Study On Molten Structure And Viscous Flow Properties Of Basic Vanadium Slag

Vanadium titano-magnetite is one of the characteristic polymetal integrated minerals in China. It is also a significant strategical resource for smelting iron and extracting valuable transition metals such as vanadium and titanium. The current pyrometallurgical process for smelting vabadium titano-magnetite is unable to remove phorsphours in the vanadium-extracting converter in which V within the hotmetal will be oxidized into the acidic slag. This will result in a heavy dephosphourization burden during the semi-steel refining process, and therefore reduce the steelmaking efficiency and eventually restrict the production of clearn steel.To addressing the problem mentioned above, adding a proper amount of alkaline slaging constituents into the V-extracting converter would be a creditable solution. By doing so, one can strip a part of P within the hotmetal into the slag while extracting V. Thus it is of fundamental and practical importance to understand the rellationships between composition, structure and properties of this newly formed basic vanadium slag in order to realize coupling V extraction and P removal in converter. To this end, we firstly investigated the structure of basic vanadium slag matrixes by using molecular dynamics(MD) simulations and spectroscopic techniques. Then we studied the viscous flow properties of basic vanadium slag under varying compositions and temperature. By combining the results from structural characterization and viscosity measurements, we revealed the effects of V2O3, P2O5 and binary basicity(Ca O/Si O2) on the structure and viscous flow properties of basic vanadium slag.The structure of ternary Fe O-Si O2-V2O3 slags was investigated in the molten and quenched states by using MD simulations and Fourier transform infrared(FT-IR) spectroscopy. An empirical two-body potential for the multi-component system has been developed in this work for performing MD simulations. The local atomic structures and the micro-heterogeneity in the molten slag have been systematically investigated using MD simulations. The bond length of V-O varies from 1.92 to 1.96 ? and the averaged coordination number of V(CNV-O) increases from 4.50 to 4.96 with the addition of V2O3. The simulation results revealed that the degree of polymerization decreases with increasing amount of V2O3, implying that V2O3 may behave as a network-modifying basic oxide in the Fe O-Si O2-V2O3 system. This was further confirmed by the FT-IR spectrum analysis, which shows that the silicate network dissociates with the presence of V2O3.The viscosity of Fe O-Si O2-V2O3-Ca O-P2O5 slags was measured via the rotating cylinder method to reveal the effects of P2O5 and basicity on viscous flow of the slags. It was found that within the investigated compostion and temperature range(1400? to 1500?), the slag viscosities ranging from 0.1 to 0.3 Pa.s, which is in well comparable with other experimental reports of similar systems. At a fixed Ca O/Si O2 of 1.3, the viscosity and the viscous flow activation energy(E?) both increase with increasing the P2O5 content, implying that P2O5 promots polymerization of the slag network. At a fixed P2O5 concentration of about 3%(mole percent), higher Ca O/Si O2 ratio results in lower viscosity and E?, implying that Ca O depolymerizes the netwok structure, while this network-modifying effect of Ca O become less profound when the Ca O/Si O2>1.3.The effects of P2O5 and basicity on the structure of Fe O-Si O2-V2O3-Ca O-P2O5 slags were systematically studied by combining spectroscopic characterization thechniques and classical MD simulations. Quanlitative structural information from FT-IR and Raman spectra of the as-quenched slag melts show that the intense high frequency 750-1200 cm-1 band shifts to higher frequency region with the addition of P2O5 while shifts to lower frequency region with increasing basicity. The simulation results show that the network connectivity(NC) of silicon oxygen network increases from 0.43 to 0.74 with increasing P2O5 content, while it dramatically decreases from 2.57 to 0.39 with the increase of Ca O/Si O2 ratio, indicating P2O5 promotes the polymerization of the Si-O based network while Ca O fragments the silicate network. This is in accordance with the findings of spectroscopic structural characterization and thus explained the viscosity changes of the slags from a microscopic perspective.In addition, we found that P mainly exists as 3-4PO and 4-2 7P O anion units in the simulated slags. Combined spectroscopic and MD results show that a large portion of V tetrahedrally coordinated with O and the [VO4] tetrahedron tend to connect with the [PO4] tetrahedral units to form complex vanadium phosphate structural units. We suggest that the formation of complex V-P units in the molten slag may bring difficults in separating V and P in the subsequent treatment of basic vanadium slag. Further works connecting the molten structure, crystallization behavior and phase transformation of basic vanadium slag are required for achieving effective separation of V and P.