Oxidation Modification Of Steelmaking Slag And The Composition,Structure And Property Of Modified Slag

Steelmaking slag,produced via separating molten steel from impurities,is a byproduct of the steelmaking industry.Dumping of the slag occupies large areas and always results in serious environmental problems.In additon,deposited slag is also a huge waste of resources.Steel slag contains some cementitious minerals,the cement industry can use slag a supplementary material for replacing part of raw materials.However,free lime,periclase and excess wustite in the slag are unfavorable.The presence of free lime and periclase leads to highly problematic swelling.Meanwhile,excess amount of wustite damages the mechanical properties of slag cement.In view of the problems existing in the current steel slag utilization process,this study proposes a high-temperature modification process for molten steel slag and a solid-phase modification process for depositing steel slag.By means of an oxidizing atmosphere?air?,wustite and periclase in the steel slag are transformed into ferromagnesium spinel groups,which can be separated by magnetic separation.Simultaneously,calcium ferrate,which has a certain hydration activity,is produced by the reaction of lime and wustite.In this paper,the influence of the modified process on the composition,structure and performance of steel slag was studied.The evolution law and hydration kinetics of modified slag were discussed.The results show that the amount of spinel in the modified slag increases first and then decreases with increasing temperature.As the modified temperature is 1300°C,spinel in slag is widely distributed and the content of which reaches a maximum.Meanwhile,the value of the magnetic flux density of the modified slag also reaches a maximum.After oxidation,the content of free lime decreases from 3.54%to 0.96%.Increased modified temperature plays a positive role in the hydration of steel slag.The hardening properties of the modified slag cement were also studied.The results show that the strength of the modified slag cement can be significantly improved by the use of water glass excitation or incorporation of fine powder after grinding.In this study,the incorporation of modified slag in cement should not exceed 30%.Based on the high-temperature modified process of steel slag,the variation of mineral phase,grain size and morphology of modified slag under different cooling regimes were studied.The results indicate that the effects of the cooling regimes on the the crystallization and growth of the spinel should be taken into account.The faster cooling rate?water cooling?has a negative effect on the crystallization of spinel.The formation of secondary spinel in the furnace cooled slag is owing to the decomposition of magnesioferrite.Furthermore,the solid phase modification for steel slag with low energy consumption was carried out.The thermodynamics and kinetic mechanism of the modification process of solid phase were deduced.The change of the crystal structure of the steel slag was discussed.The grindability and magnetic separation effect of the steel slag before and after the modification were studied in order to determine the optimal process.The results show that the transformation of non-magnetic iron oxide to ferromagnetic spinel can be achieved after oxidation.The spinel in the modified slag can be effectively separated by magnetic separation.The parameters?oxidation temperature,holding time,and oxidizing atmosphere intake rate?have a significant effect on the formation of spinel in the modified slag.Over oxidation leads to the formation of hematite in the system and results in a decrease in the amount of spinel.Variation of the oxidation temperature and holding time have a direct effect on the inversion parameter of spinel,which in turn affects the results of magnetic separation.The study on the grindability of steel slag shows that the secondary grinding of the slag can make it reach the ideal grain size.According to the kinetic reaction mechanism,the oxidation process of CaO-Si O₂-FeO-MgO quaternary slag system can be divided into three stages:initial stage,chemical reaction stage and diffusion stage.