Structure Investigation On CaO-SiO₂-‘FeO’-Al₂O₃-MgO Melts During Iron-extraction Process From Molten Nickel Slag

For aluminosilicate,the thermodynamic and kinetic properties are determined by their structures.Therefore,studying on the structure is helpful to elucidate the reactions and phenomena in many metallurgical industrial processes.The microstructure of aluminosilicate can be characterized by the types of structural units in the system and its degree of polymerization,which is closely related to the macroscopic properties of slag.Molecular dynamics simulation has been carried out to quantitatively study the structure of the CaO-SiO2-‘FeO’-Al2O3-MgO melts during iron-extraction process from molten nickel slag.Besides,the effects of‘FeO’/(‘FeO’+Al2O3)ratio and Al2O3/(Al2O3+SiO2)ratio on structure of the slags evolution were analyzed by FT-IR and Raman spectra.Additionally,the simulation results were compared with experimental results.The main conclusions are as follows:During the process of iron-extracton from molten nickel slag,the peak of Si-O radial distribution function shifts to the left as the content of Al2O3 increases,indicating that the increaseing Al2O3 content makes the network connection of[SiO4]4-tetrahedra tighter and more stable.Viscosity of the slag system increases and the particle diffusion speed becomes slower with the progress of iron reduction.When the degree of‘FeO’reduction is 100%,the diffusion rate of Al in the system is slower than that of Si,indicating that Al plays a leading role in the network structure when the reduction reaction is completed.With the process of reduction,the micro-network of the slag system becomes more complicated,and the degree of polymerization is getting larger.It also can be seen that the network of the system is dominated by the[SiO4]4-tetrahedron and then by[AlO4]5tetrahedron for change.When the reduction degree of‘FeO’is lower than 50%,the slag system is dominated by‘FeO’,and the structural units of the system are mainly Q0,Q1 and Q2.After then,the structural units are characterized by Q1,Q2 and Q3.The change of slag from‘FeO’dominant to Al2O3 dominant results in the structural units with high-bridging oxygen.The degree of polymerization of the network of CaO-SiO2-‘FeO’-Al2O3-MgO slag system can be characterized by n(BO/T).When the ratio of‘FeO’/(‘FeO’+Al2O3)is 0.63 and 0.53,the values of n(BO/T)are 1.08 and 1.18.When the ratio of is lowered to 0.43 and 0.33,n(BO/T)increases to 1.48 and 1.66,indicating that the degree of network polymerization of the system is increasing.With the increase of Al2O3/(Al2O3+SiO2)in the slag,the complexity of the network structure is increasing.When the slag system is dominated by silicate,the mainly change of network structure is[SiO4]4-tetrahedral structural unit.When the system evolves to be based on aluminate,more Al joins in the network,the mainly change of the network at this time is[AlO4]5-tetrahedron.The n(BO/T)e was adopted to discuss the contributionof[AlO4]-tetrahedra in slag.With the ratio of Al2O3/(Al2O3+SiO2)increasesing from 0.22 to 0.38,the value of n(BO/T)e increases from 1.07 to 1.42.When the ratio increases from 0.50 to 0.56,the value of n(BO/T)e increases from 2.47 to 2.60,demonstrating that the increase in the Al2O3/(Al2O3+SiO2)ratio makes the degree of polymerization of the aluminosilicate system more complicated correspondingly.The microstructure results of slag measured by Raman spectroscopy and infrared spectroscopy agree well with the results of molecular dynamics simulation.It has shown that there is a good complementarity between experimental methods and molecular dynamics simulation.