| Nowadays it is very hard to utilize sorts of steel slag.High value-added products could be made with steel slag through changing its composition,mineral structure and cementitious activity.The EAF slag hot modification process in Shandong Laiwu Iron and Steel Group is supported by the National 863 project"10000-ton liquid steel slag on-line modification demonstration project"(No.2011AA06A105).The mineral composition and microstructure of the slag is modified by declining the basicity to improve the iron recovery rate and the cementitious activity.Then,the recovery of iron,slag and residual heat of molten slag can be realized through the modification.Thus,theory and technical guidance of the modification pilot test is obtained.Sand was used as modifier and the amount which was melt by EAF molten slag sensitive heat was studied.The largest additional amount of cold modifier is calculated through thermal balance analysis of EAF slag hot modification for purpose of adding no extra energy.The basicity of modified slag declined from 1.62 to 1.19 as the optimum amount of sand was from 11%to 24%.Meanwhile,the sensitive heat was utilized efficiently and modified slag was melt uniformly.The mobility of molt modified slag was outstanding when the additional amount of sand was near 11%.The basicity of modified slag reduced significantly as the additional amount of sand was near 24%.The thermodynamics of solid phase reaction was studied as the modifier was sand,which supplied the basis of generated minerals during hot modification.The effects of basicity on iron recovery,mineral composition and microstructures of modified slag and relationship between iron recovery and mineral composition were studied.The results showed that the amount of spinel was large as the basicity of modified slag was 1.3 and 1.42 with air and water quenching respectively,leading to the largest amount of iron recovery.The effects of cooling methods on iron recovery,mineral composition and microstructures of modified slag were also studied.The crystallizing temperature of minerals was characterized by TTT diagram which was measured by confocal scanning laser microscope.It indicated that iron spinel of molten slag crystallized at a high temperature which was higher than the temperature of other minerals.The crystallization process of molten slag is controlled to improve the iron recovery through optimizing the modification process parameters.EAF slag was modified at 1500? for 1 hour followed by cooling to 1375? for 30 minutes at a rate of 20?/min before water quenching.The effects of iron on cementitious activity of modified slag were eliminated by melting at reducing atmosphere with the modifiers of mine taillings,fly ash,coal gangue and pure chemical Al2O3.The glass phase content of modified slag was judged by exothermic peak area of DSC patterns.The activity of glass phase was determined by the polymerization degree of network which was calculated by Raman spectrums.The influences of basicity and cooling methods on cementitious activity,mineral composition,glass phase content and its activity were studied.The modified slag possessed large glass phase amount and minerals with high activity as the basicity was 0.9 and 1.5 with air and water quenching respectively,leading to the maximum cementitious activity.The relationship between cementitious activity and mineral composition,glass phase amount and its activity of tailored slag was studied.The cementitious activity could be promising as the glass phase mount and its activity increased,providing theoretical basis of exploring high value-added products.EAF slag hot modification pilot test was carried out in 100-tons electric furnace factory of Shandong Laiwu Iron and Steel Group.The modifying process flow and the formulation of modifiers had been developed and optimized in pilot test.The results in pilot test agreed well with that in lab experiment. |
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