| Blast furnace slag?BFS? is the main solid by-product during the iron and steel making process and has an output of about 0.3 1.0 ton/ton pig iron. Driven by the demand for sustainable development of industries and environment, the BF slag with discharging temperature up to 1500 ? is attracting intensive attention to the further utilization of waste heat for its promising future. Traditional method for the BF slag treatment is known as water quenching, by which the slag is directly poured into water to form granules. Aiming at the waste heat recovery and water saving, dry-treatment for the BF slag has been promoted as the substitutional technology and several techniques including rotating drum process, air blast process, rotating cup atomizer?RCA? process have been experimentally investigated. In these processes, air is usually used as heat transfer medium to achieve the heat recover from the slag.Unfortunately, Dry granulating process raises a severe question, that is, the air cooling rate is quite lower than the water quenching and may not be fast enough to realize slag vitrification.Therefore, it is crucial to understand the crystallization properties of BF slag under various cooling rates and to find out the critical cooling rate, and the outputs will provide valuable guidance to the heat recovery and subsequent utilization of BF slag.The paper focuses on the phase change of BFS under different cooling conditions with the aim of revealing the crystallization properties and obtaining the critical cooling rate. And in the fixed cooling rate, the glass phase BFS is achieved finally enhancing the value in resource utilization. Furthermore, experiments about crystallization properties of different compositions BFS was carried out basing on the controlling variables method. And the expected compositions were obtained by the addition of analytical reagents. BFSs with different content of Al2O3 and MgO were prepared to investigate the crystallization properties of BFS. Besides, in view there are out of a uniform criterion about basicity guiding the phase change of BFS, the change of SiO2/Al2O3 and CaO/MgO on performance of BFS phase change were both analyzed to guide the obtainment of high content of glass slag.The main results of this paper are as follows,0.13?1? At isothermal cooling condition, the crystal incubation time is decreased first and then increased with isothermal temperature falling. There is a critical cooling rate existed which is 9±0.13 ?/s according to the local BFS. The crystal of the slag obtain is Gehlenite. And at continue cooling condition, the crystal temperature and crystal incubation time is dropped with the decreasing of cooling rate. When cooling rate is less than a certain value, no crystal is observed no matter how long the cooling time. The cooling rate which is regarded as critical cooling rate is 5.5±0.08 ?/s.?2? At a fixed basicity?R2=1.1? and MgO content?MgO=10 wt%?, Al2O3 presents as amphoteric behavior. When Al2O3 content increases from 9 wt% to 18 wt%, critical cooling rate falls and the increases. The minimum critical cooling rate appears at Al2O3 content of 12 wt%. And the crystal obtained is changed from Akermaniteto Gehlenite; At a fixed basicity?R2=1.1? and Al2O3 content?Al2O3=12 wt%?, the increasing of MgO content from 8 wt% to 14 wt%, the glass-forming ability is weak resulting the increasing of critical cooling rate. And the crystal phase is change from Akermanite-Gehlenite to Akermanite.?3? At a quaternary basicity?R4? is of 1.0 and Ca O/MgO=3.62, the glass-forming ability is promoted with increasing of the value of SiO2/ Al2O3. The critical cooling rate reduces but the trend is gradually gentle. At a quaternary basicity?R4? is of 1.0 and SiO2/ Al2O3=3.62, the increase of the value of CaO/MgO promote the precipitation of crystal. And the critical cooling rate increase. |
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