Effect Of Solid Particles On Dephosphorization In Recycling Decarburized Slag

In 2018,steel output exceeded 900 million tons in China.Based on the consumption of 100kg of dephosphorization slag per ton of steel,the amount of slag produced by dephosphorization is more than 90 million tons,and the corresponding consumption of lime is over 40 million tons.The lime used for steelmaking is calcined by non-renewable limestone,and there is still a large amount of free CaO which is unreacted but difficult to recycle in the dephosphorization slag,resulting in great waste of resources.Therefore,the development of dephosphorization technology with less lime consumption and less slag has been the goal pursued by steelmakers.In recent years,Japanese scholars have proposed the solid-liquid coexisting steel slag refining technology,which greatly improves the dephosphorization capacity by using the solid phase in the slag and further reduces the slag discharge through the recycling of the decarburized slag.In view of this,based on the decarbonized slag（premelted slag）prepared in the laboratory,the effect of solid particles on dephosphorization with or without decarburized slag is studied:（1）By changing the basicity of slag,it is found that the optimum dephosphorization basicity is 1.6 with pre-melted slag,but 2.0 without pre-melted slag.Under the optimum basicity,the dephosphorization effect is better without premelted slag.（2）Controlling the slag basicity to 1.6,the CaO particles were divided into four gradients and mixed into the slag.The effect of CaO particle size on dephosphorization with or without premelted slag was studied.It was found that both C₂S and solid solution nC₂S-C₃P were formed in the reaction process,and CaO particles were beneficial to the formation of nC₂S-C₃P in slag.In the presence of premelted slag,CaO particles have a"stagnation period"at the initial stage of the reaction,and the larger the particle size,the more obvious the phenomenon is.However,the premelted slag has no obvious effect on the dephosphorization rate.In the absence of premelted slag,there is almost no"stagnation period",but the dephosphorization effect of CaO particles with a diameter of 1550μm is the best.（3）In order to further verify the role of C₂S in the dephosphorization process,the experiments mentioned above were repeated with C₂S particles instead of CaO.It was found that there was no“stagnation period”at the initial stage of the reaction,and phosphorus was enriched on the surface of C₂S particles and form nC₂S-C₃P solid solution during the reaction.The content of phosphorus on the surface of solid solution is higher than that of the core.In the presence of premelted slag,the dephosphorization effect is better and no rephosphorization is found during the reaction.Large C₂S particles have better enrichment effect on phosphorus（the dephosphorization rate and dephosphorization rate of 1550μm and 750μm C₂S are better than 330μm and 70μm）.In the absence of premelted slag,the dephosphorization rate is higher in the initial stage of the reaction,but the slag basicity decreases at the later stage of the reaction,resulting in rephosphorization.At the same time,compared with CaO particles,the time of rephosphorization is advanced when adding C₂S particles.