Chemical Composition And Reaction Conditions On The Effect Of Composition, Property And Iron Occurrence State Of Reconstructed Slag

Converter steel slag emission accounts for 15 percent to 20 percent of steel production with the speed of nearly 100 million tons every year. The accumulative storage of steel slag is nearly 1 billion tons in our country, it belongs to the largest industrial solid wastes. By dosing adjusting materials during the discharge process,Fe Ox is reduced and the molten slag form the similar blast furnace slag in the secondary reaction with high temperature heat. It can realize the three-win utilization of "slag", "iron" and "hot".In this paper, the high alkalinity and low silicon-aluminum steel slag was selected as the research object, and the adjusting materials contain kaolin clay, coal gangue and coal cinder. Reference to calcium-silicon-aluminum ternary phase diagram, the mixture list was designed based on chemical composition. The key parameters effect on grass content and cementitious activity of reconstructed slag was proposed, and the high-temperature physical property of molten slag was used to explain it. The influence of reaction conditions effect on structure and properties of reconstructed slag was investigated, including reaction temperature, holding time, water-quenching temperature and uniformity of material. The change of iron occurrence state was discussed with different dosage of adjusting material,reaction time, type and dosage of reductant. It is expected that the work lays a theoretical foundation for the new technology for steel slag on-line reconstruction. The results suggest as follows:Alkaline coefficient and Si/Al have a great effect on grass content of the reconstructed slag. If the Si/Al is greater than 1.7, when the alkali coefficient is 0.92~1.16, the grass content of reconstructed slag is higher than 90% and the 28 d activity index can reach of S95 grade of blast furnace slag powder. When the alkaline coefficient increases from 1.20 to 1.40, the grass conten greatly drops to less than 45% and the 28 d activity index is lower than 80%. When the alkaline coefficient is higher than 1.77, the reconstructed slag is difficult to melt and water quenching. If the Si/Al is reduce to 0.5, the grass content of reconstructed slag can reach more than 80% when the alkaline coefficient is 1.69, as the melting temperature decrease. However, this slag has so bad adaptability with the cement that they were only justifiable used for high aluminum slag.The theory of slag structure and high-temperature physical property may explain its internal mechanism. By dosing silicon-aluminum adjusting materials into high alkalinity steel slag, the alkaline coefficient of slag will decrease and the chemical composition point moves to the direction of decreasing liquidus temperature in ternary phase diagram. The superheat and uniformity of molten slag increase with the melting temperature decreasing. The heat exchange between slag and water is rapid and full in the process of water quenching as the free fluidity of molten slag is improved. It leads to a sharp raise of slag viscosity and the reconstructed slag is mainly composed of glass phase.Under the condition of suitable chemical composition, the major-minor order of reaction conditions which influence the effect of steel slag reconstruction is reaction temperature > holding time > water-quenching temperature. When reaction temperature is higher than melting temperature of 50℃ above, the grass content of reconstructed slag is close to 90%. If the temperature difference is 25℃, the grass content is significantly lower. The effect of the holding time on steel slag reconstruction is related to reaction temperature. The longer holding time can improve the grass content of reconstructed slag when the reaction temperature is low.The reduction reaction of Fe Ox is carried in the order of Fe2O3-Fe3O4-Fe O-Fe step by step in steel slag. The Fe2O3 is more easily reduced than Fe O and the reduction reaction occurs at the same time. It may lead to a lot of iron exist in Fe2+ state, if the reduction component is insufficient. The reconstruction slag is completely fused and the slag-iron separation result is good with sufficient adjusting material. The recovery rate of iron can reach more than 93% and the coarse iron grade is over 82%.