of dolomite, steelmaking can be used to form slag early, reducing the erosion of initial slag on the lining, which is beneficial to increase the furnace age and reduce The refractory material is consumed and can replace fluorite. Some steel mills in China have been used in production and have achieved good technical and economic effects.
Recycling scrap steel slag generally contains 7% to 10% of scrap steel and steel granules. Of the more than 100 million tons of steel slag accumulated in China, there are about 7 million tons of scrap steel. In the capital construction, a large amount of scrap steel and some magnetic oxides can be recovered. The water-quenched steel slag is in the form of granular steel particles. The magnetic separator is easy to extract and can be used as a steel temperature regulating agent.
In short, the steel slag has a good effect on the use of metallurgical raw materials in the steel plant, and the utilization value is also high. In areas where the phosphorus content of mineral resources in China is less than 0.01%-0.04%, the return amount of steel slag in the factory can reach 50%-90%.
At the beginning of the 20th century, foreign countries began to study the use of steel slag. However, due to the complex and variable composition of steel slag, the utilization rate has not been high. With the increasing tension of mineral resources and energy, and the development of steelmaking and comprehensive utilization technologies, the utilization rate of steel slag in various countries has increased rapidly since the 1970s. The United States produces more than 17 million tons of steel slag per year, with the highest utilization rate in the 1970s. Balance has been reached. According to statistics in 1988, China's steel mills have accumulated 100 million tons of steel slag, covering an area of ​​over 10,000 mu (1 mu = 666.67 m2), which has become a serious public hazard. In the past 20 years, China has produced more than 10 million tons of steel slag every year, the utilization rate has reached about 61%, and the economic benefit of steel slag treatment is as high as 40 yuan/ton. The main use of steel slag abroad is to recycle itself in the steel company, instead of using lime as a flux, returning to the blast furnace or sintering furnace as ironmaking raw materials, and also can be used for highway subgrade, railway subgrade and as a cement raw material to improve soil. According to the survey, the comprehensive utilization of steel slag in China is: 60% of land construction, 23% of road construction, 6.4% of cement production, 5.8% of sintering flux, and 4.8% of others.
The sintered flux converter steel slag generally contains 40% to 50% of CaO, and the 1t steel slag is equivalent to 0.7 to 0.75 tons of limestone. The steel slag can be processed to a steel slag powder of less than 8mm to replace part of the limestone as a sintering flux. The addition amount depends on the ore grade and the phosphorus content. The concentrate with high grade and low phosphorus content can be added to the steel slag 4%-8 %. The rate of sintered nuggets is increased, the weathering rate is reduced, and the yield is increased. In addition, due to the looseness of the water-crushing slag and uniform particle size, the gas permeability of the material layer is good, which is favorable for sintering ball formation and increasing sintering speed. In addition, due to the oxidative heat release of Fe and FeO in the steel slag, the heat required for the decomposition of calcium and magnesium carbonate is saved, and the fuel consumption of the sinter is reduced. Steel slag is used as a sintering flux, which not only recycles the useful components such as steel particles, iron oxide, calcium oxide, magnesium oxide, manganese oxide and rare elements (V, Nb...) in the slag, but also becomes a reinforcing agent for sinter. Significantly improved the quality and yield of the sinter. China has carried out a lot of research work on steel slag for sintering, and many steel mills have achieved good results. For example, after the Jinan Steel Plant is equipped with the water quenching furnace steel slag in the sinter, the technical and economic effect is that the utilization coefficient of the sintering machine is increased by more than 10%; the drum index is increased by 2% to 4%; the coke consumption is reduced by 5%; and the FeO is decreased by 2 %. Although the iron grade is reduced by 1% to 2%, the utilization factor of the blast furnace is still increased by 0.1t (dç©–3); the coke ratio is reduced by 31kg/t of iron. The use value per ton of steel slag can reach more than 20 yuan.
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