Research On Influence Of Slag Composition On Self-pulverization

Pulverizing is one of the effective ways to utilize BOF slag at present. However BOF slag and EAF slag has the features of bad grindability and low dusting rate, which restricts it's using in building materials. To achieve efficient use of converter slag, the research on converter slag dusting behavior and chalking rate should be carried out.Steel slag mainly consist of tricalcium silicate ?C₃S?, dicalcium silicate ?C₂S?, Almandine calcium ?Ca2 ?Al, Fe? 2O5? and mafic phase solid solution ?MgO · 2FeO?, where in C₂S may transform from ?-into to ?-C₂S at 725?. This transformation leads to about 11% volume expansion and triggers strong internal stress, which results in C₂S pulverization. Based on the results, a simple, low cost and effective way to produce slag powder can be implemented through creating moderate physical chemistry environment promotes the crystal transition to achieve BOF slag self-pulverization.In this paper, based on previous experiments of BOF slag self-pulverization, the effect of Cr, P content on the crystal transition of P-C₂S to Y-C₂S was studied using XRD spectral fitting refinement method and thermodynamic equilibrium calculations ?software:Factsage?. The influences of the elements'content on the rate of C₂S crystal transition and chalking rate of BOF slag are analyzed, content ranges of the elements in which BOF slag self-pulverization are determined BOF. The results provide a theoretical basis and composition conditions, and make sense for the utilization and grindability improving of steel slag. The results of this thesis show that:?1? For C₂S mineral, when the Cr₂O₃ content is 0.5%, the ratio of ?-C₂S accounts for 68.8%, at this point, the Cr₂O₃ stabilize P-C₂S effectively. In spite of this, the mineral appears an obvious self-powdering phenomenon due to crystal transformation of C₂S. When the Cr₂O₃ content is 1%, ?-C₂S proportion is less than 18.4%, C₂S does not dust autogenously, which implies that this content Cr₂O₃ doping inhibits ?-C₂S crystal transition, in turn impacting C₂S self-pulverization.Less than 1% P₂O₅ doping has no remarkable effect on crystal transition of C₂S cooling from high temperature, C₂S still appears self-pulverizing; when the content reaches 1.25%, after cooling, ?'H-C₂S appear in C₂S mineral, and Y-C₂S accounts for less than 20.6%, the samples appear no long self-pulverizing.Thermodynamic analysis showes that the doped Cr3+ and P5+ ions replace some of Si4+ in C₂S, forming solid solution, which inhibits the crystal transition from ?-C₂S to ?-C₂S, in turn weakening the self-pulverizing effect of C₂S. Experimental results of pure C₂S doping Cr₂O₃ or P₂O₅ also shows that when C₂S contains more than 1% Cr₂O₃ or 1.25%P₂O₅, after cooling, ?-C₂S content in C₂S was less than 20.6%, the crystal transition from ?-C₂S to ?-C₂S is not sufficient, lacking enough internal stress caused by the volume expansion effect, C₂S will not appears self-pulverizing phenomenon.?2? For self-dusting experiments of BOF slag, quaternary slag is synthetized using CaO 50%-SiO2 20%-MgO 10%-Fe2O 330%. Besides, the generating amounts of C₂S in slag were predicted by thermodynamics calculation, and the influence of Cr₂O₃ or P₂O₅ content on self-dusting effect of BOF slag is analyzed.For Cr₂O₃-bearing BOF slag, a small amount ?less than 0.25%? of Cr₂O₃ has no obvious effect on ?-C₂S crystal transformation. When doping content of Cr₂O₃ ranges from 0.25% to 2%, the ability to inhibit ?-C₂S crystal transformation did not increase obviously with the increase of Cr₂O₃ content. When Cr₂O₃ doping content reaches 3%, the ability to inhibit the transformation of ?-C₂S crystal increased remarkably. The amount of ?-C₂S in the slag was less than 35.7%, and self-pulverization phenomenon didn't occur.For the slag with less than 0.25% P₂O₅ content, it dusts autogenously completely. For the slag contains 0.5% P₂O₅, crystal transition of ?-C₂S in converter steel slag is inhibited, the ratio of ?-C₂S in the slag accounts for less than 35.3%. The slag couldn't pulverize autogenously. When the content of P₂O₅ in the converter slag reaches 1.5%, ?'H-C₂S generates in the slag.The results showed that the Cr₂O₃ content in slag was lower than 3% and the content of P₂O₅ in the slag was less than 0.5%, at this point, the percent of ?-C₂S in C₂S was less than 35.3%, slag achieving self-pulverization. In particular, the content of P in the converter steelmaking slag should be controlled strictly, and overdose P in the slag will inhibit steelmaking slag powdering autogenously, decreasing grindability of steelmaking slag.