Changes Of RO Phase And Kinetics Of Iron Oxide At High Temperature In The Process Of Steel Slag Reduction Reconstruction

The crude steel production of China ranked first on a global scale, brought about 100 million tons of steel slag discharge during the steelmaking process annually. About 7 to 10% iron loss was generated following the steel slag discharge, leading to about 7 to 10 million tons cumulative amount in iron loss each year. The high iron content of the slag kept the iron element exist mostly in the form of RO phase（mainly continuous solid solution formed by the FeO and Mg O）. The relatively low cementitious activity of this phase constraint the massive utilization of steel slag as cementitious material in cement and concrete industry. However, the RO phase can be decomposed and eliminated by reconstructing the structure of steel slag which obtained by a high temperature reaction with reducing component in a molten state during the discharge process in steelmaking. Along with the reconstruction of RO phase, iron oxide（FeO_x） can be restored and recycled while higher cementitious activity of steel slag can be achieved by applying water quenching treatment to molten slag so as to utilize the product in a more comprehensive way as a high class mineral blend with considerable additional value. In this study, a high-temperature reduction kinetics model for iron oxide reconstruction process was established by analyzing the occurrence state of iron element, the technological parameters including reduction efficiency of modifying component to FeO_x, the alkalinity of steel slag and the influences induced by the elimination of RO phase during the reconstruction process, theoretical guidance for online reconstruction of steel slag was obtained.The feasibility of characterizing the change of RO phase in FeO content and occurrence of Iron element in steel slag was studied. Results shown that FeO phase occupied the main volume fraction in steel slag while Fe₂O₃ hold the second position, simple substance iron was rarely appeared in general. The content of RO phase occupied about 20% volume fraction in steel slag, among the RO phase enriched 60 90% FeO content and 30 45% Mg O content of the total amount in steel slag. In conclusion, the major content of FeO in steel slag concentrated in RO phase, thus, it is feasible to characterize RO phase change by quantitative characterize the FeO content before and after the reconstruction process.The lime-using reconstruction process and changes of RO phase during reduction reconstruction process of steel slag were studied. As modifying material used in the reconstruction process, the CaO, main effective component in lime, reacted with RO phase preferentially to decompose its original structure, accompanied the process, the decomposed iron from RO phase reacted with CaO to form calcium ferrite and calcium aluminoferrite. However, the surplus iron in steel slag impeded the formation of C₃S, neither posed positive influence on cementitious activity nor brought equivalent economic value compared with simple iron recycling. The FeO_x phase in steel slag was reduced to metallic iron in pace with the decomposition of RO phase by applying melting method.The influences of technological parameters of reconstruction process i.e. temperature, alkalinity of steel slag and the original FeO_x content on the reduction efficiency of FeO_x phase and RO phase change were studied. Results indicated that: Temperature and alkalinity of steel slag influenced the reduction efficiency of FeO_x phase and RO phase change greatly during the reconstruction process of all the technological parameters. Reduction efficiency of FeO_x improved with the increasing of alkalinity of steel slag in melting state. The original FeO_x content had no influence on the reduction efficiency of FeO_x phase and RO phase change under certain temperature and alkalinity reaction conditions. A 90% reduction rate of FeO_x while a 2% or even lower content of FeO and FeO_x can be achieved with sufficient reducing agent under following conditions: temperature was 1500 1550 ℃, original FeO_x content was 15 30%, alkalinity of steel slag was within the range of 1.0 to 3.0, reaction time was 40 60 minutes.Kinetics of iron oxide reduction at high temperature in the reconstruction process of steel slag was also studied in this study. The research result indicated that: the reduction reaction of FeO_x and decomposition reaction of RO phase is a pseudo first order reaction, the key factor which impose restriction on reaction rate is the mass propagation speed of components in steel slag.The reduction reaction rate of FeO_x and decomposition rate of RO phase can be increased by elevating temperature, improving the alkalinity of steel slag or increasing the initial content of FeO_x with sufficient reduction agent. Reaction result presented a more remarkable influence in reduction rate on FeO than FeO_x which can be represented by k*, an apparent rate constant: the constant k* of FeO_x increased to 1.2¹.3 times the original value while that of FeO increased to 1.3¹.4 times the original value when reaction temperature increased from 1500 ℃ to 1550 ℃; The constant k* of FeO_x and FeO increased to 3 times the original value when alkalinity of steel slag increased from 1.0 to 3.0; The constant k* of FeO_x increased to 1.4¹.5 times the original value while that of FeO increased to 1.5¹.7 times the original value when the initial FeO_x content in steel slag increased from 15% to 26.87%. Reduction kinetics equations on iron oxide, FeO and FeO_x respectively, was founded when alkalinity was 1.0 while the reaction temperature was within the range of 1450 ℃ 1550 ℃, can be presented in the following formulas:...