Study On The Change Of Metallurgical Properties Of Active Lime At Converter Smelting Temperature

The accumulation of steelmaking slag collected from steelmaking process is harmful to the environment,and the existence of f-CaO in slag limits the comprehensive utilization of steel slag.Therefore,how to control the content of f-CaO in steel slag is of great significance to the implementation of ecological environmental protection,the construction of circular economy and the promotion of sustainable development.In view of the large size of f-CaO produced by incomplete dissolution of lime,it is necessary to strengthen the dissolution behavior of lime in the converter process.Thus,it is of great significance to study the changing behavior of physicochemi-cal properties of lime under the conditions of converter smelting temperature for strengthening the dissolution of lime and reducing the f-CaO content in steel slag.The effects of calcining temperature,holding time,calcination rate and particle size on the physicochemical properties of lime were investigated by using the 25kW high-temperature carbon tube furnace in the laboratory to simulate the smelting conditions of the converter.The phase composition and microstructure of lime were characterized by an X-ray diffractometer and detected by a Scanning Electron Microscope and a Mercury Injection Instrument.The size of CaO crystal was measured by Photoshop according to GB/T 6394-2017 and the activity of lime was tested according to YB/T 105-2005.The conclusions are as follows.The temperature had a great influence on the physicochemical properties of lime.When the temperature increased,the activity and porosity of lime decreased,while the average pore size and CaO crystal size increased.The reactivity was only 40.6 ml,andthe CaO grain size reached 9.88?m,showing an exponential growth trend,at 1600°C.The higher the temperature,the greater the driving force for crystal growth leading larger CaO size.Compared with temperature,the holding time has less effect on physicochemical properties of lime.At 1350°C,the porosity,average pore size and CaO grain size changed little.However,the physicochemical properties of lime changed significantly,and the microstructure of lime became denser at 1450°C and 1550°C.The reactivity was only 40.80ml at 1550°C.The average size of CaO grain showed a parabolic growth trend with the increase of holding time.With the holding time increasing,the CaO size increased leading the greater the resistance to CaO growth at the same temperature.And the growth rate of CaO grain is negatively correlated with the resistance.Therefore,the size increased but the growth rate of CaO crystal decreases with holding time prolonging.The lime reactivity decreased at first,then increased,and finally decreased rapidly with the decrease of the residual ratio of calcite at 1450°C and 1550°C.The average size of CaO grain showed a trend of increasing.The reactivity reached the maximum values at 1450°C and 1550°C when the residual ratio of calcite was 14.61%.In the subsequent calcination experiments,the heat absorbed by CaCO₃ decomposition decreased,the heat absorbed by the growth of CaO grain increased and the greater driving force of CaO crystal growth with the residual ratio of calcite decreasing.The growth rate is positively correlated with the driving force,which improves the increase of CaO crystal.The lime reactivity remained unchanged at first,then increased significantly,and finally decreased rapidly with the lime size increasing at 1450°C.The maximum value was 194.80 ml at 20-25 mm of the lime particles.The CaO size had the same trend.The lime reactivity continued to increase as the particle size increased at 1550°C.The CaO-crystal size first remained unchanged,then increased,and reached the maximum value of 4.44?m at the particle size of 10-15mm,and then decreased rapidly.At the same temperature,the small size of lime has great resistance to the growth of CaO leading the slow growth of CaO.Therefore,the growth rate of CaO is related to the original lime size as well as the content of residual CaCO₃.